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Synthesis, Spectroelectrochemical Behavior, and Chiroptical Switching of Tris(-diketonato) Complexes of Ruthenium(III), Chromium(III), and Cobalt(III)
Abstract
Five tris(β-diketonato) complexes of ruthenium(III), chromium(III), and cobalt(III) [Ru(Buacac)3 (1), Ru(Oacac)3 (2), Cr(Buacac)3 (3), Cr(Oacac)3 (4), and Co(Buacac)3 (5), where Buacac = 3-butylpentane-2,4-dionato and Oacac = 3-octylpentane-2,4-dionato] with a chiral propeller-like structure have been prepared. Ligands and complexes syntheses are presented together with characterization of the compounds by 1H and 13C NMR spectroscopy, mass spectrometry, IR, UV–vis, electronic circular dichroism (ECD) spectroscopy, electrochemistry studies, and first-principles calculations. The crystal structures of 1 and 5 have also been obtained and analyzed. A comparison of the 1H NMR spectra of diamagnetic (ligands and 5) and paramagnetic (1 and 2) species is presented. Optical resolution of the five complexes has been achieved for the first time by supercritical fluid chromatography using a chiral column, giving rise to very high purity grades in all cases. ECD measurements and calculations have led to the assignment of the absolute configuration, Δ or Λ, of each enantiomer for 1−5. Spectroelectrochemical UV–vis and ECD studies have been performed on ruthenium Λ-2 and chromium Λ-4 complexes, revealing their redox-triggered chiroptical switching confirming the noninnocence character of the β-diketonate ligands.
... In that sense, the inertness of Cr(III) complexes was an addedvalue for their separation by cation-exchange chromatography using a chiral support, [34] capillary electrophoresis, [35] selective crystallisation using chiral counter ions, [36] chiral stationary phase HPLC [16b,30] as well as supercritical fluid chromatography. [37] Contrary to the CD experiment where the sample is excited with a circularly polarized light source, in a CPL measurement, the sample is irradiated with non-polarized light in an energy domain where the photons are absorbed by the sample. Spontaneous emission from one of the emissive states of the chiral enantiopure molecule will have an excess of either the right or the left circularly polarized light. ...
... Δ-[Cr(bpy) 3 ] bpy = 2,2'-bipyridine 2.1 À 1.2 (21739 cm À 1 ) À 19.5 (28090 cm À 1 ) À 21 (28818 cm À 1 ) À 75 (31746 cm À 1 ) 9.5 (34898 cm À 1 ) 9 (35714 cm À 1 ) 12 (37879 cm À 1 ) [49] No Yes [50] [ [52] 15 [Cr(Oacac) 3 ] Oacac = 3-octylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.04 (18868 cm À 1 ) + 0.025 (15798 cm À 1 ) [53] À 10 (11765 cm À 1 ) À 50 (~28570 cm À 1 ) [37] No No [37,53] 16 [Cr(3-Buacac) 3 ] Buacac = 3-butylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.05 (19048 cm À 1 ) 0.032 (15798 cm À 1 ) [54] À 40 (~28570 cm À 1 ) [37] No No [37,54] 17 [Cr(Pracac) 3 ] Pracac = 3-Propylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.05 (19048 cm À 1 ) + 0.032 (15798 cm À 1 ) ...
... Δ-[Cr(bpy) 3 ] bpy = 2,2'-bipyridine 2.1 À 1.2 (21739 cm À 1 ) À 19.5 (28090 cm À 1 ) À 21 (28818 cm À 1 ) À 75 (31746 cm À 1 ) 9.5 (34898 cm À 1 ) 9 (35714 cm À 1 ) 12 (37879 cm À 1 ) [49] No Yes [50] [ [52] 15 [Cr(Oacac) 3 ] Oacac = 3-octylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.04 (18868 cm À 1 ) + 0.025 (15798 cm À 1 ) [53] À 10 (11765 cm À 1 ) À 50 (~28570 cm À 1 ) [37] No No [37,53] 16 [Cr(3-Buacac) 3 ] Buacac = 3-butylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.05 (19048 cm À 1 ) 0.032 (15798 cm À 1 ) [54] À 40 (~28570 cm À 1 ) [37] No No [37,54] 17 [Cr(Pracac) 3 ] Pracac = 3-Propylpentane-2,4-dionato 2.1 g = Δɛ/ɛ = À 0.05 (19048 cm À 1 ) + 0.032 (15798 cm À 1 ) ...
The search for chiral chromophores with efficient circularly polarized luminescence (CPL) is an on‐going hot topic in chemistry due to their potential applications in emerging fields such as spintronics and photonics. Beyond the largely exploited p‐block, 4d/5d‐block and f‐block chiral entities, chiral chromium(III) complexes have recently attracted interest because of the abundancy of chromium in the earth's crust, its kinetic inertness and its promising metal‐centered Cr(²E) and Cr(²T1) phosphorescence. The associated spin‐flip transitions could provide large dissymmetric factor (glum ) and high luminescence quantum yields (ϕ) when six‐membered strong‐field chelate rings are coordinated to chiral six‐coordinate Cr(III) centers. In this minireview, we intend to focus our attention on the state‐of‐the‐art for the design of pseudo‐octahedral chiral mononuclear Cr(III) complexes for which chiroptical properties were investigated. The promising electronic properties of these complexes together with their low cost make these underexplored systems appealing candidates for CPL applications.
... In 2017, Cortijo et al. used X-rays, molecular spectroscopy, CV, and computational chemistry to study the novel, propeller-like, tris(b-diketonato) complexes of Ru(III), Cr(III) and Co(III) isolated in homochiral forms by supercritical fluid chromatography on a chiral column [50]. The combination of ECD measurements and DFT calculations allowed for finding the absolute configuration of each enantiomer. ...
... Insets: Reversible ECD 500 nm (e) and ECD 460 nm (f) switching processes. Reproduced with permission [50]. Copyright American Chemical Society. ...
The electronic circular dichroism (ECD) spectroscopy is probably the most important chiraloptical method, and the role of chirality in contemporary chemistry, pharmacy, and material science constantly increases. On the other hand, the electrochemical methods are also very sensitive tools for studying multivarious redox processes. Nevertheless, the first ECD spectroelectrochemical (SEC) study was only published by Daub, Salbeck and Aurbach in 1988, and since then, the ECD SEC method has been mentioned in only thirty papers. By the summer of 2020, the ECD SEC studies were mainly focused around molecular systems for organic, and marginally, inorganic chiroptical switching studies of biochemical redox reactions. The review provides more details about the ECD SEC studies carried out so far. At the end, we suggest some future applications for the ECD spectroelectrochemistry.
... For instance, metal-tris(β-diketonato) complexes are chiral octahedral metal D3-symmetric molecules with intrinsic chirality due to their typical propeller-like structure and display the classical ∆/Λ stereochemistry. 1,2 M(acac)3 (where M is a metal and acac stands for acetylacetonato) is the archetype of such complexes and has been used as a chiral model for chiroptical spectroscopies [3][4][5] and in applications such as in catalysis, 6 or in chiral liquid crystals. 7-10 Chiral resolution and racemization of metal-tris(β-diketonato) complexes have been studied extensively. ...
Chiral transition-metal complexes are of interest in many fields ranging from asymmetric catalysis and molecular materials science to optoelectronic applications or fundamental physics including parity violation effects. We present here a combined theoretical and experimental investigation of gas-phase valence-shell photoelectron circular dichroism (PECD) on the challenging open-shell ruthenium(iii)-tris-(acetylacetonato) complex, Ru(acac)$_3$. Enantiomerically pure $\Delta$- or $\Lambda$-Ru(acac)$_3$, characterized by electronic circular dichroism (ECD), were vaporized and adiabatically expanded to produce a supersonic beam and photoionized by circularly-polarized VUV light from the DESIRS beamline at Synchrotron SOLEIL. Photoelectron spectroscopy (PES) and PECD experiments were conducted using a double imaging electron/ion coincidence spectrometer, and compared to density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The open-shell character of Ru(acac)$_3$, which is not taken into account in our DFT approach, is expected to give rise to a wide multiplet structure, which is not resolved in our PES signals but whose presence might be inferred from the additional striking features observed in the PECD curves. Nevertheless, the DFT-based assignment of the electronic bands leads to the characterisation of the ionized orbitals. In line with other recent works, the results confirm that PECD persists independently on the localization and/or on the achiral or chiral nature of the initial orbital, but is rather a probe of the molecular potential as a whole. Overall, the measured PECD signals on Ru(acac)$_3$, a system exhibiting D$_3$ propeller-type chirality, are of similar magnitude compared to those on asymmetric-carbon-based chiral organic molecules which constitute the vast majority of species investigated so far, thus suggesting that PECD is a universal mechanism, inherent to any type of chirality.
... [49][50][51] Alternatively,chiral stationary phase (CSP) HPLC represents ar eliable,p ractical and straightforward method for enantiomeric separations. [52,53] In this work, resolutions were performed using as emi-preparative CHIRALPAK IC column (DAICEL) under optimized HPLC conditions (eluent:i socratic CH 2 Cl 2 /CH 3 CH 2 OH + 0.5/0.3 vol% of CF 3 COOH/ N(CH 3 ) 3 ,s ee Figure 2). ...
A series of highly emissive inert and chiral CrIII complexes displaying dual circularly polarized luminescence (CPL) within the NIR region have been prepared and characterized. The helical [Cr(dqpR)2]³⁺ (dqp=2,6‐di(quinolin‐8‐yl)pyridine; R=OCH3, Br or C≡CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC. The corresponding enantiomers show large glum≈0.2 and high quantum yield of up to 17 %, which afford important CPL brightness of up to 170 m⁻¹ cm⁻¹, a key point for applications as chiral luminescent probes. Moreover, the long‐lived CP‐NIR emission provided by these chromophores (ms range) in aqueous solution opens the way toward the quantification of chiral targets in biological systems with time‐gated detection. Thus, such chiral chromophores based on earth abundant and inert 3d metals open new perspectives in the field of CPL and represent an alternative to precious 4d, 5d and to labile 4f metal‐based complexes.
... Tris(β-diketonato) complexes of Cr(III) had excellent electronic and optical properties according to a previous literature [14]. C 15 H 21 CrO 6 serving as raw material was firstly used to synthesize the Cr-CDs due to that has similar structure with tris(β-diketonato) complexes of Cr(III). ...
We report on the synthesis of chromium(III)-doped carbon dots (Cr-CDs) by one-pot hydrothermal pathway using tris(2, 4-pentanedionato) chromium(III) and polyethyleneimine as precursors. The Cr-CDs have a graphene-analogous structure and display blue-green fluorescence with excitation/emission maxima at 350/466 nm, a 20% quantum yield, and excitation-independent emissions. Their cytotoxicity is low. The Cr-CDs were used as a fluorescence probe for p-nitrophenol (p-NP). The assay has a linear working range that extends from 0.8~150 μM and a 0.27 μM lower detection limit. The assay was applied to the detecting of p-NP in spiked human urine, and conceivably may be extended to a method for the determination of parathion.
Graphical abstractSchematic presentation for the synthesis of Cr-CDs (chromium(III)-doped carbon dots) and their application to the fluorometric determination of p-NP (p-nitrophenol) based on an inner filter effect.
... In the investigated TM metallocenes, most of the spin density is localized on the metal centers, as expected (Tables S3, S4 and Figure 3). Spin density in the ligands is caused by spindelocalization, due to spin-selective L-M donation and/or spin-selective M-L back-donation, and 'fine-tuned' by spin polarization effects, 42,97,98 as shown in Figure 4. For example, a previous study showed that for nickelocene a positive spin density, i.e. an excess of spin, around the carbons and at the carbon nuclei, as quantified experimentally by paramagnetic effects on the NMR shifts, is caused to ca. 85% by spin L-M donation and to 15% by M-L spin delocalization. ...
U(C7H7)2– is a fascinating 5f¹ actinocene whose metal-ligand bonding was assigned in the literature as being very similar to 3d⁷ cobaltocene, based on a crystal-field theoretical interpretation of the experimental magnetic resonance data. The present work provides an in-depth theoretical study of the electronic structure, bonding, and magnetic properties of the 5f¹ U(C7H7)2– vs. 3d metallocenes with V, Co, and Ni, performed with relativistic wavefunction and density functional methods. The ligand to metal donation bonding in U(C7H7)2– is strong and in fact similar to that in vanadocene, in the sense that the highest occupied arene orbitals donate electron density into empty metal orbitals of the same symmetry with respect to the rotational axis (3dπ for V, 5fδ for U), but selectively with α spin (↑). For Co and Ni, the dative bonding from the ligands is β spin (↓) selective into partially filled 3dπ orbitals. In all systems, this spin delocalization triggers spin polarization in the arene σ bonding framework, causing proton spin densities opposite to those of the carbons. As a consequence, the proton spin densities and hyperfine coupling constants Aiso1H are negative for the Co and Ni complex, but positive for vanadocene. The Aiso1H of U(C7H7)2– is negative and similar to that of cobaltocene, but only because of the strong SOC in the actinocene, which causes Aiso1H to be opposite to the sign of the proton spin density. The study contributes to a better understanding of actinide 5f vs. transition metal 3d covalency, and highlights potential pitfalls when interpreting experimental magnetic resonance data in terms of covalent bonding for actinide complexes.
Chiral transition-metal complexes are of interest in many fields ranging from asymmetric catalysis and molecular materials science to optoelectronic applications or fundamental physics including parity violation effects. We present here a combined theoretical and experimental investigation of gas-phase valence-shell photoelectron circular dichroism (PECD) on the challenging open-shell ruthenium(III)-tris-(acetylacetonato) complex, Ru(acac)3. Enantiomerically pure Δ- or Λ-Ru(acac)3, characterized by electronic circular dichroism (ECD), were vaporized and adiabatically expanded to produce a supersonic beam and photoionized by circularly-polarized VUV light from the DESIRS beamline at Synchrotron SOLEIL. Photoelectron spectroscopy (PES) and PECD experiments were conducted using a double imaging electron/ion coincidence spectrometer, and compared to density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The open-shell character of Ru(acac)3, which is not taken into account in our DFT approach, is expected to give rise to a wide multiplet structure, which is not resolved in our PES signals but whose presence might be inferred from the additional striking features observed in the PECD curves. Nevertheless, the DFT-based assignment of the electronic bands leads to the characterisation of the ionized orbitals. In line with other recent works, the results confirm that PECD persists independently on the localization and/or on the achiral or chiral nature of the initial orbital, but is rather a probe of the molecular potential as a whole. Overall, the measured PECD signals on Ru(acac)3, a system exhibiting D3 propeller-type chirality, are of similar magnitude compared to those on asymmetric-carbon-based chiral organic molecules which constitute the vast majority of species investigated so far, thus suggesting that PECD is a universal mechanism, inherent to any type of chirality.
Four types of tris-chelate ruthenium complexes bearing acetylacetonato (acac) and tropolonato (trop) ligands were synthesized and optically resolved into Δ and Λ isomers: [Ru(acac)3] (Ru-0), [Ru(acac)2(trop)] (Ru-1), [Ru(acac)(trop)2] (Ru-2), and [Ru(trop)3] (Ru-3). Chiral HPLC chromatograms, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) of the four ruthenium complexes were systematically investigated. As a result, the absolute configurations of the newly prepared enantiomeric complexes Ru-2 and Ru-3 were determined. For the case of Ru-2, its absolute configuration was also confirmed by single crystal X-ray diffraction analysis. The ECD changes upon chemical oxidation were further investigated for the four complexes. An ECD change in enantiomeric Ru-1 was observed upon oxidation, but the oxidized species soon returned to the neutral state within a few minutes. Enantiomers of Ru-3 also showed explicit ECD changes upon oxidation. Further, the lifetime of the oxidized state was the longest among the four investigated complexes, whereas they racemized in solution at room temperature. In contrast, the enantiomers of heteroleptic complexes (Ru-1 and Ru-2) concurrently exhibited ECD changes, relatively long lifetime of the oxidized state, and nil or quite slow racemization behavior. The coexistence of acac and trop ligands was key to making the competing factors compatible in the resultant ruthenium complexes.
The recent coordination chemistry of β-diketones has been reviewed. Recent developments in fluorinated, sterically hindered, and poly-chelate ligands has enabled innovations in theory and applications. This has translated into increasing control over molecular architectures and properties. A brief introduction to the topic is given, focusing on the synthesis and properties of the ligands themselves. The coordinated elements, spanning the periodic table, are reviewed systematically with attention to recurring research themes.
A family of chiral CrIII chromophores with dual circularly polarized emission within the NIR has been synthesized and characterized. The rational design of the ligand skeleton on chiral CrIII complexes improves the chiral resolution as well as the CPL brightness. These optimized chiral chromophores based on earth‐abundant metals are promising candidates for the emerging chiral technologies.
Abstract
A series of highly emissive inert and chiral CrIII complexes displaying dual circularly polarized luminescence (CPL) within the NIR region have been prepared and characterized. The helical [Cr(dqpR)2]³⁺ (dqp=2,6‐di(quinolin‐8‐yl)pyridine; R=OCH3, Br or C≡CH) complexes were synthesized as racemic mixtures and resolved into their respective PP and MM enantiomers by chiral stationary phase HPLC. The corresponding enantiomers show large glum≈0.2 and high quantum yield of up to 17 %, which afford important CPL brightness of up to 170 m⁻¹ cm⁻¹, a key point for applications as chiral luminescent probes. Moreover, the long‐lived CP‐NIR emission provided by these chromophores (ms range) in aqueous solution opens the way toward the quantification of chiral targets in biological systems with time‐gated detection. Thus, such chiral chromophores based on earth abundant and inert 3d metals open new perspectives in the field of CPL and represent an alternative to precious 4d, 5d and to labile 4f metal‐based complexes.
The reaction of a bulky acetyl acetone ligand 1,3-dimesitylpropane-1,3-dione (MesacacH) with hydrated lanthanide chlorides in the presence of tetramethylammonium hydroxide afforded a new family of neutral mononuclear LnIII complexes [Ln(Mesacac)3(DMF)] (Ln = Dy (1); Tb (2); Y0.91Dy0.09 (3); and Er (4)). The molecular structures of these complexes were confirmed by single crystal X-ray diffraction studies. The coordination geometries of the LnIII centre were analysed by SHAPE analysis which revealed a capped octahedral geometry in 1-4. Photoluminescence studies showed ligand-sensitized green emissions for 2 with an appreciable quantum yield of 0.83%. Static (dc) and dynamic (ac) magnetic studies of complexes 1 and 3 were performed. The dynamic magnetic study revealed that complex 1 exhibits zero-field slow relaxation of the magnetization without showing a clear maximum in the out-of-phase ac susceptibility plots. However, magnetic dilution of 1 with the YIII metal ion (complex 3) and/or the application of a dc magnetic field induces a strong frequency dependence of the ac susceptibility signals with χ''M peaks in the 3-10 K temperature range, thus supporting field-induced SMM behaviour of 1. The relaxation process takes place through a combination of the Orbach and Raman mechanisms. The fitting of the temperature dependence of the relaxation time to the equation τ-1 = τ0-1 exp(-Ueff/kBT) + BTn, allows the extraction of the effective energy barrier Ueff/kB = 70 K (48.7 cm-1) and pre-exponential parameter of τ0 = 2.7 × 10-7 s for the Orbach mechanism (first term) and the parameters B = 0.04 s-1 K-n and n = 6.11, for the Raman mechanism (second term).
Chiroptical switches, whose chiral optical signals such as optical rotatory dispersion (ORD), circular dichroism (CD) and circularly polarized luminescence (CPL) are reversibly interchangeable between two states, offer many promising applications in the fields of chiral sensing, optical displays, information storage, asymmetric catalysis and so on. Through various non-covalent interactions, supramolecular chiroptical switches have been constructed by combining the chiral and responsive functional components. This review summarizes the recent progress in the construction of supramolecular chiroptical switchable systems that reversibly respond to various stimuli, such as light, electricity, magnetic fields, mechanical force, solvents, pH, temperature, and chemical additives. The switching of supramolecular chirality in the forms of on/off, amplification/weakening and chirality inversion is shown. Additionally, the design of chiroptical switchable systems for chiral logic gates, data communication, chiral separation and asymmetric catalysis has been demonstrated. Future challenges in developing supramolecular chiroptical switches are also discussed.
New tetra‐ and di‐cationic azoniahelicenes provide electrochemical, spectroelectrochemical and electronic circular dichroism (ECD) data reflecting their differences in electron transfer (ET) kinetics. Di‐cationic helquats containing two seven‐membered rings are irreversibly reduced in two ET steps. Substitution by redox active ethenylpyridinium in α or γ position with respect to nitrogen atoms of helquat core yields tetra‐cationic derivatives with reversible ET steps and communicating redox centers. Redox inactive substituents in di‐cationic azoniahelicenes retain ET irreversibility. Redox switching of ECD of tetra‐cationic enantiomers was observed. Unlike fully aromatic helquat, the ECD response of tetra‐cationic helquats to periodic reduction‐oxidation cycles is slower due to a strong adsorption on electrodes. Quantum chemical calculations (DFT) indicate that the first electron transfer step of tetra‐cationic derivative substituted in γ position yields a folded structure, which favors internal donor‐acceptor interaction. This explains spectroelectrochemical differences between both tetra‐cations.
Oxidation of the stoichiometric reaction between bis(acac)cobalt(II) and a facially-capping tris(N-heterocyclic carbene)borate ligand yields a hetroleptic cobalt(III) complex with acac and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this...
Vibrational circular dichroism (VCD) spectroscopy was applied to study intermolecular interactions on the surface of a clay mineral. A montmorillonite clay loaded with two kinds of chiral molecules was prepared. Firstly a cationic ruthenium(II) complex, Δ- or Λ-[Ru(phen)3]2+ (phen = 1,10-phenanthroline), was ion-exchanged into sodium montmorillonite (denoted as [Ru(phen)3]2+/mont). Thereafter a neutral metal(III) complex, Δ- or Λ-[M(acac)3] (acac= acetylacetonato; M = Co and Cr), was adsorbed spontaneously, when the complex was added to an aqueous dispersion of [Ru(phen)3]2+/mont (denoted as [M(acac)3]/[Ru(phen)3]2+/mont). VCD measurements were performed on a KBr disk containing ca. 1 wt% of solid [M(acac)3]/ [Ru(phen)3]2+/mont. Both of the chiral components gave clear VCD peaks in the wavelength region of 1200 ~ 1800 cm-1. An attention was focussed on the spectral differences between the following two samples: the one containing a pair of co-adsorbed chelates with the same chirality (i.e. Λ-[M(acac)3]/Λ-[Ru(phen)3]2+/mont or Δ-[M(acac)3]/Δ-[Ru(phen)3]2+/mont) and the other containing a pair of co-adsorbed chelates with the opposite chirality (i.e. Δ-[M(acac)3]/Λ-[Ru(phen)3]2+/mont or Λ-[M(acac)3]/Δ-[Ru(phen)3]2+/mont). Notably a new peak shoulder appeared and the relative peak intensity of the couplet peaks varied, depending on the chirality relation between the co-existing complexes. With a help of theoretical calculation, these results were raionalized in terms of the stereoselective intermolecular interactions.
Straightforward synthesis and resolution of a series of chiral fluorescent macrocycles are presented, together with their electronic circular dichroism (ECD), strong excimer fluorescence (EF, λ 300 to 650 nm) and allied highly circularly polarized luminescence (CPL, glum up to 1.7×10⁻²). The ECD, EF and CPL responses are strongly affected by the presence of metal ions (Na⁺, Ba²⁺) thanks to deep conformational changes. While ECD signals can be almost completely reversibly inverted upon the complexation/decomplexation of metal ions in a typical binary response, CPL signals are reversibly quenched concomitantly. The designed macrocycles display thus a remarkable combination of both +/− ECD and on/off CPL reversible switching.
The charged, electroactive bipyridine-helicene-ruthenium(III) complex [4].+,PF6⁻ has been prepared from 3-(2-pyridyl)-4-aza[6]helicene and a Ru-bis-(β-diketonato)-bis-acetonitrile precursor (β-diketonato: 2,2,6,6-tetramethyl-3,5-heptanedionato). Its chiroptical properties (electronic circular dichroism and optical rotation) were studied both experimentally and theoretically and suggest the presence of 2 diastereoisomers, namely (P,Δ)- and (P,Λ)-[4].+,PF6⁻ (denoted jointly as (P,Δ*)-[4].+,PF6⁻) and their mirror-images (M,Λ)- and (M,Δ)-[4].+,PF6⁻ ((M,Δ*)-[4].+,PF6⁻). The electrochemical reduction of (P,Δ*)-[4].+,PF6⁻ to neutral complex (P,Δ*)-4 was performed and revealed strong changes in the UV-vis and electronic circular dichroism spectra. A reversible redox-triggered chiroptical switching process was then achieved.
We report on the investigation of a new series of symmetric trinuclear ruthenium complexes combined with azanaphthalene ligands: [Ru3O(CH3COO)6(L)3]PF6 where L = (1) quinazoline (qui), (2) 5-nitroisoquinoline (5-nitroiq), (3) 5-bromoisoquinoline (5-briq), (4) isoquinoline (iq), (5) 5-aminoisoquinoline (5-amiq), and (6) 5,6,7,8-tetrahydroisoquinoline (thiq). The crystal structure of complex 1, [Ru3O(CH3COO)6(qui)3]PF6, was determined by X-ray diffraction analysis, showing a high degree of co-planarity between the [Ru3O] plane and the azanaphthalene ligands. Spectroscopic (UV-visible, NMR and Infra-red) and electrochemical (cyclic voltammetry and spectroelectrochemistry) data showed to correlated with pKa values of the azanaphthalene ligands and this dependence was rationalized in terms of the molecular orbital of the [Ru3O] unit and of the structure of the ligands. By analysing the spectroscopic and electrochemical correlations, the ability of the azanaphthalene ligands to extend the electronic π-system of the [Ru3O] unit to the periphery of the compounds was demonstrated. This electronic effect accounts for the planarity of the structure of complex 1. It was also shown through molecular modeling results that, in order to explain the spectroscopic and electrochemical behvaiour of these species, it is not possible to neglect the electronic mixing between the metallic and the acetate orbitals. Finally, this work revealed that electronic coupling is more pronounced in the azanaphthalene series of complexes in comparison with pyridinic analogues and it is this coupling that determines the spectroscopic and electrochemical behaviour of the new species
This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H2L) and its bidirectional noninnocent potential. The reaction of H2L with the selective metal precursor Ru(II)(acac)2(CH3CN)2 (acac(-) = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru(III)(acac)2(HL(-)) (1; blue solid) and diamagnetic Ru(II)(acac)2(L) (2; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual trans configurated and twisted monodeprotonated HL(-) and unprecedented cis configurated nearly planar dehydroindigo (L) bind to the {Ru(acac)2} metal fragment via the N(-),O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N-H···O hydrogen-bonding interaction between the NH proton and C═O group at the back face of the coordinated HL(-), in addition to an intermolecular N-H···O hydrogen bonding between the NH proton of HL(-) of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of 1. The specific role of the electron-rich {Ru(acac)2} metal fragment in stabilizing the cis-configuration of the electron-deficient L in 2 has been pointed out. Both 1 and 2 exhibit reversible one-electron oxidation and successive three reductions with varying Kc (comproportionation constant) values in the range of 10(18)-10(6). The potentials for the redox processes of 2 are positively shifted with respect to those of 1. The involvement of the metal or HL(-)/L or mixed metal-HL(-)/L-based orbitals in the accessible redox processes of 1(n) and 2(n) has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru(acac)2} and the HL(-)/L in the redox processes, which in effect result in mixed electronic structural forms of 1(n) and 2(n) (n = +1, 0, -1, -2, -3).
Helicenes are mols. with ortho-fused arom. rings that adopt an inherently chiral helical shape. This helical topol. combined with the extended π-conjugated system provides them with excellent chiroptical and photophys. properties. These properties and peculiarities make helicenes important candidates for the conception of new chiroptical switches. Several examples of light-, redox- and pH-triggered helicene-based switches have recently appeared in the literature including examples from our group. Some of them are multi-input and/or multi-output systems in which the changes can be triggered by different stimuli and/or read-out by different techniques, an attractive advantage for functional materials.
The new compounds [Ru(acac)2(BIAN)], BIAN = bis(arylimino)acenaphthene (aryl = Ph (1a), 4-MeC6H4 (2a), 4-OMeC6H4 (3a), 4-ClC6H4 (4a), 4-NO2C6H4 (5a)), were synthesized and structurally, electrochemically, spectroscopically, and computationally characterized. The α-diimine sections of the compounds exhibit intrachelate ring bond lengths 1.304 Å < d(CN) < 1.334 and 1.425 Å < d(CC) < 1.449 Å, which indicate considerable metal-to-ligand charge transfer in the ground state, approaching a Ru(III)(BIAN(•-)) oxidation state formulation. The particular structural sensitivity of the strained peri-connecting C-C bond in the BIAN ligands toward metal-to-ligand charge transfer is discussed. Oxidation of [Ru(acac)2(BIAN)] produces electron paramagnetic resonance (EPR) and UV-vis-NIR (NIR = near infrared) spectroelectrochemically detectable Ru(III) species, while the reduction yields predominantly BIAN-based spin, in agreement with density functional theory (DFT) spin-density calculations. Variation of the substituents from CH3 to NO2 has little effect on the spin distribution but affects the absorption spectra. The dinuclear compounds {(μ-tppz)[Ru(Cl)(BIAN)]2}(ClO4)2, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; aryl (BIAN) = Ph ([1b](ClO4)2), 4-MeC6H4 ([2b](ClO4)2), 4-OMeC6H4 ([3b](ClO4)2), 4-ClC6H4 ([4b](ClO4)2), were also obtained and investigated. The structure determination of [2b](ClO4)2 and [3b](ClO4)2 reveals trans configuration of the chloride ligands and unreduced BIAN ligands. The DFT and spectroelectrochemical results (UV-vis-NIR, EPR) indicate oxidation to a weakly coupled Ru(III)Ru(II) mixed-valent species but reduction to a tppz-centered radical state. The effect of the π electron-accepting BIAN ancillary ligands is to diminish the metal-metal interaction due to competition with the acceptor bridge tppz.
Turbomole is a highly optimized software package for large‐scale quantum chemical simulations of molecules, clusters, and periodic solids. Turbomole uses G aussian basis sets and specializes on predictive electronic structure methods with excellent cost to performance characteristics, such as (time‐dependent) density functional theory ( TDDFT ), second‐order M øller– P lesset theory, and explicitly correlated coupled cluster ( CC ) methods. These methods are combined with ultraefficient and numerically stable algorithms such as integral‐direct and Laplace transform methods, resolution‐of‐the‐identity, pair natural orbitals, fast multipole, and low‐order scaling techniques. Apart from energies and structures, a variety of optical, electric, and magnetic properties are accessible from analytical energy derivatives for electronic ground and excited states. Recent additions include post‐ K ohn– S ham calculations within the random phase approximation, periodic calculations, spin–orbit couplings, explicitly correlated CC singles doubles and perturbative triples methods, CC singles doubles excitation energies, and nonadiabatic molecular dynamics simulations using TDDFT . A dedicated graphical user interface and a user support network are also available.
This article is categorized under: Software > Quantum Chemistry
Bis(acetylacetonato)ruthenium complexes [Ru(acac)2(Q1-3)], , incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q1 = 9,10-phenanthrenequinone, ; Q2 = 9,10-phenanthrenequinonediimine, ; Q3 = 9,10-phenanthrenequinonemonoimine, ) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of are involved in intermolecular hydrogen bonding and π-π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Q(n) at 1.296(5)/1.289(5) Å (C-O), 1.315(3)/1.322(4) Å (C-N), and 1.285(3)/1.328(3) Å (C-O/C-N) in , and , respectively, and the well resolved (1)H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [Ru(III)(acac)2(Q˙(-))] (spin-coupled) and [Ru(II)(acac)2(Q(0))], respectively. Complexes exhibit one oxidation and two reduction steps with comproportionation constants Kc ∼ 10(7)-10(22) for the intermediates. The electrochemically generated persistent redox states (n) (n = 0, 1-, 2-) and (n)/(n) (n = 1+, 0, 1-, 2-) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differences in the oxidation state distribution at the {Ru-Q} interface for (n)-(n). In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for Ru(II)(Q(0)) relative to Ru(III)(Q˙(-)) (neutral compounds) and for Ru(II)(Q˙(-)) over the Ru(III)(Q(2-)) alternative in the case of the monoanionic complexes.
A protected ethynyl group was introduced into a γ-position of a (β-diketonato)bis(bipyridine)ruthenium(II) complex through the reaction of the bromo complex and (triisopropylsilyl)-acetylene with very good yield under microwave irradiation. Two new mononuclear mixed-ligand ruthenium(II) complexes with bipyridine (bpy) and functionalized acetylacetonate ion (2,4-pentanedionate, acac−), [Ru(bpd)(bpy)2](PF6) (2; bpy=2,2′-bipyridine, bpd=3-Bromo-2,4-pentanedionate ion) and [Ru(tipsepd)(bpy)2](PF6) (3; tipsepd=3-((triisopropylsilyl)ethynil)-2,4-pentanedionate ion) were then prepared as candidates for building blocks. The 1H NMR, UV–Vis, electrochemistry and FAB mass spectral data of these complexes are presented. X-Ray single crystal diffraction analysis has been made on complex 2, it crystallized with empirical formula of C25H22BrF6N4O2PRu, in a monoclinic crystal system and space group C2/c with a=29.340(5)Å, b=13.282(2)Å, c=15.7492 (14)Å, β=109.452(8)°, V=5786.9(13)Å3 and Z=8.
A series of ruthenium tris(β-diketonate) complexes was investigated by using electrochemistry, UV/Vis spectroscopy, 1H NMR and 13C NMR spectroscopy and FAB mass spectroscopy. Several new mononuclear mixed-ligand ruthenium(III) complexes were prepared: with three dibenzoylmethanate ions (dbm) {[Ru(dbm)3] (1)}, one or two acetylacetonate ions (2,4-pentanedionate, acac) {[Ru(dbm)2(acac)] (2), [Ru(dbm)(acac)2] (3)}, two acetonitrile ligands {[Ru(dbm)2(CH3CN)2][CF3SO3] (4)} or a functionalized acetylacetonate ion {[Ru(dbm)2(acac-I)] (5) (acac-I = 3-iodo-2,4-pentanedionate ion), [Ru(dbm)2(acac-Br)] (6) (acac-Br = 3-bromo-2,4-pentanedionate ion)}. In addition, X-ray structures for complexes 1, 2, 3, 4 and 6 were determined. Scanning tunnelling microscopy measurements at liquid He temperature and in anultra-high vacuum (UHV-STM) were conducted on complex 1 on a Ag(111) surface. This indicates that the complex can be successfully evaporated and observed after adsorption onto a metallic substrate. Analysis of the STM images, supported by adsorption and STM image calculations, demonstrates that the molecules exist in two stable forms when adsorbed onto the surface.
The electronic and geometrical features of a recently synthesized ruthenium β-diketonato complex with a protected ethynyl ligand ([Ru(dbm)(2)(acac-TIPSA)], dbm = dibenzoylmethanate ion, acac-TIPSA = 3-(triisopropylsilyl)acetylene-2,4-pentanedionate ion), a building block for molecular spintronic devices, were analyzed as a function of its oxidation degree using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT), for ground and excited state properties, respectively, and compared to the available experimental data. The UV-Vis spectral signature of a native Ru(iii) neutral form computed at a TD-DFT level was compared to those of the oxidized Ru(iv) and reduced Ru(ii) ones, allowing us to clearly identify the nature of all bands occurring in this spectral region and thus providing important photophysical insights for the use of this complex as a building block in polynuclear organometallic mixed valence molecular systems able to perform a swapping operation under light control.
We report the implementation of the computation of rotatory strengths, based on time-dependent density functional theory, within the Amsterdam Density Functional program. The code is applied to the simulation of circular dichroism spectra of small and moderately sized organic molecules, such as oxiranes, aziridines, cyclohexanone derivatives, and helicenes. Results agree favorably with experimental data, and with theoretical results for molecules that have been previously investigated by other authors. The efficient algorithms allow for the simulation of CD spectra of rather large molecules at a reasonable accuracy based on first-principles theory. The choice of the Kohn–Sham potential is a critical issue. It is found that standard gradient corrected functionals often yield the correct shape of the spectrum, but the computed excitation energies are systematically underestimated for the samples being studied. The recently developed exchange-correlation potentials “GRAC” and “SAOP” often yield much better agreement here with experiments for the excitation energies. The rotatory strengths of individual transitions are usually improved by these potentials as well. © 2002 American Institute of Physics.
SIR2011, the successor of SIR2004, is the latest program of the SIR suite. It can solve ab initio crystal structures of small- and medium-size molecules, as well as protein structures, using X-ray or electron diffraction data. With respect to the predecessor the program has several new abilities: e. g. a new phasing method (VLD) has been implemented, it is able to exploit prior knowledge of the molecular geometry via simulated annealing techniques, it can use molecular replacement methods for solving proteins, it includes new tools like free lunch and new approaches for electron diffraction data, and it visualizes three-dimensional electron density maps. The graphical interface has been further improved and allows the straightforward use of the program even in difficult cases.
The cholesteric-liquid-crystalline structure, which concerns the organization of chromatin, collagen, chitin, or cellulose, is omnipresent in living matter. In technology, it is found in temperature and pressure sensors, supertwisted nematic liquid crystal displays, optical filters, reflective devices, or cosmetics. A cholesteric liquid crystal reflects light because of its helical structure. The reflection is selective - the bandwidth is limited to a few tens of nanometers and the reflectance is equal to at most 50% for unpolarized incident light, which is a consequence of the polarization-selectivity rule. These limits must be exceeded for innovative applications like polarizer-free reflective displays, broadband polarizers, optical data storage media, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. Novel cholesteric-liquid-crystalline architectures with the related fabrication procedures must therefore be developed. This article reviews solutions found in living matter and laboratories to broaden the bandwidth around a central reflection wavelength, do without the polarization-selectivity rule and go beyond the reflectance limit.
We present an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amount of exact exchange. The results obtained for structural, thermodynamic, kinetic and spectroscopic (magnetic, infrared and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chemistry and condensed matter physics.
Computations of natural optical activity (OA) from first principles (ab initio) have become indispensable in chiroptical studies of molecular systems. Calculations are used to assign absolute configurations and to analyze chiroptical data, providing a basis for understanding their origin as well as for assigning and predicting experimental results. In this article, methodology for OA computations is outlined and accompanied by a review of selected, mainly recent (ca. 2010–2016) achievements in optical rotation, electronic and vibrational circular dichroism, and Raman OA calculations. We discuss some important aspects of the computational models and methodological developments, along with recently proposed approaches to analyze and interpret OA parameters. We highlight applications of chiroptical computational methods in studies of helicenes and chiral nanoparticles.
In 2012, the 4 biggest pharmaceutical blockbusters were pure enantiomers and separating racemic mixtures is now frequently a key step in the development of a new drug. For a long time, preparative liquid chromatography was the technique of choice for the separation of chiral compounds either during the drug discovery process to get up to a hundred grams of a pure enantiomer or during the clinical trial phases needing kilograms of material. However the advent of supercritical Fluid Chromatography (SFC) in the 1990s has changed things. Indeed, the use of carbon dioxide as the mobile phase in SFC offers many advantages including high flow rate, short equilibration time as well as low solvent consumption. Despite some initial teething troubles, SFC is becoming the primary method for preparative chiral chromatography. This article will cover recent developments in preparative SFC for the separation of enantiomers, reviewing several aspects such as instrumentation, chiral stationary phases, mobile phases or purely preparative considerations including overloading, productivity or large scale chromatography.
This book provides an introduction to the important methods of chiroptical spectroscopy in general, and circular dichroism (CD) in particular, which are increasingly important in all areas of chemistry, biochemistry, and structural biology. The book can be used as a text for undergraduate and graduate students and as a reference for researchers in academia and industry. Experimental methods and instrumentation are described with topics ranging from the most widely used methods (electronic and vibrational CD) to frontier areas such as nonlinear spectroscopy and photoelectron CD, as well as the theory of chiroptical methods and techniques for simulating chiroptical properties. Applications of chiroptical spectroscopy to problems in organic stereochemistry, inorganic stereochemistry, and biochemistry and structural biology are also discussed, and each chapter is written by one or more leading authorities with extensive experience in the field.
A combined quantum chemistry and electrochemistry study of a series of tris(β-diketonato)-Cr(III) complexes showed that the different electron donating properties of the R and R' groups, substituted on the 1 and 3 positions of the β-diketonate ligand (RCOCHCOR')-, largely influence the redox properties of these complexes, due to the good communication between the R and R' groups and the metal via the β-diketonato-metal conjugated system. Linear relationships were obtained between the reduction potential of the tris(β-diketonato)-Cr(III) complexes and a variety of electronic parameters used to describe the electron-donating and -withdrawing power of the R and R' groups on the β-diketonate ligand.
The theory underlying calculations of electronic optical activity (circular dichroism (CD) and optical rotation (OR)) is discussed. A brief survey of computations of CD and OR for metal complexes and metal clusters using first-principles theory (specifically: time-dependent density functional theory) is provided. Emphasis is placed on the origin of the optical activity of ligand-field transitions and ligand-to-metal charge transfer excitations for complexes of the type ML3 where L is a bidentate ligand. The strong exciton coupling CD in chiral metal complexes with nonchiral ligands with π chromophores such as 1,10-phenanthroline or 2,2'-bipyridine is analyzed with the help of an exciton dipole coupling model and by comparisons of experiment and first-principles calculations.
The properties of mono- and bis-Ru-vinyl[6]helicene complexes (2 a and 2 b, respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π-helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([2 a](.) (+) , [2 b](.) (+) , and [2 b](2+) ), are analyzed with the aid of quantum-chemical calculations. The extended π-conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a,b, introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru-vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal-based helicene derivatives. Finally, the redox-triggered chiroptical switching activity of 2 a,b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.
The new compounds [(bpy)2Os(II)(μ-L1(2-))Os(II)(bpy)2](ClO4)2 ([1](ClO4)2) and [(pap)2Os(II)(μ-L1(2-))Os(II)(pap)2](ClO4)2 ([2](ClO4)2) (H2L1 = 1,4-dihydroxy-9,10-anthraquinone, bpy = 2,2(/)-bipyridine, and pap = 2-phenylazopyridine) and [(bpy)2Os(II)(μ-L2(•-))Os(II)(bpy)2](ClO4)3 ([3](ClO4)3) and [(pap)2Os(II)(μ-L2(2-))Os(II)(pap)2](ClO4)2 ([4](ClO4)2) (H2L2 = 1,4-diamino-9,10-anthraquinone) have been analytically identified as the meso and rac diastereoisomers, respectively. The paramagnetic [3](ClO4)3 was also characterized by crystal structure determination. In CD3CN solution, [3](ClO4)3 displays rather narrow but widely split (13 > δ > -8 ppm) resonances in the (1)H NMR spectrum, yet no EPR signal was observed down to 120 K. Cyclic voltammetry and differential pulse voltammetry reveal several accessible redox states on oxidation and reduction, showing that the replacement of 1,4-oxido by imido donors causes cathodic shifts and that the substitution of bpy by the stronger π-accepting pap ligands leads to a strong increase of redox potentials. Accordingly, system 3(n) with the lowest (2+/3+) potential was synthetically obtained in the mono-oxidized (3+) form. The (3+) intermediates display small comproportionation constants Kc of about 10(3) and long-wavelength near-infrared absorptions; an EPR signal with appreciable g splitting (1.84, 1.96, and 2.03) was only observed for 4(3+), which exhibits the smallest spin density on the osmium centers. An oxidation state formulation [Os(III)(μ-L(•3-))Os(III)](3+) with some [Os(II)(μ-L(2-))Os(III)](3+) contribution was found to best describe the electronic structures. UV-vis-NIR absorption spectra were recorded for all accessible states by OTTLE spectroelectrochemistry and assigned on the basis of TD-DFT calculations. These results and additional EPR measurements suggest rather variegated oxidation state situations, e.g., the pap ligands competing with the bridge L for electrons, while the oxidation produces mixed spin systems with variable metal/ligand contributions.
The compounds Ru(acac)2(Q) (1), [Ru(bpy)2(Q)](ClO4)2 ([2](ClO4)2), and [Ru(pap)2(Q)]PF6 ([3]PF6), containing Q = N,N'-diphenyl-o-benzoquinonediimine and donating 2,4-pentanedionate ligands (acac(-)), π-accepting 2,2(/)-bipyridine (bpy), or strongly π-accepting 2-phenylazopyridine (pap) were prepared and structurally identified. The electronic structures of the complexes and several accessible oxidized and reduced forms were studied experimentally (electrochemistry, magnetic resonance, ultraviolet-visible-near-infrared (UV-vis-NIR) spectroelectrochemistry) and computationally (DFT/TD-DFT) to reveal significantly variable electron transfer behavior and charge distribution. While the redox system 1(+)-1(-) prefers trivalent ruthenium with corresponding oxidation states Q(0)-Q(2-) of the noninnocent ligand, the series 2(2+)-2(0) and 3(2+)-3(-) retain Ru(II). The bpy and pap co-ligands are not only spectators but can also be reduced prior to a second reduction of Q. The present study with new experimental and computational evidence on the influence of co-ligands on the metal is complementary to a report on the substituent effects in o-quinonediimine ligands [Kalinina et al., Inorg. Chem. 2008, 47, 10110] and to the discussion of the most appropriate oxidation state formulation Ru(II)(Q(0)) or Ru(III)(Q(• -)).
The unpolarized absorption and circular dichroism spectra of the
fundamental vibrational transitions of the chiral molecule,
4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields
are obtained using Density Functional Theory (DFT), MP2, and SCF
methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use
the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP)
density functionals. Mid-IR spectra predicted using LSDA, BLYP, and
B3LYP force fields are of significantly different quality, the B3LYP
force field yielding spectra in clearly superior, and overall excellent,
agreement with experiment. The MP2 force field yields spectra in
slightly worse agreement with experiment than the B3LYP force field. The
SCF force field yields spectra in poor agreement with experiment.The
basis set dependence of B3LYP force fields is also explored: the 6-31G
and TZ2P basis sets give very similar results while the 3-21G basis set
yields spectra in substantially worse agreements with experiment.
The new compounds [Ru(R-DAB)(acac)2] (R-DAB = 1,4-diorganyl-1,4-diazabuta-1,3-diene; R = tert-butyl, 4-methoxyphenyl, 2,6-dimethylphenyl; acac– = 2,4-pentanedionate) exhibit intrachelate ring bond lengths 1.297 < d(CN) < 1.344 Å and 1.382 < d(CC) < 1.425 Å, which suggest a RuIII(R-DAB·–) oxidation state formulation. This notion is confirmed by the negligible solvatochromism of the intense (ϵ ≈ 104M–1 cm–1) charge-transfer absorption band in the visible region and by DFT calculations. Oxidation of the compounds occurs mainly at the R-DAB·– radical ligand to produce UV/Vis/NIR and electron paramagnetic resonance (EPR) spectroelectrochemically detectable RuIII species, whereas the reduction proceeds less reversibly and yields predominantly (R-DAB)-ligand-based spin for the 4-methoxyphenyl derivative, measured at low temperature. The results are discussed with respect to metal-to-ligand charge-transfer (MLCT) excited states of conventional (α-diimine)ruthenium(II) complexes and in view of other (α-diimine)metal complexes with ambiguous oxidation-state assignments.
The ‘ruthenium blue solution’ obtained by reducing hydrated ruthenium(III) trichloride with ethanol was used a convenient starting material in the synthesis of thirteen tris(β-diketonato)ruthenium (III) and six tris(β-diketonato)ruthenate(II) complexes. The procedure of preparing the ‘ruthenium blue solution’ requires no catalyst and is much simpler than the previous methods. A variety of complexes were synthesized in good yields with small changes of the conditions. The Hammett constants of the substituents on the ligand serve as a helpful guide for choosing the operating conditions for the preparation of β-substituted complexes. The yields of the complexes with β-substituted ligands are relatively small, since the presence of a bulky substituent at the β-position decreases the fraction of the enol form of the free ligand. The melting points, magnetic moments, Rf values in TLC, UV-Vis, IR, and 1H NMR spectra were measured. The substituent effects on these properties are discussed.
Doping nematic liquid crystals with optically active compounds transforms them into chiral nematic phases with helical structures. In this phenomenon, the chirality of the dopant molecules is transferred or amplified to the bulk of the liquid crystals. Δ-[Ru(acac)3] (acac = acetylacetonato) is known to work as one of the dopants with a strong helical twisting power (HTP). In this study, we have systematically modified [Ru(acac)3] to clarify the correlation between the molecular structure and HTP; we have designed and synthesized five new Ru(III) complexes, [Ru(acac)2(acacC8)] (RuC8-1, acac = acetylacetonate, acacC8 = 3-(4'-octyloxy-phenylalkynyl)-pentane-2,4-dionato), [Ru(acac)(acacC8)2] (RuC8-2), [Ru(acacC8)3] (RuC8-3), [Ru(acacC0)3] (RuC0-3, acacC0 = 3-(phenylalkynyl)-pentane-2,4-dionato), and [Ru(acacC24)3] (RuC24-3, acacC24 = 3-(3',4',5'-tri(octyloxy)-phenylalkynyl)-pentane-2,4-dionato). All the complexes, except for RuC0-3, could be separated into Δ, Λ isomers by HPLC on a chiral column and were examined as chiral dopants for a nematic liquid crystal, N-(4-methoxybenzilidene)-4-butylaniline (MBBA). The Δ isomers of RuC8-1, RuC8-2, RuC8-3, and RuC24-3 induced a right-handed (P) helix and the magnitudes of the HTPs (/μm(-1)) were determined as follows: RuC8-1 (+60) < RuC8-2 (+109) > RuC8-3 (+78) > RuC24-3 (+41). The HTPs of the ruthenium dopants were not simply proportional to their size. The highest HTP observed in biaxial RuC8-2 was attributed to the balance of the molecular helicity and high ordering in MBBA based on the surface chirality model.
The monolayer properties of tris- and bis(diketonato)metal(iii) complexes were investigated at the air–water interface. The following eight complexes were synthesized: [Cr(acacNO2)3 ] (acacNO2=3-nitropentane-2,4-dionato), [Co(acacNO2)3 ], [Ru(PHE)3 ] (PHE=1,3-diphenylpropane-1,3-dionato), [Ru(HPD)3 ] (HPD=heptane-3,5-dionato), [Ru(NND)3 ] (NND=nonane-4,6-dionato), [Ru(DMH)3 ] (DMH=2,6-dimethylheptane-3,5-dionato), fac-[Ru(acacF3)3 ] (acacF3=1-1,3-bis(trifluoromethyl)propane-1,3-dionato) and [Ru(acac)2(PHE)]. When these complexes were eluted with a methanol–chloroform mixture on a column packed with Δ-[Ru(phen)3 ]2+ /laponite, resolution was achieved for [Cr(acacNO2)3 ], [Co(acacNO2)3 ], [Ru(HPD)3 ], [Ru(NND)3 ] and [Ru(acac)2(PHE)]. To study the monolayer behavior, a chloroform solution of a ruthenium(iii) complex was spread onto a water surface and a surface pressure–molecular area (π–A) curve was measured. The π–A curves for [Ru(DMH)3 ], fac-[Ru(acacF3)3 ] and [Ru(NND)3 ] were reversible. The π–A curves for other compounds displaced irreversibly towards smaller molecular areas on the second compression, indicating that the compounds formed microcrystallites under high surface pressure. In the case of [Ru(NND)3 ], the stereochemical effects on monolayer formation were studied by comparing the π–A curves between a racemic mixture and an enantiomer. As a result, the racemic mixture of the complex was found to form a more compact monolayer than the pure enantiomer.
Summary Nonrelativistic and quasirelativisticab initio pseudopotentials substituting the M(Z-28)+-core orbitals of the second row transition elements and the M(Z-60)+-core orbitals of the third row transition elements, respectively, and optimized (8s7p6d)/[6s5p3d]-GTO valence basis sets for use in molecular calculations have been generated. Additionally, corresponding spin-orbit operators have also been derived. Atomic excitation and ionization energies from numerical HF as well as from SCF pseudopotential calculations using the derived basis sets differ in most cases by less than 0.1 eV from corresponding numerical all-electron results. Spin-orbit splittings for lowlying states are in reasonable agreement with corresponding all-electron Dirac-Fock (DF) results.
A cholesteric texture was induced in the liquid crystal (a mixture of N-(4-ethoxybenzylidene)-4-n-alkylanilines doped with (R)-(+)-1,1′-bi-2-naphthol and racemic chromium tris(3-butyl-2,4-pentanedionate) (Cr(3-Buacac)3) by the irradiation of right circular polarized light (r-CPL) and resulting chiroselective photoinversion of Cr(3-Buacac)3. After irradiation of left circular polarized light (l-CPL), the cholesteric fingerprint texture was erased.
General procedures for the synthesis of six series of 3-substituted pentane-2,4-diones are described. The diones mere used as intermediates in the preparation of pyrazoles, isoxazoles, and coordination complexes whose mesogenic properties have been studied. Nematic and smectic phases have been obtained in a number of cases, and the relationship between molecular structure and mesogenic properties has been explored.
The one-electron oxidation and reduction processes at platinum electrodes of a series of β-substituted and γ-substituted tris(β-diketonato)ruthenium(III) complexes are studied in acetonitrile, N,N-dimethylformamide, and nitromethane solutions, each containing 0.1 mol dm−3 (C2H5)4NClO4 at 25 °C. Syntheses of three new γ-substituted derivatives are described. Attempts to isolate the immediate product of the one-electron oxidation of [Ru(acac)3] in acetonitrile failed; bis(acetonitrile)bis(acetylacetonato)ruthenium(III) was obtained instead. Diffusion coefficients of the complexes in the acetonitrile medium are presented. The reversible half-wave potentials for the oxidation and the reduction in the acetonitrile medium depended linearly on the sum of the Hammett constants of the substituents (σp for the β-substituents and σm for the γ-substituents). Analysis of the dependence of the half-wave potentials on several kinds of substituent parameters suggests that the inductive effect is operative at both the β-positions and the γ-position, while the resonance effect is operative only at the β-positions.
We describe herein a concept of optical memory using a photosensitive metal complex, [Cr((-)-tfac)3] ((-)-tfac = (-)-3-trifluoroacetylcamphorato), as a dopant to induce chiral nematic phases. The memory was written by the photo-epimerization of the complex and read-out in terms of circular dichroism spectra. The rewritability of the memory was attempted by using the cycles between liquid crystals and isotropic phases.
Gold containing compounds have shown anticancer potentials, but their clinical applications have been severely limited by poor stability and high toxicity in vivo. Here, we report a novel soluble bis-chelated gold(I)-diphosphine compound (GC20) with strong anticancer activity and low toxicity. GC20 shows strong anti-proliferation potency against a broad spectrum of cancer cell lines including cisplatin-resistant cancer cells (IC50 ≈ 0.5 μM), and significantly reduces tumor growth in several tumor xenografts in mouse models at a dose as low as 2 mg/kg. Studies of its mechanism revealed that GC20 specifically inhibits the enzymatic activity of thioredoxin reductase by binding to selenocysteine residue, without targeting other well-known selenol and thiol groups containing biomolecules. Remarkably, in animal studies GC20 was shown to be well tolerated even at the high dose of 8 mg/kg. Our results strongly suggest that GC20 represents a promising candidate for the development of novel anticancer drugs.
Starting from the screening in conductors, an algorithm for the accurate calculation of dielectric screening effects in solvents is presented, which leads to rather simple explicit expressions for the screening energy and its analytic gradient with respect to the solute coordinates. Thus geometry optimization of a solute within a realistic dielectric continuum model becomes practicable for the first time. The algorithm is suited for molecular mechanics as well as for any molecular orbital algorithm. The implementation into MOPAC and some example applications are reported.
A nematic liquid crystal doped with a chiral dopant has a cholesteric texture with a regular pitch. The pitch is changed by variation of concentration of the dopant. We observed the appearance of a fingerprint texture on irradiation of a homeotropic mixed liquid crystal doped with a racemic chromium complex, Cr(Buacac)3, and an auxiliary chiral dopant, with right-circular polarized light (r-CPL); the fingerprint texture disappeared on irradiation with left-circular polarized light (l-CPL). We also measured a helical twisting power, βm, of the chromium complex from the cholesteric pitch of the mixed liquid crystal doped with optically resolved Λ -(Cr(Buacac)3; and clarified the relationship between the change in the cholesteric pitch and the quantum yield of the photoinversion reaction.
We have found that the discotic nematic liquid crystal, hexakis(4‐nonylphenylethynyl)benzene (HNEB), doped with the racemic chromium complex Cr(Ocacac)3, shows a novel straight‐needle texture with hexagonal columnar alignments, changing to a curved‐needle texture under irradiation of circularly polarized light (CPL). This novel phenomenon is specific to the mixture of HNEB and Cr(Ocacac)3. The formation of curved needles means that chiroselective photoinversion of racemic Cr(Ocacac)3 by CPL irradiation induces a needle direction change in a discotic liquid crystal. The change in chirality of Cr(Ocacac)3 in HNEB induced by CPL irradiation, and the resulting nano‐segregation of its enantiomers during cooling from the isotropic to mesophase of HNEB, are considered to influence changes in the alignment of columns and/or small domains of column aggregates in the discotic liquid crystal.
Two mononuclear mixed-ligand ruthenium(III) complexes with oxalate dianion (ox2−) and acetylacetonate ion (2,4-pentanedionate, acac−), K2[Ru(ox)2(acac)] (1) and K[Ru(ox)(acac)2] (2), were prepared as a candidate for a building block. In fact, reaction of complex 2 with manganese(II) sulfate gave a heterometallic tetranuclear complex, TBA[MnII{(μ-ox)RuIII(acac)2}3] (5) in the presence of tetrabutylammonium (TBA) bromide. The 1H NMR, UV–Vis, selected IR and FAB mass spectral data of these complexes are presented. Both mixed-ligand ruthenium(III) complexes gave a Nernstian one-electron reduction step in 0.1 mol dm−3 Na2SO4 aqueous solution on a mercury electrode at 25 °C. Comparison of observed reversible half-wave potentials with calculated values for a series of [Ru(ox)n(acac)3−n]n− (n=0–3) complexes by using Lever’s ligand electrochemical parameters is presented.
The adequate treatment of solvation effects in the calculation of UV/vis spectra is a complicated task and a general solution of this problem is still outstanding. Continuum solvation models like COSMO at least allow one to take into account a large part of the different solvent effects on electronic excitations, if the dielectric screening is properly implemented within the CI part of the underlying MO program. A comprehensive development of the respective theory is given. This ends up in a rather simple result, and it turns out that most of the former approaches to the problem have been in severe error. Geometry changes of the solute in different solvents have been taken into account for the first time and appear to be of considerable importance. A few example applications of a COSMO-MOPAC implementation are presented.
We have attempted to control the helical pitch of a chiral nematic liquid crystal by the use of a photoresponsive chiral metal complex. For this purpose, a novel Ru(III) complex [Ru(acac)2(L)] was synthesized, where acac and L denote acetylacetonato and 1,3-bis-{4-[6-(4-phenylazo-phenoxy)-hexyloxy]-phenyl}-propane-1,3 -dionato, respectively. The complex underwent cis−trans photoisomerization in methanol when under UV (λmax = 360 nm) or visible (λmax = 450 nm) light illumination, respectively. When the complex was doped into a room-temperature nematic liquid crystal (ZLI-1132), it induced a chiral nematic phase. Under illumination with UV or visible light, the helical pitch of the chiral nematic phase could be changed reversibly by up to 50%. Corresponding to this change, the helical twisting power (HTP) of the complex varied between 34.0 and 22.0 μm-1, or between −43.9 and −26.6 μm-1 at 35.0 °C, where the positive and negative signs corresponded to the Λ- and Δ-enantiomers, respectively. This has been the first attempt at combining the ΔΛ chirality of an octahedral metal complex with the cis−trans isomerization of an azobenzene group in the development of a photoresponsive dopant.
A high-power chiral dopant system involving 6-coordinate metal complexes was designed on the basis of a shape model. Accordingly, a series of mixed 1,3-diketonate complexes of Ru(III), [Ru(acac)2(L-n)], in which acac = acetylacetonate and L-n = dibenzoylmethanate substituted with n octyloxy groups (abbreviated as Ru-n hereafter), was prepared and optically resolved. Their performance as chiral dopants was evaluated in terms of helical twisting power (HTP) in a room-temperature nematic liquid crystal, N-(4-methoxybenzylidene)-4-n-butylaniline (MBBA), by measuring the helical pitch lengths and CD spectra for the induced chiral nematic phases. The Δ- and Λ-enantiomers induced macroscopic left-handed (M) and right-handed (P) helices, respectively, and the (absolute) values for HTP have proven to be remarkably large, e.g. βM = 1.8 × 102 μm-1 in the case of Λ-Ru-2. The induced CD spectra for the dilute MBBA* materials (the asterisk denotes in this paper that MBBA has been doped with a chiral substance) were fit to the interpretation that persistent helical alignment of host molecules was generated. We also performed quantum chemical calculations for the optimum configuration of model Al(III) complexes with and without MBBA molecules and found that two liquid crystal molecules will eventually form a negative dihedral angle (left-handed twist) over the Δ-enantiomer of dialkylated complex.
Ligand chemical shifts are calculated and analyzed for three paramagnetic transition metal tris-acetylacetonato (acac) complexes, namely high-spin Fe(III) and Cr(III), and low-spin Ru(III), using scalar relativistic density functional theory (DFT). The signs and magnitudes of the paramagnetic NMR ligand chemical shifts are directly related to the extent of covalent acac oxygen-to-metal σ donation involving unoccupied metal valence d(σ) acceptor orbitals. The role of delocalization of metal-centered spin density over the ligand atoms plays a minor secondary role. Of particular interest is the origin of the sign and magnitude of the methyl carbon chemical shift in the acac ligands, and the role played by the DFT delocalization error when calculating such shifts. It is found that the α versus β spin balance of oxygen σ donation to metal valence d acceptor orbitals is responsible for the sign and the magnitude of the ligand methyl carbon chemical shift. A problematic case is the methyl carbon shift of Fe(acac)(3). Most functionals produce shifts in excess of 1400 ppm, whereas the experimental shift is approximately 279 ppm. Range-separated hybrid functionals that are optimally tuned for Fe(acac)(3) based on DFT energetic criteria predict a lower limit of about 2000 ppm for the methyl carbon shift of the high-spin electronic configuration. Since the experimental value is based on a very strongly broadened signal it is possibly unreliable.
Historical Perspective on Chiral PolymersChiral Architecture Control in Polymer SynthesisAsymmetry Induction in Nonchiral PolymersChiral Memory Effects. Tuning HelicityChiral Block-Copolymers and Nanoscale SegregationTemplates for Chiral ObjectsOutlookReferences
The quest of molecular electronic devices necessitates addressing model molecular systems as starting points. Among the targeted functions, electron transfer between specic moieties inside a molecule is expected to play a fundamental role for ultimate logical gates. Here we propose a coordination complex exhibiting two inorganic centers (Ru and Si) that constitutes a step toward a more complex architecture. Starting from the complex 1 [Ru(dbm) 2 (acac-I)] (dbm = dibenzoylmethanate ion, acac-I = 3-iodo-2,4-pentanedionate ion), the complex 2 [Ru(dbm) 2 (acac-TIPSA)] (acac-TIPSA = 3-(triisopropylsilyl)acetylene-2,4-pentanedionate ion) was obtained through Sonogashira cross coupling reaction under classical conditions. This complex 2 was characterized by elemental analysis, IR, 1 H NMR, 13 C NMR, UV−vis, cyclic voltammetry, mass spectroscopy as well as X-ray single-crystal diraction. It crystallized with empirical formula of C 46 H 49 O 6 Ru 1 Si 1 in a monoclinic crystal system and space group P2 1 /c with a = 21.077(3) Å, b = 9.5130(7) Å, c = 21.8790(12) Å, β = 94.125(7)°, V = 4375.5(7) Å 3 and Z = 4. Additionally, scanning tunneling microscopy measurements at liquid He temperature and in an ultrahigh vacuum (UHV-STM) were conducted on complex 2 on a Ag(111) surface. The STM images, supported by adsorption and STM image calculations, demonstrate that the molecules exist in two stable forms when adsorbed on the metallic surface.
Introducing metal-vinyl ruthenium moieties onto [6]helicene results in a significant enhancement of the chiroptical properties due to strong metal-ligand electronic interactions. The electro-active Ru centers allow the achievement of the first purely helicene-based redox-triggered chiroptical switches. A combination of electrochemical, spectroscopic, and theoretical techniques reveals that the helicene moiety is a noninnocent ligand bearing a significant spin density.
The twisting power (β) of tris(pentane-2,4-dionato)metal(III) complexes was measured in different nematic liquid crystals at variable temperature. Th
The basic structure of the program system TURBOMOLE for SCF - including first and second analytical derivatives with respect to nuclear coordinates - and MP2 calculations is briefly described. The program takes full advantage of all discrete point group symmetries and has only modest - and (partially) adjustable - I/O and background storage requirements. The performance of TURBOMOLE is documented for demonstrative applications.
Photochemical studies on the use of chiral metal complexes in homogenous and heterogeneous systems are surveyed and commented on their significance. A main focus is laid on the utility of the ΔΛ isomerism of octahedral metal complexes as a chiral source. The reported works demonstrate that chiral metal complexes are effective as a molecular element in achieving varieties of functions such as chiral discrimination, chiral transfer, sensing and photoresponsive guests for biomolecules or liquid crystals.
Despite the remarkable thermochemical accuracy of Kohn–Sham density-functional theories with gradient corrections for exchange-correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional containing local-spin-density, gradient, and exact-exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first- and second-row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) modifying bases developed previously. A large set of more than 300 molecules representing (nearly) all elements-except lanthanides-in their common oxidation states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, density functional theory and correlated methods, for which we had chosen Møller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.
Coordination compounds [Ru(acac)(2)(Q)] (acac=acetylacetonate; Q=o-benzoquinone) were prepared as complexes 1 (Q=o-benzoquinone), 2 (Q=3-methoxy-o-benzoquinone), 3 (Q=4-methyl-o-benzoquinone), and 4 (Q=3,5-di-tert-butyl-o-benzoquinone). The structures of 1 and 2 were determined to reveal a Ru(III)/o-benzosemiquinone formulation, supported by analysis of experimental data (spectroscopy, magnetism of 1) and by DFT calculations. The S=1 ground state calculated for 1 stands in contrast to the spin-paired analogues with arylimino-o-benzosemiquinonato and diimino-o-benzoquinone ligands. The close contacts of about 5.3 Å possible between semiquinone O atoms of different molecules in the crystal allow for intermolecular spin-spin interactions and an overall complex magnetic behavior. One quasireversible oxidation and two reversible one-electron reductions yielded the corresponding molecular ions, which were characterized by UV-visible-NIR and EPR spectroelectrochemistry in terms of [Ru(III)(acac)(2)(Q(0))](+) , [Ru(III)(acac)(2)(Q(2-))](-), and [Ru(II)(acac)(2)(Q(2-))](2-) descriptions in agreement with DFT results. The use of acceptor-substituted 1,2-dioxolenes resulted in the isolation of ionic species Na[Ru(acac)(2)(Q)] (Na(5); Q=4-chloro-o-benzoquinone) and Na(6) (Q=4-nitro-o-benzoquinone), which were similarly investigated as compounds 1-4. Magnetic susceptibility and EPR results confirm an S=1/2 ground state based on ruthenium(III). The combined studies reveal a remarkable substituent sensitivity, and in comparison to recently analyzed Ru(acac)(2) complexes with o-benzoquinone monoimine and diimine ligands, the all-O-donor-containing new systems are distinguished by a qualitatively different metal-ligand interaction based on closer intermolecular radical-radical contacts and on weaker intramolecular dπ-π* interactions.