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Charge-transfer and intraligand electronic spectra of bipyridyl complexes of iron, ruthenium, and osmium. I. Bivalent complexes
Abstract
A series of spin-paired
bivalent bipyridyl complexes of iron, ruthenium, and osmium, of the type
[M(bipy)3]2+, [M(bipy)2X2]n+,
[M(bipy)2XY]n+, [M(bipy)X4]n+, [M(bipy)(X2)2]n+,
and [M(bipy)X2Y2]n+ (X and Y include a range
of monodentate ligands and X2 a range of bidentate ligands) have
been prepared. Their electronic spectra within the range 41000-7000 cm-1
have been recorded. All the complexes show two intraligand transitions which
are present in free bipyridyl. The iron and ruthenium complexes have two metal
oxidation charge-transfer bands, while the osmium complexes have a more complex
charge-transfer pattern. Trends in the positions of the bands have been related
to the bonding of the ligands X and Y to the metal ions. It is suggested that
the energy of the metal t2 type orbitals relative to the ligand
π and π* orbitals is the main factor in determining the intense
electronic spectra of these complexes.
... 48 However, reports in the literature have shown that this d-d transition can be observed even below 400 nm, as observed in our obtained spectra. 51 The reason why transitions in Ru(III) complexes appear at shorter wavelengths than in Ru(II) complexes is that Ru(III) complexes have more chloride ligands, meaning that the bonds may not be as strong as those in Ru(II) complexes with carbonyl-based ligands. Because of the longer bonds of the ligands, d-d transitions can occur at shorter wavelengths. ...
... 48 showed that it was similar to that of other octahedral complexes of Ru(III) and Ru(II). 41,48,51,52 ...
Four ruthenium complexes {[RuCl(CO)(PPh3)2L¹], [RuCl(CO)(PPh3)2L²], [RuCl2(PPh3)2L¹] and [RuCl2(PPh3)2L²]} supported with N‐acylthiourea‐based ligands were synthesized. The compounds prepared were characterized by ¹H NMR, ¹³C NMR, elemental analysis, UV–vis, and magnetic susceptibility methods. The characterization of the molecular structure of two ruthenium complexes {[RuCl(CO)(PPh3)2L¹] and [RuCl2(PPh3)2L¹]} was also performed using the single crystal X‐ray diffraction method. Single crystal X‐ray analyses indicates the existence of different non‐covalent interactions between different parts of the molecules, which led to the formation of three‐dimensional supramolecular architectures and synthons. The magnetic susceptibility and UV‐vis spectra of the prepared ruthenium complexes propose that they are of low‐spin states, where Ru(II) is d⁶ and Ru(III) is d⁵ low spin. These ruthenium compounds functioned as catalysts for the NaBH4‐mediated reduction of various nitro compounds. The catalytic results show that the [RuCl2(PPh3)2L] type complexes exhibit higher catalytic activity than the [RuCl(CO)(PPh3)2L] type complexes, and [RuCl2(PPh3)2L¹] has high catalytic selectivity and efficiency in a short time (>99 yield with catalyst loading 0.01 mol in 0.5 h). Furthermore, the catalytic activity of [RuCl2(PPh3)2L¹] was investigated using nitrobenzene as a model substrate to understand the reaction pathway, and this study proved that this nitro reduction proceeds via a direct pathway, with the formation of N‐hydroxylamine as the main intermediate followed by the occurrence of aniline.
... Also, from researchers such as Bryant et al., unmodied amino acid-functionalized borospherenes are used as a potential carrier for Lamivudine. 29 In this research, the focus centers on tuning the electronic behavior of the studied systems by Fe-group transition metal coordination of Se-doped graphitic carbon for the effective delivery and controlled release of zidovudine within the framework of rst-principles density functional theory (DFT) approach. The primary objective is to determine which of these systems offers the most effective drug delivery for zidovudine, while maintaining compatibility with human cells. ...
This study employed density functional theory (DFT) computational techniques at the ωB97XD/def2svp level of theory to comprehensively explore the electronic behavior of Fe-group transition metal (Fe, Ru, Os) coordination of Se-doped graphitic carbon (Se@g-C3N4) nanosystems in the smart delivery of zidovudine (ZVD), an antiretroviral drug. The HOMO–LUMO results of the interactions show a general reduction in energy gap values across all complexes in the following order: ZVD_Se@C3N4 < ZVD_Ru_Se@C3N4 < ZVD_Fe_Se@C3N4 < ZVD_Os_Se@C3N4. ZVD_Se@C3N4 exhibits the smallest post-interaction band gap of 3.783 eV, while ZVD_Os_Se@C3N4 presents the highest energy band gap of 5.438 eV. Results from the corrected adsorption energy (BSSE) revealed that Os_Se@C3N4 and Ru_Se@C3N4 demonstrated more negative adsorption energies of −2.67 and −2.701 eV, respectively, pointing to a more favorable interaction between ZVD and these systems, thus potentially enhancing the drug delivery efficiency. The investigation into the drug release mechanism from the adsorbents involved a comprehensive examination of the dipole moment and the influence of pH, shedding light on the controlled release of ZVD. Additionally, investigating the energy decomposition analysis (EDA) revealed that ZVD_Ru_Se@C3N4 and ZVD_Fe_Se@C3N4 exhibited the same total energy of −787.7 kJ mol⁻¹. This intriguing similarity in their total energy levels suggested that their stability was governed by factors beyond reactivity, possibly due to intricate orbital interactions. Furthermore, analyzing the bond dissociation energies showed that all systems exhibited negative enthalpy values, indicating that these systems were exothermic at both surface and interaction levels, thus suggesting that these processes emitted heat, contributing to the surrounding thermal energy.
... Furthermore, it was still interesting that there was no activity evident for complex 3's major ligand 2BUT and even its analogue complex 6 from the previous work. In that case, we suspect that, upon coordinating 2BUT with ruthenium, the 2BUT ligand became enabled or complex 2 which had no 2BUT ligand became enabled when coordinated with the 2BUT ligand, consistent with previous studies [17][18][19][20]. As for the analogue complex 6, we suspected the introduction of the bridge in complex 3 may have induced the bioactivity of this complex towards MRSA. ...
A new hexadentate 2-picolyl-polypyridyl-based ligand (4, 4'-(butane-1, 4-diylbis(oxy))bis(N, N-bis(pyridin-2-ylmethyl)aniline)) (2BUT) (1) and its corresponding Ru(II/III) complexes were synthesized and characterized, followed by assessment of their possible bioactive properties towards drug-resistant and non-drug-resistant bacteria. Spectroscopic characterization of the ligand was done using proton NMR, FTIR, and ESI-MS, which showed that the ligand was successfully synthesized. The Ru(II/III) complexes were characterized by FTIR, UV/Vis, elemental analysis, proton NMR, ESI-MS, and magnetic susceptibility studies. The analysis of ESI-MS data of the complexes showed that they were successfully synthesized. Empirical formulae derived from elemental analysis of the complexes also indicated successful synthesis and relative purity of the complexes. The important functional groups of the ligands could be observed after complexation using FTIR. Magnetic susceptibility data and electronic spectra indicated that both complexes adopt a low spin configuration. The disc diffusion assay was used to test the compounds for antibiotic activity on two bacteria species and their drug-resistant counterparts. The compounds displayed antibiotic activity towards the two non-drug-resistant bacteria. As for the drug-resistant organisms, only [Ru2(2BUT)(DMF)2(DPA)2](BH4)43 and 2, 2-dipyridylamine inhibited the growth of MRSA. Gel electrophoresis DNA cleavage studies showed that the ligands had no DNA cleaving properties while all the complexes denatured the bacterial DNA. Therefore, the complexes may have DNA nuclease activity towards the bacterial genomic material.
... e electronic spectra results are summarized in Table 2. However, reports have shown that this can be observed even below 400 nm [27,28]. ...
The potential antimicrobial properties of a tridentate polypyridyl ligand 4-butoxy-N,N-bis(pyridin-2-ylmethyl)aniline (BUT) 1 and its corresponding mixed ligand ruthenium complexes were investigated on drug-resistant and non-drug-resistant bacterial species. The ligand and its complexes were synthesized and successfully characterized by 1H NMR, UV/Vis, and FTIR spectra; ESI-MS; and magnetic susceptibility. Electronic spectra and magnetic susceptibility of these Ru(II)/(III) complexes suggest that they are of a low spin crystal field split, where the Ru(III) is a d5 and Ru(II) d6 low spin. These compounds were tested for antibacterial activity on two bacterial species: Staphylococcus aureus (S. aureus) and Klebsiella pneumoniae (K. pneumoniae), as well as their drug-resistant strains methicillin-resistant Staphylococcus aureus (MRSA) and multidrug resistant Klebsiella pneumoniae (MDR K. pneumoniae). All the compounds inhibited growth of the two non-drug-resistant bacteria and only one drug-resistant strain MRSA. However, only the ligands BUT and 2,2-dipyridylamine showed activity against MRSA, while all complexes did not show any antibacterial activity on MRSA. We observed large zones of inhibition for the Gram-positive S. aureus and MRSA bacteria, compared to the Gram-negative K. pneumoniae bacteria. DNA cleavage studies with gel electrophoresis showed denatured bacterial DNA on the gel from all the complexes, with the exception of the ligand, suggesting DNA nuclease activity of the complexes in the bacterial DNA.
... The electronic spectrum of the phendione ligand and the strontium phendione complex were measured in the ethanol solution ( Figure 2S). Phendione ligand showed absorption bands in the UV region 206, 236 nm (π→π*) and 258 nm (n→π*), the strontium complex showed absorption bands in the UV region 222, 254 nm (π→π*) and 273 nm ((n→π*) [21][22][23][24][25] . Moreover, it exhibited lowerenergy absorptions band (313 nm) indicating that solvent dependency is not present in the spectra of the ligand but there is in the complex spectra. ...
... In 1991, O'Regan and Grätzel, reported IPCE of more than 80% from a DSSC using [Figure 4 . According to Bryant et al. [8], the carboxylated complexes exhibit two t 2 → π* MLCT bands in the near UV and visible region. The absorbance of Ru(2,2′-bipyridine-4,4′-dicarboxylicacid) 2 (NCS) 2 , i.e. ...
The need to produce renewable energy with low production cost is indispensable in
making the dream of avoiding undue reliance on non-renewable energy a reality. The
emergence of a third-generation photovoltaic technology that is still in the infant stage
gives hope for such a dream. Solar cells sensitized by dyes, quantum dots and perovskites
are considered to be third-generation technological devices. This research focuses on the
development of suitable and reliable sensitizers to widen electromagnetic (EM) wave
absorption and to ensure stability of the photovoltaic system. This article discusses the
basic principles and the progress in sensitized photovoltaics.
... The intensities of these transitions occur on the lower range of those observed for many HS Fe(II) compounds containing diimine or pyridine-type ligands [53,54]. Multiple MLCT absorption features arising from the t 2g donor orbitals on the Fe (II) to the π* acceptor orbitals of the ligands [48,55,56] [51,52]. While two distinct bands are not clearly resolved for the imine and quinoline charge transfer transitions in these spectra, this phenomenon is common for d 6 compounds when the functionalities are similar to one another, such as pyridine and quinoline nitrogens [34] and, in general, high spin (HS) Fe(II) octahedral structures demonstrate a broad absorption band due to weak Jahn Teller distortion [34]. ...
One of the key concerns with the development of radical-generating reactive therapeutics is the ability to control the activation event within a biological environment. To that end, a series of quinoline–metalloenediynes of the form M(QuiED)·2Cl (M = Cu(II), Fe(II), Mg(II), or Zn(II)) and their independently synthesized cyclized analogs have been prepared in an effort to elucidate Bergman cyclization (BC) reactivity differences in solution. HRMS(ESI) establishes a solution stoichiometry of 1:1 metal to ligand with coordination of one chloride counter ion to the metal center. EPR spectroscopy of Cu(QuiED)·2Cl and Cu(QuiBD)·2Cl denotes an axially-elongated tetragonal octahedron (g|| > g⊥ > 2.0023) with a ground state, while the electronic absorption spectrum reveals a pπ Cl→Cu(II) LMCT feature at 19,000 cm−1, indicating a solution structure with three nitrogens and a chloride in the equatorial plane with the remaining quinoline nitrogen and solvent in the axial positions. Investigations into the BC activity reveal formation of the cyclized product from the Cu(II) and Fe(II) complexes after 12 h at 45 °C in solution, while no product is observed for the Mg(II) or Zn(II) complexes under identical conditions. The basis of this reactivity difference has been found to be a steric effect leading to metal–ligand bond elongation and thus, a retardation of solution reactivity. These results demonstrate how careful consideration of ligand and complex structure may allow for a degree of control and selective activation of these reactive agents.
... Its assignment, though discussed in the literature, is still controversial, and different authors have proposed a metal centered d-d transition, 59 which borrows intensity from a close-lying allowed transition or to a second 1 MLCT or to 1 LMCT transition. 60 However, TD-DFT calculations of the complexes suggest that this band is a mixture, predominantly of 1 MLCT origin with minor involvement of a LC transition (see Tables S4 and S6 in ESI †). 41 It may be noted that such a band near 345 nm is usually observed for [RuN 4 (diamine)] 2+ chromophores. ...
A novel N^N^N tridentate ligand dgpy (dgpy = 2,6-diguanidylpyridine) was synthesized by a Pd-catalyzed C–N bond-forming reaction. A novel family of [RuII(tpy')(dgpy)](PF6)2 (1 and 2) or [RuII(dpt')(dgpy)](PF6)2 (3 and 4) (tpy' = substituted-2,2′:6′,2′-terpyridine, dpt' = substituted-2,4-dipyrid-2′-yl-1,3,5-triazine) complexes are reported. The dgpy ligand (80%) and the heteroleptic complexes 1–4 (37–60%) were obtained in modest to good yields. The dgpy ligand and its complexes were fully characterized by a variety of techniques including X-ray crystallography and density functional theory (DFT). In cyclic voltammetric studies, the complexes exhibit a RuIII/II couple, which is 600–800 mV less positive than the RuIII/II couple in [Ru(tpy)2]2+. The 1MLCT absorption maxima of all the complexes (620–740 nm) are considerably red-shifted as compared to that of [Ru(tpy)2]2+ (474 nm). The 3MLCT emission maxima of complexes 1 and 2 are also red-shifted by about 270 nm compared to that of [Ru(tpy)2]2+ (629 nm) at room temperature (298 K), whereas the corresponding maxima for complexes 3 and 4 are shifted by about 330 nm at 77 K. The relative trends in redox potentials and 1MLCT maxima are in good agreement with DFT and TD-DFT calculations. Complexes 1 and 2 emit from a RuII-to-tpy 3MLCT state, which is rarely the emitting state at λ > 850 nm in [Ru(tpy)(N^N^N)]2+ complexes when the ancillary ligand is neutral. Complexes 1 and 2 also exhibit long excited-state lifetimes (τ 100 ns) at room temperature with associated quantum yield (Φ) of 0.001. The reported τ and Φ values are approximately 400–500 times and 1000 times higher compared to those of [Ru(tpy)2]2+ (τ = 0.25 ns, Φ ≤ 5 × 10−6), respectively. Complexes 3 and 4 emit from a RuII-to-dpt 3MLCT state, albeit only at 77 K (τ = 0.25 ns) due to rapid deactivation of their 3MLCT state according to the energy-gap law. The improved photophysical properties of the complexes are consequences of enlarged separation of the 3MLCT–3MC states, due to the strong donation and larger bite angles of the dgpy ligand.
A series of π-aromatic-rich cyclometalated ruthenium(II)-(2,2′-bipyridine) complexes ([Ru(bpy)2(πAr-CM)]⁺) in which πAr-CM is diphenylpyrazine or 1-phenylisoquinoline were prepared. The [Ru(bpy)2(πAr-CM)]⁺ complexes had remarkably high phosphorescence rate constants, kRAD(p), and the intrinsic phosphorescence efficiencies (ιem(p) = kRAD(p)/(νem(p))³) of these complexes were found to be twice the magnitudes of simply constructed cyclometalated ruthenium(II) complexes ([Ru(bpy)2(sc-CM)]⁺), where νem(p) is the phosphorescence frequency and sc-CM is 2-phenylpyridine, benzo[h]quinoline, or 2-phenylpyrimidine. Density functional theory (DFT) modeling of the [Ru(bpy)2(CM)]⁺ complexes indicated numerous singlet metal-to-ligand charge transfers for ¹MLCT-(Ru-bpy) and ¹MLCT-(Ru-CM), excited states in the low-energy absorption band and ¹ππ*-(aromatic ligand) (¹ππ*-LAr) excited states in the high-energy band. DFT modeling of these complexes also indicated phosphorescence-emitting state (Te) configurations with primary MLCT-(Ru-bpy) characteristics. The variation in ιem(p) for the spin-forbidden Te (³MLCT-(Ru-bpy)) excited state of the complex system that was examined in this study can be understood through the spin–orbit coupling (SOC)-mediated sum of intensity stealing (∑SOCM-IS) contribution from the primary intensity of the low-energy ¹MLCT states and second-order intensity perturbation from the significant configuration between the low-energy ¹MLCT and high-energy intense ¹ππ*-LAr states. In addition, the observation of unusually high ιem(p) magnitudes for these [Ru(bpy)2(πAr-CM)]⁺ complexes can be attributed to the values for both intensity factors in the ∑SOCM-IS formalism being individually greater than those for [Ru(bpy)2(sc-CM)]⁺ ions.
Two benchmark sensitizers used for dye-sensitized solar cells, ruthenium polypyridyl N719 and Z907 dyes were investigated with spectroscopic methods as steady-state absorption, time-gated phosphorescence and femto-/nanosecond time-resolved transient absorption at room temperature and at 160 K. Aim of this study was to perform comprehensive photophysical study of dye excited singlet and triplet metal-to-ligand charge transfer (MLCT) states including states lifetimes, dependency on temperature and dye concentration and obtain detailed information on the excitation decay pathway. Transient absorption and phosphorescence decay data provided a clearer picture of the dynamics of the excited MLCT states. Based on data analysis, the excitation decay pathway consists of rapid intersystem crossing to the triplet MLCT state that undergoes state solvation and vibrational relaxation. It was demonstrated that the lifetime of the fully relaxed triplet MLCT is also strongly dependent on dye concentration for both molecules, providing a viable explanation for a large inconsistency seen in previous studies.
The 77K emission spectra of cyclometalated ruthenium(II)-2,2’-bipyridine (CM-Ru-bpy) chromophores are very similar to those of related Ru-bpy complexes with am(m)ine or diimmine ancillary ligands and DFT modeling confirms that the lowest energy triplet metal to ligand charge transfer (</sup>3<sup>MLCT) excited states of CM-Ru-bpy and related Ru-bpy complexes have very similar electronic configurations. However, the phosphorescence decay efficiencies of CM-Ru-bpy excited states are about twice those of the conventional Ru-bpy analogs. In contrast to the similar </sup>3<sup>MLCT excited state electronic configurations of the two classes of complexes, the CM-Ru-bpy chromophores have much broader visible region MLCT absorptions resulting from several overlapping transitions, even at 87K. The emitting excited state emission efficiencies of depends on spin-orbit coupling (SOC) mediated intensity stealing from singlet excited states and this work explores the relationship between the phosphorescence efficiency and visible region absorption spectra of Ru-bpy </sup>3<sup>MLCT excited states in the weak SOC limit. The intrinsic </sup>3<sup>MLCT emission efficiency, ι <sub>em</sub>, depends on mixing with singlet excited states whose Ru</sup>III<sup>-dπ-orbital angular momenta differ from that of the emitting state. Density functional theory DFT modeling of the </sup>1<sup>MLCT excited state electronic configurations that contribute significantly to the lowest energy absorption bands have Ru</sup>III<sup>-dπ-orbitals that differ from those of their emitting 3MLCT excited states. This leads to a very close relationship between ι <sub>em</sub> and the lowest energy MLCT-band absorptivities in Ru-bpy chromophores. Thus, the larger number of </sup>1<sup>MLCT transitions that contribute to the lowest energy absorption bands accounts for the enhanced phosphorescence efficiency of Ru-bpy complexes with cyclometalated ancillary ligands.
Three tri-nuclear cyanide-bridged heteronuclear complexes, [cis-MII(bpy)2(CN)2]2MnIII(salcy) (PF6) (M = Fe, 1; M = Ru, 2; M = Os, 3; bpy = 2, 2’-bipyridine, salcy = N, N’-(1,2-cyclohexanediylethylene) bis(salicylideneiminato) dianion) were synthesized by reaction of cis-MII(bpy)2(CN)2 (M = Fe, Ru, Os) with [MnIII(salcy)]+ ion in the presence of NH4PF6, respectively. Complexes 1-3 were all fully characterized by IR, UV, MS, elemental analysis and single-crystal X-ray diffraction analysis. The magnetic susceptibilities of complexes 1-3 were measured and analyzed, and complexes 1 and 2 show low temperature antiferromagnetic order, which were confirmed by FC-ZFC (field-cooled and zero-field-cooled) measurement. This work demonstrates that the diamagnetic metal ions MII (M = Fe, Ru and Os) have effectively influence on the magnetic properties of the cyanide-bridged complexes [cis-MII(bpy)2(CN)2]2MnIII(salcy) (PF6).
The near-UV and visible light induced interfacial electron transfer (IFET) process between aqueous solution of [Fe(bipy)2Cl2][FeCl4] complex and TiO2 NPs has been proved at first time and the photochemical products were mainly characterized by electronic absorption, Fe K-edge X-ray absorption fine structure, electron paramagnetic resonance and ⁵⁷Fe Mössbauer spectroscopic method. This study makes in comprehending for the combination of semiconductor NPs and metal complex, in-particularly ionic salt like complex has potential in environmental friendly synthesis and remediation process.
For the first time, the [Sr(OH2)4(phen-dione)2](Cl)2 complex (Sr-Phen) was synthesized and characterized by different spectroscopy techniques such as ¹H-NMR, UV-Vis, FT-IR and conductometry as well as elemental analysis. The prepared complex was used for modification of graphite paste electrode for simultaneous determination of 4-aminophenol (AP), uric acid (UA), and tryptophan (Trp). Detailed investigations by electrochemical impedance spectroscopy and electrochemistry methods were used in order to elucidate the properties of the modified graphite paste electrode with Sr-Phen. The proposed modified electrode displays intense and indelible electrooxidation responses for simultaneous determination of AP, UA, and Trp to three well-separated peaks in potential range from 0.4 to 1.1V using cyclic and differential pulse voltammetry methods in pH 2.0. Based on the experimental results the detection limits of 3.40, 1.06 and 1.32 μM were obtained for AP, UA and Trp, respectively. Finally, the proposed modified electrode was used for simultaneous determination of AP, UA and Trp in real samples.
Significance
Pharmaceuticals often act within a lock-and-key model whereby molecules bind their targets nearly irreversibly, either stalling or initiating biological processes. Here, the agent itself performs no chemical transformation on its target but rather triggers an event or cascade. However, unwanted side effects become more likely as the reactivity of these molecules increases. In contrast, molecular compounds may irreversibly damage biological targets using metal-mediated radical chemistry, but controlling the onset and extent of reaction is challenging. Even so, multiple examples of metal-containing or metal-radical paradigms have been used clinically for imaging and chemotherapy. Within this framework we report a class of metal-mediated radical generators that attack DNA, outcompete DNA polymerase, and are cytotoxic in short times and modest concentrations.
A series of binuclear ruthenium(II)-polypyridyl complexes of the type [Ru2 (N-N)4 (BPIMBp)](4+) , in which N-N is 2,2'-bipyridine (bpy; 1), 1,10-phenanthroline (phen; 2), dipyrido[3,2-d:2',3-f] quinoxaline (dpq; 3), dipyrido[3,2-a:2',3'-c] phenanzine (dppz; 4), and 1,4'-bis[(2-pyridin-2-yl)-1H-imidazol-1-yl)methyl]-1,1'-biphenyl (BPIMBp) is a bridging ligand, have been synthesized and characterized. These complexes are charged (4+) cations and flexible due to the -CH2 group of the bridging ligand and possess terminal ligands with variable intercalative abilities. The interaction of complexes 1-4 with calf thymus DNA (CT-DNA) was explored by using UV/Vis absorption spectroscopy, steady-state emission, emission quenching with K4 [Fe(CN)6 ], ethidium bromide displacement assay, Hoechst displacement assay, and viscosity measurements and revealed a groove-binding mode for all the complexes through a spacer and an intercalative mode for complexes 3 and 4. A decrease in the viscosity of DNA revealed bending and coiling of DNA, an initial step toward aggregation. Interestingly, a distinctive honeycomb-like ordered assembly of the DNA-complex species was visualized by fluorescence microscopy in the solution state. The use of SEM and AFM confirmed the disordered self-organization of the DNA-complex adduct on evaporation of the solvent. The small orderly nanosized DNA aggregates were confirmed by means of circular dichroism, dynamic light scattering (DLS), and TEM. These complexes are moderately cytotoxic against three different cell lines, namely, MCF-7, HeLa, and HL-60.
The 77 K ³MLCT emission quantum yields and radiative rate constants of ruthenium(II) complexes with monodentate aromatic acceptor ligands (Ru-MDA) are smaller than those of their analogs with bipyridine acceptor ligands because “intensity stealing” from a higher energy aromatic ligand-localized excited state is more important for the Ru-bpy than for the Ru-MDA chromophores in the available excited state energy range. The radiative rate constant divided by the emission energy provides a probe of the exited state mixing.
Two synthetic approaches towards the mononuclear complex [(tbbpy)2OsII(tpphz)]2+ (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) based on the precursor [(tbbpy)2OsIICl2] and its oxidized side product [(tbbpy)2OsIIICl2]+ are presented. The first route is analogous to that for the isostructural ruthenium complex, whereas the second strategy efficiently uses the oxidized OsIII complex under reducing conditions to obtain so-called virtual dilution, which avoids the formation of the dinuclear complex [(tbbpy)2OsII(tpphz)OsII(tbbpy)2]. Concentration-dependent NMR investigations were performed, and a dimerization constant (KD = 400) could be calculated due to π-π interactions of the tpphz moiety. Solid-state structures of all synthesized complexes show comparable bond lengths and angles with respect to each other and their ruthenium analogues. Photophysical investigations show the expected absorption in the UV/Vis region and a single emission at 758 nm for [(tbbpy)2OsII(tpphz)]2+. Electrochemical measurements show comparable behavior to the structurally similar complexes [(bpy)2M(tpphz)]2+ (M = Os, Ru).
Die Elektronenspektren der teils bekannten, teils erstmalig dargestellten, sechsfach-koordinierten Komplexe (I), (II) und (III) werden aufgenommen und diskutiert, um den Einfluß der koordinierten X1-X4-Liganden auf die spektralen Intraligand- und Ladungsübertragungs-Banden zu bestimmen.
Two tetra-nuclear cyanide-bridged square complexes [cis-Fe(bpy)2(CN)2Mn(L)]2[PF6]4 (1) and [cis-Os(bpy)2(CN)2Mn(L)]2[PF6]2[ClO4]2 (2) (bpy = 2,2′-bipyridine, L = 1,6-diphenyl-2,5-bis(2-methylpyridyl)-2,5-diazahexane) were synthesized and fully characterized. The tetra-nuclear [cis-M(bpy)2(CN)2Mn(L)]24+ (M = Fe (1), Os (2)) cation is composed of two [M(bpy)2(CN)2] and two [Mn(L)]2+ centers. Each MII ion adopts a distorted [MN4C2] octahedral coordination, surrounded by four nitrogen atoms from two bpy ligands and two carbon atoms from the cyanide groups in a cis position. Each Mn2+ ion adopts a distorted [MnN6] octahedral coordination, occupied by four nitrogen atoms from L and two nitrogen atoms from the cyanide groups in a cis position. The magnetic susceptibilities measurements indicate 1 is weak ferromagnetic, and 2 is weak antiferromagnetic.
The electrochemical behaviour of the binuclear complex NC-Run(bpy)2-CNRuσ(bpy)2-CN+(1) and of the trinuclear complexes NC-Ruσ(bpy)2-CN-Ruσ(bpy)2-NC-Ruσ(bpy)2CN2+ (2), NC-Ruσ(bpy)2-CN-Ruσ(DCE-bpy)2-NC-Ruσ(bpy)2-CNP2+ (3) is described. These complexes give rise to extended redox series. Metal localized one-electron oxidation processes are assigned on the basis of the comparison with the model Ru(bpy)2(CN)2 complex. Ligand localized reductions are fully reversible at -54°C. The assignment of the redox sites, which are involved in such processes, is given taking into account the different electronic perturbation introduced at metal centres by the asymmetric bridging ligand as well as the energy difference between π* accepting orbital of the different polypyridine ligands. The experimentally determined redox series consist of nine, thirteen and fourtheen redox steps for the binuclear complex 1 and for the trinuclear complexes 2 and 3 respectively.
A series of dinuclear [(bpy)2Ru(L)Ru(bpy)2]4+ and mononuclear ruthenium(II) complexes [(bpy)2Ru(L)]2+ where bpy is 2,2′-bipyridine and L represents 2,6-di(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)aryl ligands (DIP) were synthetized and characterized. An original pathway is proposed to obtain mono and hetero bi- and polymetallic Ru complexes and the relation between the molecular structure, the photophysical and electrochemical properties of the single Ru complexes is analysed. The investigated aryl cores are benzene, pyridine and 4-tert-butyl phenol. This work is focused on the effect of the aromatic moiety on the photoinduced charge transfer in the bimetallic compounds and the results are compared with the monometallic analogues. The absence of effect on the UV-visible absorption spectra and on the redox behavior upon varying the nature of the aryl moiety show that the two metallic centres in [(bpy)2Ru(L)Ru(bpy)2]4+ complexes are independent. However, luminescence measurements coupled with DFT calculations highlight a different photophysical behaviour between mono and dinuclear compounds incorporating the benzene core. Theoretical DFT and TD-DFT modelling was used to support the studied physico-chemical properties of these molecular systems.
The 3MLCT excited states of pentaammine−Ru(II) complexes with monodentate aromatic ligands have longer lifetimes but much weaker emissions in 77 K glasses than do their Ru−bpy analogues. Density functional theory modeling of the low-energy triplet excited states of these complexes usually finds the 3MLCT states at lower energy than the triplet metal-centered states because the latter vary much less. Energies of the 3MC states appear to be dictated largely by Ru−ligand bond energies along their distortion axes.
The interaction of the aqua ligand substitution from cis-diaqua-bis(bipyridyl) ruthenium(II) complex ([Ru(bpy)2(H2O)2]2+) and hydroxopentaaqua rhodium(III) complex ([Rh(H2O)5(OH)]+2) by azide has been
studied spectrophotometrically as a function of [substrate complex], [ligand] and temperature at pH 4.5 for the first complex and pH 4.3 for the second complex, at constant ionic strength. The substitution reaction for both complexes shows two consecutive steps. Both steps are [ligand]-dependent.
The activation parameters for both steps were evaluated. Thermodynamic parameters calculated from the temperature dependence of the outer-sphere association equilibrium constants are also consistent with an associative mode of activation. The products of the reactions have been characterised
by IR, and ESI-mass spectroscopic analysis.
To investigate how the central diamagnetic cyanidometal influences the distant magnetic interaction of cyanide-bridged Fe(III)-M(II)-Fe(III) complexes, cis-[Cp(dppe)FeII(NC)MII(L)2(CN)FeII(dppe) Cp][PF6]2 (M = Os, L = bpy 1; M = Os, L = phen 2; M = Fe, L = bpy 3; M = Fe, L = phen 4), and their one-electron oxidation products 5-7 and two-electron oxidation products 8-11 were synthesized and fully characterized. The cyclic voltammetry of complexes 1-4 suggests that both NC-OsII(L)2-CN and NC-FeII(L)2-CN have electronic communication ability. The electronic absorption spectroscopy suggests the presence of the central MII to the terminal FeIII and the terminal FeII to the terminal FeIII metal to metal charge transfers (MMCTs) in 5-7 and the central MII to the terminal FeIII MMCTs in 8-11. Moreover, for the two-electron oxidation products the MMCT energy increases with the central metal of the order Fe < Os < Ru. The two-electron oxidation complexes 8 and 9 exhibit a strong antiferromagnetic coupling (J -26 cm-1) between the two distant FeIII ions although separated by the diamagnetic cyanidometal NC-OsII(L)2-CN bridge. To the best of our knowledge, this is the strongest magnetic coupling between the distant paramagnetic metal ions across a diamagnetic cyanidometal bridge reported by far. For the two-electron oxidation complexes 10 and 11 with the diamagnetic NC-FeII(L)2-CN bridge, however, the distant two FeIII ions posses only very weak antiferromagnetic coupling (J = -0.15 and -0.19 cm-1). Combined with our previous reported results, it could be found that the magnetic coupling strength between the distant FeIII ions increases with the diamagnetic cyanidometal bridge in the order of Fe < Ru < Os.
The variations in bandshape with excited state energy found for the triplet metal to ligand charge transfer ((3)MLCT) emission spectra of ruthenium-bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited state/excited state configurational mixing. This issue is more critically examined through the determination of the excited state energy dependence of the radiative rate constants (kRAD) for these emissions. Experimental values for kRAD, were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, kRAD can be anomalously small and such complexes have been identified using density functional theory (DFT) modeling. When such complexes are removed from the energy correlation, there is a strong (3)MLCT energy dependent contribution to kRAD in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10,000 cm(-1). This correlates with the DFT calculations which show significant excited state electronic delocalization between a π(bpy-orbital) and a half-filled dπ*-(RuIII-orbital) for Ru-bpy complexes with (3)MLCT excited state energies greater than about 16,000 cm(-1). Overall, this work implicates the "stealing" of emission bandshapes as well as stealing from the higher energy, strongly allowed bpy-centered singlet ππ* excited state.
The geometrical isomers, cis-dichlovo-trans-(methanol) (hydroquinone) (2,2′-bipyridine)ruthenium(II) and cis-dichlovo-cis-(methanol)(hydroquinone)(2,2′-bipyridine)ruthenium(II), [RuCl2(MeOH)(QH2)bipy] (complex I and II), were synthesized by reduction and substitution reactions of [RuO4bipy] and [RuO2(OH)2bipy] with hydroquinone in hydrochloric acid solution, and methanol. cis-Chloro(hydroquinonato)bis(2,2′-bipyridine)-ruthenium(II), cis-[RuCl(QH)(bipy)2], was obtained from the substitution reaction of complex I or II with 2,2′-bipyridine in methanol, and cis-chloro(hydroquinone)bis(2,2′-bipyridine)ruthenium(II) chloride, cis-[RuCl(QH2)-(bipy)2]Cl, was also obtained from the substitution of cis-trans-[RuCl2(MeOH)(QH2)bipy] in methanol containing hydrochloric acid. cis-Dihydroxobis(2,2′-bipyridine)ruthenium(II),cis-[Ru(OH)2(bipy)2], was obtained by heating an aqueous solution of cis-[RuCl (QH) (bipy) 2]. Trihydroxoaquo (1,10-phenanthroline) ruthenium (III), [Ru(OH)3(H2O)phen] was also synthesized from [RuO3phen]2O and [Ru(OH)3phen]2O by reduction reactions similar to those used for [RuCl2(MeOH)(QH2)bipy]. These complexes were characterized by the infrared, visible and ultraviolet absorption spectra, and also by polarographic and magnetic measurements. The structures are discussed.
Four new one-dimensional (1D) zigzag chain cyanide-bridged complexes [cis-MII(L)2(CN)2FeIII(salen)](PF6) ( M = Fe, L = bpy, 3; M = Fe, L= phen, 4; M = Ru, L = bpy, 5; M = Os, L = bpy, 6) (bpy = 2, 2’-bipyridine, phen = 1, 10-phenanthroline, salen = N, N’-ethylenebis(salicylideneaminato) dianion) have been synthesized and characterized structurally as well as magnetically, especially 3 and 4 are mixed-valence complexes. Fortunately, the crystals of complexes 3, 4 and 6 suitable for single-crystal X-ray diffraction analysis were obtained. Also, the electronic absorption spectra indicate the existence of the MMCT (metal-to-metal charge transfer) bands in complexes 3-6. Temperature dependent magnetic susceptibilities reveals that the Fe(III)-Fe(III) exchange coupling separated by diamagnetic cyanidometal -NC-M(II)-CN- bridge is weak ferromagnetic for 3-5, but weak anti-ferromagnetic for 6. What’more, the specific heat measurements suggest complexes 3-5 exhibit a phase transition at 2.8 K, 2.7 K and 2.6 K, respectively.
Three series of ruthenium complexes with the general formula Ru(bpy)n(β-diketonato)3-n (bpy = 2,2'-bipyridine, n = 0, 1, 2) were prepared and investigated using cyclic voltammetry and UV-vis spectroscopy. Variation of both the number and electronic demand of the β-diketonato ligands resulted in well-defined modulation of the potential at which oxidation of the metal centre occurred. The observed potentials were shown to be in good agreement with calculated ligand electrochemical parameters. A novel ruthenium(ii) complex with electrochemical behaviour similar to that of ferrocene was identified.
2-(5-Phenylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (Hptip) and its RuII complex [Ru(bpy)2(Hptip)](PF6)2 (where bpy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, 1H NMR spectroscopy, and mass spectrometry. The acid–base properties of the complex were studied by UV-visible and luminescence spectrophotometric pH titrations, and ground- and excited-state acidity ionization constants were derived. The DNA-binding properties of [Ru(bpy)2(Hptip)](PF6)2 were also investigated by means of UV-vis and emission spectroscopy, salt effects, steady-state emission quenching by [Fe(CN)6]4–, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. Density functional theoretical calculations were also carried out in order to understand the DNA binding properties.
A new polypyridyl ligand 2-benzo[b] thiophen-3-yl-1H-1,3,7,8-tetraazacyclopenta[l] phenanthrene (BTCP) and its Ru-II complexes [Ru(bpy)(2)(BTCP)](2+) (1) (bpy = 2,2'-bipyridine), [Ru(phen)(2)(BTCP)](2+) (2) (phen = 1,10-phenanthroline), and [Ru(dmb)(2)(BTCP)](2+) (3) (dmb = 4,4'-dimethyl-2,2'-bipyridine), have been synthesized and characterized. The DNA-binding properties of the three complexes were investigated by spectroscopic methods and viscosity measurements. The results indicate that complexes 1, 2, and 3 bind to DNA by an intercalative mode and the ancillary ligands have a significant effect on the binding strengths of Ru-II complexes to DNA. When irradiated at 365 nm, complex 2 was found to be a more effective DNA-cleaving agent than complexes 1 and 3.
The electronic spectra of a
series of six-coordinate octahedral tris-, bis-, and mono-bipyridyl complexes
of tervalent iron, ruthenium, and osmium have been recorded and spectral bands
assigned to intraligand and charge-transfer transitions. The tris-bipyridyl
complexes and bis- and mono-bipyridyl complexes containing other ligands such
as pyridine and cyanide show a metal reduction transition π(bipy) →
t2(metal). Bipyridyl complexes of osmium containing halide ligands
show a similar transition, but for the corresponding complexes of iron and
ruthenium the metal reduction transition is now X(halogen) → t2(metal),
the electron originating on the halide ligand. Bipyridyl-acetylacetonate
complexes have more complicated spectra. Trends in the spectral bands, for all
the complexes, indicate that of the three metal ions ruthenium probably forms
the strongest M→L π-interaction.
We report the engineering of zinc-finger-like motifs containing the unnatural amino acid (2,2'-bipyridin-5-yl)alanine (Bpy-Ala). A phage-display library was constructed in which five residues in the N-terminal finger of zif268 were randomized to include both canonical amino acids and Bpy-Ala. Panning of this library against a nine-base-pair DNA binding site identified several Bpy-Ala-containing functional Zif268 mutants. These mutants bind the Zif268 recognition site with affinities comparable to that of the wild-type protein. Further characterization indicated that the mutant fingers bind low-spin Fe(II) rather than Zn(II) . This work demonstrates that an expanded genetic code can lead to new metal ion binding motifs that can serve as structural, catalytic, or regulatory elements in proteins.
The Ru(II)–poly(4-vinylpyridine) complexes, [Ru(bpy)2(PVP)2]Cl2, and [Ru(bpy)2(PVP)(py)]Cl2 have been synthesized and compared spectroscopically with the monomeric [Ru(bpy)2(py)2]Cl2 complex, where py is pyridine, bpy is 2,2′-bipyridine, and PVP is poly(4-vinylpyridine). The polymeric Ru(II) complexes were synthesized by the substitution of Cl in Ru(bpy)2Cl2 for poly(4-vinylpyridine) in methanol. The six-coordinated polymeric Ru(II) complex, [Ru(bpy)2(PVP)2]Cl2, was insoluble in water due to an intermolecular ligand complex formation, while one substituted complex, [Ru(bpy)2(PVP)(py)]Cl2, was soluble in water. The absorption maximum of [Ru(bpy)2(PVP)(py)]Cl2 was red-shifted ca. 10 nm from that of [Ru(bpy)2(py)2]Cl2. Also, the red-shift was observed in the emission spectrum. The emission intensity of the polymeric Ru(II) complex was smaller than that of the monomeric one, whereas the emission lifetime was a little different. The difference in energy transfer processes for the above complexes is discussed.
Adduct formation was systematically investigated for ruthenium–ammine complex and crown ether systems. This study involved crown ether systems with different flexibility, the complex system with different numbers of ammine ligands, and the pentaammine complexes systems with aromatic ligands with different π-electron acceptability. Stability constants of the crown-ether adduct of the complexes were determined for the above systems by 1H NMR spectroscopy. The factors affecting adduct formation were discussed on basis of the stability constant.
The controlled deposition of metal complexes from solution on inorganic surfaces offers access to functional materials that otherwise would be elusive. For such surface-confined interfaces to form, specific assembly sequences are often used. We show here that varying the assembly sequence of two well-defined and iso-structural osmium and ruthenium polypyridyl complexes results in interfaces with strikingly different spectroelectrochemical properties. Successive deposition of redox-active layers of osmium and ruthenium polypyridyl complexes, leads to self-propagating molecular assemblies (SPMAs) with distinct internal interfaces and individually addressable components. In contrast, the clear separation of these interfaces upon sequential deposition of these two complexes, results in charge trapping or electrochemical communication between the metal centers, as a function of layer thickness and applied assembly sequence. The SPMAs were characterized using a variety of techniques, including: UV-vis spectroscopy, spectroscopic ellipsometry, electrochemistry, synchrotron X-ray reflectivity, angle-resolved X-ray photoelectron spectroscopy, and spectroelectrochemistry. The combined data demonstrate that the sequence-dependent assembly is a decisive factor that influences and provides the material properties that are difficult to obtain otherwise.
The binding of [Ru(IP)2(dppz-11-CO2Me)]2+ (1) {IP = imidazo[4,5-f][1,10]phenanthroline, dppz-11-CO2Me = dipyrido[3,2-a:2′,3′-c]phenazine-11-carboxylic acid methyl ester} to calf thymus DNA and yeast tRNA has been investigated by UV–Vis spectroscopy, fluorescence spectroscopy, viscosity, as well as equilibrium dialysis and circular dichroism. In addition, the antitumor activities of complex 1 have been evaluated by the MTT method. On the basis of the spectroscopic results, the binding mode of complex 1 to CT-DNA and yeast tRNA is intercalation. However, DNA binding with complex 1 is stronger than RNA binding with complex 1, and complex 1 is a better candidate for an enantioselective binder to CT-DNA than to yeast tRNA. These results indicate that the structures of DNA and RNA have significant effects on the binding behaviors of complex 1. Furthermore, complex 1 demonstrates different antitumor activities against selected cancer cell lines in vitro.
The complex [Ru(4,4′-Me2bpy)2(AsPh3)(H2O)](ClO4)2 (4,4′-Me2bpy = 4,4′-dimethyl-2,2′-bipyridine) has been prepared and their spectral and redox properties has been investigated. The catalytic activity of the complex has been investigated at pH 7.0 in the homogeneous electrooxidation of benzyl alcohol, 1-phenylethanol and cyclohexene. The reactivity was found to decrease in the order 1-phenylethanol > benzyl alcohol > cyclohexene. The higher reactivity of this complex compared to the analogous complex [Ru(4,4′-Me2bpy)2(PPh3)(H2O)](ClO4)2 is attributed to the higher hydrophobic character of the arsine ligand.
Complexes of the formula [(N–N)Cu(AsPh3)CN] (N–N=2,2′–bipyridine, 1,10–phenanthroline) have been synthesized. Ru(bpy)2Cl2.2H2O and [(η5–cp)Ru(PPh3)2Cl] react with [(N–N)Cu(AsPh3)CN] to give cyano-bridged compounds. IR spectral studies in the low frequency region (700–50 cm−1) and 4000–400 cm−1 region reveal cyano bridging in the complexes. Luminescence measurements suggest oxidation of metal centres (CuI–CuII and RuII–RuIII) on excitation at a charge transfer band. This has been substantiated with electrochemical studies of complexes which exhibit quasi-reversible reductions viz. RuIII⧹RuII and CuII⧹CuI. The deposition of metallic copper is also observed at a potential of −1.55 V. Based on these data, a mechanism for photo-redox reaction of complexes has been presented. The properties of these bimetallic complexes are compared with those of parent complexes.
New complexes of the formulae [(N-N)Cu(PPh3)CN] (N-N = 2,2′-bipyridine 1,10-phenanthroline) have been isolated and used to synthesize the novel cyano-bridged copper(I)-ruthenium(II) complexes [(N-N)Cu(PPh3)(μ-CN)Ru(bpy)2Cl]PF6 (bpy = 2,2′-bipyridine) and [(N-N)Cu(PPh3)(μ-CN)Ru(η5-Cp)(PPh3)2]PF6 (Cp = cyclopentadienyl anion). In addition, the complexes [(PPh3)2Cu(μ-CN)Ru(bpy)2Cl]PF6 and [(PPh3)2Cu(μ-CN)Ru(η5-Cp)(PPh3)]PF6 or BF4 have been synthesized using [(PPh3)2CuCN]. All the complexes have been characterized on the basis of elemental analyses, spectroscopic data (IR, UV-vis, 1H, 13C and 31P NMR), and magnetic and conductivity measurements. Spectroscopic data clearly indicate that in these complexes copper(I) and ruthenium(II) are bonded via a cyanide bridge.
The redox properties of a series of [Ru(phen)2(py)X]n+ cations (X = pyridine, NH3, Cl, Br, I, CN, SCN, N3 and NO2) have been investigated in acctonitrile. Two reversible reduction steps are seen at − 1.35 and − 1.6 V vs Ag/AgCl; the invariance of these processes with X-group is indicative of electron addition to molecular orbitals mainly of phenanthroline ligand π* origin. Irreversible multi-electron reductions follow below − 2.20 V. The Ru(II)/Ru(III) couple is seen as a reversible wave near + 0.8 V vs the normal hydrogen electrode, from calibration with ferrocene, except in the cases of the NO2 and SCN complexes, where rapid reactions involving these ligands occur.
The variation of magnetic moment with temperature displayed by cis-[Mo(OPri)2(bipy)2] shows that the complex exists in an equilibri
New complexes derived from the Ru(bpy)2(py)2+ moiety (bpy= 2,2′-bipyridine, py = pyridine) were synthesized and characterized by spectroscopic techniques. The mononuclear complex [Ru(bpy)2(py)(4-CNpy)]2+ (4-CNpy = 4-eyanopyridine) seems to be the pyridine-bonded isomer of 4-CNpy, as disclosed by IR and UV-vis data (νCN(nitrile) = 2240 cm−, λmax = 434 nm in CH3CN). The binuclear complexes [Ru(bpy)2(py)(4-CNpy) Ru(NH3)5]4+ and [Ru(bpy)2(py)(4-CNpy)Fe(CN)5]− were also prepared; they showed new absorptions in the visible region at λmaxca 450 nm ascribable to MLCT (metal-to-ligand charge-transfer) transition from dπ orbitals of ruthenium or iron to π* orbitals of 4-CNpy. The former dimer was obtained as a PF6− salt, which presented νCN(nitrile) = 2178 cm−1, as expected from an ammineruthenium(II) moiety bonded to 4-CNpy through the nitrile group. Oxidation of this species with cerium(IV) yielded the mixed-valence complex [RuII(bpy)2(py)(4-CNpy)RuIII(NH3)55+, with concomitant disappearance of the MLCT band of lowest energy.
The ruthenium(II) complex [RuI2(Me2SO)4] was synthesized and characterized. The Me2SO ligands are all S-bonded. Reactions of RuI2(Me2SO)4 with ligands containing P, N and S donor atoms have been carried out and the complexes obtained were characterized using different physical methods. [RuI2L4] (L= CH3CN, Me2SO and py), [RuI2(CH3CN)2(PPh3)2] and [RuI2(CS)(PPh3)3] have been synthesized using RuI3 as the source material and characterized as above.
New complexes with the Ru(bpy)2(py)2+ moiety (bpy = 2,2′-bipyridine, py = pyridine) connected through a cyano group to Ru(NH33+5 and Fe(CN)2−5 as electron acceptors have been prepared and their spectroscopic, electrochemical and photophysical properties investigated. Cyano-bridging is disclosed by changes in the shape and position of the cyanide stretching vibration, ν(CN), in the IR spectrum of the dinuclear ruthenium species, as compared with the mononuclear parent complex. Blue shifts in the lowest energy dπ → π* (Ru → bpy) metal-to-ligand charge transfer (MLCT) transition occur when going from [Ru(bpy)2(py)(CN)]+ (A) to [(bpy)2(py)RuIICNRuIII(NH3)5]4+ (B) and to [(bpy)2(py)RuIICNFeIII(CN)5]− (C), thus pointing to the existence of nitrile-bound pentaammineruthenium(III) and pentacyanoferrate(II) capping groups in the mixed-valence species B and C. Besides, new intense and broad absorptions at 697 (in HCl 0.01 M) and 700 nm (in H2O/Me2CO, 1:1 v/v) appear in B and C, respectively, and can be assigned to metal-to-metal charge transfer (MMCT) or “intervalence” transitions. The luminescence of A is completely quenched in B, even at 77 K, a fact which can be explained on the basis of efficient excited-state electron transfer to form the electronic mixed-valence isomer of B. The strong asymmetric nature of B, as deduced from cyclic voltammetry data (the difference in redox potentials between both ruthenium sites amounts to 1.30 V), together with a strong electronic coupling [HAB = 220 cm−1, calculated from the “intervalence” absorption data] indicate that the back electron transfer (or charge recombination) from the MMCT excited state of B probably lies in the “inverted” region.
In order to investigate the spectral properties of iron diimine complexes a new series of complexes was synthesized and characterized. Their electronic spectra were studied including solid state liquid nitrogen temperature (LNT) measurements. This study showed that in the case of the ferrous complexes three metal to ligand electron transfer (MLET) bands can be observed, in the visible region, although many authors have assigned them to vibrational structure of the main band. The d-d bands in the spectra of the ferrous complexes are discussed. Very intense internal ligand electron transfer (lLET) bands are observed in the UV region and discussed. In the case of the ferric complexes we observed two ligand to metal electron transfer (LMET) bands in the visible region and lLET bands in the UV region. A correlation between the energy of these transitions in the ferrous and ferric complexes is discussed.
Complexes with the general formuale, [Ru[VR2)3]−, [Ru(VR2)2Cl2]2−, Ru(VR2)2XNO] and [Ru(VR2)2YNO]ClO4 {where VR2 = violurate; R = H or CH3; X = Cl−, NO−3 or OH−, Y = CH3, CN, (CH3)2SO, C5H5N, C3H4N2, or H2O,}, have been synthesized by new and improved methods. Some properties of these compounds are also reported.
Preparation, UV-Vis, IR and ESR spectra, electrochemical redox and magnetic properties of novel complexes obtained by interaction of the tetracyanonitrosylferrate(2−) with 2,2′-bipyridine or 1,10-phenanthroline are described in detail. The results corroborate the previously suggested validity of stereochemical control of valence with these complexes.
Osmium complexes of the type [OsB2X2]n+ where B = 2, 2'-bipyridine (bipy) or 1, 10-phenanthroline (phen), X = Cl, Br, I, py, NH3; 2X = glycinato, acetylacetonato, ethylenediamine, oxalato, phen, or bipy and = 0, 1, 2, 3 are described. [OsB2X2]0 has the cis configuration. Usually compounds in both oxidation states (II) and (III) were stable and could be isolated. The compounds did not disproportionate and the unidentate ligands were replaced only with difficulty. The [Osbipy2phen]2+ and [Osbipyphen2]2+ ions were resolved through their (+) antimonyl tartrate salts and were found to be optically stable in both the Os(II) and Os(III) states.
Es wird gezeigt, daß man die UV- Spektren von Mono-α, αˊ-dipyridylkomplexen [MeII(dipyr)]²⁺ sowie von Mono-o-phenanthrolinkomplexen [MeII(phen)]²⁺ mit Me = Mg²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Mn²+, Co²⁺, Cu²⁺ und Ni²⁺ verstehen kann, wenn man das elektrostatische Komplexmodell verwendet. Die mit den Spektren der Monokomplexe praktisch identischen der Tris-α, αˊ-dipyridyl-Komplexe [MeII(dipyr)3]²⁺ mit Me = Zn²⁺, Ni²⁺, Co²⁺ und Fe²⁺ können analog interpretiert werden. Die intensiven kurzwelligen Banden sind den Liganden zuzuordnen, deren Termsysteme im Felde des Zentralions verändert werden. Es gelingt unter Verwendimg des verzweigten Elektronengasmodells von H. Kuhn¹ die Termverschiebungen für α, αˊ-Dipyridyl im Felde des Zentralions mit den Hilfsmitteln der Störungstheorie abzuschätzen. Die Übereinstimmung mit den spektroskopischen Befunden ist befriedigend. Die UV-Absorption des diamagnetischen, gemeinhin als typischer Durchdringungskomplex angesehenen Komplexions mit Me = Fe²⁺ unterscheidet sich nicht von derjenigen der magnetisch normalen Komplexe der Reihe. Die elektrostatische Betrachtungsweise kann auch in diesem Fall angewandt werden.
Substitution reactions of
the complex ions [RuIIX bipy trpy]+ and [RuIIX2
bipy2]0, where X = Cl, Br, I; bipy = 2,2?-bipyridine; trpy
= 2,2?2?- terpyridine, take place in aqueous solution via extremely rapid
formation of the aquoammines. The rates of substitution of the aquo groups by
NO-2 and N-3 occur by measurably
slow processes at room temperature and are not base catalysed. The aquo
complexes are immediately converted by OH- into hydroxo complexes.
The pKa values of the aquo complexes are shown to be 10.0 for [RuII(H2O) bipy trpy]2+
and about 9-10 for [RuII(H2O)2
bipy2]2+, the latter being an
estimate since oxidation to ruthenium(III) in alkaline solution could not be
avoided. The visible and ultraviolet spectra are reported.
Osmium complexes of the type (BH)[OsX4B], K[OsX4B], [OSX4B]0,
[OsX3pyB]0, [OsX3H2OB]0, [OspysB]+/2+, [Ospy4B]2+/3+,
[OsX3py3]0, [OsX2py4]0, [OsX2acaB]0, [Osaca2B]0/+,
[OsX2glyB]0, [Osgly2B]+, and [OsBen2]2+
have been prepared, where B = 1,10-phenanthroline or 2,2'-bipyridine, py = pyridine, aca = acetylacetonate, gly = glycinate, en = ethylenediamine, and X = Cl or Br. They are
generally inert to dissociation of their ligands and to disproportionation. The
existence of the possible isomeric forms among the complexes is discussed.