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Synthesis and characterization of mixed-ligand ruthenium(III) complexes with oxalate and acetylacetonate ions
Abstract
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 examples available include mono-, di-and triamine derivatives such as the following complexes: [Ru III (en) 2 (η 2 -ox)] [Ru III (en)(η 2 -ox) 2 ] (en = ethylenediamine) [1,2], [Ru II (phen) 2 (η 2 -ox)] (phen = 1,10-phenanthroline) [3], [Ru II (bipy) 2 (η 2 -ox)] (bipy = 2,2′bipyridine) [4], [Ru III (η 2 -ox) 2 (py) 2 ] − (py = pyridine), [Ru III (η 2ox) 2 (anil) 2 ] − (anil = a substituted aniline) [5], [Ru II (tpy)(η 2 -ox)(H 2 O)] (tpy = 2,2′,2′'-terpyridine) [6], cis-[Ru II (η 1 -Hox)(en) 2 NO]Cl 2 and cis-[Ru II (η 1 -Hox)(η 2 -ox)(en)NO] [7]. In addition, the diaquo complex trans-[Ru III (η 2 -ox) 2 (H 2 O) 2 ] − [8,9] and acetylacetonato (acac − ) complexes, K 2 [Ru III (η 2 -ox) 2 (acac)] and K[Ru III (η 2 -ox)(acac) 2 ] [10] have been investigated. The acac complexes have been used in the construction of oligonuclear and polymeric species [10]. ...
... In addition, the diaquo complex trans-[Ru III (η 2 -ox) 2 (H 2 O) 2 ] − [8,9] and acetylacetonato (acac − ) complexes, K 2 [Ru III (η 2 -ox) 2 (acac)] and K[Ru III (η 2 -ox)(acac) 2 ] [10] have been investigated. The acac complexes have been used in the construction of oligonuclear and polymeric species [10]. Of all these complexes only trans-[Ru(η 2 -ox) 2 More recently the oxalate ligand has been incorporated into Ru(II) arene complexes containing the PTA ligand, i.e. [Ru II (η 6 -arene)(η 2 -ox) (PTA)], where PTA = 1,3,5-triaza-7-phosphatricyclo-[3.3.1.1]decane ...
Using trans-[NH2Me2][Ru(η²-ox)2(H2O)2]·4H2O 1 as starting material, as well as its original preparation as a guide, the synthesis of trans-[NH2Me2][Ru(η²-ox)2(PPh3)2] 2, trans-[pyH][Ru(η²-ox)2(H2O)2]·4H2O 3, trans-[pyH][Ru(η²-ox)2(py)2]·2·.5H2O 4, [Ru(η²-ox)(py)4]·4CHCl35 and fac-[Ru(η²-ox)(DMSO-S)3(DMSO-O)]·1.34H2O 6 are outlined. Complexes 2–6 have been characterized using elemental analysis, IR, UV-visible, ¹H NMR, and X-ray diffraction. In addition, their electrochemical behaviour has been analyzed using cyclic and Osteryoung square-wave voltammetries with complex 6 displaying linkage isomerization.
Study the mild cyclohexane oxygenation using vanadyl(IV)acetylacetonate as the starting catalyst and H2O2 as the oxidant has shown that oxalic acid as activator alters the products ratio, increases yield and catalyst turnover number. According to the instrumental (ESI-MS, NMR, EPR, UV–vis, GC, pH, titrimetric) investigations both the parental VO(acac)2 and originated in situ vanadyl(IV)oxalate can consequently interact with H2O2 led, among others, to intermediates comprise VO(η²-O2) metal core. Such vanadium-peroxo species manifest itself as the additional oxygenation agent which generation is inspired by oxalic acid additives. The enhanced aimed products yield and improved process selectivity revealed in the presence of oxalic acid may be stipulated with these non-radical intermediates.
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.
Controllable synthesis of metallic nanocrystals (NCs) with tunable phase, uniform shape, and size is of multidisciplinary interests but has still remained challenging. Herein, a robust phase control strategy is developed, in which seeds with a given phase are added to guide the epitaxial growth of the target metal to inherit the seeds’ phase. Through this strategy, M@Ru (M = Pt, Pd) NCs in the face-centered cubic (fcc) phase, a metastable phase for Ru under ambient conditions, were synthesized with the hydrothermal method. The Pt@Ru NCs showed not only the pure fcc phase but also high morphology selectivity to tetrahedrons surrounded by {111} facets. As revealed by density function theory (DFT) calculations, the preferentially epitaxial growth of Ru atom layers on the nonclosest-packed facets of hetero fcc metal seeds led to the formation of fcc Ru shells. Furthermore, the fcc Pt@Ru tetrahedrons/C showed electrocatalytic activity enhancement with more than an order of magnitude toward hydrogen oxidation reaction (HOR) in acidic electrolyte compared with hydrothermally synthesized Ru/C. Electrochemical measurement combined with DFT calculations revealed that the optimum HOR activity should be achieved on well-crystallized fcc Ru catalysts exposing maximum {111} facets.
Despite its multidisciplinary interests and technological importance, the shape control of Ru nanocrystals still remains a great challenge. In this article, we demonstrated a facile hydrothermal approach toward the controlled synthesis of Ru nanocrystals with the assistance of first-principles calculations. For the first time, Ru triangular and irregular nanoplates as well as capped columns with tunable sizes were prepared with high shape selectivity. In consistency with the experimental observations and density functional theory (DFT) calculations confirmed that both the intrinsic characteristics of Ru crystals and the adsorption of certain reaction species were responsible for the shape control of Ru nanocrystals. Ultrathin Ru nanoplates exposed a large portion of (0001) facets due to the lower surface energy of Ru(0001). The selective adsorption of oxalate species on Ru(10–10) would retard the growth of the side planes of the Ru nanocrystals, while the gradual thermolysis of the oxalate species would eliminate their adsorption effects, leading to the shape evolution of Ru nanocrystals from prisms to capped columns. The surface-enhanced Raman spectra (SERS) signals of these Ru nanocrystals with 4-mercaptopyridine as molecular probes showed an enhancement sequence of capped columns > triangle nanoplates > nanospheres, probably due to the sharp corners and edges in the capped columns and nanoplates as well as the shrunk interparticle distance in their assemblies. CO-selective methanation tests on these Ru nanocrystals indicated that the nanoplates and nanospheres had comparable activities, but the former has much better CO selectivity than the latter.
A series of binary complexes of iron(III), cobalt(II), nickel(II), copper(II), zinc(II), cerium(III) and uranyl(VI), have been synthesized by using the organic ligand, H3L, formed by the condensation of thiocarbohydrazide with 2-hydroxy-1-naphthaldehyde. Also, ternary complexes were synthesized by using 1,10-phenanthroline or oxalic acid as a secondary ligand. Characterization and structure elucidation of the synthesized compounds were achieved by elemental and thermal analyses, spectral (IR, electronic, ESR and 1H and 13C NMR), molar conductivities as well as magnetic measurements. The spectroscopic data showed that the ligand acts as a neutral, monobasic or dibasic tetradentate ligand. All the metal complexes exhibited octahedral geometry except cerium(III) and uranyl(VI) complexes in which the metal ions are hepta- and octa-coordinated. The ligand and some metal complexes showed antibacterial activity towards Staphylococcus aureus and Escherichia coli bacteria and antifungal activity towards the fungi Candida albicans and Aspergillus flavus.
A novel cyclic dinuclear acetylacetonato ruthenium complex doubly bridged with sulfur and/or disulfur at the γ-position of acetylacetonato ligand has been obtained by two different synthetic methods. The molecular structure of the dinuclear complex has been determined by single crystal X-ray diffraction study. Other two cyclic dinuclear β-diketonato ruthenium complexes were also prepared in good yields by the reaction of single bridged dinuclear complexes as starting materials with disulfur dichloride. The cyclic voltammograms of all the dinuclear complexes exhibit two one-electron reduction and oxidation waves in acetonitrile (AN) and dichloromethane (DM). The comproportionation constants (Kc) for mixed-valence state of both RuII/RuIII and RuIII/RuIV were evaluated in both solvents at 25 or −30°C. The values of both Kc (RuII/RuIII) and log10Kc (RuIII/RuIV) for double bridged complex are large compared to those of corresponding single bridged complexes. This fact was rationally explained by the double bridging effect caused by the spread of electronic communication and also demonstrated the usefulness of the double bridged dinuclear complexes.
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.
The study of paramagnetic compounds based on 4d and 5d transition metals is an emerging research topic in the field of molecular magnetism. An essential driving force for the interest in this area is the fact that heavier metal ions introduce important attributes to the physical properties of paramagnetic compounds. Among the attractive characteristics of heavier elements vis-à-vis magnetism are the diffuse nature of their d orbitals, their strong magnetic anisotropy owing to enhanced spin-orbit coupling, and their diverse structural and redox properties. This critical review is intended to introduce readers to the topic and to report recent progress in this area. It is not fully comprehensive in scope although we strived to include all relevant topics and a large subset of references in the area. Herein we provide a survey of the history and current status of research that has been conducted on the topic of second and third row transition metal molecular magnetism. The article is organized according to the nature of the precursor building blocks with special topics being highlighted as illustrations of the special role of heavier transition metal ions in the field. This paper is addressed to readers who are interested in molecular magnetism and the application of coordination chemistry principles to materials synthesis (231 references).
Trans-Dimethylammonium bis(oxalato)diaquaruthenate(III) tetrahydrate, trans-[(CH3)2NH2][Ru(C2O4)2(H2O)2]·4H2O, was synthesized by diffusion of dimethylamine (from dimethylformamide) into a refluxed aqueous solution of diruthenium(II,III) tetraacetate and oxalic acid. The structure of the complex was determined by X-ray diffraction. The RuO (oxalate) and RuO (water) distances are 2.041(3) and 1.994(3) Å, respectively and the oxalate bite angle is 80.6(2)°. The complex displays an intricate pattern of inter- and intra-chain hydrogen bonding involving the axial water molecules, the water molecules of hydration, the dimethylammonium cation, and the carbonyl and carboxyl oxygens of the oxalate groups. Additional characterization using infrared and UV–Vis spectroscopies, magnetic susceptibility (isothermal and variable temperature), and cyclic voltammetry is also reported.
The new complexes of formulae PPh4[Cr(dpa)(ox)2] (1), AsPh4[Cr(dpa)(ox)2] (2), Hdpa[Cr(dpa)(ox)2]·4H2O (3), Rad[Cr(dpa)(ox)2]·H2O
(4) and Sr[Cr(dpa)(ox)2]2·8H2O (5) [PPh4
= tetraphenylphosphonium cation; AsPh4
= tetraphenylarsonium
cation; dpa = 2,2′-dipyridylamine; ox = oxalate dianion; Rad = 2-(4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide]
have been prepared and characterised by single-crystal X-ray diffraction. The
structures of 1–4 consist of discrete [Cr(dpa)(ox)2]− anions, tetraphenylphosphonium (1), tetraphenylarsonium (2), monoprotonated
Hdpa (3) and univalent radical (4) cations and uncoordinated water molecules (2–4). The chromium
environment in 1–4 is distorted octahedral with Cr–O bond distances between 1.982(2)–1.946(2) Å and Cr–N bonds
of 2.0716(17)–2.048(3) Å. The angles subtended at the chromium atom by the two oxalates are 83.6(2)–81.71(8)°, whereas the N–Cr–N angles are 87.76(7)–86.24(9)°. The [Cr(dpa)(ox)2]−
unit of 1–4 is also present in 5 but it acts
as a chelating ligand through its two oxalato groups towards divalent strontium cations, yielding heterobimetallic
zig-zag chains that run parallel to the a axis. Each chain is formed of diamond-shaped units sharing the strontium atoms,
while the two other corners are occupied by two crystallographically independent chromium atoms. The [Cr(dpa)(ox)2]−
unit in 5 retains the environment observed in 1–4
and the strontium atom is coordinated to eight oxalate
oxygens from four oxalate ligands. The two crystallographycally independent chromium centres within each double
chain have opposite chirality. However, the adjacent double chains are related by an inversion centre resulting
in achiral layers parallel to the ac plane. The magnetic properties of 1–5 have been investigated in the temperature
range 1.9–290 K. A quasi Curie law behaviour is observed for 1–3 and 5 in agreement with their crystal structures,
whereas a significant antiferromagnetic interaction between the chromium(III) and the radical
centre occurs in the case of 4. The synthetic possibilities offered by the use of the heteroleptic species [CrL(ox)2]−
(L =
α-diimine-type ligand) as a ligand towards metal ions is analysed and discussed in the light of the available structural results.
The oxalato complexes [Ru<sub>2</sub>(µ-η<sup>4</sup>-C<sub>2</sub>O<sub>4</sub>)Cl<sub>2</sub>(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)<sub>2</sub>] 1 and [Ru(η<sup>2</sup>-C<sub>2</sub>O<sub>4</sub>)(NH<sub>3</sub>)(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)] 2 have been prepared from the reaction of ammonium oxalate with [{RuCl<sub>2</sub>(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)}<sub>2</sub>] and [Ru(H<sub>2</sub>O)<sub>3</sub>(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)]<sup>2+</sup>, respectively. With triphenylphosphine, 1 reacted to give [Ru<sub>2</sub> (µ-η<sup>4</sup>-C<sub>2</sub>O<sub>4</sub>)(PPh<sub>3</sub>)<sub>2</sub> (η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)<sub>2</sub>]<sup>2+</sup> 3 , while 2 gave [Ru(η<sup>2</sup>-C<sub>2</sub>O<sub>4</sub>)(PPh<sub>3</sub>)(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4Me)] 4 . The dichloro complex 1 can also be converted into the cationic dimethanol complex [Ru<sub>2</sub> (µ-η<sup>4</sup>-C<sub>2</sub>O<sub>4</sub>)(MeOH)<sub>2</sub>(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)<sub>2</sub>]<sup>2+</sup> 5 by precipitation of the chloride with a silver salt in methanol. Complex 5 reacted with 4,4-bipyridine to afford a novel tetranuclear metallomacrocycle [Ru<sub>4</sub>(µ-η<sup>4</sup>-C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(µ-η<sup>1</sup>:η<sup>1</sup>-bipy)<sub>2</sub> (η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)<sub>4</sub>]<sup>4+</sup> 6 with alternating oxalato and 4,4-bipyridine bridges. The reaction between 1 and azide yielded the known azido-bridged complex [{Ru(µ-η<sup>1</sup>-N<sub>3</sub>)Cl(η<sup>6</sup>- p -Pr<sup>i</sup>C<sub>6</sub>H<sub>4</sub>Me)}<sub>2</sub>] 7 . The molecular structures of 1 (two conformational isomers), 4 , 5 and 6 have been solved by X-ray crystallography.
Diacetonitrilebis(β-diketonato)ruthenium(II) complexes were readily prepared by reducing the corresponding tris(β-diketonato)ruthenium(III) with zinc amalgam in an acetonitril–ethanol–water mixture. When a mixed-ligand β-diketonato complex [RuL2L′] is treated in this way, the more electron-donating ligand is preferentially displaced by two acetonitrile molecules. The diacetonitrile complexes are useful intermediates for the synthesis of mixed-ligand β-diketonato ruthenium( III) complexes of the type [RuL2L″].
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.
Tris(N-(R- or S-)α-phenylethyl-5-nitrosalicylaldiminato)chromium(III) and tris(N-S-α-benzylethyl-5-nitrosalicylaldiminato)rutheniurn(III) have been prepared, and two diastereomers for each complex have been isolated. Relative configurations of the Cr(III) diastereomers and their Co(III) analogs, which were reported previously, are assigned from a comparison of CD spectra and chromatographic behavior. Assignments of configuration of the Ru(III) diastereomers relative to the analogous Co(III) and Cr(III) diastereomers are based on the similarity of chromatographic behavior for these species. Empirical relationships among low-energy CD bands for Co(III), Cr(III), and Ru(III) salicylaldimine complexes believed to have the same configuration are discussed and predictions of absolute configuration of diastereomers in this series are made from stereoselectivity observations.
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.
The structure of the title compound has been found by single-crystal X-ray analysis to be a 4.5 hydrate, isomorphous with the rhodium and iridium analogs (triclinic space group P, a = 6.813(5),b = 10.519(1), c = 12.470(2) Å, α = 76.28(1)°, β = 84.26(1)°, γ = 85.60(1)°, Z = 2). The structure was refined to a conventional R value of 0.025 by using 2271 significant reflections. The structure contains the expected tris-bidentate oxalatoruthenate(III) anion with an average RuO bond length of 2.028(7) Å. Two methods of preparing this salt free of chloride ions are described. The powder diffraction pattern is tabulated with the three most intense lines of 6.05(100), 13.62(46), and 3.033(38) Å. The reduction potential was measured by cyclic voltammetry to be −0.456 V, which differs from that previously reported.
The electron transfre sequence has been determined for a series of bis 2,2′-bipyridine (bpy) complexes of ruthenium(II) [Ru(bpy)2L2)x at temperature down to −54°C. The reduction sequence at the lowest temperature is consistent with the predictions of the spatially isolated redox orbital model, for which the reduction electrons enter π* orbitals localized on the separate bipyridine ligands. The decomposition reactions that follow addition of two (or more) electrons for the complexes involve the stepwise loss of the ancillary ligand, L, and do not appear to result in the loss of bpy. Activation energies obtained for the decomposition reaction imply a solvent determined transition state.
The reaction of Ru(acac)3 in ethanol in the presence of dienes (diene = 2,5-dimethyl-2,4-hexadiene, isoprene, 1,2,4,5-tetramethyl-1,4-cyclohexadiene) with zinc as reducing agent affords Ru(acac)2(diene) complexes. For the acyclic diene ligands, the Ru(acac)2 unit exhibits a preference for the trans-diene coordination. The structures for the 2,5-dimethyl-1,3-hexadiene and 1,2,4,5-tetramethyl-1,4-cyclohexadiene derivatives have been determined crystallographically. The Ru(acac)2(hexadiene) complex crystallizes in the monoclinic space group P21/n with . The cyclohexadiene complex crystallizes in a triclinic space group , with . The solid-state structure for the dimethylhexadiene complex revealed an η4-trans-diene coordination, while for the cyclic diene it revealed isolated olefin interactions.
The correlation between the oxidation potentials for a reversible one-electron process and the valence level binding energies measured by X-ray photoelectron spectroscopy was examined with a series of M2L2X2(2+n)+ (ML2+3) complexes (M = Ru or OS, L = 2,2′-bipyridine or 1,10-phenanthroline, X2 = (py)2, (NH3)2, (NO−2)2, (CN−)2, etc). The oxidation peak potentials of these complexes varied proportionally with the energies of the lowest charge-transfer bands of the complexes. Linear correlations were obtained between the oxidation peak potentials, Ep,ox, and the valence level binding energies, ΔEv, of X-ray photoelectron spectroscopy. The slopes, −ΔEV/Ep,ox, are smaller than unity, indicating that the ligand's effect on the metal centre of the complex is weakened by the electrostatic interaction in the solid phase.
Conversion of the amino group of 2-(2-aminophenyl)pyridine into a
thiol to give the N,S-donor chelating ligand 2-(2-pyridyl)benzenethiol
(HL) afforded the oxidised disulfide L–L which was
crystallographically characterised. It shows an interesting example of
an intermolecular
N · · · S–S
interaction (N · · · S
distances are 2.778 and 2.724 Å;
N · · · S–S angles are
both ca. 11°) in which the pyridyl lone pair interacts
weakly with the σ* orbital of the S–S bond.
Reaction of L–L with
[Ru(bipy)
2
Cl
2
]·2H
2
O
(bipy = 2,2′-bipyridine) and
RuCl
3
·xH
2
O afforded
[Ru
II
(bipy)
2
L][PF
6
] 1 and
[Ru
III
L
3
] 2 respectively (following
in situ reduction of the disulfide) which have N
5
S
and mer-N
3
S
3
donor sets respectively (N
of pyridyl, S of benzenethiolate). Both were crystallographically
characterised and have the expected pseudo-octahedral geometries. An
interesting feature of both structures is that the relatively large
Ru–S distances (compared to the Ru–N) prevent the pyridyl
rings from approaching the metal centre as closely as they would if they
were not constrained, so the Ru–N distances are longer than usual.
Electrochemical studies show that the benzenethiolate ligands are more
effective electron donors to ruthenium (both +2 and +3) than are
phenolates: for example, the Ru
II
–Ru
III
couple of 1 is at -0.07 V vs.
ferrocene–ferrocenium, whereas the same couple of the related
N
5
O-co-ordinated complex (O from phenolate) was at +0.03 V.
Similarly the Ru
III
–Ru
IV
couple of
2 was at -0.21 V, compared to +0.14 V for the
N
3
O
3
-co-ordinated analogue. Complex 2
also shows a reversible ligand-based oxidation which is absent for
1, arising from stabilisation of the sulfur-based radical
cation by interaction with the lone pair on an adjacent sulfur atom in
the co-ordination sphere of the complex, which cannot happen for
1. Electronic spectral properties show that the sulfur donor of
1 weakens the ligand field with respect to
[Ru(bipy)
3
]
2+
, and that 2 has an intense
sulfur-to-Ru
III
ligand-to-metal charge-transfer band.
A novel oxalate-bridged binuclear ruthenium(III) complex, [{Ru(acac)(2)}(2)(mu-ox)] (acac(-) = acetylacetonate and ox(2-) = oxalate), has been prepared via self-dimerization of K[Ru(acac)2(OX)l in aqueous solutions containing ferric salts as catalyst. The Ru-2 III,II mixed-valence species generated electrochemically with K-c = 10(5.0) for the comproportionation constant exhibits a weak intervalence charge transfer (IVCT) band at 1430 nm. The IR spectra from spectroelectrochemistry indicate a partially localized mixed-valence state (Class II-III behavior).
A novel chromium(III)-neodymium(III) heteronuclear complex has been obtained by utilizing unsym-cis-[Cr(eddp)(ox)] as a building block. From the X-ray analysis, it is revealed that this complex is tetranuclear in which the Nd(III) ion is bridged by three oxalates in the three Cr(III) units and three water molecules forming a nine-coordinate tricapped trigonal-prism geometry.
In tetraethylammonium perchlorate-acetonitrile solution, [Ru(acac)3] was reversibly reduced at the dropping mercury electrode to [Ru(acac)3]− with a conditional electrode reaction rate-contsant estimated to be ca. 0.2 cm s−1 or larger. The reduced form was stable in the solution under an inert gas atmosphere. In aqueous solutions, [Ru(acac)3] was reduced reversibly when the depolarizer concentration was less than 0.07 mol m−3 at 25 °C. At higher depolarizer concentrations, [Ru(acac)3] molecules were adsorbed onto the mercury surface, and the free molecules in solution were reduced through the adsorbed layer at a smaller rate; the adsorbed layer was removed at a certain negative potential, and the reversible reduction took place normally at the bare surface. The difference between reversible half-wave potentials observed in acetonitrile and aqueous solutions was discussed in terms of solvation energies of the oxidized and reduced forms.
The result of an X-ray crystallographic study of the complex (P(C6H5)3)2Pt(C2H 4) is presented together with refined values of bond lengths and angles for the nickel analog (P(C6H5)3)2Ni(C2H 4). The solution behavior of both complexes has been studied by nmr spectroscopy and marked differences in behavior have been observed. (P(C6H5)3)2Pt(C2H 4) is undissociated in toluene solution but readily associates if excess ethylene is present; rapid exchange of ethylene between free sites and sites on the associated complex has been observed and the activation energy for the process has been found to be 11.7 kcal/ mol; (P(C6H5)3)2Ni(C2H 4) dissociates in toluene solution. A mechanistic scheme incorporating associative phenomena for reactions of (P(C6H5)3)2Pt(C2H 4) with acetylenes is proposed.
The crystal structure of μ-oxalato-bis(tetrapyridineruthenium(II)) fluoroborate, [Ru(C5H5N)4C2O4Ru(C 5H5N)4](BF4)2, has been determined. The compound crystallizes in the monoclinic space group P21/c with a = 10.926 (5), b = 16.740 (7), c = 13.732 (5) Å, and β = 116.51 (1)° with two molecules per unit cell. ρobsd = 1.60 and ρcalcd = 1.62 g cm-3 for Z = 2. Least-squares refinement of 3165 observed reflections collected by counter methods has yielded a final conventional R factor of 0.071 and a weighted R factor of 0.069. The two ruthenium atoms of the molecule are linked to a centrosymmetric planar tetradentate oxalate ligand. The coordinating ligands form slightly distorted octahedra about each ruthenium atom consisting of two oxygen atoms from the oxalate ligand and four nitrogen atoms from the pyridine ligands. Several features of the structure indicate that the arrangement of four pyridine molecules in the cis configuration causes significantly greater steric interaction than in comparable trans-tetrapyridine complexes. This result is in accord with the observed experimental difficulties in preparing cis-tetrapyridine complexes. The fluoroborate anion is disordered about one of the threefold B-F axes of the tetrahedron. The unique undisordered fluorine atom is probably held in position by means of a hydrogen bond to an α hydrogen of one of the pyridine rings. The bond lengths and angles of the oxalate ligand are not significantly different from those of the oxalate ion in potassium oxalate monohydrate. The average Ru-N bond distance of 2.08 Å is significantly shorter than that of 2.13 Å in chlorotetraammine(sulfur dioxide)ruthenium(II) chloride.
A hydrogen-bonded complex Ru(bpy)2(OX)·4H2O has been synthesized. Its structure consists of a unique three-dimensional network in which Ru(bpy)2(OX)·4H2O units are alternatively linked by tetracyclic and octacyclic rings. The cyclic voltammogram of the titled compound has been studied.
The preparations, i.r. spectra, electronic spectra, and magnetic susceptibilities of some ruthenium(III) complexes of the type: A[Ru(oxalate)2L2],xH2O in which A = K, NH4, or PhNH3, L = a substituted aniline, and x varies between 1 and 3 are reported. The complex anions have been assigned trans-structures.
Bis(acetonitrile)bis(β-diketonato)ruthenium(III) was readily formed through the reaction of the corresponding tris(β-diketonato)ruthenium(III) with perchloric, sulfuric, or hydrochloric acid in acetonitrile. The reaction was quantitative; the stoichiometry was 1:1 for each strong acid studied here. This reaction was employed to prepare several bis(acetonitrile)bis(β-diketonato)ruthenium(III) complexes, which proved to be convenient intermediates for the synthesis of mixed-ligand β-diketonato ruthenium(III) complexes of the [RuIIIL2L′] type.
Bis(phenanthro1ine) and
bis(bipyridine)ruthenium(~~) chelates have been prepared by the pyrolysis, at
300°C, of phenanthrolinium tetrachlorophenanthrolineruthenate(III) and
bipyridinium tetrachlorobipyridineruthenate(III). In the complexes [RuB2Cl2]
the chelating base molecules are firmly bound but the chlorine atoms are
replaceable by a variety of ligands such as water, pyridine, or acetylacetone.
The complexes are spin-paired and show no tendency to disproportionation to the
tris complexes, under normal experimental conditions.
Two new chromium(III)-containing complexes of formula AsPh4[Cr(bipy)(ox)2]·H2O 1 and [NaCr(bipy)(ox)2(H2O)]· 2H2O 2 (bipy = 2,2′-bipyridine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. The structure of 1 consists of discrete [Cr(bipy)(ox)2]– mononuclear anions, tetraphenylarsonium cations and uncoordinated water molecules. The structure of 2 reveals a novel two-dimensional framework which is made up of oxalato-bridged bimetallic CrIII–NaI helical chains which are interconnected through centrosymmetric Na2O2 units. Within the chain, a regular alternation of the metal ions is observed, the oxalate group acting as a bis(chelating) ligand. In addition to this coordination mode, two oxalates each act as monodentate ligands towards a sodium atom of a neighbouring chain thus leading to a sheetlike polymeric structure. The chromium environment is distorted octahedral in both complexes: two nitrogen atoms from a bidentate bipy ligand and four oxygen atoms from either two chelating (1) or two bis(chelating) (2) oxalate groups build the coordination polyhedron around the chromium atom. The Cr–N bond lengths [values in the ranges 2.077(3)–2.057(3) (1) and 2.067(4)–2.058(4) Å (2)] are somewhat longer than the Cr–O ones [values in the ranges 1.960(2)–1.946(2) (1) and 1.968(3)–1.949(3) Å (2)]. The sodium atom in 2 is also six-coordinated: a coordinated water molecule [2.371(5) and 2.325(4) Å for Na(1)–O(17) and Na(2)–O(18), respectively] and five oxygens from three oxalate groups [values of the Na–O (ox) bonds in the ranges 2.511(4)–2.331(4) and 2.481(4)–2.364(4) Å around Na(1) and Na(2), respectively] build a distorted octahedral NaO6 environment. The intralayer chromium–sodium and sodium–sodium distances through bridging oxalate in 2 vary in the ranges 5.657(4)–5.579(2) and 3.534(3)–3.497(4) Å, respectively. Variable-temperature magnetic susceptibility measurements of 1 and 2 reveal the occurrence of very weak antiferromagnetic interactions together with zero-field splitting effects in both compounds. The use of the [Cr(bipy)(ox)2]– unit as a ligand towards different univalent and divalent metal ions aimed at designing new heterobimetallic systems is analysed and discussed in the light of available structural data.
New ruthenium(III) complexes of the type [RuX2en2] A(en = ethylenediamine, X2= C2O4, Cl H2O, Cl l, Cl2, Br2, or l2; A = Cl, Br, l, ClO4, or p-Me·C6H4·SO2·O) have been isolated, together with complexes of the related ligands triethylenetramine and optically active propylenediamine. Magnetic susceptibilities show that all the compounds have the spin-paired d5 configuration. The cation [RuCl2en2]+ has been resolved into its optical enantiomorphs, and its structure related to that of other bis(ethylenediamine)ruthenium(III) compounds, all of which are assigned a cis configuration. Ultraviolet, visible, and infrared spectra are reported, and the use of infrared spectra in the detection of geometrical isomerism is discussed. New mono-ethylenediamine complexes [RuX4en]– have been isolated in combination with the cations [RuX2en2]+ and (phen H)+(phen = 1,10-phenanthroline; X = Cl, Br, l, or ½C2O4).
Three compounds of general formula (NBu4)[MIIRuIII(ox)3] have been synthesized; NBu4+ stands for tetra-n-butylammonium, M for Mn, Fe, and Cu, and ox2- for the oxalate dianion. The X-ray powder patterns for the three derivatives have revealed that these compounds are isostructural with (NBu4)[MnIICrIII(ox)3], whose crystal structure was known, and the cell parameters have been refined in the R3c space group. The (NBu4)[MIIRuIII(ox)3] compounds are new examples of two-dimensional bimetallic assemblies with oxalate bridges. The temperature (T) dependences of the magnetic susceptibility (χM) in both the dc and ac modes and the field dependences of the magnetization have been investigated. The local spins are SRu = SCu = 1/2, SMn = 5/2, and SFe = 2. The RuIII−MII interaction has been found to be antiferromagnetic for M = Fe and Cu and ferromagnetic for M = Mn. The two compounds (NBu4)[FeIIRuIII(ox)3] and (NBu4)[CuIIRuIII(ox)3] exhibit a ferrimagnetic behavior, characterized by a minimum in the χMT versus T plots. (NBu4)[FeIIRuIII(ox)3] exhibits a long-range magnetic ordering at Tc = 13 ± 1 K. A slight frequency dependence of the out-of-phase ac magnetic response has been observed. The field dependence of the magnetization in the magnetically ordered state has revealed a rather strong coercivity, with a coercive field of 1.55 kOe at 2 K. A theoretical model has been used to determine the magnitude of the RuIII−MII interactions, with M = Mn and Fe. This model is based on a quantum−classical spin approach together with Monte Carlo simulations. The interaction parameters have been found as J = 1.04 cm-1 for (NBu4)[MnIIRuIII(ox)3] and −9.7 cm-1 for (NBu4)[FeIIRuIII(ox)3], with a spin Hamiltonian of the type −J∑i,jSRu,i·SM,j. The magnetic properties of these compounds have been discussed. In particular, it has been emphasized that the symmetry rules governing the nature and the magnitude of the interaction between two 3d magnetic metal ions seem not to be valid anymore for 4d ions such as RuIII.
The metastable state which is produced by irradiation with the green-blue region of light was studied by IR and other spectroscopic techniques for solid states of newly synthesized nitrosyl–ruthenium complexes; cis-[Ru(Hox)(en)2NO]Cl2·EtOH, trans-[Ru(Hox)(en)2NO]Cl2, cis-K[Ru(ox)2(en)NO]·3H2O, cis-[Ru(Hox)(ox)(en)NO], and cis-K[Ru(ox)2(en)NO] [ox = (CO2)22−]. Continued irradiation at 77 K results in development of a photostationary state in the same way as for sodium nitroprusside. The population of the metastable state molecule in the photostationary state of each sample depends on the irradiation wavelength and reaches a maximum at 441.6 nm which is the shortest wavelength in the present study. A broad absorption band with an absorbance maximum at ≈600 nm is observed for the metastable state of a trans-[Ru(Hox)(en)2NO]Cl2 single crystal. The short wavelength tail of the band is considered to be involved in the photostationary equilibrium under blue light radiation. The metastable state molecules decay to the ground state at temperatures considerably higher than the two metastable molecules (MS1 and MS2) of sodium nitroprusside. The decay temperature of trans-[Ru(Hox)(en)2NO]Cl2, which is defined as the temperature at which the rate constants of the thermal decay becomes 10−3 s−1, is 277 K, which is the highest value reached among the metastable states of nitrosyl complexes reported so far. In the Raman spectra of trans-[Ru(Hox)(en)2NO]Cl2, the Ru-(NO) stretching vibrations are observed at 604 cm−1 and 476 cm−1 for the ground and metastable state molecules, respectively.
Reduction of [Ru(acac)3] with zinc amalgam or zinc dust in hot THF containing some water in the presence of an excess of cyclooctene generated in solution cis-[Ru(acac)2(η2-C8H14)2], which cannot be isolated in solid form but has been identified on the basis of its 1H NMR spectrum. It is a useful synthetic precursor because the co-ordinated olefins are easily displaced by many ligands. Treatment with pyridine, tert-butyl isocyanide, tertiary phosphines, phosphites and triphenylarsine (L) at room temperature gave red-brown complexes trans-[Ru(acac)2L2], which isomerise in solution to the more stable cis compounds on heating. In contrast, the similarly prepared trimethylamine complex, trans-[Ru(acac)2(NMe3)2], does not undergo trans to cis isomerisation. Reaction of cis-[Ru(acac)2(η2-C8H14)2] with acetonitrile or triphenylstibine (L′) gave monosubstitution products cis-[Ru(acac)2(η2-C8H14)L′], which react on heating with an excess of L′ to give cis-[Ru(acac)2L′2]. Treatment of cis-[Ru(acac)2(η2-C8H14)2] (1 mol) with Ph2PCH2PPh2 (dppm) (2 mol) at room temperature gave trans-[Ru(acac)2(η1-dppm)2], whereas the ligands Ph2P(CH2)mPPh2 (L–L, m = 2, dppe; m = 3, dppp) under the same conditions gave oligomers [{Ru(acac)2(L–L)}n], which probably contain mutually trans-phosphorus atoms. On heating all three compounds are converted into cis-[Ru(acac)2(L–L)]. Treatment of trans-[Ru(acac)2L2] (L = NMe3 or PPh3) with CO at room temperature and pressure gave trans-[Ru(acac)2(CO)L], which, in the case of L = PPh3, isomerises to the cis compound on heating; reaction of trans-[Ru(acac)2(AsPh3)2] with CO under the same conditions gave cis-[Ru(acac)2(CO)(AsPh3)] directly. The structures of trans-[Ru(acac)2(CNBut)2], trans-[Ru(acac)2(PMePh2)2], cis-[Ru(acac)2(CNBut)2] (in the form of a molecular adduct with [Ru(acac)3]), cis-[Ru(acac)2(PMePh2)2] and trans-[Ru(acac)2(η1-dppm)2] have been determined by X-ray crystallography, and trends in the metal–ligand distances are discussed. The formation of trans-[Ru(acac)2L2] from cis-[Ru(acac)2(η2-C8H14)2] may proceed via a square-pyramidal intermediate [Ru(acac)2L].
Treatment of the ruthenium(IV) chloro bridged dimer [(η3: η3-C10H16)RuCl(μ-Cl)2 (1) with silver oxalate in acetone/water gives the oxalato bridged dimer [(η3: η3-C10 H16)RuCl}2(μ-O4C2)] (2) which exists in two diastereomeric forms of Ci and C2 symmetry, 2a and 2b, respectively. Similar treatment of 1 with potassium malonate gives the bridged complex [{(η3:η3-C10H16)RuCl}2(μ-O4C3H2)] (3). The X-ray crystal structure of 2a is reported.
The following oxalate-bridged heterodinuclear Cr(III)-M(II) (M = Cu, Ni, Co, Fe, Mn) complexes have been synthesized: [Cr(salen)(ox)Cu(acpy)] (1) (salen = N,N'-ethylenebis(salicylideneaminate), ox2- = oxalate ion, acpy = N-acetylacetonylidene-N-(2-pyridylethyl)aminate) and [Cr(salen)(ox)M(taea)](BPh4) (M = Ni (2), Co (3), Fe (4), Mn(5))(taea = tris(2-aminoethyl)amine). The [Cr(salen)(ox)Cu(acpy)]2DMF.MeOH(1') complex in the monoclinic system of the space group P2(1)/n with a = 16.429(6) angstrom, b = 25.303(14) angstrom, c = 10.191(4) angstrom, beta = 109.78(2)degrees, V = 3986(3) angstrom3, and Z = 4. The refinement converges with R = 0.079 and R(w) = 0.071 based on 3327 reflections with \F(o)\ greater-than-or-equal-to 3sigma(\F(o)\). The complex has an oxalate-bridged dinuclear Cr(III)-Cu(II) core with a Cr...Cu distance of 5.482(3) angstrom. The Cr(III) has a cis-beta octahedral geometry with the tetradentate salen in the folded form and a bidentate oxalate group. The geometry around the Cu(II) ion is square-pyramidal with the three donor atoms of acpy and one of the oxalate oxygens at the basal plane and the other oxygen of the oxalate group at the apex. Magnetic investigations of 1-5 in the 4.2-300 K temperature range reveal a ferromagnetic interaction between the Cr(III) and M(II) ions for all the complexes. On the basis of the spin Hamiltonian, H = -2JS(Cr).S(M), the values for the spin coupling constant J were estimated to be +2.8, +4.6, +1.3, +0.8, and +0.5 cm-1 for 1-5, respectively. The relative magnitude of the J values is explained by the sigma- and pi-pathways through the oxalate bridge. The correlation between the J values of 1-5 and the phase-transition temperatures, T(C), of the ferromagnetic {NBu4-[MCr(ox)3]}x (M = Cu, Ni, Co, Fe, Mn) is discussed based on Heisenberg's ferromagnet model.
Zinc amalgam reduction of tris(acetylacetonato)ruthenium(III), [Ru(acac)3], in the presence of the chelate alkyne N-donor ligands o-RCCC6H4NMe2 gives the corresponding bis(acetylacetonato)ruthenium(II) complexes [Ru(acac)2(o-RCCC6H4NMe2)] (R = Ph (1), SiMe3 (2)). Treatment of 2 with K2CO3/CH3OH gives the corresponding complex of 2-ethynyl-N,N-dimethylaniline (R = H (3)). Complexes 1−3 undergo reversible one-electron oxidation to the corresponding ruthenium(III) cations [Ru(acac)2(o-RCCC6H4NMe2)]+ (R = Ph (1+), SiMe3 (2+), H (3+)) by cyclic voltammetry in CH2Cl2 at −60 °C. The E1/2(Ru3+/2+) values for this process are about 200 mV less positive than that for the corresponding pair of alkene complexes [Ru(acac)2(o-CH2CHC6H4NMe2)]0,+. Treatment of complexes 1 and 2 with [FeCp2]PF6 gives the deep blue-violet PF6 salts of 1+ and 2+, whose magnetic moments (1.92 and 1.95 μB, respectively, at room temperature) and ESR spectra are typical of monomeric ruthenium(III) complexes. In both oxidation states, as a consequence of coordination, the bands due to CC stretching in the IR spectra appear at 170−250 cm-1 to low frequency of those for the free alkynes. The X-ray structures of 1 and 1+ establish that the metal ion is coordinated in an octahedral arrangement by two bidentate acac ligands and bidentate o-PhCCC6H4NMe2. In contrast to the alkene o-CH2CHC6H4NMe2, the alkyne binds somewhat more strongly to ruthenium(III) (4d5) than to ruthenium(II) (4d6), as shown by the metal−carbon distances [2.113(5), 2.183(5) Å and 2.107(5), 2.172(5) Å for two independent molecules of 1; 2.080(3) Å, 2.133(4) Å for 1+], probably because the electron removed on oxidation comes from an antibonding orbital arising from the orthogonal π orbital of the alkyne. The corresponding CC distances [1.224(6), 1.240(6) Å in 1; 1.245(4) Å in 1+] are equal within experimental error, both being lengthened relative to that in free o-PhCCC6H4NMe2 (1.190 Å).
Reduction of Ru(acac)3 with zinc in ethanol in the presence of 1,3-dienes leads to the formation of Ru(eta-4-diene)(acac)2 complexes (diene = 2,3-dimethyl-1,3-butadiene, 2,4-hexadiene, 1,3-cyclohexadiene, 2,4-dimethyl-1,3-pentadiene). Except for the cyclohexadiene compound, these complexes involve unusual eta-4-trans-diene coordination in the ground state and may be observed in two isomeric forms. In the case of the 2,3-dimethyl-1,3-butadiene complex, small amounts of a third isomeric form may be observed, which appears to involve eta-4-cis-diene coordination. Single-crystal X-ray structural studies have been carried out for the 2,4-dimethyl-1,3-pentadiene and cyclohexadiene complexes. For the former, the space group is P2(1)/n with a = 10.614 (8) angstrom, b = 13.31 (1) angstrom, c = 12.93 (1) angstrom, beta = 90.81 (6)-degrees, and V = 1826.5 angstrom 3 for Z = 4, while, for the latter, the space group is Pbca, with a = 11.642 (4) angstrom, b = 16.162 (6) angstrom, c = 33.78 (1) angstrom, and V = 6356.0 angstrom 3 for Z = 16 (two independent molecules). The former (latter) structures were refined to discrepancy indices of R = 0.037 (0.051) and 0.035 (0.044) for 4015 (4200) reflections having I > 2-sigma(I) (2.5-sigma(I) for the latter).
Zinc amalgam reduction of tris(acetylacetonato)ruthenium(III), [Ru(acac)3], in the presence of the chelating olefinic N- and O-donor ligands (LL‘) 2-vinyl-N,N-dimethylaniline, o-CH2CHC6H4NMe2 (1), 2-isopropenyl-N,N-dimethylaniline, o-CH2C(CH3)C6H4NMe2 (2), 3-butenyldimethylamine, CH2CHCH2CH2NMe2 (3), 2-allylpyridine, CH2CHCH2C5H4N (4), isomesityl oxide (4-methyl-4-penten-2-one), CH2C(CH3)CH2COCH3 (5), 2-methoxystyrene, o-CH2CHC6H4OMe (6), and 3-butenylmethyl ether, CH2CHCH2CH2OCH3 (7) gives the corresponding bis(acetylacetonato)ruthenium(II) complexes [Ru(acac)2(LL‘)] (8−14). These undergo one-electron oxidation by cyclic voltammetry to the corresponding cations [Ru(acac)2(LL‘)]+, the process being reversible at both room temperature and −60 °C. The cations were isolated as deep blue, paramagnetic PF6 or SbF6 salts from the oxidation of the ruthenium(II) precursors 8−12 and 14 with Ag+ or [FeCp2]+ salts; they are the first stable alkene complexes of ruthenium(III). At both oxidation levels, coordination of the prochiral alkene gives rise to a pair of diastereomers, labeled a, b at the Ru(II) level, a+, b+ at the Ru(III) level, whose redox potentials E1/2 (Ru3+/2+) differ by ca. 100 mV. The equilibrium a/b ratio at the Ru(II) level is ca. 1:9, although for 8, 10, and 11 this is established only after several hours at ca. 100 °C, the ratio in the complexes immediately after isolation being ca. 2:3. Selective removal of the more easily oxidized diastereomer of the 2-vinyl-N,N-dimethylaniline complex 8a by treatment of a 2:3 mixture with ca. 0.5 equiv of Ag+ provides pure 8b, which undergoes reversible one-electron oxidation at −60 °C to 8b+. Above −10 °C, 8b+ isomerizes to an equilibrium mixture (ca. 85:15) of 8a+ and 8b+, as shown by UV−visible spectroelectrochemistry. Thus, both diastereomeric preference and rate of interconversion are strongly dependent on the oxidation state (number of metal d-electrons). The metrical parameters pertaining to alkene coordination in the diastereomers 8a and 8b do not differ significantly, the metal−carbon distances being 2.159(4), 2.144(4) Å (8a), 2.142(2), 2.153(3) Å (8b) and the CC distances being 1.383(5) Å (8a) and 1.382(4) Å (8b). The corresponding distances in the Ru(III) complex [8a]+[SbF6]- [Ru−C = 2.239(6), 2.236(7) Å; CC = 1.355(9) Å] indicate that the alkene is more weakly bound than in either of its diastereomeric Ru(II) precursors.
A ligand electrochemical parameter, EL(L), is described to generate a series which may be used to predict M(n)/M(n-1) redox potentials by assuming that all ligand contributions are additive. In this fashion it performs a purpose similar to that of the Dq parameter in electronic spectroscopy. The parameter is defined as one-sixth that of the Ru(III)/Ru(II) potential for species RuL6 in acetonitrile. The EL(L) values for over 200 ligands are presented, and the model is tested over a wide range of coordination complexes and organometallic species. The redox potential of a M(n)/M(n-1) couple is defined to be equal to Ecalc = SM[ΣEL(L)] + IM. The values of SM and IM, which are tabulated, depend upon the metal and redox couple, and upon spin state and stereochemistry, but, in organic solvents, are generally insensitive to the net charge of the species. Consideration is given to synergism, the potentials of isomeric species, and the situations where the ligand additivity model is expected to fail. In this initial study, the redox couples are restricted almost exclusively to those involving the loss or addition of an electron to the t2g (in Oh) sublevel.
The preparation, crystal structure and magnetic properties of PPh4[Cr(bpym)(C2O4)2]·H2O (1) and [Ag(bpym)][Cr(C2O4)2(H2O)2]·2H2O (2) (C2O4 2−=oxalate dianion, bpym=2,2′-bipyrimidine and PPh4 +=tetraphenylphosphonium cation) are described. The structure of 1 is made up of discrete (2,2′-bipyrimidine)bis(oxalato)chromate(III) anions, teraphenylphosphonium cations and uncoordinated water molecules. The structure of 2 consists chains of univalent silver cations bridged by bis-chelating 2,2′-bypyrimidine, cis-diaquabis(oxalato)chromate(III) anions and crystallisation water molecules. The chromium atom in 1 and 2 has a slightly distorted octahedral geometry with two bidentate oxalate groups (1 and 2), and one bidentate bpym ligand (1) or two cis-coordinated water molecules (2). The CrO(ox) bonds are in the ranges 1.951(3)–1.981(3) Å (1) and 1.9575(12)–1.9585(14) Å (2), values which are shorter than the CrO(w) bonds in 2 [1.9999(16) Å]. The CrN(bpym) bond lengths are 2.064(4) and 2.090(4) Å for 1. The silver atom in 2 is disordered with two different four-coordinated environments from two bpym groups. One of these environments can be defined as a flattened tetrahedron with AgN(bpym) distances of 2.331(2) Å (x2) and 2.360(2) Å (x2) and the second one is distorted with values of the AgN(bpym) bonds in the range 2.132(18) and 2.59(2) Å. The silver–silver separation across bridging bpym is 6.1854(8) Å. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9–290 K reveal the occurrence of weak antiferromagnetic interactions together with zero-field splitting effects. The use of the [Cr(bpym)(C2O4)2]− unit of 1 as a ligand towards different univalent and divalent metal ions is discussed in the light of the available structural information.
The deformation of a directionally solidified columnar dendritic mushy zone in a transparent succinonitrile-acetone (SCN-ACE)
alloy has been studied expermentally. In addition to solidifying dendritically like a metal alloy, this alloy also has mechanical
properties that are similar to those of metals near the melting point. The experiments are relevant, for example, to the deformation
of a partially solidified strand during continuous casting of steel slabs. A test cell was designed which allows for directional
solidification of the alloy and controlled compression of the solid-liquid mush which forms. Measurements during solidification
and deformation include temperatures, interface positions, local displacements of the solid skeleton in the mush, and liquid
concentrations. Results are presented for a range of initial test-cell thicknesses, deformation amounts, and deformation start
times. The measurements are suitable for validation of future models.
A new series of hybrid organometallic-inorganic layered magnets with formula [Z(III)Cp(2)(*)] [(MRuIII)-Ru-II(ox)(3)] (Z(III) = Co and Fe; M-II = Mn, Fe, Co, Cu, and Zn; ox = oxalate: Cp* = pentamethylcyclopentadienyl) has been prepared. All of these compounds are isostructural to the previously reported [Z(III)Cp(2)*] [(MMIII)-M-II(ox)(3)] (M-III = Cr, Fe) series and crystallize in the monoclinic space group C2/m, as found by powder X-ray diffraction analysis. They are novel examples of magnetic materials formed by bimetallic oxalate-based extended layers separated by layers of organometallic cations, The magnetic properties of all these compounds have been investigated (ac and de magnetic susceptibilities and field dependence of the isothermal magnetization at 2 K), In particular, it has been found that Fe-II and Co-II derivatives behave as magnets with ordering temperatures of 12.8 and 2.8 K, respectively, while no long-range magnetic ordering has been detected down to 2 K in the Mn-II and Cu-II derivatives. The magnetic ordering in the Fe-II derivatives has been confirmed through Mossbauer spectroscopy. This technique has also made it possible to observe the spin polarization of the paramagnetic [FeCp2*](+) units caused by the internal magnetic field created by the bimetallic layers in the ordered state. (C) 2001 Academic Press.
Absorption and emission spectra of nine (4d) 6 ruthenium(II) complexes dissolved in rigid glasses are reported. Tris(bipyridine), tris( o ‐phenanthroline), bis(tripyridine), and a series of cis‐substituted bis(bipyridine) complexes of ruthenium(II) were synthesized. The cis substituents were cyanide, ethylenediamine, pyridine, oxalate, and chloride chosen for their order in the spectrochemical series. On the basis of the structures of the emission spectra, their energy relationships with charge‐transferabsorption bands, and the lack of correlation between the energies of emission and predictions from crystal‐field theory, it is proposed that the intense luminescence observed from all the complexes under excitation by ultraviolet light is charge transfer in nature.
The aqua complexes [Ru(tpy)(acac)(H2O)](PF6) (tpy = 2,2‘,2‘‘-terpyridine, acacH = 2,4-pentanedione), [Ru(tpy)(C2O4)(H2O)] (C2O42- = oxalato dianion), [Ru(tpy)(dppene)(H2O)](PF6)2 (dppene = cis-1,2-bis(diphenylphosphino)ethylene), and their precursors have been prepared. For these and other polypyridyl aqua complexes, ΔE1/2 (=E1/2(RuIVO/RuIIIOH) − E1/2(RuIIIOH/RuIIOH2)) correlates with the sum of a set of ligand parameters defined by Lever et al. (∑iEi(Li)) but there is a dramatic change in slope at ΔE1/2 = −0.11 V as the dominant effect of the ancillary ligands changes from stabilization of Ru(II) by back-bonding to stabilization of Ru(III) by electron donation.
The reaction of Ln(III) ions with a tripodal ligand HBpz(3)(-) (hydrotris(pyrazol-1-yl)borate) and a "complex ligand" [Cr(acac)(2)(ox)](-) (acac(-) = acetylacetonate, ox(2)(-) = oxalate) in aqueous solution afforded a series of the novel 3d-4f heterodinuclear complexes [(acac)(2)Cr(ox)Ln(HBpz(3))(2)] (Ln = Eu (1), Gd (2), Tb (3), Yb (4), Lu (5)). The crystal structure of 4 has been determined by X-ray diffraction. Complex 4 crystallizes in monoclinic space group P2/n, of which the cell parameters are a = 8.594(3) Å, b = 18.538(4) Å, c = 12.093(2) Å, beta = 93.71(2) degrees, and Z = 2. The Yb atom has an eight-coordinate distorted square antiprismatic coordination geometry. The intramolecular Cr.Yb distance is 5.631(1) Å. The magnetic susceptibility data for complex 2 showed that the Cr(III)-Gd(III) interaction is weakly antiferromagnetic with an exchange coupling constant J(CrGd) = -0.09 cm(-)(1). The luminescence measurements demonstrated the energy transfers for both Ln(III) --> Cr(III) and Cr(III) --> Ln(III), of which the degree of emission quenching depends on the energy gap of the excited levels in two metal centers. These results reveal that the metal-metal interactions between Cr(III) and Ln(III) are very weak in magnetic interaction but are strong from the viewpoint of energy transfer.