Laidlaw William Michael, Denning Robert Gordon, Murphy Damien Martin, Green Jennifer C
Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR.
Dalton Trans. 2008 Nov 28(44):6257-64. doi: 10.1039/b810224d. Epub 2008 Oct 2.
The low temperature (approximately 5 K) X-band ESR spectra are reported of the cyanide-bridged mixed-valence complexes [(OC)5Cr(mu-CN)M(NH3)5]X2 (M = Ru, Os; X = PF6(-)) in frozen matrices formed from nitromethane, acetonitrile and dimethylformamide with toluene. The anisotropy (g paralell-g perpendicular) is greater for the ruthenium than for the osmium complex. It is positive in all cases and is strongly dependent on the hydrogen-bonding interaction between the solvent matrix and the metal-ammine fragment, decreasing in the order nitromethane > acetonitrile > dimethylformamide. The axial ligand field parameter, Delta, is quite insensitive to the ammine metal (M) and is mainly determined by the solvent matrix. Density functional calculations, together with a simplified MO model, show that: (a) The value of Delta is dominated by the interaction between the filled cyanide pi-orbitals and the ammine-metal d(xz,yz) orbitals, (b) Delta decreases with increasing solvent donicity because the resulting positive shift of the d-orbital energies reduces this interaction, (c) the insensitivity of Delta to the ammine-metal arises because an increase in the energy mismatch between the cyanide pi-orbitals and the d-orbitals in osmium compound is offset by an increase in the 5d resonance integrals relative to those in the 4d shell. Semi-quantitative values are obtained for the pi and pi* resonance integrals. We point out that g paralell determines that portion of the ammine-metal spin population that interacts with the cyanide bridge, and should therefore be correlated with the degree of metal-metal charge transfer in low-spin d6-d5 intervalence compounds. X-band ESR spectra of the polycrystalline powders (M = Ru, Os; X = CF3SO3(-)) are rhombic with similar axial and rhombic ligand field parameters. The rhombicity is interpreted as resulting from asymmetric cation-anion hydrogen-bonding that is apparent in the crystal structures of these isomorphous compounds.
报道了氰化物桥联的混合价配合物[(OC)5Cr(μ-CN)M(NH3)5]X2（M = Ru，Os；X = PF6(-)）在由硝基甲烷、乙腈和二甲基甲酰胺与甲苯形成的冷冻基质中的低温（约5 K）X波段电子自旋共振（ESR）光谱。钌配合物的各向异性（g平行 - g垂直）比锇配合物的大。在所有情况下它都是正的，并且强烈依赖于溶剂基质与金属 - 氨片段之间的氢键相互作用，其减小顺序为硝基甲烷>乙腈>二甲基甲酰胺。轴向配体场参数Δ对氨基金属（M）相当不敏感，并且主要由溶剂基质决定。密度泛函计算以及简化的分子轨道模型表明：（a）Δ的值主要由填充的氰化物π轨道与氨基金属d(xz,yz)轨道之间的相互作用决定，（b）Δ随着溶剂给电子能力的增加而减小，因为d轨道能量的正向移动会减少这种相互作用，（c）Δ对氨基金属不敏感是因为锇化合物中氰化物π轨道与d轨道之间能量失配的增加被相对于4d壳层中5d共振积分的增加所抵消。获得了π和π*共振积分的半定量值。我们指出，g平行决定了与氰化物桥相互作用的氨基金属自旋布居的那部分，因此应该与低自旋d6 - d5价间化合物中的金属 - 金属电荷转移程度相关。多晶粉末（M = Ru，Os；X = CF3SO3(-)）的X波段ESR光谱是菱形的，具有相似的轴向和菱形配体场参数。菱形度被解释为是由这些同构化合物晶体结构中明显的不对称阳离子 - 阴离子氢键作用导致的。
