Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, United Kingdom.
Inorg Chem. 2013 Jun 17;52(12):7280-94. doi: 10.1021/ic400903a. Epub 2013 May 23.
(1)H NMR spectra of the paramagnetic cyanide-bridged mixed-valence compound (η(5)-C5H5)Fe(CO)2(μ-CN)Ru(NH3)53 (I) have been obtained in several solvents. When traces of partially deuterated water are present, instead of a single cyclopentadienyl (Cp) resonance shifted by the hyperfine interaction, numerous well-resolved resonances are observed. The spectra were simulated satisfactorily by giving the appropriate statistical weight to 140 possible H/D isotopomers formed by deuteration in the five ruthenium(III) ammine ligands. The proliferation of distinct resonances occurs because (a) the hyperfine shifts (HSs) due to each sequential deuteration in a single ammine are different and (b) while deuteration in an ammine cis to the cyanide bridge causes a downfield shift, in the trans ammine it causes an upfield shift that is nearly twice as large. All of these shifts exhibit a 1/T dependence, but temperature-independent components, due to large second-order Zeeman effects at the Ru(III) center, are also present. Combining the results of density functional theory calculations with data from metal-metal charge-transfer optical transitions and with the effect of solvent-induced NMR HSs, it is argued that Fermi contact shifts at the Cp protons are insignificant compared to those due to the dipolar (pseudocontact) mechanism. Analytical expressions are presented for the dependence of the HS on the tetragonal component of the ligand field at the Ru(III) ion. The tetragonal field parameter, defined as the energy by which the 4d(xy) orbital exceeds the mean t(2g) orbital energy, was found to be 147, 52, and 76 cm(-1), in dimethylformamide, acetone, and nitromethane, respectively. The effects of deuteration show that there is a significant component of hyperconjugation in the Ru-ammine interaction and that ND3 is a weaker π donor than NH3. A single deuteration in an axial ammine increases the tetragonal field parameter (ν) by +2.8 cm(-1), resulting in a HS of -37 ppb in the Cp proton resonance, whereas a single deuteration in an equatorial ammine decreases the field by -1.5 cm(-1) with a HS of +20 ppb, despite a nominal separation of seven chemical bonds. We analyze the origin of this remarkable sensitivity, which relies on the favorable characteristics of the Ru(III) low-spin t(2g)(5) configuration, having a spin-orbit coupling constant ζ ≈ 950 cm(-1).
(1)已在几种溶剂中获得了顺磁氰桥混合价态化合物(η(5)-C5H5)Fe(CO)2(μ-CN)Ru(NH3)53 (I)的 1H NMR 谱。当存在痕量部分氘化水时，除了受到超精细相互作用移动的单个环戊二烯基（Cp）共振之外，还观察到许多分辨良好的共振。通过给予在五个钌（III）氨配位体中形成的 140 种可能的 H/D 同量异位素适当的统计权重，对光谱进行了满意的模拟。这种明显的共振扩散的原因是：(a) 在单个氨中的每一次连续氘化导致的超精细位移（HS）不同；(b) 虽然氰桥顺式的氨氘化导致场移向高场，但在反式氨中则导致场移向低场，其幅度约为前者的两倍。所有这些位移均表现出 1/T 依赖性，但由于 Ru(III)中心的二阶塞曼效应较大，也存在与温度无关的分量。将密度泛函理论计算的结果与金属-金属电荷转移光学跃迁的数据以及溶剂诱导的 NMR HS 效应相结合，证明与偶极（赝接触）机制相比，Cp 质子的费米接触位移微不足道。提出了超精细位移随 Ru(III)离子配体场的四方分量的依赖关系的解析表达式。定义为 4d(xy)轨道超过平均 t(2g)轨道能量的能量的四方场参数，在二甲基甲酰胺、丙酮和硝基甲烷中分别为 147、52 和 76 cm(-1)。氘化的影响表明，在 Ru-氨相互作用中有显著的超共轭成分，并且 ND3 是比 NH3 弱的 π 给体。轴向氨中的单个氘化使四方场参数（ν）增加+2.8 cm(-1)，导致 Cp 质子共振的超精细位移为-37 ppb，而赤道氨中的单个氘化使场减少-1.5 cm(-1)，尽管相隔七个化学键。我们分析了这种显著灵敏度的起源，这依赖于 Ru(III)低自旋 t(2g)(5)构型的有利特性，该构型具有自旋轨道耦合常数 ζ ≈ 950 cm(-1)。
