Metal–ligand bonding in metallocenes: Differentiation between spin state, electrostatic and covalent bonding
Metal–ligand bonding in metallocenes: Differentiation between spin state, electrostatic and covalent bonding
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茂金属中的金属-配体键合：自旋态、静电键合和共价键合之间的区别
DOI：
10.1016/j.ica.2006.07.073
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发表时间：
2007
影响因子：
2.8
通讯作者：
M. Swart
中科院分区：
文献类型：
--
作者：
M. Swart
我们用密度泛函理论（DFT）在OPBE/TZP水平上分析了金属-配体成键。这个理论水平最近被证明是唯一能够正确预测铁络合物的自旋基态的DFT方法，并且在这里发现了类似的自旋基态的准确性。我们考虑了沿着第一行过渡金属（Sc-Zn）扩展碱土金属（Mg，Ca）和几个第二行过渡金属（Ru，Pd，Ag，Cd）的双烯烃。利用能量分解分析，我们研究了这些配合物中金属-配体键合的趋势。从分解分析中得到的二茂铁的OPBE/TZP异裂缔合焓（− 658 kcal/mol）与基准CCSD（T）和CASPT 2结果非常一致。共价键在不同的烯中有很大的差异，在−155至− 635千卡/摩尔之间。泡利排斥（55- 345 kcal/mol）或静电相互作用（-480至-620 kcal/mol）的变化要小得多。共价键合，因此金属配体键合，是更大的低自旋状态比更高的自旋状态，由于受体d轨道的金属在低自旋状态的更好的适用性。因此，过渡金属配合物的自旋基态可以看作是金属-配体键合和Hund最大多重性规则之间微妙相互作用的结果。
We have analyzed metal–ligand bonding in metallocenes using density functional theory (DFT) at the OPBE/TZP level. This level of theory was recently shown to be the only DFT method able to correctly predict the spin ground state of iron complexes, and similar accuracy for spin ground states is found here. We considered metallocenes along the first-row transition metals (Sc–Zn) extended with alkaline-earth metals (Mg, Ca) and several second-row transition metals (Ru, Pd, Ag, Cd). Using an energy decomposition analysis, we have studied trends in metal–ligand bonding in these complexes. The OPBE/TZP enthalpy of heterolytic association for ferrocene (−658kcal/mol) as obtained from the decomposition analysis is in excellent agreement with benchmark CCSD(T) and CASPT2 results. Covalent bonding is shown to vary largely for the different metallocenes and is found in the range from −155 to −635kcal/mol. Much smaller variation is observed for Pauli repulsion (55–345kcal/mol) or electrostatic interactions, which are however strong (−480 to −620kcal/mol). The covalent bonding, and thus the metal–ligand bonding, is larger for low spin states than for higher spin states, due to better suitability of acceptor d-orbitals of the metal in the low spin state. Therefore, spin ground states of transition metal complexes can be seen as the result of a delicate interplay between metal–ligand bonding and Hund’s rule of maximum multiplicity.