Universität Bremen , Institut für Anorganische Chemie und Kristallographie , Leobener Straße 3 and 7 , 28359 Bremen , Germany.
Freie Universität Berlin , Institut für Experimentalphysik , Arnimallee 14 , 14195 Berlin , Germany.
Inorg Chem. 2018 May 7;57(9):4906-4920. doi: 10.1021/acs.inorgchem.7b03079. Epub 2018 Apr 19.
In the family of metallocenes, MgCp* (Cp* = pentamethylcyclopentadienyl) exhibits a regular linear sandwich structure, whereas CaCp* is bent in both the gas phase and solid state. Bending is typically observed for metal ions which possess a lone pair. Here, we investigate which electronic differences cause the bending in complexes lacking lone pairs at the metal atoms. The bent gas-phase geometry of CaCp* suggests that the bending must have an intramolecular origin. Geometry optimizations with and without dispersion effects/d-type polarization functions on MCp and MCp* gas-phase complexes (M = Ca, Mg) establish that attractive methyl···methyl London dispersion interactions play a decisive role in the bending in CaCp*. A sufficient polarizability of the metal to produce a shallow bending potential energy curve is a prerequisite but is not the reason for the bending. Concomitant ligand-induced charge concentrations and localizations at the metal atoms are studied in further detail, for which real-space bonding and orbital-based descriptors are used. Low-temperature crystal structures of MgCp* and CaCp* were determined which facilitated the identification and characterization of intermolecular pseudo-pregostic interactions, C-H···Ca, in the CaCp* crystal structure.
在茂金属家族中，MgCp*（Cp*=五甲基环戊二烯基）呈现出规则的线性夹心结构，而 CaCp* 在气相和固态中都是弯曲的。弯曲通常发生在具有孤对电子的金属离子上。在这里，我们研究了哪些电子差异导致在缺乏金属原子孤对电子的配合物中发生弯曲。CaCp* 的弯曲气相几何形状表明，弯曲必须具有分子内起源。对 MCp 和 MCp气相配合物（M=Ca，Mg）进行了没有色散效应/d 型极化函数的几何优化，确定了有吸引力的甲基···甲基伦敦色散相互作用在 CaCp 的弯曲中起着决定性的作用。金属具有足够的极化率以产生浅的弯曲位能曲线是先决条件，但不是弯曲的原因。同时还研究了配体诱导的电荷在金属原子上的集中和局域化，为此使用了实空间成键和基于轨道的描述符。确定了 MgCp* 和 CaCp* 的低温晶体结构，这有助于识别和表征 CaCp* 晶体结构中的分子间拟胎位相互作用，C-H···Ca。
