Linear MgCp∗2 vs Bent CaCp∗2: London Dispersion, Ligand-Induced Charge Localizations, and Pseudo-Pregostic C-H⋯Ca Interactions

Rumpa Pal, Stefan Mebs, Ming W. Shi, Dylan Jayatilaka, Joanna M. Krzeszczakowska, Lorraine A. Malaspina, Michal Wiecko, Peter Luger, Malte Hesse, Yu Sheng Chen, Jens Beckmann, Simon Grabowsky

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Abstract

In the family of metallocenes, MgCp∗2 (Cp∗ = pentamethylcyclopentadienyl) exhibits a regular linear sandwich structure, whereas CaCp∗2 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∗2 suggests that the bending must have an intramolecular origin. Geometry optimizations with and without dispersion effects/d-type polarization functions on MCp2 and MCp∗2 gas-phase complexes (M = Ca, Mg) establish that attractive methyl⋯methyl London dispersion interactions play a decisive role in the bending in CaCp∗2. 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∗2 and CaCp∗2 were determined which facilitated the identification and characterization of intermolecular pseudo-pregostic interactions, C-H⋯Ca, in the CaCp∗2 crystal structure.

Original languageEnglish
Pages (from-to)4906-4920
Number of pages15
JournalInorganic Chemistry
Volume57
Issue number9
DOIs
Publication statusPublished - 7 May 2018

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    Pal, R., Mebs, S., Shi, M. W., Jayatilaka, D., Krzeszczakowska, J. M., Malaspina, L. A., Wiecko, M., Luger, P., Hesse, M., Chen, Y. S., Beckmann, J., & Grabowsky, S. (2018). Linear MgCp∗2 vs Bent CaCp∗2: London Dispersion, Ligand-Induced Charge Localizations, and Pseudo-Pregostic C-H⋯Ca Interactions. Inorganic Chemistry, 57(9), 4906-4920. https://doi.org/10.1021/acs.inorgchem.7b03079