74507-64-5Relevant articles and documents
Linear MgCp?2 vs Bent CaCp?2: London Dispersion, Ligand-Induced Charge Localizations, and Pseudo-Pregostic C-H?Ca Interactions
Pal, Rumpa,Mebs, Stefan,Shi, Ming W.,Jayatilaka, Dylan,Krzeszczakowska, Joanna M.,Malaspina, Lorraine A.,Wiecko, Michal,Luger, Peter,Hesse, Malte,Chen, Yu-Sheng,Beckmann, Jens,Grabowsky, Simon
, p. 4906 - 4920 (2018)
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.
