π-Hole Tetrel Bonds—Lewis Acid Properties of Metallylenes

Sławomir J Grabowski

doi:10.3390/cryst12010112

Abstract

The MP2/aug-cc-pVTZ calculations were performed on the dihalometallylenes to indicate their Lewis acid and Lewis base sites. The results of the Cambridge Structural Database search show corresponding and related crystal structures where the tetrel center often possesses the configuration of a trigonal bipyramid or octahedron. The calculations were also carried out on dimers of dichlorogermylene and dibromogermylene and on complexes of these germylenes with one and two 1,4-dioxide molecules. The Ge⋯Cl, Ge⋯Br, and Ge⋯O interactions are analyzed. The Ge⋯O interactions in the above mentioned germylene complexes may be classified as the π-hole tetrel bonds. The MP2 calculations are supported by the results of the Quantum Theory of Atoms in Molecules (QTAIM) and the Natural Bond Orbital (NBO) approaches.

Highlights

Carbenes are often defined as neutral compounds containing a divalent carbon atom [1]
The search through the Cambridge Structural Database, CSD [13,14] (September 2021 release) was performed here to find crystal structures containing species with the tetrel (14th group element) formally divalent center being in contact with the electron donor
It seems that in the case of metallylenes, the electron donor properties are revealed for carbenes and hardly for silylenes. This is probably connected with the greater contribution of the p-character of the lone electron pair orbital of the tetrel center

Summary

Introduction

Carbenes are often defined as neutral compounds containing a divalent carbon atom [1]. The latter center possesses only six electrons in the valence shell. Two nonbonding electrons of this carbon can be located in two different orbitals; their spins are parallel for the σ1pπ triplet state (3B1 state). The singlet carbenes are characterized by the opposite spin nonbonding electrons. These electrons may occupy the same σ or pπ orbital for the σ2 or pπ configuration, respectively, this corresponds to two 1A1 states. The σ1pπ configuration corresponding to the excited singlet 1B1 state may occur

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Conclusion