Tetrel interactions from an interacting quantum atoms perspective

Abstract

Tetrel bonds, the purportedly non-covalent interaction between a molecule that contains an atom of group 14 and an anion or (more generally) an atom or molecule with lone electron pairs, are under intense scrutiny. In this work, we perform an interacting quantum atoms (IQA) analysis of several simple complexes formed between an electrophilic fragment (A) (CH3F, CH4, CO2, CS2, SiO2, SiH3F, SiH4, GeH3F, GeO2, and GeH4) and an electron-pair-rich system (B) (NCH, NCO–, OCN–, F–, Br–, CN–, CO, CS, Kr, NC–, NH3, OC, OH2, SH–, and N3–) at the aug-cc-pvtz coupled cluster singles and doubles (CCSD) level of calculation. The binding energy (EbindAB ) is separated into intrafragment and inter-fragment components, and the latter in turn split into classical and covalent contributions. It is shown that the three terms are important in determining EbindAB , with absolute values that increase in passing from electrophilic fragments containing C, Ge, and Si. The degree of covalency between A and B is measured through the real space bond order known as the delocalization index (δAB). Finally, a good linear correlation is found between δAB and ExcAB, the exchange correlation (xc) or covalent contribution to EbindAB.