Hydrogen bonding with a hydrogen bond: the methane-water complex and the penta-coordinate carbon

Abstract

Ab initio and atoms in molecules (AIM) theoretical studies have been used to show that in a 1:1 complex formed between CH₄ and H₂O, CH₄ acting as a hydrogen bond acceptor leads to the global minimum structure. There is a bond path connecting C to the H of H₂O revealing a penta-coordinate carbon that could be the precursor to the CH₅⁺. It appears to be a general feature in CH₄…HX complexes (X = F, Cl, and SH). It is in agreement with the experimental structure for analogous complexes and also the C₂H₆…HF/HCN complexes, suggesting that it is also a general feature for hydrocarbon-HX interaction.