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

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 CH 5 + . 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.