A quantum-topological analysis of short (strong) H bonds in three-dimensional periodic crystals

The characteristics of the critical electron density points of the O-H···A fragment (A = O or N) in molecular crystals with short H bonds were analyzed in terms of the Bader quantum-topological theory of molecular structure. The wave functions (B3LYP/6-31G** approximation) of the ground state of 26 three-dimensional periodic crystals with experimentally determined structures were used. Intermediate-type interactions separating the limiting cases of covalent and closed shell-type interactions were found to be characterized by the following geometric parameters: 2.45 Å ≤ D(O···O) ≤ 2.6 Å, 1.35 Å ≤ d(H···O) ≤ 1.65 Å, and 1.0 Å ≤ d(O-H) ≤ 1.10 Å. Such interactions are observed in molecular crystals with the O-H···A fragment and high bridge proton mobility. Differences between H···O and H···N interactions were quantitatively characterized by the dependence of ρ _b on d(H···A), where A = O or N. The dependence parameter values were shown to be determined by the nature of the A atom that forms the H bond. The influence of the crystalline environment on systems with strong H bonds manifested itself by changes in the position of the bridge proton. The d(O-H)/d(H···O) ratio was, however, the same for gas-phase complexes and molecular crystals with weakly bent O-H···O fragments (∠O-H···O > 160°).