Hydrogen-hydrogen bonding: A stabilizing interaction in strained chelating rings of metal complexes in aqueous phase

►H⋯H close contacts are shown to be stabilizing rather than destabilizing steric clashes in a series of Zn(II) complexes in solution. ►These close-contacts exhibit all the hallmarks of chemical bonding: Bond paths of maximal electron density linking the nuclei of the two hydrogens, elevated delocalization indices of interacting hydrogen atoms, and considerably lower atomic energy of the hydrogen atoms involved in such interaction when compared to similar hydrogens that lacks such a bond path. ►The difference between bond path angles and geometrical bond angles is found to be strongly correlated with the 6-member coordination rings strain energy and formation constants. ►Unexpectedly, the bite angle N-Zn-O is found to be the least strained.