Lengthening of the covalent O–H bond in O–H^...O hydrogen bonds re-examined from low-temperature neutron diffraction data of organic compounds

Abstract

The lengthening of the covalent O-H bond in O-H..O hydrogen bonds is re-examined from high-precision low-temperature neutron diffraction studies of organic molecules (32 crystal structures, 136 hydrogen bonds, T<130 K, R<0.06, H atoms on symmetry elements excluded). Accuracies are around or better than 0.002 A. The dependencies of the covalent O-H bond length on the H...O and O...O separations are smooth with no sign of discontinuities. For all types of O-H and O-D hydrogen-bond donors and in combination with all types of O acceptors, the O-H bond length follows the same function of the H...O separation (within the experimental accuracy)