Acta Crystallographica Section B

Structural Science

Volume 54, Part 4 (August 1998)

research papers

Acta Cryst. (1998). B54, 464-470 [ doi:10.1107/S0108768197018193 ]

Opening and Narrowing of the Water H-O-H Angle by Hydrogen-Bonding Effects: Re-inspection of Neutron Diffraction Data

T. Steiner

Abstract: For 71 water molecules donating two Ow-HO hydrogen bonds, the correlation of the covalent H-O-H angle and the OOwO angle is inspected from 49 well refined organic and organometallic neutron diffraction crystal structures. Compared to sample average, the water angle is opened for large and narrowed for small OOwO angles. Notably, the H-O-H angle is widened compared with the gas phase value even for small OOwO. Related behavior is observed for chloride anion acceptors. The correlation exhibits a considerable scatter which should not be interpreted as experimental inaccuracies, but as secondary effects. Possible secondary effects are multi-center hydrogen bonding and effects of coordination to the water O atom. In a comparative test, low-temperature X-ray diffraction data were shown to be completely unsuitable for this type of analysis. The dependence of the C-O-H angle on the C-OO angle in hydrogen bonds donated by hydroxyl groups in carbohydrates is also shown.