Hydrogen-bond directionality and symmetry in [C(O)NH](N)2P(O)-based structures: a comparison between X-ray crystallography data and neutron-normalized values, and evaluation of reliability

For [C(O)NH](N)2P(O)-based structures, the magnitude of the differences in the N โ€” H...O, H...O=P and H...O=C angles has been evaluated when the N โ€” H bond lengths, determined by X-ray diffraction, were compared to the neutron normalized values and the maximum percentage difference was obtained, i.e. about 3% for the angle even if the N โ€” H bond lengths have a difference of about 30% (0.7 โ€… ร… for the X-ray and 1.03 โ€… ร… for the neutron-normalized value). The symmetries of the crystals are discussed with respect to the symmetry of the molecules, as well as to the symmetry of hydrogen-bonded motifs, and the role of the most directional hydrogen bond in raising the probability of obtaining centrosymmetric crystal structures is investigated. The work was performed by considering nine new X-ray crystal structures and 204 analogous structures retrieved from the Cambridge Structural Database.
Source: Acta Crystallographica Section B - Category: Chemistry Authors: Tags: phosphoric triamide X-ray diffraction neutron normalization symmetry Cambridge Structural Database lone electron pair research papers Source Type: research