For [C(O)NH](N)2P(O)-based structures, the magnitude of the differences in the N—H...O, H...O=P and H...O=C angles has been evaluated when the N—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—H bond lengths have a difference of about 30% (0.7 Å for the X-ray and 1.03 Å 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.
, in order to evaluate the acceptor directionality and nearly position of lone electron pair (LEP) at the oxygen atoms. The analyses were performed based on the original deposited structure and also after neutron-normalization of the N-H values. The H…O═C angles were found in a wider range with respect to the H…O═P angles which are more directional. Moreover, the maximum populations of H…O═P angles are within 135°-140°, while the two most populated ranges for H…O═C angles are within 150°-155° and then 140°-145°. The N-H…O angles were also analyzed to update a previous work for evaluation of the hydrogen bond angles (donor directionality) and to complete our discussion. The analysis of H…O═X (X = C, P) and N-H…O angles were also considered based on the hydrogen-bonded motifs including the noted angles to study the rigidity or flexibility of the motifs and the influence on the overall tendency of the angles.
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