The competition between halogen bonds (Br...O) and C-H...O hydrogen bonds: the structure of the acetone-bromine complex revisited

• Published in: CrystEngComm Vol. 15; no. 42; pp. 8572 - 8577
• Main Authors: Jones, R H, Knight, K S, Marshall, W G, Coles, S J, Horton, P N, Pitak, M B
• Format: Journal Article
• Language: English
• Published: 01.10.2013
• Subjects: Bonding; Crystal structure; Diffraction; Elongation; Halogens; Hydrogen bonding; Hydrogen bonds; X-rays
• ISSN: 1466-8033
• DOI: 10.1039/c3ce41472h

A combination of single-crystal X-ray (at 110 and 200 K) and high-resolution neutron powder diffraction (110 K only) using perdeuterated samples has been used to re-determine the crystal structure of the well-known acetone-Br sub(2) complex. The results indicate a significant interaction between the carbonyl oxygen and the nearest Br atom leading to a marked elongation of the molecular Br-Br bond. In the earlier widely cited crystal structure, no such elongation was reported. Furthermore, the new structure indicates the presence of additional weaker C-H...O and C-H...Br interactions. In this simple complex, in which the halogen bonding is strong compared to the hydrogen bonding (C-H...O), the former interaction is found to occur close (~12 degree ) to the plane of the carbonyl group, with the C-H...Br complementing the stronger halogen bond.