Molecular conformation versus C-H•••Ph weak hydrogen bonds in 4-(4-H-1,2,4-triazol-4-yl)-2-X-phenylmethanimine (X = CH3, Cl, Br) crystals

Three 4-(4-H-1,2,4-triazol-4-yl)-2-X-phenylmethanimines where X = CH3 (1), Cl (2), and Br (3) have been synthesised and characterised by spectroscopic, theoretical, and single crystal X-ray methods. Crystallographic analysis showed that conformation of 1 is non-planar whereas of 2 and 3 are planar. In the studied crystals the C-H groups in triazole residues participate in the C-H...N hydrogen bonds and additionally in the C-H...O (water) hydrogen bond in 2. The aromatic phenyl ring is an acceptor of two intermolecular C-H...Ph hydrogen bonds only in 1. Observed non-planar conformation of 1 and results of optimisation of molecular geometry by DFT method suggest that conformation of 1 is highly influenced by very week the C-H...Ph hydrogen bonds in studied crystals. (C) 2002 Elsevier Science B.V. All rights reserved.