Extensive Intramolecular and Intermolecular Interactions in Two Quaternary Salts of the Pyridoxal Oxime

Two derivatives of pyridoxal oxime (1) were prepared by quaternization of pyridoxal oxime with phenacyl bromide and 2-methoxyphenacyl bromide. The crystal structures of the 1-phenacyl-3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methylpyridinium bromide (2) and the novel 3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-2-methyl-1-(2'-methoxyphenacyl) pyridinium bromide (3) have been determined by X-ray diffraction method. The conformation of these two pyridoxal oxime phenacyl derivatives is locked by numerous intramolecular hydrogen bonds. The O-H center dot center dot center dot Br, C-H center dot center dot center dot Br and C-H center dot center dot center dot O hydrogen bonds in 2 and 3 form complex three-dimensional network. Supramolecular structure of 3 also contains C-H center dot center dot center dot pi and pi center dot center dot center dot pi interactions which link neighbouring cations. .