Some specific features of the formation of hydrogen bonds in photosensitive crystals

The crystal structures of new substituted photosensitive azomethine N-oxides (nitrones): C-(2-phenoxy-1-vinyl)-N-p-methyl-phenyl nitrone (1), C-(3-bromo-6-phenoxy-1-vinyl)-N-p-methyl-phenyl nitrone (2), C-(3-bromo-6-phenoxy-1-vinyl)-p-phenyl nitrone (3) and C-(2-phenoxy-1-vinyl)-N-methyl nitrone (4) have been studied. As distinct from the previously studied [1, 2] C-(2-naphthyl-1-vinyl)-N-p-methyl-phenyl C-(2-naphtyl-1-vinyl)-N-phenyl (6), C-(2-phenoxy-1-vinyl)-N-p-methylphenyl (8), these nitrones have anti, and not syn, orientation of the nitrone and hydroxy groups. Because of such structural arrangement of the proton-donor hydroxy and proton-acceptor nitrone groups, the molecules in crystals 1-4 form chains with intermolecular hydrogen bonds (IHB), and not centrosymmetric dimer associates (CDA). Two types of chain arrangement have been revealed: ''head-to-tail'' and ''tail-to-head'' types. The replacement of the aryl substituent at the nitrone group nitrogen atom in 4 by the alkyl one has been shown to result in the IMB geometry alteration in the H-associate. Justified is the structural possibility of an intermolecular O --> O hydroxy proton transfer along the chain of hydrogen bonds in crystals 1-4, which may be responsible for photochemical conversions in the crystals.