V. S. Nedzvetskii

Structure and photochemical properties of [N′-(2-thienylidene)]benzhydrazide crystals

The x-ray structural study showed that [N′-(2-thienylidene)]benzhydrazide does not form a crystal hydrate. The molecules in the crystal are loosely packed and joined by linear chains of intermolecular hydrogen bonds (IHB),. Like the previously investigated [N′-(furfurylidene)] benzhydrazide, [N′-(2-thienylidene)]benzhydrazide crystals were sensitive to UV radiation. The similarity in the structure of these compounds confirms the hypothesis that intermolecular N → O phototransfer of a proton along the IHB chain can take place efficiently in loose structures in the noncrystal hydrates of the compounds investigated, in contrast to the previously studied crystal hydrates.

Effect of the orientation of the water molecules in the system of hydrogen bonds in the crystal hydrate of m-bromo-N′-(5-nitrofurylidene)benzohydrazide on its sensitivity to light

On the basis of a crystal-chemical analysis of the structure of the investigated benzohydrazides, the structural characteristics typical of light-sensitive crystal hydrates of this type were formulated: the formation of intermolecular polar chains of hydrogen bonds of the C=O...H2O...H-N type with the water molecules; “head-to-tail” stacking of the molecules. It was shown that the investigated m-bromo-N′-(5-nitrofurylidene)benzohydrazide forms 1∶2 crystal hydrates. The dimeric associates of the water molecules link the benzohydrazide molecules in the stacks by hydrogen bonds. Polar chains of hydrogen bonds, along which intermolecular N → O-phototransfer of a proton occur, are formed between the stacks with the participation of one of the water molecules. An assignment was made of the bands for the OH stretching vibrations of the water molecules in the investigated crystal hydrate.

Structural features of light-sensitive crystals of N′-[2-nitrofurfuryl-5-vinyl]benzhydrazide and [N′-furfurylidene)]benzhydrazide

An x-ray structural study found that N′-[2-nitrofurfuryl-5-vinyl]benzhydrazide and [N′-(furfurylidene)]benzhydrazide do not form crystal hydrates although they have polar syn-conformations. Molecules in the crystal are joined by linear chains of intermolecular H-bonds C=O...H-N. The light-sensitivity of the crystals increases with decreasing packing density.

Structure and photochemical properties of the crystal hydrate of 3,5-dinitro-[∩'-(5-nitrofurfulidene)]benzhydrazide with a dimer associate of water

Conclusions1.On the basis of a crystal chemical study of crystals of 3,5-dinitro-[(N′-(5-nitrofurfuliden)] benzhydrazide, we have established that the increase in their photosensitivity is due to the new way in which the crystal hydrates are formed (with participation of dimer associates of water).2.The molecules of the studied ketohydrazone are close-packed into energetically favorable shifted stacks; as a result, the stacks themselves are also close packed. The dimer water associates are located in the channels between the stacks.3.We have assigned the stretching vibration bands for the four nonequivalent hydrogen atoms of the water molecules in the IR spectra. We have shown that in the water dimer, the oxygen atom forming the N-H...OH2O hydrogen bond is a stronger proton acceptor than the oxygen atom of the monomeric water molecule.

Effect of packing of molecules of derivatives of [N′-(5-nitrofurfulidene)]-benzhydrazides on the photosensitivity of their crystals

ConclusionWe have carried out an x-ray diffraction study of photosensitive crystals of o-nitro[N′-(5-nitrofurfulidene)] benzhydrazide. On the basis of crystal chemical analysis of data obtained and published previously, we conclude that a necessary element in the structure of photosensitive crystal hydrates of derivatives of [N′-(5-nitrofurfulidene)]hydrazides is head-to-tail stacking of their molecules.

Effect of a methyl substituent on the molecular and crystal structure of (2-acetyl-5-nitrofuran)-N-benzoylhydrazone

ConclusionsAn x-ray diffraction study of (2-acetyl-5-nitrofuran)-N-benzoylhydrazone has shown that the molecules of this compound have a nonplanar structure with syn arrangement of the oxygen and nitrogen atoms of the keto and hydrazone groups and an anti arrangement of the oxygen atom of the furan fragment. With such a conformation, the molecules do not form crystal hydrates; in the crystal, they are connected with one another into chains by intermolecular hydrogen bonds N-H...O 2.26 Å. However, intermolecular N → O proton phototransfer does not occur between them.

Determining role of nonbonding intermolecular Br...Br interactions in the crystal structure of p-bromo-[N′-(5-nitrofurfurylidene)benzhydrazide

ConclusionsAn x-ray diffraction structural investigation of the non-light-sensitive crystals of p-bromo-[N′-(5-nitrofurfurylidene)]benzhydrazide showed anomalously short intermolecular Br...Br contacts, indicating a specific interaction between these atoms, which hinders packing of the ketohydrazone molecules in stacks in a head-to-tail pattern as found in previously studied light-sensitive crystals of compounds in this class.

Cocrystallization of two isomers of N′-(5-nitrofurfurylidene)benzhydrazide and features of the molecular, crystal, and electronic structure of their crystal hydrate

Conclusions1.An x-ray diffraction structural study of crystals of N′-(5-nitrofurfurylidene)benzhydrazide revealed the first case of the cocrystallization of syn and syn-anti isomers of ketohydrazone molecules. We propose that the isomerization of the ketohydrazone molecules occurs upon crystallization and is a consequence of packing effects. The crystal structure of this ketohydrazone is a rare case of the laminar packing of polar and nonpolar molecular chains.2.The formation of hydrates of N′-(5-nitrofurfurylidene)hydrazides radically alters the structure of their frontier molecular orbitals in comparison with the anhydrous molecules. This may significantly affect the properties of the crystals of these compounds.

Aspects of the structure of the nonphotosensitive crystal hydrate of p-bromo-[N′-(p-nitrobenzylidene)]benzhydrazide

Conclusions1.An x-ray diffraction structural analysis has shown the p-bromo-[N′-(p-nitrobenzyli-dene)]benzyhydrazide forms a 1∶1 crystal hydrate.2.Replacement of an N′-furfurylidene substituent by the N′-benzylidene substituent leads to a significant change in the structure of the crystal hydrate. The water molecules in N′-furfurylidenebenzhydrazide form unidimensional linear hydrogen bond chains between stacks of ketohydrazone molecules. The water molecules in N′-benzylidenebenzhydrazide form a three-dimensional hydrogen bond network, which prevents stacking of the ketohydrazone molecules. In the former case, the hydrogen bond system persumably is favorable for an intermolecular N → O proton phototransfer, while such a transformation is not favored in the latter case. Thus, the crystals of p-bromo-[N′-(p-nitrobenzylidene)]benzhydrazide are non-photosensitive.