O. A. Kozina

Structure of photochromic 1′,3′,3′-trimethyl-7-methoxyspiro (lndoline-2,2′-[2H-1] benzopyran)

ConclusionsX-ray diffraction structural analysis has established the structure of photochromic 1′,3′,3′-trimethyl-7-methoxyspiro (indoline-2,2′-[2H-1]benzopyran) and showed that the Cspiro-O bond, which is cleaved upon photoexcitation, is already extended in the ground state.

Photochemical properties and structures of substituted norbornadienes

The spectral and photochemical properties of 3-phenylnorbornadiene-2-(N-phenyl)aldimine and 3-phenyl-2-(2,2-dicyanovinyl)norbornadiene have been studied, and their structures have been established by X-ray analysis. It was found that the C(2)=C(3) bonds in these compounds are longer than those in unsubstituted norbornadienes. It was established that long-wave absorbtion boundaries and quantum yields of the photoisomerization of 2,3-disubstituted norbornadienes to give the corresponding quadricyclanes increase as the C(2)=C(3) bond length increases and as the bond order decreases.

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 the nature of the heteroatoms in the spiro group on the structure of spiropyrans and an x-ray study of spiropyran of the dithiolane series C17H16O2S2

ConclusionsWe have carried out an x-ray diffraction study of tetramethylenespiro[1,3-dithiolane-2,7′[7H]-furo[3,2-f]-[2H -1]-benzopyran], containing the three heteroatoms S, S, O in the spiro group. The orbital n-σ* interactions virtually do not affect the bond lengths in the spiro group of the molecule; therefore the Cspiro-O bond, which is ruptured upon photoexcitation, remains unlengthened in the ground state. The differences in the lengths of the chemically equivalent Cspiro-S bonds are due to electrostatic repulsions of the unshared electron pairs of the heteroatoms S and O, which have different relative orientation.

Structural features of photochromic 2,3-epoxy-2-(p-nitrophenyl)-3-phenylindan-2-one

ConclusionsOn the basis of the results from an x-ray crystallographic investigation of the photochromic 2,3-epoxy-2-(p-nitrophenyl)-3-phenylindan-2-one it was shown that the C-C bond cleaved during photoexcitation is the weakest bond in the molecule even in the ground state, as occurred in the previously investigated photochromic spiropyrans.

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.