I. I. Chuev

Synthesis and X-ray and Spectral Study of the Compounds [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu)

Iron nitrosyl complexes with general formula [Q4N]2[Fe2(S2O3)2(NO)4] (Q = Me, Et, n-Pr, n-Bu) were synthesized by the exchange reaction of K2[Fe2(S2O3)2(NO)4] with tetraalkylammonium bromides. The molecular and crystal structure of [(CH3)4N]2[Fe2(S2O3)2(NO)4] were studied by X-ray diffraction analysis. The iron atom in the four-membered cycle of the [2Fe–2S] anion is bound to another Fe atom and to two sulfur atoms and is coordinated by two nonequivalent NO groups, each bridging sulfur atom being bound to the SO3group. The structurally equivalent iron atoms are in the state Fe1–(S= 1/2). The Mössbauer spectroscopy method shows that the complexes are diamagnetic due to the strong Fe–Fe bond. It is found that the SO3group provides higher stability of the thiosulfate anion than the anion in Roussins red salt [Fe2S2(NO)4]2–.

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)7], where A=Na+, NH4+, or N(Bun)4+, and B2[Fe2S2(NO)4], where B=Na+, Cs+, or N(Bun)4+, were synthesized. Their structures and properties were studied by X-ray diffraction analysis, Mössbauer spectroscopy, and cyclic voltammetry. The effect of the crystal packing on the geometry of the tetranuclear NH4[Fe4S3(NO)7]·H2O and binuclear Cs2[Fe2S2(NO)4]·2H2O complexes was analyzed. The changes in the Fe57 Mössbauer spectral parameters of the anion in the B2[Fe2S2(NO)4] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S2(NO)2] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized through the Fe−Fe bonds explains the fact that the electronic states of the Fea(S3NO) and Feb(S2(NO)2) chromophores in the [Fe4S3(NO)7]− anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe4S3(NO)7]− complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe4S3(NO)7]− and [Fe2S2(NO4)]2− anions in CH3CN and THF solutions were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.

X-ray and IR spectroscopic studies of specific intermolecular interactions inN′-substituted isonicotinohydrazides

N′-Thenylidene- andN′-(o-nitrobenzylidene)hydrazides of isonicotinic acid have been studied by X-ray structural analysis and IR spectroscopy. In the crystalline state, these molecules are linked through intermolecular N—H ... Npy hydrogen bonds. Carbonyl groups are not involved in intermolecular hydrogen bonds. However, it was found that the C=O group participates in an attractive interaction with the sulfur atom of the thiophene group. The energy of this interaction is comparable with the energies of intermolecular C=O ... H—N hydrogen bonds in amides.

STRUCTURES AND PHOTOCHROMIC PROPERTIES OF SUBSTITUTED SPIROINDOLINONAPHTHOXAZINES

Six indolinospironaphthoxazines were studied by X-ray diffraction analysis. It was demonstrated that the electronic nature of the substituents in the naphthoxazine and indoline fragments has no substantial effect on the Cspiro−O and Cspiro−N bond lengths. Photocolorability of the compounds under study depends only slightly on the abovementioned bond lengths and correlates mainly with the energy of steric strain of the oxazine ring. The stability of the open forms of spiroindolinonaphthoxazines that formed upon photoirradiation is determined to a large extent by the electronic and steric nature of the substituents. The exception is the compound that contains the NO2 group in the indoline fragment. In the last-mentioned case, the cleavage of the ring occurs through a substantially different pathway.

Molecular structure of 1′,3′,3′-trimethyl-6-trifluoromethylsulfonyl-spiro-(indoline-2,2′-benzo[b]pyran)

Photochromic 1′, 3′, 3′ -trimethyl-6-trifluoromethylsulfonyl-spiro(indoline-2,2′-ben-zo[b]pyran) (1) was studied by X-ray diffraction analysis. In compound1, the Cspiro-O bond (1.49(1) Å (average)), broken on photoexcitation, is the longest of all the indoline spiropyrans studied.

Intra- and intermolecular interactions in crystals ofN′-furfurylideneisonicotinic hydrazide and related compounds. IR spectroscopic and X-ray diffraction studies

The reaction of isonicotinic hydrazide with furfural yieldedN′-furfurylideneisonicotinic hydrazide. IR spectroscopic studies demonstrated that crystallization from different solvents afforded products with an intermolecular NH...O=C hydrogen bond. Conditions of crystallization were chosen under which single crystals with the NH...NPy intermolecular hydrogen bond (1) were grown. X-ray diffraction analysis demonstrated that the molecular and crystal structure of1 is identical to that ofN′-thienylideneisonicotinic hydrazide (2). The crystal structure consists of layers. The molecules in the layers are linked in zigzag chains through NH...NPy intermolecular hydrogen bonds. The molecules of the adjacent chains (in the layer) are linked through C=O...H−C intermolecular hydrogen bonds between the O atom of the carbonyl group and the α-H atom of the furan ring. (In the structure of2, the chains are linked through specific intermolecular interactions of different nature but with approximately identical energy.) The replacement of the thiophene fragment (2) by the furan ring (1) is accompanied by a change in the intramolecular electronic effects, which is reflected both in the geometric and spectral characteristics of the molecules in the crystal.

Molecular and crystal structure of 2-(N-benzyl-N-phenylhydrazinoethylidene)-3-(2H)-benzo[b]-thiophenone

X-ray structural analysis was used to determine the molecular and crystal structure of 2-(N-benzyl-N-phenylhydrazinoethylidene)-3-(2H)-benzo[b]thiophenone. The crystals are monoclinic, the space group isC2/c,a=16.022(6),b=11.202(3),c=22.111(4) Å, β=81.08(3)°, and andZ=8. It was shown that the ability of hydrazones of a similar class to exhibit photochromic properties is a function of the steric stresses in the molecules and their confirmation.

Rearrangement of the crystal structure during solid-phase elimination of solvate acetic acid fromN′-(5-nitrofurfurylidene)isonicotinic hydrazide monohydrate

A new crystal modification ofN′-(5-nitrofurfurylidene)isonicotinic hydrazide (1) was studied by IR spectroscopy and X-ray structural analysis. The compound studied is the product of solid-phase desolvation of solvate hydrate1 of the composition [MeCOOH · 1 · H2O]. Spontaneous elimination of solvate acetic acid results in complex overall rearrangement of the crystal structure and formation of a new system of intermolecular hydrogen bonds. The crystal hydrate of 1 : 1 composition (1c) was formed from compound1. In the crystal structure of1c molecules1 are linked in infinite chains through intermolecular C=O...W...H-N hydrogen bonds. The second hydrogen atom of the molecule of the crystallization water is involved in formation of an intermolecular O-H...N(Py) hydrogen bond with the nitrogen atom of the pyridine ring of the molecule of the adjacent chain.

Low-temperature X-ray study of benzoid-quinoid tautomerism in crystals of 2-(N,N-diphenylhydrazinoethylidene)-3(2H)-benzo[b]thiophenone

An X-ray investigation of 2-(N,N-diphenylhydrazinoethylidene)-3(2H)-benzo[b]thiophenone was performed at room and low (−80 °C) temperatures. It was established that the structure of this compound in the crystalline state at R-20 °C is intermediate between the ketoenehydrazine and hydroxyhydrazone forms, while at −80 °C the molecular structure is completely transformed to the hydroxyhydrazone form. This confirms the dynamic nature of hydrogen atom disordering in the molecule at ∼20 °C.

Semi-empirical quantum chemical study of the mechanism of [2H]-chromene photoconversion

Abstract Semi-empirical quantum chemical investigations of three [2 H ]-chromene compounds with similar molecular structures but with different numbers of photoisomers were carried out. The reaction coordinates of pyran-ring cycle opening in the ground and the first excited singlet states were calculated. The mechanism of formation of different photoproduct isomers is suggested and the influence of [2 H ] chromene structure on the distribution of these isomers was studied.