Template synthesis and structures of apically functionalized iron(ii) clathrochelates

Template condensation of three nioxime or dichloroglyoxime molecules with monosubstituted boronic acids on an iron(ii) ion matrix afforded apically functionalized tris-nioximate clathrochelates and hexachloride precursors of apically-ribbed functionalized clathratochelates, respectively. The macrobicyclic tris-nioximates containing apical o-dimethoxyphenyl, p-bromophenyl, phenylethynyl, biphenylyl, 6-pyrimidinyl, or tert-butyl substituents and the dibenzothienyl-containing hexachloroglyoximate clathrochelate thus obtained were characterized by elemental analysis and IR, UV-Vis, ¹H and ¹³C NMR, ⁵⁷Fe Mössbauer and PD mass spectroscopies. The structures of o-dimethoxyphenyl- and phenylethynyl-containing iron(ii) tris-nioximates and the dibenzothienyl precursor were established by X-ray diffraction analysis.     

Photo- and Ionochromism of Benzoxazolyl-Substituted Spirobenzopyrans

8-Benzoxazolyl-6-formyl-substituted spirobenzopyrans with different acceptor groups in the 5'- position of the indoline moiety have been synthesized. Novel spiropyrans exhibit photochromic properties in an acetone solution at room temperature and form intensely colored complexes with heavy metal cations.     

Pinning by twin boundaries and peak effect in YBaCuO high-T c superconductors

Measurements of the imaginary part of the ac magnetic susceptibility of single crystals and melt-textured samples of YBa₂Cu₃O_x (YBCO) at T=77 K in a magnetic field ranging between 1 and 20 kOe are reported. If the dc magnetic field H _dc is rotated in the ab plane of the sample, the magnetic susceptibility and critical current density j _c have peaks corresponding to the magnetic field aligned with twin boundaries. Peaks in the curve of j _c versus magnetic field are observed at angles corresponding to these peaks, where AH _dc in a wide range of magnetic fields. The results have been interpreted in terms of the theory describing twin boundaries as a system of quasi-planar pinning sites. The pinning is strong if the elastic displacements of flux lines are of the order of the vortex lattice constant d _f. These displacements decrease with the magnetic field because of the decrease in d _f, and the contribution of the elastic energy to the Gibbs potential is reduced accordingly, which is the cause of the peak effect. Zh. éksp. Teor. Fiz. 111, 2158–2174 (June 1997)     

Photolysis of dimethyldioxirane

Phosphorescence of methyl acetate formed by isomerization of electron-excited dimethyldioxirane is observed upon excitation at the wavelength of the absorption band of dimethyldioxirane in acetone at 77 K. The quantum yield of the photodecomposition of dimethyldioxirane at 296 K is equal to 13.1±0.7 mol Einstein⁻¹. The high quantum yield of photolysis is evidence for the chain mechanism of decomposition of dimethyldioxirane. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 938–941, May, 1997.