Peculiarities of NMR spectra of heterospin complexes

Experimental investigation and theoretical simulation of the unusual phenomenon of multiple broadening and narrowing of NMR signals due to the temperature variation of a solution of the stereochemically non-rigid heterospin Ni²⁺ complex with stable nitroxide were performed. The investigation of the temperature dependence of the NMR signals of stereochemically non-rigid heterospin systems can be used for choosing conditions for growing heterospin single crystals containing molecules in a definite conformation.     

Microscopic and mesoscopic structure of pressure-synthesized intermetallic Ni3Al

Optical metallography and transmission diffraction electron microscopy are used to show that the micro- and mesostructure of cast and pressure-synthesized intermetallic Ni₃Al differ considerably. Four types of grains of the major Ni₃Al phase are revealed in the synthesized intermetallide that differ in their domain and dislocation structure. These are single- and polydomain grains with or without dislocations. Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–56, July, 1999.     

Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides

It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (HL¹) and pyrazol-3-yl-substituted imino nitroxide (HL³) with Cu(II) acetate lead to self-assembly of the Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ tetranuclear and Cu₂(OAc)₂(H₂O)₂(L³)₂ dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (HL²) gave unexpected solid Cu₂(H₂O)₂(L⁶)₂ · 2DMF, in which L⁶ is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting HL². A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (HL⁴). It led to the formation of Cu₂(DMF)₂(L⁷)₂, where L⁷ is deprotonated 2-(5-carboxy-1H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(OAc)₂(H₂O)₂(L³)₂, the L¹ and L³ paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu₂(H₂O)₂(L⁶)₂ · 2DMF and Cu₂(DMF)₂(L⁷)₂, the paramagnetic L⁶ and diamagnetic L⁷ are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu₄(OH)₂(OAc)₄(DMF)₂(L¹)₂ and Cu₂(H₂O)₂(L⁶)₂ · 2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu₂(OAc)₂(H₂O)₂(L³)₂ reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II) ← N=C–N ? O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids.     

5-Phenyl-1,3,4-thiadiazole and 5-phenyl-1,2,4-triazoline-3-thione as products of dehydrogenation of cyclic tautomeric forms of benzaldehyde thiosemicarbazone

5-Pkenyl-1,3,4-thiadiazole and 5-phenyl-1,4-triazoline-3-thione are produced from heterocyclic tautomeric forms of benzaldehyde thiosemicarbazone in the gas phase under conditions existing in a mass spectrometer, and also in the solid phase in the course of thermolysis.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1554–1560, November, 1993.     

Movement of gas-filled cavities in alkalihalide crystals produced by external force fields

The migration of gas-filled cavities in KBr, NaCl, LiF single-crystals is investigated experimentally in an electric field and a temperature gradient.It is shown, that migration in an electric field is strongly dependent on the surface purity, due to its influence on matter transport along cavity surface. It is found that the velocity of cavity (v), having a ‘dirty’ surface follows a V～1/R dependence. (R—cavity size). In case of a ‘pure’ cavity surface. V is independent of R. Different types of V-vs-R dependence result in intermediate regions.Migration in a temperature gradient is also sensitive to surface purity. When the state of surface purity is determined, an appropriate critical size (R^*) exists such that if R is smaller than R^*, V～R and if R is larger than R^*, V is independent of R.Some constants of investigated process are determined from obtained experimental data.     

Crystal Structure of Copper(II) and Cobalt(II) Hexafluoroacetylacetonate Complexes with 2,2,5,5-Tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide

The crystal structures of the copper(II) and cobalt(II) hexafluoroacetylacetonate complexes with the nitroxide 2,2,5,5-tetramethyl-4-phenyl-3-imidazoline-1-oxyl-3-oxide (PhImOx) Cu(hfac)₂(PhImOx), Co(hfac)₂(PhImOx), and Co(hfac)₂(PhImOx)₂ have been determined. The former two are chain type complexes, whereas the latter has a molecular structure. The coordination polyhedra of the copper and cobalt atoms are tetragonally distorted octahedra. In the two chain type compounds, the octahedra are formed from the hfac anion, nitroxyl, and N-oxide O atoms; in the molecular complex, the O atoms of the NO groups are not coordinated to the metal atoms. In the structure of Cu(hfac)₂(PhImOx), F...F contacts equal to 2.805 have been found.