NMR spectral study of two crystalline modifications of lithium metaborate,LiBO2

⁷Li and¹¹B NMR spectral parameters were obtained for the two structural modifications of lithium metaborate. We first studied the high-temperature -form of LiBO₂, _iso(¹¹ B) 0, e²qQ/h(¹¹B)=42.5±2.0 kHz, e²qQ/h(⁷Li)=155±5 kHz. The following values were obtained for monoclinic -LiBO₂ with tricoordination of the boron atom: _iso(¹¹ B) = 16±2, e²qQ/h(⁷Li)=32±10 kHz. The electric field gradient on the⁷Li and¹¹B nuclei in the different crystal positions was discussed.Institute of Silicate Chemistry, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 70–73, September–October, 1989.     

Reactions Occurring in Gels of Lithium Tetraalkyl Borates Promoted by Supermolecular Structure of Complexes

As Li[BOR'(OR)₃] and Li[B(OR)₄] complexes, where R’ and R are alkyls of iso- and normal structure, are formed from boron alkoxides and lithium in solutions of low dielectric permittivity, they are involved in autocatalytic polyassociation to give viscoelastic systems (gels) possessing a mechanical memory [1].     

Helical Ullazine-Quinoxaline-Based Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic azomethine ylides (PAMYs) are powerful building blocks in the bottom-up synthesis of internally nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) through 1,3-cycloaddition reactions. In this work, the cycloaddition reaction of PAMYs to asymmetric ortho-quinones is presented, which, in contrast to the addition to symmetric para-quinones, facilitates subsequent condensation reactions and allows the synthesis of three helical N-PAHs with ullazine-quinoxaline ( UQ - 1 – 3 ) backbones. UQ - 1 and UQ - 2 possess two helical centers; however, single-crystal X-ray analysis together with the computational modeling of UQ - 3 elucidate the formation of only the thermodynamically most stable geometry with four helical centers in a (P,P,M,M) configuration. For the series UQ - 1 – 3 , the number of redox steps is directly correlated with the number of ullazine or quinoxaline units incorporated into the targeted molecular backbones. A detailed investigation of the spectroscopic and magnetic properties of the radical cation and anion as well as the dication and dianion species by in situ EPR/UV/Vis-NIR spectroelectrochemistry is provided. The excellent optical and redox properties combined with helical geometries render them possibly applicable as chiral emitter or ambipolar charge transport material in organic electronics.     

Novel derivatives of 3,5-di-tert-butylpyrocatechol with pharmacophore substituents

Russian Chemical Bulletin - New potentially bioactive derivatives comprising spatially hindered pyrocatechol linked to hydrazine, acid hydrazides (including isoniazid), and acetylcysteine by a...     

Enthalpies of dissolution of NaVO3 · 2H2O in aqueous chloric acid and the standard formation enthalpy of the VO 2 + ion

The enthalpies of dissolution of sodium metavanadate dihydrate in aqueous solutions of chloric acid and sodium perchlorate were measured by calorimetry at 298.15 K at ionic strengths of I = 0.3, 0.4, 0.5, 0.6, and 1.0 M. The standard formation enthalpy of the VO ₂ ⁺ ion in aqueous solution was calculated from the resulting experimental data.     

Synthesis,structure, and properties of 2-[(4,6-di-tert-butyl-2,3-dihydroxyphenyl)thio]acetic acid amides

Russian Chemical Bulletin - New potential biologically active derivatives, in which the sterically hindered pyrocatechol moiety is linked through a 2-thioacetyl covalent bridge to a number of...     

Diamagnetic nuclear <Superscript>119</Superscript>Sn probes in the copper chromites CuCr<Subscript>2</Subscript>X<Subscript>4</Subscript> (X = O,S, Se) with a spinel structure

The CuCr₂X₄ (X = O, S, Se) spinel system has been studied by the Mössbauer spectroscopy of the nuclear diamagnetic ¹¹⁹Sn probe at low temperatures in an external magnetic field. The hyperfine magnetic fields H ^Sn induced by paramagnetic ions at tin nuclei in the CuCr₂S₄ and CuCr₂Se₄ chalcogenides have giant values and are somewhat higher than those detected in the CuCr₂O₄ oxide. This behavior is caused by the strong covalence of the chalcogenides, which is supported by the experimentally found isomer shifts. The H ^Sn field is found to be mainly contributed by superexchange 90° interactions in the B-sublattice along the Cr[B]-X-Sn[B] bond chain, whose role increases in the series O-S-Se. In the oxygen CuCr₂O₄ spinel, the partial contributions to the H ^Sn field induced by the Cu²⁺ and Cr³⁺ ions are estimated. The local magnetic structure of the CuCr₂O₄ spinel is refined, and its total magnetization is shown to be directed along the magnetic moment of copper in the A sublattice.     

Thermodynamic properties of gels of lithium poly(alkyl borates)

The temperature-viscosity dependence of structured solution (gel) of [t-C₄H₉OB(OR)₃]Li · mROH and [B(OR)₄]Li in heptane, where R = n-C₄H₉, n-C₇H₁₅, n-C₁₀H₂₁; m = 0, 1, 2, has been studied in the range of threshold shear stress. Energy, heat and entropy of activation values have been obtained for the elasto-viscous flow of gels of complexes. The energies of activation determined for the flow of gels of complexes are unaffected by the temperature in a temperature range of 293–343 K, while the heat of activation increases with temperature.