Biomedical subjects
AN Sobolev
Publications and source records attributed to AN Sobolev.
Bonding effects and the crystal structures of (NH4)2
The crystal structures of the Tutton salts (NH4)2[Cu(H2O)6](SO4)2, diammonium hexaaquacopper disulfate, formed with normal water and isotopically substituted H2(18)O, have been determined by X-ray diffraction at 9.5 K and are very similar, with Cu-O(7) the longest of the Cu-O bonds of the Jahn-Teller distorted octahedral [Cu(H2O)6]2+ complex. It is known that structural differences accompany deuteration of (NH4)2[Cu(H2O)6](SO4)2, the most dramatic of which is a switch to Cu-O(8) as the longest such bond. The present result suggests that the structural differences are associated with hydrogen-bonding effects rather than with increased mass of the water ligands affecting the Jahn-Teller coupling. The Jahn-Teller distortions and hydrogen-bonding contacts in the compounds are compared with those reported for other Tutton salts at ambient and high pressure.
The structures of the alpha-alums RbCr(SO4)2.12H2O and CsCr(SeO4)2.12H2O at 293 and 12 K
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Structure of and electron density in RbTiOAsO4 at 9.6 K.
Structure factors for rubidium titanyl arsenate, RbTiOAsO(4), were measured with Mo Kalpha radiation (lambda = 0.71069 Å) at 9.6 and 295 K. The data show that there is no phase transition between room temperature and 9.6 K. The space group is Pna2(1). Unit-cell parameters are a = 13.218 (1), b = 6.6500 (9) and c = 10.761 (1) Å at 9.6 K, and a = 13.261 (2), b = 6.6791 (8) and c = 10.769 (1) Å at 295 K. As the temperature was lowered from 295 to 9.6 K the Rb atoms moved along the c axis in the direction of the polarization vector, while no significant change was noted for the Ti-O-As network. Strong accumulation and polarization of the difference electron density (Deltarho) in exceptionally short covalent Ti-O bonds alternates with the depleted density in long Ti-O bonds. The Deltarho near the Ti atoms is polarized and aligned in the negative c direction in accordance with the ferroelectric properties of this material. However, the electron density near the Rb atoms is depleted in this direction and the excess Deltarho is moved further away from the nuclei along the c vector.