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High-temperature phenomena in RbD2PO4 and CsH2PO4 . Polymeric transformations or polymorphic phase transitions?

Bronowska W.

Materials Science Poland

2006

Vol. 24, No. 1

229--236

X-ray analysis has been performed for RbD2PO4 and CsH2PO4 over the temperature range from 288 K to 537 K and 507 K, respectively. The refinement of the crystal structure of RbD2PO4 at 430 K has revealed that the high-temperature paraelectric phase of this crystal is isomorphic with the monoclinic P21/m paraelectric phase of CsH2PO4. The X-ray diffraction CCD images obtained for RbD2PO4 have proved that the high-temperature paraelectric phase is stable up to approximately 525 K. At this temperature, polycrystallisation of the single-crystal samples and their subsequent decomposition has been observed. CsH2PO4 undergoes a structural phase transition at 504 K, from the monoclinic paraelectric phase to a cubic superionic phase (P21/m transforms to Pm-3m symmetry). The reversibility of the superionic phase transition in the crystals is a strong evidence for a polymorphic character of this solid-solid transition.

One-, Two- and Non-Coordinated Cr02- 4 Entity in the Nickel(II) Complexes. Structural and Spectroscopic Investigation

Pietraszko A., Bronowska W., Wojciechowska A., Staszak Z., Cieślak-Golonka M.

Polish Journal of Chemistry

2002

Vol. 76 / nr 2-3

309-324

A systematic investigation of the chromate ion in [Ni(II)-(2,2_-bpy)-CrO4 2_ ] systems has been carried out. The effect of the Ni(II) ion and the organic ligand on the mode of the chromate position in the [Ni(bpy)3]CrO4_7.5H2O(1), [Ni(bpy)2(OCrO3)(H2O)]_5H2O(2) and catena-(ž-CrO4-O,O_)[Ni(bpy)(H2O)2]_2H2O (3) complexes has been shown. [Ni(bpy)3]CrO4_7.5H2O crystals (1) have a monoclinic symmetry with space group C2/c and 8 chemical units, forming a unit cell with a = 13.641(3) A, b = 22.939(5) A, c = 23.351(5) A and _ = 104.69(3) deg, whereas the [Ni(bpy)2(OCrO3)(H2O)]_5H2O crystals (2) have a monoclinic symmetry with space group P21/c and 4 chemical units per unit cell with a = 10.854(2) A, b = 22.665(5) A, c = 10.623(2) A and _ = 108.93(3) deg at room temperature. The chromate ion in 1 is not coordinated to the nickel(II) ion. The geometry around the Cr(VI) atom is pseudotetrahedral. Untypical for the chromate ion monodentate coordination has been found in the complex [Ni(bpy)2(OCrO3)(H2O)]_5H2O. The chromate position has been also elucidated from the digitally resolved IR spectra. The coordination of the chromate ion in 2 and 3 was also observed for the single crystal at 4K, in reflectance and solution electronic spectra through the appearance of a new transition at ca. 15000 cm-1. The full characterization of the chromophores present in the complexes: NiN6, NiN4O2, NiN2O4 and NiO6 have been obtained on the basis of the detailed analysis of the electronic spectra at 4K(Gaussian deconvolution followed by digital filtration).