SYNTHESIS, STRUCTURES AND THERMAL-ANALYSIS OF MNV2O6-CENTER-DOT-NH(2)O PHASES (N=1, 2 AND 4)

Three manganese vanadates with different degrees of hydration, MnV2O6 . 4H(2)O, MnV2O6 . 2H(2)O and MnV2O6 . H2O, have been prepared hydroth ermally and their structures have been characterized from single-cryst al X-ray diffraction data. They are isotypic with those of CoV2O6 . 4H (2)O, CoV2O6 . 2H(2)O and NiV2O6 . H2O, respectively. MnV2O6 . 4H(2)O crytallizes in space group C2/c (n degrees 15) of the monoclinic syste m with a=13.1656(6)Angstrom, b=10.110(1)Angstrom, c=6.9816(5)Angstrom, beta=111.559(5)degrees, V=864.2(1) Angstrom(3), 2=4. MnV2O6 . 2H(2)O crystallizes in space group Pnma (n degrees 62) of the orthorhombic sy stem with a=5.6075(4)Angstrom, b=10.9094(7)Angstrom, c=12.030(2)Angstr om, V=735.9(1) Angstrom(3), Z=4. MnV2O6 . H2O crystallizes in space gr oup P (1) over bar (n degrees 2) of the triclinic system with a=5.8502 (5)Angstrom, b=6.778(1)Angstrom, c=7.9370(8)Angstrom, alpha=80.50(1), beta=80.64(2)degrees; gamma=76.33(1)degrees, V=299.55(5) Angstrom(3), Z=2. The structure of MnV2O6 . 4H(2)O is made up by the linkage of MnO 4(OH2)(2) octahedra and parallel (VO3)(n)(n-) chains comprising distor ted edge-sharing VO5 square pyramids, with water molecules situated in the tunnels thus formed. MnV2O6 . 2H(2)O contains MnO4(OH2)(2) octahe dra and parallel (VO3)(n)(n-) polyvanadate chains built up from comer- sharing VO4 tetrahedra, MnV2O6 . H2O contains similar (VO3)(n)(n-) pol yvanadate chains cross-linked by edge-sharing Mn2O8(OH2)(2) dioctahedr a. The dehydration processes of MnV2O6 . nH(2)O (n=4, 2 and 1) were st udied with the use of TGA, DSC and thermodiffractometry techniques. Al though their chemical formulas differ only in water contents, these th ree compounds are not interconvertable and undergo independent dehydra tion processes.