Structure transformations in nickel oxalate dihydrate NiC2O4 center dot 2H(2)O and nickel formate dihydrate Ni(HCO2)(2)center dot 2H(2)O during thermal decomposition

摘要

Structure and thermolysis of NiC2O4 center dot 2H(2)O (I) and Ni(HCO2)(2)center dot 2H(2)O (II) were studied for the precipitated powders from the water solutions of precursors. The compound (I) has a disordered structure (C2/c, a=11.7916(5), b= 5.31798(14), c= 9.7806(7) angstrom, beta= 127.014(6), V= 489.73(4)angstrom(3)) which is described via the displacement vector applied to the basis atoms and the part of the shifted atoms. Thermal dehydration of (I) leads to formation of the disordered beta-NiC2O4 (In), the structure of which (P21/n, a=5.8294(9), b= 5.1685(13), c= 5.2712(4) angstrom, = 117.793(12), V= 140.50(5)angstrom(3)) was refined from the powder diffraction. Oxalates (I) and (III) are both characterized by the essential part of the shifted atoms causing the extinction of some lines in XRPD pattern. The final product of thermal decomposition of (I) in air is NiO, whereas thermolysis of (II) leads to formation of Ni/Ni0 mixture. The content of Ni in the latter depends on the thickness of the decaying layer in the sample because the gaseous products of the reaction prevent the oxidation of the nickel formed initially.