Synthesis, characterization and thermal decomposition study of some nickelnitro derivatives

Abstract

Compounds with general formula [KxMyNi(NO2)6(H2O)n] (M=Ca, Sr, Ba, La;x=0–2; y=1, 2; n=0, 4) have been prepared and characterized by XRD, IR and EPR techniques. The structure of [Ba2Ni(NO2)6(H2O)2 ]2H2O has been determined by single crystal X-ray diffraction: space group P63 , a=7.525(1) A and c=14.516(1) A. The geometry of the compound consists of an intricate network of ligand-bridged coordination polyhedra, where the arrangement of the nickel(ii) ion exhibits a slightly distorted octahedral topology. The Ca, Sr and La phases have been indexed with a cubic cell, space group Pm3 m and cell parameters 10.354(5) A, 10.517(5) A and 10.571(8) A, respectively. Thermal decomposition of the different compounds using TG involves two consecutive steps: ligand pyrolysis and evolution of the inorganic residue. For the barium compound a third step appears which corresponds to the dehydration process. Further thermal treatments in tubular furnaces yield the formation of different mixed oxides of NiIII and NiIV at lower pressures of oxygen than those obtained from the ceramic method. Advantages of using the metallo–organic method can also be deduced from the SEM study.