Synthesis, characterization and thermal decomposition study of some nickelnitro derivatives

Abstract

Compounds with general formula [K_xM_yNi(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) Å and c=14.516(1) Å. 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) Å, 10.517(5) Å and 10.571(8) Å, 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 Ni^III and Ni^IV 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.