Journal of Thermal Analysis, Vol. 36 (1990) 465-472 THERMAL DECOMPOSTION STUDIES ON NICKEL(II) BIS (OXALATO)NICKELATE(II) PENTAHYDRATE N. Deb, P. K. Gogoi and N. N. Dass* DEPARTMENT OF CHEMISTRY, DIBRUGARH UNIVERSITY,DIBRUGARH - 786004, A,~AM, INDIA (ReceivedJune 11, 1988; in revised form March 15, 1989) The paper describes the synthesis and thermal decomposition of nick- el(II)bis(oxalato)nickelate(II)pentahydrate, Ni[Ni(C204)z].5H20. The complex was charac- terized by elemental analysis, infrared, electronic, e.s.r., magnetic moment measurement and X-ray powder diffraction studies. The thermal decompostion of the complex led to NiO in air at about 338~ and in nitrogen at about 720~ The activation energies (E*) for the dehydration and decompostion reactions in air and nitrogen were evaluated. Tentative reaction mechanisms have been suggested for the termal decompostion of the complex in air and nitrogen. Although the oxalato complexes of nickel and other transition and non- transiton metals of the type MC204.rH20 and MI[M2(C204).]xH20 (where M 1 = K, NH4 and Na and M 2 = nickel and other metals) are well known [1- 5], complexes of the type M[M(C204).].xH20 are relatively less known [6]. We have synthesized a series of oxalato complexes of the above type and their spectral and thermal studies were reported [7-10]. As an extension of our work reported earlier we are reporting here the synthesis, characterization and thermal decomposition of nick- el(II)bis(oxalato)nickelate(II)pentahydrate, Ni[Ni(C204)2].5H20. John lrc~ley & Sons, Limited, Chichester Akad~miai IOad6, Budapest