Thermal studies of N-phenylethane-1,2-diamine complexes of nickel(II) in the solid state

[NiL3]X-2 (where L=N-phenylethane-1,2-diamine and X=I- and ClO4-), [NiL2X2] (X is Cl-, Br-, NCS-, 0.5SO(4)(2)- or 0.5SeO(4)(2)-) and [NiL2(H2O)(2)](NO 3)(2) have been synthesized from solution and their thermal study has been carried out in the solid phase. [NiL2Cl2] upon heating undergoes irreversib le endothermic phase transition (142-152 degrees C, Delta H=0.35 kJ mol(-1) ) without showing any visual colour change. This phase transition is assume d to be due to conformation changes of the diamine chelate rings. NiLCl2 an d NiL2.5I2 have been prepared pyrolytically from [NiL2Cl2] and [NiL3]I-2 re spectively in the solid state. [NiL2(H2O)(2)](NO3)(2) upon heating undergoe s deaquation-anation reaction without showing any visual colour change. [Ni L2X2] (X is Cl-, Br-, NCS-), [NiL2(H2O)(2)](NO3)(2) and [NiL2(NO3)(2)] poss ess trans-octahedral configuration, whereas, [NiL2X2] (X is 0.5SO(4)(2)- or 0.5SeO(4)(2)-) are having cis-octahedral configuration. Amongst the comple xes, only NiLCl2 shows unusually high (5.1 BM at 27 degrees C) magnetic sus ceptibility value.