THERMAL STUDIES OF N-1-ISOPROPYL-2-METHYL-1,2-PROPANEDIAMINE COMPLEXES OF NICKEL(II)X(2) [X=I-, CF3CO2-, 0.5SO(4)(2-) AND 0.5SEO(4)(2-)] INTHE SOLID-STATE

The complexes NiL(2)X(2) . nH(2)O (L=N-1-isopropyl-2-methyl-1,2-propan ediamine; X = 0.5SO(4)(2-) when n = 0; X = I- when n = 2; X = CF3CO2- when n= 0 or 2 and X = 0.5SeO(4)(2-) when n = 0 or 3) have been synthe sized and their thermal behaviour has been studied. All the hydrated c omplexes are yellow in colour and on heating lose water of hydration a ccompained by a yellow --> light blue thermochromic transition, except in the case of the iodide complex, which retains the original yellow colour on dehydration. However, NiL(2)I(2) undergoes an irreversible e xothermic phase transition (166-193 degrees C; Delta H = -7.5 kJ mol(- 1)) with change in colour from yellow to reddish yellow. NIL(2)(CF3CO2 )(2) shows a reversible phase transition(heating cycle, 144-170 degree s C; Delta H = 3.1 kJ mol(-1); cooling cycle, 158-135 degrees C; Delta H = -3.1 kJ mol(-1)) with no visual change in colour. All the yellow complexes possess square-planar geometry and the light blue complexes NIL(2)X(2)(X = CF3CO2-,0.5SO(4)(2-) and 0.5SeO(4)(2-)) are expected to be pentacoordinated. The phase transition occurring in NiL(2)X(2) (X = I- and CF3CO2-) is due to conformational changes of the diamine chel ate rings.