The complexes [Ni(dpt) 2 ]X 2 nH 2 O (where dpt is N-(3-aminopropyl)-1,3-propanediamine;n = 0 when X is I, NCS or ClO 4 ; n = 1 when X is Cl, Br or NO 3 ; n 1 when X is 0.5SO 4 and 0.5SeO 4 ), Ni(dpt)X 2 nH 2 O (n = 0 when X is Cl or NO 3 ; n = 1 when X is Br or I; n = 2 when X is NO 3 ; n = 3 when X is 0.5SO 4 or 0.5SeO 4 ), [Ni(aepn) 2 )]I 2 , Ni(aepn)I 2 (where aepn is N-(2-aminoethyl)-1,3-propanediamine), [Ni(dien) 2 ]I 2 and Ni(-dien)I 2 (where dien is diethylenetriamine) have been synthesised from the solution and thermal investigations upon them have been carried out in the solid state. [Ni(dpt) 2 ]X 2 (X is Br or NO 3 ) undergoes endothermic reversible phase transitions upon heating (198-212°C, ΔH = 3.5 kJ mol - 1 and 205-222°C for [Ni(dpt) 2 ]Br 2 and [Ni(dpt) 2 ](NO 3 ) 2 respectively). Ni(dpt)I 2 shows exothermic irreversible phase transition during heating (193-220°C; ΔH = 4.1 kJ mol - 1 ). The thermal stabilities of dpt complexes are compared with those of the corresponding aepn and dien complexes.