Stoichiometries of thermal decompositions have been studied for the following Ni(II) nicotinamide (NA) complexes : Ni(NA)(2)Cl-2 . 2H(2)O (I), Ni(NA)(3)Br-2 . 4H(2)O (II), Ni(NA)(4)I-2 . 4H(2)O (III) and Ni(NA)(4) (NCS)(2) . 2C(2)H(5)OH (IV). Heating the compounds first results in a release of solvent molecules and desolvated compounds I’-IV’ are formed. NA molecules are released in two steps for complexes I’, II’, and III’, and in one step for complex IV’. Magnetic and spectral properties, as well as thermochemical data (quasi-equilibrium decomposition temperatures, DSC data) indicate an octahedral monomeric structure for complexes III, IV, III’ and IV’, and a polymeric structure for complexes I,II,I’ and II’, with adsorbed (I) and crystal water (II, III) or ethanol (IV).