The standard (pdegrees = 0.1 MPa) molar enthalpies of formation of the crystalline complexes bis[N-(N",N"-diethylaminothiocarbonyl)benzamidinato]nickel(II), {Ni(datb)(2)}, and bis[N-(N",N"-diethylaminothiocarbonyl)-N'-phenylbenzamidinato]nickel(II) , {Ni(datpb)(2)}, were determined, at T = 298.15 K, by high precision solution-reaction calorimetry. [GRAPHICS] From the obtained results, the metal-ligand exchange enthalpies in the crystalline phase were derived. The enthalpy of a hypothetical metal-ligand exchange reaction in the crystalline phase was derived, thus allowing a discussion of the energetics of complexation in comparison with known crystal-structural parameters. (C) 2004 Elsevier Ltd. All rights reserved.