Two substituted N-acylthioureas and the respective Ni(II) and Cu(II) complexes were synthesized, namely: N,N-di-n-butyl-N'-thenoylthiourea (Hnbtu); N,N-di-iso-butyl-N'-tlienoylthiourea (Hibtu); bis[N,N-di-n-butyl-N'-thenoylthioureato]nickel(II), [Ni(nbtu)(2)]; bis[N,N-di-n-butyl-N'-thenoylthioureato]copper(II), [Cu(nbtu)(2)]; bis[N,N-di-iso-butyl-N'-thenoylthioureato]nickel(II), [Ni(ibtu)2]; bis[N,N-di-iso-butyl-N'-thenoylthioureato]copper(II), [Cu(ibtu)(2)]. The standard (p degrees = 0.1 MPa) molar enthalpies of formation and sublimation of the two N-acylthioureas were measured, at T = 298.15 K, by rotating-bomb combustion calorimetry and Calvet microcalorimetry, respectively. The standard (p = 0.1 MPa) molar enthalpies of formation of the Ni(H) and Cu(H) complexes were determined, at T= 298.15 K, by high precision solution-reaction calorimetry. From the results obtained, the enthalpies of hypothetical metal-ligand and metal-metal exchange reactions, in the gaseous phase, were derived, thus allowing a discussion of the gaseous phase energetic difference between the complexation of Ni(II) and Cu(II) to 1,3-ligand systems with (S,O) ligator atoms. (C) 2007 Elsevier Ltd. All rights reserved.