The standard (p degrees = 0.1 MPa) molar enthalpies of formation of the crystalline diaquobis(dibenzoylmethanate)nickel(II), Ni(DBM)(2)(H2O)(2), diaquobis(thenoyltrifluoroacetonate)nickel(II), Ni(TTFA)(2)(H2O)(2) bis(monothiodibenzoylmethanate)nickel(II), Ni(DBMS)(2) and bis(monothiothenoyltrifluoroacetonate)nickel(II), Ni(HTTFAS)(2) were determined, at T = 298.15 K, by high precision solution-reaction calorimetry. The standard molar enthalpy of sublimation of the monothiothenoyltrifluoroacetone (HTTFAS) complex was measured by high-temperature Calvet microcalorimetry. From the standard molar enthalpies of formation of the complexes in the gaseous state, the mean nickel(II)-ligand molar dissociation enthalpies, < D-m >(Ni-L), were derived. Delta H-f(m)degrees(cr)/(kJ . mol(-1)) Diaquobis(dibenzoylmethanate)nickel(II), Ni(DBM)(2)(H2O)(2) -993.3 +/-3.8 Diaquobis(thenoyttrifluoroacetonate)nickel(II), Ni(TTFA)(2)(H2O)(2) -2452.0 +/- 8.3 Bis(monothiodibenzoylmethanate)nickel(II), Ni(DBMS)(2) -42.1 +/- 5.9 Bis(monothiothenoyltrifluoroacetonate)nickel(II), Ni(TTFAS)(2) -1473.5 +/- 8.1 (c) 2006 Elsevier Ltd. All rights reserved.