Thermochemistry of dichlorobis[N-(2-pyridyl)acetamide]-zinc(II), -cadmium(II), and -mercury(II)

Abstract

The standard enthalpy changes ΔH_R^⊖=–70.80 ± 0.60, –35.02 ± 0.72, and –22.90 ± 1.1 kJ mol^–1 for M = Zn, Cd, and Hg respectively have been measured from the reaction MCl₂(s)+ 2pya(s)→[M(pya)₂]Cl₂(s)[pya =N-(2-pyridyl)acetamide], by using solution calorimetry. From these values, the standard enthalpy of formation of the ligand (ΔH_f^⊖=–149 ± 21 kJ mol^–1) obtained via combustion calorimetry, and literature standard enthalpies of formation of the metal chlorides, the ΔH_f^⊖ values have been determined as –785 ± 22, –724 ± 22, and 544 ± 23 kJ mol^–1 for M = Zn, Cd, and Hg respectively. The standard enthalpy of sublimation of the ligand (103.8 kJ mol^–1) has also been obtained. The standard enthalpies of the reactions MCl₂(g)+ 2pya(g)→[M(pya)₂]Cl₂(c) and MCl₂(c)+ 2pya(g)→[M(pya)₂]Cl₂(c) have been calculated.