Thermochemistry on the Solid State Coordination Compounds M(Nic)2 • H2O(s) (M = Mn and Mg, Nic = Nicotinate)

Two novel solid state coordination compounds - manganese nicotinate monohydrate and magnesium nicotinate monohydrate were synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analyses and X-ray powder diffraction techniques were applied to characterize the structure and composition of these complexes. In accordance with Hess' law, thermochemical cycles were designed, the enthalpy changes of the solid phase reactions of nicotinic acid with manganese acetate tetrahydrate and magnesium acetate tetrahydrate were determined as Delta H-r(m,1)0 = (39.66+/-0.36) kJ . mol(-1) and Delta H-r(m,2)0 = (40.73+/-0.17) kJ . mol(-1) by use of an isoperibol Solution-reaction calorimeter, respectively. The standard molar enthalpy of formation of the title complexes M(Nic)(2) center dot H2O(s) were calculated as Delta H-f(Mn(Nic)2 center dot H2O)0 = -(1165.01+/-2.01) kJ . mol(-1) and Delta H-f(Mg(Nic)2 center dot H2O)0 = -(1390.49+/-1.99) kJ . mol(-1) by use of the enthalpies of dissolution and other auxiliary thermodynamic data. In addition, the values of the standard molar enthalpies of formation of M(Nic)(2)center dot H2O(s) (M = Mg, Mn, Zn) were compared, a law of change of [-Delta H-f(Zn(Nic)2 center dot H2O)0] < [-Delta H-f(Mn(Nic)2 center dot H2O)0] < [-Delta H-f(Mg(Nic)2 center dot H2O)0] can be obtained. and was in relation with the stability of the three monohydrated nicotinates.