Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)(2)(s) (Ala = L-alpha-alanine)

摘要

Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)(2)(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C-p,C-m) with the reduced temperatures (X), [X=f(T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)(2)(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)(2)center dot H2O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm(-3) HCl, respectively, and trans-Cu(Ala)(2)(s) in the solvent [2:1 HAc (aq) + 2 mol dm(-3) HCl] at T = 298.15 K were determined to be Delta H-s(m)degrees[Cu(Ac)(2)center dot H2O(s) + 2Ala(s)] = (6.75 +/- 0.04) kJ mol(-1), Delta H-s(m)degrees[2 : 1 HAc(aq)] = -(1.63 +/- 0.01) kJ mol(-1), and Delta H-s(m)degrees[trans-Cu(Ala)(2)(s)] = -(10.24 +/- 0.08) kJ mol(-1) by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as Delta H-f(m)degrees(trans-Cu(Ala)(2)(s), 298.15 K) = -(1038.6 +/- 3.5) kJ mol(-1) from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle.