Crystal Structures and Solution Chemical Properties of Two Lactate Complexes Mn[(C3H5O3)2(H2O)2]⋅H2O(s) and Cu(C3H5O3)2(s)

Abstract

Trihydrated manganese lactate Mn[(C3H5O3)2(H2O)2]⋅H2O(s) and anhydrous copper lactate Cu(C3H5O3)2(s) were synthesized. Crystal structures of the two compounds were characterized by X-ray single crystal diffraction technique. The compositions, spatial structures and coordination modes of the two compounds were determined by analysis of their molecular structures and crystal structures. Lattice potential energies of the compounds were calculated by using the crystallographic data. Molar enthalpies of dissolution of these metal complexes in the ultrapure water were measured by an isoperibol solution-reaction calorimeter with an accuracy of ±0.3%. On the basis of Pitzer's electrolyte solution theory, infinite dilution molar enthalpies of dissolution and Pitzer's parameters of the two lactate complexes soluble in water at T = 298.15 K were calculated. The infinite dilution molar enthalpies (ΔsHm∞) of dissolution of the title compounds were combined with lattice potential energies (UPOT) by a designed thermodynamic cycle, and the average molar enthalpy of hydration of the common lactate ion was calculated to be (407.207 ± 0.038) kJ·mol−1. The mechanism of thermal decomposition or dehydration of the trihydrated manganese lactate was explored by TG-DSC technique, and the difference between molar enthalpies (ΔsHm) of dissolution of trihydrated manganese lactate and anhydrous copper lactate at the same concentration was revealed.