Crystal structure and thermochemical properties of a novel coordination compound manganese d-gluconate tetrahydrate

Abstract A novel coordination compound of d -gluconic acid with the divalent manganese ion, Mn[(D-C 6 H 11 O 7 ) 2 (H 2 O) 2 ]·2H 2 O, is synthesized. The compound has an obvious bioactivity and can be used as a manganese dietary supplements and energy fortifier in medicine and food. Chemical analysis, elemental analysis, and X-ray crystallography are used to characterize its composition, crystal structure and chelating mode of d -gluconic acid with the divalent manganese ion. Single-crystal X-ray analysis reveals that the compound is formed by two d -gluconate anions, one manganese (II) cation, two coordinated waters and two crystal waters. And the two d -gluconate anions in Mn[(D-C 6 H 11 O 7 ) 2 (H 2 O) 2 ]·2H 2 O have two different conformations. The compound exhibits the chelate property of d -gluconate anions to manganese (II) cations, and the manganese (II) cation is six-coordinated and chelated by two d -gluconate anions and two coordinated waters. The lattice potential energy and ionic volume of the anion are obtained from crystallographic data. In accordance with Hess’ law, a reasonable thermochemical cycle is designed and the standard molar enthalpy of formation of the compound is calculated as an important physical quantity in relation with the energy state of the compound by use of an isoperibol solution-reaction calorimeter. Molar enthalpies of dissolution of the compound at various molalities are measured at T  = 298.15 K in the double-distilled water. According to Pitzer’s theory, molar enthalpy of dissolution of the title compound at infinite dilution is calculated to be Δ s H m ∞ = ( 14.56 ± 0.56 ) kJ · mol - 1 . The values of relative apparent molar enthalpies ( Φ L ) and relative partial molar enthalpies of the solvent ( L 1 ‾ ) and the compound ( L 2 ‾ ) at different concentrations m /(mol · kg −1 ) are derived from the experimental values of the enthalpies of dissolution of the compound.