Crystal structure and thermodynamic properties of the coordination compound calcium D-gluconate Ca[D-C6H11O7]2(s)

Abstract The coordination compound calcium D-gluconate, Ca[D-C6H11O7]2(s), was synthesized and characterized by chemical analysis, elemental analysis, and X-ray crystallography. Single crystal X-ray diffraction technique revealed that the compound was formed by two D-gluconate anions and one calcium (II) cation. And the D-gluconate anion had a curved chain configuration with an intramolecular bond. The compound exhibited an outstanding chelate property of D-gluconate anions to calcium (II) cations, and the calcium (II) cation was eight-coordinated and chelated by four D-gluconate anions. The lattice potential energy and ionic volume of the anion were calculated to be 1434.05 kJ⋅mol−1 and 0.4211 nm3 from crystallographic data. In accordance with famous Hess law, a reasonable thermochemical cycle was designed and the standard molar enthalpy of formation of Ca[D-C6H11O7]2(s) was calculated as Δ s H m [Ca[D-C6H11O7]2, s] = -(3545.19 ± 1.07) kJ⋅mol−1 by use of an isoperibol solution-reaction calorimeter. Furthermore, molar heat capacities of the compound were measured using a Quantum Design Physical Properties Measurement System (PPMS) with specific heat option within the temperature range from (1.9–300) K. The heat capacities of the compound increased with the temperature and no thermal anomaly was found in the whole temperature region. The experimental data was fitted to a function of the absolute temperature T with a series of theoretical and empirical models for the proper temperature ranges. The values of standard thermodynamic function, C p , m o /J⋅K−1⋅mol−1, Δ 0 T H m o /kJ⋅mol−1, Δ 0 T S m o /J⋅K−1⋅mol−1, and Δ o T G m o / T /J⋅K−1⋅mol−1 (= Δ 0 T S m o - Δ 0 T H m o /T) from T = (0–300) K was calculated based on the fitting results. The standard molar heat capacity, entropy and enthalpy of the compound at T = 298.15 K and 0.1 MPa was determined to be C p , m o = (493.20 ± 2.70) J·K−1 mol−1, H m o = (75934 ± 805) J·mol−1, S m o = (471.55 ± 2.78) J·K−1 mol−1, and G m o / T  = - (64658 ± 808) J·K−1⋅mol−1, respectively.