Crystal structure and chemical thermodynamic properties of potassium d-gluconate K(d-C₆H₁₁O₇)(s)

Abstract

An important coordination compound potassium d-gluconate K[d-C₆H₁₁O₇](s) has been synthesized by liquid phase method. The chemical component and crystal structure of the important compound are characterized by chemical analysis, elemental analysis, and X-ray crystallography. Single-crystal X-ray analysis reveals that the compound exhibits the chelate property of d-gluconate anions to K⁺ cations, a six-membered chelate ring is formed by the coordination of K⁺ with O2 of carboxylate and O4 of hydroxyl in a d-gluconate, and one cation is coordinated to six d-gluconate anions. The lattice potential energy and ionic volume of the anion [d-C₆H₁₁O₇]⁻ are obtained from crystallographic data. In accordance with Hess’ law, a reasonable thermochemical cycle is designed according to the practical synthesis reaction of the compound and the standard molar enthalpy of formation of the compound is calculated to be −(1754.17 ± 0.19) kJ mol⁻¹ as an important physical quantity in chemical thermodynamics by 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 electrolyte solution theory, molar enthalpy of dissolution of the title compound at infinite dilution is calculated to be $\Delta_{\text{s}} H_{\text{m}}^{\infty }$ = (27.92 ± 0.21) kJ mol⁻¹. In terms of the above value, the standard molar enthalpy of formation of the anion [d-C₆H₁₁O₇]⁻ in the aqueous solution is determined to be  = −(1473.87 ± 0.28) kJ mol⁻¹. The values of relative apparent molar enthalpies (^Φ L) and relative partial molar enthalpies of the solvent ($\bar{L}_{1}$) and the compound ($\bar{L}_{2}$) at different concentrations m/(mol kg⁻¹) are derived from the experimental values of the enthalpies of dissolution of the compound.