Thermochemical Properties of the Dissolution of Rubidium d-Gluconate Rb[d-C₆H₁₁O₇]₂(s) in Aqueous Solutions

Abstract

A novel coordination compound rubidium d-gluconate Rb[d-C₆H₁₁O₇](s) has been synthesized and characterized by chemical analysis, elemental analysis, and X-ray diffraction. Single-crystal X-ray analysis reveals that the crystal is monoclinic with space group P2₁ and Z = 2. Also, the d-gluconate anion in Rb[d-C₆H₁₁O₇](s) has a bent-chain conformation, in which the carbon atoms of the anion form two approximate planes. The compound exhibits an obvious chelation of the d-gluconate anions to the rubidum(I) cation and the cation is seven-coordinated to all seven oxygen atoms. The lattice potential energy and ionic volume of the anion d-${\text{C}}_{ 6} {\text{H}}_{ 1 1} {\text{O}}_{7}^{ - }$ were obtained to be U_POT = 484.23 kJ·mol⁻¹ and V₋ = 0.2004 nm³ from crystallographic data. Molar enthalpies of dissolution of Rb[d-C₆H₁₁O₇](s) in double-distilled water at various molalities were measured by use of an isoperibol solution–reaction calorimeter at T = 298.15 K. According to Pitzer’s electrolyte solution model, the molar enthalpy of dissolution of the title compound at infinite dilution was determined to be $\Delta_{\text{s}} H_{\text{m}}^{\infty } = (29.76 \pm 0.72){\text{ kJ}}{\cdot}{\text{mol}}^{ - 1}$. The values of the apparent relative molar enthalpies ($^{\phi } L_{{}}$) of the title compound and relative partial molar enthalpies ($\bar{L}_{2}$ and $\bar{L}_{1}$) of the solute and the solvent at different concentrations were derived from the experimental enthalpies of dissolution of the compound. Furthermore, the molar enthalpy of hydration of the anion d-${\text{C}}_{ 6} {\text{H}}_{ 1 1} {\text{O}}_{7}^{ - }$ was calculated to be ΔH₋ = − (166.4 ± 2.7) kJ·mol⁻¹ by use of a thermochemical cycle.