Crystal structure and thermochemical properties of n-octanammonium oxalate (C8H17NH3)2C2O4(s)

A novel compound n-octanammonium oxalate (C8H17NH3)2C2O4(s) was synthesized by the method of liquid phase reaction. Crystal structure of n-octanammonium oxalate was determined by X-ray crystallography. The lattice potential energy of the compound was calculated to be UPOT = 1050.90 kJ · mol−1. Molar enthalpies of dissolution of the compound at different concentrations m/(mol · kg−1) were measured by an isoperibol solution–reaction calorimeter at T = 298.15 K. According to the Pitzer’s electrolyte solution theory, the molar enthalpy of dissolution of the compound at infinite dilution (ΔsolHm∞) and Pitzer parameters (βMX(0)LandβMX(1)L) were obtained. The values of apparent relative molar enthalpies (ΦL  ) of the title compound and relative partial molar enthalpies (L¯2andL¯1) of the solute and the solvent at different concentrations were derived from experimental values of enthalpies of dissolution. The enthalpy change of the synthesis reaction of n  -octanammonium oxalate was determined to be ΔrHmΘ=-(153.68±0.50)kJ·mol-1 by an isoperibol solution–reaction calorimeter, and standard molar enthalpy of formation of (C8H17NH3)2C2O4(s) was calculated to be ΔfHmΘ=-(1463.6±2.4)kJ·mol-1 by using the enthalpies of dissolution and other auxiliary thermodynamic quantities.

Graphical abstractCrystal structure of n-octanammonium oxalate was determined. Lattice potential energy was calculated. Molar enthalpies of dissolution of the compound at different concentrations were measured. Molar enthalpy of dissolution of the compound at infinite dilution and Pitzer parameters were obtained. The apparent relative molar enthalpies and relative partial molar enthalpies of the solute and the solvent at different concentrations were derived. The enthalpy change of the synthesis reaction was determined and standard molar enthalpy of formation of the compound was calculated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Crystal structure of n-octanammonium oxalate was determined. ► Lattice potential energy of the compound was calculated. ► The molar enthalpy of dissolution at infinite dilution is determined. ► Standard molar enthalpy of formation of (C8H17NH3)2C2O4(s) was calculated.