Calorimetric data on n-alkyldiamines intercalated into calcium phenylphosphonates

Layered crystalline calcium phenylphosphonate, as anhydrous Ca(HO3PC6H5)2, and hydrated Ca(HO3PC6H5)2·2H2O forms were used as hosts for intercalation of n-alkyldiamine molecules H2N(CH2)nNH2 (n = 2–6) in water or 1,2-dichloroethane. The amount intercalated (nf) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated calcium phenylphosphonate (1525 ppm) and anhydrous calcium phenylphosphonate (1751 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for d or nf as a function of the number of carbon atoms in the aliphatic chain (nc): d = (1424 ± 65) + (108 ± 14)nc and nf = (3.33 ± 0.15) − (0.39 ± 0.03)nc, for the hydrated compound and d = (1643 ± 60) + (108 ± 12)nc and nf = (3.43 ± 0.12) − (0.39 ± 0.01)nc, for the anhydrous compound. The exothermic enthalpies of intercalation increased with nc, which derived from the monomolecular amine layer arrangement with longitudinal axis inclined by 58° to the inorganic sheets. The intercalation, followed by titration with amine at the solid/liquid interface with both matrices, gave the enthalpic/number of carbons correlation: ΔH° = − (0.54 ± 0.12) − (1.10 ± 0.09)nc and ΔH° = − (1.39 ± 0.15) − (1.56 ± 0.10)nc, respectively. The exothermic enthalpic value increases with nc are more pronounced for the anhydrous compound. The Gibbs free energies are negative while positive entropic values favor intercalation in these systems.