Calorimetric data on n-alkyldiamines intercalated into calcium phenylphosphonates

Abstract

Layered crystalline calcium phenylphosphonate, as anhydrous Ca(HO 3PC 6H 5) 2, and hydrated Ca(HO 3PC 6H 5) 2·2H 2O forms were used as hosts for intercalation of n-alkyldiamine molecules H 2N(CH 2) n NH 2 ( n = 2–6) in water or 1,2-dichloroethane. The amount intercalated ( n f) 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 n f as a function of the number of carbon atoms in the aliphatic chain ( n c): d = (1424 ± 65) + (108 ± 14) n c and n f = (3.33 ± 0.15) − (0.39 ± 0.03) n c, for the hydrated compound and d = (1643 ± 60) + (108 ± 12) n c and n f = (3.43 ± 0.12) − (0.39 ± 0.01) n c, for the anhydrous compound. The exothermic enthalpies of intercalation increased with n c, 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: Δ H° = − (0.54 ± 0.12) − (1.10 ± 0.09) n c and Δ H° = − (1.39 ± 0.15) − (1.56 ± 0.10) n c, respectively. The exothermic enthalpic value increases with n c are more pronounced for the anhydrous compound. The Gibbs free energies are negative while positive entropic values favor intercalation in these systems.