Crystalline-hydrated barium phenylphosphonate as a host for n-alkyldiamine intercalation

A series of n-alkyldiamines with the general formula H2N(CH2)nNH2 (n = 2–6) has been intercalated into crystalline lamellar-hydrated barium phenylphosphonate from ethanolic solutions. The amount intercalated was followed batchwise and the variation in interlayer distance (d) for the original host and the respective intercalated compounds was followed by x-ray diffraction patterns. Linear correlation with good fits were obtained for (d) or for the number of moles intercalated (nf) as a function of the number of carbon atoms in the aliphatic chains (nc): d = (1436 ± 65) + (108 ± 14)nc and nf = (2.24 ± 0.15)–(0.31 ± 0.03)nc. The energetic effect caused by amine intercalation was determined through reaction-solution calorimetry at the solid-liquid interface from ethanolic solutions. The resulting exothermic enthalpies for intercalation give rise to a monomolecular layer guest molecule arrangement with a longitudinal axis inclined by 58° to the inorganic sheets. The thermodynamic data showed that the system is favored by exothermic enthalpy, negative Gibbs free energy, and positive entropic values.