Energetic of some aliphatic amine intercalations in layered crystalline barium phenylphosphonate

Layered crystalline barium phenylphosphonate, as anhydrous Ba(HO3PC6H5)2 or hydrated Ba(HO3PC6H5)2⋅2H2O compounds, were used as hosts for the intercalation of polar n-alkylamine molecules of the general formula H3C(CH2)nNH2 (n=1 to 5) in ethanol or 1,2-dichloroethane. The lamellar compound was calorimetrically titrated with amine in ethanol or 1,2-dichloroethane solutions at 298.15±0.20K. The exothermic enthalpic values increased with the number of carbon atoms in the amine chain, being −4.50±0.37, −5.30±0.42, −6.77±0.21, −7.51±0.35 and −10.35±0.67kJmol−1 for hydrated and −6.80±0.22, −7.75±0.37, −8.95±0.19, −9.91±0.34 and −10.82±0.56kJmol−1 for anhydrous compounds, for n=1 to 5, respectively. The favorable enthalpic processes, as a in function of the number of carbon atoms (nc) of the amines, expressed by ΔHo=−(1.22±0.12)−(1.43±0.16)nc, and ΔHo=−(4.77±0.11)−(1.02±0.02)nc in ethanol and 1,2-dichloroethane, respectively, are more pronounced for the anhydrous compound. The spontaneity of these systems, reflected in the negative Gibbs free energies and the favorable positive entropic values, agrees with the displacement of coordinated solvent molecules as the intercalation takes place.