Thermochemistry of intercalation of n-alkylmonoamines into lamellar hydrated barium phenylarsonate

Hydrated layered crystalline barium phenylarsonate, Ba(HO3AsC6H5)2·2H2O was used as host for intercalation of n-alkylmonoamine molecules CH3(CH2)n-NH2 (n = 1–4) in aqueous solution. The amount intercalated (nf) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated barium phenylarsonate (1245 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for both d and nf as a function of the number of carbon atoms in the aliphatic chain (nc): d = (2225 ± 32) + (111 ± 11)nc and nf = (2.28 ± 0.15) − (11.50 ± 0.03)nc. The exothermic enthalpies of intercalation increased with nc, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60° to the inorganic sheets. The intercalation was followed by titration with amine at the solid/liquid interface and gave the enthalpy/number of carbons correlation: ΔH = −(7.25 ± 0.40) − (1.67 ± 0.10)nc. The negative Gibbs free energies and positive entropic values reflect the favorable host/guest intercalation processes for this system.