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

Hydrated layered crystalline barium phenylarsonate, Ba(HO3AsC6H5)(2)(.)2H(2)O was used as host for intercalation of n-alkylmonoamine molecules CH3(CH2)(n)-NH2 (n = 1-4) in aqueous solution. The amount intercalated (n(f)) was followed batchwise at 298 I 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 (n(c)): d= (2225 +/- 32) + (111 +/- 11)nc and n(f) = (2.28 +/- 0.15) - (11.50 +/- 0.03)n(c). The exothermic enthalpies of intercalation increased with n, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60 degrees 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: Delta H = -(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. (c) 2007 Elsevier B.V. All rights reserved.