Structural, sorption and thermodynamic correlations from a layered barium phenylarsonate/n-alkyldiamine system

The barium phenylarsonate compound, Ba(HO₃AsC₆H₅)₂·2H₂O, has the ability to intercalate n-alkyldiamine molecules, H₂N(CH₂)_nNH₂ (n=2-5). The amount intercalated (n_f) from a batchwise procedure and the variation of the original basal distance (d) of 1245 ppm determined through X-ray diffractions, gave linear correlations as a function of the number of carbon atoms in the aliphatic chain (n_c): n_f=(2.66±0.06)−(0.13±0.02)n_c and d=(2168±65)+(114±14)n_c. The intercalation process was calorimetrically followed to give exothermic enthalpy and negative Gibbs energy, reflecting spontaneous intercalation reactions at the solid/liquid interface. The displacement of solvent molecules bonded to amine and of those on the matrix during the intercalation increases the disorder to result in positive entropy, giving a favorable set of thermodynamic data for this system.