Crystalline polysilicate magadiite with intercalated n-alkylmonoamine and some correlations involving thermochemical data

Synthesized hydrated lamellar acidic crystalline magadiite (H2Si14O29.2H2O) nanocompound was used as host for intercalation of polar n-alkylmonoamine molecules of the general formula H3C(CH2) nNH2 (n = 1-6) in aqueous solution. The original interlayer distance (d) of 1500 pm, determined by X-ray powder diffraction patterns, increases after intercalation. The values correlated with the number of aliphatic amine carbon (n c) atoms: d = [(1312 ± 11) + (21 ± 2)]n c. The amount of intercalated amines (N s), decreased as n c increased: N s = [(5.82 ± 0.04) - (0.45 ± 0.01)]n c. The acidic layered nanocompound was calorimetrically titrated with the amines and the thermodynamic data gave exothermic values for all guest molecules, as shown by the correlation: Δint H = -[(24.45 ± 0.49) - (1.91 ± 0.10)]n c and d = [(1576 ± 16) - (10.8 ± 1.0)]Δint H. The negative values of the Gibbs energies and the positive entropies also presented the correlations: Δint G = -[(22.8 ± 0.2) - (0.2 ± 0.1)]n c and Δint S = [(6 ± 1) + (5 ± 1)]n c, respectively