Calorimetric study of intercalation of n-alkyldiamines into alpha-titanium hydrogenphosphate

A series of n-alkyldiamines of general formula H2N(CH2)(n)NH2 (n = 2-9) has been intercalated into the crystalline lamellar compound alpha-Ti(HPO4)(2) . H2O (TiP) from aqueous solution. The amount intercalated was followed batchwise at 298+/-1 K and the variation of the original interlayer distance for TiP (756 pm) was followed by X-ray powder diffraction. Linear correlations with good fits were obtained for the interlamellar distance (d) or for the number of moles intercalated (n(int)) as a function of the number of carbon atoms in the aliphatic chain (n(c)): d=(883.14 +/- 12.76)+(108.51 +/- 2.20)n(c) and n(int)=(5.79 +/- 0.12)-(0.28 +/- 0.02)n(c). The exothermic enthalpies for the intercalation are related to the monomolecular layer arrangement with a longitudinal axis inclined by 58 degrees to the inorganic sheets. The enthalpies for the overall reaction 2O(3)P-OH(c)+H2N(CH2)(n)NH2(c,1) = O3P-O-+H3N(CH2)(n)NH3+ - O-PO3(c); Delta(int)H, determined by reaction-solution calorimetry at 298.15+/-0.02 K are correlated with the number of carbons in the aliphatic chain or the interlamellar distance, by the equations Delta(int)H = -(56.16 +/- 0.67)-(2.06 +/- 0.12)n(c) and Delta(int)H = -(39.41 +/- 1.41)-(1.80 x 10(-2) +/- 0.10 x 10(-2))d. The enthalpic value for n(c)=0 gave - 56.17 +/- 0.67 kJ mol(-1) which corresponds to the intercalation of two moles of ammonium cation.