The heterocyclic amines, 2-,3- and 4-aminopyridine, 2-amino-4-methylpyridine and 2-aminobenzylamine, were intercalated into alpha-titanium hydrogenphosphate and characterized through infrared spectroscopy, X-ray diffractometry and thermogravimetry. On intercalation, these heterocyclic amines expanded the original 760 pm interlayer distance to 1338, 1177, 1262, 1577 and 1060 pm, for the same sequence of amines. The change in P-OH and amine group frequencies clearly indicated cyclic amine intercalation. From the combination of batch intercalation and calorimetric titration, the variation in enthalpy was calculated at 298.15 +/- 0.02 K. The exothermic enthalpic results for the intercalation process gave the sequence of values: -36.75 +/- 0.78; -20.42 +/- 0.28, -35.22 +/- 0.70, -14.02 +/- 0.10 and -29.77 +/- 0.29 kJ mol(-1), respectively. The calculated negative Gibbs free energy and the majority of the positive entropic values are in agreement with the favorable intercalation of these guest molecules inside the cavity of the host inorganic crystalline lannellar compound. (C) 2004 Published by Elsevier B.V.4351118123