The intercalation of the heterocyclic amines 2,6-lutidine, pyrazine, piperazine, and piperidine into or-titanium hydrogenphosphate gave the maximum amounts intercalated in aqueous solutions of 0.45, 0.65, 2.77, and 6.52 mmol g(-1), respectively, through a batch method at 298 +/- 1 It. The original interlamellar distance of 760 pm increased after intercalation of piperazine and piperidine molecules, while for 2,6-lutidine and pyrazine molecules no change was observed. These results suggested that the amines were bonded only on the surface of the host. All thermochemical data were obtained on a differential isothermic microcalorimetric instrument by means of a titration procedure. From thermal effect data, the variation in enthalpy for each system gave exothermic values of - 6.56 +/- 0.10, - 1.00 +/- 0.10, - 10.10 +/- 0.34, and - 31.44 +/- 0.71 kJ mol(-1) for intercalations of the above sequence of heterocyclic amines. The infrared spectra are in agreement with acid-base reactions, involving the layered acid host O3P-OH of the inorganic matrix and the basic center atoms of the guest molecules. (C) 2000 Academic Press.1542557563