A series of n-alkyldiamines of general formula H2N(CH2)nNH2 (n = 2-9) has been intercalated into the crystalline lamellar compound α-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 (nint) as a function of the number of carbon atoms in the aliphatic chain (nc): d =(883.14 ± 12.76) + (108.51 ± 2.20)nc and nint =(5.79 ± 0.12) - (0.28 ± 0.02)nc. The exothermic enthalpies for the intercalation are related to the monomolecular layer arrangement with a longitudinal axis inclined by 58° to the inorganic sheets. The enthalpies for the overall reaction 2O3P-OH(c) + H2N(CH2)nNH2(c, l) = O3P - O-+H3N(CH2)nNH3+-O - PO3(c); ΔintH, 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 Δint H= -(56.16 ± 0.67)-(2.06 ± 0.12)nC and ΔintH = -(39.41 ± 1.41)-(1.80 × 10-2 ± 0.10 × 10-2)d. The enthalpic value for nc = 0 gave -56.17 ± 0.67 kJ mol-1 which corresponds to the intercalation of two moles of ammonium cation.61219631966Alberti, G., Galli, P.C., Costantino, U., Torracca, E., (1967) J. Inorg. Nucl. Chem., 29, p. 571Clearfield, A., (1982) Inorganic Ion Exchange Materials, , CRC Press, Boca Raton, FLSuárez, M., Garcia, J.R., Rodriguez, J., (1984) J. Phys. Chem., 88, p. 159Alberti, G., Casciola, M., Costantino, U., (1985) J. Colloid Interface Sci., 107, p. 256