Intercalation behavior of some aromatic heterocyclic amines into α-titanium hydrogen phosphate

The aromatic amines 2-, 3-, 4-aminopyridine (2-, 3-, 4-amp), 1,4-phenylenediamine (phed), and 2-amino-4-methylpyridine (ammp) were intercalated into α-titanium hydrogen phosphate, α-Ti(HPO4)2·H2O (TiP). The intercalation was obtained by a batch method at 298 ± 1 K. The maximum amount intercalated was 3.37, 3.37, 6.40, 2.12, and 4.52 mmol of 2-, 3-, 4-amp, phed, and ammp, per gram of TiP, respectively. These aromatic amines expanded the original interlamellar distance of 760 pm to 1338, 1177, 1262, 1338, and 1577 pm, respectively. With the exception of 2-amp and ammp, which are disposed in an inclined position in the interlayer cavity, all of the other bases formed a monolayer in the interlamellar space, oriented in a perpendicular position in relation to the inorganic layers of the matrix. The infrared spectra demonstrated that the basic centers of the aromatic amines are protonated by the phosphate groups attached to the inorganic layers, in a typical Brönsted acid-base interaction. The intercalated compounds lost water of hydration, organic material, and water of condensation of the phosphate groups on heating, to give pyrophosphate as final product.