Intercalation behavior of n-alkylamines into a protonated form of a layered perovskite derived from aurivillius phase Bi₂SrTa₂O₉

Intercalation behavior of n-alkylamines into a protonated form of a layered perovskite, H_1.8[Sr_0.8Bi_0.2Ta₂O₇], derived from an Aurivillius phase, Bi₂SrTa₂O₉, has been investigated. H_1.8[Sr_0.8Bi_0.2Ta₂O₇] can accommodate n-alkylamines (C_mH_m+1NH₂; m = 4, 8, 12, 18) to form intercalation compounds via an acid-base mechanism. The interlayer distance increases to 2.071(2) (m = 4), 2.840(9) (m = 8), 3.83(1) (m = 12), and 5.17(2) (m = 18) nm. In contrast, H_1.8[Sr_0.8Bi_0.2Ta₂O₇] does not form any intercalation compound with pyridine, which is a weaker base, indicating that the protons in H_1.8[Sr_0.8Bi_0.2Ta₂O₇] are weakly acidic. The IR spectra of the intercalation compounds with n-alkylamines (m = 12 and 18) clearly show that n-alkyl chains possess an all-trans conformation. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains, and this corresponds to a bilayer arrangement of the n-alkyl chains with a tilt angle of 60°. Despite the relatively high proton content (1.8 H⁺ per [Sr_0.8Bi_0.2Ta₂O₇]), only 0.9-1.0 mol of n-alkylamines per Sr_0.8Bi_0.2Ta₂O₇] is intercalated. This observation can be reasonably interpreted based on the surface geometry of the perovskite-like slab and the size of n-alkylamines.