Intercalation of triethylphosphine oxide bearing a phosphoryl group into Dion–Jacobson-type ion-exchangeable layered perovskites

Abstract

Triethylphosphine oxide [(C₂H₅)₃PO; TEPO] was intercalated into protonated Dion–Jacobson-type ion-exchangeable layered perovskites, HLaNb₂O₇·xH₂O (HLaNb) and HCa₂Nb₃O₁₀·xH₂O (HCaNb), by hydrolysis of their n-decoxy derivatives (C₁₀O-HLaNb or C₁₀O-HCaNb) in the presence of TEPO. The interlayer distances of the products (TEPO/C₁₀O-HLaNb and TEPO/C₁₀O-HCaNb) were smaller than those of the corresponding n-decoxy derivatives, but still larger than those of anhydrous protonated forms of HLaNb and HCaNb. The solid-state ³¹P NMR signals of the products observed at 94 ppm (TEPO/C₁₀O-HLaNb) and 93 ppm (TEPO/C₁₀O-HCaNb) exhibited large downfield shifts from that of the physisorbed TEPO. IR spectroscopy also showed decreases in the ν(PO) band wavenumbers upon the reactions. These results clearly indicate that TEPO is intercalated and interacted with Brønsted acid sites, the surface hydroxyl groups generated via hydrolysis of n-decoxy groups. The difference in ν(PO) band wavenumbers as well as that in gallery heights suggests that TEPO exhibited different orientations with respect to the inorganic layers. The chemical shifts of solid-state ³¹P NMR signals suggested high Brønsted acidity of HLaNb and HCaNb.