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

Abstract

Triethylphosphine oxide [(C2H5)3P[double bond, length as m-dash]O; 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 (31)P 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(P[double bond, length as m-dash]O) 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(P[double bond, length as m-dash]O) 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 (31)P NMR signals suggested high Brønsted acidity of HLaNb and HCaNb.