Interlayer Surface Modification of the Protonated Triple-Layered Perovskite HCa2Nb3O10·xH2O with n-Alcohols

Abstract

Organic derivatives of the protonated triple-layered perovskite HCa2Nb3O10·xH2O with n-alkoxyl groups on the interlayer surface have been prepared by grafting n-alcohols. Interlayer surface modification of HCa2Nb3O10·xH2O is achieved by a direct reaction of HCa2Nb3O10·xH2O with methanol or ethanol, and single-phase n-alkoxyl derivatives of HCa2Nb3O10·xH2O (n ≥ 3 in n-CnH2n+1O− groups) can be formed by reacting n-alkoxyl derivatives (methoxyl and n-propoxyl derivatives) with n-alcohols in an autoclave at 150 °C. X-ray diffraction analysis shows the changes in interlayer distances upon treatment of HCa2Nb3O10·xH2O or intermediate n-alkoxyl derivatives with n-alcohols. Solid-state 13C CP/MAS (cross polarization and magic-angle spinning) NMR spectroscopy demonstrates the presence of signals due to n-alkoxyl groups originating from the reactant n-alcohol molecules. Differential thermal analysis curves of the products exhibit exothermic peaks at temperatures higher than 200 °C. These results indicate successful preparation of HCa2Nb3O10·xH2O derivatives possessing various n-alkoxyl groups (n-CnH2n+1O−, n = 1−4, 6, 8, 10, 12, 14, 16, and 18) on the interlayer surface. Although a reaction between an n-propoxyl derivative and n-decanol does not proceed at 80 °C, a single-phase n-decoxyl derivative can be obtained at 80 °C by adding a small amount of water (1 mass %), which strongly suggests a hydrolysis−esterification mechanism. IR and solid-state 13C CP/MAS NMR spectroscopies indicate that the n-alkyl chains in n-alkoxyl derivatives (n ≥ 10 in n-CnH2n+1O− groups) possess an all-trans conformation. A linear relationship with a slope of 0.166 nm/carbon atom is observed between the interlayer distance and the number of carbon atoms in the n-alkyl chains, suggesting that the n-alkyl chains of n-alkoxyl groups are present as bilayers with a tilt angle of 41° in the interlayer space.