Interlayer surface modification of the protonated triple-layered perovskite HCa2Nb3O10•xH2O with n-alcohols

Organic derivatives of the protonated triple-layered perovskite HCa2Nb3O10.xH(2)O with n-alkoxyl groups on the interlayer surface have been prepared by grafting n-alcohols. Interlayer surface modification of HCa2Nb3O10.xH(2)O is achieved by a direct reaction of HCa2Nb3O10.xH(2)O with methanol or ethanol, and single-phase n-alkoxyl derivatives of HCa2Nb3O10.xH(2)O (n greater than or equal to 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.xH(2)O or intermediate n-alkoxyl derivatives with n-alcohols. Solid-state C-13 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.xH(2)O 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 degreesC, 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 C-13 CP/MAS NMR spectroscopies indicate that the n-alkyl chains in n-alkoxyl derivatives (n greater than or equal to 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.