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-C n H2 n +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-C n H2 n +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-C n H2 n +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.

A protonated form of the Ruddlesden−Popper-type ion-exchangeable layered perovskite H2La2Ti3O10 (H2LaTi) has been modified with n-alkylamine and n-alcohols to yield intercalation compounds and alkoxy derivatives, respectively. As concerns the intercalation of n-alkylamines into H2LaTi, no reaction of H2LaTi with n-butylamine occurred in anhydrous solvent, and the addition of water was required for the successful intercalation of n-butylamine into H2LaTi. The successful uptake of n-butylammonium ions from an n-butylammonium hydroxide aqueous solution suggests that the intercalation mechanism is of the ion-exchange type rather than the acid−base type. For interlayer surface modification with n-alcohol, no direct reaction of H2LaTi with n-alcohol occurred, but the n-propoxy derivative of H2LaTi formed by using the intercalation compound of H2LaTi with n-butylamine as an intermediate. In addition, reactions between the n-propoxy derivative of H2LaTi and n-alcohols (n-butanol, n-octanol, n-decanol, and n-dodecanol) led to the formation of various n-alkoxy derivatives via an alcohol-exchange-type reaction. As the model for n-alkoxy derivatives of H2LaTi, a bilayer arrangement of the n-alkyl chain possessing an all-trans ordered state with a 75° tilting angle is proposed. The reaction mechanisms of these reactions are also discussed.

The interlayer surface of a protonated form of the Dion-Jacobson-type ion-exchangeable layered perovskite, HLaNb 2 O 7 3 xH 2 O (HLaNb), has been successfully modified with various organophosphonic acids [phenylphosphonic acid (PhPO(OH) 2 , PPA) and n-alkylphosphonic acids (n-C n H 2nþ1 -PO(OH) 2 with n = 4-18, APAs)] to produce graft-type organic derivatives using an n-decoxy derivative of HLaNb (C 10 O-HLaNb) as an intermediate. The interlayer distances of the products are changed from that of the intermediate, 2.73 nm, to 2.31 (PPA/C 10 O-HLaNb) and 2.31-5.26 (APAs/ C 10 O-HLaNb) nm. IR and solid-state 13 C CP/MAS NMR spectra of the products reveal that n-decoxy groups are removed and phenyl (PPA/C 10 O-HLaNb) or n-alkyl groups (APA/C 10 O-HLaNb) are introduced. Elemental analysis reveals that the amounts of PPA-and APA-moieties are 0.88-0.99 per [LaNb 2 O 7 ], corresponding approximately to the amount of the n-decoxy groups in C 10 O-HLaNb. The environment of interlayer species in PPA/C 10 O-HLaNb is assumed to be monodentate PhPO(OH)(ONb) based on the IR results (the P-O stretching and P-OH stretching bands at ∼1030 and ∼950 cm -1 ) and the reaction between PPA/C 10 O-HLaNb and n-butylamine (-NH 2 /POH=1.0). Scanning electron micrographs of the products reveal that the morphology is clearly preserved during the reactions with PPA or APAs, indicating that they are graft-type rather than dissolution-recrystallization-type reactions. Because water is required for the reaction between PPA and C 10 O-HLaNb, this reaction is assumed to proceed via the formation of an (HO)NbO 5 site and its subsequent reaction with PPA. A linear relationship is clearly observed between the number of carbon atoms in the n-alkyl chains and the interlayer distances of APAs/C 10 O-HLaNb, and a structural model of APAs/C 10 O-HLaNb with a n-alkyl chain tilt angle of 57°is proposed.

Organic-inorganic hybrids containing exfoliated nanosheets with a perovskite-related structure have been prepared from an n-decoxy derivative of an ion-exchangeable layered perovskite, HLaNb 2 O 7 ‚xH 2 O (HLaNb) or HCa 2 Nb 3 O 10 ‚xH 2 O (HCaNb), silanol-terminated poly(dimethylsiloxane) (PDMS), and tetramethoxysilane (TMOS) via a sol-gel process involving the reaction of the n-decoxy derivative with a PDMS-TMOS mixture and subsequent intentional hydrolysis with hydrochloric acid. The X-ray diffraction (XRD) patterns of the resultant products after intentional hydrolysis indicate both preservation of the perovskite-like slab structure and disappearance of stacking order. Partial exfoliation of layered perovskites is correspondingly observed by transmission electron microscopy (TEM). The formation of a polysiloxane network composed of PDMS chains and Q n units ((RO) 4-n Si(OSi) n : R ) H, CH 3 ) via intentional hydrolysis is shown by the solid-state 29 Si CP/MAS (cross-polarization and magic angle spinning) NMR spectroscopy. These products are expected to possess the Nb-O-Si linkage interface since a signal assignable to the (SiO)Si(CH 3 ) 2 O-Nb environment is present in the 29 Si CP/MAS NMR spectra of products prepared from an n-decoxy derivative of HLaNb (or HCaNb), PDMS, and TMOS in a similar manner without intentional hydrolysis and the Nb-O-Si bonds are expected to be preserved during hydrolysis. The exfoliated structures should be formed during the intentional hydrolysis process since the products prepared without intentional hydrolysis clearly exhibit a stacking order along the c axis.

Organically modified niobate nanosheets are promising building blocks for the design of advanced hybrid materials. Nanosheets with controlled thickness and surface composition are important for precise structural design of the nanosheet-based materials. In this work, single-layered and double-layered niobate nanosheets functionalized by phenylphosphonate moieties were selectively prepared by interlayer grafting of A-type and B-type intercalation derivatives of potassium hexaniobate (K4Nb6O17·3H2O) with phenylphosphonic acid (PPA), followed by exfoliation by ultrasonication in acetonitrile. The interlayer grafting of PPA was monitored using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and solid-state NMR spectroscopy, and the thicknesses of the exfoliated nanosheets were measured by atomic force microscopy (AFM). Transparent hybrid films were obtained by incorporating the single- and double-layered nanosheets into an epoxy matrix.