Topochemical Modification of Layered Perovskites
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1148-PP01-03
Topochemical Modification of Layered Perovskites Jonglak Choi, Elisha A. Josepha, Xiao Zhang, and John B. Wiley* Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana Abstract Topochemical reaction strategies based on two-step intercalation methods are studied. Reactions involving reductive followed by oxidative intercalation are useful in the preparation of new compounds; the syntheses and characterization of (A2Cl)LaNb2O7 (A = Rb, Cs) are presented. An alternative synthetic route, oxidative followed by reductive intercalation, is also discussed. Introduction Topochemical reactions allow one to maintain important structural features in a compound while varying local structure and valence. Topochemical reactions typically involve methods such as ion exchange and/or intercalation (deintercalation) to modify host compounds; the ion exchange can be either cationic or anionic, and the intercalation can be reductive, oxidative, or simply involve the insertion (removal) of neutral species. Recent examples using these techniques include the modification of K2Eu2Ti3O10 by ion exchange with calcium followed by reductive deintercalation to make the new layered perovskite CaEu2Ti3O9 [1], site-specific reductive intercalation of Y2Ti2O5S2 [2], oxidative intercalation with a fluoride to make Sr3Ru2O7F2 [3], insertion of neutral HgX2 (X = Br, I) into Bi2Sr2CaCu2Oy [4], and anion exchange of ZrNCl at elevated temperatures with K2S to form Zr2N2S [5]. This assortment of reactions serves to illustrate the versatility available in topochemical processes. Our interests in this area involve the development of new topochemical strategies, including those based on multistep reactions, for the construction of metal-anion layers within receptive hosts – such capabilities should contribute to rational low temperature (< 500 °C) syntheses of significant new compounds that exhibit interesting electronic, magnetic, and structural properties. Recently we reported on the insertion of transition-metal halide layers into layered perovskites; compounds of the form (MCl)LaNb2O7 have been prepared by ion exchange between ALaNb2O7 and MCl2 (M = V, Cr, Mn, Fe, Co, Cu) [6]. Building on this work, the (CuCl)LaNb2O7 ion exchange product was treated by reductive intercalation of lithium to make (LixCl)LaNb2O7 (2 ≤ x < 4). This compound was then treated with iodine to convert the copper metal byproduct to CuI for easy removal from the sample; simultaneously lithium was extracted by oxidative deintercalation to give the final product (Li2Cl)LaNb2O7 [7]. Currently we are interested in the development of two-step intercalation methods for the construction of alkali-metal halide layers within layered perovskite hosts. The sequential intercalation of both cation and anion species should be effective in the formation of the target metal-anion arrays. Two approaches are under investigation, reductive-oxidative and oxidativereductive intercalation. While these two strategies might init
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