Templated Assembly of Metal-Anion Arrays within Layered Hosts; Synthesis and Characterization of New Transition-Metal Ox
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Templated Assembly of Metal-Anion Arrays within Layered Hosts; Synthesis and Characterization of New Transition-Metal Oxyhalide Perovskites Gabriel Caruntu, Liliana Viciu, Leonard Spinu, Weilie Zhou, and John B. Wiley* Department of Chemistry and the Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148-2820 ABSTRACT Ion exchange of Dion-Jacobson-type double- and triple-layered perovskites with divalent transition-metal halides leads to the templated assembly of metal-anion layers. A whole series of compounds of the form (MCl)LaNb2O7 (M = V, Cr, Mn, Fe, Co, Cu) and (CuCl)Ln2Ti2NbO10 (Ln = Pr, Nd, Sm, Eu) have been prepared. Additionally, a new series of host compounds is being developed to exploit this exchange chemistry; the new oxyfluorides, RbLnTiNbO6F (Ln = La, Pr, Nd) and RbLaM NbO6F (M = V4+, Mn4+, Nb4+, Mo4+), have been prepared by a direct route. ′
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INTRODUCTION Layered perovskites form a distinct class of inorganic materials whose structure is conventionally described as intergrowth assemblies of n perovskite-like slabs of vertex-sharing BO6 octahedra running along the [001] direction interleaved by large electropositive cations. With respect to the density of interlayer cations, two principal families can be formulated: the Dion-Jacobson series [1-3], corresponding to the formula [AA n-1B3O3n+1], and RuddlesdenPopper [4-6] series, [A2A n-1B3O3n+1] (A,A = alkali, alkaline earth or rare earth; B = transition metal). When A is an ion-exchangeable cation, such as an alkali metal, the two-dimensional nature of their structures can be maintained even on replacing interlayer species with other cations or more complex cationic structural units [7-10]. Such chemistry is significant in that it offers a fertile ground in the search for new low-dimensional compounds with interesting properties such as ionic conductivity [11], superconductivity [12], ferroelectricity [13], colossal magnetoresistance [14-15] and magnetic transitions. Currently we are focusing on the topotactic manipulation of layered compounds like the Dion-Jacobson and Ruddlesden-Popper series of perovskites [16-17]. We believe that through the use of topotactic routes, rational synthetic methods can be developed for directing the structure and properties in new materials. To this end, we are working to develop general strategies in a number of areas including the assembly of metal-anion arrays within receptive hosts and the formation of new mixed valence compounds. Additionally, we are examining the use of multistep strategies, akin to standard molecular syntheses, for targeting a particular compound. Herein we highlight two aspects of this work 1) the construction of metal-anion arrays within layered hosts and 2) the preparation of new Dion-Jacobson perovskites for use in these topotactic strategies. ′
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EXPERIMENTAL DETAILS Known Dion-Jacobson type hosts were prepared by methods described in the literature [2, 16]. Ion-exchange reactions were typically carried out by thoroughly mixing the parent oxides D3.4.
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