Research article - Peer-reviewed, 2008
Substitution features in the isomorphous replacement series for metal-organic compounds (Nb(x)Ta(1-x))(4)O(2)(OMe)(14)(ReO(4))(2), x=0.7, 0.5, 0.3-Single-source precursors of complex oxides with organized porosityNikonova, Olesya A.; Kessler, Vadim G.; Seisenbaeva, Gulaim A.
AbstractTrimetallic oxoalkoxide complexes (Nb(0.7)Ta(0.3))(4)O(2)(OMe)(14)(ReO(4))(2) (1). (Nb(0.3)Ta(0.7))(4)O(2)(OMe)(14)(ReO(4))(2) (II) and (Nb(0.5)Ta(0.5))(4)O(2)(OMe)(14()Re0(4))(2) (III) Were obtained by the interaction of rhenium heptoxide (VII) Re(2)O(7) With niobium and tantalum alkoxides M(2)(OMe)(10) (M = Nb, Ta) in toluene. The centrosymmetric molecules (I)-(III) can be considered as a product of condensation of two M(2)(OMe)(9)(OReO(3)) molecules with the formation of two oxo-bridges. The specific feature of the structure is the uneven distribution of metal atoms in the crystallographic positions, where one symmetry-independent position, connected via mu-O with a perrhenate ReO(4)(-) group, is predominantly Occupied by niobium atoms, while the other one connected via alkoxide groups has a higher tantalum content. The distribution of Nb and Ta in the structure is truly even only for compound III. The niobium and tantalum content is varied to a different extent for I (less) and for II (more), which is apparently due to small differences in the sizes of these two cations, resulting in preferences for packing of different molecules in the structures. Thermal decomposition of (Nb(1-x)Ta(x))(4)O(2)(OMe)(14)(ReO(4))(2)(x = 0.3, 0.5, 0.7) in air leads to the formation of crystalline species of solid solutions based oil tantalum and niobium oxides displaying semi-ordered pores with the size of 100-250 nm. In the dry nitrogen atmosphere, the decomposition leads to the amorphous complex oxides containing rhenium, niobium and tantalum. (C) 2008 Elsevier Inc. All rights reserved.
KeywordsRhenium; Niobium; Tantalum; Single-source precursors; Mixed-metal oxoalkoxide; Metal-organic decomposition; Porous oxide
Published inJournal of Solid State Chemistry
2008, volume: 181, number: 12, pages: 3294-3302
Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE
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