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A heterometallic oxalate compound with square {;Cr2Nb2(μ-O)4}; core as precursor for mixed oxide

Recent research related to the multicomponent Nb-containing oxide materials revealed their very appealing structural and physical properties, leading to their development for a wide range of technological applications, such as ferroelectric and piezoelectric materials, ion conductors, and also as promising catalysts in several highly challenging processes.[1] Lately, metal−organic coordination systems have been used as single-source precursors for the preparation of mixed-metal oxides through thermal decomposition. This method, compared with conventional methods, has several advantages: (i) the obtained material is more homogeneous because the metals are mixed at the molecular level ; (ii) the resulting materials have relatively high specific surface areas because the oxides are formed under significantly milder conditions ; (iii) there is much greater control of the metal stoichiometry in the final products ; and (iv) there are no long-term and repeated grinding procedures. The oxalate anion, C2O42− easily decomposes to the vapor phases CO2 and CO, through the low-temperature routes, and hence, the heterometallic oxalate-based compounds are suitable for the use as molecular precursors for mixed oxides .[1–3] Hence, due to the growing need for Nb-based oxides, further investigation of the Nb-containing heterometallic oxalate compounds that could serve as single-source precursors is of great importance. As a continuation of our studies, [1–3] novel compound [Cr(bpy)2(μ-O)2Nb(C2O4)2]2·3H2O (1) (bpy = 2, 2’-bipyridine) was synthesized and characterized by single-crystal X-ray diffraction, IR and UV/Vis spectroscopy and thermal analysis. The molecular structure of 1 exhibits a square shaped {; ; ; Cr2Nb2(μ-O)4}; ; ; core in which oxo-bridged Cr3+ and Nb5+ ions reside in alternate corners (Figure 1). Both metal ions display the octahedral coordination geometry. Thermal treatment of 1 at 1000 °C leads to molecular precursor-to-material conversion that yields the mixed-metal CrNbO4 oxide, explored by powder X-ray diffraction. [1] M. Jurić, J. Popović, A. Šantić, K. Molčanov, N. Brničević, P. Planinić, Inorg. Chem., 2013, 52, 1832−1842 ; [2] L. Androš, M. Jurić, J. Popović, A. Šantić, P. Lazić, M. Benčina, M. Valant, N. Brničević, P. Planinić, Inorg. Chem., 2013, 52, 14299–14308 ; [3] J. Habjanič, M. Jurić, J. Popović, K. Molčanov, D. Pajić, Inorg. Chem., 2014, 53, 9633−9643.

heterometallic complex; oxalate ligand; oxo bridges; molecular precursor-to-material conversion; chromium niobate

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