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Single‐step preparation of the mixed-metal oxides from the versatile oxalate precursors – characterization and properties

Mixed-metal oxides are an important class of advanced materials due to their chemical stability, low cost, low toxicity, large scale of useful photophysical properties and wide range of technological applications. It is known that the microstructure of oxide materials can be tuned in part by changing the synthesis methods. Full control over particles dimensions and morphology is also prerequisite for the photocatalytic applications of oxide materials where large surface area promoting substrate adsorption at the surface and increasing the number of active sites, is considered to be an imperative. However, in general, synthesis approaches for obtaining highly crystalline materials utilize high temperature treatments, which often lead to the increase of particle size and consequently the decrease of the surface area. Thus, it is still challenging to attain both high crystallinity and high surface area in the same synthesis. Due to these limitations, in recent times, heteropolynuclear systems have been used as molecular precursors for the preparation of the mixed-metal oxides by their thermal decomposition. It has been observed that the use of a well-defined precursor can produce crystalline oxide materials under conditions that are significantly milder than those applied in traditional solid-state synthesis. Also, the single-source precursors provide better control over the stoichiometry of the metal ions in the final products as well as the homogeneity of the materials due to the mixing of the metals at the molecular level, and offer kinetically attractive low temperature decomposition. An effective molecular precursor-to-material conversion requires a reasonable choice of ligands. The nature of the ligand employed endows the precursor with a clean, low-temperature thermolysis leading to the phase-pure target material. Importantly, low cost of the ligand makes heterometallic precursor highly attractive to industrial applications. One of the suitable ligands for the synthesis of molecular precursors for oxides is the oxalate dianion, C2O42-, due to its easily decomposition on gaseous CO2 and CO at low temperatures. Another advantage of this ligand is low cost. However, heterometallic complexes do not always contain the appropriate stoichiometry for the formation of the desired single phase oxide by thermal degradation in one step. Also, it is not easy to prepare coordination compound with three or more different metals (in an appropriate ratio), having also suitable coordinated ligand. So, sometimes multimetallic oxides could be prepared by mixing two or more agreeable precursors in appropriate ratio prior to thermal decomposition. In our group we explore the ability of the heterometallic oxalate‐based complexes to act as the single-source precursors for the formation of the mixed‐metal oxides by heat treatment. We focused on the structural, optical, photocatalytic, and magnetic properties of the (nano)crystalline oxides prepared for the first time by facile molecular precursor‐to‐material route, investigated by powder X‐ray diffraction, electron microscopes, UV‐vis diffuse reflectance spectroscopy and magnetization measurements, where long‐term heating at high temperatures and repeated grinding procedures are successfully bypassed. References [1] J. Popović, M.Jurić, D. Pajić, M. Vrankić, J.Zavašnik, J. Habjanič, Inorg. Chem. 56 (2017) 3983-3989 [2] L. Androš Dubraja, D. Pajić, M.a Vrankić, J. Dragović, M. Valant, M.Benčina, M. Jurić, J. Am. Ceram. Soc. (2019) DOI:10.1111/jace.16521

mixed-metal oxides ; oxalate precursors ; thermal conversion ; powder X‐ray diffraction ; electron microscopes

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