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A 3D oxalate-bridged [CuIIFeII] network as a photocatalyst and precursor for the preparation of CuFe2O4 spinel oxide

In recent years, great efforts have been made to develop new metal-organic frameworks (MOFs) and coordination polymers (CPs) with photocatalytic potential, especially with respect to the development of photocatalysts for organic pollutant degradation, CO2 reduction, and water splitting for H2 production. Compared to conventional metal oxide semiconductors, well- defined and tailored structures of MOFs offer great advantages for understanding the structure- activity relationship. Their high porosity enables the exposure of active sites for catalysis and facilitates the transport of substrates by creating short migration paths for charge carriers prior to their reaction with substrates, thus improving electron-hole separation.[1] The use of heterometallic complexes or frameworks containing more than one metal as single source precursors provides simplified synthetic routes through one- step thermal decomposition to form mixed metal oxide materials. The advantage of a solid phase transition is the retention of the elemental composition defined by the molecular precursor with only a loss of volatile decomposition products – allowing excellent stoichiometric control of the intermetallic ratio in the oxide products. It is known that the release of organic gases affects the particle size and porosity of the produced oxide ; a higher content of organics in the starting materials allows larger porosity and smaller particle sizes in the decomposition products. In addition, control of the heating rate is important to control decomposition and avoid melting/vaporisation of molecular species that can occur with rapid heating. High temperatures also determine the crystallinity, particle size and porosity of the produced materials, limiting the ability to develop specific properties for applications. By using lower synthesis temperatures, oxides with small particle sizes and large surface areas can be produced.[2] Since it is known that Fe–O clusters can be directly excited by visible light[3], leading to more efficient use of solar energy, and that compounds with iron are much cheaper due to the abundant Fe element on Earth, an oxalate-bridged heterometallic coordination polymer [CuII(H2O) (terpy)FeII2(C2O4)3]n (terpy = 2, 2′:6′, 2′′- terpyridine) with a three-dimensional (3D) network[4], was tested as a photocatalyst for the photodegradation of Rhodamine B (RhB) and methylene blue (MB). The optical band gap and photocatalytic activities were studied in detail. This 3D network [CuIIFeII2(H2O)(terpy)(C2O4)3]n was also tested as a single molecular precursor for the preparation of spinel oxide CuFe2O4 due to the suitable metal ratio. The oxalate group, C2O42-, easily decomposes at low temperatures into gaseous CO2 and CO, and therefore the oxalate‐ based solids can serve as suitable precursors for oxides. The (micro)structural, optical and photocatalytic properties of the (nano)crystalline spinel CuFe2O4 samples, prepared for the first time by a simple molecular precursor‐to‐material route, were presented.

heterometallic complexes ; oxalate-based ; single source precursors ; photocatalytic activities

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