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Charge transfer in bimetallic oxalate-bridged coordination polymer with the [Fe(C2O4)3]3- core induced by light irradiation

Photochromic materials are able to reversibly change in their molecular and electronic structure by light irradiation. It is the reversible transformation of a chemical species between two forms, A and B, with different absorption spectra, induced by the absorption of electromagnetic radiation in one or both directions. The thermodynamically stable form A is is converted by irradiation to the less stable form B, which has different absorption spectra and can be returned to form A both thermally or photochemically. The interconversion of two states is usually accompanied by the change of some physical properties, such as the refractive index, dielectric constant, electric conductivity, redox potential, phase transition, solubility, viscosity, surface wettability, magnetism, luminescence, or a mechanical effect. These materials have attracted much attention due to their convenient visual monitoring and their real or potential applications in the fields such as optical switches, solar energy conversion, data storage, photomasks, and so forth. In the last decade, a large number of photochromic organic– inorganic hybrids have been investigated and reported. We have explored compound {; ; NH4[{; ; Cu(bpy)}; ; 2(C2O4)Fe(C2O4)3]·H2O}; ; n (1 ; bpy = 2, 2'-bipyridine), which has [Cu(bpy) (C2O4)Cu(bpy)]2+ cationic species units mutually connected through oxalate groups of [Fe(C2O4)3]3 in a 1D ladder-like coordination polymer, as a new type of photoactive solid state system [1, 2]. This heterometallic compound exhibits significant photocoloration after exposure to direct sunlight or UV/Vis irradiation in the solid state. This was investigated by powder and single-crystal X-ray diffraction, diffuse reflectance, IR and EPR spectroscopy.

ladder-like coordination polymer ; oxalate-based ; photoactive solid state system ; photocoloration

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