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Electrical and magnetic features of a 3D oxalate- bridged [CuFe] molecular precursor

Due to the rich variety of metal species and ligands, coordination geometry, guests inside the pores, and supramolecular structures, an enormous number of coordination polymers with various structures, dimensionality, and nuclearity have been synthesized and reported. This area of molecular chemistry is the basis for design of the molecule-based materials that combine two (or more) physical properties of interest, especially upgrading and expanding the molecular magnetism toward multifunctional systems. Most of the oxalate-based molecular magnets described to date have been obtained by the “complex-as-ligand approach” ; a molecular building block, the tris(oxalato)metalate [MIII(C2O4)3]3 anion is used as a ligand toward other metal cations. The topology of these oxalate-bridged compounds is controlled by a templating counterion. Two polymorphs of 3D coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (1 ; terpy = 2, 2′:6′, 2′′-terpyridine), formed hydrothermally, contain homometallic 2D oxalate-bridged honeycomb anionic layers, [FeII2(C2O4)3]n2n-, mutually linked by complex cations of copper(II) ions, [Cu(H2O)(terpy)]2+, through oxygen atoms from oxalate bridges. Recently published oxalate-based networks have shown proton conductivity related to the presence of ammonium and/or crystallization water [1]. Therefore, in addition to magnetic, electrical properties of 1 have been also investigated ; it exhibits antiferromagnetic phase transition at 25 K and proton conductivity. Furthermore, the ability of this 3D polymer, due to their appropriate stoichiometry of metal ions, to act as single-source precursor for the formation of spinel CuFe2O4 oxide by heat treatment has been explored [2].

coordination polymers ; oxalate-bridged ; crystal structure ; electrical property ; magnetic property

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