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Synthesis, crystal structures and spectroscopic characterization of the oxalate-bridged networks ([Cu(bpy)3][M2(C2O4)3]•H2O)n (M = Cu2+, Mn2+)

There has been a constant growing interest in the last decade or so for novel solid-state architectures with potential applications as functional materials in the fields such as catalysis, conductivity, luminescence or magnetism. In synthesizing and designing homo- and heteropolynuclear complexes as potential molecule-based magnetic materials, a very essential role belongs to the oxalate ion, C2O42–, because of its ability to adopt a bis(chelating) coordination mode as well as to mediate magnetic interactions between paramagnetic metal centres. On this account, stable mononuclear anionic oxalate complexes are often used as ligands toward the second metal ion, an approach known as “complexes as ligands” or “building-blocks chemistry”. The use of the tris(oxalato)metallates, [MIII(C2O4)3]3– (MIII = Cr, Mn, Fe, Ru, V) as building blocks provides a very efficient way for the synthesis of homo- and heterometallic oxalate-bridged two- (2D) and three-dimensional (3D) assemblies, which also exert a range of distinct magnetic properties. Related to our current magneto-structural studies on polynuclear transition metal complexes, the homometallic ([Cu(bpy)3][Cu2(C2O4)3]•H2O)n (1) and the bimetallic ([Cu(bpy)3][Mn2(C2O4)3]•H2O)n (2) compounds (bpy = 2, 2'-bipyridine) have been synthesized using liquid diffusion method. In addition to the single crystal X-ray diffraction study, characterisation of the new complexes has been accomplished by means of the IR and EPR spectroscopy. The compounds crystallise in the cubic space groups, P4132 (1) and P4332 (2) and the structures of both compounds consist of a 3D, polimeric anionic network [M2(C2O4)3]nn–, with the tris-chelated cations occupying the vacancies of the framework (Figure 1). So far, only a few single-crystal structures of this type of 3D metal oxalates have been described.

metal complexes; copper(II); manganese(II); EPR

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