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Structural and magnetic properties of new heterometallic compounds with dinuclear oxalate-bridged cations

There is a constant quest for novel metal-organic complexes with potential application in catalysis, conductivity and magnetism ; fields that are crucial for the development of modern materials science. While designing metal–organic coordination systems with specific properties, special attention is paid to the nature of metal ions and the geometry, flexibility and coordination preferences of the bridging ligands. Due to variety of coordination modes, rigidity and good donor ability of oxalate dianion, the oxalate chemistry of various transition metals was a subject of numerous studies. Moreover, this ligand is frequently used for the design and synthesis of molecule-based magnets, since it can mediate the magnetic exchange interaction between metal centres, when coordinated as a bridge between two paramagnetic metal atoms. (Clemente-León et al., 2011) A facile approach for the preparation of heteropolynuclear species with predetermined structures and spin topologies, known as “complexes as ligands” or “building-blocks chemistry”, involves the use of anionic mononuclear complexes as ligands towards a second metal ion. Good control over the reaction products is achieved by utilizing stable anionic complexes which are inert to ligand substitution, such as anionic chromium(III) complexes with potentially bridging oxalate groups. Moreover, the fact that chromium(III) ion is a spin carrier (S = 3/2) makes anionic chromium(III) complexes suitable for the preparation of heterometallic compounds with interesting magnetic features. (Marinescu et al., 2011) Following this rational synthesis approach we have focused on the use of [Cr(phen)(C2O4)2]– anion as building block (phen = 1, 10-phenanthroline) ; a versatile tecton in designing heterometallic oxalate-bridged compounds. Reaction of aqueous solutions of [Cr(phen)(C2O4)2]– anions with bis(phenanthroline)metal(II) cations (M = Mn, Co, Ni, Cu, Zn) resulted in a series of five new compounds 1–5, of general formula [{;M(phen)2};2(μ-C2O4)]0.5[Cr(phen)(C2O4)2]·2H2O [M2+ = Mn (1), Co (2), Ni (3), Cu (4), Zn (5)]. In addition to the single crystal X-ray diffraction studies, characterization of the new complexes was accomplished by means of IR and UV/Vis spectroscopy and magnetic measurements on SQUID magnetometer. References: Clemente-León, M., Coronado, E., Martí-Gastaldo, C. & Romero, F. M. (2011). Chem. Soc. Rev., 40, 473–497. Marinescu, G., Andruh, M., Lloret, F. & Julve, M. (2011). Coord. Chem. Rev. 255, 161–185.

Heterometallic Compounds ; Oxalate Bridges ; Crystal Structures ; Magnetic Measurements

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