engleski

Heterometallic compounds containing various (oxalato)tantalum(V) complex anions - synthesis and properties

In designing and synthesis of metal-organic coordination systems with specific properties (electrical, optical, catalytic and/or magnetic) due to their potential applications, special attention has been paid to the nature of metal ions and the geometry, flexibility and coordination preferences of the bridging ligands. Due to extraordinary coordination and electronic properties of the oxalate anion, C2O42–, a great number of oxalate-based, polynuclear (homo- and heterometallic) as well as mononuclear, discrete or polymeric, complexes has been isolated and characterized. The introduction of organic ligands containing N-donors, like 2, 2'-bipyridine or 1, 10-phenanthroline, into the metal-oxalate systems further stabilizes their solid-state structures. Weak non-covalent interactions such as π–π stacking and hydrogen bonding may adjust the dimensionality and lead to new topologies and desired functions of these supramolecular assemblies. Searching for suitable methods of synthesis leading to novel and promising polynuclear species, of significant importance has been to find appropriate mononuclear complexes that could be used as ligands towards other metal ions. Along with the frequently utilized tris(oxalato)metallate(III) anions, in our research group the tris(oxalato)oxoniobate(V) anion was first used for the same purpose. More recently, we have extended our investigation also on the (oxalato)tantalates(V) as possible building (bridging) units for the creation of new inorganic-organic frameworks. In the reactions of such (oxalato)tantalate solutions and [Ni(phen)3]2+ (phen = 1, 10-phenanthroline) cations, we managed to synthesize new transition-metal complex systems. It was found that the coordination sphere around the tantalum ion is subject to change due to the solvent change. Depending on the ratio of reactants and solvent we isolated four new heterodimetallic compounds [Ni(phen)3][phenH][Ta(C2O4)4]•7H2O, [Ni(phen)3][Ta(OC2H5)(C2O4)3]•H2O, [Ni(phen)3][Ta(OCH3)(C2O4)3]•H2O and [Ni(phen)3][Ta(OH)(C2O4)3]•8H2O. In addition to the single-crystal X-ray diffraction studies, the characterization of the new complexes has been accomplished by means of IR and UV-vis spectroscopy as well as by the TG/DTA analysis.

Heterometallic compounds; nickel; tantalum; oxalate

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