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New mononuclear oxalate complexes of manganese(II) and nickel(II) with three-dimensional architecture

Owing to the well-known, extraordinary coordination and electronic properties of the oxalate anion, C2O42–, an enormous 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 metallosupramolecular assemblies. Related to our current magneto-structural studies on the mono- and polynuclear transition metal species, two new mononuclear complexes have been synthesized: [Mn(bpy)(C2O4)(H2O)2] (1) and [Ni(bpy)2(C2O4)]•5H2O (2) (bpy = 2, 2'-bipyridine). Both compounds crystallize in the monoclinic P21/c space group. The structural analysis reveals that hydrogen-bonding layers formed in 1 and 2 are further linked through the finite π–π stacking interactions of the aromatic systems, into an overall three-dimensional (3D) arrangement. In addition to the single crystal X-ray diffraction study, characterization of the new complexes 1 and 2 has been accomplished by means of the IR and EPR spectroscopy as well as by the TG/DTA analysis. The complexes obtained could be used as convenient building blocks in further attempts to prepare new polynuclear compounds. Additional endeavours on the synthesis of new heteropolynuclear systems using 1 and/or 2 as precursors are in progress.

oxalate complexes; manganese(II); nickel(II); EPR

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