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Synthesis and characterization of Cu(II), Fe(III), Cr(III) polynuclear carboxylate complexes

Studies of structural features of polynuclear metal carboxylate complexes (known as “basic carboxylates”) is gaining a lot of attention recently because of their interesting magnetic and electronic properties. These compounds display different magnetic properties (ferro-, ferri-, antiferromagnetic), depending upon molecular and crystal structure. They can also be used as precursors for the synthesis of higher nuclearity clusters. In this work, polynuclear complex with Cu(II), Fe(III) and Cr(III) were synthesized by reactions of acetic and benzoic acid with appropriate metal salts in presence of template molecules (hexamine and guanidine) at room temperature. Prepared complex compounds were characterized by the single crystal X-ray diffraction (sc-XRD), FT- IR spectroscopy and elemental analysis. Under these conditions crystals of two novel polynuclear (Fe(III) and Cu(II)) complexes were obtained and characterized by sc-XRD (FeHEXOK and CuGUABA). X-ray structure analysis of FeHEXOK has shown that compound crystallize in the orthorhombic crystal system, P nma space group (Z=4). The complex compound is comprised of one Fe-basic acetate unit (trinuclear), a non-coordinated nitrate anion, hexamine molecule, and water of crystallization molecules. The positive charge of central Fe- basic acetate unit is neutralized by presence of nitrate anion in the crystal structure and the formal oxidation state of all three iron atoms is +3 (d5 configuration). In the crystal structure, the molecules are primarily linked via strong O‒H∙∙∙N and O‒H∙∙∙O hydrogen bond interactions. X-ray structure analysis of CuGUABA has shown that compound crystallize in the triclinic crystal system, P -1 space group (Z=2). Interestingly, in the crystal structure of CuGUABA there are several different dinuclear Cu-benzoate moieties. The molecular structure of discrete moieties is typical paddle-wheel structure, often observed in Cu- carboxylate complexes. Results of FT-IR spectroscopy and elemental analysis are in agreement with proposed structures. Several other Cr(III), Cu(II) and Fe(III) complexes were synthesized and characterized by FT-IR and elemental analysis.

polynuclear complexes, carboxylate, copper, iron(III), chromium(III)

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