Synthesis And Characterization Of Low Oxidation State Cobalt Chelates

ABSTRACT

Square planar complexes of cobalt in any of its common oxidation states are rare and attempt to make them either yield tetrahedral or octahedral complexes. The aim of this study was to synthesize and characterize low oxidation state complexes of cobalt using selected chelating ligands including 8-hydroxyquinoline (oxine) and glycine. It was of interest to synthesize cobalt (I) complexes of square planar geometry as these are expected to have the same mode of action as the square planar cis-platin used in the treatment of some forms of cancer. Square planar cobalt (I) complexes are rare in the literature. The reactions of CoCl2 with 8-hydroxyquinoline (oxine) and glycine were studied under different solvent conditions under inert conditions. Reaction of cobalt (II) chloride with oxine in tetrahydrofuran (THF) solvent gave unexpected blue crystals of the tetrachloridocobaltate (III) complex [CoCl4] - [C9H7NOH]+ , in which protonated oxine is the counter cation. The molecular structure of the complex [CoCl4] - [C9H7NOH]+ was confirmed using single crystal X-ray crystallography. It forms monoclinic crystals in the C2/c space group with respective unit cell parameters being  = 90.00,  = 91.0900,  = 90.00; a = 15.1890(3), b = 7.99120(10), c = 16.6770(3). When the same reaction was carried out in water/ethanol mixture, a yellow non crystalline solid, [Co(oxine)2(H2O)2]Cl2 was obtained. On the other hand, reaction of cobalt (II) chloride with glycine in 1:1 methanol/ethanol mixture gave purple crystals of a compound formulated as [Co(gly)Cl3. These compounds were characterized by melting point determination, elemental analysis and FTIR spectroscopy. Reduction of Co(gly)Cl3 with NaBH4 and CoCl2.6H2O with NaBH4 in the presence of oxine led to dark solids whose elemental analysis results were inconclusive.