Synthesis and properties of Fe and Co complexes: structures

Three mononuclear half-sandwich iron() (S = 1⁄2) complexes [(L/L)FeCl3] H2O (1/2) and [(L)Fe(N3)3] (3) have been synthesized and their properties investigated [L = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine; L = N-methyl-N,N-bis(2-pyridylmethyl)amine]. X-ray structural analysis revealed that in 3 the FeN6 unit is attained by co-ordination of three nitrogens of facially capping L and three azide nitrogens. The X-ray structural results on [(L)2Fe2(μ-O)(μ-O2CMe)2][ClO4]2 2H2O (4), revealed a bioctahedral structure with one oxo and two bridging acetate ligands, similar to that found in various forms of marine invertebrate oxygen transport protein, haemerythrin. Temperature-dependent (51–300 K) magnetic susceptibility measurements revealed for complex 4, J = 130 cm , and for a brownish orange diiron() complex [(L)2Fe2(μ-O)(μ-O2CMe)2][ClO4]2 2H2O (5), J = 114 cm , demonstrating that the extent of exchange coupling is more for the complex with unsymmetrical terminal ligand L than that with symmetrical ligand L. A new binuclear triply-bridged dicobalt() complex [(L)2Co2(μ-OH)2(μ-O2CMe)][ClO4]3 MeCN (6) has been synthesized, structurally characterized (L 2 is terminally co-ordinated in a facial mode) and its spectroscopic and redox properties investigated. To the best of our knowledge, this is the first structural report for a such a core formation with a facially capping tridentate N-donor ligand. The redox behaviour of mononuclear and dinuclear complexes has been investigated by cyclic voltammetry, and the results rationalized.