Synthesis and properties of Fe^III and Co^III complexes: structures of [(L²)Fe(N₃)₃], [(L²)₂Fe₂(μ-O)(μ-O₂CMe)₂][ClO₄]₂·2H₂O and [(L²)₂Co₂(μ-OH)₂(μ-O₂CMe)][ClO₄]₃·MeCN [L²= methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine]

Abstract

Three mononuclear half-sandwich iron(III) (S =½) complexes [(L²/L³)FeCl₃]·H₂O (½) and [(L²)Fe(N₃)₃] (3) have been synthesized and their properties investigated [L² = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine; L³ = 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 L² and three azide nitrogens. The X-ray structural results on [(L²)₂Fe₂(μ-O)(μ-O₂CMe)₂][ClO₄]₂½2H₂O (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^-1, and for a brownish orange diiron(III) complex [(L³)₂Fe₂(μ-O)(μ-O₂CMe)₂][ClO₄]₂½2H₂O (5), J = -114 cm^-1, demonstrating that the extent of exchange coupling is more for the complex with unsymmetrical terminal ligand L² than that with symmetrical ligand L³. A new binuclear triply-bridged dicobalt(III) complex [(L²)₂Co₂(μ-OH)₂(μ-O₂CMe)][ClO₄]₃½MeCN (6) has been synthesized, structurally characterized (L² 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.