Synthesis and properties of FeIII and CoIII 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 (1/2) 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]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⁻¹, and for a brownish orange diiron(III) complex [(L³)₂Fe₂(μ-O)(μ-O₂CMe)₂][ClO₄]₂·2H₂O (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]₃·MeCN (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.