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

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 [L^2= methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine; L^3=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^2 and three azide nitrogens. The X-ray structural results on [(L^2)2Fe2((mu)-O)((mu)-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((mu)-O)((mu)-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 L^3. A new binuclear triply-bridged dicobalt(III) complex [(L2)2Co2((mu)-OH)2((mu)-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.