Synthesis and properties of Fe-III and Co-III complexes: structures of [(L-2)Fe(N-3)(3)], [(L-2)(2)Fe-2(mu-O)(mu-O2CMe)(2)][ClO4](2)center dot 2H(2)O and [(L-2)(2)Co-2(mu-OH)(2)(mu-O2CMe)][ClO4](3)center dot MeCN [L-2 = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine]

Three mononuclear half-sandwich iron(III) (S = 1/2) complexes [(L-2/L-3) FeCl3] . H2O (1/2) and [(L-2) Fe(N-3)(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)(2)Fe-2(mu-O)(mu-O2CMe)(2)][ClO4](2) . 2H(2)O ( 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 [(L-3)(2)Fe-2(mu-O)(mu-O2CMe)(2)][ClO4](2) . 2H(2)O (5), J = - 114 cm(-1), demonstrating that the extent of exchange coupling is more for the complex with unsymmetrical terminal ligand L-2 than that with symmetrical ligand L-3. A new binuclear triply-bridged dicobalt(III) complex [(L-2)(2)Co-2(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.