Synthesis and properties of Fe~(III) and Co~(III) complexes: structures of [(L~2)Fe(N_3)_3], [(L~2)_2Fe_2(μ-O)(μ-O_2CMe)_2][ClO_4]_2·2H_2O and [(L~2)_2Co_2(μ-OH)_2(μ-O_2CMe)][ClO_4]_3·MeCN[L~2 = methyl[2-(2-pyridyl)ethyl](2-pyridylmethyl)amine]

摘要

Three mononuclear half-sandwich iron(III)(S = 1/2) complexes [(L~2/L~3)FeCl_3]·H_2O(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 FeN_6 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)_2Fe_2(μ-O)(μ-O_2CMe)_2][ClO_4]_2·2H_2O (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)_2Fe_2(μ-O)(μ-O_2CMe)_2][ClO_4]_2·2H_2O (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)_2Co_2(μ-OH)_2(μ-O_2CMe)][ClO_4]_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.