Synthesis and characterization of mu-hydroxido- and mu-polycarboxylato-bridged iron(III) complexes with 2,2 '-bipyridine

Abstract

Four novel polymeric iron(III) complexes with 2,2'-bipyridine (bipy) and different aromatic polycarboxylato ligands as anions of phthalic (pht), isophthalic (ipht), terephthalic (tpht) and pyromellitic (pyr) acid were synthesized by ligand exchange reaction. The complexes were characterized by elemental and TG/DSC analysis, FTIR and diffuse reflectance UV-Vis-NIR spectroscopy and magnetic susceptibility measurements. Based on the analytical and spectral data, the formulae of the complexes were {[Fe-4(bipy)(2) (H2O)(2)(OH)(6)(pht)(3)]center dot 2H(2)O}(n) (1), {[Fe-4(bipy)(2)(Hipht)(2)(ipht)(2)(OH)(6)]center dot 4H(2)O}(n) (2), {[Fe-4(bipy)(2)(Htpht)(2)(OH)(6)(tpht)(2)]center dot 4H(2)O}(n) (3) and {[Fe-4(bipy)(H2O)(8)-(OH)(4)(pyr)(2)]center dot H2O}(n) (4). All complexes were red brown and low-spin with a distorted octahedral geometry with FeO6 or FeN2O4 chromophores. The polycarboxylato ligands played a bridging role in all cases, whereas monodentate COO groups were present in 2 and 3, while bridging and chelate COO groups were established in 1 and 4. The thermal behaviours of 1-4 were investigated in detail and the molar dehydration enthalpies were calculated. According to the all those results, the structural formulae of complexes 1-4 were proposed.