Synthesis and characterization of μ-hydroxido- and μ-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 analytical and spectral data the formulae of the complexes are {[Fe4(bipy)2 (H2O)2(OH)6(pht)3]?2H2O}n (1), {[Fe4(bipy)2(Hipht)2(ipht)2(OH)6]?4H2O}n (2), {[Fe4(bipy)2(Htpht)2(OH)6(tpht)2]?4H2O}n (3) and {[Fe4(bipy)(H2O)8(OH)4 (pyr)2]?H2O}n (4). All complexes are red brown and low-spin with a distorted octahedral geometry and FeO6 or FeN2O4 chromophore. Polycarboxylato ligands have a bridging role in all cases, whereas monodentate COO groups are present in 2 and 3, bridging and chelate COO groups are established in 1 and 4. The thermal behaviour of 1-4 was investigated in detail and the molar dehydration enthalpies were calculated. According to the all those results, the structural formulae of the complexes 1-4 were proposed.