Synthesis, characterization and electrochemical properties of trinuclear iron(III) complexes containing unsaturated carboxylate bridging ligands

A series of ore-bridged, tri-iron cluster complexes, [Fe3O(O2C4H5)(6)(L)(3)](+) (L = H2O Pyridine, 3- and 4-methylpyridine), [Fe3O(O2C3H3)(6)(L)(3)](+) (L = H2O, 3- and 4-methylpyridine, 3-bromopyridine) has been prepared as NO3- salts. Mixed metal complexes [Fe2CoO(O2C4H5)(6)(L)(3)] (L = H2O, pyridine), [FeCo2(O2C3H3)(6)(C5H5N)(2)](+) and cobalt(II) complexes [Co-3(O(2)CR)(6)(H2O)(2)] (R = C2H3, C3H5) have been isolated. The complexes have been characterized by electronic and infrared spectrophotometry, mass spectrometry and cyclic voltammetry. Cobalt(II) complexes and the mixed metal acrylate complexes present a linear arrangement. The triangular structure of the iron complexes remains when the water molecules are replaced by pyridine derivatives. The effects of this change in electron content on the chemical and physical properties of the clusters have been investigated by spectral and electrochemical measurements. The cyclic voltammograms of all the iron complexes revealed an Fe-III-Fe-II reduction. Complexes [Fe3O(O2C4H5)(6)(L)(3)] NO3 (L = H2O, pyridine, 4-methylpyridine) and [Fe3O(O2C3H3)(6)(3-BrC5H4N)(3)]NO3 exhibit an electrochemically quasi-reversible metal reduction but [Fe3O(O2C3H3)(6)(H2O)(3)]NO3 shows a reversible iron reduction.