The synthesis, structures and characterisation of new mixed-ligand manganese and iron complexes with tripodal, tetradentate ligands

The preparation of new manganese and iron complexes with the general formula [M(tripod)(anion)] is described, where M = FeIII or MnIII, “tripod” is a dianionic tetradentate tripodal ligand and the anion is a chelating β-diketonate, 8-oxyquinoline or acetate. The synthesis of this type of complexes was found to be straightforward, which allows for the preparation of a large variety of such coordination compounds. The complexes are characterised by X-ray crystallography, infrared spectroscopy, UV/Vis spectroscopy, cyclic voltammetry and elemental analysis. A correlation between the ligand sets and the electron density at the metal centre in the complexes is proposed, based on the UV/Vis data and the CV measurements. The tripodal ligands are significant π-donor ligands, and electron-withdrawing or electron-donating substituents on the phenolate arms were found to have a large influence on both the position of the d–d transitions in the UV/Vis spectra and the peak potentials in the CV measurements. The “secondary” β-diketonate or acetate ligand does not have such a large effect on the electron density of the metal centre.