Among 3d metal complexes, the most unusual and rarest are the seven-coordinate structures. The chemistry of these unique species is extremely challenging as a largely undefined, new area with horizons waiting to be expanded. But the biggest fascination arises from recent demonstrations that the best synthetic superoxide dismutase (SOD) enzymes known to date are of the class of seven-coordinate Mn(II) and Fe(III) complexes with macrocyclic ligands. Although it has been postulated that only seven-coordinate complexes of macrocyclic ligands with prominent conformational flexibility can exhibit SOD-activity, our complex with an acyclic extremely rigid dapsox^2- ligand (H2dapsox = 2,6-diacetylpyridine-bis(semioxamazide)) has demonstrated a potential to have even an improved catalytic activity.
The intriguing questions are: how does the seven-coordinate geometry around the metal centre engender remarkable catalytic activity, knowing that the metal centre in the native MnSOD and FeSOD has a five-coordinate geometry, and which chelate systems lead to the SOD-activity of seven-coordinate species? To find an answer on this question it is necessary to understand the relations between structure, kinetic and redox properties of seven-coordinate 3d metal complexes and for this goal we work on:

• synthesis and characterization of the manganese and iron seven-coordinate complexes with the different pentadentate ligands
  

• kinetic and thermodynamic investigations of the reactions with superoxide in aprotic solvents and organic solvent mixtures (for measurements down to -90 °C) and
  

• identification of intermediate species along the catalytic cycle.
  

Results of these studies would certainly explain the role of the coordination number seven in creating qualitatively new redox properties and potential catalytic ability of 3d metal complexes and would allow the design of a new class of efficient redox catalysts and biomimetics.