Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II. A synthesis, characterisation and reactivity study.

In this work we report the preparation of two metallamacrocyclic tetranuclear manganese(II) complexes, L1(4)Mn44 and L2(4)Mn44 where L1 and L2 are the anions of the heptadentate ligands 2-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)(methyl)amino)acetic acid and 2-(benzyl(2-(bis(pyridin-2-ylmethyl)amino)ethyl)amino)acetic acid), respectively. The complexes have been fully characterized by ESI-MS, elemental analysis, single-crystal X-ray diffraction, magnetic susceptibility, and EPR spectroscopy. Electrochemical reactions as well as reactions with different chemical redox reagents have been performed and a reversible two electron oxidation per manganese ion has been identified. The reaction of L1(4)Mn44 with oxone or cerium(IV) results in the evolution of oxygen which makes this system interesting for future studies in the search for a functional mimic of the oxygen evolving complex in Photosystem II.