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)Mn4](ClO4)4 and [L2(4)Mn4](ClO4)4 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)Mn4](ClO4)4 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.