The Front Cover shows how the discovery of manganese containing enzymes has prompted a range of synthetic small‐molecule complexes to be used as structural and functional mimics of the metalloenzyme chemistries. On the basis of this work, aza‐macrocyclic ligands have resulted in a small library of Mn(III) and bis μ‐oxo Mn(III)/Mn(IV) complexes, which built on the earlier work established with open‐chain ligand scaffolds. The characterization and structural information from these studies has now allowed studies to be expanded to applications beyond mimicking the metalloenzymes that inspired their synthesis, making the transit between monomeric Mn(III) and Mn(III)/Mn(IV) μ‐oxo dimer complexes of great interest. More information can be found in the Review by K. N. Green and co‐workers.
The oxygen‐evolving complex (OEC) located in photosystem II (PSII) of green plants is one of the best‐known examples of a manganese‐containing enzyme in nature, but it is also used in a range of other biological processes. OEC models incorporate two multi‐dentate nitrogen‐containing ligands coordinated to a bis‐μ‐oxo Mn(III,IV) core. Open‐chain ligands were the initial scaffold used for biomimetic studies, but their macrocyclic counterparts have proven to be particularly appropriate due to their enhanced stability. Dimer and monomer complexes with such ligands have shown to be useful for a wide range of applications, which will be reviewed herein. The purpose of this review is to state with some clarity the different spectroscopic and structural characteristics of the Mn complexes formed with tetraaza macrocyclic ligands both in solution and solid‐state that allow the reader to successfully identified the species involved when dealing with similar complexes of Mn.
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