Manganese (III/IV) μ‐Oxo Dimers and Manganese (III) Monomers with Tetraaza Macrocyclic Ligands and Historically Relevant Open‐Chain Ligands

Abstract

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.

Hydrogen Peroxide Disproportionation Activity Is Sensitive to Pyridine Substitutions on Manganese Catalysts Derived from 12-Membered Tetra-Aza Macrocyclic Ligands

“…The dimer complex [Mn 2 (μ-O) 2 ( OH PyN 3 ) 2 ]­[ClO 4 ] 3 was dissolved in water, exhibiting its characteristic dark forest green color. Spectroscopic features matched the bands reported for other bis-μ-oxo complexes of manganese, LMCT absorptions in the region from 350 to 450 nm, the characteristic sharp band at 550 nm corresponding to a Mn­(III) d–d transition, broad absorbance centered at 650 nm (LMCT oxo to Mn­(IV)), and an intervalence band at low energy (∼750 nm) (Figure , bottom). , …”

“…Spectroscopic features matched the bands reported for other bis-μ-oxo complexes of manganese, LMCT absorptions in the region from 350 to 450 nm, the characteristic sharp band at 550 nm corresponding to a Mn(III) d−d transition, broad absorbance centered at 650 nm (LMCT oxo to Mn(IV)), and an intervalence band at low energy (∼750 nm) (Figure 4, bottom). 28,29 Single crystal X-ray diffraction (SC-XRD) analysis was carried out on the crystalline materials obtained from metalation of the ligand series. Mononuclear Mn(III) species were modeled from manganese complexation with ligands OMe PyN 3 and Py 2 N 2 , [Mn( OMe PyN 3 )F 2 ][BF 4 ], and [Mn-(Py 2 N 2 )Cl 2 ][BF 4 ] (Figure 5).…”