A new mixed-valence binuclear complex containing the [Mn^IV(µ-O)₂(µ-O₂CMe)Mn^III]²⁺core: synthesis, magnetism, electron paramagnetic resonance and redox properties

Abstract

The complex [Mn,(p-O),(p-O,CMe)L,] [CIO,],-H,O 1 {L = methyl[2-(2-pyridyl)ethyl] (2-pyridyl-methy1)amine) has been synthesised and isolated in the solid state. In MeCN solution complex 1 exhibits absorption spectral features characteristic of the [ Mn,(p-O),(p-O2CMe)I2+ core. Variable-temperature (1 9.8-300 K) solid-state magnetic susceptibility data are consistent with a doublet ground state with J = -144 cm-l. The X-band EPR spectrum at 77 K exhibits a sixteen-line pattern centred at g = 2. This spectrum is attributed to the overlap of hyperfine splitting of two chemically distinct manganese nuclei (/ = $) with one hyperfine coupling constant being roughly twice the magnitude of the other. Cyclic voltammetry of 1 shows a quasi-reversible one-electron oxidation [€; = +1 .O V vs. saturated calomel electrode (SCE)] to the MnIV, species a s well a s an irreversible one-electron reduction (€,,= = -0.10 V vs. SCE) to the Mnl'l, species. Coulometric or perchloric acid oxidation generates the orange MnIV, species. The redox stability and the absorption spectral properties of this oxidised species have been investigated.

Binuclear Manganese Compounds of Potential Biological Significance. Part 2. Mechanistic Study of Hydrogen Peroxide Disproportionation by Dimanganese Complexes: The Two Oxygen Atoms of the Peroxide End up in a Dioxo Intermediate

“…The CV of the reduced solution shows a broad oxidation peak at 1.1 V NHE associated with a shoulder at 0.7 V NHE . This suggests that the Mn III Mn III species derived from 2a is unstable as already observed for other dioxo Mn 2 III,IV complexes. ,, On the other hand the resulting solution does not still exhibit the typical absorption band of the di-μ−oxo species at 460 nm. This indicates that the reduction of 2a involves probably the breaking of the oxo bridges and leads to some unidentified manganese(II) complexes.…”

Electro‐ and Photoinduced Formation and Transformation of Oxido‐Bridged Multinuclear Mn Complexes

“…The synthesis and the basic electrochemical behaviour (CV) of the triply‐bridged [Mn 2 III O(O 2 CCH 3 ) 2 (L) 2 ] 2+ , [Mn 2 III,IV O 2 (O 2 CCH 3 )(L) 2 ] 2+ and [Mn 2 IV O 2 (O 2 CCH 3 )(L) 2 ] 3+ complexes was reported by Armstrong et al for L = bpea90–92 and Mukherjee et al93–95 for L = pepmma. These authors also showed the ability of these compounds to interconvert chemically by disproportionation reactions.…”

Redox‐Induced μ‐Acetato and μ‐Oxo Core Interconversions in Dinuclear Manganese Tris(2‐methylpyridyl)amine (tpa) Complexes: Isolation and Characterization of [Mn2III(μ‐O)(μ‐O2CCH3)(tpa)2]3+

“…[Equation (3)], which reacts with residual water in the solvent [25][26][27][28][29]43] to form the binuclear complex 3 3+ by substitution of one acetato bridge by an oxo bridge [Equation (6)]. (6) However, since 3 3+ is more easily oxidizable than 2…”

“…[23] µ-Acetato/µ-hydroxo or µ-oxo bridging ligand changes in relation to Mn oxidation have been reported for synthetic binuclear Mn complexes with multidentate ancillary N and/ or O ligands. [24][25][26][27][28][29][30][31][32][33][34] Electrochemistry is a convenient way to investigate these kinds of redox-induced structural changes, and we have previously demonstrated the efficiency of the electrochemically induced core interconversion in an organic medium (CH 3 [35][36][37] have been structurally and spectroscopically characterized previously, and the electrochemical properties of 3 3+ have been briefly studied in CH 3 CN. [37,38] In contrast, complex 2 3+ , which possesses a rare mono-(µ-oxo) mono-(µ-acetato) motif, [39][40][41] has not been isolated previously and we report here its characterization by X-ray crystallography.…”