Chemical and Electrochemical Behaviours of a New Phenolato‐Bridged Complex [(L)Mn II Mn II (L)] 2+ . Pathways to Mononuclear Chlorido [(L)Mn II/III/IV Cl] 0/1/2+ and Dinuclear Mono‐µ‐Oxido [(L)Mn III (µ‐O)Mn III/IV (L)] 2+/3+ Species

The X‐ray structure of a new dinuclear phenolato‐bridged Mn 2 II complex abbreviated as [(L)MnMn(L)] 2+ ( 1 ), where LH is the [N 4 O] phenol containing ligand N , N ‐bis(2‐pyridylmethyl)‐ N′ ‐salicylidene‐ethane‐1,2‐diamine ligand, is reported. A J value of –3.3 cm –1 ( H = – JŜ 1 · Ŝ 2 ) was determined from the magnetic measurements and the 9.4 GHz EPR spectra of both powder and frozen acetonitrile solution samples were analyzed with temperature. The cyclic voltammetry of 1 displays a reversible anodic wave at E 1/2 = 0.46 V vs. SCE associated with the two‐electron oxidation of 1 yielding the dinuclear Mn 2 III complex [(L)MnMn(L)] 4+ ( 2 ). The easy air oxidation of 1 gives the mono‐μ‐oxido Mn 2 III complex [(L)Mn(μ ‐ O)Mn(L)] 2+ ( 3 ). A rational route to the formation of the mixed‐valence Mn 2 III,IV complex [(L)Mn(μ ‐ O)Mn(L)] 3+ ( 4 ) starting from 1 by bulk electrolysis at E P = 0.75 V vs. SCE in the presence of one equiv. of base per manganese ion is also briefly reported. Addition of chloride ions to 1 led to the cleavage of the phenolato bridges to give the mononuclear Mn II complex [(L)MnCl] ( 5 ). Cyclic voltammetry of 5 displays two reversible anodic waves at E 1/2 = 0.21 and E 1/2 = 1.15 V vs. SCE, assigned to the two successive one‐electron abstractions giving the Mn III and Mn IV species [(L)MnCl] + ( 6 ) and [(L)MnCl] 2+ ( 7 ), respectively. The electronic signatures from UV/Visible and EPR spectroscopy of the electrochemically prepared samples of 6 and 7 confirmed the respective oxidation states. For instance, 7 displays a broad and intense absorption band characteristic of a phenolato to Mn IV charge‐transfer transition at 690 nm (2000 M –1  cm –1 ) and its 9.4 GHz EPR spectrum shows a strong transition at g = 5.2 consistent with a rhombically distorted S = 3/2 system with a zero‐field splitting dominating the Zeeman effect. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)