Magnetic and Spectroscopic Study on a New Asymmetric Mixed‐valence Mn2(II,III) Coordination Compound

A new dinuclear mixed-valence compound [MnIIMnIII(bttpnol)(O2C–C6H4–NO2)2]ClO4 was synthesized by using the asymmetric heptadentate ligand N-(2-hydroxybenzyl)-N,N′,N′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (H2btppnol). One central manganese atom assumes N3O3 and the other N2O4 coordination sphere. Both manganese ions are bridged by the alkoxy-group of the dinucleating ligand and two bidentate carboxylate groups of the nitrobenzoate ligands. The structural data show clearly that MnIII prefers the more oxygen rich donor set. Cyclic voltammetry measurements reveal that the mixed-valence state Mn2(II,III) could be reduced to Mn2(II,II) at E1/2(1) = –0.53 V and oxidized to Mn2(III,III) at E1/2(2) = 0.52 V (vs. ferrocene). Measurements of the magnetic susceptibility reveal a weak antiferromagnetic coupling with J = –8.5 cm–1. The mixed valence state was additionally confirmed by EPR spectroscopy showing the hyperfine signal of the S = 1/2 state of Mn2(II,III).

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