Binuclear metal complexes. Part 55. Dimanganese(II) and mixed-valence manganese(II,III) complexes of ‘strati-bis’ Schiff bases with two salen-like donating sites

Abstract

Dimanganese(II) complexes with ‘strati-bis’(two planar metal ions in a face-to-face configuration in one molecule) Schiff bases, 2,3-dimethyl-1,2,3,4-tetrakis(salicylideneimino)butane(H₄L¹) and 1,2-bis(salicylideneimino)-1,2-bis(salicylideneiminomethyl)cyclohexane, have been examined. They are fairly stable to oxidation by molecular oxygen in the solid state, but they are air-oxidized in dichloromethane to mixed-valence Mn^II–Mn^III species. The mixed-valence complex with (L¹)^4– has been isolated and characterized by electrochemical, magnetic, and spectroscopic methods. An antiferromagnetic spin-exchange interaction (–J= 6.0 cm^–1) operates between the Mn^II and Mn^III ions. It shows the transition arising from the Mn^III site and a new transition at 7.7 × 10³ cm^–1. The latter near-i.r. band has been assigned to the inter-valence transition based on the agreement of its half-bandwidth with the predicted value by Hush's theory and the solvent dependence on the band frequency. The delocalization parameter α is estimated to be 0.05, which corresponds to the class II type in the classification of Robin and Day.