Synthesis, electrochemical and photophysical properties of heterodinuclear Ru–Mn and Ru–Zn complexes bearing ambident Schiff base ligand

Abstract

While ruthenium tris(diimine) complexes have been extensively studied, this is not the case with ruthenium bis(diimine)X₂ complexes where X represents a pyridinyl-based ligand. The synthesis of a new complex ([2][PF₆]₂) bearing two ambident Schiff base ligands (HL) constituted by the assembly of phenol and pyridinyl moieties is reported. Thanks to the heteroditopic property of HL, compound [2]²⁺ was used as an original metalloligand for the coordination of a redox-active (Mn(III)) and redox-inactive (Zn(II)) second metal cation affording three heterodinuclear complexes, namely, [(bpy)₂RuL₂Mn(acac)][PF₆]₂ ([3][PF₆]₂; acac = acetylacetonate), [(bpy)₂RuL₂Mn(OAc)][PF₆]₂ ([4][PF₆]₂, OAc = acetate), and [(bpy)₂RuL₂Zn][PF₆]₂ ([5][PF₆]₂). The influence of the second metal with regard to the photophysical and electrochemical properties of the ruthenium bis(diimine)X₂ subunit was then investigated. In the case of Ru(II)–Mn(III) heterodinuclear complexes, a partial quenching of the luminescence was observed as a consequence of an efficient electron transfer process from the ruthenium to the manganese. EPR and spectrophotometric analyses of the oxidized species resulting from the one-electron oxidation of compounds [3]²⁺ and [4]²⁺ showed the formation of a Mn(IV) species for [3]²⁺ and an organic free radical for [4]²⁺.