Photoinduced reversible assembly of polynuclear complexes from Ru-containing ionic liquids with accompanying ionic conductivity modulations

Abstract

Solvent-free strategies for constructing coordination assemblies are desirable but remain challenging. We investigated the photochemical reactivity of ionic liquids (ILs) composed of a sandwich-type Ru complex bearing a dialkylaniline ligand [CpRu(PhNMeC₆H₁₃)]⁺ and cyanoborate anions (B(CN)₄⁻, BEt₂(CN)₂⁻, BF₂(CN)₂⁻). Upon UV irradiation, these ILs underwent ligand dissociation and formed polynuclear Ru complexes with quantitative or near-quantitative conversions: the B(CN)₄ salt yielded a cubane-type tetranuclear complex, whereas the BEt₂(CN)₂ and BF₂(CN)₂ salts produced salts containing anionic dinuclear complexes. These structural transformations resulted in a reduction of ionic conductivity by more than one order of magnitude, with full reversibility observed for the B(CN)₄ salt and near-complete reversibility for the others. The IL incorporating a cyanoalkyl-substituted arene ligand, [CpRu(PhC₄H₈CN)]BF₂(CN)₂, also formed an anionic dinuclear complex upon irradiation, but showed no thermal reversibility. This study presents a solvent-free, photoinduced approach to the formation of thermally reversible coordination assemblies, with associated tunable changes in ionic conductivity.