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: the B(CN)₄ salt yielded a cubane-type tetranuclear complex, whereas the BEt₂(CN)₂ and BF₂(CN)₂ salts produced dinuclear species. 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, which exhibited minor thermal decomposition. In contrast, the IL incorporating a cyanoalkyl-substituted arene ligand, [CpRu(PhC₄H₈CN)]BF₂(CN)₂, formed an amorphous, viscoelastomeric coordination polymer and did not exhibit thermal reversibility. This study presents a solvent-free approach for the construction of reversible, photoresponsive ionic assemblies with tunable ionic conductivity.