Phase Behavior and Solid-State Photoreactivity of Organometallic Ionic Plastic Crystals with Cyanoborate Anions

Ionic plastic crystals (IPCs) exhibit long-range translational order with orientational disorder and enhanced molecular mobility, yet their chemical reactivity remains unexplored. Salts of the sandwich-type Ru complex cation [Ru(Cp)(C6H6)]+ ([1]+) often exhibit IPC phases, while cyanoborate salts of [1]+ undergo photochemical reactions to form polynuclear complexes in solution and in the ionic-liquid state. These properties prompted us to synthesize [1]BE(CN)3 (E = F, H, or Me) and [1]BE2(CN)2 (E = F or Et) and investigate their phase behavior and photoreactivity in IPC phases. All five salts exhibited IPC phases, with transition temperatures from the low-temperature crystalline phase to the IPC phase ranging from 277 to 378 K; three underwent the transition below 300 K. UV irradiation of these three salts in their IPC phases afforded cubane-type tetranuclear complexes from [1]BF(CN)3 and [1]BH(CN)3 with conversions of 50-77%, whereas [1]BF2(CN)2 gave an anionic dinuclear complex along with decomposition products. In contrast, irradiation of [1]BH(CN)3 and [1]BMe(CN)3 in their low-temperature crystalline phases gave conversions of only 18% and 11%, respectively. These results demonstrate that the high molecular mobility of IPCs enables solid-state photochemistry, with the salts acting as both reactants and reaction media.