Organometallic Plastic Crystals

While plastic crystals (dynamically-orientationally disordered mesogens) are so far rare in organometallic chemistry, we discovered that formally five-coordinate ionic Ni(II) complexes [(π-allyl)NiL₃]Y and neutral M(I) complexes (π-allyl)ML₃ (M = Co, Rh, Ir) with L = PMe₃, P(OMe)₃, and other ligands undergo a phase transition from the ordered to a plastic phase. The plastic properties arise from mobility of the π-allyl group in the solid-state. For the ionic Ni compounds, besides motion of the anions Y, the cations appear to tumble on their site in the lattice, whereas the neutral M(I) complexes rotate about an axis. For recrystallization, some compounds require partial ordering in a glassy-crystalline state.