Crystal Structure offac−Ir(ppy)₃and Emission Properties under Ambient Conditions and at High Pressure

Solution and refinement of the crystal structure of fac − Ir(ppy) 3 is severely hampered by systematic twinning and pseudo-symmetry. fac − Ir(ppy) 3 crystallizes in the centrosymmetric space group P 3̄ as has been deduced from single-crystal structure refinement and investigations of the second harmonic generation (SHG) of fac − Ir(ppy) 3 powder as compared to two standard materials. The topology of the molecular packing of fac − Ir(ppy) 3 is identical to the packing observed for [Ru(bpy) 3 ] 0, however, the site symmetry of all Ir(ppy) 3 molecules is necessarily lowered from D 3 to C 3 . Packing motifs with intermolecular “π−π interactions” of T-shaped and “shifted π stack” geometry are realized. The systematic twinning leads to the occurrence of crystalline domains with rigorously alternating chirality within the bulk of the domains but with homochiral fac -Ir(ppy) 3 contacts at the domain interfaces. These differences in packing motifs are displayed in the emission spectra and in the high-pressure-induced shifts of the emission. The emission maximum of the bulk material at 18 350 cm - 1 (545 nm) and of the domain interfaces at 19 700 cm - 1 (507 nm) experience for p < 25 kbar and T = 295 K red shifts of Δν̄/Δ p = −(12 ± 2) cm - 1 /kbar, and −(22 ± 4) cm - 1 /kbar, respectively.