Zusammenfassung
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 P3⁻ 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 ...
Zusammenfassung
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 P3⁻ 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 D₃ to C₃. 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 Δν/Δp = -(12 ± 2) cm⁻¹/kbar, and -(22 ± 4) cm⁻¹/kbar, respectively.
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