Structure and Three-Dimensional Crystal Packing Preferences for mer-Tris(8-quinolinolato)Indium(III) Vapor-Phase-Grown Crystals

Evaluation of indium(III) tris(8-quinolinolato) (Inq 3 ) chelate crystals grown slowly from the vapor phase under vacuum (∼10 - 6 Torr) was compared to the aluminum analogue, Alq 3 . In both cases, a previously unidentified close π−π interaction is identified, which likely impacts charge conduction. In the case of Inq 3, we observe a mixture of both meridianal ( mer ) and facial ( fac ) crystals. The larger pseudohexagon mer -Inq 3 crystals were analyzed by single-crystal X-ray diffraction and showed average In−N and In−O bond lengths significantly longer (0.22 and 0.26 Å, respectively) than Alq 3 and bond angles about the In 3+ ion more distorted from an ideal octahedral geometry. The crystalline packing of mer -Inq 3 is found to closely resemble the β-Alq 3 phase, where both metal chelates are characterized by pairing of symmetry-related mer -optical isomers in three-dimensional π−π stacking interactions (∼3.5 Å or less). The smaller needlelike crystals were determined to be pure fac -Inq 3 by powder X-ray diffraction studies. An equivalent is not observed when Alq 3 is processed in an identical manner.