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) (Inq3) chelate crystals grown slowly from the vapor phase under vacuum (~10-6 Torr) was compared to the aluminum analogue, Alq3. In both cases, a previously unidentified close (pi)-(pi) interaction is identified, which likely impacts charge conduction. In the case of Inq3, we observe a mixture of both meridianal (mer) and facial (fac) crystals. The larger pseudohexagon mer-Inq3 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 A, respectively) than Alq3 and bond angles about the In3+ ion more distorted from an ideal octahedral geometry. The crystalline packing of merInq3 is found to closely resemble the (betta)-Alq3 phase, where both metal chelates are characterized by pairing of symmetry-related mer-optical isomers in three-dimensional (pi)-(pi) stacking interactions (~3.5 A or less). The smaller needlelike crystals were determined to be pure fac-Inq3 by powder X-ray diffraction studies. An equivalent is not observed when Alq3 is processed in an identical manner