The molecular structure of indium oxine

The radiopharmaceutical use of [111In]oxine for radiolabeling of blood products has recently met with FDA approval. The molecular structure of tris(8-quinolinolato) indium(III), "indium oxine", was determined by x-ray crystallography using a single yellow crystal grown from ethanol solution. The structural study reveals an asymmetric pseudo-octahedral N3O3 metal coordination sphere with meridional stereochemistry. This asymmetry is not detected in solution by proton NMR spectroscopy at room temperature; however, at -90 degrees C spectroscopic changes suggest slowing of a fluxional process. The molecule unexpectedly crystallized with a molecule of ethanol hydrogen-bonded to an oxygen atom of one of the oxine ligands, suggesting that hydrogen-bonding will play a role in the solvation of this complex in protic solvents.