Spectroscopic and crystallographic studies of adducts of aluminium trichloride with cyclic ketones, para-quinones and ortho-quinones

Adducts of aluminium(III) chloride with 9-fluorenone, xanthenone and dibenzosuberenone have been characterised spectroscopically and by single crystal X-ray crystallography. These coloured pseudo-tetrahedral species, which are diamagnetic in both solid and solution states, serve as models for 1 : 1 adducts of AlCl3 with substituted p-quinones. These latter compounds undergo intramolecular one-electron transfer in non-aqueous solution, giving rise to paramagnetic species which have been characterised by electron spin resonance spectroscopy. The 1 : 1 adducts of AlCl3 with o-quinones show similar behaviour, although the solution chemistry reflects the differences between mono- and bi-dentate ligands.