Performance of Tris(2-methyl-8-quinolinolato)aluminum as Fluorescent Anionophore

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An X-ray crystallographic study demonstrated that the tris complex of Al³⁺ with 2-methyl-8-quinolinol (Hmq), [Al(mq)₃], had a discrete octahedral geometry in a meridional configuration with respect to mq^- the Al-N bonds were appreciably elongated. In organic solvents, the complex reacted with water to give a lower species of a μ-oxo dimer, [Al₂O(mq)₄], and a protonated ligand, depending on the concentrations of water and of excess ligand. None of Cl^- Br^- I^- ClO₄^-, and CH₃COO^- showed any reactions with [Al(mq)₃]. The anions having high affinities to Al³⁺, such as H₂PO₄^- and F^- replaced all the ligand. The anion having a lower affinity, HSO₄^-, exclusively formed a mixed-ligand complex of [Al(mq)₂HSO₄], which had a more intense fluorescence than the others. In contrast, the corresponding 8-quinolinol (Hq) complex, [Alq₃], showed no reactions with any anions.