Molecular Design of Highly Selective Ligand Controlling the Geometry of the Donating Atoms

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Studies on the solvent extraction with the modified beta-diketones revealed that the complexations of group 13 metals depend on the bite size (O-O distance in the chelate ring) and the interligand contact in the complex. The O-O distance in the In complex is one of the longest and the complexation of In is disturbed by the substituent at the alpha-position of beta-diketone, which prevents the bite size from widening to fit the structure of the complex. The complexation of Al was found to be under the great influence of the interligand contact due to its remarkably small ionic radius. The extraction is lowered by the bulky terminal substituents. Highly selective ligands for group 13 metals have been successfully designed taking the two factors into consideration.Five 1-phenyl-3-methyl-4-acyl-5-pyrazolone derivatives have been prepared. Being derived from the five membered heterocyclic 5-pyrazolone, the O-O distances of the acylpyrazolone derivatives are confirmed to be longer than those … More of the conventional beta-diketones by the semiempirical MNDO/H calculations. Owing to their long O-O distances, the extraction of In was not disturbed and made at pH 1-2. The extraction of Al was made in the higher pH region, although its ionic radius is much smaller than that of In. Considering that the acylpyrazolones are bulky and their acidities are quite similar, it is clear that the extraction of Al is under the effect of the interligand contact. The extraction reduces as the substituent at the 4-position becomes bulkier. The quantitative separation of Al from In can be achieved with the naphthoylpyrazolones. The extraction of In does not depend on the size of the substituents. The effect of the interligand contact is also seen in the extraction of Ga. The extraction is similar to that of In and decreases as the substituents becomes bulkier. Owing to the steric repulsion between the 4-pivaloyl and 3-methyl groups, the O-O distance of pivaloylpyrazolone is narrowed and the extraction of In comes close to that of Al, resulting in a quantitative separation of Ga from Al and In. Less