Outer-sphere complexation of tris(8-quinolinolato)-aluminum(III), -gallium(III) and -indium(III) with 3,5-dichlorophenol: Effect of water on the synergistic extraction

Synergistic extraction of Al(III), Ga(III), and In(III) with 8-quinolinol ( Hq) in chloroform has been studied using 3,5-dichlorophenol (DCP) as the sy nergist. The distribution ratio of the metal (III) was greatly enhanced in the presence of DCP. This enhancement is ascribed to the outer-sphere compl exation of tris(8-quinolinolato)metal(III) (Mq(3); M = Al, Ga, and In) with DCP in the organic phase through hydrogen bonding. The composition of the complexes was found to be Mq(3). nDCP (n = 1-3) for all three metals (III). The formation constants of the outer-sphere complexes, beta(s,1), beta(s,2 ), and beta(s,3), were determined by a least-squares method. To evaluate th e hydrogen bonding ability of Mq(3), an IR study was carried out in anhydro us chloroform. The existence of hydrogen bonding between Mq(3) and DCP was ascertained and the formation constants, beta(s,1)-beta(s,3), were determin ed. It is found that the formation constants in the water-saturated solvent (the extraction system) were less compared with those in anhydrous conditi ons. The hydration of Mq(3) chelates, evidenced by IR, can be held responsi ble for this reduction.