On the complex forming tendencies of phenolic hydroxyls with scandium(III)

Abstract

The complex forming tendencies of some diphenols: 1,8-dihydroxynaphthalene- 3,6-disulphonate (chromotropic acid: CTA: (H2L)2-] and 3,4-dihydroxybenzaldehyde (3,4-DHBAL: H2L) with scandium(III) were investigated in aqueous solution by potentiometry and spectroscopy. The measurements were carried out at 25.0 ± 0.1°C and at an ionic strength of 0.1 mol.dm-3 KCl. The stochiometric protonation constants of 3,4-DHBAL, CTA and the stochiometric formation constants of their Sc 3+(aq) complex species were determined. (ScL)- type binary complex of CTA is stronger than (ScL)+ type binary complex of 3,4-DHBAL. The hydrolysis of CTA complexes resulted in [ScL(OH)] 2- and [ScL(OH)2]3- type mixed hydroxo complexes, whereas Sc3+-3,4-DHBAL complex hydrolysis also occurs and the existence of only [ScL(OH)2]- type is complex verified. Sc3+(aq) can achieve coordination number seven in CTA complex while it is six in 3,4-DHBAL complex.