Complex formation reaction of polypyrazolylborates with divalent metal ions in aqueous solution studied by solvent extraction technique

Abstract

Extraction behavior of divalent transition and group IIA metals with five polypyrazolylborates, H4-nB(pz)n- (pz: 1-pyrazolyl or 3,5-dimethyl-1-pyrazolyl; n = 2, 3 and 4) has been studied. Bidentate bispyrazolylborate ligands extract divalent transition metals but do not group IIA metals. The selectivity of dihydrobis(1-pyrazolyl)borate for transition metals resembles that of 8-hydroxyquinoline. Methyl substituents in the pyrazole ring increase the stability of chelates through inductive effect and decrease that for small metal ions through steric hindrance. Hydrotris- and tetrakis(1-pyrazolyl)borate, which can act as a tridentate ligand, are highly strong extracting ligands for divalent transition metals. Moreover, these ligands extract Be(II), Mg(II) and Ca(II). Steric characteristics of the ligands contribute to anomalously high stability of the chelates and selectivity for the metal ions. © 1991, The Japan Society for Analytical Chemistry. All rights reserved.