Polynuclear complex formation and peroxodisulphate oxidation of copper(II)–dimethylglyoximate complexes

Abstract

The interaction of copper(II) with dimethylglyoxime (H₂dmg) has been studied potentiometrically in the range pH 2.5–11.0. For H₂dmg : Cu^II= 2 : 1, only [Cu(Hdmg)₂] is present in solution; no [Cu(Hdmg)]⁺ has been detected. At H₂dmg : Cu^II= 1 : 1, the predominant species at pH 5 is still [Cu(Hdmg)₂], but at higher pH (5–6.5) there is evidence that the predominant species is a tetramer. This complex. and its glyoxime analogue. can be isolated and spectroscopic data and elemental analysis indicatean empirical formula [{Cu(Hdmg)(OH)}₄], for which a hydroxo-bridged structure retaining two [CuN₄] units is suggested. The same structure is retained in solution. The kinetics of oxidation of alkaline solutions of H₂dmg : Cu^II= 1 : 1 have been studied. The reactions proceed by interaction of the tetramer with peroxodisulphate to give two molecules of a dimer having mixed oxidation states for the metal. It is suggested that oxidation occurs preferentially at the hydroxo-bridges of the tetramer.