Titrimetric studies of Cu(II)-dimethylglyoxime complexes in solution.

Abstract

This thesis describes investigations into the nature of the complexes formed between the copper(II) ion and dimethylglyoxime in solution. Titrimetric methods were employed. The pH and/or the absorbance of the solutions being titrated were monitored. When a copper(II) solution is titrated with sodium dimethylglyoximate (Na2dmg), a grey-green precipitate is formed and a sharp increase in pH occurs at a point corresponding to a Cu : dmg stoichiometry of 1 : 1. In the photometric studies, a buffered solution of Na2dmg was titrated with Cu(II), while monitoring the absorbance at 430 nm. A plot of absorbance against volume of titrant shows two points of discontinuity, one corresponding to a Cu : dmg ratio of 1 : 2 and a second at a Cu : dmg ratio of 2 : 1. This result is direct evidence for the existence not only of the well-known 1:2 complex but also of a previously unreported 2: 1 complex. A further investigation of the variation of absorbance with pH suggests that this 2:1 complex contains four copper atoms. Although the precipitate has a 1: 1 stoichiometry, and although other workers have postulated the existence of a complex of this composition in solution, no evidence for this complex in solution was found in these investigations. The resolution of this contradiction is a compelling motive for further investigations on this system.