Comparison of the formation constants of some chromium(II) and copper(II) complexes
Abstract
The stability constants of the complexes formed in the Cr2+–tartronate (taro), –L-tartrate (tart), –phthalate (phtal), –diethylenetriamine (dien), –triethylenetetramine (trien), –L-aspartate (asp), –L-glutamate (glu), –N-methyliminodiacetate(mimda), –ethylenediamine-N,N′-diacetate (edda), and –glycylglycine (glygly) systems in aqueous solution of 1 mol dm–3 KCl at 25 °C, determined pH-metrically, are as follows: log K1taro= 3.86, log K2taro= 2.08, log K1tart= 2.04, log K1phtal= 2.48, log K1dien= 6.67, log K2dien= 2.68, log K1trien= 7.33, log K1asp= 4.67, log K2asp= 3.46, log K1glu= 4.53, log K2glu= 2.96, log K1mimda= 5.42, log K2mimda= 3.28, log K1edda= 7,86, log K2edda= 2.1 8, log K1glygly= 2.15. Protonated complexes are formed in the Cr2+–tartronate, –tartrate, –aspartate, –glutamate, and –glycylglycine systems. The formation constants of the Cr2+ and Cu2+ complexes are compared and the effects of the different ionic radii and ligand structures are discussed. The significant similarity in the co-ordination properties of these two metal ions can be explained if it is assumed that the Jahn-Teller distortion affects their co-ordination behaviour in the same way.