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 K₁^taro= 3.86, log K₂^taro= 2.08, log K₁^tart= 2.04, log K₁^phtal= 2.48, log K₁^dien= 6.67, log K₂^dien= 2.68, log K₁^trien= 7.33, log K₁^asp= 4.67, log K₂^asp= 3.46, log K₁^glu= 4.53, log K₂^glu= 2.96, log K₁^mimda= 5.42, log K₂^mimda= 3.28, log K₁^edda= 7,86, log K₂^edda= 2.1 8, log K₁^glygly= 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.