Effect of steric hindrance in the 1,1,7,7-tetraethyldiethylenetriamine complexes of copper(II)

Abstract

The proton stability constants of 1,1,7,7-tetraethyldiethylenetriamine (Etidien) are slightly lower than those of dien with log K values of 9.66, 8.62, and 3.55 for Etidien compared to 9.94, 9.13, and 4.34 for dien. On the other hand the stability constant for Cu(II)-Et4dien (log = 10.1) is very much less than for Cu(II)-dien (log K, = 16.0). The ethyl groups severely hinder coordination of ligands to the out-of-plane positions of copper. The 10s-fold decrease in the stability constant is attributed primarily to blocking the coordination of water in these axial positions. The log (stability constant) of [Cu-(Et4dien)OH] + is 6.0 compared to 4.9 for [Cu(dien)OH] +, which is consistent with increased binding of coordinated water in the fourth planar position due to reduced coordination of water in the axial positions. All Etidien constants are at 25.0°a nd 0.1 M ionic strength.

Stability constants of N-methyl- and N-ethyl-substituted diethylenetriamine complexes of copper(II)

“…Proton Stability Constants, , K2, and K¡.-Proton stability constants have been reported previously for dien,7'11•14-17 l,l,4,7,7-Me3dien,18 and I,l,7,7-Et4dien. 19 Where measurements have been made at an ionic strength near 0.1, our results are in good agreement with literature values for dien. In the case of I,l,7,7-Et4dien, the literature values19 for , K2, and K% are 9.66, 8.62, and 3.55, respectively.…”

Steric effects in the complexation kinetics of cyclic and open-chain polyamines with copper(II) in basic aqueous media

“…After removal of the methanol by steam bath distillation, the product was dissolved in water, Meacyclam was synthesized and purified by the method of Kolinski and Korybut-Daszkiewicz.17 Etadien was obtained from Ames Laboratories and purified as EtadienUHCl as previously described. 18 All ligand stock solutions were standardized either by potentiometric titration with standard acid solution or by spectrophotometric mole ratio plots with standard Cu(II) solution. Cu(C104)2-6H20 was recrystallized from water and standardized by EDTA titration.…”

Spectroscopic studies of the type 2 and type 3 copper centres in the mercury derivative of laccase

“…co-ordinated water ligand has been shown to deprotonate with pK 6.8 at room temperature [20]. The hydrolysis equilibrium is evident in the low-temperature e.p.r.…”