Structure of copper(II) ethylenediamine complexes in aqueous and neat ethylenediamine solutions and solvent-exchange kinetics of the copper(II) ion in ethylenediamine as studied by EXAFS and NMR methods

Abstract

The structures of copper(II) complexes with ethylenediamine (en) in aqueous and neat ethylenediamine solutions have been determined by the EXAFS (extended X-ray absorption fine structure) method. The copper(II) ion in en has an axially elongated octahedral structure with three en molecules. The Cu-N bond lengths in the four equatorial and two axial positions are 204(1) and 239(2) pm, respectively. The dynamic exchange reaction between en molecules in the bulk and en molecules bound to the copper(II) ion has been studied by the nitrogen-14 NMR line-broadening method. The rate constant and activation parameters for the ethylenediamine solvent exchange are as follows: kn = (1.4 ± 0.3) X 107 s"1 at 25 °C, AH* = 9.2 ± 2.5 kJ moH, and AS* = -77 ± 10 J moH K_1. The exchange reaction may be activated via the dissociative-interchange mechanism, followed by the formation of an intermediate with two monodentate en molecules and the occurrence of substantially fast axial-equatorial interconversion in the intermediate.

Functionalization of adsorbent with different aliphatic polyamines for heavy metal ion removal: Characteristics and performance

“…The fitted coordination number (CN), bond length (R), Debye-Waller factors (r 2 ), threshold energy shift (DE 0 ), and residue (R residue ) for all the four P-Amine-b-Cu from the analysis are given in Table 2. It can be found that the Cu-C distance (distance between Cu and neighboring C atoms) was in the range of 2.84-2.87 Å, in good agreement with the results reported in the literatures [36][37][38]. In addition, the r 2 values for the Cu-C bonds were all larger than those for Cu-O or Cu-N.…”

“…In an effort to solve this problem, a data fit approach was used to match the bond length of the Cu-O and Cu-N, respectively. According to the literature, the coordination bond lengths of Cu-O and Cu-N were mainly in the range of 1.90-1.94 and 2.00-2.04 Å, respectively [33][34][35][36][37][38]. Therefore, the constraint of 1.90-1.94 Å was applied to Cu-O bonds and that of 2.00-2.04 Å was applied to Cu-N bonds in this study.…”

Solvation Structure Determination of Nickel(II) Ion in Six Nitriles Using Extended X-Ray Absorption Fine Structure Spectroscopy

“…Recently, the studies of the solvation structure of the first-row transition metal(II) ions in some non-aqueous solvents have pointed out that the bulkiness of solvent molecules can reduce the solvation number of a metal(II) ion in some instances, due to the large steric repulsion between the bound solvent molecules in the first coordination sphere. [2][3][4][5][6][7][8][9] For example, the coordination number of Mn(II), Fe(II), and Ni(II) ions is 5 and that of Co(II), Cu(II), and Zn(II) ions is 4 in a bulky solvent of 1,1,3,3-tetramethylurea (TMU).2 A similar characteristic is also observed in the bulkier hexamethylphosphoric triamide (HMPA) solvent. 3 It should be noted that the molar volume of a solvent is not a measure of the bulkiness of coordinated solvent molecules.…”

The inhibitory effect of ethylenediamine on mushroom tyrosinase

“…Ethylenediamine is a diamine with a small size which can form a complex with Cu 2+ [49] and hence block it so no more ligands can bind to it. So it is expected that it can easily approach and form a complex with it.…”