A spectrophotometric study of the complex formation between cobalt(III) and trans-1,2-cyclohexanedinitrilotetraacetic acid (CyDTA)

Abstract

An intriguing and unique system has been observed during the otherwise routine study of the cobalt(III) complex of trans-1,2-cyclohexanedinitrilotetraacetic acid (CyDTA). Using classical spectrophotometric methods to determine the stoichiometry and the stability of a complex, significant deviations from the predicted 1:1 complex were observed in a system buffered at pH = 4.6. It is postulated that in addition to the usual 1:1 complex, the propensity of the reactants to form complexes and the strong oxidizing conditions used in this investigation result in the formation of a second, higher order complex between Co(III) and CyDTA. When the concentration of CyDTA exceeds that of Co(III), the metal:ligand ratio for this complex is 1:2. A structure is proposed, and approximate stability constants of both complexes are discussed.

NMR-Responsive Paramagnetic [M-EDTA] (M = Fe3+, Mn2+, Cu2+) Complexes to Differentiate T2-Distribution Signals of Crude Oil and Brine

“…Metal-EDTA complexes have been extensively explored using various techniques such as cyclic voltammetry, X-ray crystallography, mass spectrometry, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), negative ion photoelectron spectroscopy (NIPES), and Fourier transform infrared (FTIR) spectroscopy . However, we have applied UV–visible spectroscopy to characterize these [M-EDTA] complexes Figure a depicts UV–visible reference spectra of (i) DI water, (ii) brine, and (iii) EDTA-brine.…”

“…37 However, we have applied UV−visible spectroscopy to characterize these [M-EDTA] complexes. 38 Figure 2a depicts UV−visible reference spectra of (i) DI water, (ii) brine, and (iii) EDTA-brine. The brine and EDTA-brine solutions exhibit the absorption maxima (λ max ) at 215 and 218 nm, respectively.…”