Concentrated Fe(III)–nitrilotriacetate solutions: study by Raman spectroscopy and ab initio calculations

Abstract

Fe(III)-nitrilotriacetate(NTA) aqueous solutions are used in various redox desulfurization processes. The nature of stable Fe-NTA complexes depends highly on parameters such as [Fe(III)] concentration, NTA/Fe ratio and pH value. These complexes can be characterized by potentiometric measurements or UV-vis spectroscopy, but only at rather low concentrations. Using synthesis of solids, Raman spectra of these solids and ab initio calculations, a rational determination of the nature of complexes stable in water at high iron concentrations was proposed from the position sensitivity of the main low wavenumber band to the coordination sphere of iron cations. This band was assigned to n(Fe-N) stretching vibrations from ab initio calculations. Depending on the pH and NTA/Fe ratio of the prepared solutions, different species were identified from the Raman spectra. The present methodology can be extended to other metal-ligand systems to elucidate the nature of stable complexes in aqueous solution.

Structure and Dynamics of Chromatographically Relevant Fe(III)-Chelates

“…Figure shows the vibrational density of states, resembling the Fe–O H 2 O stretching motions of [Fe(MSIDA)(H 2 O) 3 ] + and [Fe(MSNTA)(H 2 O) 2 ] derived via VACFs. The bands in the 450 cm –1 region may result from the Fe–O H 2 O stretching frequencies, which is in agreement with a Raman spectroscopic study of concentrated Fe–NTA solutions, where a band at 410–416 cm –1 was observed which was assigned to a coupling of FeO stretching vibrations and ligand deformations . The Fe–O H 2 O stretching motions of the studied complexes are slightly lower as for Fe(III) in pure water (513 cm –1 ), indicating reduced bond strengths and higher exchange rates.…”

Metal‐assisted regioselectivity in nucleophilic substitutions: a study by Raman spectroscopy and density functional theory calculations

“…6,7-Dichloroquinoline-5,8-dione (1) prepared according to Shaikh et al, [16] (10 mg, 0.044 mmol) and dissolved in CH 3 …”

“…[1] In particular, the investigation of bidentate coordination involving N,O donor atoms, which is of our interest as reported below, has beeen carried out for Fe complexes of benzimidazolyl phenols [2] and nitrilotriacetate. [3] In our recent studies on the synthesis of molecules with potential anti-tumour activity, [4] we investigated the reaction with pyridine and methylacetoacetate of metal complexes where 6,7-dichloroquinoline-5,8-dione is implied as ligand by its N,O donor atoms. Two different products were obtained with the same molecular composition but showing a unit introduced in different regions of the molecule (regioisomers) by a substitution reaction.…”

“…The assignment can be carried out by a thorough comparison with the theoretical spectra, which can be computed by conventional quantum mechanical methods such as the effective and widely employed density functional theory (DFT) calculations made in gas phase or in solution 1. In particular, the investigation of bidentate coordination involving N,O donor atoms, which is of our interest as reported below, has beeen carried out for Fe complexes of benzimidazolyl phenols2 and nitrilotriacetate 3…”

Recent advances in linear and nonlinear Raman spectroscopy II

“…These include: Raman spectra of Fe(III)-nitrilotriacetate aqueous solutions were analyzed at high concentrations close to those used in industrial processes by Loridant et al 156 ; a Raman study of the lithium coordination in 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (EMI-TFSI) additive systems as lithium-ion battery ionic liquid electrolytes by Hardwick et al 157 ; a solvation structure study of magnesium, zinc, and alkaline earth metal ions in N, Ndimethylformamide, N, N-dimethylacetamide, and their mixtures studied by Raman spectroscopy and DFT calculations; ionic size and electronic effects on steric congestion by Asada et al 158 ; a line shape analyses on the C O stretching bands of acetone using a vibrational coupling model by Kobayashi and Kanesaka 159 ; a Raman and ab initio study of the conformational isomerism in the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid by Lassègues et al 160 ; a study of the anomalous concentration dependence of the coordination behavior of Cl ion to Ln 3C ion (Ln 3C D rare-earth ion) in anhydrous LnCl 3 alcohol solutions by Yoshimura et al 161 ; experimental and computational studies of the solvation of lithium tetrafluorobrate in dimethyl sulfoxide by Xuan et al 162 ; modeling the physico-chemistry of acid sulfate waters through Raman spectroscopy of the system FeSO 4 -H 2 SO 4 -H 2 O by Sobron et al 163 ; and finally, a Raman spectroscopic study on the dissociation of C 6 F 5 SO 3 Li in two organic solvents with different dielectric constants by Hirankumar et al 164 …”