Dicyanamide Ions as Complexing Agents of Co(II): From Weak Ligands in Water to Strong Ones in an Ionic Liquid

Abstract

The complexation of cobalt cations (Co(II)) by dicyanamide (DCA-) in water and 1-butyl-1methylpyrrolidiniumbis(trifluoromethanesulfonyl)imide ([C1C4Pyrr][NTf2]) has been investigated by recording UV-vis spectra at 20 °C for solutions containing different ratios for the concentrations of DCAvs. Co(II) (R = [DCA-]/[Co(II)]). The variation of the absorbance at a fixed wavelength as a function of R was expressed using the Beer Lambert law, based on a chemical model assuming the formation of up to four successive cobalt-dicyanamide complexes. This allowed us to determine the speciation of cobalt and the complexation constants of all complexes in both aqueous and ionic liquid media. In water, a unique complex of [Co(H2O)5(DCA)] + exhibiting a weak complexation constant (K = 20.5) is observed. In the ionic liquid, cobalt is shown to coordinate with up to four dicyanamide anions. All species coexist until the ratio R reaches 5000 where more than 90 % of the fourth and last complex [Co(NTf2)(3-x)(DCA)4] (x-5) is formed.In addition, the extraction of cobalt towards hydrophobic ionic liquids trihexyltetradecylphosphonium dicyanamide ([P66614][DCA]) and trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)imide ([P66614][NTf2]) was carried out using various concentration of DCA both in the aqueous and ionic liquid phases. Results were found to correlate very well with the speciation of Co(II) obtained in this work.

Selective and Efficient Gold Extraction from E-Waste by Pyrrolidinium-Based Ionic Liquids with Various N-Substituents

“…NTf 2 − was chosen as the anion since it can provide low viscosity, increased hydrophobicity, and strong stability for ILs. 24 Alkyl (−R), ester (−COOR), and alkoxy (−OR) are selected as the N-substituents of the cation, among which −R is the most frequent substituent, −COOR the hydrophobic substituent, and the ether group the hydrophilic substituent and that can significantly reduce the viscosities of ILs. 25,26 The viscosities of three pyrrolidinium-based ILs at different temperatures are shown in Figure 1 With the increase of temperature, the viscosities of these three ILs drop sharply, and at 65 °C, the viscosities are 19.8, 28.6, and 16.6 mPa•s, respectively.…”

“…In this work, three pyrrolidinium-based ILs with different N-substituents were successfully synthesized. NTf 2 – was chosen as the anion since it can provide low viscosity, increased hydrophobicity, and strong stability for ILs . Alkyl (−R), ester (−COOR), and alkoxy (−OR) are selected as the N-substituents of the cation, among which −R is the most frequent substituent, −COOR the hydrophobic substituent, and the ether group the hydrophilic substituent and that can significantly reduce the viscosities of ILs. , …”

Separation of Co(II) and Ni(II) Using an Analog of Glycine-Betaine Based on Task-Specific Ionic Liquids

“…The dicyanamide anion forms moderately stable complexes with Co(II) ions in ionic liquids and in the absence of salt; more precisely, this anion is known as a weak complexing agent in water but a strong one in ionic liquid media [50]. Dicyanamide-based AGB-ILs are therefore prime candidates for reversible extraction systems based on the above-mentioned equilibrium.…”

Description of strontium precipitation in highly concentrated nitric acid

“…Eventually, Phreeqc can be connected to scripts (for example in Python or in C++) in order to allow data fittings [30,31]. However, other solutions do exist and are also relevant according to other experience of model fitting [32,33].…”