Complexation thermodynamics of tetraalkyl diglycolamides with trivalent f-elements in ionic liquids: Spectroscopic, microcalorimetric and computational studies

Seraj A. Ansari, Prasanta K. Mohapatra (Corresponding Author), Sk Musharaf Ali, Neetika Rawat, Bhupinder S. Tomar, Andrea Leoncini, Jurriaan Huskens, Willem Verboom

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Abstract

The thermodynamics of lanthanide complexation with a series of diglycolamides (DGAs) containing varying alkyl chain lengths (methyl, ethyl, n-butyl and n-hexyl) was studied in [C4mim][Tf2N], a room temperature ionic liquid. The stability constants, enthalpies and entropies of complexation were determined by spectrophotometry and calorimetry. All the DGA ligands formed a 1:3 (Nd3+/DGA) complex as the limiting species, and their stability constants increased linearly with increasing alkyl chain length. The stability constants of the Nd3+/DGA complexes are orders of magnitude higher in [C4mim][Tf2N] as compared to those observed in aqueous medium. For all the complexes, the enthalpy of complexation was negative with a positive entropy change, indicating that the complexation was driven by both enthalpy and entropy. The enthalpy changes observed in [C4mim][Tf2N] medium were more exothermic than those in the aqueous medium. Fluorescence lifetime data indicated that the complexation proceeded via the replacement of water molecules from the primary coordination sphere of the metal ion. DFT calculations were performed on the structures of the different Nd3+/tetramethyl DGA (TMDGA) complexes, and the corresponding free energies in both gas and solution phases were calculated. Insights into the structural features by DFT studies confirmed that the nature of Ln3+/DGA complexes formed in [C4mim][Tf2N], n-dodecane, and aqueous medium and that in the crystalline state is identical.

Original languageEnglish
Pages (from-to)708-716
Number of pages9
JournalNew journal of chemistry
Volume42
Issue number1
Early online date29 Nov 2017
DOIs
Publication statusPublished - 7 Jan 2018

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Ionic Liquids
Complexation
Ionic liquids
Thermodynamics
Enthalpy
Entropy
Chain length
Discrete Fourier transforms
Lanthanoid Series Elements
Spectrophotometry
Calorimetry
Rare earth elements
Free energy
Metal ions
Gases
Fluorescence
Ligands
Crystalline materials
Molecules
Water

Cite this

Ansari, Seraj A. ; Mohapatra, Prasanta K. ; Musharaf Ali, Sk ; Rawat, Neetika ; Tomar, Bhupinder S. ; Leoncini, Andrea ; Huskens, Jurriaan ; Verboom, Willem. / Complexation thermodynamics of tetraalkyl diglycolamides with trivalent f-elements in ionic liquids : Spectroscopic, microcalorimetric and computational studies. In: New journal of chemistry. 2018 ; Vol. 42, No. 1. pp. 708-716.
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Complexation thermodynamics of tetraalkyl diglycolamides with trivalent f-elements in ionic liquids : Spectroscopic, microcalorimetric and computational studies. / Ansari, Seraj A.; Mohapatra, Prasanta K. (Corresponding Author); Musharaf Ali, Sk; Rawat, Neetika; Tomar, Bhupinder S.; Leoncini, Andrea; Huskens, Jurriaan; Verboom, Willem.

In: New journal of chemistry, Vol. 42, No. 1, 07.01.2018, p. 708-716.

Research output: Contribution to journalArticleAcademicpeer-review

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T2 - Spectroscopic, microcalorimetric and computational studies

AU - Ansari, Seraj A.

AU - Mohapatra, Prasanta K.

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AU - Rawat, Neetika

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AU - Verboom, Willem

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N2 - The thermodynamics of lanthanide complexation with a series of diglycolamides (DGAs) containing varying alkyl chain lengths (methyl, ethyl, n-butyl and n-hexyl) was studied in [C4mim][Tf2N], a room temperature ionic liquid. The stability constants, enthalpies and entropies of complexation were determined by spectrophotometry and calorimetry. All the DGA ligands formed a 1:3 (Nd3+/DGA) complex as the limiting species, and their stability constants increased linearly with increasing alkyl chain length. The stability constants of the Nd3+/DGA complexes are orders of magnitude higher in [C4mim][Tf2N] as compared to those observed in aqueous medium. For all the complexes, the enthalpy of complexation was negative with a positive entropy change, indicating that the complexation was driven by both enthalpy and entropy. The enthalpy changes observed in [C4mim][Tf2N] medium were more exothermic than those in the aqueous medium. Fluorescence lifetime data indicated that the complexation proceeded via the replacement of water molecules from the primary coordination sphere of the metal ion. DFT calculations were performed on the structures of the different Nd3+/tetramethyl DGA (TMDGA) complexes, and the corresponding free energies in both gas and solution phases were calculated. Insights into the structural features by DFT studies confirmed that the nature of Ln3+/DGA complexes formed in [C4mim][Tf2N], n-dodecane, and aqueous medium and that in the crystalline state is identical.

AB - The thermodynamics of lanthanide complexation with a series of diglycolamides (DGAs) containing varying alkyl chain lengths (methyl, ethyl, n-butyl and n-hexyl) was studied in [C4mim][Tf2N], a room temperature ionic liquid. The stability constants, enthalpies and entropies of complexation were determined by spectrophotometry and calorimetry. All the DGA ligands formed a 1:3 (Nd3+/DGA) complex as the limiting species, and their stability constants increased linearly with increasing alkyl chain length. The stability constants of the Nd3+/DGA complexes are orders of magnitude higher in [C4mim][Tf2N] as compared to those observed in aqueous medium. For all the complexes, the enthalpy of complexation was negative with a positive entropy change, indicating that the complexation was driven by both enthalpy and entropy. The enthalpy changes observed in [C4mim][Tf2N] medium were more exothermic than those in the aqueous medium. Fluorescence lifetime data indicated that the complexation proceeded via the replacement of water molecules from the primary coordination sphere of the metal ion. DFT calculations were performed on the structures of the different Nd3+/tetramethyl DGA (TMDGA) complexes, and the corresponding free energies in both gas and solution phases were calculated. Insights into the structural features by DFT studies confirmed that the nature of Ln3+/DGA complexes formed in [C4mim][Tf2N], n-dodecane, and aqueous medium and that in the crystalline state is identical.

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