Complexation of thorium with pyridine monocarboxylate-N-oxides: Thermodynamic and computational studies

Abstract

a b s t r a c tThe feed wastes and waste water treatment plants are the major sources for the entry of N-oxides into the soils then to aquatic life. The complexation of actinides with potentially stable anthropogenic ligands facilitate the transportation and migration of the actinides from the source confinement. The present study describes the determination of thermodynamic parameters for the complexation of Th(IV) with the three isomeric pyridine monocarboxylates (PCNO) namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO). The potentiometric and isothermal calorimetric titrations were carried out to determine the stability and enthalpy of the formations for all the Th(IV)-PCNO complexes. Th-PANO complexes are more stable than Th-NANO and Th-IANO complexes which can be attributed to chelate formation in the former complexes. Formation of all the Th-PCNO complexes are endothermic and are entropy driven. The geometries for all the predicted complexes are optimized the energies, bond distances and charges on individual atoms are obtained using TURBOMOLE software. The theoretical calculation corroborated the experimental determinations.

Reduction in Coordination Number of Eu(III) on Complexation with Pyrazine Mono- and Di-Carboxylates in Aqueous Medium

“…Effective core potential (def-ECP) with core 28 and septet spin state for Eu atom was used for optimization of Eu 3+ complexes with both the ligands . The total energies were calculated with B3LYP functional using triple-ζ valence plus polarization (TZVP) basis set as implemented in literature reports. − The present calculations neglects spin–orbit interactions which will be less effective in ligand field complexes with 4f shells of Eu . All the complexes studied here show real vibrational frequencies, confirming the minimum energy structures on the potential energy surfaces.…”

Solution Thermodynamics for the Thorium Complexation with N-(2-Hydroxyethyl) Iminodiacetic Acid

“…The details of the calorimeter are given elsewhere. 16 For the measurement of heat changes in the complexation reaction, the acidic metal solution was taken in the titration vessel and the half neutralized ligand solution was added stepwise. All the titrations were carried out at I = 1.0 M NaClO 4 and T = 298 K. The total heat output (Q i r ) for each injection was obtained by integration of power versus time data obtained from calorimeter.…”

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study

“…Upon complexations, extractants with dissociable protons are prone to protonation and deprotonation, and thus, a change in the hydrogen ion concentration (pH) is a good indicator of complexation progress. − In the present study, the sequential progress of complexation is probed by adding a concentrated ligand solution into a fixed concentration of a metal solution and monitoring the pH after each addition of the ligand. Potentiometric data were analyzed by Hyperquad program , to deduce the species present along with stability for complex formation during the course of the reaction.…”