Solvation Effects on the Sustainability of Lanthanum Complexes

In this article, we performed a detailed computational study of the interaction La³⁺ ion with eight perfluorinated β-diketones bearing heterocyclic rings and trifluoromethyl groups. The chelation process between trivalent lanthanum and furoyl-trifluoroacetone, thenoyl-trifluoroacetone, selenoyl-trifluoroacetone, tellurophen-trifluoroacetone, benzoyl-trifluoroacetone, pyridine-trifluoroacetone, N-methyl-pyrrol-trifluoroacetone, and N-methyl-pyrazole-trifluoroacetone has been simulated by means of DFT using three scalar relativistic effective core potentials (CRENBL ECP, Def2-ECP, and LANZL2DZ ECP) and three solvation models (C-PCM, SMD, and COSMO). Coordination models with different numbers of water molecules in the solvation shells have been tested for the calculation of stability constants and to estimate the influence of the coordination environment on the thermodynamic stability of complexes. Formation constants were evaluated using a thermodynamic cycle involving complex species with two, four, five, six, seven, eight, and ten coordination numbers. The performed calculations demonstrate that the number of water molecules in the solvation shell is a key factor for the sustainability of dicarbonyl chelates. Theoretical values of stability constants lie in the range of -10 to 23 logarithmic units and are in agreement with the experiment for low-coordinated models. TD-DFT simulation also indicates six-coordination as the most acceptable at the cc-pVDZ/CAM-B3LYP level of theory.