Structure and stability of Eu3+ complexes derivatives from non-steroidal anti-inflammatory drug ibuprofen through a DFT study

Abstract

This work presents a study based on density functional theory (DFT) calculations of electronic structural, thermodynamic, and spectroscopic parameters of Eu3+ ibuprofenate complexes containing the ancillary bipyridine ligands 4,4′-dimethyl-2,2′-bipyridine (4,4′-dmbpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-dmbpy) or 6,6′-dimethyl-2,2′-bipyridine (6,6′-dmbpy). Formation reactions of these Eu3+ complexes as a function of the –CH3 groups position in the ancillary ligands were analyzed. Our DFT results obtained at B3LYP/MWB52/6-31G(d,p) level demonstrated that in equilibrium of ethanol solution, through a DFT study with molar fraction × = 0.05, the [Eu(Ibf)3(H2O)2] monometallic complex is thermodynamically more stable than the [Eu2(Ibf)6(6,6′-dmbpy)2] homobimetallic complex. The [Eu(Ibf)3(H2O)2] complex had a Gibbs free energy of formation about 19.2 kcal mol−1 less than the homobimetallic complex containing the 6,6′-dmbpy ligand. In addition, the [Eu2(Ibf)6(6,6′-dmbpy)2] complex is electronically less stable among the homobimetallic complexes investigated. These results were justified by increasing the distance between Eu3+ ions, low concentration of electronic density and by the QTAIM analysis performed in the coordination region of the bipyridine ligands in the optimized geometry of homobimetallic complex. In addition, the simulated IR spectra for the Eu3+ complexes studied showed a good agreement with previous experimental results. This work provides important DFT results for the modeling of photoluminescent lanthanide compounds with ancillary bipyridine ligands.