Theoretical study of geometric and spectroscopic properties of Eu(III) complexes with Ruhemann's Purple ligands

The present work aims to report the theoretical study on the geometry and spectroscopy of different Ruhemann's Purple (RP) isomers and the spectroscopic study on different [Eu(RP)2(H2O)Y-X(Cl)X] coordination compounds, where Y = 2 or 3 and X = 0, 1, 2 and 3 (for Y = 3). Density functional theory (DFT) calculations were performed to examine the coordination energies, solvent effects and theoretical intensity parameters using B3LYP/MWB52/6‐311++G(d,p) level of theory. Examination of the RP isomers geometries, tilt angles, relative coordination energies and excitation spectra indicate that the deprotonated RP is more suitable to coordinate with a lanthanide ion. The inclusion of solvent effects causes a blue shift in all theoretical excitation spectra, being crucial for a better description of the electronic situations of RP isomers and coordination compounds. The DFT calculations indicated that the probable coordination modes of the studied compounds have a distorted D2d symmetry. In addition, there is the participation of chlorides in the composition of the first coordination sphere, a fact that was neglected by many authors. The values of the theoretical intensity parameters were obtained with acceptable values of α′, αOP and g. These Ωλ parameters are in excellent agreement with that obtained experimentally in the literature. With all the theoretical data, two structures can be assigned to the Eu3+ complex with RP: [Eu(RP)2Cl2]- (coordination number = 8) and [Eu(RP)2(H2O)Cl2]- (coordination number = 9).