Application of scalar-relativistic DFT approach for calculation of structural and electronic properties of mercaptobenzothiazolyl lanthanide complexes with luminescent activity

The geometry and electronic structure of thiolate complexes of rare earth metals Ln(SR)3(thf)2, HSR = 2-mercapto-benzothiazole and Ln = Y, La, Ce, Sm, Eu, Tb, Gd, Er, Tm, in ground and first excited states were studied using nonempirical density functional PBE approach to focus the problem of theoretical description of their luminescent properties. It was found that a scalar-relativistic approximation with four-component basis set of triple-polarized quality allows to describe well the coordination of ligands. Nonrelativistic calculations with the extended basis set of the same quality and explicit treatment of f-shell electrons using SBK pseudopotential, which takes into account inner shell relativistic effects, lead to strong overestimation of Ln-S bond lengths up to 0.5 Ǻ. Meridional arrangement of SR ligands was found to be more favorable than facial one in accordance with experiment. The first excited state in all complexes correspond to π-π∗ excitation of ligand shell for exception of Sm and Eu complexes with LMCT type excited state. The difference in energy of LMCT states for Sm and Eu complexes and the difference of the geometry distortion in the excited state for Tb and Tm complexes allows qualitatively explain the strong difference in yield of luminescence of metal ions in these cases. Calculated optical properties of the complex studied are in good correspondence with the available experimental data.