On the effect of 4f electrons on the structural characteristics of lanthanide trihalides: Computational and electron diffraction study of dysprosium trichloride

The molecular and electronic structure of dysprosium trichloride, Dy Cl3, was calculated by high-level quantum chemical methods in order to learn about the effect of the partially filled 4f subshell and of the possible spin-orbit coupling on them. High-temperature electron diffraction studies of Dy Cl3 were also carried out so that we could compare the computed geometry with the experimental one, after thermal corrections on the latter. Dysprosium monochloride, DyCl, and the dimer of dysprosium trichloride, Dy2 Cl6, were also investigated by computation. We found that the electron configuration of the 4f subshell does not influence the geometry of the trichloride monomer molecule as the ground state and first excited state molecules have the same geometry. Nonetheless, taking the 4f electrons into account in the calculation, together with the 5s and 5p electrons, is important in order to get geometrical parameters consistent with the results from experiment. Based on electron diffraction and different levels of computation, the suggested equilibrium bond length (re) of Dy Cl3 is 2.443 (14) Å, while the thermal average distance (rg) from electron diffraction is 2.459 (11) Å. The molecule is trigonal planar in equilibrium. Although the ground electronic state splits due to spin-orbit coupling, the lowering of the total electronic energy is very small (about 0.025 hartree) and the geometrical parameters are not affected. In contrast with the monomeric trichloride molecule, the bond angles of the dimer seem to be different for different electronic states, indicating the influence of the 4f electronic configuration on their structure. We carried out an anharmonic analysis of the out-of-plane vibration of the trichloride monomer and found that the vibration is considerably anharmonic at 39.5 cm-1, compared with the 30.5 cm-1 harmonic value.