Lanthanide bisphthalocyanine single-molecule magnets: A DFT survey of their geometries and electronic properties from lanthanum to lutetium

By using density functional theory (PBE functional and Grimme's dispersion correction) we studied how a stepwise addition of 4f electrons influences the geometries and electronic properties of lanthanide bisphthalocyanine (LnPc(2)) single-molecule magnets (SMMs). To handle the convergence problems, which are common for lanthanide compounds, we tested DN, DND and DNP basis sets. The calculations for all fifteen bisphthalocyanines were possible to complete only with DN basis set, for which geometries optimized are in a reasonable agreement with the experimental X-ray diffraction data; on the other hand, the use of DND and DNP produces convergence problems and unrealistic geometries. Selected electronic parameters including HOMO, LUMO, HOMO-LUMO gap energies, charge and spin of central metal atom calculated with DN basis set were analyzed. In the case of closed-shell ions La3+ and Lu3+ no spin transfer to phthalocyanine ligands is observed. In most complexes (Ce, Pr, Tb-Yb) unpaired electrons are transferred to phthalocyanine ligands, whereas for Nd-Eu, the spin of Ln atom increases. The most unexpected observation is a loss of the sole unpaired f-electron of cerium, which means that its oxidation state is Ce4+ and not Ce3+: this converts CePc2 into a closed-shell species.