|Title||Lanthanide-Radical Magnetic Coupling in [LnPc2]0: Competing Exchange Mechanisms Captured via Ab Initio Multi-Reference Calculations|
|Publication Type||Journal Article|
|Year of Publication||2020|
|Authors||Huang, H, Van den Heuvel, W, Soncini, A|
|Journal||QUANTUM MATERIALS RESEARCH|
We present a computational investigation of the intramolecular exchange coupling in [LnPc2]0 (Ln = Tb, Dy, Ho, and Er) between the Ln3+ 4f electrons and the spin-1/2 radical on the phthalocyanine ligands. A series of ab initio multi-configurational/multi-reference Complete/Restricted Active Space Self-Consistent-Field calculations (CASSCF/RASSCF), including non-perturbative spin–orbit coupling, were performed on [LnPc2]0 and on the smaller model compound [LnPz2]0. We find that the exchange coupling mechanisms are restricted by symmetry, but also dependent on the spin polarization effect triggered by the Pc2 ligands π–π∗ excitations. The calculated exchange splittings are small, amounting to at most a few cm−1, in disagreement with previous literature reports of strong antiferromagnetic coupling, but in good agreement with recent EPR experiments on [TbPc2]0. Furthermore, the coupling strength is found to decrease from [TbPc2]0 to [ErPc2]0, with decreasing number of unpaired electron spins in the lanthanide ground (Hund's rule) Russell–Saunders term.