Exchange coupling and magnetic anisotropy in a family of bipyrimidyl radical‐bridged dilanthanide complexes: Density functional theory and ab initio calculations

The origin of the magnetic anisotropy energy barriers in a series of bpym^? (bpym = 2,2′‐bipyrimidine) radical‐bridged dilanthanide complexes (Cp*₂Ln)₂(μ‐bpym)]⁺ Cp* = pentamethylcyclopentadienyl; Ln = Gd^III ( 1 ), Tb^III ( 2 ), Dy^III ( 3 ), Ho^III ( 4 ), Er^III ( 5 )] has been explored using density functional theory (DFT) and ab initio methods. DFT calculations show that the exchange coupling between the two lanthanide ions for each complex is very weak, but the antiferromagnetic Ln‐bpym^? couplings are strong. Ab initio calculations show that the effective energy barrier of 2 or 3 mainly comes from the contribution of a single Tb^III or Dy^III fragment, which is only about one third of a single Ln energy barrier. For 4 or 5 , however, both of the two Ho^III or Er^III fragments contribute to the total energy barrier. Thus, it is insufficient to only increase the magnetic anisotropy energy barrier of a single Ln ion, while enhancing the Ln‐bpym^? couplings is also very important. © 2014 Wiley Periodicals, Inc.