Results of SDFT calculations were used to construct and check features of a generally applicable qualitative approach to understanding magnetic coupling in rare-earth-rich compounds. Using fragments based on structures of metal-rich lanthanide compounds, we have investigated molecular and low-dimensional extended structures, including Gd3I6(OPH3)12, Gd6I12Co(OPH3)6, and Gd2Cl3. Open-d-shell clusters facilitate strong ferromagnetic coupling whereas in the closed-d-shell systems prefer antiferromagnetic coupling. The f-d exchange interaction, mediated by spin polarization of both filled and partially-filled metal-metal bonding orbitals, was described for the model system Gd3I6(OPH3)12
n+ using basic perturbation methods. This method has been successful for predicting the magnetic ground state for models of Gd[Gd6I12Fe] and Gd2Cl3.