A family of binuclear dysprosium(III) radical compounds with magnetic relaxation in ON and OFF states.

Four binuclear dysprosium compounds incorporating the radical ligand 2-(4-oxidopyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (PyNONIT) have been successfully synthesized under appropriate conditions. Centrosymmetric bimetallic Dy(2)O(2) cores in all of the compounds through double-μ(2)-oxygen atoms of the N-oxide groups are realized in a metal-radical approach for the first time. Dimers 1 and 2, of the same formula {Dy(hfac)(3)(PyNONIT)}(2) (hfac = hexafluoroacetylacetonate) but obtained by different methods, which contain almost identical local symmetry of D(4d) and Dy-(O)(2)-Dy bridging fashion, however, display no out-of-phase alternating-current (ac) signal for 1 and slow relaxation of the magnetization for 2 corresponding to the difference of the crystal packing mode. The adduct (Dy(hfac)(3)(PyNONIT)Dy(0.5)(hfac)(1.5)(H(2)O)) (3) consists of two items, the dimer Dy(hfac)(3)(PyNONIT) and the monomer [Dy(hfac)(3)(H(2)O)(2)], where the symmetry of Dy(III) ion in Dy(2)O(2) decreases to D(2d), showing slow relaxation of the magnetization at lower temperature. Interestingly, a moisture-mediated reversible solid transformation between 1 and (Dy(hfac)(3)(H(2)O)(PyNONIT)) (4) has been investigated. Spongelike 1 can undergo a transition from eight to nine coordination at room temperature through hydration. A different coordination field is mostly responsible for no ac signal noticed for 4. The structural diversity of the Dy(2) family provides an opportunity to expand the investigation on 4f single-molecule magnets. Approaches that the relaxation of the supramolecular dimer can be tuned to ON and OFF states modulated by the packing mode and ligand field are presented.