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A Family of Binuclear Dysprosium(III) Radical Compounds with Magnetic Relaxation in ON and OFF States

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journal contribution
posted on 03.12.2012, 00:00 by Tian Han, Wei Shi, Xiao-Ping Zhang, Lei-Lei Li, Peng Cheng
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 Dy2O2 cores in all of the compounds through double-μ2-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}2 (hfac = hexafluoroacetylacetonate) but obtained by different methods, which contain almost identical local symmetry of D4d 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)]2[Dy0.5(hfac)1.5(H2O)]2) (3) consists of two items, the dimer [Dy­(hfac)3(PyNONIT)]2 and the monomer [Dy­(hfac)3(H2O)2], where the symmetry of DyIII ion in Dy2O2 decreases to D2d, showing slow relaxation of the magnetization at lower temperature. Interestingly, a moisture-mediated reversible solid transformation between 1 and ([Dy­(hfac)3(H2O)­(PyNONIT)]2) (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 Dy2 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.

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