Research Progress and Prospect on the First Series Transition Metal-Dy Single Molecule Magnets

Among the first series transition metal (TM) ions, not only the paramagnetic TM ions (such as Cr-III, Mn-II/Mn-III, Fe-II/Fe-III, Co-II, Ni-II and Cu-II) but also diamagnetic TM ions (such as Co-III and Zn-II) can assemble with Dy-III to form the TM-Dy single molecule magnets (TM-Dy SMMs). In this paper, we survey most of the TM-Dy complexes with SMM behavior. For the TM-Dy SMMs, two interesting phenomena should be emphasized on. One is some Cr-Dy complexes possessing relatively high blocking temperature (T-8) and large coercivities, which could be ascribed to the strong magnetic couplings between Cr-III and Dy-III ions (vertical bar J vertical bar>10 cm(-1)). Another is the Fe-2(II)-Dy complex with the energy barrier of 319 cm(-1) (459 K), which is high among the TM-Dy SMMs. The reason might be that the axial symmetry of the coordination of Dy-III ion is high (D-5h). Additionally, ab initio calculations indicate the excited state also possess high axial symmetry. Besides the Cr-III-Dy and Fe-2(II)-Dy complexes, other TM-Dy SMMs usually exhibits relatively low energy barriers, which may be due to the weak magnetic interactions between paramagnetic TM ions and Dy(III )ions. To elimate the effect of the weak magnetic couplings on the relaxation behavior, the study of the DTM-Dy SMMs (DTM=diamagnetic the first series transition metal ions such as Co-III and Zn-II) has been received wide attention and their number is dramatically increasing. For the Zn-Dy SMMs, the number of the Zn2Dy trinuclear complexes is larger than that of other Zn-Dy complexes, indicating that the Zn2Dy received more attention. The reason might be that the coordination geometry of the Dy-III in the Zn2Dy complexes can be more easily modulated. Finally, we provided sonic reseach thoughts for further improving the SMM performance of the TM-Dy eoniplexes; the most important thoughts are that the axial symmetry of the coordination geometries of Dy(III )ions and the distribution of charge density of Dy-III ions in TM-Dy complexes should be controlled. For Dy-III in the TM-Dy complexes, the electrostatic repulsion between the Dy(III )ground-m(j) charge density and the ligand charge density should be minimized.