Syntheses, Structures And SMM Behaviors Of 8/9/10-nuclearity Oxygen-bridged Cr-4f Clusters

Polynuclear oxygen-bridged 3d-4f clusters have been demonstrated to be good candidates for SMMs because not only the preferred ferromagnetic coupling between metal ions could lead to a high-spin ground state, but also some Ln3+ ions (such as Dy3+ and Tb3+) could provide considerable single-ion anisotropy, deriving from the large unquenched orbital angular momentum. However, Cr-Ln SMMs are still rare, which may be due to the relatively inert nature of the Cr3+ ion. Therefore, in this thesis some new structures containing Cr-Ln cluster units were designed and synthesized. Their magnetic properties were investigated.(1) Base on phthalic acid, mixed solvent DMF/H2O and different anions, two series of Cr-Ln clusters with two kinds of structure types were synthesized:the double capped hexagonal-bipyramidal metal skeleton structure:(Me2NH2)3[Ln4Cr6(?4-O)3(?3-OH)6(L1)6(NO )6(HCOO)3] (Ln=Gd(1); Tb(2); Dy(3)) and the distortion square antiprism geometry: [Ln4Cr4(?4-O)4(?3-OH)4(L1)4(H2O)12]·(ClO4)4 (Ln=Gd(4); Tb(5); Dy(6)). The success on preparing of 8-nuclearity and 10-nuclearity compounds in DMF at high temperature provides a new way to obtain multi-nuclear Cr-Ln compounds. Magnetization versus dc magnetic field analysis shows that 1 and 4 bear obvious ferromagnetic interaction,2 and 3 exhibit antiferromagnetic interaction, the magnetization of 5 and 6 decreases with the decreasing temperature; AC magnetic susceptibility measurements reveal that 2 is a SMM excluding the Spin Glass Behavior and the Three-Dimensional Magnetic Order Phenomenon.2's blocking temperature is about 4.OK, pre-exponential factor ?0 and effective energy barrier ?eff/kB are 4.2×10-7s and 22.7K.3 shows relaxation of the magnetization and has SMM behaviors,3's blocking temperature is about 4.OK, pre-exponential factor To and effective energy barrier ?eff/kB are 3.0×10-/ s and 24.23K.6 shows relaxation of the magnetization at T=2.0K. Using the Debye model we estimated compound 6's ?eff/kB is 10.82K. and it has a single relaxation progress.(2) With sodium chloroacetate as ligand and partially hydrolyzed glycoic acid as co-ligand, three common-vertex-ditrigonal bipyramids configuration Na3[Ln6Cr3(?3-OH)12(ClCH2COO)6(OCH2COO)6(H2O)12]·24H2O (Ln=Gd(7), Tb(8);Dy(9)) clusters were synthesized. Magnetization versus dc magnetic field for 7?8 and 9 analysis shows that they all bear obvious ferromagnetic interaction. In addition, compound 8 and 9 exhibit the magnetic phase transition phenomenon below 6K. Ac magnetic susceptibility test was carried out for 8 and 9, both bear slow magnetic relaxation behavior of single molecule magnets and the blocking temperature of 8 is up to 4.2K but 9's blocking temperature is below 2.OK. Arrhenius fitting of x" values of 8, gives pre-exponential factor ?0 and effective energy barrier ?eff/kB are 1.01×10-9s and 41.8K.9 have SMM behaviors.(3) The assembly rules of the 8/9/10-nuclearity oxygen-bridged Cr-Ln clusters in this thesis were summarized.