Construction And Magnetic Research Of Octacyano-bridged Molecule-based Magnets

Designing and synthesizing the cyanide-bridged molecule-based magnets have become one of the most attractive topics in the past two decades. Recently, octacyanometalate [MⅣ/Ⅴ(CN)g]3-/4-(M=W, Mo, Nb) has attracted strong interests because of their excellent characteristics such as multiple spatial configurations, variable valence and strong coupling. However, there are still some problems in this field. For example, the eight cyanides of [M(CN)8]3-/4-(M=W, Mo, Nb) anions are not restricted in spatial dimension, as a result, it is more difficult to construct the low dimension complexes. Furthermore, the operating temperature of the functional materials is still too low, which restricts the application of the meterials in the future. In this paper, in order to realize the directional synthesis of specific function molecular magnetic materials, crystal engineering and coordination chemistry methods are used to optimize the spin carriers and the auxiliary ligands, which includes using the monodentate or polydentate organic ligand to enhance or reduce the interaction between moleculars, changing the component ratio and adjusting the coordination environment of the functional element. Therefore, this thesis includes several aspects as follows:(1) Four cyanide-bridged multinuclear cluster complexes 1-4 and nine one-dimension chain complexes 5-13 were synthesized by the versatile octacyanometalate [MⅣ/Ⅴ(CN)8]3-/4-(M=W, Mo, Nb) building units to react with the transition metal ions (CoⅡ (2,9,13), NiⅡ(1, 3,5-8), CuⅡ (4,10-12)) in the presence of large sterically hindered ligands. The cluster complexes included a pentanuclear (1), a hexanuclear (2), a fifteen-nuclear (3) and a trinuclear (4) complex. The magnetic analysis revealed that complexes 2,4,9 and 10 exhibit antiferromagnetic coupling, the rest of the complexes exhibit ferromagnetic coupling, and 13 exhibits the coexisting of the single-chain magnet and spin-glass behaviors.(2) Nine cyanide-bridged two-dimension layer complexes 14-22 were synthesized by adjusting the proportion of the octacyanometalate building unit [Wv(CN)8]3-, transition metal ions (CoⅡ (19-21), NiⅡ (22), CuⅡ (14-18)) and the monodentate organic ligand. The magnetic analysis revealed that all complexes exhibit intralayer ferromagnetic coupling, complexes 17, 18 and 22 exhibit metamagnetic behaviors; complexes 19-22 exhibit spin glass behavior because of the spin confusion in the layer caused by the interlayer antiferromagnetic coupling.(3) A double zigzag chain complex 23, two three-dimension complexes 24-25, three two-dimension complexes 26-28 and a single zigzag chain complex 29 were synthesized by the octacyanometalate building units [WⅤ(CN)8]3- and [Mov(CN)8]3- to react with FeⅡ ion in the presence of a long ditopic, rigid organic ligand to adjust the coordination environment of the metal center. The magnetic analysis revealed that complexes 23 and 24 exhibit antiferromagnetic coupling; complexes 25-27 exhibit spin crossover behavior; complex 28 exhibits both spin crossover behavior in the range of room temperature and the light induced excited spin-state trapping (LIESST) effect; complex 29 exhibits double bistable state character because of the anisotropic thermal-expansion effect. Accroding to the analysis of structure and magnetic properties, a synthesis law can be summarized, which can direct the synthesis of the spin crossover complexes in the future.