Design, Construction And Research Of Tricyanometalate-based Low-Dimensional Molecular Magnets

Cyano-bridged molecule-based magnetic materials with reduced dimensionality, such as single-molecule magnets (SMMs) and single-chain magnets (SCMs), have attracted great research interest during the last decade. Among the cyano-based molecular precursors with ample coordinating capability, we note the ability of the tricyanometalate to link various metal ions lead to a wide diversity of structural architectures ranging from discrete polynuclear complexes to various one-dimensional (1D) assemblies. Some of them are promising cyano-bridged SMMs and SCMs. Another important subject in this field is the preparation of tunable molecular magnetic compounds. Tunable compounds are those in which the magnetic properties can be switched by some external perturbation such as light, heat, pressure, and guest molecules. This is an important objective, because such tunable compounds can be used for future molecular memory and switching devices. Furthermore, studies of the way in which magnetic properties respond to external perturbations give us some insight into the intrinsic nature of the materials. Along this line, this thesis includes several aspects as follows.1. Eighteen new cyano-bridged polynuclear compounds based on three versatile tricyanometalate building blocks [Fe(L)(CN)3]-(L=Tp, pzTp, Tp*) and M2+ions (M=Ni(1-5), Cu(6), Mn(7), Fe(9,10,12-15,17), Co(8,11,16,18)) have been rationally prepared by introducing a neutral secondary ligand (Imidazole, N-methylimidazole,4-cyanopyridine,3-aminopyridine, benzimidazole,2,2’-dipyridyl amine,1,10-phenanthroline,2,2’-bipyridine,2-acetylpyridinealdoxime, triethylenetetramine, tris(2-aminoethyl)amine), and all of them have been characterized structurally and magnetically. We succeeded in synthesizing nine trinuclears (1-9), three tetranuclears (10-12), four molecular squares (13-16), and two oxime-bridged trinuclear compounds (17,18). Magnetic measurements indicated that compounds1,2,4-6,10,16,17exhibited intramolecular ferromagnetic coupling and compounds3,8exhibited weak intramolecular antiferromagnetic interaction. In addition, compound17exhibited two types of relaxation processes and single-molecule magnets behavior.2. Eleven new cyano-bridged zigzag chain compounds based on three versatile tricyanometalate building blocks [Fe(L)(CN)3]-(L=Tp, pzTp, Tp*) and M2+ions (M=Cu(20,21), Fe(22,23,25), Mn(24), Co(26,27), Ni(19,28,29)) have been rationally prepared by introducing a neutral secondary ligand (N-methylimidazole,4-styrylpyridine,(1R,2R)-1,2-diaminocyclohexane) or coordinated solvent molecules, and all of them have been characterized structurally and magnetically. Magnetic measurements indicated that compounds19-23exhibited intrachain ferromagnetic coupling and single-chain magnets behavior. And compounds24-26exhibited weak intrachain antiferromagnetic interaction, while compound27exhibited intrachain ferromagnetic coupling. In addition, compound28showed two types of relaxation processes and long range antiferromagnetic ordering, providing a rare model example for studying the evolution from finite size chain to infinite single chain magnet, and three dimensional magnetic ordering. And compound29exhibited one single relaxation process, and the results suggested that the low temperature relaxation process in28were induced via finite size effect.3. Four new cyano-bridged{Fe2Co}(30-33) heterometallic compounds based on two versatile tricyanometalate building blocks [Fe(L)(CN)3]-(L=Tp, pzTp) and Co2+ions have been rationally prepared by introducing a neutral secondary ligand (N-methylimidazole,4-styrylpyridine,4-pyridinealdoxime), and all of them have been characterized structurally and magnetically. Compound30showed reversible, thermally and photoinduced electron transfer. Accompanying the electron transfer, the Fe2Co complex showed reversible polar-nonpolar transformation as a result of breaking of the inversion center induced by charge transfer between Fe and Co ions. Compound31was a well-isolated cyanide-bridged FeoCo double-zigzag chain that showed reversible MMCT on cooling and heating. The charge-transfer-induced spin transition occurs cooperatively between the cobalt sites and one of the two iron sites at about230K. By exploiting the light-induced transformation from diamagnetic FeⅡLS(μ-CN)CoⅢLs units to paramagnetic FeⅢLS(μ-CN)CoⅡHS units, an SCM state could be successfully photoswitched from a paramagnetic state with isolated FeⅢ ions in the complex. Furthermore, a significant change in the magnetic properties was observed as a result of electron transfer and spin transition at the Co site. Compound32was a well-isolated cyanide-bridged Fe2Co double-zigzag chain that showed single-chain magnets behavior. Dehydrated compound33showed reversible thermally induced electron transfer and single-chain magnet behavior.