Syntheses,Structures,and Magnetism Of Some Cyanide Bridged Complexes

Molecule-based magnetic materials have been explored intensively not only because of their fundamental interest but also due to their potential applications as mutifunctional materials. Of all the molecular magnetic materials, the cyano-bridged compounds are of great importance. Various cyano-bridged materials of interesting magnetic properties, including single-molecule magnets (SMMs), single-chain magnets (SCMs), high Tc magnets, photo-responsive magnets, chiral magnets, spin-crossover (SCO) compounds and so on, have been prepared and reported. This thesis investigated the abilities of several cyanide bridges, including the [Mn(CN)6]3" and [M(CN)4]2-(M= Ni, Pd, Pt), to construct molecule-based magnets. The main results are as following.1. With three pentadentate Mn2+ macrocyclic ligands, three new [Mn(CN)6]3-based complexes, have been synthesized and characterized structurally and magnetically. Compound 1 was found to be a linear MnⅡ 2MnⅢ trinuclear cluster with paramagnetic behavior, while compounds 2 and 3 are cyano-bridged 2D networks. Ferrimagnetic ordering was observed, with magnetic phase transition temperatures (Tc) around 7.0 K. These compounds are the rare examples of a small number of the [Mn(CN)6]3- based magnetic materials.2. Two tetranuclear macrocycle were synthesized and their structures, thermogravimetric analysis (TGA), and magnetic properties were characterized. Compounds 4 exhibit complete SCO behavior with thermal hysteresis loops about 20 K centered above the room temperature (T1/2↓=323 K, T1/2↑=343 K), whereas 5 exhibit gradual SCO behavior with two steps.3. Four one-dimensional heterobimetallic coordination polymers were synthesized and their structures, differential scanning calorimetry (DSC), and magnetic properties were characterized thoroughly. All the compounds are connected into 1D zigzag chain structures through cyano groups. Examination of the intermolecular contacts in compounds reveals the existence of the hydrogen bonding interactions involving the hydrogen donor groups of the ligands and the nitrogen atoms of the non-bridging cyanide groups of the [M(CN)4]2-anions. Weak π-π interactions were also found to be important for the formation of the 3D structures for compounds 8 and 9. Compounds 6 and 7 exhibit complete SCO behavior with narrow thermal hysteresis loops about 2 K centered near the room temperature. (T1/2↓=270 K and T1/2↑=272 K for 6 and T1/2↓= 272 K and T1/2↑= 274 K for 7), whereas 8 and 9 exhibit abrupt SCO at 186 and 180 K, respectively.4. Nine two/three-dimensional heterobimetallic coordination polymers were synthesized and their structures and magnetic properties were characterized thoroughly. Complexes 10-12 contain parallel stacks of rigid 2D (4,4) planar grids{Fe[M(CN)4]}∞ with the Fe(Ⅱ) axial positions occupied by monodentate ligands. Complexes 13-15 show new 3D topology structure with point symbol{32.42.52}{32.62.72}{34.43.52.65.7}2. Compared with complexes 10-12, the monodentate ligands were replaced by bis-monodentate ligands, which locate the above and below of the 2D (4,4) planar grids Fe[M(CN)4]}∞. While in complex 17, the bis-monodentate ligands bridge the 2D (4,4) planar grids into a Hofmann-like 3D coordination polymer. Magnetic studies show that complexes 10-17 are in their high-spin states and display characteristic paramagnetic behavior in the temperature range investigated.