Syntheses, Structures And Magnetic Properties Of Complexes Based On Mn(Ⅲ)-(Schiff Bases)

Molecule-based magnetic materials have always been a hot research field for the chemists not only because they exhibit peculiar superiorities such as better insulation, better solubility and plasticity as compared with the traditional magnetic materials but also especially because the low dimensional magnets such as Single-Molecule Magnets (SMMs) and Single-Chain Magnets (SCMs) in molecule-based magnetic materials will have their tempting potential applications in high-density information storage and quantum computation, etc. The commonly used strategies for constructing molecule-based magnet are to link the paramagnetic metal centers by the bridging ligands with strong magnetic mediating abilities such as COO, N3 and CN, etc into OD, 1D and high-dimensional molecular structures. The low dimensional structures maybe exhibit low dimensional magnetic behaviors such as SMMs and SCMs if the systems possess high spin ground state (ST) and large magnetic anisotropy while the high-dimensional arrangement will result in the long range magnetic ordering such as the ferromagnets, ferrimagnets, metamagnets arising from the contribution of strong magnetic couplings between the paramagnetic metal centers. Although the molecule-based magnetic materials with Curie temperature (Tc) above room temperature have already been discovered nowadays, none of them can be used in our life due to the air-sensitivity. Furthermore, the Tc of many structural already characterized complexes is low especially for the SMMs and SCMs, which are still very rare as well as the uncertainty of the internal magneto-structural correlation in these systems. Therefore, it seems to be very meaningful and indispensable to synthesize new complexes and investigate them to clarify the real internal magneto-structural correlation for the purpose of designing new molecule-based magnetic materials with ideal magnetic properties. MnⅢis an excellent candidate for the constructing molecular magnets because it has high ground state spin (S=2) and large magnetic anisotropy, however, the MnⅢis rather instable. Tetradentate Schiff bases ligands of Salen (N, N'-ethylenebis (salicylideneiminato) dianion) and its analogues will effectively stabilize the MnⅢand the two available axial sites for coordination enable the Mn(III)-(Schiff bases) analogues to be a suitable electron acceptor for coordination. By adjusting the substituted groups on the Salen analogues and the reaction conditions, complexes constructed by Mn(III)-(Schiff bases) analogues exhibit various different structure styles. Since the different structure often leads to different magnetic behaviors, investigating these related complexes will not only probably obtain new molecule-based magnetic materials but also help us systematically study the internal magneto-structural correlation, providing valuable information for the further work in future. In this paper, we have constructed a series of complexes based on the coordination acceptor Mn(Ⅲ)-(Schiff bases) analogues and the various coordination electron donors, Cs3[Wv(CN)8]-2H2O, K3CrⅢ(CN)6, K3FeⅢ(CN)6,K3CoⅢ(CN)6, K3CrⅠ(CN)5NO·H2O, PPh4[FeⅢ(CN)4(bpy)], K2NiⅡ(CN)4, NaN(CN)2 and KCrⅢ(Salen)(OH)2, etc. These complexes include ten OD discrete clusters,1. [MnⅢ(3-CH3)Salen]3Wv(CN)8·7CH3OH·2H2O2. [MnⅢ(5-CH3)Salen]4(OH)WⅤ(CN)8·8H2O3. [MnⅢ(3-CH3O)Salen]FeⅢ(CN)4(bpy)·5H2O4. [MnⅢ(R,R)-Salcy]4[CrⅢ(CN)6](ClO4)2·4CH3CN·6H2O5. [MnⅢacphen]6[CrⅢ(CN)6]2·8CH3OH·2H2O6.{[MnⅢ(3-CH3O)Salen]2[CrⅢ(Salen)(OH)2]}ClO4·7H2O7. [MnⅢ(Salen)]3WⅤ(CN)8·19H2O8. [MnⅢ(4-CH3O)Salen]6[FeⅢ(CN)6]2·12H2O9. [MnⅢ(3-CH3O)Salen]6CrⅢ(CN)6(ClO4)6·12H2O10. [MnⅢ(Salen)6][CoⅢ(CN)6]2·12H2O; Six 1 D chain structure,11. [MnⅢ(5-Br)Salen]N(CN)2·H2O12. [MnⅢ(5-CH3)Salen]2(0H)C104-2H2013. [MnⅢ(3-CH3)Salen]3[Crl(CN)5NO]·1.5H2O14. [MnⅢ(Salen)]6[CrⅢ(CN)6]2·8CH3OH 15. [MnⅢ(5-CH3)Salen]6[FeⅢ(CN)6]2-2CH3CN·10H2O16. [MnⅢ(5-CH3)Salen]6[CoⅢ(CN)6]2-2CH3CN·10H2O; and two 2 D complexes,17. [MnⅢ(5-CH3)Salen]6[CrⅠ(CN)5NO]2-3CH3OH·15H2O18. [MnⅢ(5-CH3)Salen]2[NiⅡ(CN)4]·3CH3OH·15H2O.IR spectroscopy characterization, elemental analyses, single crystals structure characterization and the magnetism studies of these complexes have been carried out. The result indicates that substituted groups and reaction condition play a crucial role in determining the structure styles of the complex obtained. Meanwhile, different structure results in different magnetic properties. Among these synthesized complexes, 1,2,7; 4,5,9,10 and 13,17 exhibit obvious structure transition induced by the controlling of the assembling process. For the magnetism aspect, complexes 4,5,6,8, 14 and 15 show slow magnetic relaxation in low temperature, which is reminiscent of low dimensional magnetic properties. Because of the intermolecular interactions, complexes 6,8,9,13,14 and 15 behave as the long range antiferromagnetic ordering properties. Complex 17 is a typical ferrimagnet while 10,16 only exhibit the paramagnetic properties.