Structure And Magnetic Properties Of Transition Metal Complexes Based Tetradentate Schiff Bases

In recent years, Schiff bases and their transition-metal coordination compounds have attracted people extensively attention due to their unique structures and excellent magnetic properties. This paper aims to synthesising Schiff base ligands and corresponding metal compounds, structures characterization and magnetic property measurements. The main research contents as follows:Firstly, three Schiff ligands (H2L1, H2L2and H2L3) have been synthesized under alkaline conditions based on three different chains of diamine and5-chloro-salicylaldehyde, and the structures have been characterized by elemental analyses, IR and H1NMR.Secondly, based on three main ligands (H2L1, H2L2and H2L3), twelve novel compounds are synthesized through solution method and hydrothermal method by introducing ancillary ligands (N3-, SCN-, CH3OH, N(CN)2-and Co(CN)63-) and corresponding center metal ions (Mn3+, Mn2+, Cu2+and Fe3+). Coordination compounds composition, structures and thermal stability have been characterized by elemental analyses, IR, single-crystal X-ray diffraction and thermogravimetric analysis. Structural analysis reveals that compounds1,2,3,5,10and11are of binuclear systems in which two central atoms are connected by μ2-oxo-bridged. The asymmetric unit of compound4contains two moieties, which is composed of a dimeric unit [Mn(L1)(SCN)]2and two monomeric units [Mn(L1)(SCN)(C2H5OH)]. Compounds7-9exhibit1D chain structure in which each central atoms through CN-bridged. Compounds6and12are a trinuclear structure by di-μ2-phenoxo-bridged.In the end, the magnetic properties of compounds are studies by Quantum Design MPMS-XL-7magnetometer. The results indicate that compounds1,2,4,5and12exhibit a field-induced ferromagnetic behaviour, whereas compounds3,6,7,8,9and11show antiferromagnetic interaction. In addition, we investigate the magnetostructural correlation. The study found that Jahn-Teller elongation effect plays an important role in the characteristics of the magnetic coupling for phenoxo-bridged Schiff-Mn(III) of zero dimensional compounds, and coming to the following conclusions:the Mn-0*distances are relatively longer in the case of compounds having ferromagnetic interaction, while the shorter Mn-0*distances reveal antiferromagnetic behaviour. However, the bending of the Mn-NC angle is decisive factor that affects the magnetic behaviour in cyanido-bridged Schiff-Mn(Ⅲ) of one dimensional chain-like compounds.