Schiff Base Transition Metal Clusters Synthesis, Characterization And Magnetic Study

In recent years, a rapid expansion has been witnessed on the research of Schiff-base compounds because of their potential applications in the areas of catalysis, optics, bioactivity, electrochemistry and magnetic. In most cases, Schiff-base derivatives are very easily combine to metal ions because of having more coordinating atoms. Metal clusters featuring Schiff-base ligands, however, are still quite limited in number. In this paper, the syntheses, characterization and magnetic properties of clusters which are formed with Schiff-base ligands and metal of manganese ions have been investigated. Four manganese Schiff-base compounds have been synthesized. two manganese clusters have been structurally determined and their magnetic properties have been studied. In addition, a cobalt compound formed with (bnzim)₂CH₂ ligand has been synthesized. The structure, UV-vis spectra and electrochemical property of this compound has been discussed.The contents include four parts as follows:(1) Four manganese and an iron Schiff-base compounds have been synthesized and characterized by EA, IR, TGA, and two Mn clusters have been structurally determined, including: [Mn₃(O₂CPh)₄(sae)2](1), [Mn₆O₂(O₂CPh)₂(salox)₆(CH₃OH)₃ (CH₃CN)]·3H₂O(2·3H₂O). The core of compound 1 includes three linear array manganese ions, The central metal Mn is accordingly determined as Mn(II) ion and coordinated octahedrally by the Schiff-base ligand, two terminal manganese ions are regarded as Mn(III) ion and have a distorted square pyramidal geometry. The compound 2 has of two same {Mn₃(μ₃-O)} units, the atoms of Mn₃ units almost exist in a plane(dihedral angle 0.2348 A). Apart from the participation of the ligands, the Mn1 of one Mn₃ units is coordinated with two independent MeOH; the Mn4 of another Mn₃ units is coordinated with one independent MeOH and one independent MeCN. six of the salox^2- ligands show two different coordination modes, four of the salox^2- ligands show the commonμ₂:η¹:η¹:η¹ coordination mode, while the other two adopt the rareμ₃ :η¹:η²:η¹ mode. All manganese ions are regarded as Mn(III) ion in compound 2. (2) Variable temperature susceptibility measurement indicates compound 1 exhibits dominant anti-ferromagnetic interactions between the manganese ions. The susceptibility data is fit according to Hamiltonian on the base of the structure, leading to parameters: J/k = -11.62 K, g = 1.98. Investigating magnetic property of compound 2 indicates dominant anti-ferromagnetic interactions also exist between the Mn(III) ions. The Curie-Weiss constant (θ= -0.071K) is obtained from a linear fit of the 1/x_m data between 45-300 K.(3) A (bnzim)₂CO of cobalt compound [Co((bnzim)2CO)Cl2] has been synthesized reacting (bnzim)₂CH₂ with CoCl₂. The process of ketonization of methylene of (bnzim)₂CH₂ was investigated using spectroscopy and electrochemistry method. The experimental results reveal that there were new species forming in the reaction system and the formation of new species was related to the dissolving oxygen in the mixture. Oxygenation mechanism was thus proposed, in which oxygen atom transfer from a superoxo intermediate species {(bnzim)2CH₂)Co(III)-O-O} to the methylenic carbon of (bnzim)₂CH₂, and then goes O-O hemolytic cleavage and hydrogen migration to give intermediate species [Co((bnzim)2CHOH)]²⁺. The ketonization was achieved after [Co((bnzim)2CHOH)]²⁺ repeating the process.