Synthesis And Characterization Of Co～Ⅱ Polymers For Molecular Magnetic Materials

Molecular magnetic materials were newly developed in past decades. As highly orderedmolecular systems, they are superior to traditional magnetic materials in many fields, such aslow density, solubility, tuning properties, flexibility and so on. Molecular magnetic materialsinclude pure organic molecules, organic-inorganic hybrid structures, inorganic compounds,single molecular magnets and spin crossover complexes.Metal-organic hybrid structures of paramagnetic metal ions are particularly interesting, asthese may give rise to a series of novel framework structures with potential applications in thefields of molecular magnetism and materials chemistry. A commonly used strategy in buildingsuch extended network structures is to employ bridging ligands capable of transmittingmagnetic interactions in addition to propagating.Our interests lie in the design of 1D magnetic polymers containing cobalt (II) ions linkedby first ligands with strong anisotropy and the achievement of tuning the magnetic propertyby crystal engineering of second ligands. Our studies here aimed at constructing such 1Dcobalt polymeric chain using pdc2-as first ligand, namely bridging ligand, and 2,4′-bipyridine(2,4′-bpy) as well as its derivative 5-phenyl-2,4′-bipyridine (5-ph-2,4′-bpy) as second ligands.We have obtained two families of 1D polymeric cobalt complexes in the reaction ofpyridine-2,6-dicarboxylic acid (pdcH2) with Co(NO3)2?6H2O under hydrothermal conditionsin the presence of bipyridyl as second ligands. The structure of [Co(pdc)(2,4′-bpy)2·H2O]n (1)and [Co(pdc)(5-ph-2,4′-bpy)2·H2O]n (2) was confirmed by X-ray measurement. Themagnetism characters for 1 and 2 were investigated. Antiferromagnetic coupling between CoIIions in 1 has been observed, polymer 2 possesses ferromagnetic coupling due to its distortedstructure of polymeric cobalt chains. The steric hindrance of the phenyl substituent results inthe distorted structure of neighbouring polymeric chains. As a result, the steric hindrance insecond ligand plays an important role for tuning magnetic transform. To the best of ourknowledge, this is the first example of substituent tuned magnetic transform. This report mayprovide a promising strategy for design and exploitation of new polymeric coordinationcompounds for useful applications.