Metal Azido/Formate Molecule-Based Magnetic Complexes

The construction of new molecule-based magnetic materials has become a fascinating subject in the fields of material and coordination chemistry for magneto-structural correlations as well as the development of new molecule-based materials. However, the rational arrangement of spin carriers in the solid state with desired properties by bridging ligands is still a great challenge. Azide and formate have similar coordination modes and transfer analogous interactions associated with it. In the past two decades, dozens of metal-azido/formate complexes with peculiar structures and magnetic properties have been reported. The co-ligands and synthesis condition are the primary factors in determining the structures of the complexes. In our efforts to construct new molecule-based magnetic materials and investigate the magneto-structural correlations, in this dissertation, a series of new magnetic complexes have been successfully obtained by the selection of suitable bridging ligands and spin carriers under different contitions, and structure and magnetic properties as well as the magneto-structural correlations were investigated. The main points are summarized as follows:1、The copper-azido complexes with substituted carboxylate as co-ligand have been synthesized and studied. By using a series of structurally related carboxylate with different uncoordinated substituents as co-ligand, nine new azido-copper complexes were obtained. Structural analysis indicated the structures were based on the syn,syn carboxylate/EO azido mixed coordinating copper units and the coordination modes of the azido anions were affected greatly by the uncoordinating groups of the co-ligand. Magnetic study revealed that the syn,syn carboxylate/EO azido mixed bridges transfer ferromagnetic interactions between copper ions nearly irrelevent to the size of Cu-N-Cu angles, and azido ligands acting as high connecting mode such asμ-1,1,3 andμ-1,1,3,3 were significant in constructing complexes with long-range magnetic order.2、The metal-formate complexes with heterocyclic carboxylate as co-ligand have been synthesized and studied. As the smallest carboxylate, formate displaying multiple bridging modes and being able to mediate magnetic coupling effectively between metal ions, has been well used in preparing molecular magnetic materials. The more important thing is that it has similarity with azide both in coordination modes and transferring magnetic coupling. By using our experience in preparing metal-azido complexes with carboxylate as co-ligand, we constructed a series of complexes with interesting structure and magnetic behaviors by using formate and different heterocyclic carboxylate as bridging ligands. Different from the metal-azido complexes, the formate tends to give helix and porous structures. Magnetic study revealed that dominating anti-ferromagnetic interactions were conducted by formate, and in some cases homospin ferrimagnetism and spin canting companying with the anti-ferromagnetic interactions.3、Heterometallic 3d-3d complexes have been synthesized and studied. In the hydrothermal condition the assembling two or more kinds of metal ions in one pot give birth to series of heterometallic 3d-3d complexes. The polydentate ligands used coordinate to different kinds of metal ions using its different coordinated group for the variety of the 3d metal ions in coordination geometry and ionic radius. The introducing of two kinds of metal ions enriches the metal-azido/formate complexes. Magnetic study revealed that the magnetism of those complexes were distinct from the homometallic ones. And the magnetism can be tuned by varying the kinds of spin carriers. The successes of the magnetic control in the heterometallic 3d-3d complexes give us a new way to achieve "designing synthesis" and enrich the study of magneto-structural correlations.4、Heterometallic 3d-4f complexes have been synthesized and studied. Using the 4f ions to partly substitute the 3d ions in some structure constructed by the ligand 2-Hydroxymethylpyridine brings series of 3d-4f homometallic complexes. The lanthanide 4f ions with large radius and, in some cases, high magnetic anisotropy bring novel srtucrure and amusing magnetic behavior. The azido/formate link dicubane-like 3d-4f clusters giving a 1D chain. And without azido/formate two cubane based cluster was separated. The introducing of the 4f ions not only change the magnetic interactions between metal ions but also enhance the anisotropy and single chain magnet behaviors of the 1D chain.