Effects of ligand substituents on the single-molecule magnetic behavior of quinonoid-bridged dicobalt compounds.

A series of quinonoid-bridged dicobalt compounds [(N4Co)2LX](ClO4)2 (1-4) (X = H, Cl, Br and OMe; N4 = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane) are synthesized and well characterized. Single crystal X-ray diffraction analyses reveal that the coordination geometry of one side Co in compounds 1-4 changes from a triangular prism to distorted octahedron with a change in the bridged-ligand substituent. Magnetic measurements show that compounds 1 and 3 exhibit single-molecule magnetic behavior. Magneto-structural analyses indicate that the difference in the relaxation barrier U between the four compounds results from the different orientations of the anisotropy axes of the two Co centers in the molecule.