The iron complexes [(tpaR)Fe]– (tpa = tris(pyrrolyl-α-methyl)amine; R = Mes, tBu, Ph) are the first mononuclear transition metal complexes found to exhibit single-molecule magnet behavior. In these compounds, the iron(II) center adopts a trigonal pyramidal geometry, the environment of which facilitates large magnetic anisotropy and accordingly single-molecule magnet behavior. However, slow magnetic relaxation was observed only under an applied magnetic field due to the presence of fast quantum tunneling of magnetization under zero field. In order to mitigate through-barrier relaxation, several anisotropic metal centers have to be coupled into a multinuclear cluster. We will describe the use of tris(2-(dimethylamino)ethyl)amine (Me6tren) as a chelating, capping ligand which enforces a robust trigonal pyramidal geometry on the metal center. With this scaffold, a semiquinone radical can be installed between two transition metal-Me6tren units, resulting in the first example of a radical ligand bridging trigonal bipyramidal metal centers. The synthesis and characterization of three complexes of the formula [(M(Me6tren))2(µ2-C6H4O2)]3+ (M = Fe, Co, Ni) will be discussed. The semiquinone radical, stabilized between two metal centers, is characterized by FTIR spectroscopy and X-ray crystallography. Strong magnetic coupling is achieved through the direct exchange mechanism facilitated by the radical ligand, as is evident from dc magnetic susceptibility data. Magnetic anisotropy in this system is confirmed by magnetization measurement, and single-molecule magnet behavior is observed.

Strong magnetic exchange in dinuclear transition metal-Me6tren single-molecule magnets facilitated by a radical bridging ligand

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.