Slow magnetic relaxation in a trigonal prismatic uranium(III) complex.

Results of ac magnetic susceptibility measurements performed on the trigonal prismatic complex U(Ph(2)BPz(2))(3) demonstrate the presence of slow magnetic relaxation under zero applied dc field. Analysis of both the temperature and frequency dependence of the ac susceptibility indicate a temperature regime (T > approximately 3 K) where Arrhenius behavior dominates the relaxation processes, leading to a spin relaxation barrier of U(eff) = 20 cm(-1). The dc-field dependence of the relaxation time was studied to reveal evidence of quantum tunneling processes occurring at lower temperatures. The results suggest a general strategy for identifying further uranium(III)-based single-molecule magnets by concentrating the ligand-field contributions above and below the equatorial plane of an axially symmetric coordination complex.