title: Exchange coupling and magnetic blocking in bipyrimidyl radical-bridged dilanthanide complexes.
abstract: The synthesis and magnetic properties of three new bipyrimidyl radical-bridged dilanthanide complexes, [(Cp*(2)Ln)(2)(μ-bpym(•))](+) (Ln = Gd, Tb, Dy), are reported. Strong Ln(III)-bpym(•-) exchange coupling is observed for all species, as indicated by the increases in χ(M)T at low temperatures. For the Gd(III)-containing complex, a fit to the data reveals antiferromagnetic coupling with J = -10 cm(-1) to give an S = (13)/(2) ground state. The Tb(III) and Dy(III) congeners show single-molecule magnet behavior with relaxation barriers of U(eff) = 44(2) and 87.8(3) cm(-1), respectively, a consequence of the large magnetic anisotropies imparted by these ions. Significantly, the latter complex exhibits a divergence of the field-cooled and zero-field-cooled dc susceptibility data at 6.5 K and magnetic hysteresis below this temperature.
authors.affiliation: Department of Chemistry, University of California, Berkeley, 94720, United States.
authors.forename: Selvan
authors.initials: S
authors.lastname: Demir
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Zadrozny
authors.forename: Michael
authors.initials: M
authors.lastname: Nippe
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D060328:Magnetic Phenomena; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; D011743:Pyrimidines