Exchange Coupling and
Magnetic Blocking in Bipyrimidyl
Radical-Bridged Dilanthanide Complexes
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Abstract
The synthesis and magnetic properties of three new bipyrimidyl
radical-bridged dilanthanide complexes, [(Cp*<sub>2</sub>Ln)<sub>2</sub>(μ-bpym<sup>•</sup>)]<sup>+</sup> (Ln = Gd, Tb, Dy),
are reported. Strong Ln<sup>III</sup>-bpym<sup>•–</sup> exchange coupling is observed for all species, as indicated by the
increases in χ<sub>M</sub><i>T</i> at low temperatures.
For the Gd<sup>III</sup>-containing complex, a fit to the data reveals
antiferromagnetic coupling with <i>J</i> = −10 cm<sup>–1</sup> to give an <i>S</i> = <sup>13</sup>/<sub>2</sub> ground state. The Tb<sup>III</sup> and Dy<sup>III</sup> congeners
show single-molecule magnet behavior with relaxation barriers of <i>U</i><sub>eff</sub> = 44(2) and 87.8(3) cm<sup>–1</sup>, 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