Systematic Study of a Family of Butterfly-Like {M<sub>2</sub>Ln<sub>2</sub>} Molecular Magnets (M = Mg<sup>II</sup>, Mn<sup>III</sup>, Co<sup>II</sup>, Ni<sup>II</sup>, and Cu<sup>II</sup>; Ln = Y<sup>III</sup>, Gd<sup>III</sup>, Tb<sup>III</sup>, Dy<sup>III</sup>,
Ho<sup>III</sup>, and Er<sup>III</sup>)
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Abstract
A family
of 3d–4f [M<sup>II</sup><sub>2</sub>Ln<sup>III</sup><sub>2</sub>(μ<sub>3</sub>-OH)<sub>2</sub>(O<sub>2</sub>C<sup><i>t</i></sup>Bu)<sub>10</sub>]<sup>2–</sup> “butterflies”
(where M<sup>II</sup> = Mg, Co, Ni, and Cu; Ln<sup>III</sup> = Y,
Gd, Tb, Dy, Ho, and Er) and [Mn<sup>III</sup><sub>2</sub>Ln<sup>III</sup><sub>2</sub>(μ<sub>3</sub>-O)<sub>2</sub>(O<sub>2</sub>C<sup><i>t</i></sup>Bu)<sub>10</sub>]<sup>2–</sup> molecules
(where Ln<sup>III</sup> = Y, Gd, Tb, Dy, Ho, and Er) has been synthesized
and characterized through single-crystal X-ray diffraction, SQUID
magnetometry, and ab initio calculations. All dysprosium- and some
erbium-containing tetramers showed frequency-dependent maxima in the
out-of-phase component of the susceptibility associated with slow
relaxation of magnetization, and hence, they are single-molecule magnets
(SMMs). AC susceptibility measurements have shown that the SMM behavior
is entirely intrinsic to the Dy and Er sites and the magnitude of
the energy barrier is influenced by the interactions between the 4f
and the 3d metal. A trend is observed between the strength of the
3d-4f exchange interaction between and the maximum observed in the χ″<sub>M</sub>(<i>T</i>)