Lanthanide-BasedSingle-Molecule Magnets Derived fromLacunary Polyoxometalates

Toward the development of new functional materials with single-molecule magnet (SMM) behavior, novel lacunary Dawson-type polyoxometalate (POM)-based clusters containing lanthanide ions (Dy³⁺ and Tb³⁺) were synthesized and their applicability as SMMs was verified. Four discrete complexes were obtained at a mixing ratio of lanthanide ions to lacunary POM clusters of 2:2 or 1:2, yielding K₁₄[Dy₂(P₂W₁₇O₆₁)₂]·52H₂O (<b>1</b>), K₁₇[Dy­(P₂W₁₇O₆₁)₂]·52H₂O (<b>2</b>), K₁₄[Tb₂(P₂W₁₇O₆₁)₂]·52H₂O (<b>3</b>), and K₁₇[Tb­(P₂W₁₇O₆₁)₂]·53H₂O (<b>4</b>), which were characterized by single-crystal X-ray structural analysis. Detailed measurements of the alternating current (ac) magnetic properties revealed that <b>1</b> and <b>2</b> exhibited the SMM behavior (<i>U</i>_eff/<i>k</i>_B = 2.19 and 22.23 K, τ₀ = 9.02 × 10^–7 and 4.56 × 10^–5 s, <i>H</i>_dc = 3000 and 1000 Oe, respectively), unlike <b>3</b> and <b>4</b>. The distorted geometry of Dy³⁺ ions in <b>2</b> in relation to that in <b>1</b> resulted in slow magnetic relaxation caused by SMMs with larger energy barrier values, according to temperature-dependent ac susceptibility measurements and theoretical calculations. Therefore, new hybrid materials as SMMs from trivalent lanthanide ions and lacunary POM clusters can be fabricated. This study opens new avenues for constructing next-generation compounds that exhibit interesting slow magnetic relaxation based on the assembly of lanthanide ions and lacunary POMs.