Heterodinuclear Lanthanoid‐Containing Polyoxometalates: Stepwise Synthesis and Single‐Molecule Magnet Behavior

Polyoxometalates (POMs) with heterodinuclear lanthanoid cores, TBA 8 H 4 [{Ln(μ 2 ‐OH) 2 Ln′}(γ‐SiW 10 O 36 ) 2 ] ( LnLn′ ; Ln=Gd, Dy; Ln′=Eu, Yb, Lu; TBA=tetra‐ n‐ butylammonium), were successfully synthesized through the stepwise incorporation of two types of lanthanoid cations into the vacant sites of lacunary [γ‐SiW 10 O 36 ] 8− units without the use of templating cations. The incorporation of a Ln 3+ ion into the vacant site between two [γ‐SiW 10 O 36 ] 8− units afforded mononuclear Ln 3+ ‐containing sandwich‐type POMs with vacant sites ( Ln1 ; TBA 8 H 5 [{Ln(H 2 O) 4 }(γ‐SiW 10 O 36 ) 2 ]; Ln=Dy, Gd, La). The vacant sites in Ln1 were surrounded by coordinating WO and LnO oxygen atoms. On the addition of one equivalent of [Ln′(acac) 3 ] to solutions of Dy1 or Gd1 in 1,2‐dichloroethane (DCE), heterodinuclear lanthanoid cores with bis(μ 2 ‐OH) bridging ligands, [Dy(μ 2 ‐OH) 2 Ln′] 4+ , were selectively synthesized ( LnLn′ ; Ln=Dy, Gd; Ln′=Eu, Yb, Lu). On the other hand, La1 , which contained the largest lanthanoid cation, could not accommodate a second Ln′ 3+ ion. DyLn′ showed single‐molecule magnet behavior and their energy barriers for magnetization reversal (Δ E / k B ) could be manipulated by adjusting the coordination geometry and anisotropy of the Dy 3+ ion by tuning the adjacent Ln′ 3+ ion in the heterodinuclear [Dy(μ 2 ‐OH) 2 Ln′] 4+ cores. The energy barriers increased in the order: DyLu (Δ E / k B =48 K)< DyYb (53 K)< DyDy (66 K)< DyEu (73 K), with an increase in the ionic radii of Ln′ 3+ ; DyEu showed the highest energy barrier.