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

• Published in: Chemistry : a European journal 2013-09, Vol.19 (39), p.12982-12990
• Main Authors: Sato, Rinta, Suzuki, Kosuke, Sugawa, Midori, Mizuno, Noritaka
• Format: Article
• Language: English
• Subjects: Acetal resins; Adjustment; Barriers; Cations; Chemistry; Equivalence; Ethylene Dichlorides; heterometallic complexes; Ions - chemistry; lanthanides; Lanthanoid Series Elements - chemical synthesis; Lanthanoid Series Elements - chemistry; Ligands; magnetic properties; Magnets - chemistry; Models, Molecular; polyoxometalates; Polyoxometallates; single-molecule magnets; Tungsten Compounds - chemical synthesis; Tungsten Compounds - chemistry; Tuning
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201302596

Polyoxometalates (POMs) with heterodinuclear lanthanoid cores, TBA8H4[{Ln(μ2‐OH)2Ln′}(γ‐SiW10O36)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‐SiW10O36]8− units without the use of templating cations. The incorporation of a Ln3+ ion into the vacant site between two [γ‐SiW10O36]8− units afforded mononuclear Ln3+‐containing sandwich‐type POMs with vacant sites (Ln1; TBA8H5[{Ln(H2O)4}(γ‐SiW10O36)2]; Ln=Dy, Gd, La). The vacant sites in Ln1 were surrounded by coordinating WO and LnO 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(μ2‐OH) bridging ligands, [Dy(μ2‐OH)2Ln′]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 (ΔE/kB) could be manipulated by adjusting the coordination geometry and anisotropy of the Dy3+ ion by tuning the adjacent Ln′3+ ion in the heterodinuclear [Dy(μ2‐OH)2Ln′]4+ cores. The energy barriers increased in the order: DyLu (ΔE/kB=48 K)