Lanthanoid-containing open wells-dawson silicotungstates: Synthesis, crystal structures, and properties

摘要

Five novel lanthanoid-containing silicotungstates with polymeric crystal structures [Ln2(H2O)7Si2W 18O66]n10n- [Ln = GdIII (Gd-1 and Gd-2), TbIII, HoIII] and [Dy2(H 2O)6.5 (C2H4O2) 0.5Si2W18O66]n 10n- were obtained from the one-step reaction of Na10[SiW9O 34] ? nH2O with Ln(NO3)3 ? nH2O in a sodium acetate buffer. The compounds were characterized by single-crystal X-ray diffraction and a wide range of analytical methods, including FT-IR, UV/vis, and photoluminescence spectroscopy as well as electrochemistry and thermogravimetric analysis. This new polyoxotungstate series is the first example of lanthanoids embedded in the open Wells-Dawson silicotungstate anion [α-Si2W18O66] 16-. The lanthanoid-containing Wells- Dawson-type polyoxoanions [Ln2(H2O)7Si2W18O 66]10- [Ln = GdIII (Gd-1 and Gd-2), Tb III, HoIII] and [Dy2(H2O) 6.5 (C2H4O2)0.5Si 2W18O66]10- are linked by Ln 3+ cations to form 3D architectures for Gd-1 or 2D frameworks for the isostructural compounds Tb-2, Dy-2, Ho-2, and Gd-2. The structure-directing influence of the lanthanoid cation on the local structure of the dimeric building blocks and on the crystal packing motifs is investigated in detail. The photoluminescence properties of Tb-2 and Dy- 2 were investigated at room temperature, and Ho-2 exhibits an interesting photochromic behavior. The magnetic susceptibility of Gd- 1 and Gd-2 was studied in the temperature range between 2 and 300 K for its effective magnetic moment.