Synthesis, Crystal Structure And Characterization Of Rare Earth-Polyoxotungstates

In this paper, eleven unreported compounds have been synthesized by utilizing the pre-synthesized pseudo-Keggin and Anderson clusters as precursors and adjusting reaction conditions and reaction materials via water solution synthesis methods. These compounds are structurally characterized by elemental analyses, IR, UV, TG and single crystal X-ray diffractions. The magnetic properties of 8-10, the fluorescent activity of 3 and 9, and the cyclic voltammograms of 7 have been studied.1. Seven 1D chain compounds have been gained, based on [H2W12O40]6- polyoxoanions as building blocks and lanthanide ions as bridging ions: (NH₄)₅[Ce(NO₃)₂(H₂O)₃H₂W₁₂O₄₀] (1) (NH₄)₅[Pr(NO₃)₂(H₂O)₃H₂W₁₂O₄₀] (2) (NH₄)₅[Nd(NO₃)₂(H₂O)₃H₂W₁₂O₄₀] (3) (NH₄)₅[Gd(NO₃)₂(H₂O)₃H₂W₁₂O₄₀]·H₂O (4) (NH₄)₅[Dy(NO₃)₂(H₂O)₃H₂W₁₂O₄₀] (5) (NH₄)₅[Ho(NO₃)₂(H₂O)₃H₂W₁₂O₄₀]·H₂O (6) (NH4)6[Ce(H2W12O40)(C4H₂O4)(NO3)(H₂O)3] (7)1-6 are constructed by inorganic components. In their structures, polyanions are bridged by Ln ions via the coordination of the bridging oxygen atoms and terminal oxygen atoms, forming a W–Ot′–Ln–Ob–W linkage; and through the W–Ot′–Ln–Ob–W linkage a one-dimension infinite linear chain with alternating cations and anions is formed. 1-6 represent the first example that two types of inorganic oxoanions (NO3- and [H2W12O40]6-) simutaneously coordinate to LnIII. When added the C4H4O4 into the similar synthesis system to 1-6, 7 was attained. X-ray structural analysis reveals that the structure of 7 is similar to 1-6 except that one [C4H4O2]2- replaced one NO3- ion. 7 represents the first characterized compound that maleinate as organic ligands in constructing LnPOM architecture, and the Ce³⁺ ions are coordinated by four different types of ligands.2. Four novel compounds have been gained, based on [Cr(OH)6Mo6O18]3- polyoxoanions as building blocks and lanthanide ions as decorated or connected radicle: [Ce(H₂O)7Cr(OH)6Mo6O18]n·4nH₂O (8)[Sm(H₂O)7Cr(OH)6Mo6O18]n·4nH₂O (9)[Eu(H₂O)7Cr(OH)6Mo6O18]n·4nH₂O (10) [Er2(H₂O)14Cr(OH)6Mo6O18][Cr(OH)6Mo6O18]·14H₂O (11)The structure feature in 8-10 is that the [Cr(OH)6Mo6O18]3- polyoxoanion acts as a bidentate ligand coordinating to two Ln cations via terminal oxygen atoms of two non-adjacent MoO6 octahedra to generate a zig-zag polymer -ABABAB- chain through the Mo-Ot-Ln-Ot-Mo linkage in the crystal. When Er3+ was used instead of Ce³⁺, Sm3+ and Eu3+ in the similar condition, 11 was attained. In the structure of 11, one [Cr(1)(OH)6Mo6O18]3- anion as a bidentate ligand coordinates to two [Er(H₂O)7]3+ complex fragments to form a polyoxoanion-supported complex through the terminal oxygen atoms of two opposite MoO6 octahedra, the other [Cr(2)(OH)6Mo6O18]3- as the charge compensating anion.