Synthesis, Crystal Structure And Characterization Of Rare Earth-Keggin Polyoxotungstates

In this paper, nine unreported compounds have been synthesized by utilizing the pre-synthesized (NH4)6[H₂W₁₂O₄₀]·3H₂O andα-H4SiW₁₂O₄₀ clusters as precursors, and rare earth metal coordination complexes or rare earth ions as linkers, by water solution synthesis methods. These compounds are structurally characterized by elemental analyses, IR, UV, TG and single crystal X-ray diffractions. Magnetic properties and photoluminescence properties of partial conpounds have also studied and discussed.1. Eight two- and three-dimensional structure compounds have been gained, based on [H₂W₁₂O₄₀]6- polyoxoanions as building blocks and lanthanide-pyridine-2,6-dicarboxylic acid coordination complexes as linkers: [La₄(HL)₂(L)₂(H₂O)1₄(H₂W₁₂O₄₀)]·14H₂O [Ce₄(HL)₂(L)₂(H₂O)1₄(H₂W₁₂O₄₀)]·12H₂O [Pr₄(HL)₂(L)₂(H₂O)1₄(H₂W₁₂O₄₀)]·14H₂O [Nd₄(HL)₂(L)₂(H₂O)1₄(H₂W₁₂O₄₀)]·17H₂O [La3(HL)3(H₂O)10(H₂W₁₂O₄₀)]·10H₂O [Ce3(HL)3(H₂O)10(H₂W₁₂O₄₀)]·10H₂O [Pr3(HL)3(H₂O)10(H₂W₁₂O₄₀)]·10H₂O [Nd3(HL)3(H₂O)10(H₂W₁₂O₄₀)]·10H₂OIn compounds 1?4, Ln cations coordinate with pyridine-2,6-dicarboxylic acid ligands forming a 1D double-chain structure, and [H₂W₁₂O₄₀]6- polyanions acting as a tetradentate ligand with four terminal oxygen atoms connect these 1D double-chain to form 2D layer structure. In compounds 5?8, [H₂W₁₂O₄₀]6- clusters link Ln cations forming 2-fold parallel interpenetration networks, and the networks were linked together by pyridine-2,6-dicarboxylic acid ligands forming the first example 3D structure constructed from [H₂W₁₂O₄₀]6- anions modified by lanthanide-organic framework. The compounds 1 and 5, 2 and 6, 3 and 7, and 4 and 8 were obtained in the same solution system, respectively. The formation of these compounds with two types of multidimensional structures mainly depends on solution acidity and the coordination modes of the ligands, which is based on the analyses on properties of organic and inorganic ligands and synthetic conditions.Furthermore, the luminescent properties of compounds 4 and 8 display three characteristic emission bands for Nd3+ ions in the near IR region and the variable temperature magnetic study indicates antiferromagnetic coupling in compounds 2?4.2. One compound has been gained by utilizingα-H4SiW₁₂O₄₀ clusters and rare earth metal as precursors and adjusting reaction conditions K2H2{Ce(H2O)6[Ce(H2O)2(α-SiW11O39)]}2·26H2O (9)In compound 9, the coordination of the monovacant Keggin anions to the Ce3+ ions creates a double-chain structure. The K+ cations link the double-chain to form corrugated layers.The magnetic property of compound 9 shows a characteristic of antiferromagnetic interaction.