Surface-grafted lanthanoid complexes of the tungstosilicate polyanion [SiW₁₂O₄₀]^4−: a synthetic, structural and computational investigation

As an extension of our continued interest in the preparation of inorganic–organic hybrids, we report the successful hydrothermal synthesis of sodium tris[triaqua(μ-1,10-phenanthroline-2,9-dicarboxylato)dysprosium(III)] silicododecatungstate dodecahydrate, {[DyNa(C₁₄H₆N₂O₄)₃(H₂O)₉(SiW₁₂O₄₀)]·12H₂O}_n or Na[Dy(PDA)(H₂O)₃]₃[SiW₁₂O₄₀]·12H₂O (1), and sodium aqua tris[tetraaqua(μ-4-hydroxypyridine-2,6-dicarboxylato)praseodymium(III)] silicododecatungstate dodecahydrate, {[NaPr(C₇H₃NO₅)₃(H₂O)₁₃(SiW₁₂O₄₀)]·12H₂O}_n or Na(H₂O)[Pr(pydc-OH)(H₂O)₄]₃[SiW₁₂O₄₀]·12H₂O (2) (in which H₂PDA is 1,10-phenanthroline-2,9-dicarboxylic acid and H₂pydc-OH is 4-hydroxypyridine-2,6-dicarboxylic acid or chelidamic acid). Both compounds have been characterized using elemental analysis, IR spectroscopy and X-ray diffraction methods. Structural characterization by single-crystal X-ray diffraction reveals that these compounds consist of [SiW₁₂O₄₀]^4− Keggin-type polyoxometalates (POMs), where a single {W₃O₁₃} triad is decorated with a trinuclear Ln complex. Moreover, the decorated polyanions are involved in a series of intermolecular interactions, such as hydrogen bonds and anion–π interactions, resulting in three-dimensional supramolecular architectures. Density functional theory (DFT) studies were conducted to support these intermolecular interactions in both 1 and 2, and have been rationalized using molecular electrostatic potential (MEP) surface calculations.