H-shaped oxalate-bridging lanthanoid-incorporated arsenotungstates

Abstract

Three oxalate-bridging lanthanide-based polyoxometalates (Ln-POMs) K₁₇Na₂H₅[{(As₂W₁₉O₆₇(H₂O))Ln(H₂O)₂}₂(C₂O₄)]·50H₂O. [Ln = Sm³⁺ (1), Pr³⁺ (2), and Ce³⁺ (3)] were successfully synthesized. The structures were further characterized by single-crystal X-ray diffraction analyses, Raman spectroscopy, elemental analyses, powder X-ray diffraction (PXRD), IR spectra, UV/vis diffuse reflectance spectroscopy, and thermogravimetric analysis (TGA). The structural characterization study reveals that Ln-POMs 1–3 crystallize in the form of the triclinic space group P and consist of an oxalate bridging di-Ln³⁺-incorporated H-shaped dimer, which can also be viewed as a combination of two half-units {Ln(As₂W₁₉O₆₇(H₂O))(H₂O)₂}₂²²⁻ related by an inversion center. It is worth noting that the opening angle (33.01°) from the [As₂W₁₉O₆₇(H₂O)]¹⁴⁻ fragment in 1–3 is less than that of the [As₂W₁₉O₆₇(H₂O)]¹⁴⁻ precursor (40.99°). Furthermore, the stability of 1–3 in aqueous solution and their solid-state photoluminescence properties have also been investigated in this work.