H-shaped oxalate-bridging lanthanoid-incorporated arsenotungstates.

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 P1[combining macron] 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.