Synthesis, characterization, and photoluminescence properties of three two-dimensional lanthanide-containing Dawson-type polyoxometalates

Abstract

Three [α₂-P₂W₁₇O₆₁]¹⁰⁻-based lanthanide-containing polyoxometalates (LCPs) [N(CH₃)₄]₃H₈{Ln(H₂O)₇[Ln(H₂O)₃Ln(H₂O)₄(α₂-P₂W₁₇O₆₁)₂]}·48H₂O [Ln = La³⁺ (1), Ce³⁺ (2), and Pr³⁺ (3)] were successfully obtained by the reaction of a trivacant Dawson-type precursor [P₂W₁₅O₅₆]¹²⁻ and lanthanide ions under hydrothermal conditions. The compounds 1–3 were fully characterized by single-crystal X-ray diffraction and a series of analytical methods, including elemental analyses, powder X-ray diffraction (PXRD), IR spectroscopy, Raman spectroscopy, UV/vis diffuse reflectance spectroscopy, and thermogravimetric analysis (TGA). Single-crystal X-ray diffraction analyses indicated that 1–3 were isostructural and exhibited a 2D network architecture through the alternative connection of [α₂-P₂W₁₇O₆₁]¹⁰⁻ and lanthanide ions. The photoluminescence properties of 1–3 were investigated at room temperature, and 3 displayed the characteristic emissions of a Pr³⁺ emitting center, indicating that POMs can transfer energy and sensitize Pr³⁺ emissions. The reason for the weak emission intensity of Pr³⁺ emitting ions was because the radiationless losses via a charge-transfer Pr → W state negatively affected the emission of the Pr³⁺ ions in LCPs.