A series of pinwheel-shaped Ln21-oxo-cluster-embedded polyoxometalates as single-crystal proton-conductive and tunable photoluminescent materials

Abstract

The integration of high-nuclearity lanthanide-oxo (Ln-O) clusters into polyoxotungstates (POTs) represents a formidable synthetic challenge due to intricate assembly mechanisms and the labile nature of lanthanide coordination. Herein, we present an innovative alkaline-mediated templating strategy for constructing unprecedented Ln-oxo-cluster-encapsulated POTs through synergistic assembly of lacunary polyoxotungstate precursors with in situ generated Ln-oxo clusters. This approach employs basic N-containing ligands and selenite (SeO32−) anions as synergistic structure-directing agents. Guide by this approach, we have successfully synthesized two series of giant Ln21-oxo-cluster-embedded polyoxotungstates, H23K30(H2O)18{[Ln21(H2O)9(WO6)(SeO3)6][Ln3(SeO3)2]2(GeW10O38)9}·solvent (1-Ln) (Ln = Eu, Gd, Tb, Dy), and H27Na3K21(H2O)11(MePIP)2{[Ln21(H2O)9(WO6)(SeO3)6][Ln3(SeO3)2]2(GeW10O38)9}·solvent (2-Ln) (Ln = Eu, Tb, MePIP=N-methylpiperazine). Notably, these compounds feature a rare pinwheel-shaped high-nuclearity Ln21-oxo-cluster-embedded polyanion, {[Ln21(H2O)9(WO6)(SeO3)6][Eu3(SeO3)2]2(GeW10O38)9} ({Ln27Se10Ge9W91}) with a three-layered sandwich structure. Compounds 1-Eu and 2-Eu exhibit distinct proton conduction properties due to their different packing structures. In particular, 1-Eu demonstrates a high single-crystal proton conductivity of 1.8×10−2 S·cm−1 at 98% RH and 25°C along the [001] channel direction, outperforming most crystalline porous materials.Additionally, 1-Eu exhibits temperature-dependent fluorescence. 1-Eu0.25Dy0.75 sample can emit macroscopic white light under blue irradiation. This work paves a feasible strategy for the constructing high-nuclearity Ln-oxo-cluster-containing POTs and expands their application in smart proton conductive materials and multicolor luminescent systems.