Chiral Networks Assembled from Hexalanthanide Polyoxometalate Sandwich Building Units Showing Solid-State Temperature-Dependent Photoluminescence

A new series of all-inorganic lanthanide-containing polyoxometalate (Ln–POM) hybrid clusters, Na 5 [{Ln 6 (μ 3 -OH) 3 (H 2 O) 9 }{SiW 9 O 34 } 2 ]·50H 2 O ( 1-Ln; Ln 3+ = Pr, Nd, Sm, Eu, Gd), featuring a rare 6:2 lanthanide-to-POM motif, has been synthesized. The clusters consist of a hexanuclear {Ln 6 (μ 3 -OH) 3 (H 2 O) 9 } 15+ unit sandwiched between two achiral trilacunary { A -α-SiW 9 O 34 } 10– polyanions. Each unit is bridged to three neighboring clusters via Ln–O–W bonds, forming a robust three-dimensional chiral network with srs topology, crystallizing in the cubic I 2 1 3 space group. Electrospray ionization mass spectrometry studies confirm intact polyanions in variable charge states. The solid-state temperature-dependent photoluminescence studies of 1-Eu reveal the characteristic Eu 3+ -centered 5 D 0 → 7 F J (J = 0–4) emissions sensitized via ligand-to-metal charge transfer (LMCT, O→W, 334 nm) transition and direct 4f–4f excitation ( 5 L 6 ← 7 F 0, 396 nm). At 300 K, the LMCT absorption is quenched, and the emission is induced upon direct 4f–4f excitation. The temperature-dependent evolution of the 5 D 0 → 7 F 0 transitions underscores the utility of Eu 3+ emission as a sensitive probe of site symmetry and dynamic structural modulations. These results highlight the potential of the trilacunary POM { A -α-SiW 9 O 34 } 10– as an all-inorganic achiral ligand for stabilizing high-nuclearity, light-emissive lanthanide-based sandwich clusters forming a chiral network.