Open frameworks based on mono-lanthanide-substituted polyoxometaloaluminate building units: Syntheses, structures and properties

Metal-substituted polyoxometalates are one of the most important research branch in polyoxometalate chemistry and have attached an increasing attention due to not only their intriguing structural diversity but also their special properties applicable to material science. In this paper, A series of novel lanthanidesubstituted polyoxometaloaluminates (LSPs), K₂(H ₂O)₄Ln(Ln(H₂O)₃HAIW ₁₁O₃₉] · nH₂O (Ln=Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Tb 6; for 1, n=8; for 2,4,5,6, n=7; for 3, n=9), have been hydrothermally made and characterized by infrared (IR) spectra, thermal gravimetric analysis (TGA), powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction, respectively. The experimental results indicate these compounds exhibit 3-D frameworks with Gra-type topology constructed by lanthanide cations, mono-lanthanide-substituted [Gd (H₂O) ₃HAIW₁₁O₃₉]^5- cluster units and K⁺ cations. The photoluminescence measurements show that Compounds 2, 4, 6 exhibit the characteristic emission for Nd³⁺, Eu³⁺ and Tb³⁺ cations, respectively. In addition, this series of LSPs show weak second harmonic generation effects and ferroelectric properties. The success in making 1-6 not only provides innovative examples in search of new POM species, but also may open up possibilities for the design of LSP-based materials with related functions.