Synthesis,Structure And Properties Studies Of Lanthanide(?)Complexes Decorated Keggin-type Polyoxometalates

Polyoxometalates?POMs?,as one type of outstanding class of nanosized metal-oxygen clusters,have attracted more and more attentions,owing to their fantastic structural diversities and various physical and chemical properties.In this paper,by utilizing hydrothermal method,we combined lanthanide metals with common organic ligands to decorate Keggin-type POMs,and obtained five unique polyoxometalates.Their structures have been characterized by the single crystal X-ray diffractions,IR spectra,thermogravimetry?TG?,and Powder X-ray diffraction?XRD?in detail.Meanwhile,we also studied their properties,such as electrochemical behavior,and photoluminescence et al.1.Compound 1 was successfully synthesized by hydrothermal method of a mixture containing Cs₆H[SiW₉Nb₃O₄₀]?8H₂O,La?NO₃?₃?6H₂O and pyridine-3-carboxylic acid in a stoichiometric ratio.Meanwhile,the stability,electrochemical behavior and photolum-inescence properties of 1 have also been discussed.[H₃La₈?H₂O?₃₂?C₆H₅NO₂?₆][Si W₉Nb₃O₄₀]₃?8H₂O?1?The unprecedented 3D framework of 1 is built from 1D hexagonal channel via O_t?Nb?-La1-O_t?Nb?connected to each adjacent{Si Nb₃W₉O₄₀}units;and La2³⁺cations fill in the central gap of the three adjacent{SiNb₃W₉O₄₀}units to make the framework much firmer.Noteworthily,the higher nucleophilicity O_t?Nb?of the surface of[SiW₉Nb₃O₄₀]^7-units,the oxyphilic Ln cations with diverse coordination and bonding modes,and the special carboxylic coordination modes of pyridine-3-carboxylic acid ligand play important roles in constructing the resulting 3D framework.2.We successfully isolated four unique 3D supramolecular compounds by mixing Keggin-type polyoxometalate[SiW₁₂O₄₀]^4-,Ln?NO₃?₃?6H₂O?Ln=Gd,Tb,Sm,and Eu?with pyridine-4-carboxylic acid?HIN?ligand in a stoichiometric ratio under hydrothermal conditions.Furthermore,the photoluminescence properties of 3 and 5 have been investigated as well.[Gd₄?HIN?₁₄?H₂O?₈][SiW₁₂O₄₀]₂?NO₃?₄?10H₂O?2?[Tb₄?HIN?₁₄?H₂O?₈][SiW₁₂O₄₀]₂?NO₃?₄?10H₂O?3?Na₂[Sm₂?HIN?₆?H₂O?₆][SiW₁₂O₄₀]₂?4H₂O?4?Na₂[Eu₂?HIN?₆?H₂O?₆][SiW₁₂O₄₀]₂?4H₂O?5?Among these four compounds,2 and 3 are isostructural,and each comprises of discrete[SiW₁₂O₄₀]^4-Keggin-type polyoxometalates and tetranuclear lanthanide clusters,which are further linked by H-bonding interactions to yield 3D supramolecular inorganic-organic hybrid frameworks;As for isostructural 4 and 5,their basic units consist of two Keggin-type clusters[SiW₁₂O₄₀]^4-and binuclear lanthanide clusters,which are furether packed into 3D supramolecular frameworks through H-bonding interactions.