Syntheses, Structures And Properties Of Keggin Polyoxometalates Functionalized By Coordination Complexes

Polyoxometalates (POMs), a fascinating class of metal–oxygen cluster compounds with a unique structural variety and interesting physicochemical properties, have been found to be extremely versatile inorganic building blocks in view of their potential applications in catalysis, medicine, and materials.Seventeen new compounds based on polyoxometalate building blocks have been synthesized via water solution synthesis methods together with hydrothermal technique, and structurally characterized by elemental analyses, IR, TG, XPS, NMR, ESI-MS and single crystal X-ray diffractions. The thermal stabilities, photoluminescence and magnetic properties of these compounds have been studied.1. Four new polyoxometalate compounds based on Keggin type polyoxoanion cluster have been hydrothermally synthesized and structurally characterized:Compound 1 and 2 are examples that arsenicum-centered vanadomolybdate anion acts as an active building block in the fabrication of polyoxometalates-supported hybrid solids. While in compound 3, a polyoxoanion and a neutral component coexist in the crystal structure. Compound 4 exhibits a layer structure with both anionic layers through coordination bonds and cationic layers by the hydrogen bond contacts.2. Choosing K6 [SiW11NiO40H2] and Na8H[AsVW9O34] as the starting materials, combining water solution synthesis methods together with hydrothermal technique, three lanthanide-decorated polyoxometalates, one dysprosium citrate-incorporated tungstoarsenate and one dysprosium citrate coordination polymer were obtained and structurally characterized:Compounds 5 and 6 show one-dimensional chains structures based on [α-SiW₁₁O₃₉]^8– building blocks and decorated by lanthanides. Compound 7 shows a traditional sandwich structue based on [α-SiW₁₁O₃₉]^8–. Compound 8 is the first example of monomeric di-substituted Ln-POM derivatives with the two non-adjacent vacant sites coordinating towards two Dy3+ ions. At room temperature, compound 8 shows yellow-luminescent in the solid state. The structure of 9 exhibits a two-dimensional layer structure, in which Dy2O2 dimer serves as the building block. The photoluminescence spectrum shows blue-luminescent in the solid state at room temperature. Owing to the special frustration structure, unusual magnetic relaxation has been found in compound 9.3. Designed and synthesized two tris(hydroxymethyl)aminomethane derivatives, with the obtained polyol ligands we got two functionalized polyoxometalates:Both compound 12 and 13 show a dimer structure with the polyol ligands as the bridge. There structures were confirmed by NMR and ESI-MS spectra. The successful synthesis of these two compounds proved that oranic group-grafting is one of the most effective ways to obtain POM-based materials.4. Four metal-organic coordination polymers based on 2-mercaptonicotinic acid derivatives have been synthesized with the ligand generated in situ:Compound 14 exhibites a novel one-dimensional chain structure containing both the enantiomers of the subunit Mn(2-sinic)(DMSO)2. The main magnetic pathway of complex 14 is through Mn—O—S—O—Mn with the anti-anti conformation showing weak antiferromagnetic couping with J = -1.16 cm-1, zJ? = 0.55 cm-1 and g = 1.97. Compounds 15-17 show a double-chain structure built up from two chiral single-chain motifs. Compound 17 shows strong red fluorescent emissions in the solid state at room temperature.