Reactivity of Heteropolytungstate and Heteropolymolybdate Metal Transition Salts in the Synthesis of Dimethyl Carbonate from Methanol and CO2

A series of Keggin-type heteropoly compounds (HPC) having different countercations (Co, Fe) and different addenda atoms (W, Mo) were synthesized and characterized by means of Fourier-Transform Infrared Spectrometer (FT-IR) and X-ray powder diffraction (XRD). The catalytic properties of the prepared catalysts for the dimethyl carbonate (DMC) synthesis from CO2 and CH3OH were investigated. The experimental results showed that the catalytic activity is significantly influenced by the type of the countercation and addenda atoms transition metal. Among the catalysts examined, Co1.5PW12O40 is the most active for the DMC synthesis, owing to the synergetic effect between Co and W. Investigating the effect of the support showed that the least acidic one (Al2O3) enhanced the conversion but decreased the DMC selectivity in favor of that of methyl formate (MF), while that of dimethoxy methane remained stable

An ionic organic–inorganic hybrid: tetra­kis[bis­(1,10-phenanthroline)copper(I)] dodeca­tungstophosphate(V)

Single crystals of the title polyoxometallate-based organic–inorganic hybrid, [Cu(C12H8N2)2]4[SiW12O40], were grown under hydro­thermal conditions. The discrete [SiW12O40]4− anions are of the Keggin type and are packed in a slightly distorted ortho­rhom­bic F-centred mode, with the complex [CuI(phen)2]+ cations (phen is 1,10-phenanthroline) located in the voids of this arrangement. The four independent CuI cations are situated in the centres of more or less distorted tetra­hedra made up of N atoms from the phen ligands. The anions and cations are linked together via weak hydrogen-bonding inter­actions, forming an extended three-dimensional network. Additional stabilization is achieved via π–π inter­actions between different phen mol­ecules of adjacent [CuI(phen)2]+ cations with shortest distances between 3.416 and 3.499 Å

Transition Metal Substitution Effects on Metal-to-Polyoxometalate Charge Transfer

A series of heterobimetallic transition metal substituted polyoxometalates (TMSPs) have been synthesized based on the CoII-centered ligand [CoIIW11O39]10-. The eight complex series, [CoII(MxOHy)W11O39](12-x-y)- (MxOHy = VIVO, CrIII(OH2), MnII(OH2), FeIII(OH2), CoII(OH2), NiII(OH2), CuII(OH2), ZnII(OH2)), of which six are reported for the first time, was synthesized starting from [CoIIIW11O39]9- and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [CoIIW12O40]6- and demonstrate the same MPCT transition as the plenary complex, but have shorter excited state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited state lifetimes at least 50% of that of [CoIIW12O40]6- while more than tripling the absorbance at 400 nm

Luminescent polyoxotungstoeuropate anion-pillared layered double hydroxides

Novel luminescent polyoxometalate anion-pillared layered double hydroxides (LDHs) were prepared by aqueous ion exchange of a Zn–Al LDH precursor in nitrate form with the europium-containing polyoxotungstate anions [EuW10O36]9–, [Eu(BW11O39)(H2O)3]6– and [Eu(PW11O39)2]11–. The host– guest interaction has a strong influence on the nature of the final intercalated species, as evidenced by elemental analy- Introduction Layered double hydroxides are an important class of ionic lamellar solids with the general formula [M2+ 1–xM3+ x(OH)2](Am–)x/m·nH2O (M2+ = Mg2+, Zn2+, Ni2+ etc., M3+ = Al3+, Cr3+, Ga3+ etc).[1] The positively charged layers, containing divalent and trivalent cations in octahedral positions, are separated by charge balancing anions and water molecules. The water molecules are connected to both the metal hydroxide layers and the interlayer anions through extensive hydrogen bonding. A range of organic or inorganic guests may be incorporated into LDHs by either ion exchange, direct synthesis or hydrothermal reconstruction of calcined precursors.[2,3] In particular, intercalation chemistry has been explored with the aim of introducing catalytically active sites and photo- and electroactive species. Many different types of metal coordination compounds and oxometalates have been immobilized in LDHs, including phthalocyanines, cyanocomplexes, oxalate complexes and polyoxometalates (POMs).[4] The first report of LDHs containing polyoxometalates concerned their use as exhaust gas and hydrocarbon conversion catalysts.[5] Since then, a variety of iso- and heteropolyanions with different nuclearities and structures (Keggin, Dawson, Preyssler, Finke) have been incorporated into the interlayer space of these materials.[6–18] Two factors assume considerable importance for the successful intercalation of polyoxometalates into an LDH compound. First, the heteropoly species should carry sufficient charge in order to be [a] Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal E-mail: [email protected] [b] Department of Physics, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal © 2006 Wiley-VCH Verlag 726 GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2006, 726–734 sis, powder X-ray diffraction (XRD), infra-red (IR) and Raman spectroscopy, solid state magic-angle spinning (MAS) 11B and 31P NMR spectroscopy, and photoluminescence spectroscopy.FCT - POCT

Lanthanopolyoxotungstates in silica nanoparticles: multi-wavelength photoluminescent core/shell materials

We thank Dr Marc Willinger and the RNME (National Electronic Microscopy Network, Portugal) for HRTEM images. Electronic supplementary information (ESI) available: FT-IR and FT-Raman spectra, additional HRTEM images and complementary photoluminescence spectra details, see DOI: 10.1039/b919691a.Photoluminescent lanthanopolyoxotungstate core/shell nanoparticles are prepared by the encapsulation of lanthanide-containing polyoxometalates (POMs) with amorphous silica shells. The preparation of morphological well-defined core/shell nanoparticles is achieved by the hydrolysis of tetraethoxysilane in the presence of POMs using a reverse microemulsion method. The POMs used are decatungstolanthanoates of [Ln(W(5)O(18))(2)](9-) type (Ln(III) = Eu, Gd and Tb). Photoluminescence studies show that there is efficient emission from the POM located inside the SiO(2) shells, through excitation paths that involve O --> Eu/Tb and O --> W ligand-to-metal charge transfer. It is also shown that the excitation of the POM containing europium(III) may be tuned towards longer wavelengths via an antenna effect, by coordination of an organic ligand such as 3-hydroxypicolinate. The POM/SiO(2) nanoparticles form stable suspensions in aqueous solution having the advantage of POM stabilization inside the core and the possibility of further surface grafting of chemical moieties via well known derivatization procedures for silica surfaces. These features together with the possibility of tuning the excitation wavelength by modifying the coordination sphere in the lanthanopolyoxometalate, make this strategy promising to develop a new class of optical bio-tags composed of silica nanobeads with multi-wavelength photoluminescent lanthanopolyoxometalate cores.FCT- POCI/QUI/58887/2004FCT- PTDC/ QUI/67712/2006FCT- SFRH/BD/30137/2006FCT- SFRH/BPD/14954/200