Stéphane Daniele

Low temperature and aqueous sol–gel deposit of photocatalytic active nanoparticulate TiO2

TiO2 nanoparticles with a mesoporous structure have been synthesised by a one step, simple, efficient, low temperature (100 °C) and environmentally friendly sol–gel process using ammonium bromide salts as catalysts. They have been characterised by FT-IR, TGA/TDA, XRD, BET and TEM techniques. Their photocatalytic activities are compared to highly porous commercial TiO2 in liquid/solid and gas/solid systems. Deposition of a uniform crystalline TiO2 coating with high adhesivity was achieved on organic substrates such as cellulose fibers.

Metal 2-ethylhexanoates and related compounds as useful precursors in materials science

This critical review deals with the chemistry and applications of metal alkanoates with medium size (C5 to C12) carbon chain length. A particular emphasis is given to metal 2-ethylhexanoates, which find wide applications as metal-organic precursors in materials science, as catalysts for ring opening polymerizations and also in painting industries for their properties as driers. After a brief introduction and an overview of synthesis, structural and physico-chemical properties, this article discuses extensively the applications of these compounds in materials science. Finally, it identifies and signifies the areas for future research in the looking ahead section. The aim of this review is to bridge the areas of precursors chemistry and materials science by providing a reference text for researchers working either in or at the interface of these two areas (125 references).

Solid- and solution phase transformations in novel hybrid iodoplumbate derivatives templated by solvated yttrium complexes.

Solvated yttrium iodide precursors [Y(L)8]I3 [L = dimethylformamide (DMF) or dimethylsulfoxide (DMSO)], prepared in situ by stirring YI3(Pr(i)OH)4 in DMF/DMSO, react with 3 equiv of PbI2 in the presence of NH4I to give novel hybrid derivatives based on either a one-dimensional (1D) straight chain, [Y(DMF)8][Pb3(mu-I)9](1infinity) x DMF (1), or discrete pentanuclear iodoplumbates, [Y(DMSO)8]2[(DMSO)2Pb5(mu3-I)2(mu-I)8I6] (2a). The complex 2a and a closely related [Y(DMSO)8][Y(DMSO)7(DMF)][(DMSO)2Pb5(mu3-I)2(mu-I)8I6] (2b) were obtained in good yield by solution phase transformation of 1 in DMSO under slight different conditions. Derivatives 1 and 2 also undergo unique solid-state transformation in a confined environment of paratone to give 1D polymers based on zigzag iodoplumbate chains; crystals of 1 transform into [Y(DMF)6(H2O)2][Pb3(mu3-I)(mu-I)7I](1infinity) (3) via an exchange reaction, whereas those of 2a and 2b are converted into [Y(DMSO)7][Pb3(mu3-I)(mu-I)7I](1infinity) (4) via a decomposition pathway. The trifurcate H-bonding between water ligands on yttrium cation and iodide of the iodoplumbate anion plays a pivotal role in transforming the straight 1D polymeric Pb-I chain of 1 into a zigzag chain in 3. The thermogravimetry-differential thermal analysis studies indicate that complexes with DMF ligands are thermally more stable than those with DMSO ones, the mixed DMF-H2O ligand complex 3 being the most stable one because of the presence of strong H-bonding. Diffuse-reflectance UV-visible spectral analyses of 1-4 show an optical band gap in the 1.86-2.54 eV range, indicating these derivatives as potential semiconductors. In contrast to non-emissive 3 and 4, derivatives 1, 2a, and 2b show remarkable luminescent emission with peak maxima at 703 nm, assigned as an iodine 5p-lead 6s to lead 6p charge transfer (XM-M-CT).

Practical oxidation of sulfides to sulfones by H2O2 catalysed by titanium catalyst

The oxidation of thianisole and other substituted arylalkyl and diaryl sulfides with aqueous H2O2 as the oxidant and heterogeneous TiO2 catalyst exhibits a high selectivity affording the corresponding sulfones with 80–98% isolated yields. It should be noted that H2O2 provided better results as compared with tBuOOH in terms of the reaction rate and yields of sulfones. The use of hydrogen peroxide and heterogeneous nanocrystalline titania catalyst is a green alternative to the traditional stoichiometric oxidation providing high yields of sulfones in one step.

Thermal condensation of trinuclear lanthanide butoxides. Molecular structure of La5(μ5-O)(μ3-OtBu)4(μ-OtBu)4(OtBu)5

Abstract Refluxing of Ln3(OtBu)9(tBuOH)2 (Ln=La, Nd, Yb) in toluene led to Ln5O(OtBu)13 which was characterised by X-ray diffraction in the case of lanthanum. Aggregates of higher nuclearity were obtained in similar conditions for yttrium and praseodymium.

Aerobic methylcyclohexane-promoted epoxidation of stilbene over gold nanoparticles supported on Gd-doped titania

Aerobic partial oxidations of alkanes and alkenes are important processes of the petrochemical industry. The radical mechanisms involved can be catalyzed by soluble salts of transition metals (Co, Cu, Mn...). We show here that the model methylcyclohexane/stilbene co-oxidation reaction can be efficiently catalyzed at lower temperature by supported gold nanoparticles. The support has little influence on gold intrinsic activity but more on the apparent reaction rates which are a combination of catalytic activity and diffusion limitations. These are here minimized by using gadolinium-doped titania nanocrystallites as support for gold nanoparticles. This material is obtained by mild hydrolysis of a new Gd(4)TiO(O(i)Pr)(14) bimetallic oxoalkoxide. It leads to enhanced wettability of the < 3 nm gold particles in the tert-butyl hydroperoxide (TBHP)-initiated epoxidation of stilbene in methylcyclohexane; Au/TiO(2):Gd(3+) is in turn as active as the state-of-the-art hydrophobic Au/SiO(2) catalyst. The rate-determining step of this reaction is identified as the gold-catalyzed homolytic decomposition of TBHP generating radicals and initiating the methylcyclohexane-mediated epoxidation of stilbene, yielding a methylcyclohexan-1-ol/trans-stilbene oxide mixture. Methylcyclohexan-1-ol can also be obtained in the absence of the alkene in the gold-catalyzed solvent-free autoxidation of methylcyclohexane, evidencing the catalytic potential of gold nanoparticles for low temperature C-H activation.

Combination of two catalytic sites in a novel nanocrystalline TiO2–iron tetrasulfophthalocyanine material provides better catalytic properties

Mesoporous titania nanocrystals containing iron tetrasulfophthalocyanine (FePcS) have been synthesised by a one-pot hydrolytic process from a modified Ti alkoxide; the novel hybrid catalyst was efficient in heterogeneous oxidation of 2,3,6-trimethylphenol and β-isophorone suggesting a cooperative effect between TiO2 and FePcS catalytic sites.

Solution routes to lead titanate: synthesis, molecular structure and reactivity of the Pb–Ti and Pb–Zr species formed between various lead oxide precursors and titanium or zirconium alkoxides. Molecular structure of Pb2Ti2(μ4 -O)(OAc)2(OPri)8 and of PbZr3(μ4-O)(OAc)2(OPri) 10

The reactions between Ti(OR) 4 (R = Et, Pr 1 ) or [Zr(OPr 1 ) 4 (Pr 1 OH)] 2 and various lead oxide precursors [anhydrous Pb(OAc) 2 , alkoxides or oxoalkoxides] have been investigated in different experimental conditions (solvent, temperature). Various mixed-metal species have been isolated in high yields and characterized by microanalysis, FTIR and multinuclear NMR ( 1 H, 13 C and 207 Pb) spectroscopies. The mixed-metal oxoacetatoalkoxides Pb 2 Ti 2 (μ 4 -O)(μ-OAC) 2 (μ-OPr i ) 5 (OPr i ) 3 1 and PbZr 3 (μ 4 -O)(μ-OAc) 2 (μ-OPr i ) 5 (OPr i ) 5 2 have been characterized by X-ray crystallography at -100°C: for 1, monoclinic, space group C 2 /c with a= 38.916(17) A, c = 12.045(2) A, c = 19.046(4) A, β= 112.84(3)°, V=8224(4)A 3 , Z = 8, R = 0.068, R w = 0.076; and for 2, monoclinic, space group P2 1 /n with a=10.618(2) A, b=25.157(11) A, β=18.611(5)1, β=90.35(2)°, V=4971(3)A 3 , Z=4, R =0.060, R w = 0.072. Hydrolysis-condensation reactions have been achieved especially for the species having a Pb: Ti stoichiometry appropriate for access to PbTiO 3 . Effects of the solvent on the temperature of crystallisation and on the particle size are discussed.

Novel Heteroleptic Heterobimetallic Alkoxide Complexes as Facile Single-Source Precursors for Ta5+ Doped TiO2-SnO2 Nanoparticles

The nanometric mixed tin-titanium oxide doped with a M(5+) cation was recently shown as a promising thermoelectric material. We report here synthesis of novel molecular precursors for above material using a convenient approach of reacting a metal chloride with a metal alkoxide. Heterometallic complexes with simple addition formula [(EtOH)(2)(OEt)(2)Ti(μ-OEt)(2)SnCl(4)] (1·EtOH) and [(EtOH)(OEt)(3)Ta(μ-OEt)(2)SnCl(4)] (2) were isolated in quantitative yield, which on recrystallization from isopropanol afforded mixed-alkoxide complexes [(Pr(i)OH)(2)(OPr(i))(2)Ti(μ-OEt)(2)SnCl(4)] (3) and [(Pr(i)OH)(OPr(i))(3)Ta(μ-OEt)(2)SnCl(4)] (4), respectively, thus indicating the robustness of the heterometallic M(μ-OEt)(2)Sn core in the solution phase. Facile conversion of these precursors to halide-free spinodal form of Ta(5+)-doped TiO(2)-SnO(2) as a potential thermoelectric material is reported.

Molecular structures of volatile Ce(IV) tetrafluoroisopropoxide complexes with TMEDA and diglyme. CVD experiments

Abstract The structures of the cerium tetrafluoroisopropoxide adducts with TMEDA (1) and diglyme [Me(OC2H4)2OMe] (2) were established by single crystal X-ray diffraction (TMEDA=tetramethylethane-1,2-diamine). The cerium atom is hexa- and heptacoordinated for 1 and 2, respectively. The CeO(hfip) bond distances are quite short [2.115(5)–2.152(6) A] and are associated to large CeO(hfip) angles (>156°). Both complexes display a range of short F⋯C contacts, the shortest ones having values of 3.754 and 4.060 A for 1 and 2, respectively. Decomposition experiments were achieved in a cold-wall reactor. The films deposited on glass substrates were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectroscopy.