Marie-Joëlle Menu

Crystal and molecular structures of transition metal complexes with N- and C-bonded diazoalkane ligands

Abstract The review covers structural and physicochemical studies on diazoalkanes N-coordinated to transition metals and encompasses all collected crystal structures. Our goal is to provide a classification of the complexes based on the metal, ranging from early to late transition metals, the nuclearity of the complex (mono, dinuclear, clusters), the electronic configuration of the metal (d 0 to d 10 ) and the bonding mode of the diazoalkanes. Interestingly, the variety of structures may be rationalized within the valence bond formalism, the reactions being essentially oxidative addition of diazoalkane on the metal complexes giving hydrazonido (-2- ligand). C-coordinated diazoalkyl complexes are still restricted to a few metals and a few diazosubstituents and their chemistry is not well developed.

An efficient route to aqueous phase synthesis of nanocrystalline γ-Al2O3 with high porosity: from stable boehmite colloids to large pore mesoporous alumina.

In this paper we emphasise the important role of Pluronic F127 on the porosity of mesoporous alumina prepared from boehmite colloids. By focusing on the F127/boehmite interactions we show how the concepts of interface science may help to predict and improve the textural characteristics of mesoporous alumina. By varying the synthetic parameters, in particular the copolymer content, we show that the porosity of γ-Al(2)O(3) can be enhanced by 400% and the average pore diameter can be expanded from 5 to 14 nm. These results are discussed in terms of interactions between the Pluronic F127 and boehmite colloids, and are correlated to the critical micelle concentration (CMC) of the copolymer. The textural characteristics of the mesoporous alumina can be further improved either by introducing hydrocarbons in the preformed boehmite/copolymer sols or by concentrating the sols. In comparison with as-synthesised alumina, those prepared with F127 showed improved thermal stability. Furthermore, boehmite/copolymer sols were stable for all surfactant concentrations investigated and can give high quality coatings suitable for catalytic applications.

Functionalization of synthetic talc-like phyllosilicates by alkoxyorganosilane grafting

A range of talc-like phyllosilicates were prepared via a hydrothermal synthesis performed at five different temperatures from 160 to 350 °C. The organization of the lattice and the degree of crystallinity of the new materials were evaluated by different techniques such as XRD, FTIR, solid-state 29Si NMR, TEM, FEG-SEM and TG-DTA. When synthesized at low temperature the material presents high degree of hydration, low crystallinity and flawed structure. This was attributed to stevensite-talc interstratified product present in the samples. The stevensite/talc ratio and the hydration decrease in the talc-like phyllosilicate samples when the hydrothermal synthesis temperature increases and so the crystallinity becomes higher. A thermal treatment at 500 °C allowed a significant flaw reduction in talc-like phyllosilicate structure; the synthesized sample at 350 °C and heat treated presents a structure close to that of talc. The different talc-like phyllosilicates were grafted covalently by two organoalkoxysilane reagents, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (IM2H) and 2-hydroxy-4-(3-triethoxysilylpropoxy)-diphenylketone (HTDK). The grafted amounts of the hybrids, determined by elemental analysis and confirmed by thermogravimetric data, are dependent on the hydrothermal synthesis temperature and organoalkoxysilanes; they become smaller when the synthesis temperature increases and when HTDK is used. FTIR and solid-state 13C CP MAS NMR were applied to characterize the grafted organic groups. So, in this work it is shown that by choosing the hydrothermal synthesis temperature or by performing an additional annealing it is possible to adjust the amount of defects in the structure of talc-like phyllosilicates which seems to be strongly correlated to the grafting performance.

Organosilylated Complex [Eu(TTA)3(Bpy-Si)]: A Bifunctional Moiety for the Engeneering of Luminescent Silica-Based Nanoparticles for Bioimaging

A new highly luminescent europium complex with the formula [Eu(TTA)3(Bpy-Si)], where TTA stands for the thenoyltrifluoroacetone, (C4H3S)COCH2COCF3, chelating ligand and Bpy-Si, Bpy-CH2NH(CH2)3Si(OEt)3, is an organosilyldipyridine ligand displaying a triethoxysilyl group as a grafting function has been synthesized and fully characterized. This bifunctional complex has been grafted onto the surface of dense silica nanoparticles (NPs) and on mesoporous silica microparticles as well. The covalent bonding of [Eu(TTA)3(Bpy-Si)] inside uniform Stöber silica nanoparticles was also achieved. The general methodology proposed could be applied to any silica matrix, allowed high grafting ratios that overcome chelate release and the tendency to agglomerate. Luminescent silica-based nanoparticles SiO2-[Eu(TTA)3(Bpy-Si)], with a diameter of 28 ± 2 nm, were successfully tested as a luminescent labels for the imaging of Pseudomonas aeruginosa biofilms. They were also functionalized by a specific monoclonal antibody and subsequently employed for the selective imaging of Escherichia coli bacteria.

Triethoxysilyl-substituted aminoethanethiol ligands for zinc and cadmium complexes and aminoethanethiol-modified silica gel. Evaluation of the corresponding supported molecular trap for metallic pollutant uptake (Cd2+, Hg2+ and Pb2+)

The reaction of 2-[3-(triethoxysilyl)propylamino]ethanethiol (LH, a) and 1-methyl-2-[3-(triethoxysilyl)propylamino]ethanethiol (LH, b) with ZnX2 and CdX2 (X = Cl, Br, I, NO3) in tetrahydrofuran (THF) or CH2Cl2 gives several complexes depending on the experimental conditions. Elemental analyses, IR, Raman, 13C[1H], 1H NMR and mass spectroscopies indicated the formation of mononuclear and dinuclear complexes. In the absence of NEt3 as proton quencher, the protonated ligands react in their zwitterionic form giving dinuclear [M(LH)X2]2 [M = Zn (1), Cd (2); LH = a, b; X = Cl, Br, I] or mononuclear M(NO3)2(LH)2 [M = Zn (5), Cd (6); LH = a] complexes. In both cases, coordination occurs through the S atoms, the ligands acting as terminal and bridging species. With NEt3, the deprotonated ligands are chelated through their N and S atoms and bridging occurs through the S atoms in [MLX]2 [M = Zn (3), Cd (4); LH = a; X = Cl, Br] complexes. The LH ligand is chemically grafted onto silica, the procedure optimized and the resulting material characterized by 13C and 29Si cross-polarization, magic-angle spinning (CP-MAS) NMR and DRIFT. This material is evaluated as a supported molecular trap for binding heavy metals (Cd2+, Hg2+, Pb2+) in aqueous solution. In both batch and column processes, it appears that Hg2+ and Pb2+ are trapped more than Cd2+, but in all cases values lower than those allowed were obtained.

Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO(3))(3), CeCl(3), Ce(CH(3)COO)(3) and Ce(2)(SO(4))(3)) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO(3))(3) and CeCl(3) whereas an equilibrium value was reached with Ce(CH(3)COO)(3). The addition of Ce(2)(SO(4))(3) with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free NO(3)(-) anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce(3+) ions and NO(3)(-) anions adsorbed on boehmite i.e. to [Ce(NO(3))(4)(H(2)O)(x)](-) complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO(3))(3) compared to CeCl(3) and Ce(CH(3)COO)(3). In contrast, Ce(2)(SO(4))(3) formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle-particle interactions and consequently on the rheological behaviour of the sols.

Bifunctional silica nanoparticles for the exploration of biofilms of Pseudomonas aeruginosa

Luminescent silica nanoparticles are frequently employed for biotechnology applications mainly because of their easy functionalization, photo-stability, and biocompatibility. Bifunctional silica nanoparticles (BSNPs) are described here as new efficient tools for investigating complex biological systems such as biofilms. Photoluminescence is brought about by the incorporation of a silylated ruthenium(II) complex. The surface properties of the silica particles were designed by reaction with amino-organosilanes, quaternary ammonium-organosilanes, carboxylate-organosilanes and hexamethyldisilazane. BSNPs were characterized extensively by DRIFT, 13C and 29Si solid state NMR, XPS, and photoluminescence. Zeta potential and contact angle measurements exhibited various surface properties (hydrophilic/hydrophobic balance and electric charge) according to the functional groups. Confocal laser scanning microscopy (CLSM) measurements showed that the spatial distribution of these nanoparticles inside a biofilm of Pseudomonas aeruginosa PAO1 depends more on their hydrophilic/hydrophobic characteristics than on their size. CLSM observations using two nanosized particles (25 and 68 nm) suggest that narrow diffusion paths exist through the extracellular polymeric substances matrix.

On the structure of high performance anticorrosive PMMA–siloxane–silica hybrid coatings

Environmentally compliant organic–inorganic hybrid coatings for efficient corrosion protection of metallic surfaces are potential alternatives to the current method based on chromate passivation. In this context PMMA–siloxane–silica (PMMA–SS) hybrid films were prepared using the sol–gel process from the radical copolymerization of methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate followed by acidic hydrolysis and polycondensation of tetraethoxysilane (TEOS), under variation of the ethanol to H2O ratio (0.0–1.0). The structural properties of about 2 μm thick coatings, deposited by dip-coating onto carbon steel, were related with their corrosion protection efficiency. The correlation of data obtained by X-ray photoelectron spectroscopy, nuclear magnetic resonance and small angle X-ray scattering has shown for intermediate ethanol to H2O ratios the highest connectivity (∼83%) of the inorganic phase, bonded covalently to organic moieties, yielding a dense and homogeneous nanocomposite structure with high thermal stability, very good adhesion to the metallic substrate and excellent barrier properties. The electrochemical impedance spectroscopy measurements have shown for coatings prepared at intermediate EtOH/H2O ratios a high corrosion resistance of almost 10 GΩ cm2, which remained unchanged for more than 6 months in contact with 3.5% NaCl solution and more than 3 months exposed to an acidic NaCl environment.

Interaction of Zn2+ with N-(2-pyridyl)-3-phenyl-2-propene amide, a model in lignin biosynthesis inhibition by cinnamides. Crystal and molecular structure of [Zn(ON)2(CH3OH)2](CF3SO3)2

Abstract Reacting Zn(CF3SO3)2 with the title ligand (ON) yields a 1:2 complex which precipitates from methanol as the [Zn(ON)2(CH3OH)2](CF3SO3)2 salt. The crystal structure of this complex (P11/c, a=13.711(2), b=10.401(2), c=16.358(2) A, β=124.27(1)°, R=0.059, 1918 observed reflections) reveals the presence of a centrosymmetric, nearly octahedral, complex cation. The all-trans configuration about Zn2+ is achieved by two methanol hydroxyl groups and two bidentate ligands bonded via their pyridyl nitrogens and amide oxygens. The amide group nitrogen is not coordinated to the metal, but it forms an NH.…O hydrogen bond to the CF3SO3− counterions. The influence of the amide substituent on the structure is discussed on the basis of comparisons with the [Zn{N-(2-pyridyl)acetamide}2(H2O)2]2+ ion containing a similar amidopyridine chelate ring.

Bulk or surface grafted silylated Ru(II) complexes on silica as luminescent nanomaterials

A series of Ru(II) complexes with monosilylated-dipyridine ligand have been synthesized and fully characterized and were then covalently attached to silica nanoparticles. Two types of hybrids were obtained depending on the experimental procedure. In the first approach, metal complexes were incorporated inside the silica nanoparticles leaving a free hydroxylated silica surface for further functionalization. These silica based nanohybrids are similar to the well known nanoparticles encapsulating [Ru(bpy)3]2+ complexes preventing the release of the dye when used in aqueous or organic solutions. Size and luminescence properties vary throughout the series of metal complexes. The second approach leads to ruthenium(II) complexes covalently attached to the silica nanoparticle surface via hydrolysis and condensation of the ethoxysilyl group with silanol sites of Ludox type silica nanoparticles. This leads to the grafting of a monolayer for complexes with the monoethoxysilyl dipyridine ligand. In contrast, the complexes with triethoxysilyl ligands can lead to small amounts of oligomers, but their quantity is limited by the sterical constraints imposed by the molecular structure. The size of the hybrids depends on the starting particles. 29Si and 13C solid state NMR are used to characterize silica surface properties whereas TEM and SEM confirm nanosize and morphology of the hybrids. The complexes and the nanohybrids are luminescent, with variations for ruthenium(II) complexes that are covalently incorporated or grafted on the silica surface.