Lorenza Suber

Weak charge-transfer polyoxoanion salts: the reaction of quinolin-8-ol (Hquin) with phosphotungstic acid and the crystal and molecular structure of [H2quin]3[PW12O40]·4EtOH·2H2O

Different solvated charge-transfer salts between quinolin-8-ol (Hquin) and phosphotungstic acid have been synthesized and characterized. Spectroscopic data support the presence of a sizeable electronic interaction between electron-rich aromatic organics and the inorganic acid, both in the solid state and in solution, provided that a large excess of the organic is present. This interaction is responsible for the formation of photosensitive compounds and provides a rationale for the subsequent facile photo-oxidation of the organic substrate. The crystal and molecular structure of [H2quin]3[PW12O40]·4EtOH·2H2O has been solved by the heavy-atom method and refined to a final R= 0.083, for 4 902 reflections with I 3σ(I): triclinic space group P; with a= 11.721(3), b= 12.818(3), c= 12.878(3)A, α= 89.20(2), β= 104.10(2), γ= 117.30(2)°, and Z= 1. The anion structure consists of an α-Keggin-type molecule in two-fold disorder. The 8-hydroxyquinolinium moieties (three per [PW12O40]3–) are stacked approximately along the x direction, with alternative interplanar spacings of 3.25 and 3.57 A. The crystal structure determination reveals the absence of any substantial, direct interaction between the organic cations and the phosphototungstate anions. Therefore no clear structural basis for the electronic interaction noted above can be given.

Oxidations by a H2O2-VO3 ?-pyrazine-2-carboxylic acid reagent: 1. Oxidation of alkanes in CH3CN to produce alkyl peroxides

Alkanes (cyclohexane, hexane, heptane isomers) are effectively oxidized in CH3CN at 20–70°C by hydrogen peroxide when catalyzed by a Bu4NVO3-pyrazine-2-carboxylic acid system. Alkyl hydroperoxide is the main product; an alcohol and a ketone or an aldehyde are also formed. Under these conditions benzene is oxidized to give phenol, while alkyl benzenes yield oxygenation products both of the ring and the side chain. It has been assumed that the interaction of H2O2 with VO3− gives rise to generation of HO radicals and other radical-like vanadium containing species that abstract a hydrogen atom from an alkane, RH. The radical R. formed reacts with O2 to produce ROO. which is then transformed to alkyl hydroperoxide.

Sonochemical synthesis of versatile hydrophilic magnetite nanoparticles.

Hydrophilic magnetite nanoparticles in the size range 30-10nm are easily and rapidly prepared under ultrasonic irradiation of Fe(OH)(2) in di- and tri-ethylene glycol/water solution with volume ratio varying between 7:3 and 3:7. Structural (XRD) and morphological (SEM) characterization reveal good crystalline and homogeneous particles whereas, when solvothermally prepared, the particles are inhomogeneous and aggregated. The sonochemically prepared particles are versatile, i.e. well suited to covalently bind molecules because of the free glycol hydroxylic groups on their surface or exchange the diethylene or triethylene glycol ligand. They can be easily transferred in hydrophobic solvents too. Room-temperature magnetic hysteresis properties measured by means of Vibrating Sample Magnetometer (VSM) display a nearly superparamagnetic character. The sonochemical preparation is easily scalable to meet industrial demand.

High Yield Synthesis of Pure Alkanethiolate-Capped Silver Nanoparticles

One-phase, one-pot synthesis of Ag(0) nanoparticles capped with alkanethiolate molecules has been optimized to easily achieve a pure product in quantitative yield. We report the synthesis of dodecanethiolate-capped silver particles and the chemophysical, structural, and morphologic characterization performed by way of UV-vis, (1)H NMR, and X-ray photoelectron (XPS) spectroscopies, X-ray powder diffraction (XRD) and X-ray absorption fine structure analysis (XFAS), electron diffraction and high-resolution transmission electron microscopy (HR-TEM), and scanning and transmission electron microscopy (SEM and TEM). Depending on the molar ratio of the reagents (dodecylthiosulphate/Ag(+)), the mean Ag(0) particle size D(XRD) is tuned from 4 to 3 nm with a narrow size distribution. The particles are highly soluble, very stable in organic solvents (hexane, toluene, dichloromethane, etc.), and resistant to oxidation; the hexane solution after one year at room temperature does not show any precipitation or formation of oxidation byproducts.

Organic-inorganic charge-transfer salts based on the β-[Mo8O26]4- isopolyanion : synthesis, properties and X-ray structure

The complex reaction between the organic electron donor N,N,N′,N′-tetramethyl-p-phenylenediamine (tmpd) and the inorganic acceptor [Mo6O19]2– in air has been investigated. Conversion of the inorganic polyanion to β-[Mo8O26]4–, as well as protonation and/or oxidation of the organic base are possible. Different charge-transfer salts of the type β-[Htmpd]x[tmpd]4–x[Mo8O26] and β-[Htmpd]x[tmpd]3–x[HMo8O26] have been isolated and characterized. They contain positively charged tetramethyl-p-phenylenediamine molecules which may be present, simultaneously or not, as monoprotonated units (Htmpd+) or radical cations (tmpd+). According to optical and magnetic properties, isolated radicals or tightly bound dimers have been found. The X-ray crystal and molecular structure of β-[Htmpd]2[tmpd]2[Mo8O26] has been solved by the heavy-atom method and refined to a final R= 0.057 for 3129 reflections with I 3σ(I); monoclinic, space group P21/c with a= 11.607(5), b= 24.830(9), c= 11.047(4)A, β= 106.82(3)° and Z= 2. The β-octamolybdate polyanion has the well known Lindqvist structure. The radical cations from eclipsed dimeric units with an intradimeric distance 3.35 A and do not interact with the polyanion. The protonated molecules are isolated from one another, but linked to the polyanion through bifurcated hydrogen bonds of 2.87 and 3.11 A.

Hierarchical Formation Mechanism of CoFe2O4 Mesoporous Assemblies

The development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by β-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of Fe(III) ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the β-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule.

Control of silver–polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry

Silver nanocrystals have been prepared by reacting silver nitrate with ascorbic acid in aqueous solution containing a low concentration of a commercial polynaphthalene sulfonate polymer (Daxad 19). Various crystalline morphologies have been obtained simply by tuning the reaction temperature. We have investigated the nanoparticle formation mechanism at three different temperatures by in situ and time resolved small angle X-ray scattering measurements. By modeling the scattering intensity with interacting spherical particles in a fractal-like polymer-Ag matrix, we found signatures of nucleation, growth and assembly of primary particles of about 15-20 nm. We observed how the time evolution of both spatial correlations between primary particles and the dynamic fractal geometry of the polymer-Ag matrix could influence and determine both the aggregation mechanism and the morphology of forming nanostructures in solution.

Photochemical oxidation of hydrocarbons by a vanadium(V) peroxo complex

The oxidation of alkanes and benzene by VO(O2)L·2H2O (L=2-picolinate) in acetonitrile is accelerated upon irradiation with visible and, especially, UV light. Cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone in approximately 2:1:1 ratio are formed from cyclohexane both in the dark and photochemical reactions. Benzene is oxidized to phenol.

Polyoxoanion-supported, atomically dispersed cyclooctadieneruthenium(II) complexes

The cation [Ru(C8H12)]2+ was supported on [P3O9]3–, [V4O12]4– and [Nb2W4O19]4– polyoxoanions. All the complexes were stable in air and were characterized by elemental and thermogravimetric analysis, IR, 1H, 13C and 31P NMR spectroscopy. The crystal and molecular structure of [NBu4][Ru(C8H12)(MeCN)-(P3O9)]·Et2O has been determined [space group C2/c, a= 38.359(4), b= 9.907(5), c= 26.437(3)A, β= 127.720(4)°]. Ruthenium(II) is octahedrally co-ordinated to the two C8H12-diene groups, to one acetonitrile molecule and through three O atoms to the P3O93– ligand. In the case of [Ru(C8H12)(MeCN)2-(HV4O12)– and [Ru(C8H12)(MeCN)2(V4O12)]2– where a bidentate co-ordination to the polyanion is observed, two MeCN molecules are co-ordinated by Ru, resulting in the 18-valence-electron configuration. The [Nb2W4O19]4– anion behaves differently: its reaction with [RuCl(C8H12)(MeCN)3]PF6 leads to a product which, on the basis of IR, elemental analysis and the literature, we formulate as [NBu4]3[{RuCl(C8H12)(MeCN)}5(Nb2W4O19)2]·3H2O. In this case two Nb2W4O194– anions are probably linked, face to face, by five organometallic centres.

Hierarchic self-assembling of silver nanoparticles in solution

Abstract Facile chemical synthesis and understanding of the formation mechanism of silver nanoparticles, ordered on the microscale on one-dimensional (1D), 2D or in 3D structures of complex forms is challenging for advanced applications, in electronics, optoelectronics, and medicine, to mention a few. Significant results obtained in the comprehension of assembling mechanisms in solutions of silver nanoparticles in 1D, 2D, and 3D organic-inorganic mesostructures are surveyed together with details on their preparation and characterization. Emphasis will be placed on very recent results obtained in our laboratories on self-assembly of silver nanoparticles in 1D microstructures and hierarchic ordering in 3D flower-like mesostructures monitored and studied by in situ and time-resolved small angle X-ray scattering (SAXS) measurements.