Reactive Zr(IV) and Hf(IV) butterfly peroxides on polyoxometalate surfaces: bridging the gap between homogeneous and heterogeneous catalysis.

At variance with previously known coordination compounds, the polyoxometalate (POM)-embedded Zr(IV) and Hf(IV) peroxides with formula: [M(2)(O(2))(2)(α-XW(11)O(39))(2)](12-) (M=Zr(IV), X=Si (1), Ge (2); M=Hf(IV), X=Si (3)) and [M(6)(O(2))(6)(OH)(6)(γ-SiW(10)O(36))(3)](18-) (M=Zr(IV) (4) or Hf(IV) (5)) are capable of oxygen transfer to suitable acceptors including sulfides and sulfoxides in water. Combined (1)H NMR and electrochemical studies allow monitoring of the reaction under both stoichiometric and catalytic conditions. The reactivity of peroxo-POMs 1-5 is compared on the basis of substrate conversion and kinetic. The results show that the reactivity of POMs 1-3 outperforms that of the trimeric derivatives 4 and 5 by two orders of magnitude. Reversible peroxidation of 1-3 occurs by H(2)O(2) addition to the spent catalysts, restoring oxidation rates and performance of the pristine system. The stability of 1-3 under catalytic regime has been confirmed by FT-IR, UV/Vis, and resonance Raman spectroscopy. The reaction scope has been extended to alcohols, leading to the corresponding carbonyl compounds with yields up to 99% under microwave (MW) irradiation. DFT calculations revealed that polyanions 1-3 have high-energy peroxo HOMOs, and a remarkable electron density localized on the peroxo sites as indicated by the calculated map of the electrostatic potential (MEP). This evidence suggests that the overall description of the oxygen-transfer mechanism should include possible protonation equilibria in water, favored for peroxo-POMs 1-3.

Peroxo-Zr/Hf-containing undecatungstosilicates and -germanates.

A family of dimeric, peroxo-containing heteropolytungstates, [M(2)(O(2))(2)(XW(11)O(39))(2)](12-) [M = Zr(4+), X = Si (1), Ge (2); M = Hf(4+), X = Si (3)], have been synthesized by reacting ZrCl(4)/HfCl(4) with the respective monolacunary Keggin precursor [XW(11)O(39)](8-) (X = Si, Ge) in an aqueous acidic medium (pH 4.8). The isostructural polyanions 1-3 are composed of two (XW(11)O(39)) Keggin units encapsulating a central diperoxo-dimetal fragment {M(2)(O(2))(2)}(4+) (M = Zr(4+), Hf(4+)). Cyclic voltammetry and exhaustive electrolysis studies indicate fast reductive release of the peroxo ligands upon reduction of 1-3. Stoichiometric oxo-transfer studies from 1-3 to the substrate l-methionine were performed, and the reactions were monitored by (1)H NMR.

Water oxidation at a tetraruthenate core stabilized by polyoxometalate ligands: experimental and computational evidence to trace the competent intermediates.

Converging UV-vis, EPR, rRaman, and DFT calculations highlight the evolution of [Ru(4)(H(2)O)(4)(mu-O)(4)(mu-OH)(2)(gamma-SiW(10)O(36))(2)](10-), 1, to high-valent intermediates. In analogy with the natural enzyme, five different oxidation states, generated from 1, have been found to power the catalytic cycle for water oxidation. A high electrophilic tetraruthenium(V)-hydroxo species is envisaged as the competent intermediate, undergoing nucleophilic attack by an external water molecule as a key step in the formation of a new O-O bond under catalytic conditions.

The birth of a chemical society.

A short description of the events leading to the birth of the Italian Chemical Society is given. The first Italian Chemical Society was established in 1909, and resulted from the merging of the Milan and Rome sections.

Metal-free, retro-cycloaddition of fulleropyrrolidines in ionic liquids under microwave irradiation.

Quantitative cycloreversion of fulleropyrrolidines to [60]fullerene is achieved in ionic liquids within minutes under microwave irradiation without any further additives.

Polyoxometalate embedding of a tetraruthenium(IV)-oxo-core by template-directed metalation of [gamma-SiW10O36]8-: a totally inorganic oxygen-evolving catalyst.

Solid state and solution evidence confirms the embedding of an adamantane-like, Ru4O6 fragment by the divacant, gamma-decatungstosilicate ligand. The resulting complex catalyzes water oxidation to oxygen with TON up to 500 and TOF > 450 h-1.

Hybrid polyoxotungstates as second-generation POM-based catalysts for microwave-assisted H2O2 activation.

[structure: see text] Organic-inorganic hybrids synthesized from lacunary polyoxotungstates (POMs) have been screened as oxidation catalysts with H2O2 under MW irradiation. Yields up to 99% have been obtained in 25-50 min depending both on the POM structure and on the organic moiety. The reaction scope, optimized with the best performing catalyst [gamma-SiW10O36(PhPO)2]4-, includes epoxidation of terminal and internal double bonds, alcohol oxidation, and sulfoxidation, as well as oxygen transfer to electron-deficient substrates as chalcone, ketones, and sulfoxides.

Solvent-free, heterogeneous photooxygenation of hydrocarbons by hyflon membranes embedding a fluorous-tagged decatungstate.

Hybrid fluoropolymeric membranes with 25% loading of the fluorous-tagged (RfN)4W10O32 effect the solvent-free photooxygenation of benzylic C-H bonds with up to 6100 TONs in 4 hours.

An atmospheric pressure chemical ionization study of the positive and negative ion chemistry of the hydrofluorocarbons 1,1-difluoroethane (HFC-152a) and 1,1,1,2-tetrafluoroethane (HFC-134a) and of perfluoro-n-hexane (FC-72) in air plasma at atmospheric pressure.

A report is given on the ionization/dissociation behavior of the title compounds within air plasmas produced by electrical corona discharges at atmospheric pressure: both positive and negative ions were investigated at different temperatures using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). CHF(2)CH(3) (HFC-152a) undergoes efficient ionic oxidation to C(2)H(5)O(+), in which the oxygen comes from water present in the plasma. In contrast, CF(3)CH(2)F (HFC-134a) does not produce any characteristic positive ion under APCI conditions, its presence within the plasma being revealed only as a neutral ligand in ion-molecule complexes with ions of the background (H(3)O(+) and NO(+)). Analogously, the perfluorocarbon FC-72 (n-C(6)F(14)) does not produce significant positive ions at 30 degrees C: at high temperature, however, it undergoes dissociative ionization to form many product ions including C(3)F(6)(+), C(2)F(4)(+), C(n)F(2n+1)(+) and a few families of oxygen containing cations (C(n)F(2n+1)OH(2)(+), C(n)F(2n)OH(+), C(n)F(2n-1)O(+), C(n)F(2n-1)O(2)H(2)(+), C(n)F(2n-2)O(2)H(+)) which are suggested to derive from C(n)F(2n+1)(+) in a cascade of steps initiated by condensation with water followed by steps of HF elimination and H(2)O addition. Negative ions formed from the fluoroethanes CHF(2)CH(3) and CF(3)CH(2)F (M) include complexes with ions of the background, O(2)(-)(M), O(3)(-)(M) and some higher complexes involving also water, and complexes of the fluoride ion, F(-)(H(2)O), F(-)(M) and higher complexes with both M and H(2)O also together. The interesting product O(2)(-)(HF) is also formed from 1,1-difluoroethane. In contrast to the HFCs, perfluoro-n-hexane gives stable molecular anions, M(-), which at low source temperature or in humidified air are also detected as hydrates, M(-)(H(2)O). In addition, in humidified air F(-)(H(2)O)(n) complexes are also formed. The reactions leading to all major positive and negative product ions are discussed also with reference to available thermochemical data and relevant literature reports. The effects on both positive and negative APCI spectra due to ion activation via increasing V(cone) are also reported and discussed: several interesting endothermic processes are observed under these conditions. The results provide important information on the role of ionic reactions in non-thermal plasma processes.

Detecting intermolecular NOEs by means of a novel DPFGSE pulse sequence. Application to the solvation of carbohydrates in binary mixtures.

We present a pulse sequence based on solute-to-solvent NOE enhancement and aimed at the detection of intermolecular NOE's. Thus, a W3 pulse cluster is used to selectively filter the solvent signals in a DPFGSE sequence. The sequence has been tested on a sample of glucose dissolved in two binary aqueous mixtures (water-acetonitrile and water-DMSO). We show how the resulting enhancements may derive from intermolecular cross-relaxation or, in the water-DMSO sample, also from chemical exchange. In each case, a quantitative interpretation of the data is also supplied, both in terms of local enrichment in one specific solvent (preferential solvation), and by means of a kinetic model for a two-site chemical exchange.

Solar cells based on a fullerene-azothiophene dyad.

A power conversion efficiency of 0.37%, under white light of 80 mW cm-2 intensity, was obtained when a fullerene-azothiophene dyad was used as the active layer of a photovoltaic cell.

Pathways of Nitrosobenzene Reduction by Thiols in Alcoholic Media.

The biologically important reaction of nitrosobenzenes with thiols has been investigated in 2-propanol solution at room temperature, experimental conditions which allow for the detection and characterization of key intermediates. Final stable products of such complex reactions include azoxybenzenes and anilines, formed in relative proportions and at a rate which depend on the reagents initial molar ratio. A detailed description of the reaction of 4-chloronitrosobenzene with benzenethiol in 2-propanol was achieved by means of (1)H NMR in situ analysis. The reaction is initiated by rapid and quantitative coupling of the two reagents into a covalent adduct, an N-hydroxysulfenamide (N(OH)S), which decays to N-(4-chlorophenyl)hydroxylamine. This second intermediate is then converted via competing paths to 4,4'-dichloroazoxybenzene and to N-(4-chlorophenyl)benzenesulfenamide (4-ClC(6)H(4)NHSPh), which in turn decays to 4-chloroaniline. Interestingly, sulfinamides (ArNHS(O)R), major products of the reaction in aqueous media, do not form in 2-propanol.

DFT Calculation of Intermolecular Nuclear Spin-Spin Coupling in van der Waals Dimers.

A small but detectable intermolecular spin-spin coupling (JC,H ) is predicted by density functional calculations on van der Waals bonded dimers like methane-benzene and benzene-benzene, as shown in the picture.

Oxygenic polyoxometalates: a new class of molecular propellers.

The oxygen evolving catalyst [Ru(4)(µ-OH)(2)(µ-O)(4)(H(2)O)(4)(γ-SiW(10)O(36))(2)](10-) effects H(2)O(2) dismutation at rates (k = 36.8 ± 1.4 M(-1) s(-1)), one/two order of magnitude higher compared to related tetra-substituted Cu, Fe, Mn, Ni and even Co polyoxometalates, thus providing localised oxygen gas bursts to power nano-propulsion of composite materials.

Photo-induced water oxidation with tetra-nuclear ruthenium sensitizer and catalyst: a unique 4 x 4 ruthenium interplay triggering high efficiency with low-energy visible light.

The combined use of a tetranuclear Ru(II) dendrimeric photosensitizer (1) and of a tretraruthenium substituted polyoxotungstate (2) as the catalyst enables photo-induced water oxidation at 550 nm producing O(2) with an outstanding quantum yield of 0.30.

Ruthenium polyoxometalate water splitting catalyst: very fast hole scavenging from photogenerated oxidants.

The tetraruthenium polyoxometalate water oxidation catalyst 1 performs very fast hole scavenging from photogenerated Ru(iii) polypyridine complexes, both in homogeneous solution and at a sensitized nanocrystalline TiO(2) surface.