Cathodic behaviour of nickel(II) in acetonitrile in the presence of carbon monoxide and substituted phosphines

Summary The reduction of nickel perchlorate in the presence of carbon monoxide and substituted phosphines or diphosphines has been studied in acetonitrile by cyclic voltammetry. The results show that only mono- and bis-carbonylphosphinenickel(O) complexes are formed, while no evidence for the formation of carbonyl-nickel(I) and -nickel(II) species was obtained. Although the oxidation processes are not reversible, a good correlation between the anodic peak potentials relative to nickel(O) complexes and the -donor--acceptor abilities of the phosphines employed was observed.     

Spherical tensor analysis of nuclear magnetic resonance signals

In a nuclear magnetic-resonance (NMR) experiment, the spin density operator may be regarded as a superposition of irreducible spherical tensor operators. Each of these spin operators evolves during the NMR experiment and may give rise to an NMR signal at a later time. The NMR signal at the end of a pulse sequence may, therefore, be regarded as a superposition of spherical components, each derived from a different spherical tensor operator. We describe an experimental method, called spherical tensor analysis (STA), which allows the complete resolution of the NMR signal into its individual spherical components. The method is demonstrated on a powder of a (13)C-labeled amino acid, exposed to a pulse sequence generating a double-quantum effective Hamiltonian. The propagation of spin order through the space of spherical tensor operators is revealed by the STA procedure, both in static and rotating solids. Possible applications of STA to the NMR of liquids, liquid crystals, and solids are discussed.     

Controlling the self-assembly of a deoxiguaninosine on mica

We report a tapping mode scanning force microscopy investigation on the growth from solutions of a lipophilic deoxiguanosine derivative on the basal plane of a muscovite mica surface. By varying the chemical composition of the substrate surface it is possible to drive the self-assembly towards either layered thin films, which are very likely to consist of guanosine quartets, or nanoribbons, comprising hydrogen bonded networks. Both these two architectures, which are peculiar to the guanine base itself, are of notable importance for the fabrication of molecular nanowires. Moreover, the first arrangement provides evidence that the guanosine is able to behave as ionophore, thus, suggesting its utilization in the development of solid-state ion selective sensors.     

One-pot palladium-catalyzed synthesis of 2,3-disubstituted bicyclo[2.2.1]heptanes and bicyclo[2.2.1]hept-5-enes

A new and highly stereoselective palladium-catalyzed synthesis is reported, based on two subsequent insertions of the bicyclo[2.2.1]heptene system into an aryl or vinylpalladium bond, formed in situ from aryl or vinyl bromides.     

Densities and excess molar volumes for binary mixtures of N,N-dimethylformamide+ 1,2-dimethoxyethane

Densities are reported for N,N-dimethylformamide and 1,2-dimethoxyethane binary mixtures at different mole fractions covering the whole miscibility range and at 19 temperatures ranging from –10 to 80°C. The experimental density data have been fitted by empirical relations and the excess volumes by a Redlich-Kister equation. The 11 N,N-dimethylformamide and 1,2-dimethoxyethane adduct appears to be stable throughout the temperature range. A comparison with other DMF containing mixtures is made.     

Spectrophotometric, EPR and kinetic characterisation of the >N-O* radical from 1-hydroxybenzotriazole, a key reactive species in mediated enzymatic oxidations

Characterisation of the aminoxyl (>N-O*) radical BTNO, generated from 1-hydroxybenzotriazole (HBT) by the one-electron oxidant CAN (a Ce(IV) salt), confirms BTNO as the reactive intermediate in oxidations run with the laccase/HBT system.     

The determination of the gases released during heating of a flame retardant for polymers

The oxidative degradation of HET-acid (1,4,5,6,7,7-hexachlorobicyclo [2.2.1] hept-5-en-2, 3-dicarboxylic acid) is studied by the combination of TG, FTIR, MS and GC-MS. The gases evolved during the decomposition of this flame retardant are investigated on-line by FTIR and by MS. Simultaneously the evolved gases are collected by an adsorbent and, after the thermal experiment, desorbed to release the volatile products for identification using GC-MS. The combination of these techniques offers the unambiguous identification of the evolved products as a function of temperature. The main identified products are CO₂, H₂O, Cl₂, HCl, C₂Cl₄, maleic acid anhydride, HET-acid anhydride, chlorinated cyclic hydrocarbons and chlorinated unsaturated linear hydrocarbons.     

New [g]-fused [1,2,4]triazolo[1,5-c]pyrimidines: Synthesis of pyrido[3,2-e] and [4,3-e][1,2,4]triazolo[1,5-c]pyrimidine,pyrimido[5,4-e][1,2,4]triazolo[1,5-c]pyrimidine and [1,2,4]triazolo[1,5-c]pteridine derivatives

A number of 2-aryl-substituted pyrido[3,2-e] and [4,3-e][1,2,4]triazolo[1,5-c]pyrimidines and [1,2,4]triazolo[1,5-c]pteridines 11,12a,b,e , their corresponding 5-carbonyl derivatives 7,8a,b,e and some pyrimido[5,4-e][1,2,4]triazolo[1,5-c]pyrimidin-5-ones 7,8c,d have been synthesized, according to different pathways. The new tricyclic heterocycles were prepared with the aim of studying their possible benzodiazepine receptors affinity.     

Synthesis, properties and structures of the two “electron rich” cobalt-sulphur clusters [Co6(μ3-S)8(PEt3)6]

The reaction of hydrogen sulphide with [Co(H₂O)₆](BF₄)₂ and triethylphosphine in the presence of sodium tetraphenylborate or tetrabutylammonium hexafluorophosphate gave the paramagnetic clusters [Co₆(μ₃-S)₈(PEt₃)₆](Y) (Y = BPh₄, (1), PF₆, (2)). These compounds can be easily reduced by sodium napthalenide to the diamagnetic species [Co₆(μ₃-S)₈(PEt₃)₆] · 2C₄H₈O (3). The molecular structures of 1 and 3 have been established by single-crystal X-ray diffraction methods. Crystal data: (1) space group P , a = 19.481(9), b = 15.562(7), c = 12.390(b) Å, α = 92.70(8), β = 94.50(7), γ = 94.10(9)°, Z = 2, (3) space group R , a = 11.780(6) Å, α = 92.50(7)°, Z = 1. Both structures were solved by the heavy atom method and refined by full-matrix least-squares techniques to the conventional R factors values of 0.050 for 1 and 0.044 for 3 on the basis of 4251 and 1918 observed reflections, respectively. The two clusters [Co₆(μ₃-S)₈)(PEt₃)₆]^1+,0 are isostructural, the inner core consisting of an octahedron of cobalt atoms with all the faces symmetrically capped by triply bridging sulphur atoms. Each metal centre is additionally linked to a triethylphosphine group so that each cobalt atom is co-ordinated by four sulphur atoms and one phosphorus in a distorted square pyramidal environment. The addition of one electron whilst leaving unchanged the geometry of the inner framework, induces small changes in the structural parameters, the average Co---Co and Co---P distances being 2.794 (3) and 2.162 (2) Å for 1 and 2.817 (3) and 2.138 (2) Å for 3 respectively. Electrochemistry in non-aqueous solvents shows the electron-transfer sequence

Full-size image (3K)

The tricationic species is stable only in the short time of cyclic voltammetric tests.     

V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V₂O₅/TiO₂ catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm^–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm^–1 and 770 to 850 cm^–1. The Raman spectra do not exhibit characteristic peaks of crystalline V₂O₅. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V⁴⁺ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V⁴⁺ ions are located in sites with octahedral symmetry substituting for Ti⁴⁺ ions in the rutile structure. Magnetically interacting V⁴⁺ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V₂O₅, a partial oxidation of V⁴⁺ to V⁵⁺ is apparent from the EPR results.