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931.
Roberto Della Pergola Luigi Garlaschelli Carlo Mealli Davide M. Proserpio Piero Zanello 《Journal of Cluster Science》1990,1(1):93-106
Electrochemical studies show that it is possible to move step-wise and reversibly between the redox congeners of the series [Fe3Pt3(CO)15]
n
,n=2-/1-/0. By contrast, a multielectron reduction of the dianion leads to an irreversible demolition of the species. When [Fe3Pt3(CO)15]2– is treated with one or two equimolar amounts of the oxidant [Fe(C5H5)2]+, the oxidized species (n=1- andn=0) can be also obtained. It can be established or extrapolated from the already known structures of the dianion and the monoanion that the successive oxidations strengthen the inner Pt-Pt linkages of the overall quasiplanar Fe3Pt3 skeleton. MO analysis, by establishing the antibonding nature of the frontier level from which the electrons are added or subtracted, allows the correlation of the bonding features of the inner Pt3 skeleton with the redox propensities of the system. 相似文献
932.
933.
Mastrorilli P Latronico M Nobile CF Suranna GP Fanizzi FP Englert U Ciccarella G 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1117-1119
Exposure of solid trans-[Pt(PHCy2)2(PCy2)Cl] (1) to dry oxygen unexpectedly leads to [PtCl(PHCy2)[(PCy2O)2H]] (2) as the major product, the formation of which has been followed by NOESY 1H NMR techniques. 相似文献
934.
Mirti P Gulmini M Perardi A Davit P Elia D 《Analytical and bioanalytical chemistry》2004,380(4):712-718
Samples from Greek figure vases were investigated by scanning electron microscopy coupled with energy dispersive X-ray analysis, X-ray diffraction, thermomechanical analysis and reflectance spectroscopy to achieve a technological characterisation. The vases, dating from the end of the sixth to the fourth century BC, had been excavated at Locri Epizephiri (Calabria, Italy) and attributed to Attic or local workshops, respectively. Information on the morphology of black slip areas and firing temperatures was compared with that previously obtained for Attic and local black gloss pottery from the same site; results show that the peculiar technique required for the production of black slips was mastered by both Attic and local potters and employed for monochrome and figured products. The black coating is usually well vitrified and 15- to 20-m thick; the evaluated maximum firing temperature is around 900°C, while a temperature lower than 800°C is generally estimated for ceramic body re-oxidation. 相似文献
935.
Sozzani P Comotti A Bracco S Simonutti R 《Chemical communications (Cambridge, England)》2004,(7):768-769
Advanced 2D solid state NMR techniques reveal weak intermolecular interactions that cooperatively sustain nanostructures of high molecular mass aliphatic polymers entrapped as guests in channels formed by an aromatic host. 相似文献
936.
937.
Small angle neutron scattering intensity distributions taken from cytochrome C and lysozyme protein solutions show a rising intensity at a very small wave vector Q, which can be interpreted in terms of the presence of a weak long-range attraction between protein molecules. This interaction has a range several times that of the diameter of the protein molecule, much greater than the range of the screened electrostatic repulsion. We show evidence that this long-range attraction is closely related to the type of anion present and ion concentration in the solution. 相似文献
938.
The influence of superplasticizers on the first steps of tricalcium silicate hydration studied by NMR techniques 总被引:1,自引:0,他引:1
Pirazzoli I Alesiani M Capuani S Maraviglia B Giorgi R Ridi F Baglioni P 《Magnetic resonance imaging》2005,23(2):277-284
The influence of superplasticizer sulfonated naphthalene formaldehyde (SNF) on the hydration process of tricalcium silicate (C3S) paste was investigated by (1)H nuclear magnetic resonance spin-spin and spin lattice relaxation times. The addition of SNF superplasticizer to C3S paste clearly affects the morphology and growth rates of the hydration products, mainly by increasing the dormant period length, which lasts for several hours more than in conventional C3S hydrated paste, while reducing the acceleration period length. The relaxation data indicated that a pronounced delay occurs in the C3S hardening when sulfonated polymers are added to the makeup water. For all the analyzed samples, prepared with a water-to-C3S ratio of 0.4, the decay of the echo magnetization has been fitted by adopting both a monoexponential and a biexponential relaxation model in order to evaluate the contributions from water in different regimes of hydration. 相似文献
939.
Sozzani P Bracco S Comotti A Simonutti R Camurati I 《Journal of the American Chemical Society》2003,125(42):12881-12893
Ethanol associates easily with MgCl(2) to form adducts of complex architecture, but until now available characterization methods have failed to identify the pure stoichiometric compounds and their structures. To remedy this, we set about applying homonuclear and heteronuclear 2D correlated solid-state NMR spectroscopy to identify the pure compounds and the ethanol-to-magnesium coordination pattern. High spinning speed and Lee-Goldburg sequences were able to reduce the hydrogen spin-diffusion and homonuclear coupling in the crystalline solid, thus achieving high resolution also in the hydrogen domain. On this basis, the pure adducts, of interest as catalyst supports for Ziegler-Natta polymerization, were isolated for the first time. Magnesium coordination sites with given numbers of ligands and their multiplicity in the crystal cells were determined in the new-found stoichiometric complexes. Variable temperature and 2D carbon-carbon exchange NMR, as well as relaxation times in the fast motion regime, revealed the disordering phenomena generated by ethanol dynamics in the crystal. Decoding the intriguing polymorphism of the precursors permits to trace the genealogy of tailored MgCl(2) titanate granules, active as highly productive catalysts for the stereospecific polymerization of olefins. 相似文献
940.
Pieraccini S Masiero S Spada GP Gottarelli G 《Chemical communications (Cambridge, England)》2003,(5):598-599
Axially chiral bis(azo) derivative 1 undergoes photochemical isomerisation, which can be seen with circular dichroism and pitch measurements of the induced cholesteric phases. 相似文献