9 research outputs found
Tribological properties of fullerenes C60 and C70 microparticles
The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to clump and compress into high shear strength layers rather than due to the impurities in the fullerenes. The benzene-solvated C60 · 4C6H6 and C70 · xC6H6 showed a lowered friction coefficient (0.25 for C60 · 4C6H6 and 0.3 for C 70 · xC6H6), which might result from the lowered shear strength of the hcp structure of C60 · 4C6H6 and C70 · xC6H6 molecular crystals in which the benzene molecules were intercalate
Tribological properties of fullerenes C60 and C70 microparticles
The frictional behaviors of fullerenes C60 and C70 were studied because they were speculated to be solid lubricants. For the sublimated pure C60 films on Si(001), a high friction coefficient (0.55–0.8) was observed under different loads and pin materials. For the C70 film, the friction coefficient showed a pin dependence, which changed from 0.5 with an Al2O3 pin to about 0.9 with a 440 stainless steel pin. The relatively high friction coefficients of C60 and C70 films were due to the tendency of the C60 and C70 particles to clump and compress into high shear strength layers rather than due to the impurities in the fullerenes. The benzene-solvated C60 · 4C6H6 and C70 · xC6H6 showed a lowered friction coefficient (0.25 for C60 · 4C6H6 and 0.3 for C 70 · xC6H6), which might result from the lowered shear strength of the hcp structure of C60 · 4C6H6 and C70 · xC6H6 molecular crystals in which the benzene molecules were intercalate
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Catalytic Hydrogenation Activity and Electronic Structure Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt Alkyl and Hydride Complexes
The bis(arylimidazol-2-ylidene)pyridine cobalt methyl complex, ((iPr)CNC)CoCH(3), was evaluated for the catalytic hydrogenation of alkenes. At 22 °C and 4 atm of H(2) pressure, ((iPr)CNC)CoCH(3) is an effective pre-catalyst for the hydrogenation of sterically hindered, unactivated alkenes such as trans-methylstilbene, 1-methyl-1-cyclohexene and 2,3-dimethyl-2-butene, representing one of the most active cobalt hydrogenation catalysts reported to date. Preparation of the cobalt hydride complex, ((iPr)CNC)CoH was accomplished by hydrogenation of ((iPr)CNC)CoCH(3). Over the course of 3 hours at 22 °C, migration of the metal-hydride to the 4-position of the pyridine ring yielded (4-H(2)-(iPr)CNC)CoN(2). Similar alkyl migration was observed upon treatment of ((iPr)CNC)CoH with 1,1-diphenylethylene. This reactivity raised the question as to whether this class of chelate is redoxactive, engaging in radical chemistry with the cobalt center. A combination of structural, spectroscopic and computational studies was conducted and provided definitive evidence for bis(arylimidazol-2-ylidene)pyridine radicals in reduced cobalt chemistry. Spin density calculations established that the radicals were localized on the pyridine ring, accounting for the observed reactivity and suggest a wide family of pyridine-based pincers may also be redox active