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- Volume 45, Issue 1, 2001
Platinum Metals Review - Volume 45, Issue 1, 2001
Volume 45, Issue 1, 2001
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Molecular Design for Long-Range Electronic Communication between Metals
More LessTo construct molecular devices it is necessary to use mixed-valence metal complexes which have a large metal-metal separation distance and which exhibit strong coupling between the metals, so that errors which might arise from electrostatic interaction between the metal ions are prevented. Bridges, or spacers, are needed between two metal terminal sites to operate as effective molecular wires when one metal terminal site is in the excited state, and/or when both the terminal components are in the ground state. Binuclear ruthenium complexes, consisting of tris(β-diketonato)ruthenium(III) units, which are suitable as the terminal redox sites, can be used to evaluate how well the bridges function as molecular wires in the ground state. This is because their Ru(III)-Ru(II) and Ru(IV)-Ru(III) mixed-valence states are accessible for experimental use. In this article, a polyyne system and an ethynylated aromatic system are evaluated as molecular wires, using the binuclear (β-diketonato)ruthenium(III) complexes containing these systems as the bridges. In the Ru(IV)-Ru(III) mixed-valence state, the ruthenium complexes show relatively strong electronic interactions between the metal centres. This is interpreted by a superexchange (through-bond) hole transfer mechanism via the highest occupied molecular orbitals of the bridge. Molecular orbital calculations provide a guide to the molecular design of bridging ligands for long-range electronic coupling.
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The Ruthenium/TEMPO-Catalysed Aerobic Oxidation of Alcohols
Authors: By Arné Dijksman, Isabel W. C. E. Arends and Roger A. SheldonThe combination of RuCl2(PPh3)3 and 2,2′,6,6′-tetramethylpiperidine N-oxyl (TEMPO) affords an efficient catalytic system for the aerobic oxidation of a variety of primary and secondary alcohols, giving the corresponding aldehydes and ketones, in > 99 per cent selectivity in all cases. This interesting catalytic system is probably based on a hydridometal mechanism, involving a ‘RuH2(PPh3)3’-species as the active catalyst. TEMPO acts as a hydrogen transfer mediator and is regenerated by oxygen.
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Improved Start-Up for the Ammonia Oxidation Reaction
Authors: By V. I. Chernyshev and S. V. ZjuzinThe start-up operation in a nitric acid plant is one of the most important stages, from the viewpoint of safety and platinum loss, in the entire ammonia oxidation process. Usually, flame burners using hydrogen or hydrogen-containing gas preheat the platinum alloy gauze catalyst to the operating temperature. However, there are disadvantages and peculiarities in this method of initiating the start-up reaction. These are discussed here and a new electrical heating device and a new technique are described for preheating the platinum alloy gauze catalyst. The device and technique are free of these disadvantages, and together they reduce the explosive hazard and platinum losses during start-up. Results from their commercial utilisation over a 12-year period at various nitric acid plants are described.
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Volumes & issues
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Volume 58 (2014)
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Volume 57 (2013)
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Volume 56 (2012)
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Volume 55 (2011)
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Volume 54 (2010)
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Volume 53 (2009)
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Volume 52 (2008)
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Volume 51 (2007)
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Volume 50 (2006)
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Volume 49 (2005)
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Volume 48 (2004)
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Volume 47 (2003)
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Volume 46 (2002)
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Volume 45 (2001)
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Volume 44 (2000)
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Volume 43 (1999)
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Volume 42 (1998)
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Volume 41 (1997)
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Volume 40 (1996)
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Volume 39 (1995)
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Volume 38 (1994)
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Volume 37 (1993)
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Volume 36 (1992)
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Volume 35 (1991)
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Volume 34 (1990)
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Volume 33 (1989)
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Volume 32 (1988)
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Volume 31 (1987)
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Volume 30 (1986)
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Volume 29 (1985)
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Volume 28 (1984)
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Volume 27 (1983)
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Volume 26 (1982)
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Volume 25 (1981)
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Volume 24 (1980)
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Volume 23 (1979)
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Volume 22 (1978)
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Volume 21 (1977)
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Volume 20 (1976)
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Volume 19 (1975)
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Volume 18 (1974)
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Volume 17 (1973)
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Volume 16 (1972)
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Volume 15 (1971)
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Volume 14 (1970)
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Volume 13 (1969)
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Volume 12 (1968)
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Volume 11 (1967)
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Volume 10 (1966)
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Volume 9 (1965)
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Volume 8 (1964)
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Volume 7 (1963)
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Volume 6 (1962)
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Volume 5 (1961)
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Volume 4 (1960)
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Volume 3 (1959)
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Volume 2 (1958)
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Volume 1 (1957)