Electron-Spin Exchange Coupling Transmitted by 58,60Ni (I = 0) and 59Co (I = 7/2): Does the Nuclear Magnetic Moment of the Spacer Atom Show?,1

Autor: Bernhard Metz, Christoph Elschenbroich, and Bernhard Neumüller, Andreas Behrend, Klaus Harms, Martin Wünsch
Rok vydání: 2005
Předmět:
Zdroj: Organometallics. 24:5509-5517
ISSN: 1520-6041
0276-7333
Popis: The trinuclear complexes {(Me 2 P-η 6 -C 6 H 5 )2M}2Ni 7 (M = V), 8 (M = Cr), {(Me 2 P-η 6 -C 6 H 5 ) 2 M} 2 CoH 10" (M = V), 11 (M = Cr), and {(Me 2 P-η 6 -C 6 H 5 )(η 6 -C6H6)M}2Ni(CO)2 14" (M = V) and 15 (M = Cr) have been prepared and characterized by means of X-ray crystal structure analysis in two representative cases (11, 15). The "closed" complexes 7", 8, 10", and 11 are semirigid, and the "open" species 14 and 15 are conformationally flexible. Magnetocommunication has been studied for the diradicals 7", 10", 14", and 15. + . + by fluid solution EPR spectroscopy. Comparison of 7" with 10" shows that the magnetic moment of the nucleus 5 9 Co fails to shape the 5 1 V hyperfine structure in any discernible way. The flexibility of 14" furnishes this complex with the largest exchange coupling constant J in the series and is responsible for a pronounced temperature dependence, as demonstrated by alternating EPR line widths upon lowering the temperature. Isoelectronic replacement of V. by Cr. + in the terminal sandwich units yielding 15. + . + profoundly attenuates the exchange coupling. Cyclic voltammetry reveals that the complex 10" engages in a five-step redox chain 2- -‖0‖+‖2+‖3+. Since the central couple 0‖+ represents the oxidation of the spiro cobalt atom, the redox splitting δE 1 / 2 (0‖-,-‖2-) is governed by a neutral spacer and δE 1 / 2 (3+‖2+,2+‖+) by a cationic spacer. The positive charge on the spacer exerts a leveling effect in that δE 1 / 2 (reduction) = δE 1 / 2 (oxidation), contrary to spacers of constant charge, for which δE 1 / 2 (reduction) > δE 1 / 2 (oxidation) is commonly observed.
Databáze: OpenAIRE
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