Synthesis, structure and electrochemistry of nitrogen base adducts of tetraacetatodiruthenium(II,III): dependence of redox potential and Ru-Ru bond length on axial ligand donor strength
Journal Publication ResearchOnline@JCUAbstract
Diadduct complexes of the mixed-valent form of diruthenium tetraacetate, [Ru-2(mu-O2CCH3)(4)L-2](PF6), with L = N-heterocyclic axial ligands quinuclidine (quin) (1), 4-methylpyridine (4-Mepy) (2), pyridine (py) (3), 4-cyanopyridine (4-CNpy) (4), 3-cyanopyridine (3-CNpy) (5) and 4-phenylpyridine (4-Phpy) (6) have been synthesized and all but 5 were characterized by X-ray crystallography to study the effect of the variation of the donor number (DN) of L on the Ru-Ru and Ru-L-ax bond lengths, the magnetic moment, the electronic spectral properties and the redox potential. When data from previous studies on O-donor adducts was also included a DN range of 18-61 could be established. Over this range the Ru-Ru bond length increases slightly from 2.265(1) to 2.2917(6) Angstrom as the donor number is increased from 18 (in [Ru-2(mu-O2CCH3)(4)(H2O)(2)](PF6)) to 61 in 1. UV - Vis measurements show a very slight increase in energy of the pi(Ru-O, Ru-2)-->pi*(Ru-2) transition, however, room temperature magnetic susceptibility measurements show no change in the magnetic moment over the same range of donor numbers. Electrochemical measurements in 1,2-dichloroethane of the Ru-2(4+/5+) redox couple show a decrease in the E-1/2 of 292 mV on going from complex 5 (weakest N-donor) to complex 1 (strongest N-donor). The E-1/2 range is over 400 mV when the unligated [Ru-2(mu-O2C(CH2)(6)CH3)(4)] complex is included (DN = 1 for dichloromethane). The variation of axial ligand base strength does not effect, the near-degeneracy of the (pi*delta*)(3) HOMO or the pi-->pi* energy gap, however, the actual (pi*delta*)(3) HOMO energy varies significantly and increases as the basicity of the axial ligand increases allowing selective tuning of the redox potential. (C) 2000 Elsevier Science S.A. All rights reserved.
Journal
Inorganica Chimica Acta
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Volume
304
ISBN/ISSN
1873-3255
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Issue
1
Pages Count
12
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Publisher
Elsevier
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DOI
10.1016/S0020-1693(00)00076-1