Tetraammineruthenium(II) and -ruthenium(III) Complexes of<i>o</i>-Benzoquinone Diimine and Their Redox Series

Abstract

The complexes [Ru(NH(3))(4)(4,5-R(2)-bqdi)](n)(+) where bqdi is o-benzoquinone diimine, R = H, Cl, or OMe, and n = 2 or 3 have been characterized by elemental analysis, optical spectroscopy, electrochemistry, spectroelectrochemistry, and electron paramagnetic and nuclear magnetic resonance spectroscopies. ZINDO/S calculations provide a very detailed picture of the degree of mixing existing between metal and ligand orbitals. Both pi back-donation and ligand pi-d mixing are important such that these compounds are considered to be extensively delocalized. In the Ru(III) systems compared with the Ru(II) systems, ligand pi-d mixing is somewhat more important and pi back-donation somewhat less important. Assignments of the electronic spectra are presented in detail in terms of the degree of mixing in the various orbitals. Surprisingly, on the basis of the ZINDO analysis, the lowest energy, strong, visible-region band in the electronic spectra of the Ru(III) species is shown to be predominantly MLCT and not LMCT as might have been assumed.