TETRAAMMINERUTHENIUM(II) AND TETRARUTHENIUM(III) COMPLEXES OF O-BENZOQUINONE DIIMINE AND THEIR REDOX SERIES

The complexes [Ru(NH3)(4)(4,5-R-2-bqdi)](n+) where bqdi is o-benzoquin one diimine, R = H, Cl, or OMe, and n = 2 or 3 have been characterized by elemental analysis, optical spectroscopy, electrochemistry, spectr oelectrochemistry, and electron paramagnetic and nuclear magnetic reso nance spectroscopies. ZINDO/S calculations provide a very detailed pic ture of the degree of mixing existing between metal and ligand orbital s. Both pi back-donation and ligand pi-d mixing are important such tha t 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 term s of the degree of mixing in the various orbitals. Surprisingly, on th e basis of the ZINDO analysis, the lowest energy, strong, visible-regi on band in the electronic spectra of the Ru-III species is shown to be predominantly MLCT and not LMCT as might have been assumed.