TETRANUCLEAR PENTAAMMINERUTHENIUM COMPLEXES BRIDGED BY PI-CONJUGATED TETRACYANO LIGANDS RELATED TO TCNE - SYNTHESES AND SPECTROSCOPY OF DIFFERENT OXIDATION-STATES

The complexes {(mu(4)-TCNX)[Ru(NH3)(5)](4)}(n+), TCNX = TCNE (tetracyanoethene), TCNQ (tetracyano-p-quino-dimethane), TCNP (2,3,5,6-tetracyanopyrazine), and TCNB (1,2,4,5-tetracyanobenzene), were synthesized in the respective (8+) states with PF6- (TCNE, TCNQ, TCNP) or CF3SO3- counterions (TCNB). IR, UV/vis/near-IR, and XPS spectroscopies were used to characterize the tetranuclear (8+) ions which exhibit four equivalent nitrile and pentaamminemetal groups and intense long-wavelength optical absorptions. The(8+) ions are easily oxidized to (10+) species and reduced stepwise to (7+) and (6+) ions; EPR, UV/vis/near-IR, and, in part, IR spectroelectrochemical techniques were applied to these oxidation states in the case of the TCNE, TCNQ, and TCNB systems. The complexes may be described as fully delocalized symmetrical tetrametalla pi systems {(TCNX(delta))[Ru-II+delta/4(NH3)(5)](4)}(n+) with partially reduced ligands and fractionally oxidized metal centers. The extent ''delta'' of metal-to-ligand electron transfer in the ground state is higher for the TCNQ and TCNE complexes than for the tetranuclear TCNP and TCNB compounds.