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 (tetracya noethene), TCNQ (tetracyano-p-quino-dimethane), TCNP (2,3,5,6-tetracya nopyrazine), and TCNB (1,2,4,5-tetracyanobenzene), were synthesized in the respective (8+) states with PF6- (TCNE, TCNQ, TCNP) or CF3SO3- co unterions (TCNB). IR, UV/vis/near-IR, and XPS spectroscopies were used to characterize the tetranuclear (8+) ions which exhibit four equival ent nitrile and pentaamminemetal groups and intense long-wavelength op tical absorptions. The(8+) ions are easily oxidized to (10+) species a nd reduced stepwise to (7+) and (6+) ions; EPR, UV/vis/near-IR, and, i n part, IR spectroelectrochemical techniques were applied to these oxi dation states in the case of the TCNE, TCNQ, and TCNB systems. The com plexes may be described as fully delocalized symmetrical tetrametalla pi systems {(TCNX(delta))[Ru-II+delta/4(NH3)(5)](4)}(n+) with partiall y 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.