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The complexes { ~~~-TCNX)[RU(NH~)~]~}"+, TCNX = TCNE (tetracyanoethene), TCNQ (tetracyano-p-quinodimethane), TCNP (2,3,5,6-tetracyanopyrazine), and TCNB (1,2,4,5-tetracyanobenzene), were synthesized in the respective ( 8 f ) states with PF6-(TCNE, TCNQ, TCNP) or CF3S03-counterions (TCNB). IR, UV/vis/near-IR, and XPS spectroscopies were used to characterize the tetranuclear (8f) ions which exhibit four equivalent nitrile and pentaamminemetal groups and intense long-wavelength optical absorptions. The (8+) ions are easily oxidized to (IO+) species and reduced stepwise to (7+) and ( 6 f ) ions; EPR, Whishear-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 n systems { (TCNX6-)[Ru"f"4(NH3)5]4}"+ with partially reduced ligands and fractionally oxidized metal centers. The extent "d" 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.The coordinatively unsaturated pentaammineruthenium fragment [Ru(NH3)5]"+ has played a prominent role in the development of our understanding of thermal and photoinduced electron transfer reactivity. Highlights include ion-or molecule-bridged heterodinuclear complexes L,M-@-X)-Ru(NH3)5 as examples for inner-sphere electron transfer processes,' the homodinuclear Creutz-Taube ion (l), which is now recognized as a delocalized 1 (class III) mixed-valent system? and various ruthenium-modified cytochromes as models for long-range electron transfer in proteins.The [Ru(NH3)5]"+ complex fragment is distinguished by unusually inert bonds formed from the metal to nitrogen donor ligands in both the n = 2 and n = 3 states, by generally reversible redox processes Ru(II/III) at convenient potentials and with small reorganization energies, and by the hydrophilic nature of the resulting complexe~.~ Furthermore, the 4d5 or 4d6 ruthenium species are generally assumed to have well-defined electronic structures with low-spin configurations and chargetransfer excited states lying lower than ligand-field excited configuration^.^ Although a vast number of symmetrical dinuclear complexes has been reported in relation to the Creutz-Taube system (1) ' Dedicated to Henry Taube on the occasion of his 80th birthday.

The room-temperature reactions of closo- exo-4,5-[(µ-H) 2 Li(TMEDA)]-1-Li(TMEDA)-2,3-(SiMe 3 ) 2 -2,3-C 2 B 4 H 4 with anhydrous LnCl 3 (Ln ) Sm, Gd, Dy, Ho, Er), in molar ratios of 2:1 in dry benzene (C 6 H 6 ), produced the sandwich paramagnetic species [Li(TMEDA 1), Gd (2), Dy (3), Ho (4), Er ( 5)) in yields of 65%, 88%, 71%, 90%, and 93%, respectively. The compounds were characterized by IR spectroscopy, magnetic susceptibility measurements, and single-crystal X-ray diffraction studies. Compounds 2 and 3 were further characterized by EPR spectroscopy, and compound 1 was also characterized by 1 H, 13 C, 11 B, and 7 Li NMR spectroscopy. All compounds are bent-sandwich complexes in which a Ln(III) atom is coordinated to two carborane ligands and two chloride ions. The room-temperature magnetic susceptibilities of 1-4 were found to be 1.1, 7.3, 9.4, and 10.1 µ B per metal atom, respectively. Experimental SectionMaterials. Benzene, N,N,N′,N′-tetramethylethylenediamine (TMEDA), and n-hexane were dried over NaH and Na metal and doubly distilled before use. All other solvents were dried over 4-8 Å molecular sieves (Aldrich) and were either saturated with dry argon or degassed before use. The syn

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