Inorg. Chem. 1980, 19, 345-350
345
Contribution from the Department of Chemistry, The University of North Carolina, Chapel Hill, North Carolina 27514
The Oxo-Bridged Ions [(NH3)5R~OR~(NH3)5]n+ ( n = 4, 5 ) J O H N A. BAUMANN and THOMAS J. MEYER*
Received May 2, I979 The oxo-bridged dimer [ ( N H 3 ) 5 R ~ O R ~ ( N H 3 ) 5and ] 4 + the analogous 5+, mixed-valence ion have been prepared and characterized. The properties of the ions are consistent with strong electronic coupling between the ruthenium ions through the oxo ligand, and the mixed-valence ion, which is formally a Ru(II1)-Ru(IV) case, appears to be delocalized. junction potential effects. The measurements were made by using a PAR Model 173 potentiostat for potential control with a PAR Model 175 universal programmer as a sweep generator for voltammetric experiments. Values of n, where n is the number of moles of electrons transferred per mole of complex in an exhaustive electrolysis at constant potential, were calculated after measuring the total area under current [ ( b p y ) 2 C 1 R u O R u C l ( b p y ) 2 ]2+ ( b p y is 2 , 2 ' - b i ~ y r i d i n e ) , ~olivs. time curves for complete electrolysis. Reactions were judged to gomers like "ruthenium-red", [ ( N H 3 ) 5 R u O R u ( N H 3 ) 4 0 R u be complete when the current had fallen below 1% of its initial value. (NH!)5]6+,3 a n d clusters like [ R u ~ O ( C H ~ C O ~ ) ~(py ( ~ is ~ ) ~ ] +Electrochemical reversibility was determined by cyclic voltammetry, on the basis of the ratio of cathodic to anodic peak currents ( f C / i a ) p y r i d ~ n e ) . ~O n e reason for a n interest in such systems is t h a t and the potential separation of the oxidation and reduction peaks (A,!?,) the oxo g r o u p can support strong electronic interactions befor each electron-transfer process. All voltammetric measurements tween the metal sites,2 which can, in turn, lead to an extensive, were carried out at platinum electrodes. The solutions were deaerated reversible redox c h e m i ~ t r y . ~In, ~more general terms, strong by a stream of dry argon or nitrogen when potential scans or elecelectronic coupling c a n lead t o new chemical systems w h e r e trolyses were carried out at negative potentials. the c h e m i c a l a n d physical properties at the metal sites are Solution conductivity measurements were made in acetone and significantly modified compared to related monomers. In this acetonitrile at 25 OC by using an Industrial Instruments, Inc., Model context, oxo-bridged dimers and oligomers are potential sources RC- 16B1 conductivity bridge. Cell constants for the platinized of n e w materials t h a t may h a v e their own distinct c h e m i c a l platinum electrode conductivity cell were determined at 25 " C from measurements of the conductivity of 0.0100 M aqueous solutions of and physical properties. potassium chloride.I0 For spectrophotometric titrations, solutions T h e ion [ R u ( N H 3 ) , ( H 2 O ) I 2 + and the related 2+ hexaof Br2 in CH3CN were standardized by using c = 183 f 4 M-' cm-' ammine ion are known to be air sensitive in water. They react at 395 nm.' The titrations were carried out by adding aliquots of w i t h oxygen t o give t h e nearly colorless R u ( I I 1 ) ions Ruoxidant (Br,) to solutions of the complex and monitoring the changes (NH3)5H203+ and R u ( N H ~ ) ~ ~By+ contrast, .~ t h e ion [Ruin absorbance at 503 and 342 nm. (NH3>,(S)l2+(S = acetone), which has proven useful as a Materials. Tetra-n-butylammonium hexafluorophosphate (TBAH) synthetic ir~termediate,"~is also air sensitive, but exposure of was recrystallized three times from hot ethanol-water mixtures and the ion to oxygen in acetone results in a d r a m a t i c color change vacuum dried at 70 OC for 10 h. Acetonitrile (MCB Spectrograde) f r o m t h e characteristic d e e p orange of t h e acetone complex was dried over Davidson 4-A molecular sieves for electrochemical to an intense red. The details of t h e reaction with O2 will be measurements and used without drying for spectral measurements. Water was deionized and then distilled from alkaline permanganate. discussed in more detail in a later paper, b u t the point of All other solvents (reagent grade) were used without further puriinterest here is the fact t h a t t h e major product of t h e reaction fication. Argon was purified by passing it through a heated column is the dimer [ ( N H 3 ) 5 R ~ O R ~ ( N H 3 ) 5 ] 4 The + . dimer and its of activated Catalyst R3-11 (Chemical Dynamics Corp.) and then properties are of value because t h e existence of the ion fills through drying tubes containing Drierite. Elemental analyses were i n a g a p for t h e simple d i m e r i c a n a l o g u e of ruthenium-red, carried out by Galbraith Laboratories, Knoxville, Tenn., and Integral and its properties are of interest in comparison with other Microanalytical Laboratories, Raleigh, N.C. dimers. Preparations. [ R U ( N H ~ ) ~ C I ](1). C ~ ~The salt was prepared according to the procedure of Vogt et al." and recrystallized from hot Experimental Section (ca. 80-90 "C) 0.1 M hydrochloric acid. Measurements. Ultraviolet and visible spectra were recorded by [(NH,),Ru(OH,)](PF~)~.H~O (2a). The [(NH3)5Ru(OH2)]2' ion using Cary Models 14 and 17 and Bausch and Lomb Model 210 was generated essentially by the method of Harrison et al.,Iz slightly spectrophotometers. Infrared spectra were recorded on a Perkin-Elmer modified by Callahad and appearing in several paper^.^-^ The only 421 spectrophotometer in KBr pellets, at room temperature. Elecfurther modification was the use of a Schlenk-type apparatus. A trochemical measurements made were vs. the saturated sodium chloride solution containing [ (NH3)5RuC1]C12 was reduced over Zn-Hg calomel electrode (SSCE) at 25 f 2 OC and are uncorrected for amalgam in the upper portion of the apparatus and filtered into a saturated aqueous solution of NH4PF6,which caused the precipitation (1) J. D. Dunitz and L. E. Orgel, J . Chem. Soc., 2594 (1953). of the desired complex as the PF6- salt. Argon was passed into the (2) T. R. Weaver, T. J. Meyer, S. Adeyemi, G. M. Brown, R. P. Eckberg, bottom chamber, through the frit, and out the top during the reduction W. E. Hatfield, E. C. Johnson, R. W. Murray, and D. Untereker, J. step. The Ar flow was reversed to effect filtration of the solution of Am. Chem. SOC.,91, 3039 (1975). [ R U ( N H ~ ) ~ ( H ~ Ofrom ) ] ~ +the Zn-Hg amalgam. (3) J. E. Earley and T. Fealey, Inorg. Chem., 12, 323 (1973). [("3)5R~(S)](PF6)2 (2b) (S = Acetone). The aquo ligand was (4) (a) A. Spencer and G. Wilkinson, J . Chem. SOC.,Dalton Trans., 1570 (1973); (b) J. A. Baumann, D. J. Salmon, S. T. Wilson, T. J. Meyer, replaced by acetone by dissolving a portion of the pentaammine-aquo and W. E. Hatfield, Inorg. Chem., 17, 3342 (1978). complex, 2a, in deaerated acetone. After being stirred for 1 min, the ( 5 ) J. R. Pladziewicz, J. A. Broomhead, T. J. Meyer, and H. Taube, Inorg. solution was transferred through a needle to a flask of stirred, deaerated Chem., 12, 639 (1973). (6) R. W. Callahan, Ph.D. Dissertation, The University of North Carolina, Chapel Hill, N.C., 1975, p 115. (7) R. W. Callahan, G. M. Brown, and T. J. Meyer, Inorg. Chem., 14,1443 (10) H. H. Willard, L. L. Merritt, and J. A. Dean, "Instrumental Methods (1975). of Analysis", 4th ed., Van Nostrand, New York, 1965, p 720. (1 1 ) L. H. Vogt, Jr., J. L. Katz, and S . E. Wiberly, Inorg. Chem., 4, 1157 (8) R. W. Callahan, G. M. Brown, and T. J. Meyer, J . Am. Chem. SOC., 96, 7829 (1974). (1965). (9) B. P. Sullivan, J. A. Baumann, T. J. Meyer, D. J. Salmon, H. Lehmann, (12) D. E. Harrison, H. Taube, and E. Weissberger, Science, 159, 320 and A. Ludi, J . Am. Chem. SOC.,99, 7368 (1977). (1968).
Introduction A number of chemically well-defined dimeric and oligomeric complexes of r u t h e n i u m a r e known w h e r e t h e link between m e t a l sites is a p-oxo bridging ligand. T h e systems known include dimers like [ C I , R U O R U C ~ ~ ] ~ - and
'
0020-1669/80/1319-0345$01.00/0
0 1980 American Chemical Society
346 Inorganic Chemistry, Vol. 19, No. 2, 1980
Baumann and Meyer
diethyl ether, which caused precipitation of the PF6- salt. After The two could be physically separated to obtain the green crystals. collection and drying in a vacuum, the complex was immediately used ~ : 0.0; H , 5.34; Anal. Calcd for 4b, [ ( N H , ) , R u O R U ( N H , ) ~ ] C ~C, N, 24.76; CI, 31.33. Found: C,
