of Two Tris-Cobalt(lll) Compounds Donald C. Jackman and D. Paul Rillema' University of North Carolina-Charlotte, Charlotte, NC 28223
A standard experiment used in inorganic laboratory courses is the synthesis of tris(ethylenediamine)cobalt(III) a n d the subsequent separation a n d s t u d y of the optical isomers of this m a t e ~ i a lThe . ~ techniques for preparation of this compound are standard but suffer from t h e problem of reouirine a 4-h soaree with air t o oxidize t h e cobalt(I1) com&ex to the desire; cobalt(II1) complex. We report here a method of ~ r e ~ a r a t i oofn tris(ethvlenediamine)cobalt(III) a n d tris(2,i'-bipyridine)cobalt(lllj that will shorten the preparation time by approximately 3 h. Synthesis of Trls(ethylenedlamlne)cobalt(lll) ion Fourteen grams (50 mmol) of CoS04.7HzO was dissolved in 25 mL of HzO.Twelve milliliters (10.8 g, 180 mmol) of anhydrous ethylenediamine(en) was dissolved in 25 mL of H20, reacted with 5 mL of concentrated (12 M) hydrochloric acid, and then cooled to room temoerature in an ice bath. These two solutions were added. with stirring, t o n 250-mI. Srhlenk-ware flask, and 2 i:of activated charcoal wna added to the resultmi: xdutron. The mixture war sparged (wrth stirring! with a raprd stream of Clr from a lecture bottle for 2 min during which time the reaction mixture hecame quite warm due to the exothermicity of the reaction. The excess Clz was removed from the solution by vacuum aspiration until frothing ceased. Then the solution was heated ( 4 0 'C) to remove remaining CB from the reaction mixture. The pH of the solution (still hot) was adjusted to about I with aqueous ethylenediamine, reheated, and suction filtered (Buchner funnel, Whatman #I qualitative filter paper) to remove the charcoal from the reaction mixture. The hot filtrate was cooled in an ice bath, treated with saturated aqueous NHdPFs dropwise, and an orange solid slowly formed. The orange solid was isolated with a 60-mL medium-frit Buchner funnel, washed once with 30 mL of roo1water and three times eachwith 30-mL portions of roomtemperature ethanol and room-temperature ethyl ether, and dried in a room-temperature vacuum oven. The yield of [Co(en)a](PFs)a was 12.8 g (38%yield). The time required for synthesis and isolation of the product was approximately 1h. The UV-visible spectrum of the product in aqueous solution showed peaks a t 339 nm (r = 119M-'em-') and 467 nm (c = 138M-' em-'). These values are consistent with the literatu~e.~ Cyclic voltammetry in aqueous 0.1 M KNOa (Pt working electrode and P t counter electrode) yielded an irreversible Co3+"+ reduction wave at
approximately +0.10 V versus SSCE (sodium saturated calomel electrode). Synthesis of Trls(2,2'-blpyridlne)cobalt(lll) Ion One-tenth of agram (0.77 mmol) of anhydrous CoClz was addedto 0.42 g (2.7 mmol) of 22'-hipyridine(bpy) dissolved in 50 mL of 0.1 M HCI stirred in a 100-mL Schlenk-ware flask. To this solution was added 0.1 g of activated charcoal, and the resulting mixture was sparged, while stirring, with a rapid stream of C12 from a lecture bottle for 30 s. The excess Clz was removed from the solution as described above. The hot mixture was suction filtered (Buchner funnel, Whatman #1 qualitative filter paper) to remove the charcoal. The filtrate was cooled to room temperature and treated with saturated aqueous NH4PFs dropwise, whereupon a yellow solid formed immediately. The product, tris(2,2'-bipyridine)cobalt(III) heaafluorophosphate, [Co(hpy)a](PFs)a,was isolated on a mediumfrit Buchner funnel and washed twice each with room temperature water, ethanol, and ethyl ether. The product yield was 0.53 g (71% yield). The total time required for preparation and isolation was about 50 min. The product was dried in a room-temperature vacuum oven. The UV-visible spectrum of this compound dissolved in acetonitrile exhibited three peaks: 309 nm (e = 4.34 X lo4 MM-'cm-'), 318 nm, sh ( r = 3.89 X 10" M-1 em-'), and 453 nm (e = 77.5 M-' cm-') and are in agreement with previously published r e ~ u l t s .Cyclic ~ voltammetrv (0.1 M tetrabutylammonium hexafluorophosphate in nretmitrile.as supportmz ;lectrol~.te/solvent, Pt working and counter electrodes, gave reversible Co'Co'? Ir, and C d * " waver at t0.31, -0.99, and -1.60 V versus SSCE.respecti\,ely.
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Acknowledgment We thank t h e Office of Energy Science of t h e Department of Energy under Grant I)E-FfiOS-84ER-I3263for support. p~
' Author to whom correspondence should be addressed.
Angelici. R. Synthesis and Technique in Inorganic Chemistfy. 2nd ed.: ~~.Saunders: 1977: DD 71-80. Mead, A. Trans. F&aday Soc. 1934. 30, 1052. Ell~s.P.: Wnlkins. R. G.; Williams, M. J. G. J. Chem. Sac. 1957. 4456. Tnis reference reported only the visible peak. ~~~
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Volume 66
Number 4
April 1989
343
