chromite were bright green by transmitted light. Precautions to be Observed.-Appreciable attack of the platinum crucibles was observed when the concentration of sought compound to PbO or Bi203was too high. Dilute solutions, such as the ratio 1 : 6 used, produced little or no attack. Furnace linings should be new or uncontaminated by previous runs with other solvents. The presence of certain volatile substances in the muffle have been known to cause reduction of the PbO with
[ COXTRIBUTION FROM
THE
subsequent loss of the crucible due to the alloying of Pt and Pb. Acknowledgments.-The author wishes to thank Prof. L. Nee1 for a stimulating correspondence. Many helpful discussions were held with B. T. Matthias, S. Geller, M. A. Gilleo and E. A. \\Toad. The quantitative chemical analysis was done by J. P. Wright and the rare earth spectrochemical analysis by E. K. Jaycox. MURRAY HILL,S.J.
DEPARTMENT OF CHEMISTRY, UNIVERSITY OF SOUTHERN CALIFORNIA]
Halogenopentacyano Compounds of Cobalt(II1) BY ARTHURW, ADAMSON RECEIVED APRIL2, 1956 The new compounds K$Co(CN)iBrand K3Co(CN)61are described. They may be prepared either by the action of the appropriate halogen on aqueous pentacyanocobaltate( 111) ion or by t h a t of potassium cyanide on the appropriate aqueous halogenopentamminecobaltate( 111) species Possible mechanisms are discussed.
The number of known cyano complexes of Co- g. of metallic sodium was added gradually. After about two hours, the solution was cooled, and 50 cc. of water (111) is quite limited, in contrast to the extensive added. T h e solution was then acidified with nitric acid family of complex ammines. The species C O ( C N ) ~ - ~and t h e bromide present determined b y the 1.olhard method. is, of course, well known, and the following mixed Found for K , 30.5 f.0.4%; Co, 15.7 f O.lcG; Br, 19.4 i cyano complexes have been reported : KzCo(CX),- 0.05%. Calcd. for KCo(CiSLBr: K. 30.4: Co. 15.3: Br. " Calcd., assumrng 6.3%-K&O(CN),(HzOj impurity: (HzO) KCo (CN)4(H20)2 2 and K4Co(CiY)5(S203). 20.7. K, 30.2; Co, 15.6; Br, 19.4. The existence in aqueous solution of the ion CoT h e compound is very soluble in water and insoluble in (CN)4(OH)2-3has been p ~ s t u l a t e d ,but ~ the evi- organic solvents; as with Co( CN)6-3, insoluble salts are dence is not unambiguous. Finally, a binuclear formed with a number of transition metal ions. T h e dry potassium salt is light brown in color, and, in aqueous solucomplex containing five cyanides per cobalt ap- tion gives a n absorption maximum a t 393 mp with a n expears to result from the air oxidation of C O ( C N ) ~ - ~tinction ,~ coefficient of 163. No mixed halogenocyano complexes of Co(1II) Rate Studies.-Qualitative rate d a t a were obtained for are known, nor, indeed, do there appear to be any the above reaction by adding aqueous potassium bromo111)t o solutions of potassium cyanide known for any other central metal ion. In what pentamminecobaltate( buffered to the desired $H by either acetate or phosphate follows the properties of the new compounds K3Co- buffer. Qualitative rates were obtained either by noting (CN)5Br and K ~ C O ( C N )will ~ I be described, along the rate of color change or, in some cases, from a spectrowith evidence for the probable existence of K3Co- photometric measurement of the optical density. Preparations by the Reaction of Halogen with Co( CN)5-3. (C?r')&I, and a discussion of the rather interesting -The procedure for the preparation of the bromide was as reactions whereby these species may be prepared. follows. .isolution of 20 g. of cobalt(I1) nitrate hexahydrate Experimental Preparation of K,Co(CN)5Br by the Ray and Dutt reaction.--'~~ Twenty-one grams of potassium bromopentamrninocobaltate( 111) was added, with stirring, to a n aqueous solution of 24 g. of potassium cyanide, giving a dark reddish-yellow solution which evolved ammonia copiously. .iddition of alcohol t o about 7 s c ; by volume gave a voluminous cream colored precipitate which was filtered off, washed with alcohol and ether, and dried in a vacuum desiccator. The product \ v a s analyzed for potassiuin bj- the cliloroplatinate metliod,C for cobalt by the a-nitroso-8-naphtiiol method7 (after evaporation with hydrochloric acid to decompose the complex), and for bromide by an adaptation of a method reported by ELarnni.8 One quarter of a gram of the complex ~ i l refluxed s with 35 cc. of absolute ethanol and 3.5 (1) P I
