Reaction of osmium tetroxide with iodide ions

Notes

387

effected by the usual high vacuum techniques in thoroughly dried glass systems. The reaction vessel, which consisted of a 10 nun Pyrex glass ampoule provided with a filling arm (subsequently sealed off) and a break-off tip, was covered with opaque paint and a layer of aluminium foil to exclude light, and pre-treated with inactive chlorceilane (subsequently pumped off) to insure anhydrous conditions. The heterogeneous exchange runs at 0°C were carried out in an ice-water bath held in a large capacity Dewar flask. Complete liquefaction of the solid (liquid N~ cooled) trimethylchlorosilanein 30 sec was noted in all runs. The reaction flask was shaken intermittentlyto insure mixing. At the end of the exchange run, the reactants were separated at --78°C and radioassayed, using the gas phase counting method described elsewhere,c1°~ Concentrations of the reactants were calculated on the basis of known gas dosage volumes, pressures and temperatures. No corrections for the solubility of HC1 in liquid (CHs)sSiCI were applied. Part of this work was carried out at the University of Illinois. The support of the U.S. Atomic Energy Commission is gratefully acknowledged.

Nuclear Science Center Rutgers, The State University New Brunswick, New Jersey

Departmentof Biochemistry

ROLF~ H. H~RBER

SHIH-CH~NCHANG

University of Pittsburgh Pittsburgh, Pennsylvania (le) R. H. HERBER,Rev. Sci. Instrum. 28, 1049 (1957).

Reaction of osmium tetroxide with iodide ions (Received 26 July 1960; in revised form 14 October 1960) Tim reduction of osmium tetroxide by iodide ions in the presence of hydrochloric acid yields a variety of products. Earliercl,j~ it had been ~eported that four equivalents of iodine are produced, but the other reaction products were not identified; although one expects to obtain Os(IV) e.g. as OsClsI-, the formation of improbable derivatives such as HsOs!, had also been suggested. ~8~ After the removal of the iodine from the solution a dark green-blue solution containing the Os(IV) compounds remains. This investigationset out to identify the nature of these reduction products. The results are of interest because unusual mixed crystals with potassium hexachloro-osmate of a new chloro-iodo osmium IV complex are formed. The reaction between osmium tetroxide and potassium iodide was carried out in hydrochloric acid solution to minimize hydrolysis and the iodine liberated was extracted with chloroform (see flow sheet). The yield of four iodine atoms per osmium tetroxide molecule wasconfirmed.~l,~) Extraction of the aqueous solution with ether removed a deep green ether-soluble compound but all attempts to isolate this as a solid material were unsuccessful. Decomposition occurred on evaporation under partial vacuum, even in the cold. Also, the green colour was destroyed when the ether solution was treated with drying agents; this ether solution contained osmium and iodine in the ratio 1:5, but no potassium. It was concluded that the green solute was probably H[OsIs.H20] or perhaps Ht[OsIsOH] but owing to its instability it was not further investigated. By concentrating the aqueous solution until crystallization just began, two different crystalline substances were isolated, one soluble--subsequentlyshown to be potassium hexa-iodo-osmate (TV)--and the other insohible in acetone. Small amounts of potassium chloride and iodide were removed by fractionation and the two substances then separated by treatment with acetone. The acetone insoluble portion, analysed as KjOsCls.TsIe.isand at first a mixed crystal of KmOsCle and KsOsIs was suspected. X-Ray powder photographs showed that the compound was cubic as for (x~ D. J. RIAirrscmKov,Y. Appl. Chem. Russ. 17, 326 (1944). (s) F. KaAUHand D. WXLKEN,Z. Anorg. Chem. 137, 352 (1924). (s~ E. P. ALV,~EZ, C. R. Acad. Sci.,Paris 140, 12.54, 1905; Chem. News 91, 173 (1905). 13

388

Notes

Flow Sheet Os04 in 2.0 N HCI Excess KI Dark green solution Extract with chloroform

J

l

Aqueous Residue

CHCI8 solution-Contains four equivalents iodine

Extract withI ether |

Green ether extract: probably contains H[Osls.H.O]

Aqueous residue: Concentrated

I

t

1

(Acetone Insoluble) Hixed Crystals of KsOsCIe and K=OsCInle_n

Acetone

Soluble

K=Osl6

14,000 12~00 tO~O0

!,o

m

8000 6000 //// 4000 2000

500

600

700

Wavelength,

800

900

m/.,t

F/G. 1.--Visible spectra of: K,OsC16 (Ia and Ib), K=Osla (II), K2OsI e 0.044 g/l.) and K~OsCI e (0-72 g/l.) (III), [II one hour later (IV), KaOsCls.vsI0.=s (0"72 g/i.) (V). The e values for curve V were calculated assuming that all the iodine is present in the form of OsIe-. Spectra were taken within 20 rain of the dissolution of the crystals and the solvent was 1.2 M HC104, except for II where a hydroiodic-perchloric solution was used. The values of e for curve Ia m u s t be divided by 100.

Notes

389

K~OsCle with a --- 9"87 & 0.02/~, the reported figure for KzOsCle being 9.73 -4- 0.02 ,~;c~ the increase in cell size was apparently due to the presence of larger iodide ions in place of chloride ions. The molecular weight calculated from these X-ray data and from the density is 511 -4- 13. The average molecular weight for the formula K2OsCl,.7sI0.z5 is 504. Spectra have been found useful in establishing the nature of the mixed crystals. In Fig. 1 is shown the spectrum of K2OsC16 (I) in 1"2 M perchloric acid; the absorption due to the OsCl6 ~- ion above 500 mp, the region where all other compounds absorb, is clearly negligible and hence can be ignored for our purposes. The spectrum of K~Osle, however, depends critically on the time taken for measurement; a solution of K2OsI6(,~10 -4 m) in 1.2 M perchloric acid is initially violet but decomposes in less than one minute to give a blue solution (III) which undergoes decomposition much more slowly. The spectrum of this solution after one hour is given in curve IV. The true spectrum of OsI6 ~- is given in curve II, excess iodide ions having been added; this violet solution is quite stable, the spectrum agreeing with that reported by J~IRGENSEN151. NOW the spectrum of K2OsCls.Tslo.25 is given in curve V. This has been drawn by deliberately assuming (wrongly, of course) that all iodine is present as [Osld 2ion, i.e. that the substance contains 4.5 ~ K2OsI6. This assumption is clearly incorrect because curve V has a different shape from curve II and e is too large, 13,400 as compared with 7800 for the true [Osld 2- ion. Furthermore, unlikethe behaviour of [Osld 2- in solution the spectrum of the mixed compound K~OsC15.TsO6.2~ remained unchanged on standing in solution indefinitely; thus it is still blue-green after five days whereas a solution containing a mixture of K~OsC16 and K2OsI6 changes rapidly in colour owing to aquation of the [OsI6] ~- ion as discussed above. Indeed it changes to a yellow colour after only 12 hr. Thus both the spectrum and the remarkable stability of K2OsC15.7~I0.2s in aqueous solution rule out the existance of a discrete [OsI6] 2- group in the mixed crysta L We have come to the conclusion that the crystals contain a mixture of K~OsC16 and a hitherto unknown iodo-chloro complex of the type K2OsCI~Is_~. We believe that x is 3 or 4; this tentative suggestion is based upon the following argument. If we postulate that the hand at 6.55 m/~ has an e value of about 7000-8000 as for OsI8 ~-, then one calculates e = 4500 for [OsC14I~]~- [i.e. (13400)/3], e = 6750 for [OsClsIs] ~- and e = 9000 for [OsClzld a-. The expected value of e is thus intermediate between the values for [OsClaI~] ~- and [OsCl~Id ~-. At best the above is a very empirical procedure. The mixed crystal contains about 15 ~ [OsCl,I~] ~- if it is a di-iodo complex and about 9 per cent [OsCl,Is] ~- if it is a tri-iodo derivative. The compound is one of the few iodo-chlorides known and appears to be the first such compound of osmium, although several chloro-bromido mixed halides such as OsCl~Br~- and OsClaBr~ ~- have been reported among the platinum group metals, te~ All our attempts to prepare pure iodo-chlorides other than in these mixed crystals have been unsuccessful. Also, attempts to obtain a mixed chloroiodide containing a different CI:I ratio were unsuccessful. When the iodine concentration in the crystals is decreased the spectrum remains the same but the intensity is diminished indicating simply a smaller yield o f the chloro-iodo compound. This strongly suggests that only one chloro-iodo complex ion is present in the crystals. The value of the magnetic moment of the compound, determined at 20°C is 1.54 B.M. For comparison purposes we determined the magnetic moment of K~OsCle and the value observed (1.42 B.M.) agrees with previous work. ~7~ Experimental lodide ion reduction

Osmium tetroxide, obtained by heating K2OsO,.2HzO (0.05 g) with 2 N sulphuric acid (20 ml) and sodium persulphate (0.5 g) was distilled into 4 N hydrochloric acid (60 ml) and treated with excess potassium iodide (I.0 g) in an inert (CO2) atmosphere. The iodine was extracted with chloroform and titrated with thiosulphate. As the mean of several determinations 3'97 -4- 0.05 equivalents of iodine were liberated. ~4~j. D. McCULLOUGH,Z. Krist. 94, 143 (1936). ~5~C. K. JORGSNSEN,J. Mol. Phys. 2, 309 (1959). cs~ N. V. SIOGWICK,The Chemical Elements and their Compounds Vol. I I p . 1497. Oxford University Press

(1950).

~7~D. P. MELLOR,J. Proc. Ro7. Soc., N.S.W. 77, 145 (1944).

390

NOtes

Reduction products Osmium tetroxide (2 g) in water (200 ml) was added to 4 N hydrochloric acid (200 ml) containing potassium iodide (20 g). The liberated iodine and the ether soluble compound were removed by ether extraction. The resulting turquoise blue aqueous solution was evaporated on the steam bath until crystallization began. On cooling the crystals (1.6 g) were filtered, washed with water to remove potassium chloride and iodide, then with 90 % acetone and finally with pure acetone in which they are insoluble. (Found: K, 15.6; Os, 37.8; CI, 39.7; I, 5"9~o. KiOsCl6.TsI0.s5requires: K, 15.6; Os, 37.7; CI, 40.4; I, 6.3. Further evaporation yielded more of this compound but eventually the acetone soluble K~Osle was obtained. Ana~is Potassium was determined as potassium sulphate, and osmium by precipitating the element as the sulphide, then reducing this to the metal with hydrogen. Chlorine was determined gravimetrically, as silver chloride and iodine as palladous iodide, osmium having been previously removed by reduction to the metal with metallic zinc. Iodine was determined as paUadous iodine and chlorine obtained by weighing total halogen as (AgO + AgI), the known iodine content being substracted. Absorption spectra. These were determined with a Unicam SP 500 spcctrophotometer, for the visible region. The solution required for the OsI6 = spectrum was prepared a few minutes before use by dissolution of potassium iodide (8 g) in 1.2 M pcrchloric acid (100 ml), potassium pcrchlorate being removed by centrifuging. Infra-red spectra were measured in perfluorokeroscne mulls, and were recorded on a Perkin Elmer 21 double beam spcctrophotometer. X-Ray results. X-ray powder photographs showed the unit cell to be cubic, a = 9.87 -4- 0"02 A, the intensities of the lines being consistent with the fluorite-type structure. The density, measured by displacement of bromobenzcne from a pycnomcter, was 3.53 :k 0.08 g/cc. The molecular weight, assuming four molecules in the unit cell, is therefore 511 4- 13. Single crystals of the material were octahedral, and were not piezo-clectric; X-ray rotation photographs showed only the spots characteristic of the fluorite structure (more strictly, in this case, the anti-finorite structure), with no evidence of a lower symmetry. The X-ray evidence is thus consistent with a structure like that of KiOsCl0 c'~ with approximately I chlorine atom in 20 replaced by iodine, in a more or less random fashion, to givv the effective formula KsOsC1p~6Io.ll.

Acknowledgements--A grant to one of us (A. T.) from the Italian National Research Council is gratefully acknowledged.

Chemistry Department University College London Laboratory of Inorganic Chemistry University of Padua

E. FENN R . S . N'~aOLM P. G. OWSTONt A. Tugco

* Originally studied by Mr. E. FBh~q, now at E.L Du Pont de Nemours and Co., Wilmington, Delaware, U.S.A. I" Now at l.C.l. Akers Research Laboratory, Welwyn, Hertfordshire, England.