N I T R O S O P E N T A ~ I M I N E C O B h L THALIDES AKD
Rug. 5 , 1059
deformation vibrations of coordinated NH3 gives added strength to the assignments. A similar approach is suitable for the coordinated NOS- and sod- groups. The band observed a t 1604 cm.-l in the spectrum of [Co(NH3j4C03]C1 decreases to some extent in intensity on deuteration, indicating t h a t this band is an overlapping of two bands. One band is assigned to the NH3 degenerate deformation and
0 the other to a Stretching vibration of the C=O, \ / 0 in which the terminal CO group has considerable
‘d
double bond character. The band a t 1287 cm.-l, which is shifted considerably upon deuteration, is assigned to the NH3 symmetric deformation ; its observed value is compatible with the calculated value.14 The band a t 12GS cm.-l does not shift,
0 and may be attributed to one of the
\
C stretch-
/
0
ing vibrations. This frequency would correspond to the observed 1284 cm.-’ band of dimethyl carbonate, (CH30)zC0, assigned to the 0-C-0 stretching vibration. 2o The very broad absorption observed a t ca. 845 cm.-l in the spectrum of [ C O ( N H ~ ) ~ C O ~ ]isC Iassociated with the NH3 rocking vibration, as is evident from the degree of isotopic shift and from the comparison with calculated v a 1 ~ e s . l ~A sharp band a t 832 cm.-’ which does not shift on deuteration can be assigned to one of the carbonate skeletal vibrations. In the spectrum of [Co(NH3)5C03]I,the bands a t 1 t4S and 136-1 ciii.--l are assigiicd to tlic -0-C
stretchiiig vibrations.
0 /
\ 0 T h a t a t 908 tin.-' cor-
( 2 0 ) 13. Tschamler and R . Leutner, Monolsiz. Ciiem., 83, 1602 (19.52).
[CONTRIBCTION FROM THE
DEPARTMENT OF
3S2 1
NITRATE /
responds to the -0-C
0 deformation.
The ab-
\
0 sorption frequencies a t 1G12, 1310 arid 849 cni.-l are assigned to the NH3 degenerate deformation, symmetric deformation and rocking vibrations, respectively. Thus the infrared spectra of [Co(NHI)4CO1]Cl and [Co(NH3)&03]I confirm the bidentate struc-
turf of the first, Co
0 d\
C=O, and the iiionoden\ / 0 /O
tate structure of the second, Co+O-C
\
0
In the spectrum of [Co(NHa)$304]C1four welldefined bands, observed a t 1278, 1137, 1045 and 975 cm.-’ appear in addition to the characteristic NH3 deformation bands. These four replace the single, rather broad, and very intense infrared absorption frequency characteristic of the free s04- ion,21j22 u-hich appears a t about 1120 cm.-l. I t is evident that upon coordination the tetrahedral symmetry of the free SO4- is lost, and that this ligand involves an essentially covalent bond. In the spectra of [ C O ( N H ~ ) ~ S ~ O and ~ ] C[Co~ (KH3)&1]SzO3, the absorption frequencies in the 8-10 1.1 region are almost the same in regard to shape and relative intensity. It is noticed, however, that the frequencies in the spectrum of the compound containing coordinated S203’ are appreciably higher than those of the isomer containing free S203-. This implies that the symmetry of the free S203- ion remains essentially unchanged upon coordination, even though an essentially covalent bond is formed. (21) T. Wu, “Vibrational Spectra and S t r u c t u r e of Polyatomic Molecules.” National University of Peking, Kun-?ding, China, 1939, p. 217. 233. (22) F. A. hliller and C. H. W’ilkins, A i d C h e m . , 2 4 , 1233 ( 1 9 3 2 ) .
SOTRE DAME.INDIANA
CHEXISTRY, UNIVERSITY O F NOTRE D A M E ]
Infrared Absorption Studies of Inorganic Coordination Complexes. XXI. Nitrosopentamminecobalt Halides and Nitrate B Y E. P. BERTIN,*SAN-ICNIRO MIZUSHIMA, T . J. LANEAND J. v. QUAGLIAXO RECEIVED DECEMBER 30, 19% T h c iiilrared ahsorptioii spectra of the black nitrosopentamminecobalt halides and tlic red nitrosopentaiiitnitiecohalt nitrate were studied. From a consideration of the deformation vibration frequencies of the coordinated ammonia group, it is concluded t h a t both series contain cobalt in t h e 4-3 oxidation state and t h a t the differencebetween t h e series lie5 in t h e nature of t h e NO linkage.
Introduction The black shiny crystalline substance formed by bubbling nitric oxide gas through an ammoniacal (1) Paper X X in this series, 1 ~ 1 JsO U R N A L , 81, 3818 (1959). (2) R e v . Ernest P. Bertin, S.J., Seattle University; supported in p a r t under A . E . C . contract AT (11-1)-38,Radiation Project of t h e University of B o t r e D a m e ; presented a t t h e l:l3rd meeting of t h e American Chemical Society, San Francisco, April, 1058.
solution of cobalt(I1 j chloride satisfies the empirical formula C O ( N H ~ ) ~ N O CI t~ ~ liberates .~ nitric oxide when treated with water or dilute acid but is thoroughly stable when dry.4 hlany workers have investigated the nature of this compound in the (3) 1. S a n d and 0. G e n d e r , Ber., 36, 2083 (190:3), (1) A. Werner and P. Karrer, Helw. Chitn. A d a , 1. 54 (1318).
past.”-8 However, it has been established recently by X s m ~ s s e n ,et~ al., t h a t all previous workers who reported that the compound was paramagnetic were using an impure material and t h a t unless a very pure specimen was prepared and used for investigation, any conclusion drawn concerning the structure must be regarded as invalidated. The oxidation state of the cobalt atom has been designated by some a ~ t h o r s ~ .as ~ J+.2~ ~and by as +3. One group6 postulates a resonance between Co(1) and Co(II1). Another group* suggests an equilibrium mixture between two forms : one in which the promoted electron of the cobalt(I1) atom (presupposing 3d24s4p3 electron configuration) has its spin parallel to the odd electron of the three-electron bond in the NO group; thc other in which the spin of this promoted electron is antiparallel to that of the KO group. Dimeric3,13and m ~ n o m e r i c ~structures , ~ , ~ ~ have both been assigned to this black compound. Since Asmussen has shown that the paramagnetism is due to the impurity [ Co(KH3)6]C12,suggested structures6-8 which attempt to reconcile the paramagnetism with other properties need not be seriously considered. Red nitrosopentamminecobalt nitrate is apparently stable in water and acid^,^,^ is diamagnetic6,6 and is explained on the basis of cobalt(II1) and a NO- group coordinating like CN- or C1-. Short13 has reported the NO infrared absorption frequencies at 1172 and 1614 cm.-l for [Co(h’H3)6NOjClz and 1047 cm.-’ for [ Co(NH3)6NO](N03)2. The purpose of the present study is to determine the oxidation state of the cobalt atom in the black nitrosopentamminecobalt halides and the red nitrosopentamminecobalt nitrate. I t has been shown14that the deformation frequencies of the coordinated NH3 group characteristic of spin-free ( ; , e . , “outer orbital”) hexamminecobalt ( I I j halides differ greatly from those for the corresponding vibrations in spin-paired (k.,“inner orbital”) hexamminecobalt(II1) complexes. Consequently, in order to determine the oxidation state of the cobalt atom in the black and red nitrosopentamminecobalt coordination complexes, i t will suffice to compare the spectra of our complexes with those previously reported. Experimental Preparation of Compounds.-Kitric
oxide was prepared
by the reaction of sodium nitrite with acidic iron(I1) sulfate, the higher oxides of nitrogen being removed x i t h sodium
hydroxide .I* Black nitrosopentan~mitlec~)l)alt chloridc was prepared by bubbling nitric oxide gas for 4 hr. tlu-ough an ammonia soluP.R a y and H. R h a r , J , I v d i a l i Chfrrz. S o r . , 5 , 107 (1928). ( R ) J . L. hlilward, W .Wardlaw a n d W . J . R . R’ay, J . Chcm. SOL., 23:3 (1998). ( 7 ) J . H. Frazer and N. 0 . Long, J . Ciieni. P h y s . , 6 , 402 (19a8). (8) S. P. Ghosh and P . R a y , J . l i i d i q z Chcin. S O L .20, , 409 (194:3). (9) R . W . Asmussen, 0 . Bostrup and J . P. Jensen, Acln Chera. S c m i d . , 12, 24 (1958). ( I O ) T. hloeller, J . C h e w E d . , 23, 512 (1946). (11) N. Sidgwick and K . Bailey, P r o c . R o y . .Sot. ( I , o ? i d o n ) , 8 1 4 4 , 521 (1934). (12) U . I’. Rlellor and L). P.Crdig. J P r n c . R o y . . S i x . 5 . A . Lt’dfT, 7 8 , 23 (1911). (13) I,. 9 . S h o r t , Rpv. Pnvc Ap@i ChPin , 4, 4 1 (19,54), ( 1 4 ) E . P. Rertin, I . Kakagawa, S. hfizushima, T . J . Lane and J . V. Qu:,gli;lno. THISJ O U R N A L . 80, 526 (19581, (1.5) A . A . Blanchard, I n o r g . S y n . , 2, 126 (1946). (5)
tion of cobalt(I1) chloride a t 0 ” and ill the absence of A closed system was employed and kept uiider partial vacuum t o facilitate the flow of h-0. Black nitrosopentamminecobalt bromide and iodide were prepared in the same way as for the corresponding chloride, but the aqueous solutions of the cobalt(I1) halides used were more dilute. CoBrz.6HzO and CoI26H20 were prepared, and H I was regenerated, as previously reported.': Red nitrosopentammitiecobalt nitrate was prepared in the same way as [ C ~ ( N H ~ ) S S Obut ] Ca~t room ~ temperature and in the presence of air. Cobalt analysis \vas carried out by cathodic clcctrotlcposition.” Anal. Calcd. for [Co(KHd)5SO]Clz: Co, 24.05. Found: Co, 24.00. Calcd. for [Co(K1-la)jSO]Brz: Co, 17.69, Found: Co, 17.83. Calcd. for [ C O ( S H ~ ) ~ S O ] ICo, Z: 13.78. Found: Co, 13.40. Calcd. for [Co(NHs)sSOj(h-OS)?: Co, 19.20. Found: Co, 19.25. Absorption Measurements.-The illfrared spectra were obtained by means of a model 21 Pcrkin-Elmer recording infrared spectro~)hotometerwith a sodium chloride prism. The potassium bromide disk technique was employed1a and t h e results irerc clieclied i i i S u j o l mulls.
Results Table I lists the infrared absorption frequencies of the black nitrosopentamminecobalt halides and of red nitrosopentamminecobalt nitrate. Figure 1 shows the infrared absorption spectra of hexamminecobalt(II1) chloride, hexamminecobalt(I1) chloride and black nitrosopentamminecobalt chloride. TABLE I”
3240~s 3210~s 3230~s 3150~s 3110~s 3150~s
....
, . . .
....
1820~s 1628~s 1 6 4 4 ~ s
.. . ....
. .. ....
1293s
1293s
1208rn
117~lI11
11’74111
1192s
....
....
. ..
....
....
....
S12m =
798111 strong; 1x1
,
, .
.
. ,
XIi stretchirig S H stretching Coinbinctticin or civcrtrinc 1 6 2 8 ~ K H j degenei-atc deformation ( + S O vibration in halides)
3280vs 3180vs l770vrv
149L5tn
1 3 7 0 ~ s SO:, - degenerate frequeucy l2M1ii S H : , syiiitnetric tleforniatioil .. S H , s!~niiiietric deforriiaticin of ,
[Co(NH3)61X2 impurities ... 10-+3vw S O j - symmetric stretching , . 1010v \Y , . 830m KOd - out-nf-plaiie hcnditig 784111 ((1. S30iii KH3 nicking = medium; w = weak; Y = very.
Discussion Comparison of Table I with the infrared absorption values of hexamminecobalt(I1) and (111) halides previously reported14 and inspection of Fig. 1 makes i t evident that the deformation frequencies ( I O ) 7‘. lfoeller and G . 1, K i n g . i b i d . . 4, 168 ( I ( l i ) 1%’. F. Hillebrand a n d G. E. Lundell,
.4nalysis,” 2nd Ed. John R’iley a n d Sons, I n c . , ‘Sew York, S . Y . 1953, p. 419.
(18) J . P. l’aust and J . V. Quaglianu. ‘1111sJ O U R N A L , 76, 53.16 (1954).
Aug. 5 , 1059
NITROSOPENTAMMINECOBALT
HALIDES
AND XITRATE
3823
of the coordinated NH3 group in the black nitrosopentamminecobalt halides are essentially the same as those of the hexamminecobalt(II1) halides. On the other hand, they differ greatly from the absorption values of the hexamminecobalt(I1) halides. For example, the NH3 rocking vibration appears a t ca. 820 cm.-l in hexamminecobalt(II1) halides, whereas this same vibration is a t ca. 630 cm.-' in hexamminecobalt(I1) halides.14 The conclusion, Fig. 1.-Intrared absorption spectra: the spectra were therefore, is t h a t the cobalt atom in the black ni- obtained bl- means of a model 21 Perkin-Elmer recording trosopentamminecobalt halides has an oxidation infrared spectrophotometer with sodium chloride and cesium stateof +3. bromide prisms. T h e concentrations were cn. 0.6 mg. of each The only appreciable differences in spectra be- sample per 298 mg. of potassium bromide. The icniperature tween those of the black nitrosopentamminecobalt was 2 5 " : ~-, hexamminecobalt(I1) chloride, [Cohalides and the corresponding hexamminecobalt- (XH,'G] c12; - - - -, hcsamminecobalt(II1) chloride, [Co(111) halides are in the 6 and 8.5 p regions. We have ( i\TH3'6]C13; - . - * -, black t ~ i t r o s c i p e n t a ~ n ~ ~ ~ i ~ i chloecobalt previously shown14 t h a t hexaniminecobalt(I1) and ride [C~(NHB!:SO]CI.. hexamminecobalt( 111) complexes are distinguished from one another by the fact that the NH3 rocking trate, the frequencies a t 1'770, 1370 arid 830 c m - ' vibration in the Co(I1) appears in the region 630 are assigned to the free nitrate ion, from a comparicm.-l whereas that of the Co(II1) appears a t about son with the spectra of NaNOs, KNOa and AgS%Ocm. - I . The 1620 cm. -l band in the black nitroso- NO3.?I The very weak absorption peak a t 104% pentamminecobalt chloride is considerably more cm. -' may be another example of the infrared inacintense than the 1285 cm.-' band. In hexammine- tive totally symmetrical NO3- stretching vibration cobalt(II1) chloride, however, the 1600 cm.-l band becoming infrared active because of its arrangement is far less intense than that a t 1323 em.-*. This in the crystal lattice.22 The NHa deformation suggests that the high intensity of the absorption frequencies, though partly masked by KO3- vibraband a t 1620 cm. -I in the spectrum of the black ni- tions, are clearly discernible as those of the NH3 trosopentamminecobalt chloride arises from the group coordinated to cobalt(II1). The most dissuperposition of two separate bands of nearly the tinctive of these NH3 deformation frequencies, that same frequency. The other difference in spectra is of the rockit:g vibration, is a t ca. S30 c m - l . This in the 8.5 I.L region. The peak a t 1170 cm.-' in the peak is clearly recognized in the original spectrum spectrum of black nitrosopentamminecobalt chlo- as a superposition of a sharp, intense KO3- deformaride is absent in t h a t of the hexamniinecobalt(II1) tion absorption frequency upon a broad, less intense chloride. The absorption values a t 1170 cm.-' (for NH3 rockirg frequency. The NHa degenerate dethe chloride), 1174 cm.-l (for the bromide) and formation frequency is found a t 16% an.-'. T h a t 1192 cm.-' (for the iodide) are best explained as of the NHa symmetric deforniation would be exNH3 symmetric deformation frequencies of hexam- pected a t abcut 1320 cm.--' b u t is obscured by the niinecobalt(I1) halide impurities (1160, 1165 and strong NO- absorption in that region. The NO frequencies characteristic of the black 1190 cm.-' for chloride, bromide and iodide, respectively).l 4 Apparent magnetic susceptibilities nitrosopen tamminecobalt halides are not present in of the samples w h x e spectra are given above were the same part of the spectrum of the red nitrosokindly determined by F e r g u s ~ o n 'to ~ be the follow- pentamminecobalt nitrate. Hence, it may be conthat the isomerism of the black and red ing: [Co(NH3)5NO]C11-~e~= 1.5; [ C O ( N H ~ ) ~cluded NO]Br2-pefi = 1.6. In the light of the work of As- series is deperdent upon the nature of the cobrdinmussen and co-workers, this implies contamina- ated NO linkages and not upon a difference in oxidation state of the central cobalt atoms.23 tion by hexamminecobalt(I1) halides. The fact t h a t the XH3 rocking vibration, the A.cknowledgment.-Gratitu?e is expressed t o most distinctive deformation frequency, has slightly Professor Therald Moeller for first sendinq us a different values in the spectra of black nitrosopent- sample of black nitrosopentamminecobalt chloride amminecobalt chloride (812 cm.-') and in hexam- and arousing our interest in this problem. minecobalt(II1) chloride (827 mi.-') is not unex- SEATTLE, ~VASIIINGTON pected. Among other factors, coordinated elec(21) F. A . Miller and C. H . Wilkins, Aizol. C h c n z . , 24, 1253 (1'352). tronegative groups, such as C1-, C03=, NOs-, may ( 2 2 ) T . J L a n e , D . hT,Sen and J . V. Quagliano. J . Chum. P h y s . , 22, influence the deformation frequencies of coordin- 1856 (19313 ( Z a ) T h e revie\+er brought to our attention the paper of W . P. ated NH3.20 On the other hand, the difference beJ . Lewis and C. Wilkinson. J . I n o v g . h ' i i c l . C h e m . , 7 , 38 (1958), tween the NH3 rocking frequency of hexammine- Griffith. which appeared after t h e completion of our work. Evidence for cobalt(1I) chloride (634 cm.-l) and t h a t of black t h e hyponitrite structure for t h e black series suggested by Mellor nitrosopentamminecobalt chloride (812 cm. -I) is so a n d CraiglP apparently has been confirmed b y Wilkinson, el a i . , o n great that one can exclude the existence of cobalt- t h e basis of chemical evidence. T h e black complex salts, similar i o t h e simple hyponitrites, react with carbon dioxide t o form nitrous oxide (11) in the latter compound. The same reasoning and a carbonato complex. T h e y also, upon reaction with water, t u r n holds for the corresponding bromides and iodides. pink a n d produce mainly t h e aquopentammine with a little carbonato In the spectrum of nitrosopentamminecobalt ni- complex. Analysis of t h e gas, obtained b y heating t h e black salt with
....
L."*l
(19) J. E. Fergusson, University College, London, private communication, August, 1958. (20) D. G. Hill a n d A . F. Rosenberg, J . C k e m . P h y s . , 24, 1219 (1930).
I"
"/-.I..
water or dilute acid a n d then treating with solid potassium hydroxide, showed strong absorptions characteristic of nitrous oxide. T h e black chloride has been o i t a i n e d , in small yields, b y t h e addition of solid sodium hyponitrite t o a solution of anhydrous cobaltous chloride in liquid ammonia.
