FAR-INFRARED SPECTRA OF COBALT-XITROAMMINS COMPLEXES
Oct., 1963
area X Clausing factor) and B’ is constant. Combining eq. 1 and 2 and eliminating g gives
(3) where Bo is a constant for samples of the same compositioii.I5 If apparent pressures Pk, arid P k l are measured a t the same sample composition and temperature with two different orifices of effective areas al and az, then two equations in the form of eq. 3 result. Solving these equations simultaneously, the result is Peq
PIc,Pk2(al- @i)/(alPk, -
d k , )
(4)
Substituting the data from Fig. 1 in eq. 4, the equilibrium decomposition pressure of P-Kb5Ge3was found atm. a t 1757OK. to be 2.44 f 0.10 X (15) It should be noted that eq. 3 is of the same form as the simpllfied
Whitman-Xotzfeld equation. face area oi the sample.
The constant, Ba, is analogous t o the sur-
2 147
Assuming the free energy functions of a- and pNb6Ge3 to be additive from the elements, = 95.7 =I= 3 kcal. for reaction 11. Taking the enthalpy of sublimation of germanium as 90.0 =k 1.0 kcal./mole, for the reaction 1/0,67Nb(s)
+ Ge(s)
=
l/0.67NbGeo.~~(s), AHODS = -22.9
i2
kcal.
NbGez.-NbGez has the hexagonal CrSiz type crystal structure. Quenching experiments5 have shown that KbGez disproportionates at 1756 15OK. By estimating the activity of germanium in the liquidus as 0.85 =I= 0.10, the free energy may be calculated for the disproportionation reaction
+
0.752KbGez(s) = 0.752XbGeo.67(~) Ge(1) Assuming the free-energy functions to be additive, the enthalpy of formation of one-half mole of NbGez from the solid elements a t 298’K. is - 10.4 f 2 kcal.
FAR-INFRARED SPECTRA OF SOME COBALT-NITROAICIILIINE COMPLEXES BY GEORGE BLYHOLDER ASD ALLAXKITTILA Department of Chemistry, University of Arkansas, Fayetteville, Arlcansas Received February 15, 1963 The infrared spectra in the CsBr region have been obtained for sodium hexanitrocobaltate( 111), nitropentaamminecobalt(II1) chloride, nitritopentaamminecobalt(II1) chloride, cis-dinitrotetraamminecobalt(II1) chloride, and trans-dinitrotetraamminecobalt(II1) chloride. Vibrational assignments are discussed on the basis of treating the NOS- group as a single unit. A rocking vibration of the NO%-group is assigned to a strong band near 600 cm. -I. ‘The principal spectral difference in the CsBr region between the nitro- and nitritopentaammine complexes is the absence for the nitrito complex of the strong band near 600 cm.-’ for the NO%-rocking vibration. As well as a strong band a t 615 cm.-l, the hexanitro complex ion has strong bands a t 370 and 446 cm.-’. On the basis of a correlation with the hexaammine complex ion, four bands for the nitropentaammine complex a t 490, 475, 455, and 430 cm.-l are assigned t o symmetry species A and E of the Cqv group representation of the nitropentaariimine complex.
hexaammine complex ion. Also included in the series htroduction studied are the nitro- and nitritopentaammine comhave dealt with the infrared A number of plexes. We thought it would be of interest to examine spectra of the hexanitrocobaltate(II1) ion and various the effect of this structural isomerism on the skeletal cobalt-nitroammine complexes in the NaCl region of vibrations. the spectrum. Only vibrations of the NH, and NOzligands and a ISH3 rocking mode are found in the KaC1 Experimental region of the spectrum. I n order to observe frequencies [Co(NHZ)alJOz]Clz was prepared? by treating chloropentaammine cobalt(II1) chloride with sodium nitrite. of skeletal vibrations of these complexes it is necessary t r a n ~ - [ C o ( N H ~ ) ~ ( NC1 0 ~was ) 2 ] prepared? by treating cobaltous to obtain spectra in the CsBr region. The oiily work chloride with sodium nitrite in an ammoniacal solution. The published concerning the spectra of these ions in the cobalt was oxidized by a stream of air bubbled through the soluCsBr region was the inclusion of a spectrum of [Cotion. (N02)6]-3in a large collection6 of spectra of inorganic cis-[Co(NHs)4(NO~)~lCl was made7 by oxidizing cobaltous acetate with a stream of air in the presence of ammonia and ions in the CsBr region. This spectrum was presented sodium nitrite. with no comment on vibrational assignments. In this ~itritopentaamminecobalt(II1) chloride was prepared? by work the spectra in the CsBr region of a number of coolingfor several hours a solution containing chloropentaamminecobalt-nitroammine complexes are presented along cobalt(II1) chloride and sodium nitrite. with a redetermination of the spectra of [ C O ( K O ~ ) ~ ] - ~ . Naa[Co(N02)t] was prepared? by dissolving cobalt nitrate in an acetic acid solution with sodium nitrite. Vibrational assignments are discussed on the basis of I n all cases the infrared spectra in the NaCl region agreed with treating the NO2- group as a single unit and making a the published spectra of these complexes. correlation with the more thoroughly studied cobalt The spectra were obtained using the KBr pellet technique. (1) J. P. Faust and J. V. Quagliano, J . Am. Chem. Soc., 76, 5346 (1954). (2) D. G. Hill and A. F. Rosenberg, J . Chem. Phys., 24, 1219 (1956). (3) R. B. Penland, T. J. Lane, and J. V. Quagliauo, J . Am. Chem. Soc., 78, 887 (1956). (4) I. R. Beattie and D. 1.’ N. Satchell, Trans. Faraday Soc., 52, 1590 (1966). (5) I. R. Beattie and H. J. V. Tyirell, J . Chem. SOC., 2849 (1956). (6) F. A. Miller, G. L. Carlson, F. F. Bentley, and W. H. Jones, SpecIrochzm. Acta, 16. 135 (1960).
Samples containing 0.2 and 1.O% complex in KBr were pressed in an evacuated die a t 20,000 pounds pressure. The spectra were taken with a Perkin-Elmer Model 21 spectrophotometer equipped with CsBr optics. To avoid interference by atmospheric water vapor the sample area in the instrument was sealed with a sheet of plastic and the entire instrument purged with dry air. (7) G. Brauer, “Handbuoh der Praparativen Anorganischen Chemie,” Ferdinand Enke. Stuttgart , 1954.
"
100 BO
"
60
'"1
v
5 20
[ColNH,IsNOp]CIZ
500
600
450
400
310
300
WAVENUMBERS ICM-'].
Fig. 1.-Infrared spectra in the CsBr region of [Co("sh] +3, [ C O ( N H ~ ) ~ Yf2,Oci~-[Co(n-H~),(~\11)~)?] ~] +I, and trans- [CoiK&)r [NO,),] +I. The check marlis in the t?p spectra indicate the location of the Raman lines for [CJ(NH~)SJ +3.
__
19
,
25
18
20
,
22
24
28
28
30
3pp
[COINHJsNOz]C~e BOO
E40
450
4cQ
3%
skeletal vibrations of the [ C O ( S O ~ ) ~ion ] - ~will be considered on the basis of treating KO,- groups as single units. To this approximation the 51 total Tibratioiis break down into 15 vibrations for the octahedral skeleton, 18 internal vibrations of the KO2- groups, 6 rotations of the S O 2 - groups, and 12 rocking modes of the KO,- groups. In the ammine complexes since the NH3 group is a symmetric top the 2 rocking modes contributed by each NH3 are degenerate. For NO2 groups which do iiot form a symmetric top the 2 rocking modes would not he degenerate unless the NO2 groups were rotating rapidly enough to effectively form a symmetric top. Vibrational analysis of the skeleton indicates that there should be only 2 infrared active vibrations and these both belong to symmetry species Flu. In summary for the hexanitro complex ion the infrared spectrum is expected to contain two bands for skeletal vibrations and one or two rocking vibration bands as \vel1 as three principal bands for KO2- group vibrations. Comparison of the spectra of all of the complexes containing NOz- ligands in Fig. 1 and 2 reveals that all of them contain a strong band near 600 cm. -l and that at no other frequency is there a strong band in all of the spectra. Therefore this band is attributed to a EO,rocking vibration. This leaves tlie other two bands in the spectrum of Naa[Co(NOz)6] a t 370 and 445 cm.-l as the two skeletal vibrations of Flu. The spectrum of the nitropentaammine complex ion mill be discussed as a perturbation of the hexaammine complex ion. The correlation diagram relating the O h symmetry group for tlie hexaammine to the symmetry group for the pentaammine is shown below.
300
Oh
WAVE NUMBERS (Ch
