May, I%iI
~ I A G S E T I C1’HOPERTIES A S D
SPECTRUM OF COBaLT ORTHOSILICATE
and standzrd heat of combustion for the four thiaalkancs were used in computing values of standard heat of formtrtion, AHfo?y8 according to reaction 11. The results nC(c, graphit?) i- h/3 HJg)
+ $(e, rhornhic.) = C’,HbS(l)
Tli1
The heat of formation of S,(g) from rlionibic h11lfurZ3 was used to compute values of heat of formation of the thiaalkanes from Ss(g). These results and related properties are in Table 11.
Acknowledgments.-Dr. 1). 11. Fairbrother, Mrs. T . C. Rincheloe, and J . 1). D a w o n assisted are in Tahle XI Value3 of entropy from Table and ref. 27 wwe used in calculating the values of AFj”298 l o ant1 in some of the measurements reported in this paper. ,TT\
“I’
log Kf,g8 lo for reaction I1 given in Tahlr X I .
(28) W.I T . E l a n s and D 11. Waunian. 1614 49, 141 ( I r l i 2 )
X 4 G N ETIC INVESTIGATIONS OF SPIN-FREE COBA4LTOUSCOMPLEXES. IVo 1fAGNETIC PROPERTIES AND SPECTRUM OF COBALT(I1) ORTHOSILICATE BY ;\I \RGARET GOODGAME AND F.ALBERT COTTON Departmrnt of ChuntstrU, Jlassachusetfs Instztute of Technology, Cambridge, Mass. Rerewed November 2 , 1960
The temperature dependence of the magnetic susceptibility and the reflectance spectrum of the purple compound CozSi04 are reported. Although the color of the compound might suggest the presence of tetrahedrally coordinated Co( 11) ions, I t is shown that the magnetic data and the details of the spectrum lead unambiguously to the conclusion that the Co(I1) ions are octahedrally coordinated. This is in agreement with the previously reported X-ray powder pattern which indicated that Co&iOc has the olivine rather than the phenacite (Willemite) structure.
Cobalt (11) orthosilicate, Co2Si04,has been r~ ported’ to have the olivine structure. This meaiis that the Co(I1) ioiii occupy octahedral interiti in a close-packed array of oxygen atoms2 des the fact that the compound has a purplr color which ic; very reminiscent in both hue and intensity of the colors of some compounds cmtaining tetrahedrally c+oordinated Co(I1). Working with a Yery pure sample of Co2Si04 which had been prepared and used for a heat capacity determination in the Berkeley Thermodynamics Laboratory of the Bureau of Mines, we have measured the magnetic susceptibility and the yisible reflectance spectrum of this substance, in order to see whether they are in accord with the proposed olivine structure. As the data in Table I show, the cobalt(I1) ions follow the Curie-Weiss law in their magnetic behavior with a moment of 5.01 B.N. and a 8 value of -60‘. This B value may be attributed to a substantial antiferromagnetic interaction, which is not unexpected in view of the proximity of the Co(I1) ions to one another in the oliyine structure. The magnetic moment itself is in the range typical for octahedrally coordinated Co( I I ) .4~ Similarly, the reflectance spectrum is quite consistent with theoretical expectations for octahedrally coordinated cobalt (11). Ignoring the Pffcct of 4Tlg(F)-4TlK(P)interaction, we can estimate from the position of band B, which we assign to the 4T1K(F I-.~&~(F) transition, that A, the modulus of the octahedral ligand field, is about (1) P Carlitelli and SCI
M. Cola, A t t ~accad. naz. Ltncez, Rend. Classe
ps. mat. nat , 17, 172 (1954).
(2) A. F. ’Wells, “Structural Inorganic Chemistry,” 2nd Ed., Oxford t-niversity Press, 1Q!iO. pp. 387-388. (3) B. N. Figgis and R. 8. Nyholm, f. Chem. Soc., 12 (1954). (4) F. A Cottoa and R . H. Holm J Am Chent. S o c , 89, 2983 (1960) ( 5 ) C J Pdlhausm and C. K.J#rgensen, Acta Cham, Scand , 9 , 397 (lQ55)
‘7200 em.-’ us compared to a A value of about 9000 em.-‘ similarly estimated5 for the hexayuo ion. Band A a t -18,000 cm.-l is assigned as the “1,(F)-.4Tlg(P) transition. 30 25
300
Frequency, cm.-’ X 20 15
12
10
500 600 700 800 ROO 1000 Kave length, mp. Fig. 1.-The reflectance spectrum of Co2Si04. 400
Yo satisfactory interpretation of the qpectral and magnetic data would be possible a w m i n g tetrahedral coordination of the Co(I1) iom. If band A were assigned to the 4h2(F)+4T1(P) transition, this transition being commonly observed
792
J. P. DISMUKES, L. H. JONES AND JOHN C. BAILAR,JR.
in the visible in tet(rahedra1 complexes, band B a t 12,900 cm.-' would have no reasonable assignment. Moreover, with a tetrahedral field of the magnitude required to give the 4Az(F)-t4T1(P) transition a t the position of band A a magnetic moment of 4.34.5 B.M. would be expected, in serious conflict with the experimental result. Experimental The magnetic susceptibilities were measured using a sensitive Gouy balance, following procedures already described .E The experimental data and some derived quantities are collected in Table I. The reflectance spectrum of Co2Si01was measured using a Beckman DU spectrophotometer equipped with the standard reflectance attachment, MgCOs serving as the reference. The reflectance spectrum is shown in Fig. 1. (6) R. H. Holm and F. A. Cotton, J . Chem. Phys., 31,788 (1959).
Temp., OK.
T-ol. 65
TABLE I MAGNETIC DATAFOR CozSiOc XCor Diamagnetic Mol x lo', c.g.s.u.
cor., c.g.s.u. X 106
reff
299 (3)" 17,382 f 165b 73 4.58 193 (2) 24,284 910 73 4.35 77 (2) 46,979 f 495 73 3.80 a Figures in brackets show number of measuremente deviation from used to calculate mean values. "verage mean.
*
We thank Dr. Kelley of the Berkeley Laboratory of the Bureau of Mines for his kindness in supplying the sample, and the United States Atomic Energy Commission for financial support under Contract No. AT(30-1)-1965.
THE MEASUREMENT OF METALLIGAND BOND VIBRATIOKS IS ACETYLACETONATE COMPLEXES1 BY J. P. DISMUKES, L. H. JONES AND JOHN C. BAILAR,JR. william Albert Noyes Laboratory of Chemistry, University of Illinois, Urbana, Illinois and the Los Alamos Scientific Laboratory Los Alamos, New Mexico Receiaed November 3,1960
The infrared spectra of a large number of metal-acetylacetonate complexes have been recorded. The abRor tion frequencies below 700 cm.-1 are discussed in terms of coupling of metal-oxygen vibrational modes with three low-Kequency xibrational modes of the acetylacetonate anion at 654,520 and 410 cm.-I. It is concluded that no absorption band between (00-350 crn.-' can be assigned to a pure metal-oxygen vibration.
Introduction The infrared spectrum of acetylacetone has been investigated in a large variety of coordination compounds, but only a few measurements of the low-frequency vibrations of the metal-ligand bond have been reported. Measurements of metalligand vibrations have two advantages over the measurements of the internal vibrations of the coordinated ligand. First, trends in the metalligand vibrational frequencies are more directly related to the strength of the metal-ligand bond than are the trends of the internal vibrations of the coordinated ligand. Second, from the frequency of the metal-ligand stretching vibration, the force constant of the metal-ligand bond can be calculated. Such force constants give a measure of the bond strength independent of values derived from stability constants. The present study of the low-frequency infrared spectra was undertaken to investigate metal-oxygen bond strengths in metal-acetylacetonate complexes. It was hoped that metal-oxygen stretching vibrations could be identified and that force constants could be calculated for the metal-oxygen bond. The infrared spectra of acetylacetone2-6 and (1) Most of the preparative work reported here was done a t the University of Illinois and the infrared work a t Los Alamos. One of the authors (J.P.D.) wishes to thank the National Science Foundation, Minnesota Mining and Manufacturing Company, and the University of Illinois for fellowship assistance which made this work possihle. Inquiries concerning this article should he addressed to J.P.D. a t R.C.A. Laboratories, Princeton, New Jersey. (2) K. W. F. Kohlrausch and A. Pongratz, Ber., 67, 1465 (1934). (3) H. W.Morgan, U. S. Atomic Energy Commission Report AECD 2659 (1949).
many acetylacetonate have been measured by a number of investigators. The vibrations above 700 em.-', where there is little difference in the spectrum of acetylacetone and that of any metal-acetylacetonate complex, have been generally assigned to various normal modes of the acetylacetonate group. The lowering of the carbonyl frequency is the most noticeable change above 700 em.-' produced by coordination. Several investigators have found absorption bands in acetylacetone and its metal complexes in Morgan,* the region between 700-400 cm.-'. L e c ~ m t eand ~ ~ ~Mecke and Funk6 noted three strong absorption bands for acetylacetone in this region, and Lecomte assigned these bands to vibrational modes of two coupled acetone molecules. Morgan and Lecomte observed a number of bands in the spectra of divalent, trivalent and tetravalent metal acetylacetonates between 700-400 ern.-', but they could find no correlation between these bands and the oxidation state or character of the metal. Costa and Puxeddu'O obtained almost identical spectra for the acetylacetonate complexes of Cr(I1) and Cr(II1) in the 700-400 cm.-' region, and therefore assigned these bands to vibrations of the acetylacetonate ion. Martell," however, has (4) J. Lecomte, Disc. Faraday Soc.. 9, 125 (1950). (5) J. Lecomte, C. Duval and R. Freymann, B d . uoc. chim., France, 19, 106 (1952). (6) R. Mecke and E. Funk, 2. Elektrochem., 60, 1124 (1956). (7) L. J. Bellamy and R. F. Branch, J . Chem. Soc., 4491 (1954). (8) H. F. Holtzclaw, Jr., and J. P. Collman. J . Am. Chem. Soc.. 79, 3318 (1957). (9) R. West and R. Riley, J . fnorg. Nucl. Chem., I,295 (1958). (10) G. Costa and A. Puxeddu, rbid., 8, 104 (1958).
