J O U R N A L O F THE AMERICAN CHEMICAL SOCIETY (Registered in U.S. Patent Office)
VOLUME
(0Copyright, 1961, by the American Chemical Society) NUMBER 8
MAY 3, 1961
83
PHYSICAL AND INORGANIC CHEMISTRY [CONTRIBUTIOX FROM
THE
DEPARTMENT OF CHEMISTRY OF THE MASSACHUSETTS INSTITUTE OF TECHSOLOGY, CAMBRIDGE, MASS.]
Magnetic Investigations of Spin-free Cobaltous Complexes. V. Tetracyanato Cobaltate (11) Ions B Y F. ALBERTC O T T O N ‘
Tetra-azido and
AND M A R G A R E T GOODGAME
RECEIVED KOVEMBER 25, 1960 The electronic spectra between 0.4 and 2.0 microns and the magnetic susceptibilities between 70 and 300°K. of the tetra] [eo(NC0)4] -z, are reported. These results are interpreted azido- and tetra-isocyanatocobaltate( 11) ions, [ C O ( N ~-*) ~and using ligand field theory to show the following structural and electronic features of these complex ions: (1) they are tetrahedral; (2) in [C0(h’C0)4]-~it is almost certainly the nitrogen atoms which are bound to the Co(I1); (3) -h’CO- lies toward the stronger end in the spectrochemical series but toward the weaker end in the nephelauxetic series relative t o Kx-; (4) the metal-ligand bonds possess covalent character; (5) the spin-orbit coupling constants of Co(1I) in these complexes are -80% of the free-ion value.
Introduction the spectral band expected for all tetrahedral To extend the program of study of the magnetic Co(I1) complexes in the 1-2 micron range occurs properties of spin-free cobaltous c o m p l e x e ~ , ~we - ~ near the high energy end of the range, thus making have investigated the tetra-azido and the tetra- its observation and measurement unusually con~ ] - ~[CO(NCO)~]-~.venient. cyanato complexes, [ C O ( N ~ ) and Experimental The existence of the former was reported recently6; Materials.-Tetraphenylarsoniurn tetra-azidocobaltate the latter has been known for some time6though no recent investigations of it have been reported.’ (11) was prepared and recrystallized from acetone/carbon In conjunction with the magnetic study, the elec- tetrachloride as directed by Senise.6 Anel. Co, 5.86; C , 57.40; H, 3.81. M.p. 153.5 (lit.,5 tronic spectra have also been examined. The elec- 153-154’). tronic spectra together with the magnetic data leave The potassium tetracyanatocobaltate (11)was prepared by no doubt that these anions are tetrahedral and per- adding a hot solution of potassium cyanate (32.4 g., 0.4 mit us t o evaluate certain parameters of the elec- mole) in uTater (30 ml.) to a hot solution of C o ( N O ~ ) ~ . 6 H ~ O tronic structures. The methods by which the (29.1 g., 0.1 mole) in ethanol (140 ml.). On cooling, a mixof deep blue crystals with a pink powder was formed. spectral and magnetic data may be analyzed to ture This was filtered off and the blue compound dissolved out yield a considerable amount of information about with acetone and then reprecipitated from the hot acetone the electronic structure of the metal ion and its with dioxane. It u-as immediately filtered off and dried in interaction with the ligands are presented and ap- vacuum. The yield was 5.4 g. of dark blue crystals. Anal. Calcd. for C4CoKzN404: C, 15.74; Co, 19.31; S, plied to these two complex ions. This kind of analy- 18.36. Found: C, 15.59; Co, 19.30; N, 18.46. About sis is applicable to any tetrahedral complex and the 0.27, hydrogen was also found due, presumably, to the methods described here will be applied subsequently slightly hygroscopic nature of the compound. to a number of others. However, because of the The new compound butyltriphenylphosphonium tetrarelatively strong ligand fields in these two species, cyanatocobaltate(I1) was prepared by adding a solution of (1) Alfred P. Sloan Foundation Fellow. (2) R. H . Holm a n d F. A. Cotton, J. Chem. P h y s . , 31, 7 8 8 (1959); 32, 1168 (1960). (3) F. A Cotton and R. H . Holm, J . Am. Chem Soc., 82, 2979 (1960). (4) M. Goodgame and F. A. Cotton, J. Phys. Chem., in press. ( 5 ) P. Senise. J. A m . Chcm. Soc., 81, 4196 (19.59). (6) C. W Blomstrand, J. brakt. C h e m . , [ Z ] 3, 221 (1871). (7) P. Pascal, BtrZl soc. chim. France, [ 4 ] 16, 19 (1914).
3.8 g. of Co(P1’03)243H20in 4 ml. of water to 50 g. of KCSO in 30 ml. of cold water; 8 g. of butyltriphenylphosphonium bromide in 30 ml. of hot water was added, and the blue precipitate filtered, washed with water, and dried in vacz~o. The yield was 7.9 g. of dark blue crystals, m. p., 120.5121.5’. Anal. Calcd. for C4sH&oN40aPs: C, 66.59; H, 5.59; N, 6.47; P, i.15. Found: C, 66.65; H, 5.47; N, 6.74; P, 7.08. Magnetic Measurements.-The magnetic susreptibilities mere measured a t various temperatures using a Gouy bal-
1777
1778
F. ALBERTCOTTON AND MARGARET GOODGAME
ance as previously described.*-‘ The Gouy tube was calibrated with Mohr’s salt (taking x~ as 31.67 X 10” c.g.s. units at 299”). The calibration was checked by measuring the susceptibility of CuSOc5HzO for which a value of xp equal to 6.01 f 0.05 X 10” c.g.s. units was obtained. This agrees satisfactorily with the values 6.05 X lo-$,* 6.14 X IOdo and 5.95 X given in the literature. The experimental results and derived quantities are recorded in Table I. The diamagnetic corrections used were -500 X 10-6, -120 X and -511 X c.g.s. units per mole for the [( C&hAsl z [co( Na 141 , &Co( iYC0 )d and [( C& )a( n-GH 0)P]2 [ Co(NCO)4] respectively. The gram susceptibility of Kz/Co(NC0)4]was reported by Pascal’ as 8.10 X 10” c.g.s. units a t an unspecified temperature. From this datum, perf assuming a temperature of 20’ would be 4.38 B.M., which agrees with our result (4.39 B.M. a t about 20°, calculated making no correction for
ELECTRONIC SPECTRA OF Medium Acetone
Nitromethane
CHCli
CHINOY
{z
TIP).
Electronic Spectra.-The spectra were measured usiiig a Beckman DK recording spectrophotometer for solutions and a Beckman DU spectrophotometer equipped with the standard reflectance attachment for powders.
Discussion Electronic Spectra.-We shall first discuss the electronic spectra since certain information derived therefrom will be required in the treatment and interpretation of the magnetic data. I n a tetrahedral field, the 4F ground term of Co(I1) is split to give the following states, in increasing order of energies: 4A2,4T2,4T1(F). In addition, there is a (T1(P) state originating from the 4P term of the free ion. We denote the frequemies (an.-;) of the 4T1(F)and 4Az -+ transitions 4A2+ 4T2,4A2 IT1(P) respectively as vi, v2 and v3. From Tanabe and Sugano’s results” we can derive these convenient expressions for these frequencies
-
A 1.5A 7.5B’ Q va = 1.5A 7.S‘ Q Q = ’/2[(O.6A - 15B’)a VI ~2
+ +
-
+
+ 0.64A*]1/a
(1)
in which A is the modulus of the ligand field strength and B’ is the effective value of the Racah interelectronic repulsion integral. It has also been shown by Lowi2 that each of the three upper states will be split by spin orbit coupling, w-ith the splitting in the two Tl states
The transitions vz and v3 have bcen observed in each of the complexes reported here. The experimental data are collected in Table I. While the solution spectra mill be the basis for subsequent discussion because of their superior resolution, the reflectance spectra of the v3 bands in each case are important because they show that, allowing for the poorer resolution of the reflectance spectra, there is no significant change in the complex ions upon solution in the solvents used. Turning first to the v3 bands, we note that each one consists of three reasonably strong components. (8) B. N . Fig& and R. S. Nyholm, J . Chem. Soc., 331 (1959). (9) S. Sugden, ibid., 161 (1932). (IO) C. J . Gorter and W.J. de Haas, Comm. Kammrlingh Onses Lab., Leiden, No. 210 d, p. 39 (1930). (11) Y.Tanabe and S. Sugano, J , Phyr. SOC.,Jopon, 9.753 (1954). (12) R. Stahl-Brada and W. Low, Phys. Rn.,119, 775 (1969).
Acetone
Solid (reflectance) CHICN
Solid (reflectance)
Acetone
TABLE I [Co( IONS
THE
Crn.-l 16,260 15,270 14,600 16,180 15,150 14,490 7,220 6,410 -5,880 7,330 6,760 5,970 5,800 7,300 1370 1520 6,580 -5,880 -1700 -625 16,000 14,500 690 >1200 I200 Se(C2H& > Te(CzHd2
>
As(n-GH,)s
>
It will be noted that there is little indication of how this series can be leaved into the major one given above. In this paper we describe magnetic and spectral studies of Co(I1) complexes of the types [Co(R3P)2X2]and [Co(R,P)X,]- which have been made with the objective of obtaining information about the relative positions of the ligands R3P relative to the ligands X in the spectrochemical series. Other results of the studies reported here concern the interrelation of the spectral properties and the magnetic properties, the origin of Weiss constants in these complexes and the effect of the differences in the positions of the two kinds of ligands in a particular complex in the spectrochemical series upon the degree of splitting of the spectral bands. It may be noted that the com( 5 ) R. J. P. Williams, J Chem S o ? , 8 (1958). ( 8 ) T Chatt, C, A Gamlin, L E Orgel, l h i d , 1047 (1959).
