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of our value for (3 In NIbT,),. We note further that our calculated value is of the same sign and agrees moderately well in magnitude with the difference in the partial specific volumes of PBG a t 25" in pure DCA and DCE. The interesting question of why the direct dilatometric measurement is so anomalous is thus raised. (The possibility of the anomaly arising solely from the somewhat different PBG concentrations used in the various experiments seems to us remote.) Barring any irreversible behavior, it is required that the change in volume (and in enthalpy) on passing through the conformational transition would be totally independent of the path. I n particular, we would expect AVO obtained by varying T ( N and P constant) to equal AVO obtained by varying N ( T and P constant). The analogous paths have actually been followed in the case of the heat of transition, AHothe former in heat capacity measurements,' and the latter in a heat of mixing experiment? Unfortunately, the latter results were qualitative only, but the signs of AH" were in agreement in the two cases. It should therefore be of considerable interest to determine the partial molal or specific volume of PBG, at 25" and at atmospheric pressure, as a function of solvent composition, over the entire composition range, in an attempt to resolve the apparent anomaly.
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whole to longer wavelengths, i.e., from 725, 625, and 580 mp to 740, 650, and 620 mp, respectively. On the contrary, with the system CoIz(P(Et)2Ph)zc~C16MgC1,the bands shifted to shorter wavelengths; Le., the bands a t 775, 710, and 680 mp of Co12(P(Et)zPh)2 shifted t o 765,705, and 675 mp, respectively. Similarly, with the system C O C ~ Z ( P ( E ~ ) ~ P ~ ) ~ - M ~ RiIgBr, absorptions were observed a t 760, 670, and 630 mp. On the other hand, yellow solutions obtained by the reaction of CoXz(P(Et)2Ph)2 with excess Grignard reagents showed no absorptions in the region 600-800 mp Hence we can consider that the green compounds, R C O X ( P ( E ~ ) ~(R, P ~C&16 ) ~ or Me), are tetrahedral and that, according to the rule of average environment18 the ligand field strength of these anions is fairly weak and is represented by C1- > CEC16- > Me- > I- in the spectrochemical series. The esr study supports the above conclusions; Le., the green solutions as well as CoClt(P(Et)zPh)z showed symmetrical signals with g factor close to 2, whereas the yellow solutions showed broad unsymmetrical signals with fine structures (at -196"), which might be ascribed t o g anisotropy. In contrast to tetrahedral complexes of Co2+ ion, the trans square planar complexes would have an anisotropic g f a ~ t o r . ~ In glassy state at low temperature, anisotropy is observed as (7) H. Block and J. B. Jackson, Proc. Chem. SOC.,381 (1963). separate absorptions and, at the same time, signals become broad owing to the lack of Brownian m ~ t i o n . ~ GENERAL ELECTRIC RESEARCH AND F. E. KARASZ DEVELOPMENT CENTER J. M. O'REILLY Anhydrous C0C12 dissolved into 10% toluene solufhIENECTADY, N E W Y O R E tion of various pyridine derivatives showed visible RECEIVED SEPTEMBER27, 1966 spectra with three fine structures in the region 600800 mp which were quite similar t o that of tetrahedral CoClz (pyridine)Pl6the wavelengths of these absorptions being nearly the same for all complexes. By the reaction of CoClz(pyridinederivatives)zwith Remarks on the Structure and Properties MeMgBr at - 30", violet-red solutions were obtained, of Some Organocobalt Compounds, which were quite unstable at room temperature. By analogy with the results of RzCo(P(Et)pPh)z, we can RCoX(L)2 and RZCo(L)2 consider that square planar compounds, MezCo(pyriSir: By the reaction of CoBrz(P(Et)zPh)z with Grigdine derivatives)s, were formed. nard reagents, Chatt' obtained yellow compounds, Figure 1 shows the esr spectra of these solutions at R2Co(P (Et )zPh)z (R, mesityl-, pentachlorophenyl-, - 130". The g factor decreases as the basicity of cooretc.), and their structures were determined to be trans dinating base increases. The contribution to the g factor square planar.'J On the other hand, green compounds obtained by the reactions of equimolar amounts of (1) J. Chatt and B. L. Shaw, J . Chem. SOC.,286 (1961). CoBrz(P(Etf)zPh)zand Grignard reagents were con(2) P. C. Owston and J. M. Rowe, ihid., 3411 (1963). sidered t o be RCoBr(P(Et)zPh)z,l but their structures (3) C. K. JZrgensen, "Absorption Spectra and Chemical Bonding in Complexes,"Pergamon Press, Ltd., London, 1964, p 109. remain unsettled. (4) W. Low, "Paramagnetic Resonance in Solids," Solid State Recently, we observed that the visible spectra of the Physics, Supplement 2, Academic Press, New York, N. Y., 1959, p green solution obtained by CoCh (P (Et)zPh)z-CaCls39. MgCl was quite similar to that of CoClz(P(Et)2Ph)z (5) F. K. Kneubuhl, J. Chem. Phys., 33, 1074 (1960). (tetrahedral), the bands a t 600-800 mp shifting as a (6) J. Ferguson, ihid., 32, 528 (1960). The Journal of Physical Chemistry
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of the orbital magnetic moment is reduced when unpaired electrons spread out t o ligands through covalent metal-ligand bonds.’ Hence, for the present systems, we can consider that the unpaired electron of cobalt ion is increasingly back-donated to ligand molecules as the coordinating base becomes more basic.
ovridine
2 methylpyridine
2,4 dimethylpyridine
*
/
nJ
\\
A
2 1
v v A
,.
pyridine
Figure 1. The esr spectra of reaction products between CoCh (pyridine derivatives)z and MeMgBr (observed at - 130”).
I n the present work, most compounds were fairly unstable and, therefore, the esr study was carried out mostly a t low temperature. KneubiihF showed that in the glassy state the esr signals become broad and the anisotropy becomes observable separately owing to the lack of Brownian motion. Above -60” the esr signal of yellow solution from C O C I ~ ( P ( E ~ ) ~ P ~ ) ~ / Cbecame & I ~ Mfairly ~ C ~ sharp and symmetrical, showing that ferromagnetic impurities were not responsible for the line width. Details of results and discussions will be presented in the near future.
Comments on the Paper, “A Chemical Kinetics Computer Program for Homogeneous and FreeRadical Systems of Reactions,” by R. H. Snow
Sir: A recent article by Snow1dealt with the numerical computation of a homogeneous reaction system with emphasis on the use of the steady-state assumption. I should like to comment on three aspects of this article. The article states that “. . . so far as we know such calculations have been reported only for oxidation of hydrogen in addition to ethane pyrolysis.” There are, however, numerous published papers and reports dealing with the numerical calculation of reacting gases. References 2 through 6 constitute a very brief list of such work. Each of these references gives the equations used in the respective computer program plus detailed results for various chemical systems. These programs generally allow for an arbitrary system of reacting species whose composition is determined by an arbitrary system of reactions. A constant temperature is not assumed, as it is in ref 1. Instead, the programs are for more complicated physical processes such as shock tube or nozzle flow. Of course, most of them are adaptable to a constant-temperature calculation. The problem of numerical instability that frequently plagues this type of calculation has also been investigated? -g These studies encompass Runge-Kutta, predictor-corrector, and other numerical methods. Reference 9, for example, derives a simple criterion for maintaining stability when the Runge-Kutta method is used. Finally, Libbylo has previously discussed the partial
(1) R. H. Snow, J . Phys. Chem., 70, 2780 (1966). (2) A. Q . Eschenroeder, D. W. Boyer, and J. G. Hall, Phys. Fluids, 5, 615 (1962). (3) A. A. Westenberg and S. Favin, “Complex Chemical Kinetics in Supersonic Nozzle Flow,” Ninth Symposium (International) on Combustion, Academic Press, New York, N. Y . ,1963, pp785-798. (4) G. Emanuel and W. G. Vincenti, “Method for Calculation of the One-Dimensional Nonequilibrium Flow of a General Gas Mixture Through a Hypersonic Nozzle,” Report AEDC-TDR-62-131 for Arnold Engineering Development Center, June 1962. ( 5 ) R. E. Duff and N. Davidson, J. Chem. Phys., 31,1018 (1959). (6) G. Moretti, A I A A J., 3 , 223 (1965). (7,) J. Certaine, “The Solution of Ordinary Differential Equations (7) Reference 4, p 96. with Large Time Constants,” Mathematical Methods for Digital Computers, John Wiley and Sons, Inc., New York, N. Y., 1960 pp 128-132. DEPARTMENT OF INDUSTRIAL CHEMISTRY KEI MATSUZAKI (8) C. F. Curtiss and J. 0. Hirschfelder, Proc. Natl. Acad. Sei. U.S., FACULTY OF ENQINEERING TAMIO YASUKAWA 38, 235 (1952). OF TOKYO UNIVERSITY (9) G. Emanuel, “Numerical Analysis of Stiff Equations,” Report No. HONGO, TOKYO, JAPAN TDR-269(4230-20)-3, Aerospace Corp., Jan 1964. RECEIVED NOVEMBER 1, 1966 (10) P. A. Libby, ARS J., 32, 1090 (1962).
Volume 71, Number 4 March 1967
