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The Journal of Physical Chemistty, Vol. 84, No. 22, 1980 +IO
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Flgure 1. First-derivative EPR spectrum observed at 20 O C in 0.5 M p-bromothiophenoi in methanol containing "FeCI, and "NO. O
SC(",),
C,H,SH
a
g factor
2.0321" 2.0270 2.0280 2.0281 2.0283 2.0279
UFJG 12.1" 12.1 12.1 12.1 12.1 12.1
p-FC,H,SH p-CIC, H, SH p-BrC,H,SH p-CH,C,H,SH Errors are 5 1in last digit throughout.
examined at room temperature with a Varian E12 spectrometer. In all cases an intense spectrum such as that shown in Figure 1 was observed, in which a 12-G interaction with a single 67Fe(I= 1/2) nucleus was evident. The spectroscopic parameters obtained with the various sulfur compounds are summarized in Table I. When working with the thiophenols it was found necessary to add small quantities of a base (NaOH or Et3N in CH30H) before the spectrum was detected. Alternatively, the spectra could all be generated by using NaN02 dissolved in CH30H rather than NO gas. This suggests that for the thiophenols the stabilizing ligands are anions RS- and that the paramagnetic species is Fe(N0)2(SR)2-. With thiourea, on the other hand, the complex is probably the cation Fe (NO),(SC(NH,) 2) 2+. Our measurements indicate a limit of detectability for the iron-dinitrosyl-thiourea complex by EPR of approximately 10 ppb of Fe in CH30H. In blank experiments we have detected weak spectra of the complex which probably arise from trace impurities of Fe in the sulfur compounds or the solvent. Evidently in Yang and Joshi's experiments one of their reagents was contaminated with iron. By their own admission' their sulfur compounds were not totally void of iron impurities.
Acknowledgment. We thank Dr. M. J. Graham of these laboratories for the gift of a small sample of 67Femetal.
TABLE I: ESR Parameters for Iron Dinitrosyls in Methanol at 20 C complexing molecule
Additions and Corrections
UN( 2)/G
2.03a 2.40 2.60 2.41 2.40 2.46
References and Notes (1) G. C. Yang and A. Joshl, J . Phys. Chem., 84, 228 (1980). (2) A. R. Forrester, "Magnetic Properties of Free Radicals", LandoltBornstein I1 9(C1), Sprlnger-Veriag, Berlin, 1979. (3) C. C. McDonald, W. D. Phillips, and H. F. Mower, J. Am. Chem. Soc., 87, 3319 (1965). (4) G. Martini and E. Tiezzi, Trans. Faraday Soc., 67, 2538 (1971). NRCC No. 18594.
solved in a 0.5 M methanolic solution of one of the following sulfur compounds: thiourea, thiophenol, p-fluorothiophenol, p-chlorothiophenol, p-bromothiophenol, and p-methylthiophenol. In each case the solution was degassed, shaken under a pressure of 507 14N0, and then
Division of Chemistry National Research Council of Canada Ottawa, Ontario, Canada, K1A OR9 Received; May 19, 1980
ADDITIONS AND CORRECTIONS 1980, Volume 84
E.S. Sennhauser, D. A. Armstrong,* and F.Wilkinson: The Onset of Diffusion Control for Ion-Ion Neutralization in Ammonia Vapor. Page 124. Eauation 2 should read
Page 126. The units of the ordinate scale on the bottom part of Figure 3 (i.e., Figure 3b) should read: ~ O ' C Y , ~ (cm3 s-l) In the third paragraph the sentences starting on the eighth line should read They were computed with CY = 3.7 X and 3.0 X cm3 s-l. We estimate a value of CY = 3.1 f 0.3 X cm3 s-l at 10 torr for the NH3-CC14 system.
M. P. Boyer J. R. Morton K. F. Preston"
