2324
Communications to the Editor
The binuclear complex involving Fe( CN)$and Cu'(SR), is not surprising in view of the propensity of Cu(1) to coordinate with either S- or N-containing ligands. The oxidation of mercaptans by Cu(I1) is well known.' Attempts to separate K and k by increasing the Fe(CN)s3- concentration to the point where deviation from first order in this substance could be detected failed. [Cu2+]could not be varied substantially because Cul(SR) is quite insoluble a t higher Cu(1) concentrations. The slight variation in rate caused by variation in mercaptan concentration very likely results from variation in n in the above intermediate formula. This could in turn cause variation in k or K . The results are listed in Table I.
J
References and Notes (1) R. C. Kapoor, 0. P. Kachwaha, and E. P. Sinha, J. Phys. Chem., 73, 1627-1631 (1969). (2) 0 . P. Kachwaha, E. P. Sinha, and R. C. Kapoor, hdkn J. Chem., 8, 806-808 (1970). (3) I. M. Kolthoff, E. J. Meehan, M. S.Tsao, and Q. W. Choi. J. fhys. Chem., 66, 1233 (1962). (4) E. J. Meehan, I. M. Kolthoff, and H. Kakinchi, J. fhys. Chem., 68, 1238 (1962). ( 5 ) K. Wiberg, H. Maltz, and M. Okano, lnorg. Chem., 7, 830 (1968). (6) G. J. Bridgart, M. W. Fuller, and I. R. Wilson, J. Chem. Sac., Dalton Trans., 1274-1280 (1973). (7) P. F. Warner and J. A. McBridge, U.S. Patent 2503644 (1940): Chem. Abstr., 44, 5896 (1950).
v-
4pZn
Figure 1. ESR spectrum of AgZn generated in an argon matrix. The sharp, off-scale doublets are due to Ag atoms.
Frederick R. Duke' Vernon C. Buigrin
Department of Chemistry University of Wyoming Laramie, Wyoming 82071 Received June 1 7 , 1975
Electron Spin Resonance Study of the Intermetallic Molecules AgZn, AgCd, and AgHg Publication costs aseisted by the Union Carbide Corporation
Sir: The nature of metal-metal bonds found between pairs of metal atoms in complex compounds1 as well as those existing between ligand free metal atoms2 has been the subject of many recent investigations. We wish to report here the generations in rare-gas matrices, and observation by electron spin resonance (ESR) spectroscopy of three intermetallic diatomic molecules, AgZn, AgCd, and AgHg. The cryostat-spectrometer assembly that would permit trapping of high-temperature vapor phase species in a raregas matrix a t -4 K, and observation of the resulting matrix by ESR has been detailed earlier.3 In the present series of experiments the Ag atoms were vaporized from a resistively heated tantalum cell, and were trapped in argon matrices together with the atoms of other metal independently vaporized from the second cell. The frequency of the spectrometer locked to the sample cavity was 9.410 GHz and all the spectra were obtained while the matrices were maintained at -4 K. The molecular symmetry of AgM (M = Zn, Cd, Hg) dictates that their ESR spectra be compatible with the spin hamiltonian of the form = gllPHzSz + glP(HxSx + HySy) + A11Izsz + A I ( I x S x ZySy) All'Zz'Sz Al'(Zx'Sx Z y ' S y )
Xspm
+
+
+
The Journalof Physical Chemistry, Vol. 79, No.21, 1975
+
(1)
Figure 2. ESR spectrum of AgCd generated in an argon matrix. The brackets indicate the groups of satellites due to 'Cd and 13Cd nuclei.
where A 11 and A represent the hyperfine coupling tensor to the Ag nucleus, and the last two terms involving A 11' and A 1' are to be added when the atom M possesses a magnetic nucleus. The ESR spectrum of Ag atoms (4dl0 5s') isolated in an argon matrix is known4 It consists of two sets of sharp isotropic doublets with the spacings of -620 and -720 G attributed to the couplings to lo7Ag (natural abundance = 51%,I = %, p = -0.1130 &) and lo9Ag (natural abundance = 49%, I = %, p = -0.1299 PN). The ESR spectra obtained from an argon matrix containing Ag and Zn atoms, and that containing Ag and Cd atoms, are shown in Figures 1 and 2. In addition to the sharp doublets due to Ag atoms described above, one notes the presence of additional doublets with the spacings slightly less than those of Ag atoms, and with the patterns expected from an ensemble of randomly oriented radicals possessing an axially symmetric spin hamiltonian. We propose to assign these doublets to AgZn and AgCd, respec-
2325
Communications to the Editor
TABLE I: Spin Hamiltonian Parameters of AgM (M = Zn, Cd, Hg) AgM
g,,“
gla
AgZn
2.0025
1.9905
AgCd
2.0014
1.9711
AgHg
1.9958
1.9136
a Accuracy *0.0002. legHg.
b
A,,(= A,) ,b GHz
A,,’, GHz
Alp,
2.18 (k0.25) 3.13 (iO.20)
1.99 (i0.03) 2.52 (h0.03)
c
GHz
1.324
( i o .003) 1.327 (h0.003) 1.562 (,t0.003)
Coupling
to
C
Coupling
to
1 W d
or
tively. The assignments of the parallel and perpendicular components for the case of AgZn are indicated in Figure 1. The major pattern of the AgCd spectrum is quite similar to that of AgZn, although one of the high-field perpendicular components is masked by the strong Ag signals. A closer inspection of the AgCd spectrum revealed, however, the presence of four groups of satellites (see Figure 2). They were recognized as the perpendicular components of the spectra due to AgCd possessing lllCd (natural abundance = 13%, I = lh, p = -0.5922 PN) or lI3Cd (natural abundance = 1296, Z = l/2, p = -0.6195 PN) nucleus. The corresponding parallel components of these species were too weak to be observed. The major pattern of the spectrum assigned to AgHg is also similar to that of AgZn. In this case, however, the satellite signals attributable to the perpendicular components of AgHg possessing lg9Hg (natural abundance = 17%, I = l/z, p = 0.4993 ON) or 2olHg (natural abundance = 13%,I = %, p = -0.607 PN) were observed providing a further support to the assignment. In each case of AgM discussed above, the large hyperfine coupling interactions with the magnetic nuclei prevented the accurate evaluation of the spin hamiltonian parameters using the usual second-order solutions. The g and the hyperfine coupling tensors of the AgM were, therefore, determined from the observed signal positions resorting to the exact diagonalization of the hamiltonian (1).Table I shows the results. The All% of the magnetic Cd and Hg nuclei were evaluated from the observed perpendicular components of the relevant species. This is possible because, when the magnetic field is perpendicular to the symmetry axis, the off-diagonal elements of the hamiltonian (1) are A 1’and A 11’ - A 1’.5 The large uncertainrelated to A 1 ’ ties indicated for the A 11”s are due to this indirect approach. In spite of the different separations of the parallel and the perpendicular components, the coupling tensor to the Ag nucleus was found to be completely isotropic (All = A1 = Aiso) in each case. The coupling tensors to the lllCd and lg9Hg nuclei are also essentially isotropic. For Ag atoms isolated in an argon matrix the coupling constant to 107Ag has been measured to be 1.806 G H z 4 Using the Goudsmit’s relation6 and the known coupling constants of Ag and Au atoms,4 the isotropic coupling constants of unpaired electrons localized, respectively, in the valence s orbitals of l W d and lg9Hg are estimated to be 12.5 and 40.0 GHz. In the present series of AgM the unpaired electron should occupy the orbital given essentially by an antibonding combination of the valence s orbitals of Ag and M. The ionization potentials of these orbitals are 7.6, 9.4, 9.0, and 10.4 eV for
+
Ag, Zn, Cd, and Hg atoms, respectively. The dominance of the Ag 5s orbital in the semifilled, antibonding orbital of the present series of AgM is thus expected. The small but clearly observed anisotropies of the coupling tensors to the lllCd and lg9Hg nuclei indicate admixture of the valence pz orbital of the atom M, however. Such admixture would also account for the observed anisotropies of the g tensors with the increasing trend of AgZn < AgCd < AgHg. We have also succeeded in generating and observing the ESR spectra of Ag-alkaline earth intermetallic molecules. The results obtained from these species together with more detailed accounts of the AgM spectra communicated here will be reported soon. References a n d Notes (1) F. A. Cotton, Acc. Chem. Res., 2 , 240 (1969). (2) K . A. Gingerich, J. Cryst. Growth, 9, 31 (1971). (3) P. H. Kasai, E. 6.Whipple, and W . Weltner, Jr., J. Chem. fhys., 44, 2581 (1966). (4) P. H. Kasai and D. McLeod, J r . , J. Chem. fhys., 5 5 , 1566 (1971). (5) See, for example, ref 4. (6) S . Goudsmit, Phys. Rev., 43, 636 (1933).
Union Carbide Corporation Tarrytown Technical Center Tarrytown, N e w York 1059 1
Paul H. Kasal. D. McLeod, Jr.
Received July 2 1, 1975
Intra- and Intermolecular Hydrogen Bonding in Chlorinated Phenols and Related Compounds Publication costs assisted by the U.S.Environmental Protection Agency
Sir: Paramagnetic relaxation reagents such as trisacetylacetonatochromium [Cr(acac)3] are good proton acceptors, hydrogen bonding to molecules with both strongly and weakly acidic hydrogens.lq2 We wish to show that the combination of intermolecular 13C TI’S (Tie in solutions containing paramagnetic reagents) along with T1 measurements in diamagnetic solutions (intramolecular 13C-lH dipolar TI’S) gives a significant increase of information in studies of solution dynamics for liquids where hydrogen bonding occurs. This is the first report to our knowledge of the use of both techniques to probe chemical dynamics. The I3C TI’Sfor the diamagnetic solution of 3,5-dichlorophenol (solution 1 in Table I) monitor the presence of intermolecular hydrogen bonding in this phenol. The Ti's are half as long as those of the other two dichlorophenols (solutions 2 and 3). Formation of hydrogen bonded molecular aggregates causes the averaged molecular correlation time ( T ~ to ) be approximately twice as long and thus the Tl’s are shortened. For 2,5- and 2,6-dichlorophenol the data indicate less extensive aggregation in solution. This may be explained by a combination of intramolecular hydrogen bonding between the phenolic OH and ortho chlorine atoms and by steric inhibition of intermolecular hydrogen bonding. Interestingly the molecular motion as probed by 13C T1 data is not indicated by the solution macroscopic viscosities (Table I). The 13C Tl’s for 2,5-dichlorophenol are somewhat shorter than those of the 2,6-disubstituted phenol. If one asThe Journalof Physical Chemistry, Voi. 79, No. 21, 1975
