45 Table 11. Calculation of
(Y
in Ground and Excited States
Substituent
01
a
a*
aT
S02CHa SOCH3 SCHI
0.59 0.52 0.25
0.18 0.16 0.31
0.8
0.5
0.7 0.3
0.6 0.2
further evidence that no net enhancement of conjugation is noted in photoexcited aryl sulfides unless prdonor resonance is sterically unfavorable. It would be most interesting to compute a values for hindered sulfides; unfortunately, however, attempts to prepare 0-
“Dewar structures” are considered to make important contributions. This similarity suggests that the postulation of canonical forms with external three-membered rings in excited states of meta-substituted sulfonium salts is unnecessary. A more suitable description of the first excited singlet of these compounds would involve contributions from (inter alia) structures such as those in eq 5. The essential point is that, while any description of excited-state charge distributions in terms of contributing structures is likely to be highly imprecise, descriptions based solely upon data obtained from absorption spectra should be viewed with particular reservation. 2o
0
.O
SMe,
Hhindered derivatives of m-hydroxythioanisole were not successful. Direct conjugation between the phenolic group and sulfonium function may be responsible to some unusual frequency shifts in the ultraviolet spectra of m-dimethylsulfoniophenol. It has previously been that conjugative interactions in that compound involve canonical forms with external three-membered rings, particularly in photoexcited states. The present results suggest that conjugation in m-sulfoniophenols is not significantly different from that exhibited in excited singlet states of other meta-substituted phenols, in which (31) See Table I, footnote k .
Acknowledgments. This research was supported in part by Grant 547-G2 from the Petroleum Research Fund, administered by the American Chemical Society. Thanks are extended to M. E. Roselli for assistance in obtaining some preliminary spectral data and to D. R. Johnson and J. N. Grote for assistance in synthesis of compounds.
Vibrational Spectra of Polynuclear Hydroxy Complexes of Lead( 11)la Victor A. MaroniIband Thomas G . Spiro Contributionfrom the Department of Chemistry, Princeton University, Princeton, New Jersey. Received May 28, 1966 Abstract: Raman spectra for solutions and Raman and infrared spectra for crystals containing polynuclear hydroxy complexes of lead(I1) are reported. The close similarity of Raman spectra for solutions and crystals indicates the presence of identical structural units in the two phases, for a hydroxy1:lead ratio of both 1.00 and 1.33. In the former case, where Pb4(0H)44+ is the complex present, the vibrational features are entirely consistent with the tetrahedral structure previously proposed on the basis of solution X-ray scattering measurements. In the latter case, where the complex is probably Pbs(OH)s4+,the spectrum is interpretable on the basis of an octahedral structure, although other structures are not excluded. There is no vibrational evidence of perchlorate binding to any of the lead species, either in solution or in the crystals.
R
ecently we presented the results of an infrared and Raman spectroscopic investigation of a polynuclear product of bismuth(II1) hydrolysis. * We now (1) (a) This investigation was supported by the Public Health Service under Grant GM-13498-01 from the National Institute of General Medical Sciences. (b) NASA Predoctoral Fellow. (2) v. A. Maroni and T.G. Spiro,J. Am. Chem. SOC., 88, 1410 (1966).
wish to report on a similar study of the hydrolytic polymers of lead(I1). Lead(I1) is isoelectronic with bismuth(III), and they share the convenient characteristic that their hydrolysis leads predominantly to the formation Of a single polynuclear complex which is highly soluble in water. Whereas, however, for bismuth(II1) the main product is Maroni, Spiro / Vibrational Spectra of Lead(II) Complexes
46
Figure 1. Structure proposed by Esval for Pb4(OH)44+,redrawn from ref 8. Lead and oxygen atoms are represented by the small and large circles, respectively.
Bi6(OH)126+,for lead(I1) it is Pb4(0H)44+. This is the conclusion of several potentiometric studies3-5 and has been strongly supported by equilibrium ultracentrifugation6 and light scattering' measurements. Furthermore, EsvaP has carried out an X-ray scattering investigation of a solution containing predominantly this tetramer. The resulting radial distribution function is interpreted in terms of three Pb-Pb interactions at 3.83 A and six Pb-0 interactions at 2.57 A. Figure 1 shows the structure proposed on this basis: a distorted cube consisting of lead and oxygen atoms arranged tetrahedrally. A similar structure has been determinedg for the closely related thallium(1) methoxide. Although Pb4(0H)44+is the main product, PbOHf and possibly Pb20H3+ are formed at low degrees of h y d r ~ l y s i s . ~In addition, clear solutions can be prepared with a hydroxy1:lead ratio of 1.33. O h ' s careful potentiometric measurements are interpretable in this region in terms of an equilibrium3 between Pb3(0H)42+ and Pb6(OH)84+. Esval and Johnson's ultracentrifugation data6 also show degrees of polymerization tending toward six at higher concentrations in this region.
Experimental Section Hydrolyzed lead(I1) solutions were prepared by dissolving appropriate quantities of reagent grade lead oxide (Matheson Coleman and Bell) in concentrated perchloric acid with sufficient digestion t o complete dissolution. They were analyzed for lead by precipitation as the sulfate and for perchlorate by passage through a cationexchange resin in the acid form and titration of the liberated acid. Solution I was 4.47 M in lead and 4.63 M in perchlorate, corresponding to a hydroxyl :lead ratio of 0.960. This solution was similar to the one used by Esval for his X-ray measurements.* In it essentially all of the lead should be present as Pb4(OH)44+. Solution I1 was 5.72 M in lead and 7.50 M in perchlorate ( 0 H : P b = 0.688). Solution 111 was 4.82 M in lead and 9.64 M in perchlorate; in this solution the lead should be essentially unhydrolyzed. The solutions, which were kept free of carbon dioxide to prevent carbonate precipitation, were filtered through a fine-glass frit under nitrogen pressure and transferred t o a standard Cary 7-mm Raman liquid cell, and their spectra were recorded at 28 =t1" on a Cary Model 81 Raman spectrophotometer using the 4358-A mercury line for excitation. Solutions I and I1 were slightly supersaturated, (3) A. O h , Actu Chem. Scand., 14, 126, 814, 1999 (1960); Soensk Kem. Tidskr., 73, 482 (1961). (4) I
