COMMUNICATIONS TO THE EDITOR
761
Results The observed resonance frequencies are given in Table I. The similarity between the observed spectra of Et4NAsC16and Et4NPC162aat 77°K is to be noted. At 195"K, however, the hexachlorarsenate gives rise to six detectable chlorine resonances indicating a phase change to a considerably more complex structure. The relatively low intensities of the resonances in this compound precluded the identification of all of the C13' resonances corresponding to the C136 resonances reported at 195°K) but it seems unlikely that the field gradients at arsenic would be large enough to give arsenic resonances in this region. The weighted Acknowledgment. The experimental assistance of average resonance frequency of the chlorines in AsC&W. B. Bowe, Jr., is gratefully acknowledged. at 77°K is 29.20 f 0.58. The temperature coefficient of the average resonance frequency for AsCh- is (16) G R. Freeman, J. Chem. Phw., 46, 2822 (1967). (OK)-', which compares well with the R. A. HOLROYD -171 X ATOMICSINTERNATIONAL DIVISION values -190 X (OK)-' found for Et4"& and NORTHAMERICANROCKWELL CORPORATION - 153 X (OK) -l for Et,NSbCI,-. CANOGA PARK, CALIFORNIA91304
based on a model of electron scavengingI6 in which G(e-) is assumed to be 3. The yields of G(N2) for 2,2,4-trimethylpentane solutions are in excellent agreement with the theoretical values, which indicates that the principal reaction of N20 in 2,2,4-trimethylpentane is electron scavenging. For cyclohexane solutions the yield of N2 in excess of that due to electron scavenging is attributed to excited molecules. From the concentration dependence of the excess N2 yield and from the re1,ative value of k2 derived from the photolysis results, G(excited cyclohexane molecules) is estimated to be -1.2.
RECEIVED NOVEMBER 17, 1967 Table I : Chlorine Nuclear Quadrupole Resonance Frequencies in (CgH&NAsCle
Chlorine Nuclear Quadrupole ~(Clas),MHz
&'/N
V(Cla'), MHz
SIN
77
28.37 i 0.05 29.15 f 0.05 30.07 f 0.05
5/1 5/1 5/1
22.38 f 0.05 22.97 f 0.05 23.68 i 0.05
2/1 2/1 2/1
195"
27.82 f 0.06 28.12 f 0.05 28.50 f 0.05 28.81 f 0.04 28.90 f 0.03 29.55 f 0.04
3/1 5/1 3/1 3/1 4/1 3/1
Temp, KO
Resonance in (C2H5)4NAsCla1 Sir: We wish to report the observation of chlorine nuclear quadrupole resonance (nqr) in the hexachloroarsenate ion. Although the existence of free AsC15 has not been demonstrated, a number of arsenic(V) chlorine compounds have now been prepared. As part of our program of study on tetrahedral and octahedral chloride complexes, we have reported chlorine nqr in the AsC14+ ion.2a Schmulbach2b has reported the preparation and isolation of the compound (C2&)4' , ~ reported NAsC16, and recently Beattie, et ~ l . have the vibrational spectrum and assigned frequencies to the fundamental vibrations of the AsCl6- species in that compound. An independent study of the vibrational spectrum of this compound by DiLorenzo4 confirms their assignments, and we wish to report here the results of an investigation of chlorine nqr in this compound at 77 and at 195'8.
Experimental Section (C2H6)4NAsClewas prepared according to the method described by Schmulbach.2b The compound was recrystallized from acetonitrile (redistilled from P206)by dissolving at 25" and quickly initiating crystallization at 0". This procedure was repeated three times. The product was analyzed for chlorine. Anal. Calcd for C1: 50.40. Found: C1, 50.12. The nuclear quadrupole resonance spectrometer used has been previously described.2a Bidirectional squarewave modulation was used with a considerable increase in sensitivity. Temperatures of 195°K were maintained by a Dry Ice-methylene chloride bath.
300°K
,..
22.18 f 0.05
2/1
,..
... .., ...
No resonance detected
The results on this ion are particularly interesting in view of the recent results of Chihara, Nakamura, and Seki6on molecular Pc15and our own results6 on SbCl6. We can then summarize the effective quadrupole coupling constants at 77°K for all the known binary chlorides and chloride ions of phosphorus, arsenic, and antimony. This is done in Table 11. The most striking regularity which suggests itself is the close parallel in behavior between the trichlorides and hexachloride ions. The ratios of leg41 in the tri-, tetra-, and hexachlorides of P, As, and Sb are sum(1) Work supported by NSF Grant GP-3838. (2) (a) J. V. DiLorenzo and R. F Sohneider, Inorg. Chem., 6, 766 (1967); (b) C. D. Sohmulbaoh, ibid., 4, 1232 (1965). (3) I. R. Beattie, T. Gilson, K. Livingaton, V. Fawcett, and G. A. Ozin, J . Chem. SOC., A , 712 (1967). (4) J. V. DiLorenso, Ph.D. Thesis, State University of New York.
a t Stony Brook, Stony Brook, N. Y., 1967. (5) H. Chihara, N. Nakamura, and 8.Seki, BUZZ.Chem. SOC.Japan, 40, 60 (1967). (6) R. F. Schneider and J. V. DiLorenso, f. Chem. Phye., 47, 2434 (1967). Volume 78, Number 8 February 1968
COMMUNICATIONS TO THE EDITOR
762
(905°).2 They found that the coexistence curve obeyed the Guggenheim equation which was developed for molecular fluids. I n addition, they found that the PClaa 52.3 ASCla" 50.3 SbCla" 40.2 observed critical properties compared very well with PC14+b 64.8 ASCI^+^ 73.9 [SbCla+]' ... those predicted for a normal molecular fluid. They PCl6*xC 58.6 [AsCls] ... SbClo*xE 55.5 therefore concluded that BiCla is a molecular fluid near eq 67.5 we 60.4 the critical temperature. On the basis of the above PC16-b 60.0 ASCla-d 58.4 SbC1ewb 47.6 and the results of Grantham and Yosim3which showed a Data from R. Livingston, J. Phys. Chem., 57, 496 (1953). that the electrical conductivity reaches a maximum a t Data from DiLorenzo and Schneider, ref 2a. Data from 475" when BiCI3 is heated, they suggested that the This work. E Data from Chihara, Nakamura, and Seki, ref 5. Schneider and DiLorenzo, ref 6. 'There is evidence that molar electrical conductivity at the critical temperature SbClaF, the only known compound thought to have contained should be near zero, compared to about 50 at the boilthe SbCl4+ ion, is actually polymeric in the crystal (L. Kolditz, ing point.2 Therefore, it was of interest to determine private communication). We have in fact observed a weak the conductivity of this salt to the critical temperature. isolated resonance in this compound near 40 MHz but have not Both BiCL and HgClz were examined because of the been able to confirm its identification as a chlorine resonance. widely different electrical conductivities of these two liquids near their melting points. BiCla has a relatively high molar electrical conductance of 28 cmz/ marized in Table 111. In both these types of molecules, ohm mole a t its melting point (232°).4 Conductivities 7r-type bonding should be minimal. In these cases, of this magnitude are associated with ionic fluids rather the chlorides of phosphorus and arsenic are very similar than molecular fluids. Mercuric chloride, on the other while those of antimony show a marked decrease in hand, has a molar conductance of only 0.0018 cm2/ohm (e&[. I n the tetrachlorides where ?r bonding is more mole a t its melting point (274"). It has been well likely and has in fact been proposed by Schawlow7 as established that HgClz is a molecular fluid which is a mechanism for the C135 field gradient lowering of slightly ionized. SiCL compared with GeCb, we see that the increase The electrical conductivities of molten BiC4 and in e&q from phosphorus to arsenic is significant. It HgClz were measured throughout their entire liquidus seems probable now that PCL+ is the anomalous group range. I n addition, the conductivities of the saturated V tetrachloride ion and that the likely mechanism for vapor above these melts were measured near the critical the field gradient lowering in the third-period elements temperature. The cell assembly and conductivity is involvement of the chlorine ?r orbitals. apparatus have been described elsewhere.6v6 In order to compare the conductivities of the two systems, the Table 111: Chlorine-35 e&q Ratios in the Group V molar conductivities were calculated using the reported Chlorides MCla, MC&+, and MCledensity data;2J the results are shown in Figure 1. The shapes of the two curves are quite similar; however, the molar conductivities are orders of magnitude apart, even a t the critical temperature, and the conductivity maximum of BiCla is much broader than that of HgCIz.* In both systems the conductivity of the 1.24 1.47 ... saturated vapor is negligible a t temperatures less than 100" below the critical temperature. The gradual increase in gas conductivity from 100 to 50" below the (7) A. L. Schawlow, J . Chem. Phys., 2 2 , 1211 (1954). critical temperature is probably not real but may be J. V. DILORENZO due to surface conduction; therefore these portions of DEPARTMENT OF CHEMISTRY Table 11: Summary of CIS6 Effective Quadrupole Coupling Constants for the Chlorides of P, As, and Sb a t 77'K
STATEUNIVERSITY OF NEW YORK AT STONY BROOK STONYBROOK,NEWYORK 11790
R. F. SCHNEIDER
RECEIVED NOVEMBER 30, 1967
Electrical Conductivity of Liquid and Saturated Vapor of BiCla and HgClz to Their Critical Temperatures1
Sir: Recently, Johnson and Cubicciotti reported the coexistence curve of BiCla to the critical temperature The Journal of Physical Chemistry
(1) This work was supported by the Research Division of the U. 9. Atomic Energy Commission. (2) J. W. Johnson and D. Cubicciotti, J . Phys. Chem., 68, 2235 (1964). (3) L. F. Grantham and S. J. Yosim, ibid., 67, 2506 (1963). (4) L. F. Grantham, J . Chem. Phys., 43, 1415 (1965). (5) L. F.Grantham, E. B. Harrelson, P. H. Shaw, and C. M. Larsen, Rev. Sei. Instr., in press. (6) L. F. Grantham and S. J. Yosim, J . Chern. Phys., 38, 1671 (1963). (7) J. W.Johnson, W. J. Silva, and D. Cubicciotti, J . Phys. Chem., 70, 1169 (1966). (8) L. F. Grantham and 5. J. Yoaim, J . Chern. Phya., 45, 1192 (1966).
