138
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structure was assumed and the Au-C stretching force con- monia complex1 of zeolite 4A, four sorption sites containstant was taken as equal to the A1-C force constant. The ing 8, 4, 8, and 12 NH3 molecules, respectively, were Au-C interatomic distance of 1.86 A was obtained by found. The most favorable site a t lesser loadings, or the comparison of the vdues from AuSi and AuB with the Pt, site selected by the first molecules to enter each unit cell, Rh, Ru, and l:r carbides, silicides, and borides.13-15 The was not determined. Accordingly, the heat of sorption negative of the free-energy functions in JK-1 mol-1 a t which might be calculated from the initial slope of the 2000, 2100, and 2200 K are 284.79, 287.40, and 289.90 for sorption isotherm1 cannot be associated with a particular ALCZ(gj; 347.1Y7 350.93, and 354.52 for A12C~(g); and site. To resolve this issue, the eight ammonia (per Pm3m 379.55, 383.32, and 386.94 for AlAuCz(g). unit cell) complex was prepared and studied by crystalloThe atomiza.tion energies for the molecules were calcu- graphic procedures similar to those previously employed.1 A single crystal of zeolite 4A, a cube 0.070 mm on an l a t d by combining the third-law heats of the reactions listed in Table I1 with the heat of formation of C(g), edge, was dehydrated a t 350" and 10-6 Torr for 24 hr, and was then exposed to zeolitically dried ammonia gas a t 28" A&.f0 = 709.5 i 1.9 kJ mol-l,l@the dissociation energy and a t a pressure of 12 Torr for 30 hr. The crystal in its of Ai&), DO"= 249,8 i 14 kJ mol-1.?2a and the dissociaglass capillary was then sealed off from the vacuum systion energy of AIAu(g), Ilo" = 322.2 f 6 kJ molk1:16 tem and studied without exposure to the atmosphere. The Do,,l,,,,o(AIC2) = 1104 I 21 kJ mol--I, DO,atomso(AlpCp)= 1507 f 25 kJ m01-I~ and D O , ~ ~ ~ ~ ~ " ( =A 1418 ~AU fC 21~ ) cell constant based on a least-squares treatment of 15 inkJ K I O I - ~The ~ atomization energy of A12C2(g) is in good tense reflections is 12.289(5) A. Of the intensities observed, 137 unique reflections were significant at the 3a agreement with the ,value calculated from the experimenlevel and these were used throughout. tal results of Chupka, et d . , 3 of 1556 f 42 kJ mol-l. The initial structural parameters used in least-squares The measurement of the dissociation energies of AlCz refinement were those previously found1 for Na, Si, Al, and A1262 is an extension of previous work in this laboraand 0 atoms in the 32 ammonia zeolite 4A complex. The tory on the determination of the stabilities of the transitwelfth sodium ion, found in the structure of dehydrated tion metal dicnrbides and comparison of metal-carbide 4A2 was included and refined well. The error indices a t and -oxide bond energies.2b Again we see that dicarbide convergence with this model were R1 = 0.067 and R2 = molecules are formed which are analogous to the stable 0.076, and the goodness of fit was 0.92. The final paramemonoxides A10 and ,4120. For most metal dicarbide moleters are given in Table I, and a tabulation of structure cules it is found that the dissociation energy of the M-Cz bond is 40-130 kJ mol-l less than that of the correspond- factors is available.3 A difference Fourier synthesis was prepared and refineing M-0 bond. The AI-C bond in AlCz is an apparent exments were attempted a t the positions of several small ception to this empirical rule because E(A1-C2) of 514.2 i peaks found there, even though this function appeared to 21 is slightly highor than Do"(A1Qj of 502 f 15 kJ be particularly featureless. The positions for nitrogen m 0 l - ~ . 1On ~ the other hand, each A1-C bond in A& of atoms as determined in the filled ammonia complex1 were 459 kJ mol-' i s 63 kJ mol-1 lower in energy than the subjected to least-squares refinement a t occupancies corAI-8 bonds in Al@(g) and follows the trend for most responding to four nitrogen atoms per equipoint, Positions metal dicar'r)ides. off threefold axes were also considered and their refineFor the AlAuC2 niolecule we have assumed the strucment was attempted. In no case was a site located which ture Ai-CX-Aan. If the energies of the A1-C and 6-C satisfied the elementary crystallographic criteria of statisbonds are subtractedi from the experimentally determined tically significant occupancy and lowered error functions. atomization energy, the balance (365 kJ mol-1) may repIt appears that even a t a loading of as few as eight amresent the energy for an Au-I: bond. This value is consismonia molecules per unit cell the sorbed molecules are tent with an upper limit (375 kJ mol-1) determined14 for not predominantly found a t one kind of sorption site. PerDo" of the unobserved. AuC molecule. haps all three kinds of Na+ compete favorably a t room (13) A. VanderAuwera-Mahieu, R , Peeters, N. S. Mclntyre, and J. temperature for NH3 association, all at sites where further Drowart, 'rrans. Faraday Soc., 66, 809 (1970). (14) A. VanderAbwera-Mahteu and J. Drowart, Chem. Phys. Lett., 1, hydrogen bonding can occur to framework oxygen atoms. 311 (1967). This result is consistent with the complete absence of any (15) pi. S. Mcinfyre, A. VanderAuwera-Mahieu, and J. Drowart, Trans. Faraday Soc., 64, 30116 (1968). indication of plateauing or unevenness in the sorption iso(16) K. A. Gingerick, J. QystalGrowth, 9, 31 (1971). therm;l even the first derivative decreases entirely regu(17) M Farber, K. D. Srivastava, and 0 . M, Uy, J. Chem. Soc., Faraday larly as a function of ammonia content. Trans. 1, 68, 2,49 (1972). The zeolite framework and cation positions have altered Nafionai Aeronautics arid Carl A. Stearns slightly upon the introduction of eight ammonia moleSpace A dniinistra tiorl Fred J. Kohl* cules, confirming that sorption has indeed occurred (see Lewis Research Center Table 11). The geometries of the fully ammoniated and Cieveiand, Ohio 44 7 35 fully hydrated 4A structures are very s i n ~ i l a r ,and ~ , ~may Rsctaived September 18, 7972 be referred to as the relaxed conformation, the conformation of zeolite 4A a t its synthesis. Eight ammonia molehie Study of the Structure led Ammonia Sorption Complex of Zlealite 4A Publication costs assistecl by The National Institute of Health
Sir: In the cr:qstal structure of the nearly filled 32 amThe Journal of ,PhpicaI Chemistry, Vol. 77, No. I , 1973
(1) R. Y. Yanagida and K. Seff, J. Phys, Chem.. 78,2597 (1972). (2) R . Y . Yanagida and K. Seff, J. Phys. Chem., in press. (3) Listings of the observed and calculated structure factors for both structures wili appear following these pages in the microfiim edition of this volume of the journai. Single copies may be obtained from the Business Operations Office, Books and Journals Division, American Chemical Society, 1155 Sixteenth St., N.W., Washington, D. C. 20036. Remit check or money order for $3.00 for photocopy or $2.00 for microfiche, referring to code number JPC-73-138. (4) V. Gramlich and W. M , Meier. Z. Kristallogr , 133. 134 (1971).
COMMUNICATIONS 'TO THE EDITOR
139
TABLE I: Positional, Thermal, and Occupancy Parametersa Mlyckoff position
6.A2 or b t i and b12
x
Y
z
24(k)
0
O(2) ~ ( 3 ) Ma(1)
12(h) :2 ( i ) %4(rn) 8W
0 0 0.1 124(8) 0.2016(9)
0.1831 (5) 0.2251 (15) 0.2917(11) 0.1124(8) 0.2016(9)
0.3721 (4) 1/2 0.291 7(11) 0.3433(11) 0.2016 (9)
NaP)
24(n?)
Na(3)
12(i)
0.027(5) 0.23 (2)
0.431 (3) 0.23 (2)
0.431 (3) 1/2
(Si,AI) O(1)
Occupancy factor
l.70(8) 2.1 (4) 2.9(4) 2.8(3) 0.0064(8)b O.OO52(16) 3.3(15)
1 1 t 1
1 1/ 8 1/12
10(8)
a Standard deviations are in the units of the least significant digit given for the corresponding parameter. See ref 1 for the identities of the atoms. N a ( l ) , the anisotropic Lewperature iactor = expi-bll(h2 t k2 t 1') - b,,(hk t hl i- ki)].
For
TABLE II: Selected Structural Parameters
Cell constant Distance of Na(1) from O(3) plane Framework angle at O(1) Framework angle at O(2) Framework angle at O(3) Na( 1)-0(3) Nla( 1 ) - 0 ( 2 ) Na(2)-0(2)
Na(;?)-o(l) Na(3)-0(3)
Na(:I)-O(?) a
Reference 2.
* Reference 1.
Dehydrated 4Aa
4A.8NH3
4A. 3 2 N H 3''
12.263(2) 0.20(1) 145(1) 166(1) 146(1) 2.32 (1) 2.90(1) 2.40(6) 2.64 (3) 2.47(7) 2.51 (7)
12.289(5) 0.26(1) 143(1) 163(1)
12.29 (1)
144(1)
2.33(1) 2.92(1) 2.43(6) 2.68(3) 2.75(25) 2.77(25)
Achnowledgnaent. This work was supported by the U. S. Army Research Officcb---Durham. We are also indebted to the NSF for their assistance (Grant No. GP-18213) in the purchase of the diffractometer, and to the University of Hawaii Computation Center.
methylbenzyl tert-butyl nitroxide, can be collected in a liquid nitrogen trap d ~ w n s t r e a m .The ~ contents of the trap are analyzed by esr after the addition of benzene and warming to room temperature. The apparatus used and typical results have been shown.2 Methyl radicals were also detected from the photolysis of acetone and ethyl radicals from the photolysis of 3-pentanone, tetraethyllead, and diet hylmercury . CH,N=NCHJ 0
R. Y. Yanasgida, M. S..Thesis, Universityof Hawaii, 1973.
Department of Ghern/sfry University of Ha w w Honoiulu, Hawaii 96822
Russell Y. Yanagida Karl Seff *
Fleceived August 28, 1972
Detection of F ~ ~ o r o a i kand y i Acyl Radicals in the Gas-Phase Photolysis of Ketones and Aldehydes by Electron Spin Resonance Gas-Phase Spin
Pubbcahon costs assisted b) fhe Environmental Protection Agency
Sir: In recent ccmmunications2 a technique for the detection and identification of gas-phase free radicals at relatively low pressures (naO.1 Torr) has been described. Thus when azomethane is photolyzed a t 0.10-0.20 Torr in a flow experiment upstream from powdered phenyl N-tert-butyl nitrone (PBN the methyl radical addition product, a) 9
c c
Na(3) was not located in this structure.
cuies, then, suffice t o return the dehydrated 4A structure part of the way to its relaxed state. Qualitatively similar effects are observed in a trimethylamine sorption complex5 of zeolite 4A prepared in a similar way.
(5)
0.59(1) 145( I ) 159( I ) 142 (7 ) 2.35(2) 2.98(1) 2.70(14) 2.130 ( 14)
CH,.
+-
I
kv --+
-
C~H',CH=I~C(CHJ~
2CH3* -1- N2 0.
I
C~H~CI-[(CHJ~C(CH,),
In a continuation of this study, the results summarized in Table I have been obtained. Trifluoromethyl and pentafluoroethyl radicals are readily detected by PBN in the photolysis of the iodides in the gas phase. The spectrum obtained from 1,3-dichlorotetrafluoroacetone is almost identical with that obtained from photolysis of pentafluoroethyl iodide and is assigned on this basie to the ch!orodifluoromethyl spin a d d ~ c t Although .~ methyl or trifluoThis work Is supported by the Environmental Protection Agency Air Pollution Control Office, Public Health Service, Grant No. AP 01096. E. G. Janzen and I. G. Lopp, J. Phys. Chem., 78, 2056 (1972); see also E. G. Janzen and J. L. Gerlock, Nature (London). 222, 867 (1969). This method of detecting radicals has wide appiication in liquid soiution and has been named spin t r a ~ p i n g The . ~ riitroxide produced is called a spin adduct. For reviews see E. S . Janzen, Accounts Chem. Res., 4, 31 (1971); C. Lagercrantz, J. Phys. Chem., 75, 3466 (1971); M. J. Perkins, Chem. Soc., Spec, Pub/., No. 24, 97 (1970). E. G. Janzen and B. J. Blackburn. J. Amer. C'iem. Soc., 91, 4487 (1969). Presumably the radical could also be produced from the loss of chlorine atomG but no evidence for chlorine atom chemistry was found. The Journal of Physical Chemistry. Vol, 77, No. 7 . 7973
