ttuc
fP
Gas-phtm electron diffraction pattsfns of CZF6 were recorded with the sample reservoir at rdom temperature. Least-squares analysis of .the reduced intensity data gave (DM spnretry) r,(C-C) = 1.645 (6) A, rg(GF) = 1.326:(2) A, and&CF.= 109,7a(0,12)0, with the indicated error estimates. These values *ere compared with corresponding distances reported for an4ogous compounds.Analysis of the torsional mcilbond axis led to a mer dldihedral angle of 67.3(2.7)p'(60° = stslggePed),'whichcormlation about the sponds to an effective shrinkage of 0.004 A for the. lcn$Ct F- F distance. A baiiier height 'to internal rotation of 3.7 kcal/mol wq'derived from the preeen(.djffraction data by taking into a w u n t ample cooling due to the rapid expansion in'the jet.
qc,
The study of fluopine subtitution (CD.and elon molecuk etrudure and reactif& hm beena!. topic of continuing hbrt%t in OUP 1eboratoty.h the c ~ g eof the mbdtutd rn@thmm ethanm, the. C-F bond length ,
--
correlates with the numhr of F substitutions: 1.38-1.39.A, 1.34-1.86 A, and 1,32-1.38 A for the attachment of one, two, and three fluorinm, mpectiwly. The auhstitution effect upon the adjacent C-C bond length, however, is uncertain, Fop gmmplg, a e C-C separation ported fernthe previourm Ieetron diffraction crtudy of hexafluomtbne,! thQJwme/ormyslcrlChsmkrh)r, vor. 7th NO. 23,TO74
about bon&,' Insedion of.T m an >tidditiod I1 h& the ex&~eff&~Thederived ci nds to khe .1 t?&& average .2de:*tiori (7.3 &,::2.7 siiiggered- codcidation'; the .\torsion , F]e,,uc&dQcreasq while tGe tokfonaI"deviatiotl, p r d 'an effective'shrinkage of 0.0036(-0.b02,+b.O03,:.prith respect-tothe trans F i;;F distance. Mean Amplitudes. In contrast 9the structural,p'&ame: tere, the magnitudesof theme& &plitud& deduced from diffraction datd ire subjat W systcme'ticerrors. for which correctioG ¬"be made with dnfidence. There ar ~
LBB
dum.
nal backgrounds are shown in Wb chosen on the basis of itivity criterion proposed by Karle.I3 Throughout this study an analytical fit of the elastic and inelastic scattering factors of Tavard,14 et,aE., were in the used, along with the phase shift approximation of Bonham mental conditions were not precisely dugli~n~ted present experiments. We thbrefore tested a spread of emand Uksji.15 . ctions.frorn 3 to 896; the obseiyed*ampIitudes A preliminary set oP.p&iiBfne&& w& ;obtained from a res-' d with calculated values in Table 111. The r h t olution of the redial distribution curve. Final structural paated for sample temthe basis of a simple ts derived from d values are consisa1,,4 ae compared in examined. Model I was constrained to the D M (staggered) configuration whereas in the torsional angle was . The calculated fij's, for 1(F F)g.uche, aw alue ( 0 3 ,.eymmetry).,The mast independent of at& and agree with the vdum'derived from diffraction data' to within the esperi.mentaI error: The mean amplituden of the gauche pair do have a large temperature' dependence, which might be uaed .to gauge the mperature of the sample in the jet, were thS. 'crrora dgnificantly reduced. In thin connection, iccbrding to a m n t kinetic and gas dydyh'this laMratory$ban~plscooling due to jet tween the nozzle lip and its intersection by the elsctron beam ehould be appreciable. For a h the limita 1.MI and 1.662 A; hence weapropoee the value ratio of 1.10 the trenelational tetnperatupe at estimated to be about 26VK.e .,1.546 & 0.008. The EoPrseponding cbfive&d values for C-F Pote)ll;ialBairier to Internal Rotation. seve~dmethods are 1,326and 1.326 A; rrtepctively. are available for estimating (L .bant~rheight from electmn diffraction e is based on the harmonic approxima. Strhture: The geometric parameters obtsrind in this tion, which the torsional motion to be an intinftea=
- --
npa'.lniimal nt Wvslcnl cheml~nhsVat, 78. Ma. 23. lo94
0 1. Phot
IO
. 2 0 ‘-.30 40
5 0 . 60
70
80
90
100
110. I20
130
q (a-9
&tmsfw y8. u, wkh r e w becftnaounds drawn In.
c 2 F6
RF i.039
TABLE I 0-c
C-F
4m.F T
’.
*1.646(8)’ 1.32’8(2)“ 109.76(0.12) 60.O(fixed) 0.039(8). 0.046(1)
1.646(3) 1.326(2) 109.76(0.11) 67.3 (2 .7)
0.067(1)
0.087(1)
O.ose(2) 0.122(6) . 0.067(6) 0.0209
-
imal dscillation around thg equilibrium .(Le., conformation. Under them conditions, the C ~ O >of this ethane-type molecule [V(T) (v0/2) (1 ma 3r)] is .related.to the effective shrinkago, a,, of %he“tpane”
+
pair‘distance.**M
o .oai?(sj
0346(1)’
0 .&(2)
In the &nd, the mean mation’i$“hird,based on
0.102(19) 0,087(6) 0.0197
Valup in p a k n t h h , in 10L*aA or degre&, are 38, 88 obtained from,leaetequared analyeie of the qM(q) function, or 0.16% of the respixtiite pahnetar, whichever b lamer.
where Jr.)s the mean am only; it w q :$dculebd by a normal mbde mdpte. , . In thi’thhd’mpthbdthe exprimen4 radial distributforn curve, f(rt’bepproxlmated .by,t&$w the int+md rdta-
. .
.
'2 8 4. structure of C#8.
6.
R factor tor WI radial litstributkn function of ~ 2 to internal rotation, bahd on eq 3. Thsw curves abpy to T a w = 300°1
