COMMUNICATIONS Bis(trifluoromethy1)trioxide: First Structure of a Straight-Chain Trioxide** K a r i n a 1. G o b b a t o , Martin F r a n k K l a p d o r , Dietrich M o o t z , Wolfgang Poll, S o n i a E. Ulic, Helge Willner, and Heinz Oberhammer* Dedicated to Professor Herbert W Rorsky on the occasion of his 65th birthdaj> Straight-chain polyoxygen compounds of the type R,O, ( n = 1, 2, 3 , 4 . . .) become less stable with increasing chain length. The parent compounds H,O, are of general and theoretical interest.''] Numerous compounds of the type R,O, are known, but polyoxygen compounds with n 2 3 were reported almost exclusively with R = F, SF,, alkyl, or perfluoroalkyl groups. At room temperature only trioxides with perfluoroalkyl groups can be isolated. The simplest derivative of this class of compounds, bis(trifluoromethy1) trioxide, CF,OOOCF, ,which was reported for the first time in 1Y63['] and isolated as pure substance shortly after,[31is the best characterized trioxide. The colorless gas with a boiling point of - 16 'C and melting point of - 138 "C decomposes at room temperature within months to give CF,OOCF, and oxygen.[31 VibrationaI,I3,41 NMR,13] mass,[31 and X-ray photoelectron spectra (XPS)['] of this interesting compound are known, but the molecular structures of this and any other covalent straight-chain trioxidef6' have not been deteimined unequivocally. The result of an electron diffraction study of a mixture of CF,OOCF, and CF,OOOCF, appears to be uncertain,"] as demonstrated by a later investigation of CF,OOCF, .Is1 We therefore decided to synthesize this trioxide again and to determine its structure in the gas phase by electron diffraction and in the crystalline state by X-ray diffraction. The experimental studies are supplemented by a b initio calculations. The derived structural parameters are listed in Table 1. Analysis of the radial distribution curve of CF,OOOCF, (Fig. I ) , calculated by Fourier transform of the molecular intensiTable I . Experimentally and theoretically determined structural parameters of CF,OOOCF,. Gas [a] C-F 0-c 0-0 0-0-0 0-0-c F-C-F x(CF,) [cl 0-0-0-c 1.326(3) 1.37X( 12) 1.45?(5) 106.7(20) 105.8(6) 108.3(4) 5.4(7) 96.0(38) Crystal [b] HF & I l G 1.315(2) 1.389(2) 1.437(2) 106.4(1) 106.5(1) 109.3(7) 5.0(2) 1.327 1.3Y3 1.453 104.4 107.4 109.6 4.0 97.6 95.9(8) --. L 0 . -L.-J- 1 2 L - 3 KIA . I . - L 4 _ _ I 5 6 Fig. 1 . Experimental radial distribution function and difference between experimental and caiculated curve. The positions of interatomic distances are indicated by vertical bars. ties, yields a skew structure with trans orientation of the two CF, groups (C, symmetry). This result agrees with the interpretation of Raman spectra,[4b1but is in contrast to the interpretation of IR spectra. which indicate C , symmetry.[4c1In the least-squares refinement local C,, symmetry was assumed for the CF, groups with a possible tilt angle between the C, axis and the 0 - C bond. The fit of the experimental molecular intensities improves slightly if a small amount of impurity ( 5 % CF,OOCF,), which was observed immediately after the synthesis, is taken into account in the structure analysis. In the crystal (unit cell in Fig. 2). the asymmetric unit comprises a whole molecule, twisted as in the gas phase and with a trans orientation of the CF, groups. Deviations from C, symmetry are only small. As an example. the dihedral angles C1-01-02-03 and 01-02-03-C2 have been determined independently. but the obtained values of Y6.8(1) and 95.1(1)" are quite similar. The same holds for the individual values of other geometric parameters (only their averages are listed in Table 1). as well as for the dihedral angles F1-C1-01-02 and 02-03-C2-F4 of 178.1(2) and 176.7(1)". These dihedral angles show that the trans position (antiperiplanar orientation) of the F atoms with respect to the central 0 2 is almost ideal. The distinct widening of all bond [a] Electron diffraction, I', [A] and r [ 1, 30 values in parentheses. [b] X-ray diffraction; mean parameters; o values in parentheses. [c] Tilt angle between the C , axis of the CF, group and 0 - C bond. [*] Prof. Dr. H . Oherhammer. K. 1. Gobbato lnstitut fur Physikalische und Theoretische Chemie der Unlversitit D-72076 Tiibingen (Germany) Telefax: Int. code (7071)296910 e-mail: heinz.oherhammerra,uni-tueblngen.de + [**I M. E Klapdor, Prof. Dr. D. Moot7. Dr. W. Poll lnstitut fur Anorgdnische Chemie und Strukturchemie der Universitlt Diisseldorf (Germany) Dr. S . E. Ulic Facultdd de Ciencas Ex;ictas. Universidad Nacional de La Plata (Argentina) Prof. Dr. H. Willner lnstitut fur Anorganische Chcmie der Universitdt Hannover (Germany) K. 1. G. and S. E. U are grateful for fellowships from the DAAD and CONICET (Rephhlica Argentine). respectively. H. W. and H. 0. acknowledge financial support by the DFG. b Fig. 2. Unit cell of a crystal ofCF,COOOCF, with two molecules (ellipsoids represent 25 % probability: viewed down the .v axis). COMMUNICATIONS angles F-C-0 when the F atom is guuche rather than fram (mean values 112.1(1) and 104.7(1)". tilt angle x(CF,) = 5.0(2)") correlates with the smallness of the nonbonding intramolecular distances: F(guu&). . ' 0 2 mean value: 2.65(3) A: for F(trcrn.c) . ' 0 2 : 3.399(2) A. Although systematic differences exist between structural parameters for the gaseous and crystalline state, the agreement of the results obtained with electron and X-ray diffraction is very good. In particular the bond angles and the 0 - 0 - 0 - C dihedral angle. which are most easily affected by packing effects in the crystal,l"i possess identical values within experimental uncertainties in both phases. The good agreement of the geometric parameters optimized with the HF/3-21G method with the experimental \,dues is most likely due to a fortuitous compensation of several inadequacies of this method. Ab initio calculations for HOOOH with different basis sets result in 0 - 0 bond lengths between 1.373 and 1.539 A,['] The HF/3-21G calculations for CF,OOOCF,predict the existence of a second stable conformer ~ ; i t hcis orientation of the two CF, groups (C , symmetry). 3.3 kcal mol-' higher in energy. The 0 0 bond in CF,OOOCF, is slightly shorter than that in hydrogen peroxide (1.464 Ailoi), but longer than that in CF,OOCF, ( I .419(20) A[*]). As expected. this distance is longer than in ozone (1.2716(2) or in the 0; ion (1.291.35 A['''). The 0-0-0 bond angle in the trioxide is smaller than a tetrahedral angle and considerably smaller than in 0, (117.79(3j')or in 0; (113-119'). The 0 - 0 - 0 - C dihedral angle is larger than the predicted value for HOOOH of about 80",1'' but distinctly smaller than the C-0-0-C angle in CF,OOCF, (123.3(40) 1 8 1 j . A value similar to that in the trioxide was observed for the S-S-S-C angle in CF,SSSCF, (89(3)' in the and 88.5(1) in the c r y ~ t a l ~ ' ~ ~ ) . [I] D. Cremer. J. Chcni. P/I,v.Y.1978. 69. 4456  V. A. Ginshurg. E. S. Vlasva. N. M . Vasil'eva. N . S. Mirzabekova, S. P. Makarov. A. I . Schchekotikhin, A. Ya. Yakubovich. Doh/ . 4 X d .Vauk S S S R . 1963. 149. 97; Do/?/. C/irni. fEngI. Trrm.sl.J 1963. 149. I X X  a ) P. G. Thompson. J A m . (%eiIi. Soi.. 1967. XY. 4316: b) L R. t\nderson. W. B. FOX.!hid. 1967, 89. 4313. 14) a ) R. A. De Marco. R. R. Smardzewski. J. Fluorinr Chrwr. 1976. 7. 347: b) J. D. Witt. J. R. Dung. D. D . DesMarteau. R. M. Hainmaker. liiorg. Clicni. 1973. 12. 807: c) R. P. Hirschmann. W. 8.Fox, L. R. Anderson. . S p ~ c r r o ~ / i i mAi,tu . A 1969. 25. 811. [S] P. Brmt. J. A. Hashmall. F L. Carter, R. A. De Marco. W. B. Fox. J Am. C h m . Soi.. 1981, 1113. 329. 161 Only one crystal structure of a cyclic compound has hem reported, namely, that of the transannular primary ozoiiide of to./-butyl-l (I-methyl-anthracene: Y Ito. A. Matsuura. R. Otani. T. Matsuura. J Am. Chern. . S i x 1983, 105,5699. Moreover. the central oxygen atom appears to be disordcred.  A. Yokozeki. S. H. Bauer. Top. Ciirr. Cheni. 1974, 53. 71. R L. Hilderbrandt, S . H. Bauer, 7Yiird AU.S/IIIS i w p s n i f n on Go,r Phew Molrwi/ur S/rucrure. Austin, Texas, 1970. 18) C. J. Marsden. L . S. Bartell. F. P. Diodati. J Mid. S t r i r i i 1977, 39, 253.  N o interinolecular distance in the crystal is shorter than the sum of the respective van der Waals radii. The \hortest contact (2.956(2) h ) occurs between an F2 and an 0 2 atom. (101 J. Koput. J. Mol. S p v / r o w . 1986. 115. 4 3 . [I 11 J C. Depannemaecker. J. Bellct. J M I , / Spc,( uwc. 1977. 66. 106.  W. Hesse. M. Jansen. W. Schnick. Prog. Solid SIUWChrw 1989. 19. 47. [I31 M. ti;ienssleii. R. Minkwitz. W. Molzbeck. H. Oberhainmer, fnors. ( I c m . 1992. 31. 4147. [I41 C. Meyer. Dissertation, Universitit Dusseldorl: 1994. (151 E. L Varetti. P. J. Ayrnonino. Arm. Asoc. Quim. Argcni. 1970. 23. 5X. [I61 H. Oherhammer. W tiombler, H. Willner. J Mol S / r m i. 1981. 70. 273.  G. M. Sheldrick. A ~ r uCrwrrlliigr. Sect. A 1990. 46. 467. 118) G. M . Sheldrick. Progrom f o r ihe Rr.finemwil of Cr,,.s/o/,S[rii([uri's. Univer~itdt Gottingen, I993 1191 SHELXTL PLUS. Structure Determination Systems. Revision 4.21. Siemens Anolytical X-Ray Instruments Inc., Madison. WI. 1990 E.Yp<v.il?l~,ntc//Procrdule Caution ('F,OOOCF, is potentially explosive, especially in the presence of organic or oxidizable iiutei-ials. I t should he handled only in millimolar quantities and with propel- d i c t y prcc;iutions. The synthesis was performed according to a modified literature method 1151. A 4 L round-bottomed flask. equipped with a water-cooled high-pl-esw~-c mei-cury lamp (TQl50, Heraeus) at its center. was filled with a mixture 01.100 mhnr CF,C(O)CP, (ca. 16 mmol). 200 mbar F,,and 300 mbar 0,. After 24 hour\ photolwi5. excess Fi and 0, was pumped off at - 196°C. and the residue fractionaled i n i a c u o through ii series of traps held at -80. 120. and -196 ' C . In the tIap .it 120 C CF,OOOCF, was collected. which after repeated fractionation contained 'I\ thc only impurity 5 % CF,OOCF,. as determined by IR and 19F NMR \pectroscopq. Yield 1.2 g (6.5 mmol). ~ The elccti-on d1l'lr:iction intensities were recorded with a Gasdiffraktograph KD-G2 iit no/Lle-to-pl:itc distances o f 2 5 and 50 cm and with an accelerating voltage ofca. 60 kV. The electron wavelength was calibrated with ZnO powder. The temperature ofthe sample i-e\ervoir was -90 C, that of the inlet nozzle 1 5 C. The photographic plates wrie an;ilyied with the usual methods (161and scattering intensities in the .Y range\ 7 I X and 8 35 (A= ( 4 n : i ) sinO12. 2. = electron wavelength. 0 = sc;it~eriiiganglc) wei-c used iii the structure analysis C'rksttil growth \\:is performed from the melt in a thin-walled quartz glass capillary. The s;iinpIc \%'L\ cooled iit a rate of I C m i n - ' in the cold yas stream of a diffractoineter (Sienicns Stoe AED2) equipped for work at low temperatures; Mo,, r ~ i d i x ~ i o i i0. = 0.71073 A ) , graphite monochromator. R-H scan. 20md.= 65 /'= 170 C . .;pace group PT. Z = 2: N = 4.810(2), h =7.477(4). c =7.993(4) A. Y =7X 9 l t 3 ) . /i= X6.12(3). 1' = 83.49(3) . V = 280.0(2)A3. The structure was solvcd h! direct methods Mith SHELXS-86 [I?), and refined with 2026 independent I f ; , ! ' i.iiliie\ I d thcse 1763 with 1 f ; ) I > 4n, were classified as observed) with SHELYL.-X [ l X ] : R(f.') = 0.146 with all and R ( F ) = 0.048 only with the observed rellcctioii\. Tlic rcsiduiil electron density was bctween -0.33 and 0.48 e k ' The program SIiFL.XTL PLUS  was used to draw the crystal structure (Fig. 2 ) . Further (letails 01' the crystal structure investigation are aiailable on request from f'achinlbrniati~r~i\/entrumKarlsruhe. D-76344 Eggenstein-Leopoldshafeii (Germiin?) b! quoting the depository number CSD-401780. I ~ Electronically Tuned trans Labilization Controls the Substitution Behavior of Rhodoximes** Carlos Ducker-Benfer, Renata Dreos, and Rudi van Eldik* Substitutions of axial ligands of alkyl(aqua)bis(dimethylglyoximato)rhodium(m) complexes were studied in earlier reports [Eq. (a); Hdmg = dimethylglyoximate anion].[' The reactivity of the rhodium complexes shows a strong dependence on the nature of the alkyl substituent R. The lability of these complexes is affected by the size of the alkyl group and the electronic tr~ins-[Rh(Hdmg),(R)(H~O)] +L - /raiis-[Rh(Hdmg),(R)L] + H,O (a) x-2 state of the nonlabile ligands. In all cases the reaction rate is nearly independent of the nucleophilicity of the incoming ligand. This observation as well as the thermal activation parameters suggest a dissociative interchange mechanism. The high lability of these complexes results from two effects, namely, the trans in[*] Prof. Dr. R. van Eldik. Dipl.-Chem. C. Ducker-Benfer Institut fur Anorganische Chemie der Universitiit Erlmgen-N iirnberg Egerlandstrasse 1 . D-91058 Erlangen (Germany) TekfaX. Int. code (9131)85-7387 e-mail: vaneldikm anorganik.chernie.uni-erlangen.de + Received: May 29. 1995 [Z8033IE] German version: Angeii'. Chem. 1995. 107, 2433 -2434 Keywords: electron diffraction oxygen compounds * structure elucidation trioxides x, F = [**I Prof. Dr. R. Dreos Universiti di Trieste 1-34127 Trieste (Italy) The authors acknowledge financial support from the Dcutsche Forschungsgerneinschaft. Fonds der Chemischen Industrie. MURST. and the Max Buchner Forschungsstiltung.