239 Acta Chim. Slov. 1999, 46(2), pp. 239-252 CRYSTAL STRUCTURE OF (Xe2Fn+)(VF6 ) f Primož Ben kič , Ljubo Golič , Jože Koller , Boris Žemva * Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia (Received 31.3.1999) Abstract Single crystal of (Xe2F11+)(VF6-) has been prepared. Compound crystallises in monoclinic space group P21/n (No. 14) with a =8 55.1(1) pm, b = 889.6(1) pm, c = 1570.3(1) pm, ß = 93.31(2)°, V = 1.1925(9) nm3, Z = 4 and pc = 3.545 Mg/m3. A structure determination using three-dimensional MoKa X-ray data resulted in conventional R and wR factors of 0.046 and 0.066 respectively, for 2217 unique reflections for which I > 3g(I). The structure shows two groups; the essentially octahedral VF6- anion and Xe2F11+ cation, which consists of two XeF5 units bridged by additional common fluorine atom. Calculation of Mulliken charges for structural units Xe2F11 VF6 and Xe2F11 AuF6 has been performed. Introduction The system vanadium pentafluoride - xenon fluorides has been extensively investigated in the past [1], [2], [3], [4], [5]. 2XeF6-VF6 was the first compound prepared in this system [4]. VF5 is strong enough fluoro acid to form adducts not only with medium strong fluoro bases like XeF6, but also with weak fluoro bases like XeF2 [2], [3] and KrF2 [6]. Later the system XeF6-VF5 was reinvestigated and two new adducts XeF6-VF5 and XeF6-2VF5 have been isolated [7]. Since there are only two known crystal structures of the cation Xe2F11+ (Xe2F11AuF6 [8] and (Xe2F11)2NiF6 Dedicated to the memory of Prof. Dr. Jože Šiftar 240 [9]), it was decided to prepare single crystal of Xe2F11VF6 and determine its crystal structure. For comparison quantum-mechanical calculations on neutral structural units of Xe2F11MF6 with M = Au and V were also performed. Experimental 1. Apparatus The preparation of Xe2F11VF6 was carried out in FEP reaction vessel with Teflon valve. For the manipulation of the reactants and products a nickel vacuum line was used. It was equipped with mechanical pump connected to the system cross soda lime scrubbers for removal of fluorine, hydrogen fluoride and volatile oxidising fluorides, and mercury diffusion pump to achieve high vacuum in the system. Monitoring of pressure was done with Monel Helicoid pressure gauges. 2. Reagents XeF6 was prepared by the reaction between xenon (L’Air Liquide, 99.5%) and fluorine (Solvay, 98-99%) in the presence of nickel difluoride (Alfa Ventron, 99.5%) at 393 K [10]. Traces of XeF4 that might be still present in XeF6 were not problematic, since XeF4 is much weaker fluoride ion donor as XeF6 [11]. Vanadium pentafluoride was prepared by fluorination of pure vanadium metal (Alfa Ventron, 99.7%) with step-by-step fluorination at temperature 523 K in a nickel reaction vessel [12]. Quality of the product was tested with IR spectroscopy showing only bands of VF5 with some traces of VOF3. 3. Preparation of Xe2F11VF6 649.9 mg (4.45 mmol) of vanadium pentafluoride was condensed in FEP reaction vessel. Then excess of XeF6 (15.90 mmol) were introduced in the vessel with condensation. At room temperature mixture looked like yellowish mash. The vessel was kept at 313 K for one day. 241 When reaction was finished, excess of XeF6 was pumped out, while the reaction vessel was kept at temperatures between 248 to 258 K till constant weight (2.913 g) was reached (Figure 1). This weight is in experimental error limits of theoretical yield for Xe2F11VF6 (2.832g). The compound was identified with Raman spectrum (Renishaw Raman Imaging Microscope, System 1000, wavelength 623.8 pm, 25 mW) of the solid product. It was identical with Raman spectrum of (Xe2F11+)(VF6), known from the literature [7]. The compound is white crystalline material well soluble in anhydrous HF (aHF). Raman spectrum of the solution was also recorded (Figure 2). The compound does not decompose in aHF, since Raman spectrum of the recrystallised compound is identical with Raman spectrum of the compound before recrystallisation. 5 4,5 < Weight/ g co Ol 4^ 3 2XeF6VF5 0 R N. .. ~. ^P ^P 4 248 K ! 258 K >j< 253 K .L 256 K i ™: • ™: ć,0 C ) 20 40 60 80 Time / h Figure 1: Pumping curve during the preparation of Xe2F11VF6 compound. 242 * V359 * 406 Raman shift / cm- Figure 2: Raman spectrum of 0.4 mmol (Xe2F11 +)(VF6-) dissolved in 1 ml of aHF in FEP vessel (Asterisks denote lines arising from the FEP material). 4. Preparation of single crystal On the top of reaction vessel colourless needle like crystals were found, but they were quickly disappearing in a dry box (MBraun, Garching). Reason for this was complete dissociation of compound’s vapours on volatile molecules of XeF6 and VF5 what has been already shown with IR spectroscopy [4]. Because of the problem with vanishing crystals, powdered solid compound was packed in 7-10 cm long fluorinated thin walled quartz capillaries (0.5 mm inner diameter) in dry box. Capillaries were temporarily closed with Kel-F grease and flame sealed outside the drybox. Powdered compound was pressed to the bottom of sealed capillaries by throwing the capillary down the 30-cm long vertical tube. Then capillaries were kept in a vertical position and lower part of capillaries was warmed up between 308 and 318 K. On the walls of the capillaries needle like crystals were formed. Raman spectrum of the group of grown crystals in the capillary showed that the compound is still the same as was synthesised. Some of the crystals decomposed in the capillaries because of the reaction of the compound with quartz forming colourless droplets. It was shown by Raman spectroscopy that these droplets are XeOF4 [13]. 620 I 183 0 200 400 600 800 1000 243 5. Structure determination Out of 30 crystals prepared in capillaries only two of them had appropriate diffractive properties for structure determination. One of them showed properties of twin crystal with common b axis and opposite a and c axis (probably coincidentally orientated two crystals in the capillary). Other crystal showed similar feature, but it was possible to separate reflections of the individual crystal. Single crystal data were collected on an ENRAF-NONIUS CAD4 diffractometer at 296(1) K using the co-26 scan technique to a maximum 26 value of 60.0°. Scans of (0.5+2-tan6)° were made with maximal counting time of 10 s. Profiles of reflections were recorded for all data. The counter aperture consisted of a variable horizontal slit with a width range of (2.7+0.4-tan6) mm and a vertical slit set to 2.0 mm. The smallest necessary set of diffraction data was collected. Further details are given in Table 1. Table 1: Crystal Data and Structure Refinement. Empirical formula Molecular weight I Space group a = 855.1(1) pm ; b = 889.6(1) pm ; c = 1570.3(1) pm ; Volume of unit cell Z Pcalc \1 F(000) Crystal dimension Index range Number of independent data Number of observed (I > 3gi) R(F0) = 0.046 (I > 3gI) R(F0) = 0.083 (all data) Xe2VF17 636.51 g/mol 71.069 pm P21/n (No. 14) oc = 90° ß = 93.31(2)° Y= 90° 1.1925(9) nm3 4 3.545 Mg/m3 6.60 mm-1 284 0.45 mm x 0.14 mm x 0.19 mm 0 < h < 12 0 < k < 12 -21 < l < 21 3460 2217 wR(F0) = 0.066 (I > 3gI) wR(F0) = 0.173 (all data) 244 The structure was solved using Patterson and Fourier methods and refined with Xtal 3.4 system of programs [14]. There was no absorption correction done, because size of the crystal was close to 2/m and not commercial capillary was used. Details of the structure refinement are given in Table 2. Table 2: Final Positional and Displacement Parameters. Atom x y z Ueq (pm2) Xe1 0.73359(9) 0.28654(8) 0.62091(4) 386(2) Xe2 0.75264(8) 0.20082(7) 0.34200(4) 361(2) V 0.7499(2) -0.1636(2) 0.5227(1) 351(5) F1 0.5716(13) 0.2050(11) 0.6788(7) 800(40) F2 0.8809(15) 0.1886(12) 0.6933(7) 910(40) F3 0.7351(14) 0.4097(11) 0.7128(6) 780(40) F4 0.8946(11) 0.4153(11) 0.5994(7) 760(40) F5 0.5939(10) 0.4310(9) 0.5812(6) 640(30) F6 0.7570(9) 0.2695(8) 0.4785(5) 503(23) F7 0.8962(10) 0.3524(9) 0.3442(5) 566(25) F8 0.6043(11) 0.3482(10) 0.3445(6) 660(30) F9 0.7353(11) 0.2595(11) 0.2313(5) 610(30) F10 0.5881(11) 0.0799(11) 0.3009(6) 690(30) F11 0.8983(11) 0.0751(10) 0.2940(5) 620(30) F12 0.7264(12) 0.0094(9) 0.5828(5) 660(30) F13 0.7571(11) -0.0434(8) 0.4300(5) 556(25) F14 0.5471(10) -0.1691(10) 0.5063(7) 710(30) F15 0.7673(14) -0.3199(9) 0.4599(7) 770(40) F16 0.7403(12) -0.2670(10) 0.6152(6) 670(30) F17 0.9503(10) -0.1452(12) 0.5373(7) 780(40) Ueq is defined as one-third of the trace of Uij tensors. Supplemental material is available from authors. 6. Quantum-mechanical calculations Mulliken charges [15] on the smallest neutral part of Xe2F11AuF6 and Xe2F11VF6 structures were calculated with Gaussian 94 program system [16]. LanL2MB (5D, 7F) [17] basis set has been used. Results are given in Table 3. 245 Table 3: Calculated Mulliken Charges (in units e0) of Structural Units Xe2F11AuF6 and Xe2F11VF6. Xe2FiiVF6 Xe2FiiAuF6 Xe2Fii XeF5 Atom Charge Xe2Fii XeF5 Atom Charge group units F3 -0.315 group units F4 -0.317 F5 -0.309 F6 -0.315 +0.748 < F4 F2 -0.305 -0.296 +0.752 < F6' F5' -0.315 -0.302 Fl -0.314 F5 -0.302 i Xel 2.287 i Xe2 2.303 +0.930 F6 -0.548 +0.931 F7 -0.549 Xe2 2.299 Xel 2.277 F7 -0.316 F2 -0.310 +0.730 < F8 FIO -0.314 -0.304 +0.728 < F2' F3 -0.310 -0.310 Fil -0.316 F3' -0.310 i F9 V -0.319 0.744 F1 Au -0.309 VF6 group AuF6 group 0.742 F12 -0.362 F12 -0.364 F13 -0.354 F8 -0.355 -0.930 ( F14 -0.251 -0.931 ( F9 -0.202 F15 -0.227 Fil -0.209 F16 -0.232 FIO -0.272 F17 -0.248 F9' -0.271 *Each line of table represents ‘equivalently’ positioned atoms in both structures. 7. Description of structure Structure analysis defined the VF6 and Xe2F11 groups as shown in Figure 3. Some distances and angles are given in Table 4. Xe2F11 group is composed of two XeF5 units connected by additional bridging fluorine atom. The VF6 group is approximately octahedral with quite different V-F distances (Table 4). Cis angels are close to 90°, the greatest deviations being for F12-V-F13 = 85.8(4)° and F15-V-F16 = 93.5°. Each XeF5 unit approximates to a square-based pyramid, with xenon atom placed bellow the base. The Fax-Xe-Feq angles are close to 79°, while cis Feq-Xe-Feq angles are 246 not equivalent (Table 4). Both XeF5 units forming a Xe2F11 group are crystallographically distinct, and the bridge bonding by the shared fluorine atom (F6) is slightly asymmetric. Bridging distances Xe1-F6 and Xe2-F6 (226.2(8) pm and 222.7(8) pm respectively) are short enough to justify the identification of Xe2F11 group, since other intergroup distances are longer. Present structure is closely comparable to structure of Xe2F11AuF6 (space group Pnma, No. 62), where major differences in crystallographic sense arise because of mirror plane perpendicular to b axis that is not present in structure of Xe2F11VF6 (atoms Xe1, Xe2, Au and some fluorine atoms have to be placed on mentioned mirror plane). Asymmetric units are packed in the crystal lattice as layers with approximately parallel (Xe, V, Xe) planes. (Figure 4). Figure 3: ORTEP [18] view of structural unit (Xe2F11+)(VF6-). 247 Table 4: Interatomic Distances and Angles for Xe2F11VF6 compound Xe2F11+ CATION: Distances (pm) Xel-Fl 185(1) Xe2-F10 185.7(9) Xel-F2 186(1) Xe2-Fll 186.5(9) Xel-F3 181.2(9) Xe2-F9 181.2(7) Xel-F4 184(1) Xe2-F7 182.3(8) Xel-F5 183.8(8) Xe2-F8 182.6(9) Xel-F6 226.2(8) Xe2-F6 222.7(8) Xel-F12 253.7(8) Xe2-F13 257.4(7) Angles (Deg) Axial F3-Xel-Fl 79.4(5) F9-Xe2-F10 79.3(4) F3-Xel-F2 79.8(5) F9-Xe2-Fll 78.7(4) F3-Xel-F4 78.4(5) F9-Xe2-F7 79.8(4) F3-Xel-F5 79.8(4) F9-Xe2-F8 78.2(4) F6-Xel-F3 146.2(4) F6-Xe2-F9 147.1(4) Cis-equatorial Fl-Xel-F2 90.9(5) F10-Xe2-Fll 91.3(4) F2-Xel-F4 85.2(5) Fll-Xe2-F7 89.2(4) F4-Xel-F5 88.9(4) F7 -Xe2-F8 86.4(4) F5-Xel-Fl 87.2(4) F8 -Xe2-F10 84.8(4) VF6- ANION: Distances (pm) Cis Angles (deg) V-F12 182.2(8) F12-V-F13 85.8(4) V-F13 181.1(8) F12-V-F14 87.8(5) V-F14 174.0(9) F12-V-F16 90.2(4) V-F15 171.6(9) F12-V-F17 89.4(5) V-F16 172.5(9) F13-V-F14 88.7(5) V-F17 172.3(9) F13-V-F15 90.5(4) F13-V-F17 88.4(5) F14-V-F15 90.6(5) F14-V-F16 90.8(5) F15-V-F16 93.5(3) F15-V-F17 92.0(6) F16-V-F17 92.0(5) 248 rv ar P« »s. ATI m. rPtz ß> €0> (Gl ^A ' «MA. . ----------»—/ V \l_------^r dp ^ Figure 4: Projection of Unit Cell Packing down the a Axis. Results and discussion The cation Xe2F11+ was first crystallographically defined in the compound Xe2F11AuF6 [8] and latter in (Xe2F11)2NiF6 [9]. Interaction between Xe2F11+ and anion (AuF6- and NiF62- respectively) was considered as Coulombic interaction. In agreement with mentioned model, Raman spectrum of (Xe2F11+)(VF6-) compound dissolved in aHF (0.4 mmol Xe2F11VF6 in 1ml of aHF) clearly shows dissociation of compound and further dissociation of Xe2F11+ species resembling the tautomerism of XeF6 solutions [19] (Figure 2). Strong lines at 671 cm-1 and 620 cm-1 indicate presence of XeF5+ ions. Lines at 406 cm-1, 359 cm-1 and around 200 cm-1 indicate presence of Xe2F11 +, XeF5+ ions and tetrameric clusters of [(XeF5+)F-]4. The shoulder at approximately 750 cm-1 might be assigned to n1 (a1g) of VF6-. Because of vanadium (V) electron configuration (no electrons in 3d-orbitals) there are no Jahn-Teller distortions of VF6- species, so regular octahedral geometry of VF6- 249 anion is favourable. Any departures of octahedral symmetry, in this structure, can be interpreted as a consequence of interaction with the Xe2F11+ cations. So V-F distances of bridging fluorine atoms F12 and F13 are considerable elongated in comparison with other nonbridging fluorines on VF6- species. Consequence of bonding interaction with positive Xe2F11+ species are also calculated higher negative Mulliken charges on mentioned atoms (Table 3), what is due to the delocalization of charge from negatively charged VF6- species to positive Xe2F11 + cation, and indicate ionic character of interaction. The situation with Xe2F11AuF6 compound is very similar. It should be mentioned here, that LanL2MB (5D, 7F) basis set is not considered as very precise one, but is good enough for at least some of qualitative comparisons, especially because it supports wave functions of heavier atoms down to the bismuth. In Xe2F11+ species close approach of bridging F6 atom to each Xe atom and the departure of Xe-F-Xe angle from linearity suggest that a measure of covalence should be incorporated into bond description, what was already noticed by (Xe2F11+)(AuF6-) compound [8]. The bond in Xe2F11+ can be described as a resonance hybrid of canonical forms [XeF5+XeF6]«[XeF6XeF5+] with unequal weights [8], [9], and comparable contribution of ionic canonical form [XeF5+F-XeF5+]. That is also evident from distribution of Mulliken charges on Xe2F11+ species (Table 3). Bridging F6 atom in vanadium compound is carrying negative charge (-0.548e0), with unequally distributed positive charges on XeF5 units (0.748e0 on unit with Xe1 atom and 0.730e0 on unit with Xe2). That is in accordance with asymmetric bridging Xe1-F6-Xe2 distances. The same is true for Xe2F11+ species in gold compound (Table 3). In vanadium compound there is also indication of steric activity of nonbonding lone electron pair as noticed in some already known structures [8], [20], [21]. Close approach of bridging F6 atom to Xe1 and Xe2 could deflect nonbonding lone electron pair from its axial position. Because of repulsion of F1 and F2 atoms on Xe1, and F10 and F11 on Xe2 with lone electron pair there is increase of angles F1-Xe1-F2 and F10-Xe2-F11 and lengthening of corresponding atomic distances. VF6 group is slightly 250 tilted from (Xe1, V, Xe2) plane (Table 5) what can give additional insight in distortions of XeF5 unit from C4v symmetry. Table 5: Distances of some Atoms from (Xe1, V, Xe2) Plane in Structural Unit Xe2F11VF6. Atom F3 F6 F9 F12 F13 F15 F16 Distance (pm) 8.49 12.21 -19.36 -13.54 3.57 8.44 -5.41 In both, gold and vanadium compound Xe-F-Xe angles are close to 170° (169.2(2)° and 166.5(4)° respectively) and calculated total charges on VF6 and AuF6 groups are practically the same (-0.930e0 and –0.931e0 respectively). So the most probable reason for mentioned tilt of VF6 group, which is not property of Xe2F11AuF6 structure, is packing of asymmetric units in unit cell (Figure 4). With such tilt probably stronger interaction of smaller VF6- anion with Xe2F11+ cation is achieved, since steric activity of nonbonding valence pair on Xe atoms is weaker, if interacting fluorine atoms approach little off the plane (Xe1, V, Xe2). In (Xe2F11+)(VF6-) more steric freedom by interaction of F12 and F13 ligands with Xe1 and Xe2 atoms respectively is also indicated by quite large reduction of angle F12-V-F13 (85.8(4)°) on VF6- group from 90°. The reduction of the analogous angle in AuF6- group is smaller (F8-Au-F12 = 88.0(5)°) [8]. Conclusion An usual way of understanding the structure is its comparison with similar structures. In case of compounds with Xe2F11+ cation now only three crystal structures are known. Since there are many compounds with different anions, which compositions suggest they contain Xe2F11+ cation [22], it would be of great interest to compare their structures, charges, molecular electrostatic potential and lattice energies. Unfortunately preparation of suitable single crystal is difficult. Some efforts have been done in the past 251 with 2XeF6-AsF6 compound [23] and Xe2F11RuF6 compound [24], but they failed because all crystals showed disorder or gross twinning features and were not suitable for an X-ray structure determination. Acknowledgement We are thankful to Ministry of Science and Technology of Republic Slovenia for financial support and to Dr. Karel Lutar and Mag. Zoran Mazej from Jož ef Stefan Institute in Ljubljana for help with experimental work and fruitful discussions. References [I] B. Cohen, R.D. Peacock, J. Inorg. Nucl. Chem. 1966, 28, 3056-3057. [2] B. Žemva, J. Slivnik, J. Inorg. Nucl. Chem. 1971, 33, 3952-3953. [3] V.A. Leagasov, A.S. Marinin, Zh. Fiz. Chem. 1972, 46, 2420-2421. [4] G.J. Moody, H. Selig, J. Inorg. Nucl. Chem. 1966, 28, 2429-2430. [5] A. Turičnik, H. Borrmann, B. Žemva, Reaction of Tetrafluorides with Xenon Difluoride in anhydrous Hydrogen Fluoride, 12th European Symposium on Fluorine Chemistry, Berlin, Germany, 1998, Abstracts, pp PII-1. [6] B. Žemva, J. Slivnik, A. Šmalc, J. Fluorine Chem., 1975, 6, 191-193. [7] A. Jesih, B. Žemva, J. Slivnik, J. Fluorine Chem. 1982, 19, 221-226. [8] K. Leary, A.Zalkin, N. Bartlett, Inorg. Chem. 1974, 13, 775-779. [9] A. Jesih, K Lutar, I. Leban. B. Žemva, Inorg. Chem. 1989, 28, 2911-2914. [10] B. Žemva, J. Slivnik, Vest. Slov. Kern. Druš. 1972, 19, 43-46. [II] J.Berkowitz, W.A. Chupka, P.M. Guyon, J.H. Holloway, R. Spohr, J. Phys. Chem. 1971, 75, 1461-1471. [12] B. Žemva, J. Slivnik, J. Inorg. Nucl. Chem., 33, 3952 [13] G. M.Begun, W.H. Fletcher, D.F. Smith, J. Chem. Phys. 1965, 42, 2236-2242. [14] S.R. Hall, G.S.D. King, J.M. Steward, The Xtal3.4 User’s Manulal, University of Western Australia, Lamb, Perth, 1995. [15] R.S. Mulliken, J. Chem. Phys. 1955, 23, 1833-1840. [16] Gaussian 94, Revision D.1, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B.B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995. [17] Gaussian 94, User’s Reference, Gaussian, Inc., Pittsburgh PA, 1995, pp 178-180. [18] CK. Johnson, ORTEPII. Report ORNL-5138. Oak Ridge National Laboratory, Tennessee, ZDA, 1976. [19] C.J. Adams, N. Bartlett, Israel J. Chem. 1978, 17, 114-125. [20] K.Leary, D.H. Tempelton, A. Zalkin, N. Bartlett, Inorg. Chem. 1973, 12, 1726-1730. [21] N. Bartlett, M. Gennis, D.D. Gibler, B.K. Morell, A. Zalkin, Inorg. Chem. 1973, 12, 1717-1721. [22] B. Žemva, Croatica Chemica Acta 1988, 61, 163-187. [23] N. Bartlett, M. Wechsberg, Z. Anorg Allg. Chem. 1971, 5, 385-397. [24] N. Bartlett, F.O. Sladky, J. Amer. Chem. Soc. 1968, 90, 5316-5217. 252 Povzetek Pripravljen je bil monokristal spojine (Xe2F11+)(VF6-). Spojina kristalizira v monoklinski prostorski skupini P21/n (No. 14) z a =855.1(1) pm, b = 889.6(1) pm, c = 1570.3(1) pm, ß = 93.31(2)°, V = 1.1925(9) nm3, Z = 4 in pc = 3.545 Mg/m3. Struktura analiza, narejena na 2217 neodvisnih uklonov z I > 3g(I) zbranih na štirikrožnem difraktometru z MoK „ svetlobo, je dala rezultat z R = 0.046 in wR = 0.066. Dobljeno strukturo sestavljata dve skupini; približno oktaedralni anion VF 6- in kation Xe2F11+, ki je sestavljen iz dveh enot XeF5 povezanih preko dodatnega mostovnega fluorovega atoma. Narejen je bil tudi izračun Mullikenovih nabojev za strukturni enoti Xe2F11 VF6 in Xe2F11 AuF6.