1974 541New Preparations of Chromium Oxide Tetrafluoride and ChromiumDioxide DifluorideBy Anthony J. Edwards,t Warren E. Falconer, and Walter A. Sunder, Bell Laboratories, Murray Hill, NewJersey 07974, U.S.A.CrO,F, and CrOF, are conveniently prepared from CrO, by direct fluorination in a static thermal system, the productdepending on the reaction temperature. The vapour pressure of CrOF, has been measured by a static method,using a diaphragm gauge of high sensitivity, and physical constants and thermodynamic data have been derivedfrom the vapour pressure measurements.NUMEROUS reports 1-6 have appeared on the preparationof chromium dioxide difluoride. The majority of thepreparations involve the reaction of chromium trioxidewith a fluorinating agent, such as HF, IF,, or SF4;all present soine difficulties in the separation andpurification of the product.The only preparation of chromium oxide tetrafluoridepreviously reported involved the fluorination ofchromium metal, the oxide tetrafluoride resulting as aby-product iii the preparation of chromium penta-fluoride.The interaction of chromium trioxide with elementalfluorine has not previously been reported.This is aconvenient preparative route to both the dioxidetlifluoride and the oxide tetrafluoride, the particularproduct depending on the reaction temperature.EXI'iXIMENTALI-'re$avntions. --Chromium trioxide (2 g ; Fisher, certifiedA.C.S. grade) was loaded into a 250 ml Atone1 reactor ina dry-box. -After evacuation of the reactor, fluorine(Matheson, 999, inin.) was added to a pressure of 4 atm.The reactor was heated to the appropriate temperature(controlled to u-ithin &5 "C) while the lid was cooled withwater.After thc: reaction, the excess of fluorine was re-iiioved a t - 1 % ~ ' . The volatile products were then dis-tilled at 25" arid collected in a Kel-F trap, held a t -196",aiicl subsequently analysed mass spectrometrically. Thereactor was then closed off from the vacuum line antlremoved to the drv-box for inspection. Any solidproducts were loaded into a mass spectrometer effusionsource for examination. The molecular beam massspectrometer nsed in this rvork has becn described pre--viously.8When tlie r.c>action was carried out a t 150 OC for 41 11,all the product \\.as volatile a t 25" and rapidly collectedin thc cooled Kd-1; trap.Tlie mass spectrometric crackingpattern was ill good agreement with that reported pre-viously for ('r02F, (Table 1). No impurities were de-tected by the mass spectroscopic examination, and thcconversion was quantitative.When the reaction temperature was increased to 220 "C1 Pei.marieiLt nddvr-ss : Chemistry Department, Uiiilw-sity ofBiriningham, I).( ). B m 363, Birmingham B15 2TT.A. Eng~.:lbrc.clit antl -1. 1.. Grosse, J . Awzei.. Chem. Soc., 1952,74. 5262. " E. E. AynsIcy, 11. Nichols, and I). L. Robinson, J . CJieitz.Soc., 3953, 633.E. E. Aynslcy, G. Hctherington, and P. L. Robinson, J .Chew. Soc., 1954, 11 19..I. G. D. Flesch aiitl H. J . Svec, J .A m e r . Chenz. SOC., 1958, 80,3 169.and the time to 70 h, only a little CrO,F, was formed.This was removed by pumping at -23 "C (CC1, slush),collected in a Kel-F trap, and characterised mass spectro-metrically as before. When the reactor was warmed to25", a crimson product collected in the cooled Kel-F trapmore slowly than the CrO,F, sample. Mass spectro-metric examination showed this t o be chromium oxidetetrafluoride (Table 1). When the reactor was openedin the dry-box, all the CrO, had been consumed and acrimson crystalline deposit was found on the cooled lid.The mass spectrum of this solid was identical with that ofthe oxide tetrafluoride. Tlie effect of varying the reactiontime on the yield of CrOF, was not investigated.At higher reaction temperatures (250" for 4 0 h) theyield of CrOF, was greatly reduced, arid when the reactorwas opened in the dry-box, a sticky red deposit was foundon the cooled lid. The mass spectrum of this material(heated effusion source) showed a cracking patterncharacteristic of CrF, at lower temperatures, changingto that of CrF, as the temperature was raised (Table 1).Vapour Pressure Measurements-These were made ol-crthe temperature range 0-70 "C in Pyrex glass apparatus,using a diaphragm gauge of high sensitivity as a nullinstrument.The apparatus and technique have beendescribed previously.1° After removal of CrO,F,, thesample for measurement was slowly sublimed from a trapa t 0 "C.RESULTS AND DISCUSSIONThe fluorination of chromium trioxide appears toproceed by stepwise replacement of oxygen by fluorineatoms.Thus at lower temperatures one oxygenatom is replaced to give the dioxide difluoride. Re-placement of a second oxygen atom to give the oxidetetrafluoride occurs at intermediate temperatures.At higher temperatures the products are CrF, andCrF,. It therefore appears that replacement of thethird oxygen atom initially gives chromium hexa-fluoride ; this decomposes to the pentafluoride, whichis itself subject to decomposition to the tetrafluoridea t elevated temperatures.llEI. L. Krauss and 1'. Schwarzbach, Chem, Beit., 1961, 94,X. Bartlett and P. L. Robinson, J . Chewz. SOC., 1961, 3549A. J . Edwards, Pvoc. Chem. Soc., 1963, 205.8 M. J. Vasile, G. R. Jones, and W.E. Falconer, Iiztaurzat. J0 G. D. Flesch, R. M. White, and H. J. Svec, Intevnat. J . Moss10 G. H. Cady and G. 13. Hargreaves, J . Chenz. SOC., 1961, 1563.11 0. Glemser, H. Roesky, and K. H. Hellberg, -4~zgew. Chem.1205.l i a s s Spectvornrtvy I o n Phys., 1973, 10, 457.Spectrornetvy Ion Plzys., 1969, 3, 339.Internat. Edn., 1963, 2, 266542 J.C.S. DaltonChromium oxide tetrafluoride reacts with Pyrex physical properties of chromium oxide tetrafluoride areglass apparatus. After several weeks at room tem- unlike those of the oxide tetrafluorides of second- andperature, CrOF, in sealed ampoules formed Cr02F,. third-row transition elements.13 The much smallerThe presence of the dioxide difluoride was verified by liquid range is the most noticeable difference, and aX-ray examination of single crystals.12 After a further similar difference is found in a comparison of vanadiumTABLE IMass spectrometric cracking patterns of CrO,F,, CrOF,, CrF,, and CrF4--------* , r----.h I___( (-..---d-.___ CrO,F, CrOF, CrF,7 r - Sourcc temp ("C) 25 96 25 35Orifice size (cm) 0.02 (2.02 0.02 0.02RelativeintensityThis Ref. lklative Relativeinle Ion work 9 iuje Ion intensity mle Ion intcnsity w j e106 CrOF,+ 47 42 125 CrOF3+ 100 100 128 CrF,t+ 100 10990 CrF,+ 100 100 106 CrOF,+ 45 43 90 CrF,+ 25 7187 CrOF+ 23 16 '30 CrF2+ 36 22 71 CrF+ 32 5271 CrF+ 20 11 87 CrOF+ 12 12 52 cs-- 3868 CrO+ 6 3 71 CrF' 20 1952 Cr+ 23 16 68 CrO+ 2 253 Cr-i- 25 21122 CrO,F,+ 58 58 144 CrOF,+ 147 CrF,+ 5 138103 CrO,F+ 33 22 109 CrF,+ 17 7 109 CrF,+ 86 90Relative intensities are reported for the ,*Cr isotope; 70 eV electron cncrgies.CSF,--7 1010.02RelativeIon intensityCrF,+ 43CrF,+ 100CrF,+ 18CrF+ 17Cr -1- 28period, a bright red, involatile solid was formed, whichwas shown to be chromium trioxide by X-ray powderphotography.The vapour pressure data for CrOF, are sunimarisedby the following equations :Solid CrOF4 (below 24.1") log$ (Torr) =Solid CPOE', (24.1 - 55.2") log$ (Torr) =Liquid CrOI;, (55.2 - 70") log? (Torr) =The value of the triple point determined by the solutionof the equations was 55.2", and was in good agreementwith the m.p.determined directly in a thin-walledcapillary, The solid-solid transition point of 24.1"was obtained from the intersection of the two sublim-ation curves.This could notbe checked directly owing to rapid attack of Pyrexglass apparatus at temperatures above 70".Thermo-dynamic values were derived from the vapour-pressuredata using the Clapeyron-Clausius equation. The heatsof sublimation are 67.7 kJ mol-l for the solid below24.1 "C and 52.4 kJ mol-l above this temperature,and the heat of transition is 15.5 kJ mol-l. The heatof vaporisation is 41.6 kJ rnol-l, the heat of fusion10-7 kJ mol-I, and the entropy of vaporisation 113 Jmol-1 K-1.The vapour pressure measurements show that the13.22 - 354611'10.48 - 2732/T8.78 - 2174/TThe b.p. found by extrapolation is 95".pentafluoride with the second- and third-row transitionmetal pentafluorides (Table 2).The solid-solid transition found for CrOl', is paralleledonly by TcOF4 of the other oxide tetrafl~orides.~J~The low-temperature form of Crop, (below 24.1 "),-~ A B L E 2Comparison of physical properties of soiiie transitionmetal pentafluorides and oxide tetrafluoridesCompound M.p.("C) B.p.("C) Compound ?*l.p.("C) B.p.("C)CrOF, 55 95 VF, 19 48MoOF, 97 186 NbF, 80 235RuOF, 115 184 NoF, 67 214WOF, 105 186 KuF, 86 327ReOF, 108 172 ReF, 48 221has an endless chain structure, similar to that of R.IoOF,and ReOF,, although the details of this structure havenot been fully elucidated.14 The transition may there-fore correspond to a rearrangement of the packing ofthese chains in the crystal, although no X-ray measure-ments have yet been made on the high-temperatureform.We thank M.J. Vasile for assistance with the massspectrometric analyses.[3/1881 Received, 12tA Septembev, 19731l2 A. J . Edwards and P. Taylor, Chem. Comm., 1970, 1474.l 3 R. Colton and J . H. Canterford, ' Halides of the, First RowTransition Metals;' J. €3. Canterford and R. Colton, Halides ofthe Second and Third Row Transition Elements,' Wiley, London,1969.14 A. J. Edwards, uiipublished work