Textbook Errors, 116 Peter M. Watkins The University of the West lndies st. Augustine, Trinidad West lndies
Modem textbooks list the hexavalent fluorides of main group VI elements as SFe, SeFe, TeF6, SzFlo, and TezFlo saying there appears to he no reason why SezFlo should not also exist. Examination of the recent literature raises great doubt that ditellurium decafluoride has in fact been prepared. The history of ditellurium decafluoride is as long as that of its well characterized sulfur analog. A paper by Yost and Claussen in 1933 (1) showed that the reaction of fluorine with tellurium gave a small amount of volatile liquid of molecular weight about 342, together with tellurium hexafluoride and a white solid believed to be the difluoride (almost certainly this solid was the tetrafluoride, TeFI: no difluoride is vet characterized). The volatile liauid was available in such small quantity that it was n i t pcssihle to characterize with facilities then available. I t was obviously impure, but from the high molecular weight the major component was believed to contain two tellurium atoms. Shortly after the appearance of this paper Denhigh and Whytlaw-Gray prepared and characterized disulfur decafluoride from sulfur and fluorine (2). These authors suggested that Yost's and Claussen's higher fluoride might have been the impure ditellurium decafluoride. Yost accepted and repeated-this suggestion in a hook in 1944 (3). In 1953 the first claim to have prepared pure ditellurium decafluoride was made by English and Dale (4), who passed gaseous fluorine over mixtures of tellurium and calcium fluoride. They noted that using sodium fluoride instead gave no ditellurium decafluoride. Their product was characterized by analysis and vapor density molecular weight (see the table). Other volatile products were tellurium hexafluoride (62%) and a small amount of an unidentified yellow oil (hp 92"C/480mm). A more thorough investigation of the fluorination of tellurium and its oxides was published in 1956 by Campbell and Robinson (ti), in which an earlier unsuccessful attemnt to reDeat Yost's and Claussen's work is mentioned (6). 'campbkll found only trace quantities of 'ditellurium decafluoride' hv reveatine the exneriment of Enelish and Dale or by mixing t e l l u h n with various other solids. Much better yields of decafluoride were ohtained by passing fluorine diluted with oxygen over mixtures of Te:TeOz cooled to 50-60°C (direct fluorination is a very exothermic process). More concentrated fluorine gave rise to higher temperatures and more of the hexafluoride (which was still the major product even in the dilute gas stream). More dilute fluorine and lower temperatures favored the formation of tellurium tetrafluoride which, being solid, soon brought further reaction to a halt. By this means yields of 40-50% of 'TezFlo' were produced together with much smaller yields of the oxyfluoride Te8Fl10z and higher molecular weight oxyfluorides. 'TezF~o'was again characterized by analysis and molecular weight detemination (see the table). The purification procedure and physical properties described indicate that this colorless volatile liquid was a pure compound, the data agreeing well with those of English and Dale. 520 1
Journal of Chemical Education
Ditellurium Decafluoride-
A Continuing Myth The colorless higher boiling liquids also formed were at first thought to be TeaFla and higher homologous Te(VI) fluorides, but analysis figures and the observation that they only formed when TeOz was present indicated that they probably contained oxygen. The authors suggested that these compounds were Te8Fl40z and Te6Fz605,the tellurium atoms heine connected hv oxvnen atoms. Thev were reticent about thk formula of the latier as it was only available in verv small auantitv. .. hut were certain it was a single compound. Since ditellurium decafluoride now seemed well characterized its infrared and Raman spectra were studied by Dodd, Woodward, and Roberts, along with those of SzFlo as both compounds were assumed to have analogous structures (7~). Assignments were given for SzFlo, for which electron diffraction data were available to confirm the structure, but suggested assignments for the tellurium compound seemed less satisfactory to the authors. The following paper (76) gave force field calculations for SzFlo and explained that these could not be done for TezFlo for want of hond-length data. To this end an electron diffraction study of ditellurium decafluoride was said to be underway. As far as can he ascertained, this study has never appeared. Using hindsight we may assume difficulties occurred because of the erroneous idea of the expected structure and symmetry. During the mid-1960's, Engelhrecht and his group (8) working on reactions of fluorosulfuric acid tried to prepare the unknown oxyfluoride TeOzFz in a similar manner to that they had successfully used to prepare SeOzFz from barium selenate. Instead, from barium tellurate (BaHnTeOs), they ohtained, besides some TeFe and variable amounts of SOa, pentafluoroorthotelluric acid HOTeFe (I) and a number of derivatives, all containing the F5TeOgroup in which the five fluorines and the oxygen were octahedrally arranged around the central tellurium atom
This difference in reaction between selenium and telluriSuggestions of material suitable for this column and columns suitable for publication directly should be sent with as many details as possible, and particularly with reference to modern textbooks, to W. H. Eberhardt, School of Chemistry, Georgia Institute of Technology, Atlanta, Georgia 30332. Since the purpose of this column is to prevent the spread and continuation of errors and not the evaluation of individual texts, the sources of errors discussed will not be cited. In order to be presented, an error must occur in at least two independent recent standard books.
Analyses of Ditellurium Decafluoride
TRFIO (Cald) TbFm ( R e f (4)) TRFX(Ref ( 5 ) ) TeaFxaO (Csled)
57.3 42.7 445.2 56.9 42.5 450 5 7 . 1 42.6 447 -t 2 55.5 41.2
*C'
-34.3
-33.7
54 59
2.88
2.839
9
um was explained as heing due to the expected tendency of tellurium to a higher coordination number. The structural analogy between (n) (F5Te0)2SO~and (F5TeO)lTeF4 of Campbell and Robinson was noted. In a subsequent paper (9); his(pentafluorotellurium) sulfate, (F5Te0)2SOz, was shown to undergo the following reactions
The new compound (V) had similar properties to Campbell's and Robinson's 'TezF~o'(compare table). The Raman and infrared spectra were identical to those found for 'Te2Flo.' Other physical properties varied only slightly between the products reported by all authors, the variations heing readily ascribed to different degrees of purity. The compound (V) was purified for physical measurements by gas chromatography, a technique not available to the earlier workers. The compound (V), p-oxohis(pentafluorotellurium), was established to have a composition involving a hridging oxygen atom by its mass spectrum, its mode of preparation, and its hydrolysis. Acid hydrolysis gives the parent acid (I), HOTeF5. Using the hridged structure as a guide Burger made a much more satisfactory complete reassignment of the infrared and Raman spectra, using more complete data than available to the earlier spectroscopists (10). Somewhat surprisingly Engelbrecht did not give a chemical analysis or an experimental molecular weight for compound (V). The fluorine nmr spectrum of (V) has also been studied (11). Unfortunately, the system of ten fluorine atoms gives a very complex spectrum which is not readily solved. It approximates well to a second-order ABI system as is found for other TeF5 groups (11-14) and is now well known for similar SF5- and SeF5- groups (15), showing the coordination around the tellurium to he approximately octahedral with five fluorines and one oxygen atom. Coupling is observed between the TeFs- groups, giving a quintet appearance for many of the B lines. We cannot definitively distinguish between FsTeTeF5 and F5Te-O-TeF5 from the nmr evidence, but comparison with the analogous sulfur compounds (15) shows that the true decafluoride should have much stronger c o u.~ l i n e the TeF5- groups, in an even 'Om~ l e soectrum. x evidence we can he quite confident From the of the formulation of F5TeOTeF5, fi-oxohis(pentafluorotellurium). The identity of the infrared and Raman spectra with those of 'ditellurium decafluoride' show these comnounds to he identical. Further work on Camohell's and kohinson's method by the author (16) showed ihe fluorine nmr spectrum of 'Te2Flo' to be identical to that of F5TeOTeF5, and also showed that if damp Te:Te02 is used, some of the ~ a r e n acid t HOTeFs is also produced, of as might he expected, together with s&,al number of unidentified products. ,Preliminary fluorine nmr spectra show that the heavy mobile liquid claimed to and (5) probably 'Onhe Te6F2605 tains cis-F4TeOzunits.
a
We require an explanation of how English and Dale (4) prepared TezFloO without the apparent presence of oxygen. It may be assumed that either their calcium fluoride was contaminated with oxide, or their nitrogen with oxygen. The former is most likely, as changing from calcium fluoride to sodium fluoride reduced the yield to nothing. Campbell and Rohinson (5) found oxide necessary too, as fluorinating tellurium alone with nitrogen or oxygen diluent gave negligible yields of 'decafluoride,' that might he explained by residual oxide on the tellurium. They certainly found no higher oxyfluorides unless TeOa was also present. Now that the characterization of ditellurium decafluoride is disproved, there is no reason to suppose that it cannot he prepared, though it might he expected on thermodynamic grounds to be unstable with respect to its decomposition products. Yost's and Claussen's material appeared less stable than TezFloO to heat ( I ) and Peacock prepared (6) traces of a compound of similar molecular weight and different physical properties than Te2Flo0. These compounds have not been noted since. Direct fluorination may not he the best ore~arativemethod for more complex fluorides, because bf t h e variety of products formed. Ditellurium decafluoride might he more rationally prepared from other complex startlng materials such as tellurium chloridepentafluoride, TeFsCl (12) or dialkylaminotellurium(V1 pentafluorides (13). The properties of the tellurium(V1) oxyfluorides prepared by Engelbrecht et al. (8, 9), and those more recently prepared by Fraser's and Peacock's groups (14) show the oxygen to he very tenaciously hound to tellurium (HOTeFs is a strong acid); so it seems unlikely that these compounds will he useful starting points in the quest for ditellurium decafluoride. This textbook error is usefully pointed out to students to show the state of continuing change and advancement in chemistry, and the great difficulty of keeping textbook writers up to date! It is probable that if the techniques used to show up the structure of F5TeOTeF5 had been readily available to the original groups of authors, ditellurium decafluoride would never have reached the textbooks; and disulfur decafluoride would have been the oddity, not the non-existence of the selenium analogue. Our sympathies must lie with textbook writers too; for while Professor Engelbrecht made this case fairly forcibly at a conference in 1967 (171, it was not the main point of his published paper (9), and has obviously escaped attention. Students' attention is drawn to the small difference in analysis between TetFlo and TezFloO to show the caution that must he exercised in drawing conclusions from experimental data. In this case the analytical data lead to the wrong compound! Literature Cited 111 Yoaf. D.M.,andClsusen, W. H . , J . A r n e i . Chpm S o c . 55,885 11933). 121 Denbigh. K.G.,and Whnlaw-Clay. R..J. Chem Soc.. 114611931). I31 Yort, 0. M., and Russpll. "Syrtemafic Inoreanie Chemistry." Prentice-Hall. Inc.. NewYork. 1944, pp295-9. 141 English. W.D., and0ale.J. W.. J . Chem Soc.. 2498119531. (51 carnobell. R.. a n d ~ o b i n s a n . ~ .J~ c. .h p m sac.. 3454 119561 161 ~ e s c b c kR.D.. , PhDTheais. ~ n i v e r d t yofDurham. 1Kine.r College), 1951. 17) la) h d d , R. E.. Woodward. L. A,, and Roberts, H . L.. Trans. Ferndo? Soc., 53, 15"s 119671;I ~ woodward. I L. A.. end ~ ~ b ~H.r L.. t ~T ~ , M ~~~d~~ . sot. 53. 1557 (1957). 181 Engelhrecht. A , and Slsdky, F.. Monaish. C h m . 95. 1 5 9 1 ~ 9 6 5 1Enge1brocht.A.. : a n d ~ ~ e d k yF..AP~W. . cham. i h t E ~ J3.383 . 11966). 191 ~ n e ~ ~ h r ~ ~ h t . ~ . w.. , ~ oand r e ~e ekh. o d sW . . Z . A ~ O ~ cZh.r m , 360.88119881. wm.. 360.97 lL9881. Sperf,orhim, ,.., ., u......,. I. H.. Crusbio, K. D.. and Sharp, D, D. W, A,, A,. Sperfrorhim. A C ~ O .~ L A . Z Z Z119701. I Rk .D . , and Walkins, P . M . . Chem. Chem Commun.. ,257 1257 119881. (121 F r s s e ~ G W . . . P e a ~ ~ cR.D., (131 Frarer. G. W.. Peacock. R. D., and Waikinr. P. M.. Chsm Commun.. 1218 119671; J cham. soc.A. 112611971\. iii971\. I141 CIO.=~O.. A. C.;FIB~.L G. Poacoek. R. D., c h p m commun.. 1197 119701: RaaerG. W.. lpemnaleommunicatlonl, 1913. (151 Memill, C. I., w i ~ ~ i . ~ . ~S.. M.. . cady, G. H., E ~ D. R., ~ lnorg. ~ chpm., ~ , 215119621:~ e i c h e r tW . . L.. and cadv. G . H.. h o r g c h m . 12,769 11gi81. 116) Watkins. P.M.. PhDThesis, UnlvoisityofLeicester. 1968. 117) Engelbreehr, A . paper presented at Euchem Fluorine Conference. Univemty of ~ e i e e r tADY~I ~ ~ , 1867.
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Volume 5 1 . Number8. August 1974
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521
