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The CanadianMineralogist Vol.33,pp. 187-188 (1995)

tezAulylggSBAUER STUDV OF THE - DITELLURIDES , KRENNERITEAND : REPLY

FRIEDRICHE. WAGNER Phv*sik-DepartmentEl5. TechnischeUniversifit Miinchen, D-8046 Garching, Gennany

JERZYA. SAWICKI AECL Reseorch, Cltalk River ktboratories, Cltalk River, Ontario KOJ 1J0

JOSEFFRIEDL Phtsik-Department E l 5, TechnischeUnive rsittit Miinchen, D-8046 Garching, Gemtany

We welcomethe commentsof J. Stanek,who pounds with a fourfold planar coordination, bonding correctlypoints out that thereare someuncertainties arguments are usually used to assign a positive sign to concerningthe sign of the electric quadrupoleinter- the electric quadrupole interaction (Parish 1984). action in gold compounds.This is so becauseit is Since the sign the electric quadrupole interaction is not experimentallyquite difficult to measurethe sign of normally obtained from the Mdssbauer spectra, one the electricquadrupole interactions of le7Au.First usually plots only the magnitude of the electric of all, the measurementrequires the use of oriented quadrupole interaction versus the isomer shifts. This single-crystalabsorbers. The sign of the electric results in plots like that shown in Figure 3 of our quadrupoleinteraction can then be determinedfrom paper. the asymmetryof the line intensitieswithin the Stanek claims that the electric quadrupole interac- quadrupoledoublet, but this asymmetryremains tion is positive in the Au+ halides, AuCl and AuI, alwayssmall for leTAubecause of the nuclearproper- whereas he concedesthat for all other Au+ compounds ties of the 77 keY transition(Prosser et al. 1975). it is negative, as is commonly taken for granted. Properlyoriented single- absorbers alone, how- Stanek's assumption implies a tremendously large ever,are not sufficientfor a determinationof the sign. change of the electric field gradient between the Rather,the crystal structuremust also permit a sub- monohalides and their closest neighbors on the cor- stantialalignment of the axesof the electric- field- relation line, e.g., the (AuCl2)- complex anion in gradienttensor in the laboratoryframe of reference. (AsPha)AuCl2,for which one obtains an electric This is, for instance,not necessarilythe casewhen the quadrupoleinteraction of -6.1 mm/s (sign assumed,not unit cell containsseveral atoms of gold, for which measured)and an isomer shift of +0.5 mm./s(Jones et theseaxes are orientedin differentdirections. The al. 1977 this compound has not been included in structureof the gold dilelluridesand of many other Figure 3 of our paper). We feel that it is difficult to gold compounds,in fact,renders a measurementof the believe that a difference in the sign of the electric field sign of the electric-fieldgradients difficult or even gradient exists between the linear Cl-Au-Cl bonds in impossibleeven in the casewhere single-crystal AuCl and in (AsPh/AuCl2, but since Stanek's inter- absorbersare available.This is why we have not pretation hinges uniquely on the sign of the quadru- attempteda determinationof the signin the caseof the pole interaction in the monohalides of gold, the final ditellurides. decision between the two views can only be made by It is mainly dueto thesedifficulties that the sign of measuring the sign for at least one of these. Such a the electricquadrupole interaction has beendeter- measurement is rendered difficult, though not alto- minedunambiguously only in KAu(CN)2(Prosser gether impossible, by the zig-zag chain structure of et al. 1975),The existenceof a ratherclear correlation AuCl and AuI, and also meets with the difficulty bexweenthe quadrupolesplittings and the isomer of obtaining sizeable single of these com- shifts for Au+ compoundsis, however,usually (see, pounds. Efforts to arrive at such a determination ofthe for instance,Parish 1984)considered as proof for a sign should, however, be made, since in this way negativesign for the electricquadrupole interaction in the interesting question whether Orgel's bonding all tinearlycoordinated Au+ compounds. In Au3*com- concept (Dunitz & Orgel 1960) is borne out by the 188 THE CANADIAN MINERALOG]ST hyperfine interactions in gold compounds could be REFERENCES answered. Self-consistent calculations of the electric field gradients in Au+ compounds (Guenzburger & DuNrrz, J.D. & Oncrr-, L.E. (1960): Stereochemistryof ionic Ellis 1980) would rather indicate a negative sign in the solids. Adv. Inorg. Cltent. Radiocltem.2, 1-60. halides. It is true that the electric quadrupole interactions we GUENzBURGER,D. & Er-lrs, D.E. (1980): Electronic structure find for the (2 + 2 + 2) sites in the ditellurides coincide and Mtjssbauer hyperfine interaclions of Au* compounds. better with Stanek's correlation line than with the Phys.Rev. B 22,4203-4214. standard one, whichever sign one attributes to our results. We do not believe. however. that this should JoNEs,P.G., MADDoCK,A.G., Mevs, M.J., MurR, M.M. & WILLTAMS,A.F. (1977): Sffuciure and bonding in gold (I) be considered as supporting Stanek's view. The rela- compounds. 2. Mdssbauer spectrum of linear gold (I) tively small magnitude of the quadrupole splitting in complexes../. Cltem. Soc. Dalton, 1434-1439. the ditellurides also can be attributed to the fact that the (2 + 2 + 2) configuration is not truly linear, but ORCEL,L.E. ( I 958): Stereochemisry of of the B sub- rather a distorted octahedralone in which two bond groups. I. Ions with filled d-electron shells. J. Cltem. Soc., lengths are substantially shorter than the other four. 4t86-4190. Whatever kirid of hybridization one invokes, such an environment should give an electric field gradient PentsH,R.V. (1984): Gold-197 Mdssbauerspectroscopy in intermediatebetween that of an isolated linear the characterizationof gold compounds. /n Mdssbauer Applied to Inorganic Chemistry 1 (G.J. arrangementand that of a symmetrical octahedron, Spectroscopy Long, ed.).Plenum hess, New York, N.Y. (577-617). which should give no electric field gradient at all. In conclusion, we wish to reiterate that an experi- PRossER,H., WAGNER,F.E., WonruaNN, G., KALVlus,G.M. mental clarification ofthe question raised by Stanek is & WAppLING,R. (1975): Mdssbauer determination of the highly desirable and should be possible if sizeable E2llll mixing ratio of the 77 keV transition in IeTAuand single crystals of the gold monohalides can be grown. of the sign of the electric field gradient in KAu(CN)r. Hyperfine Inte ract ions "1,,25 -32.

STANEK,J. (1982): High pressureM6ssbauer study ofreTAu in Cs"Au2Cl6, Cs2AgAuCl6 and Aul. J. Chem. Phys.76, 23t5-2320.

WAcNER,F.E., Sawrcr