Redetermination of the crystal structure of Cs2AuAuCl6

Mat. Res. Bull. Vol. 9, pp. 1667-1670, 1974. P e r g a m o n Press, Inc. Printed in the United States.

REOETERMINATION OF THE CRYSTAL STRUCTURE OF Cs2AuAuC16 J.C.M. Tindemans-v. Eijndhoven and G.C. Versohoor Gorlaeus Laboratories, Oepart:ment of Theoretical Inorganic Chemistry and Oepartment of X-ray and Electron Oiffraction Leiden University, P.O. Box 75, Leiden, The Netherlands

(Received October Ii, 1974; Communicated by 7~. Rabenau)

ABSTRACT The structure of Cs~AoAuCI~o crystal X-ray analysis. The dance with the one proposed Chem. Soc. 60, 1846 [1838].

is redetermined using single overall structure is in accorby Elliott and Pauling in J.Am. The ~pacegroup is I4/mmm with

axes a = 7 . 4 9 ~ 1 ] ~ and o = 1 0 . 8 8 0 ( 2 ) A , Z=2. The s h o r t e s t g o l d - c h l o r i n e d i s t a n c e s are 2.28112)~ in the l i n e a r [ A u [ I ) C l ? ] - and 2.29512]~ in the square p l a n a r ['Au(III]CI4]- unit. The last figure as contrasted ~;alue of 2.42~ found by Elliott and Pauling.

to the

Introduction In 1938 Elliott and Pauling [I] determined the crystal structure of Cs2AuAuCI 6 using the Guinier-powdermethed. They found a structure that was essentially a distorted perovskite structure with square planar [AoCI4] and linear [AoCI2] units, with spacegroup I4/mmm. The AuCI distance found in the unit[AuC1~ was 2.42~. Relating this figure to rAu_Cl=2.30~, found in Cs2AgAuC16 (I] for the same unit and Knowing that Cs2AuAuC16 is diamagnetic (2], they concluded to a partial d i s o r d e r of [Ao[III]CI4]- and [Au[I]Cl2T-units. A few years ago Brauer and Sleater [3] investigated the system A2AuAuX 6 [with A=Cs, Rb and X=CI, Br, I] by decomposing AAuX 4 in N2-flow a.o. with the purpose 1:o find new methods for preoaring these compounds. In this way they did not obtain single crystals in a form usable in single crystal X-ray work. By using a modified version of this method we were able to prepare small single crystals of Cs2AuAuCla; wlth these we decided to redetermine the crystal structure in order to investigate the hypothesis of Elliott and Pauling. Experimental We obtained small single crystals of Cs2AuAuC16 by heating intimately mixed CsCI, Au and CsAuOl 4 in the calculated amounts in a sealed quartz tube at 450°C and cooling down slowly during some weeks. The axes of the unit cell were ca] culated from a powderdiffractogram as a=7.485[I] and c=I0.860(2]~ at 20oc. Zn_ 1667

1668

CRYSTAL

STRUCTURE

OF

CSzAUAuCI

6

Vol.

9, N o .

lZ

tensities of an irregularly shaped crystal of apprimate size O.01xO.O4xO.04 mm were measured on a three-circle diffractometer (Enraf-Nonius). The crystal was mounted with the plane [112] perpendicular to the axis of rotation. The radiation used (MoK~,~=0.71069 ~) was monochromatized with graphite. We used a 8-2@ scan [scan angle q.2-I.7 °) with a speed of 1.25°/min,In all 2855 reflexions with positive h k and I and sin e/~ between 0.07 and 0.09 ~-I were measured. The calculated density of Cs2AuAuCIB(Z=2, mol. weight=438) is 4.74 g/cm 3 [expe ~ rimental value 4.57, Elliott and Pauling (I)). Structure Refinement The standard deviations of the intensities were calculated from counting statistics. Reflexions with intensities less than twice the standard deviation were considered as not significant. The shape of the crystal was difficult to determine exactly, therefore the absorption corrections, calculated with a computer program [4) were adapted to the measured intensities of the head reflexions 112, 224, 336 and 448. The transmission varied between 0.03 and 0.25. New standard deviations of were computed taking into account the inaccuracy of the absorption correction. We refined using a full matrix least-squares program [5) 325 significant observed reflexions out of 580 independent reflexions, in the space group I4/mmm, after reduction of the intensities to F values. From corrected intensities of some reflexions we concluded that the Laue symmetry class of the_system might_be 4/m instead of 4/mmm and that structures with spacegroups I4, I4/m and I42m were also possible. Refinement of models having these spaoegroups showed that only I4 lowered the discrepancy factor; therefore I4 and I4/mmm were retained. From 1827 independent reflexions in I4 [reflexions and counterreflexions taken apart), 812 were observed and signif2cant [31 not significant); in the further refinement of I4/mmm and I4 this set of 912 reflexions was used. Scattering factors for ions, corrected for anomalous dispersion [&f' and if") were taken from the compilation of Cromer and Waber (6) and the intensities of the reflexions were corrected for extinction according to the method given by Zaohariasen ( 7 ) . The positions of the ions in the spacegroups I4/mmm and I4 are (8): I4/mmm[+½½½)

I 4 [ + )' 1~'

Cs Au(III) Au(I) C1

[4d): (2a): (2b): (4e):

0½¼ ½0¼ 000 00½ 00z 00~

[2c): (2a): (2b): (4e):

Cl~

[sh): xxO xx0 xx0 x~0

0½¼ 000 00½ 00z 00~

[2d):

1 1 ~0~

Csg): xyz xyz y ~ yx~

A l l r e f i n e m e n t s were made w i t h a n i s o t r o p i c t e m p e r a t u r e - p a r a m e t e r s f o r each i o n . The r e s u l t f o r t h e space g r o u p s I4/mmm and I 4 a r e c o m p i l e d i n T a b l e I . E s t i m a t e d s t a n d a r d d e v i a t i o n s a r e g i v e n i n b r a c k e t s Ca l i s t of F-values is available from the authors),

We minimized Oiscrepancy

Rf=

the f u n c t i o n

~w[

factors referred

Z(IFol-IFcl~ r~IFo ]

IFoi-IFcl:l

2

with weighting

factor ~ [ o f )

to are.

[~wC IFoI-IFcI )2] ½ mwf I

ZW]Fo ]2

J

-2

Vol. 9, No, IZ

CRYSTAL

Comparison

Positional

parameters

STRUCTURE

C11 z Cl 2 x Y

0.2904(2} 0.216412}

0.87511

Scalefactor parameters

Cs Cs Au[I}

Au(III) C11

Cl 2

1669

TABLE I of parameters in I4/mmm and I4 14/mmm

Z

Thermal

OF CszAuAuCl 6

Uli U33

}

0,2904[2} 0,,2161[3} 0.2165(3} -0,0058[79] 0.67611 }

0.041712] 0.0419(3}

9,0327(8] 0.0361(12}

U11

0.0538(14}

U33 Ull U33

0.0241(2} 0.0186(2)

0.0486(16) 0,023g(21 0.0187(2)

U11 U33 U11

0.0205(2) 0.0194(2) 0.04g[I}

0.0207(2} 0.0192(2) 0.051(6}

U22 U33 2U12 Uli U22 U33 2U12 2U23 2U31

0.019(1] 0.0357{6} 0.0451(9) -0.0300[14) 0 0

(2c ~2c [2d (2d

0.049(6} 0,018(I) -0.002(9) 0.0364(11} 0.0366(11} 0.0454(9] -0.0300(15) 0.0084(56) -0.0079(55}

Number of the parameters

14

Rwf Rf

3.06% 2.6E%

23

2.98% 2.63%

* In 14/mmm:U11 = U22 for all ions, in 14:UlI = U22 for Cs, Au(l] All others not mentioned are zero.

and Au(l!l}.

Oiscussion With Hamilton's test (9} the possibJ]~y that 14/mmm is the right spacegroup (as opposed to 14} can be rejected with a probability of 88.5% or g0% respectively (on R f or Rf respectively). Therefore on statistical grounds one has to conclude ~hat I4 is the right spacegroup. The Hamilton test,however, is only to be used if the errors are statistical, not if there are systematic errors; in this case we had to apply a very large absorption correction so that a systematic error could easily be introduced. A statistical analysis of the results revealed that the reflexions in the regions with transmission less than 10%, show a larger Rwf (about 10} than the overall R ~, but we wT were not able to detect a systematic error, e.g. no systematic over- or undercompensetion was found nor a correlation with 8. If we compare the structures with spacegroups 14/mmm and I~ the only difference that might; b e _ s i g n i f i c a n t is the difference in the thermal parameters of the Cs ions. In 14 Cs occupies two independent positions. The r e f i n e m e n t gives much larger temperature parameters for one Cs than for the other. The surroundings nf the Cs-ions being the same in both specegroups, it is difficult to see why the Cs-ions would behave differently. F u r t h e r m o r e we n o t i c e ~ that the imaginary part of the anomalous dispersion has great influence, notably on the thermal parameters and the values found with

1670

CRYSTAL S T R U C T U R E OF CsZAuAuC16 u (m}

Vol. 9, No. 1Z

Hamilton's test, so wrong figures for Af" would influence the result. So despite Hamilton's test we assume that I4/mmm is the right spacegroup. Refinement using 325 independent reflexions in 14/mmm gave Rf=1.72 and Rwf=l.98 with the same positional parameters as given in the table and no significant change in the thermal parameters. With these resultsa difference Fouriersynthe~ sis was calculated; no significant peaks w e r e found.

CI2

2.295

)ch

Conclusion

4 ) Au(I)

The spacegroup proposed by Elliott and Pauling CI], is confirmed by this structure analysis. But in contrast to their results we find no evidence of disorder of [ A u O l 2 ] - a n ~ [AuC14]groups. We find the same Au-C1 distance in the square planar [AuC14]- complex as is found for this complex in other compounds, The chlorine ions have no large vibration amplitudes in the direction towards the two kinds of gold ion (see fig. I), therefore there is no sign of a tendency to form CsAu(II)CI 3. Furthermore from the Fourier analysis npindication of Qis~ placement of part of the chlorine ions to a position next to the "wrong" gold ion, indicating a disorder of AuCI 4- and AuCI~- complexes, could be found. Therefore we conclude that Cs2AuAuCl 6 at room temperature has spaeegroup 14/mmm, and shows no disorder of Au[III]C14 and Au[I]CI 2- groups.

2.281

¢)

~

C12

FIG. 1 Thermal elllpsoides of the main units in Cs2AuAuC18 (I4/mmm).

Acknowledgement We thank Or. W.J.A. discussions.

Maaskant

for stimulating

Literature I. N. Elliott 2. N. Elliott,

and L. Pauling,

J. Am. Chem.

J. Chem. Phys.

3. G. Braver and G. Sleater,

2, 419

Soc. 60, 1846

(1934]

J. Less Common

Acta Cryst. A29,

4. R.A.G.

de GraaTf,

5. R.A.G.

de Graaff and E. Rutten-Keulemans,

8. D.T.

Cromer and J.T. Waber,

7.

Z a c h a r i a s e n , Acta C r y s t .

W.H.

Acta Cryst.

283 (1970)

uq~ublished 18, 104 (1965)

558 (1967)

8. Int. Tables for X-ray Crystallography, Birmingham. England (1965] 9. W.C. Hamilton,

Net.21,

298 (1973)

Acta Cryst. 23,

(1938)

Vol.

18, 502 (1965)

1,The

Kynoch Press,