Refinement of the crystal structure of stibnite, Sb2Sg 1

Transcription

1 Zeitschrift fiir Kristallographie Bd. 135 S (1972) Refinement of the crystal structure of stibnite Sb2Sg 1 By PETER BAYLISS and WERNER NOWACKI * Abteilung fur Kristallographie und Strukturlehre Universitat Bern (Received 20 September 1971) Auszug Fur Antimonit Sb2S3 wurde ein verfeinerter Satz von Atomkoordinaten und Temperaturparametern erhalten. Diese Struktur enthalt parallele (Sb4S6)n- Ketten welche miteinander verbunden sind und gewellte Netze bilden (zwei pro Einheitszelle). Das fiinfwertige Sb weist eine Funferkoordination in Form einer quadratischen Pyramide mit Sb leicht aus dem Basiszentrum verschoben auf. Das dreiwertige Sb hat eine Dreierkoordination in Form einer trigonalen Pyramide mit Sb als Spitze. Zwei dreiwertige S-Atome besitzen eine Dreierkoordination in Form einer trigonalen Pyramide mit S als Spitze. Das andere zweiwertige S-Atom hat eine Zweierkoordination. Die physikalischen Eigenschaften stehen mit der Kristallstruktur in Beziehung. Abstract A refined set of atomic coordinates and temperature parameters have been obtained for stibnite Sb2S3. This structure contains parallel (Sb4S6)n chains which are linked to form crumpled sheets (two per unit cell). The quinvalent Sb has fivefold coordination in a square pyramid where the Sb is slightly displaced out of the base center. The trivalent Sb has threefold coordination in a trigonal pyramid where the.sb occupies the vertex. Two trivalent S have threefold coordination in a trigonal pyramid where the S occupies the vertex. The other divalent S has twofold coordination. The physical properties are related to the crystal structure. Introduction The crystal structure of stibnite (8b283) was initially solved with a trial and error method by HOFMANN (1933). Later SCAVNICAR(1960) redetermined the structure with a Fourier from two-dimensional Weissenberg-film data. The crystallochemical relations between 8b and 1 Contribution No. 222 Part 64 on sulfides and sulfosalts. Present address: Department of Geology University of Calgary Alberta * Canada.

2 Refinement of the crystal structure of stibnite 309 S appear in the stibnite structure without any interference from other elements. Therefore it is worthwhile to refine such an important structure in the sulfosalt-mineral class with three-dimensional counter data to obtain more accurate interatomic distances and bond angles because of their deviation from the expected more ideal structure. Experimental Stibnite crystals donated by Mr. S. LIECHTI (Number 212 Mineralogisch-Petrographisches Institut Universitat Bern) were examined. Since the mineral is both too soft (hardness 2) and easily cleavable along perfect cleavage (100) to grind a cylinder without crystal distorsion a needle with dimensions 23 X 296 X 29 pm was used to measure the lattice constants and intensities. The lattice constants were determined from two back-reflection Weissenberg photographs of hol and Okl which were calibrated for film shrinkage by the diffraction pattern of silicon (a = A). A least-squares best fit of the lattice constants was calculated by the program written by N. D. JONES (unpublished). The results are Present study SCAVNHJAR (1960) HOFMANN (1933) a (9) A (2) A kx b (4) 3.84 (1) 3.83 c (5) (2) The observed density given by DANA (1941) is 4.63 (2) g cm-s and that calculated for 4 Sb2Sson the basis of the new lattice constants is 4.62 g cm-s. The space group Pnma was chosen as assigned by both SCAVNICAR(1960) and HOFMANN (1933) after reorientation to the standard setting with systematic absences of Okl with k + 1 = 2 n + 1 and hko with h = 2n + 1. Three-dimensional data was collected by a Weissenberg counter autodiffractometer (Supper-Pace type) with CUKlX radiation ( A). The intensities were corrected for both background and Lorentz and polarization factors. Corrections for absorption were calculated by a local version of the ACAC program written by WUENSCH and PREWITT (1965) because the linear absorption coefficient is high (p = 1011 cm-1 for CUKlX). The structure was refined from the coordinates of SCAVNICAR(1960) with a local version of the block -diagonal least-squares program

3 310 PETER BAYLISS and WERNER NOWACKI Table 1. Observed and calculated structure tactors tor stibnite IF.I IFI IF.I IFI IF.I IFI IF.I IFI lh..8. ' J ' " t.1t } J t } J.J '.8 J.l J 'H.B ' J " J.9 J 10% " t J } J 95.5 glt "' ' 1.J lt :33.4 JJ.J !tlt.s " It ' t6.6 1J o /t t6.2 1t J 64.7 M.3 J J J t 61t J H ' 2 72./t ' ItO.9 1t J JJ a.o t t.O o /t.a t J J /j a J.' 1J a } } /j 1 0 J }a.9 } t.} } ".J 56.1 J 7.J 5.J J.l J 41.4 lto t o } ' J4.9 1t1t /t.1 J 81t } I.i J 1}.} t 6.' 8 1t t } '5} ' t J }6.} }} ' '5 1 o 13 1t '5.9 J J } } t }.1 5 ItO.7 J t.l J J l11t t 61t.6 9 }2.5 } t ; ; ; 7 1} t.O J t.3 1 }1.4 } J.J J J J.9 ' t l1t J J J J J J } a.5 % J0.3 1t1.} l1t % lj J" J 12J".a a a la9.0 21a J J lltj" J '.J t J 11t a J /j t 11} t J %. 91.' J ' ao %8.a t.O 7 1t J }5.% 1 Ita.l J a } J J J" J J 5.J '.9 ' t ".7 '.0 ' J } IJ } a '5.0 1t1t t } J J 9' J" " J J } t 78.} } J 192.a ' J J 13.2 J '5 J

4 Refinement of the crystal structure of stibnite 311 Table 1. (Continued) k 1 IF.1 IFI IF.I IFI IF.I IFI IF.I IFI lt9.3 1j t2.'!t1t.S ' 6 :n.lt ' "'1.3 "' BIt.l j ".9?'t.o. 5.1 " 1.' 10 "' ' ' Id t ' "' :H :n It??. " t } 59.} Q ' }/a :? t :H It " 22.2 :n " ' " ' " ' " " "" " " " "8.5 written by D. VANDER HELM. The neutral-atom form scattering factors corrected for the real dispersion correction for Sand Sb were taken from the International tables (1962). The final discrepancy index R is for all 532 reflections. Both observed and calculated structure amplitudes are shown in Table 1. No secondary-extinction correction has been made although it has had an effect as shown by the results in Table 1. Discussion of the structure The atomic coordinates and temperature parameters which are given in Table 2 are similar to both HOFMANN(1933) and SCAVNICAR (1960). The interatomic distances and bond angles are tabulated in Table 3. A projection of the structure on the (010) plane is shown in Fig. 1. The structure is formed of infinite Sb4S6 chains parallel to the b axis (needle axis) with interatomic distances between and A. These chains are linked to form crumpled sheets perpendicular to the a axis with interatomic distances of A. These sheets (two per unit cell) are held together with interatomic distances between and A whereas the sum of van der Waals radii for Sb and S is 4.05 A. The Sb to S bonds are mainly covalent. Each trivalent Sbr at the vertex of a trigonal pyramid is bonded to three S atoms (two divalent and one trivalent) which occupy the corners of the basal plane. This trigonal pyramid is slightly distorted as shown by the interatomic distances of Sm at A and two Sn

5 312 PETER BAYLISS and WERNER NOWACKI at A and also the bond angles Sn-SbI-SIII of and Sn- SbI-Sn of In addition another four S atoms (two SI at A Sn at A and SIll at A) lie near SbI. Each quinvalent Sbn which lies just below the center (0.17 A) of the basal plane of a distorted square pyramid is bonded to five trivalent S atoms which occupy the corners of the square pyramid. This square pyramid is distorted as Table 2.Atomic coordinates and temperature parameters of stibnite HOFMANN SCAVNICAR Present (1933) (1960) study SbI x (3) (1) fjll (2) Y 1/4 1/4 1/4 fj (15) z (4) (1) fj (2) fj (1) 8bu x (4) (1) fjll (2) Y 3/4 3/4 3/4 fj (15) z (4) (1) fj (2) fj (1) SI x (15) (3) fjll (2) Y 1/4 1/4 1/4 fj (25) z (15) (3) fj (3) fj (3) Su x (14) (3) fjll (3) Y 3/4 3/4 3/4 fj (25) z (14) (3) fj (3) fj (3) Sill x (14) (3) fjll (3) Y 1/4 1/4 1/4 fj (26) z (13) (3) fj (3) fj (3) shown by the interatomic distances of SI at A two SIll at A and two SI at A and also the bond angles given in Table 3. In addition another two S atoms (two Sn at A) lie near Sbn. Both SbI (three S bonded and four S nearby) and Sbu (five S bonded and two nearby) are surrounded by seven S atoms which have a similar orientation as shown by their bond angles in Table 3. Both the trigonal pyramid (trivalent SbI) and square pyramid

6 Table 3. Interatomic distances and bond angles of stibnite Sbr -Sm A (3) Sn-Sbr-Sm(2) (8) 0 Sr -Sbn-Sm(2) (8)0 Sbn-Sr -Sbn (8) 0 ~(!) -Sn(2) (2) Sr - -Sm(2) (8) Sr -Sr(2) (8) Sbn- -Sbn(2) (9) ' (!) S(!) t::i -Sr(2) (3) Sr - -Sr (5) Sr -Sr (6) "'" Sn (3) Sr - -Sn(2) (7) Sr -Sm (2) (6) Sbr -Sn -Sbr(2) (11) "'" ::r' (!) 0.. -Snr (3) Sn- ~Sn (8) Snr- -Snr (7) '<: 00 e:.. "'" Sn- -Sn(2) (8) Sr - -Sn (2) (7) Sbr -SIlI-Sbn(2) J8).. "'" 0>= Sbn-Sr (3) Sr - -Sm(2) (7) Sn- -Sm (2) (8) Sbn- -Sbn (9) "'" >=.. (!) -Sm(2) (2) Sn- -Snr (7) Sn- -Sn (4) "'" 0: -Sr(2) (2) S. (!) "'" -Sn(2) (2) 00

7 314 PETER BAYLISS and WERNER NOWACKI (quinvalent Sbn) are joined together with their basal planes parallel to the b axis through common S atoms to form infinite chains. Each trivalent SI at the vertex of a trigonal pyramid is bonded to three quinvalent Sbn (Sbn at A and two Sbn at A) which occupy the corners of the basal plane. Two additional Sbl at A also lie near SI. Each divalent Sn is bonded to two trivalent Sbl at A with an angle of Three additional Sb atoms (Sbl at A and two Sbn at A) also lie near Sn. Each trivalent SIll at Fig.1. Projection on b axis to show atomic arrangement and interatomic distances in stibnite. Thick circles - 8b atom with heights t and 1 thin circles -8 atom with heights t and! the vertex of a trigonal pyramid is bonded to three Sb atoms (trivalent Sbl at A and two quinvalent Sbn at A) which occupy the corners of the basal plane. An additional Sbl (3.642 A) also lies near Snl' The physical properties of stibnite described by DANA (1941) such as (1) habituallong slender prismatic crystals (2) perfect cleavage (100) and imperfect cleavages (001) and (101) (3) translational gliding parallel to (100) in the [010] direction (4) flexibility about [001] and (5) hardness 2 may be related to its crystal structure.

8 Refinement of the crystal structure of stibnite 315 Acknowledgements Dr. P. ENGEL Dr. M. OHMASAand Mr. A. EDENHARTER are thanked for their help. We are grateful to the International Business Machines Extension Suisse for the use of their IBM 360/65 system at Basel. Some financial assistance was provided by National Research Council of Canada Grant Number A References J. D. DANA and E. S. DANA (1941) The system of mineralogy Vol. 1. J. Wiley and Sons New York. W. HOFMANN (1933) Die Struktur der Minerale der Antimonitgruppe. Z. Kristallogr International tables for x-ray crystallography (1962) Vol. III. Kynoch Press Birmingham. S. SCAVNICAR(1960) The crystal structure of stibnite. A redetermination of atomic positions. Z. Kristallogr B. J. WUENSCH and C. T. PREWITT (1965) Corrections for x-ray absorption by a crystal of arbitary shape. Z. Kristallogr