688 NOTIZEN
N O T I Z E N
Synthesis and Crystal D ata o f the Bism uth Sulphide Chloride B 19Si27Cl3
Vo l k e r Kr ä m e r
Kristallographisches In stitu t der Universität Freiburg
(Z. N aturforsch. 39 b, 688-689 [1974]; received A pril 22, 1974)
Crystal growth, Crystal data, Bismuth sulphide chloride
The title compound was synthesized by a sinter technique at 560 °C. X ray powder data are listed, the hexagonal lattice parameters are a = 15.403(3) and c = 4.015 (2) Ä; possible space groups are P 6 3 and P 6 3/m.
Preparation
Recently, the synthesis of bismuth sulphide bromideBia 9S2 7Br31 by reacting stoichiometric quan
tities of the high purity elements or the compounds BiSBr and Bi2S3 in the molal ratio 3:8 in closed ampoules at 600 °C was reported. The analogous synthesis of the corresponding chloride failed, be
cause of the high dissociation pressure of BiCl3 over Bi19S27Cl3. The reaction product consisted of Bi2S3 and a small amount of a mixture of BiSCl and Bi4S5Cl2 (another new compound in the system Bi2S3-BiCl3), condensed on the colder parts of the ampoule. However, the compound Bi19S27Cl3 did form if the partial pressure of BiCl3 in the system was increased by employing a surplus of BiCl3.
A charge of BiSCl and Bi2S3 in the molal ratio 2:1 - total weight 10 grams - was reacted in evacuated (< 10_3 Torr) quartz ampoules (length 15 cm, inner diameter 15 mm) at a temperature of 560 °C for 3 days. The empty end of the ampoule was kept at 640 °C to avoid condensation of volatile components.
From the sintered charge, hexagonal, prismatic single-crystals of needle-like habit up to 3 mm in length had grown. Their composition was determined thermogravimetrically (decomposition into Bi2S3 and volatile BiCl3) to be Bi19S27Cl3= 9 B i2S3 • BiCl3.
Crystal Geometry and Results
Precession and Weissenberg photographs of selected single crystals yielded rough lattice con
stants and the possible space group P 6 3 or P 6 3/m.
Sonderdruckanforderungen an Dr. Volker K r ä m e r ,
Kristallographisches Institut der Universität, D-7800 Freiburg, Hebelstraße 25.
Table I shows the X-ray powder data obtained with a Philips diffractometer (CuKa-radiation, X = 1.5418 Ä) employing As20 3 (cubic, a = 11.0810Ä) as an external standard. Table I I gives the unit cell parameters refined with a least-squares computing program.
The new compound belongs to an isomorphic series of bismuth sulphide halides of the type Bi19S27X3 (X: Cl, Br, I). Their unit cell data are compared in Table II.
Table I. X ray powder diffraction data for B i19S27Cl3.
d o b s d calcd hkl I /I 0
13.3392 100
7.711 7.7014 110 6
6.678 6.6696 200 2
5.038 5.0417 210 6
4.453 4.4464 300 1
3.8485 3.8507 220 2
3.8443 101
3.6986 3.6996 310 100
3.5657 3.5599 111 1
3.4436 3.4396 201 1
3.3371 3.3348 400 2
3.1433 3.1406 211 9
3.0610 3.0602 320 3
2.9772 2.9797 301 5
2.9099 2.9108 410 8
2.7753 2.7790 221 6
2.7211 2.7206 311 2
2.6678 500
2.5671 330
2.5647 2.5652 401 4
2.5228 2.5209 420 4
2.4324 2.4338 321 2
2.3955 2.3958 510 4
2.3545 2.3566 411 1
2.2232 600
2.2219 2.2220 501 1
2.1924 2.1929 430 4
2.1628 2.1628 331 1
2.1355 2.1360 520 1 , ft
2.1349 421 / 30
2.0561 2.0573 511 4
2.0342 610
2.0073 002
1.9849 102
1.9449 601
1.9424 112
1.9253 440 )
1.9241 1.9245 431 \ 2
1.9221 202 J
1.9056 530
1.8866 1.8857 521 3
1.8649 212
1.8499 1.8498 620 8
NOTIZEN 689 Table II. Comparison of crystal data for bismuth
sulphide halides of the type B i19S27X 3 (X: Cl, Br, I).
Formula Bi19S2:C13 B ii9S27Br3 B i19S27I 3 a A 15.403 (3) 15.486 (2) 15.640 (2)
c A 4.015 (2) 4.018 (1) 4.029 (2)
V A3 824.8 834.4 853.4
Z 2/3 2/3 2/3
£>meas gem-3 6.53 6.65 6.72
ßcalcd gem-3 6.63 6.73 6.76
The crystal structure of Bi19S27I 3 has been deter
mined by M i e h e and K u p c i k 2. The close resem-
The Role o f Copper Ions in Copper Catalyzed Autoxidation o f Sulfite
J o s e f V e p ř e k - Š i š k a and S t a n i s l a v L u ň á k In stitute of Inorganic Chemistry,
Czechoslovak Academy of Sciences, Praha, CSSR
(Z. N aturforsch. 29b, 689-690 [1974]: received May 27, 1974)
Autoxidation, Sulfite, Copper ions, Catalysis mechanism
Sulfito-cuprous complexes as intermediates of copper catalyzed autoxidation of sulfite and the confrontation with the radical mechanism are d e
scribed.
Catalyzed oxidation of sulfite ions by oxygen has long been considered to proceed via a chain mecha
nism1-5. The copper catalyzed thermal reaction has been assumed2 to involve steps (1-7).
Initiation
Cu2+ + SO|- -> Cu+ + S 03 (1) (2 Cu+ + 02 + 2 H+ -> 2 Cu2+ + H20 2) (2) Propagation
so; + o2 sor
(3)SO5 + HSOä -> HSOr + SO3 (4) Termination
(HSOJ + SO2- -> HS07 + SO2-) (5)
SOä + SO3 (6)
sor + S 07 (7)
Requests for reprints should be sent to Dr. J.
Ve p r e k-s i s k a, Tschechoslowakische Akademie der W issenschaften, Institut für anorganische Chemie, 16000 P rah a 6, Majakovskeho 24/Tschechoslowakei.
blance of the powder diagrams and of the single- crystal photographs suggest that the two other compounds have the same atomic arrangement.
Further studies of the system Bi2S3-BiCl3 - involving the new bismuth sulphide chloride Bi4S5Cl2 - are in progress.
The author wishes to thank Prof. R. Ni t s c h e for helpful discussions. Numerical com putations were performed on a Univac 1106 of the ‘Rechenzentrum der Universität Freiburg’.
Financial support of the ‘Deutsche Forschungsge
meinschaft’ is greatly acknowledged.
1 V. Kr ä m e r, J. Appl. Cryst. 6, 499 [1973].
2 G. Mi e h e and V. Ku p c i k, Naturwissenschaften 58, 219 [1971].
The reaction mechanism was proposed on the basis of a few qualitative findings5: The reaction is sensitive to trace impurities and in extremely pure systems proceeds at an almost negligible rate.
The reaction velocity is significantly increased by trace quantities of some metal ions; very strong effects are observed with copper cations. As in an inert atmosphere copper(II) cation oxidizes sulfite to dithionate the catalytic effect of copper ions was explained by the assumption that copper(II) ion oxidizes sulfite ions to SO3 radicals which initiate the reaction with oxygen. Attempts to verify the suggested mechanism by kinetic studies5 meet with difficulties typical for trace metal catalyzed reactions and are, therefore, not very successful. Recently6, new information on the reactions of the intermedi
ates assumed were obtained from flash photolysis and pulse radiolysis of S 0 3. These results made the authors modify the mechanism of propagation and to postulate the S07 radical as a chain carrier. The original idea assuming the initiation of the chain reaction by one-electron transfer (reaction (1)) was maintained. This idea, however, considers neither formation of sulfito-cuprous complexes nor oxida
tion of cuprous ion by oxygen. If these reactions are taken into account several discrepancies result which are hardly compatible with the assumption of the radical mechanism.
Investigating the autoxidation of sulfite catalyzed by copper(II) ion it was found that the cupric ion was immediately and quantitatively reduced by sulfite to cuprous ion which reacts to form sulfito- cuprous complexes (see also ref. 7). The change was proved spectrophotometiically by the disappearance of absorption of the cupric ion and by the formation of a poorly pronounced absorption band in the vicinity of 450 nm. According to ref. 8 cuprous cation reacts with sulfite anion to form complexes of the type [Cu(S03)n]-2n+1 with stability constants
ß 1 = lQ7’85, /?2 = 108'70, /?3 = 109'36. In case th at ana-
690 NOTIZEN lytical concentration of copper ions is much lower than the concentration of sulfite (i.e. in the case of trace catalyzed reaction) the equilibrium concentra
tion of cuprous ion may be given by (8)
[Cu+] = ccu/(l+ ^ [ S O ii + &[SO|-]2+ ß3[SO§-] 3) (8) and the concentration of individual sulfito-com
plexes by (9)
[Cu(S03)n2n+1] = /5n[SO§-]n[Cu+]. (9) As it could be seen from equations (8) and (9) teh concentration of hydrated cuprous ion is extremely low and negligible when compared with the concen
tration of sulfito-cuprous complexes. For instance, in a solution containing 1 m sulfite and copper ions in analytical concentration ecu = 1 X 10-7 m, the equilibrium concentration of cuprous ion (i.e. the highest concentration possible) is [Cu+] = 3.5 X
10- 17M.
For initial concentrations [SO§—] = 1 m, [0 2] = 1.3 X 10-4Mandccu = 1 X 10_7m the rate constant found was k = 2 x 10-4 sec-1 (20 °C). When experi
mental kinetic equation is compared with the relations following from the radical mechanism (equations 1-7), expression (10) is obtained (for d[Cu+]/dt = d[S O j]/dt = d[SOF]/dt = 0)
— d [SOf- ] I dt = k [SOjj-] = 2 k3 [SO3 ] [0 2] =
= 2 k * k2[Cu+] [0 2], (10) k = experimental rate constant, k2 and k3 are rate constants for steps (2) and (3), k* = the kinetic chain length. Using the value10 k2 = 3.5 X 104 mole-11 sec-1
for the rate constant of the oxidation of cuprous ions by oxygen the kinetic chainlengthk* =6.3 X 1011
was calculated. Due to this value, the reactions of the radical SO3 with oxygen (equation 3) should be at least 6.3 X 1011 times more probable than its recombination and relation (1 1) should, therefore, hold
d[SOjj-]/dt = k[SOf-] = 2 k3 [SO3] [0 2] >
> 2 x 6.3 x 1011 x k 6[SOg]2. (11) Using k6= 5 .5 x 108 mole-1 1 sec-1 for the rate constant6 of radical recombination the concentration
1 H . J. L. Bä c k s t r ö m, J. Amer. Chem. Soc. 49, 1460 [1927].
2 H. J. L. Bä c k s t r ö m, Z . Phys. Chem. B 25, 122 [1934].
3 F. Ha b e r, Naturwissenschaften 19, 450 [1931].
4 J. Fr a n c k and F . Ha b e r, Ber. Berl. Akad. 1931, 250.
5 Gmelins Handbuch der anorganischen Chemie;
Schwefel, Teil B, Lieferung 3, 8. Auflage, Verlag Chemie, W einheim 1963.
6 E . Ha y o n, H . Tr e i n i n, and J. W ilf , J. Amer.
Chem. Soc. 94, 47 [1972].
of [S03] < 5.4 X 10-13 M will be obtained from equation (11) for k = 2 x 10-4sec-1 and [SOg- ] = l m.
For this concentration of S 0 3 radical, however, a value k3 > 1.4 x 1012 mole-1 1 sec-1 follows from relation (11). Considering that the theoretical value of the rate constant9 for a diffusion-controlled pro
cess between uncharged particles is 7 X 109 mole"1 1 sec-1 and the rate constant for a diffusion-con
trolled process between oppositely charged particles is ~ 1011 mole-1 1 sec-1, the calculated value of k3 is too high and, consequently, reaction (11) seems to be improbable.
The ratio between concentrations of cuprous ion and individual sulfito-cuprous complexes in the solution under consideration (1 M sulfite) is [Cu+] : : [CuS03] : [Cu(S03)3-] : [Cu(S03)|- ] = 1 :107-85:108-70 : 109-36. When concentrations and rate constants for reactions of the individual particles with oxygen are compared, the oxidation of sulfito-cuprous com
plexes is much more probable than the oxidation of cuprous ions. The rate constant of oxidation of cuprous ions with oxygen10 is k 2 = 3 .5 X 104 mole-1 I sec-1 and at pH > 4 independent of pH. Rate constants for autoxidation of cuprous complexes given in the literature10-11 are in the range 1 x 103-
4 x 104 mole-1 1 sec-1. Rate constants for autoxi
dation of sulfito-cuprous complexes are not known;
there is, however, no reason to assume th at they should be lower. But even if they were lower by several orders of magnitude the rate of oxidation of cuprous ion as compared to the rate of oxidation of sulfito-cuprous complexes would still be negligible due to the ratio [Cu(S03)7t2n+1]/[Cu+].
The discrepancies outlined above lead to the conclusion that reactions (2) and (3) and conse
quently also reaction (1) do probably not represent individual steps of sulfite aut oxidation. The problem now is whether thermal reaction of sulfite with oxygen proceeds really via radicals as has been assumed. If oxygen should react with sulfito-cuprous complexes instead of cuprous ion particles of the type [0 2Cu(S03)n]-2n+1 would result as intermediary products, and their reactions could be explained by a non-radical mechanism.
7 A. Fo f f a n i a n d M . Me n e g u s- Sc a r p a, G a z z . 83,
1068 [1953].
8 L. G . Si l l e n a n d A . E. Ma r t e l l, S t a b i l i t y C o n s t a n t s
of Metal Ion Complexes, The Chemical Society, Special Publication No. 17, p. 230, London 1964.
9 D. N. Ha g u e, Fast Reactions, p . 12, W iley-Inter- science, New York 1971.
10 A. Zu b e r b ü h l e r, Helv. Chim. Acta 83, 473 [1970].
II J. Pe c h tand M . An b a r, J. Chem. Soc. A 1968, 1902.
