The room temperature phase of (CH,NH&Bi&I, Ann. Chim. Sci. Mat, 1998,23, pp. 203-207

THE ROOM TEMPERATURE PHASE OF (CH,NH,),Bi,CI,

I. BELKYAL, R. MOKHLISSE*, B. TANOU!II*, R-F. HESSE**,W. DEPMEIER**

Facultb des Sciences et Techniques, Marrakech, Maroc.

Dopartement Chimie, Universite Cadi Ayyad, B.P 618,

* Faculto des Sciences, Dopartement Chimie, Universitb Cadi Ayyad, B.P S15, Marrakech, Maroe. ** Mineralogisches Institut, Universitat Kiel, D-24098 Kiel, Germany.

Summary : The structure of (CHJNH&Bi2C19 was determined at room temperature. It is orthorhombic, space group Pmua, with four formula units in the unit cell of dimensions a = 20.43(3), b = 7.71(l) and c = 13.26(2) A. The structure was refined to R = 0.045 for 911 non-equivalent observed reflections. It is formed by infinite BizCld- polyanions which form zig-zag double-chains running along [OlO]. The chains are separated by three crystallograpbically inequivalent CH3NH,+ cations. The structure consists of a close-packed arrangement of CH&H< cations and Cl- anions, with the stacking direction parallel to [ lOO]. The Bi3’ occupy exclusively Cl- coordinated octahedral voids in this packing. The Bi” coordination is distorted by the stereoactive 6s’ lone pair.

Phase ambiante de (CH~NH3)&i2C&A temperature ambiante, (CH;NH3hBiZC19 cristallise dans le Resume : systeme orthorhombic avec le groupe d’espace Pmna. La maille cristalline contient quatre groupements formulaires et les parametres cristallins sont a = 20.43(3), b = 7.71( 1) and c = 13.26(2) A. L’afIinement de la structure est obtenu avec un facteur de reliabilite (R) egal a 0.045 pour 911 reflexions non-equivalentes observees. La structure est formee de doubles chaines zig-zag de polyanions BiCl:- le long de l’axe [OlO] ainsi que par un arrangement compact de cations CHjNH; et d’anions Cl suivant 1’axe [ lOO]. Les chaines sont stparees par trois type de cavites occupees par les cations CH3NH3*. Les sites octaedriques form& par Cl’ et occupes par les ions Bi3’ sont deform& 8 cause de la paire libre (6s’) des ions Bi3’.

1. INTRODUCTION

The crystal structures of tris-alkylammonium-nonahalogenodiantimonates(III) and bismuthates(II1) of general formula [NI&,(CH3),]3M2X9 (M = Sb, Bi ; X = Cl, Br, I) have attracted a lot of interest in recent years because many structures of this type exhibit dielectric anomalies, and the dynamics of alkylammonium cations have been reported to induce order-disorder type phase transitions [l-3]. Of the various compounds of this family, the most characteristic seem to be those containing (CH3NH3)’ cations (n = 1). It was shown that the structure of the anions MzXg3- of these compounds, as well as their physical properties, depend on the type of halogen atoms present [2]. In the case of chlorine derivatives (CH3NH3)sSb& and (CH3NH3)3Bi& they are isostructural with b-Cs3SbzCl, [4]. This structure is characterized by zig-zag double-chains of polyanions [5]. The bromide crystals contain corrugated layers of octahedra connected by three common comers and, finally, iodine analogues have simple pairs of face-sharing octahedra in their crystalline lattice. The purpose of the present paper is to report on the results of a crystal structure examination of tris(monomethylammonium)nonachlorodibismuthate(III), (CH3NH3)3Bi& (abbreviated MACB), and to compare its structure witb that of (CH,NH3)3SbzC19 (MACA).

Reprints : I. BELKYAL, Departement de Chimie Fat. SC. Tech. B.P. 618 Marrakech MAROC

204 1. Belkyal et al.

LEXPERIMENTAL

The preparation of (CH3NH&Bi2C19 and its identification are described elsewhere [6,7]. The crystal data are as follows : orthorhombic, Pnma (in fact, Jakubas et al. [5] have adopted the non-standard Pmcn setting), a = 20.43(3), b = 7.71(l), c = 13.26(2) A. Z = 4, V = 2090(9) A3, D=2,65g.&. F(OOO) = 1432, p (MoKa,) = 17.95 mni’, T = 293 K.

A crystal measuring 0.532 x 0.076 x 0.076 mm3 was chosen for the X-ray measurements, with data collection made on an automatic Siemens AED four-circle diffractometer using graphite monochromatized MoKa radiation (1 = 0.71069 A) and q-2q scans. The 2q-range was 4-60”, the range of h, k, 1 0110, O/18, 0128. The intensities of 3519 reflections were recorded ; 911 had 1>3s(I) and were used for the subsequent structure refinement. The unit cell dimensions as given above were determined by least-squares with the program DIM (Siemens-Software): using 36 well-centred reflections in the range 16’<2q<25”. Lorentz, polarization and empirical absorption corrections were applied (Sicmens-Software : REDW, EMPIR). The positions of the non-hydrogen atoms could be found by direct method (SHELXS-86 [S]). Anisotropic atomic displacement parameters were used for Bi, Cl atoms, individual isotropic ones were applied to C and N atoms. Refinement was carried out by full-matrix least-squares methods using the program SHELXL-93 [9], The atomic scattering factors for neutral atoms Bi and Cl were taken from the International Tables for X-ray Crystallography [lo], and for C and N from Cromer and Mann [ll]. The refinement converged at R, = 0.045 (R, = Cl/F,1 - IFell / CIFOl) for 911 reflections with I > 3s(I) and 0.267 for all 3305 data (at present it is not quite clear whether this high value reflects simply the generally weak intensity of the high order reflections, or is rather related to the most recent detection of a slight splitting of certain reflections, detected by employing our new Image Plate system. Note that neither plots of the reflections profiles on the four-circle diffractometer, nor preceding Weissenberg photographs of the crystal used showed any particularly conspicuous features of the reflections) ; wRz = 0.156 (wR2 = [C[w(F,,2 - Fc’)2] / C[W(F,~)‘]]“‘) and GOOF is 0.923 (GOOF = [C[w(Fz - F,‘)‘] / (n-p)]“’ , where n is the number of reflections and p is the total number of parameters refined). Weights were calculated according to w = I/s~(F,~). Maximum and minimum values in the final difference Fourier synthesis map were 2.64 and -I .86 eA”. respectively. close to Bi atoms.

2. RESULTS AND DISCUSSI0.w

The positional and thermal parameters are hsted in table 1, and most important interatomic distances and angles are to be found in tm.

The structure contains two crystallographically independent Bi atoms (figure 1). Each one is coordinated by six Cl atoms in the form of a distorted octahedron. Three short distances (2.55(l), 2 x 2.574(8) A for Bi( 1) and 2.575(9), 2 x 2.576(7) A for Bi(2)) from terminal chlorine atoms and three long (2.X5(1), 2 x 2.874(8) A for Bi(1) and 2.83(l), 2 x 2.852(8) A for Bi(2)) ones from bridging chlorine atoms make up the (3 + 3) coordination of each Bi atom. The distortion is attributable to the sterically active 6s2 lone-pair electrons of Bi3’.

The distorted octahedra are linked together to form infinite chlorobismuthate polyanions. Analogously to MACA [5], the Bi atoms linked by the bridging chlorine atoms form zig-zag chains along [OIO] (figure 2). Two parallel zig-zag chains linked via additional Cl atoms, show a rectangular cross-section, and are called here beams. The beams are held together

FIG. 1 : The crystal structure of MACB projected along [OlO].

The room temperature phase of (CH,NH&Bi,CI,

b!. three non-equivalent meth~~lammomum cations. There is good reason to assume that the cations are connected to the beams via N-H...Cl hydrogen bonds. It was not possible to determine H atom positions in this x-ray experiment. However, some of the shorter N.. .CI distances are in agreement with accepted acceptor-donor distances for N- H...Cl hydrogen bonds (2.91- 3.52 A [ 121: cf. table 2). 1-

b.

FIG. 2 : SchematIc view ot’the anion lattice (layer structure) oPMACB along [OlO), showing the zig-zag double-chain-stack. The smaller ellipsoids represent Bi atoms, the larger ones CI atoms.

Table I : Positional (~10~ for Bi and Cl, ~10.~ for N and C) and thermal parameters (A’) (x10“ for Bi and Cl, x lo“ for N and C), U,, or U,,, in MACB with standard deviations in parentheses. The anisotropic temperature factors have the form : esp[-2p’(U, ,h’a*‘+ U-2k’b*‘+ U;$C*’ + ZUzjklb*C* + 2U13hla*c* + 2LJ)&ka*b*)J

Atom Wyckoff Site s letter symmetry

Bi( 1) 4c .m. 171 l(1) Bi(2) 4c .m. 47(l) Cl(l) 4c .m. 4261(j) W2) 4c .m. 7533(6) Cl(3) 4C .m. 5769(6) Cl(d) 8d 1 23 1 l(4) Cl(j) 8d I 4049(j) qw 8d 1 5664(4) N(1) 4c .m. 783(2) N(2) 4c .m. 441(3) N(3) 4c .m. 56(2) C(l) 4c .m. 723(2) C(2) 4C .m. 880(Z) C(3) 4c .m. 130(3)

Atom Bi(1) Bi(2) Cl(l) W) Cl(3) Cl(4) W) N(1) NW N(3) C(1) C(2) C(3)

UIl u22 u33 U23 u13 u12 21.0(8) 24.4(6) 29.8(6) 0 -0.1(6) 0 24.0(9) 25.5(6) 31.8(6) 0 -0.2(7) 0

65(9) 83(8) 34(j) 0 -14(j) 0 45(8) 9W) 70(6) 0 -38(6) 0 41(8) 135(11) 54(6) 0 -22(5) 0 W2 61(j) 70(4) 20(4) -8(4) 24(j) 65(6) 6fw 77(5) -24(4) O(j) 41(j)

Y

2500 7500 2500 2500 2500

79( 12) 5022( 10) W’) 250 250 250 250 250 250

z

9266(I) 7420(l)

797(6) 7 185(8) 4144(7)

230(j) 3 148(j) 1658(j) 277(2) 579(3) 582(3) 2 17(3) 860( 3) 563(3)

Ueq/Uiso 25.1(4) 27.1(4)

61(3) 6W) 77(4) 65(2) W2)

7(l) 13(2) 9(l) 6(l) j(l) 8(2)

206 I. Belkyal et al.

In an alternative approach the structure can be described as consisting of close-packed arrangements of CH3NH3’ cations and Cl atoms. These are stacked along [ 1001 in the sequence ABACBC The Bi atoms occupy octahedral voids which are exclusively coordinated by Cl atoms. In the six-layer arrangement, two layers (B) contain Cl(2) and Cl(4) atoms and C(l)-N(1) cations and four layers (A, C) contain Cl(l), Cl(j), Cl(5) and Cl(6) atoms and C(2)-N(2), C(3)-N(3) cations.

The differences between the isostructural bismuth and antimony [5] salts are small, the largest concerning the terminal Bi-Cl bonds (2.55(l), 2 x 2574(S) and 2575(g), 2 x 2.576(7) A) as compared with (2 446(3). 2 x 2.459(2) and 2.433(4), 2 x 2.437(3) A) for Sb-Cl. The bridging Bi( 1)-Cl bonds (2,85(l) and 2 x 2.874(S) hi) are not significantly shorter than the corresponding Sb(l)-Cl distances (2 x 2.859(3) and 2.912(4) A), whereas Bi(Z)-Cl (2,83(l) and 2 x 2.852(S) A) are shorter than Sb(2)-Cl (2.930(4) and 2 x 2.937(3) A).

Table 2 : Bond lengths (A) and angles (“). The standard deviations in parentheses refer to the last digit.

Symmetry codes

(1) x Y 2 (2) 1/2+x 1/2-y 112-z (3) -x 112+y -z (4) 112-x -y 1/2+z (5) -x -Y -z (6) 1/2-x 1/2+y l/2+2 (7) x 112-y Z

(8) 1/2+x Y 112-z

Bi( 1) Cl(2)iii 2.55(l) Cl(4)1,7 2.574(S) Cl(3)iii 2.85(l) Cl(5)4,6 2.874(8) Cl( 1)i 5,59(l) C1(6)3,5 5.85(l)

Cl(l) Cl(3) N( 1)iii 3.48(4) N(2)i 3.52(5) N(3)iii 3.42(4)

N( l)-C( 1) 1.47(5)

Bi( 1) Cl(4) 1,7 A Cl(2)iii 93.5(3) Cl(5)4,6 A CI(2)iii 88.1(3) Cl(3)iii A C1(4)1,7 87.4(2) C1(5)4,6 A Cl(3)iii 91.0(3) Cl(4) 1 A C1(4)7 93.0(4) C1(5)4 A Cl@)6 83.4(4)

C](4) N(l)iii 3.42(3)

(9 x (ii) -x

(iii) 1/2+x (iv) 1/2-x

Cl( 1)iv Cl(3)iv C1(5)4,6 C1(6)4,6 Cl( 1)iii C1(6)2,8

Cl(5) N(l)iii 3.38(3) N(3)iv 3.71(3)

l/4 Z

314 -2 l/4 1/2-z 314 1/2+z

Bi(2) 2.575(9) 2.83( 1) 2.852(S) 2.576(7) 5,971(g) 5,90(l)

Cl(6) N(3)iv 3.38(4) N(3)iii 3.79(3)

N(2)-C(2) 1.50(6) N(3)-C(3) 153(6)

Bi(2) Cl(6)4,6 A Cl( 1)iv 88.9(2) C1(5)4,6 A Cl( 1)iv 85.8(2) Cl(3)iv A C1(6)4,6 89.1(2) C1(5)4,6 A Cl(3)iv 96.2(2) C1(6)4 A Cl(6)6 93.3(4) C1(5)4 A Cl(5)6 86.0(4)

MACB undergoes two structural phase transitions at Tc, z 349K and TcZ D 247K (on heating). The two phase transitions have been detected by means of DSC measurements [6,7]. The transition at Tc, is accompanied by anomalies in the thermal evolution of dielectric constants, whereas the transition at Tc2 cannot be characterized by this technique. The latter transition could be detected by means of ‘OgBi and 35C1 NQR experiments [ 131.

The room temperature phase of (CH,NH~,Bi,CI, 207

An X-ray diffraction study at 215K has shown that the phase transition at Tcz leads to a structure with probably P2,2,2, symmetry. Results of our studies on the phase transitions and the low temperature phase will be published elsewhere.

Acknowledacments : This work was performed during a stay of I. BELKYAL at the Mineralogisches Institut, Universimt Kiel, Germany. The stay was made possible by a grant in the frame work of the cooperation between the CNR (Centre National de Coordination et de Planification de la Recherche Scientifique et Technique, Rabat - Marocco) and the DFG (Deutsche Forschungsgemeinschafl, Bonn - Germany).

4. REFERENCES

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(1986). [6]- I. Belkyal, R. Mokhlisse, B. Tanouti, N.B. Chanh and M. Couzi, J. Allovs and Compounds 188, 186-189

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[S]- G.M. Sheklrick, SHELXS-86. Program for Crystal Structure Determination. Univ. of Gottingen, Germany (1986).

[9]- G.M. Sheldrick, SHELXL-93. Program for Crystal Structure Determination. Univ. of Gottingen, Germany (1993).

[lo]- International Tables for X-ray Crystallography, Vol. IV Kvnoch Press, Birmingham (1974). [I l]- D.T. Cromer and J.B. Mann, Acta CrvstalloPr. m, 321-324 (1968). [ 12]- G.A. Jeffrey and W. Saenger, Hydrogen Bonding in Biological Structures. Second Printing, p. 29.

Oxford : Berlin Heidelberg New York Sprinter-Verlag (1994). [ 13]- H. Ishihara, K. Watanabe, A. Iwata, K. Yamada, Y. Kinoshita, T. Okuda, V.G. Krishnan, S.-Q. Dou

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