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Crystal structure and phase transitions of [(C2H5)4N]6Bi8Cl30
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J. ZALESKI et al.
1266 Table
1. Positional parameters and equivalent values of the anisotropic thermal parameters with e.s.d.s in parentheses
Atom Bi(1) Bi(2) Bi(3) Cl(J) Cl(2) Cl(3) Cl(4) Cl(5) Cl(6)
ci(7j
cw Cl(9) N(l) N(2) N(3)
x 0.6318(l) 0.5605(l) 0.5000(0) 0.7313(5) 0.573 l(5) 0.6855(5)
0.5745(6j 0.5138(4) 0.6745(5) 0.6079(4) O&86(6) 0.4431(5) 0.2170(15) 0.3387(14) 0.4131(16)
Y 0.3236(l) 0.5000(O) 0.3187(l) 0.3373(9) 0.1985(S) 0.1821(9) o.sooo(oj 0.3532(8) 0.5000(O) 0.3394(7) 0.5000(O) 0.1854(9) 0.5000(0) 0.5000(O) 0.0000(0)
The positional and thermal parameters are listed in Table 1 and the interatomic distances and angles are given in Tables 2 and 3. Bismuth (III) and antimony (III) complexes most commonly represent only a few possible structures, namely MXq [6], MX:- [7], MXi- [8] and M,X;- [3, 51. There are, however, a few more complicated anionic structures, verified by X-ray studies, which contain either isolated Bi,Clyr [9], B&B& [lo], Sb,I& [ll], Sb,I& [12] anions or polymeric endless chains [Sb*I;], or [Sb,I,], v31. The compound studied contains a stoichiometritally and structurally novel anion Bi,Cl$;. Its structure and labelling scheme is presented in Fig. 1. The anion consists of eight edge-sharing octahedra, having as a whole, symmetry 2/m. The coordination sphere for Bi(1) consists of three bridging and three terminal chlorine atoms, Bi(3) has four bridging and two terminals, whereas the environment of Bi(2) consists of six bridging chlorine atoms. The nine independent Bi-CI contacts lie in two ranges: termiTable 2. Interatomic distances (A) with e.s.d.s in parentheses Bi(l)Cl(l) Bi(l)-Cl(Z) Bi( l)-Cl(3) Bi( 1)X1(4) Bi(l)-Cl(S) Bi( 1)X1(6)
2.477(9) 2.469(10) 2.547(11) 2.855(S) 3.163(9) 3.207(8)
Bi(2)-C1(5) Bi(2)<1(5’) Bi(2)<1(6) Bi(2)<1(7) Bi(2)-C1(7’) Bi(2)-Cl(8)
2.544(9) 2.544(9) 2.677(11) 2.907(7) 2.907(7) 2.793(12)
Bi(3)-Cl(7) Bi(3)<1(7”) Bi(3)-Cl(8) Bi(3)-Cl(8”) Bi(3)-Cl(9) Bi(3)-c1(9”)
2.726(8) 2.726(8) 3.108(7) 3.108(7) 2.471(10) 2.471(10)
Position codes: i: x, 1 ii: 1 -x, y, 1 - .z.
y, z;
z
&?
0.1640(l) 0.3327iij 0.5000~0~ o.o980(4j 0.0884(5) 0.2379(5) 0.0948(6) 0.2588(4) 0.2708(6) 0.4256(4) 0.4082(5) 0.4287(5) 0.4431(14) 0.1089(16) 0.2130(17)
3.5(l) 2.7( 1) 2.9(l) 5.5(S) 5.6(6) 6.5(6) 3.9(7) 4.6(5) 3.3(6) 4.2(4) 3.1(6) 5.7(6) 2.0(16) 2.2(16) 2.8(18)
nal bonds in the ones in the range anion is closely antimony iodide chains.
range 2.469-2.543 A and bridging 2.5443.207 A. The structure of the related to [Sb,IJ, [13] in which octahedra are joined to endless
Table 3. Selected (degrees)
interatomic angles with e.s.d.s in parentheses
Cl(l)-Bi(lwl(2) Cl( 1)-Bi( lECl(3) Cl( l)-Bi( 1)X1(4) Cl( I)-Bi( 1)X1(5) Cl( I)-Bi( l)-Cl(6) C1(2)-Bi(l)Cl(3) Cl(Z)-Bi( l)Cl(4) Cl(Z)-Bi( 1)X1(5) Cl(2tBi( 1)X1(6) Cl(3)-Bi( 1)-Q(4) Cl(3)-Bi(l)Cl(5) CJ(3tBi(l)-Cl(6) C1(4)-Bi( 1)-G(5) Cl(4)-Bi( 1)X1(6) Cl(StBi(l)-Cl(a)
94.5(3) 92.4(3) 89.6(3) 168.1(3) 97.2(3) 95.2(3) 91.6(3) 96.2(3) 167.0(3) 172.8(3) 91.7(3) 90.0(3) 85.0(2) 82.9(3) 71.6(2)
Cl(S’tBi(2)-Cl(S) Cl(S’)-Bi(2)-Cl(6) Cl(S’)-Bi(2)-cl(7) Cl(5’)-Bi(2)-Cl(7’) Cl(5’)-Bi(2)-C1(8) Cl(6)-Bi(2)-C1(7) Cl(6)-Bi(2)-C1(8) Cl(7)--Bi(2)-Cl(7’) C](7)-Bi(2)-Cl(8)
94.1(3) 91.1(3) 175.4(3) 88.3(3) 92.5(3) 92.7(3) 174.7(3) 88.9(2) 83.5(3)
Cl(7”)-Bi(3)-C1(7) Cl(7”)-Bi(3w1(8) Cl(7”)-Bi(3sl(9) Cl(7kBi(3)-Cl(9) Cl(7)-Bi(3)-Cl(8) Cl(8)-Bi(3)-C1(8”) Cl(S~Bi(3)-Cl(9) Cl(S~Bi(3)Cl(9”) Cl(S)-Bi(3)-Cl(9”)
168.9(3) 80.9(2) 92.1(3) 95.5(3) 90.8(2) 84.6(2) 91.3(3) 171.8(3) 93.7(3)
Bi(l)Cl(4)-Bi(1’) Bi( l’)Cl(5)-Bi(2) Bi( 1)X1(6)-Bi( 1’) Bi(l)-C1(6)-Bi(2) Bi(2)-C1(7)-Bi(3) Bi(2)<1(8kBi(3) Bi(3)<1(8)-Bi(3’)
103.1(3) 100.6(3) 88.4(2) 96.6(3) 100.8(3) 94.6(3) 95.4(2)
Crystal structure and phase transitions of [(C,H,),N],Bi,Cl,
Fig, 1. Structure of the ~i~~~
anion showing the atomic num~ring
A stereoview of the cantent of one unit cell is given in Fig. 2. The crystal of (TEA),Bi,Cl, lattice consists of large anions which form cavities situated along the [OOI] direction. Part of the cavity ~longing to one unit is composed of five anions and is occupied by six cations which are situated relatively close together, in a common space. The distance between the centres of the cations is equal to about 7.5 A. It is important to remark that, if during the refinement we took into acc5unt all the atoms, including the carbon ones, it would result in values of the structural parameters slightly different from those listed in Tables l-3. At that stage of refinement we obtained R, = 0.073 and R, = 0.091 for 2460 reflections. The static electric ~rrnitt~~ty plotted vs temperature for ~EA)~Bi~Ci be n 230 and 248 K along the b-axis is presented in Fig 3. On cooling from room temperature, down to 240 K, the ci value remains constant being equal to about six, and below 240 K a strong, complex anomaly is observed within a very narrow temperature range of about 1 K. A careful examination reveals two peaks (c&,, =i 10.5 at 241.2 K and 66, = 14.2 at 240.7 K). On heating we observe only one small peak, centred at 243.8 K, the increase of c; being much
Fig. 2. A stereoview of the unit cr.11of ~~)~3i~CI~
1267
scheme.
smaller (AC; = 1). This is probably connected with a breaking of the crystal during the first run through a structural phase transition (SPT). Thus the experiments carried out on a single crystal above T, are continued below T, on a ~lycrystalline sample. The temperature dependence of EL in Fig. 3 reveals thermal hysteresis (AI”, = 2.5 K). In Fig. 4 the plot of the dielectric losses (tan Bb) vs T for this com~und is presented between 230 and 248 K along the b-axis. It is easily seen that the tem~rature de~nde~~ of tan 6, in this tem~rature range is very simiiar to that of ti. The maxima of tan & coincide exactly with the maxima of CL. The measurements of e’(T) and tan 6 (T) were also carried out in the (ac) plane but sibilant anisotropy was not observed. In addition, it can be noted that the relative height of the two observed peaks varied from sample to sample, the one at the lower temperature always being higher. The magnitudes of the dielectric anomalies were closely related to the quality of the single crystal. Tbe complex shape of the anomalies suggests that on cooling the compound undergoes two SPT in this range, one at T,, = 240.7 K and the other at T,, = 240.2 K. Both transitions are of first order as confirmed by the temperature hysteresis (ALST, ‘si2.5 K).
crystal. The thermal ellipsoids of the nitrogen atoms
show centres of TEA cations.
J. ZALESKI et al.
1268
230
235
2‘0
2L5
T/K
Fig. 3. Temperature
dependence of the electric permittivity for (TEA), BiBCl,, along the b-axis.
On heating the t’(T) plot suggests only one SPT. This fact may be explained either by the presence of a metastable phase in this temperature range or by the fact that the second anomaly was diffused because of the breaking up of the single crystal during the first run through SPT on cooling. The DSC studies revealed only one reversible anomaly at about 242 K (on cooling) confirming the first order phase transition. The width of the observed thermal hysteresis is equal to 2 K. The estimated transition enthalpy and entropy are equal to 8 kJ mol-’ and 33 J Km’ mol-‘, respectively. Further extended analysis of the DSC data will be possible after completing the results for other tetraethylammonium halogenobismuthates and antimonates [ 141. The TEA cation possesses two stable conformations. They resemble a Greek cross (I) and a Nordic cross (II) when observed along the ? axis [18]. Both conformations were found in crystal structures, e.g. I in [15] and II in [16]. There are two orientations of
the TEA cations which are mirror images to each other, when superimposed. They differ mainly in the position of the c( carbon atoms. In most crystal structures of compounds with TEA cations at room temperature the cx carbon atoms are found to be disordered. In the case of (TEA),Bi,Cl,, it was not possible to localize the carbon atoms, which may indicate a more complicated disorder. This can be understood by taking into account the fact that in the sublattice of the big compact B&Cl& ions the TEA cations are arranged in a common space, motions of the cations being probably highly correlated and therefore much more complicated. The disorder of the TEA cations is realized by the reorientation of the cations themselves, by the rotation around the C-N axis (the ethyl group rotation), by the methyl group rotation, or in a combination of some or all of the above-mentioned motions. The NMR studies for TEA salts [17] showed that at room temperature all of the above-mentioned motions are present. On cooling they are consecutively frozen, firstly rotations of the cations around the zi axis, then the ethyl group rotations and, below about 120 K, the rotations of the methyl groups around the 3 axis. The freezing of some of these rotations is reflected in a complex sequence of dielectric anomalies of (TEA),Bi,Cl,, and other compounds with TEA cations [18]. The NMR studies were carried out on (TEA),ZnCl, , (TEA), CoCl, [ 181 and (TEA), SbF, [19]. The analysis of the results obtained based on theoretical values of the second moment of a proton NMR line [17] suggests that the observed phase transitions are associated mainly with the freezing of the reorientational movements of TEA cations (jump of a second moment from about 0.6 to 18 for (TEA)2 SbF,: and from about 2 to 18 for (TEA),CoCl,). In all the crystals studied the contribution of the motions of the anions has to be taken into account, as shown for (TEA)2SbF, [19]. In (TEA),Bi,Cl,,, however, the bulky rigid B&Cl& anions cannot reorientate, and therefore the transitions are presumably associated only with freezing of the motions of the cations. Acknowledgements-This work was supported by the Polish Academy of Sciences within project CPBP 01.12. REFERENCES
0
l210
0
_
-~-_f~-
Fig. 4. Temperature
2‘0
“-
4
dependence of tan S for (TEA),Bi,Cl,, along the b-axis.
1
1. Jakubas R. and Sobczyk L., Ferroelectrics 78,69 (1988). 2. Jakubas R., Czapla Z., Galewski Z., Sobczyk L., Zogai 0. J. and Lis T., P&s. Status Solidi (a) 93, 449 (1986). 3. Gdaniec M., Kosturkiewicz Z., Jakubas R. and Sobczyk L., Ferroelectrics 77, 31 (1988). 4. Kallel A. and Bats J. W.. Acta crvsralloar. C41. 1022 (1985). 5. Hall M., Nunn M., Begley M. J. and Soverby D. B., J. them. Sot. Dalton Trans. 1231 (1986). 6. Robertson B. K., MC Pherson W. G. and Meyers E. A., J. phys. Chem. 71, 3531 (1967). I
-
Crystal structure and phase transitions of [(C,H5),N],Bi,C1,, 7. McPherson W. G. and Meyers E. A., J. phys. Chem. 72, 532 (1968). 8. Lazarini F., Acta crystallogr. C43, 637 (1987). 9. Aurivilius A. and Stalhandske C., Acta them. stand.
A32, 71.5 (1978). 10. Rheingold A. L., Uhler A. D. and Landers A. G., Inorg. Chem. 22, 3255 (1983).
11. Pohl S., Lotz R. and Saak W., Z. Narurf. 43b, 1144 (1988). 12. Pohl S., Haase D., Lotz R. and Saak W., Z. Naturf: 43b, 1033 (1988). 13. Pohl S., Saak W. and Haase D., 2. NaturjI 42b, 1493 (1987).
1269
14. Zaleski J., Jakubas R., Galewski Z. and Sobczyk L., Z. Naturf. A (in press). 15. Hackert M. L., Jacobson R. A. and Keiderling T. A., Inorg. Chem. 10, 1075 (1978).
16. Stuckv G. D.. Folkers J. B. and Kirstenmacher
T. J..
Acra crystallo&. 23, 1064 (1967). 17. Szafranska B. and Pajak Z., J. molec. Struct. 99, 147
(1983). 18. Wolthuis A. J., Huiskamp W. J., De Jongh L. J. and Carlin R. L., Physica BC (Amsterdam) 142, 301 (1986). 19. Reynhardt E. C. and Rash J. P. S., J. magn. Reson. 42, 88 (1983).
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J. ZALESKI et al.
1266 Table
1. Positional parameters and equivalent values of the anisotropic thermal parameters with e.s.d.s in parentheses
Atom Bi(1) Bi(2) Bi(3) Cl(J) Cl(2) Cl(3) Cl(4) Cl(5) Cl(6)
ci(7j
cw Cl(9) N(l) N(2) N(3)
x 0.6318(l) 0.5605(l) 0.5000(0) 0.7313(5) 0.573 l(5) 0.6855(5)
0.5745(6j 0.5138(4) 0.6745(5) 0.6079(4) O&86(6) 0.4431(5) 0.2170(15) 0.3387(14) 0.4131(16)
Y 0.3236(l) 0.5000(O) 0.3187(l) 0.3373(9) 0.1985(S) 0.1821(9) o.sooo(oj 0.3532(8) 0.5000(O) 0.3394(7) 0.5000(O) 0.1854(9) 0.5000(0) 0.5000(O) 0.0000(0)
The positional and thermal parameters are listed in Table 1 and the interatomic distances and angles are given in Tables 2 and 3. Bismuth (III) and antimony (III) complexes most commonly represent only a few possible structures, namely MXq [6], MX:- [7], MXi- [8] and M,X;- [3, 51. There are, however, a few more complicated anionic structures, verified by X-ray studies, which contain either isolated Bi,Clyr [9], B&B& [lo], Sb,I& [ll], Sb,I& [12] anions or polymeric endless chains [Sb*I;], or [Sb,I,], v31. The compound studied contains a stoichiometritally and structurally novel anion Bi,Cl$;. Its structure and labelling scheme is presented in Fig. 1. The anion consists of eight edge-sharing octahedra, having as a whole, symmetry 2/m. The coordination sphere for Bi(1) consists of three bridging and three terminal chlorine atoms, Bi(3) has four bridging and two terminals, whereas the environment of Bi(2) consists of six bridging chlorine atoms. The nine independent Bi-CI contacts lie in two ranges: termiTable 2. Interatomic distances (A) with e.s.d.s in parentheses Bi(l)Cl(l) Bi(l)-Cl(Z) Bi( l)-Cl(3) Bi( 1)X1(4) Bi(l)-Cl(S) Bi( 1)X1(6)
2.477(9) 2.469(10) 2.547(11) 2.855(S) 3.163(9) 3.207(8)
Bi(2)-C1(5) Bi(2)<1(5’) Bi(2)<1(6) Bi(2)<1(7) Bi(2)-C1(7’) Bi(2)-Cl(8)
2.544(9) 2.544(9) 2.677(11) 2.907(7) 2.907(7) 2.793(12)
Bi(3)-Cl(7) Bi(3)<1(7”) Bi(3)-Cl(8) Bi(3)-Cl(8”) Bi(3)-Cl(9) Bi(3)-c1(9”)
2.726(8) 2.726(8) 3.108(7) 3.108(7) 2.471(10) 2.471(10)
Position codes: i: x, 1 ii: 1 -x, y, 1 - .z.
y, z;
z
&?
0.1640(l) 0.3327iij 0.5000~0~ o.o980(4j 0.0884(5) 0.2379(5) 0.0948(6) 0.2588(4) 0.2708(6) 0.4256(4) 0.4082(5) 0.4287(5) 0.4431(14) 0.1089(16) 0.2130(17)
3.5(l) 2.7( 1) 2.9(l) 5.5(S) 5.6(6) 6.5(6) 3.9(7) 4.6(5) 3.3(6) 4.2(4) 3.1(6) 5.7(6) 2.0(16) 2.2(16) 2.8(18)
nal bonds in the ones in the range anion is closely antimony iodide chains.
range 2.469-2.543 A and bridging 2.5443.207 A. The structure of the related to [Sb,IJ, [13] in which octahedra are joined to endless
Table 3. Selected (degrees)
interatomic angles with e.s.d.s in parentheses
Cl(l)-Bi(lwl(2) Cl( 1)-Bi( lECl(3) Cl( l)-Bi( 1)X1(4) Cl( I)-Bi( 1)X1(5) Cl( I)-Bi( l)-Cl(6) C1(2)-Bi(l)Cl(3) Cl(Z)-Bi( l)Cl(4) Cl(Z)-Bi( 1)X1(5) Cl(2tBi( 1)X1(6) Cl(3)-Bi( 1)-Q(4) Cl(3)-Bi(l)Cl(5) CJ(3tBi(l)-Cl(6) C1(4)-Bi( 1)-G(5) Cl(4)-Bi( 1)X1(6) Cl(StBi(l)-Cl(a)
94.5(3) 92.4(3) 89.6(3) 168.1(3) 97.2(3) 95.2(3) 91.6(3) 96.2(3) 167.0(3) 172.8(3) 91.7(3) 90.0(3) 85.0(2) 82.9(3) 71.6(2)
Cl(S’tBi(2)-Cl(S) Cl(S’)-Bi(2)-Cl(6) Cl(S’)-Bi(2)-cl(7) Cl(5’)-Bi(2)-Cl(7’) Cl(5’)-Bi(2)-C1(8) Cl(6)-Bi(2)-C1(7) Cl(6)-Bi(2)-C1(8) Cl(7)--Bi(2)-Cl(7’) C](7)-Bi(2)-Cl(8)
94.1(3) 91.1(3) 175.4(3) 88.3(3) 92.5(3) 92.7(3) 174.7(3) 88.9(2) 83.5(3)
Cl(7”)-Bi(3)-C1(7) Cl(7”)-Bi(3w1(8) Cl(7”)-Bi(3sl(9) Cl(7kBi(3)-Cl(9) Cl(7)-Bi(3)-Cl(8) Cl(8)-Bi(3)-C1(8”) Cl(S~Bi(3)-Cl(9) Cl(S~Bi(3)Cl(9”) Cl(S)-Bi(3)-Cl(9”)
168.9(3) 80.9(2) 92.1(3) 95.5(3) 90.8(2) 84.6(2) 91.3(3) 171.8(3) 93.7(3)
Bi(l)Cl(4)-Bi(1’) Bi( l’)Cl(5)-Bi(2) Bi( 1)X1(6)-Bi( 1’) Bi(l)-C1(6)-Bi(2) Bi(2)-C1(7)-Bi(3) Bi(2)<1(8kBi(3) Bi(3)<1(8)-Bi(3’)
103.1(3) 100.6(3) 88.4(2) 96.6(3) 100.8(3) 94.6(3) 95.4(2)
Crystal structure and phase transitions of [(C,H,),N],Bi,Cl,
Fig, 1. Structure of the ~i~~~
anion showing the atomic num~ring
A stereoview of the cantent of one unit cell is given in Fig. 2. The crystal of (TEA),Bi,Cl, lattice consists of large anions which form cavities situated along the [OOI] direction. Part of the cavity ~longing to one unit is composed of five anions and is occupied by six cations which are situated relatively close together, in a common space. The distance between the centres of the cations is equal to about 7.5 A. It is important to remark that, if during the refinement we took into acc5unt all the atoms, including the carbon ones, it would result in values of the structural parameters slightly different from those listed in Tables l-3. At that stage of refinement we obtained R, = 0.073 and R, = 0.091 for 2460 reflections. The static electric ~rrnitt~~ty plotted vs temperature for ~EA)~Bi~Ci be n 230 and 248 K along the b-axis is presented in Fig 3. On cooling from room temperature, down to 240 K, the ci value remains constant being equal to about six, and below 240 K a strong, complex anomaly is observed within a very narrow temperature range of about 1 K. A careful examination reveals two peaks (c&,, =i 10.5 at 241.2 K and 66, = 14.2 at 240.7 K). On heating we observe only one small peak, centred at 243.8 K, the increase of c; being much
Fig. 2. A stereoview of the unit cr.11of ~~)~3i~CI~
1267
scheme.
smaller (AC; = 1). This is probably connected with a breaking of the crystal during the first run through a structural phase transition (SPT). Thus the experiments carried out on a single crystal above T, are continued below T, on a ~lycrystalline sample. The temperature dependence of EL in Fig. 3 reveals thermal hysteresis (AI”, = 2.5 K). In Fig. 4 the plot of the dielectric losses (tan Bb) vs T for this com~und is presented between 230 and 248 K along the b-axis. It is easily seen that the tem~rature de~nde~~ of tan 6, in this tem~rature range is very simiiar to that of ti. The maxima of tan & coincide exactly with the maxima of CL. The measurements of e’(T) and tan 6 (T) were also carried out in the (ac) plane but sibilant anisotropy was not observed. In addition, it can be noted that the relative height of the two observed peaks varied from sample to sample, the one at the lower temperature always being higher. The magnitudes of the dielectric anomalies were closely related to the quality of the single crystal. Tbe complex shape of the anomalies suggests that on cooling the compound undergoes two SPT in this range, one at T,, = 240.7 K and the other at T,, = 240.2 K. Both transitions are of first order as confirmed by the temperature hysteresis (ALST, ‘si2.5 K).
crystal. The thermal ellipsoids of the nitrogen atoms
show centres of TEA cations.
J. ZALESKI et al.
1268
230
235
2‘0
2L5
T/K
Fig. 3. Temperature
dependence of the electric permittivity for (TEA), BiBCl,, along the b-axis.
On heating the t’(T) plot suggests only one SPT. This fact may be explained either by the presence of a metastable phase in this temperature range or by the fact that the second anomaly was diffused because of the breaking up of the single crystal during the first run through SPT on cooling. The DSC studies revealed only one reversible anomaly at about 242 K (on cooling) confirming the first order phase transition. The width of the observed thermal hysteresis is equal to 2 K. The estimated transition enthalpy and entropy are equal to 8 kJ mol-’ and 33 J Km’ mol-‘, respectively. Further extended analysis of the DSC data will be possible after completing the results for other tetraethylammonium halogenobismuthates and antimonates [ 141. The TEA cation possesses two stable conformations. They resemble a Greek cross (I) and a Nordic cross (II) when observed along the ? axis [18]. Both conformations were found in crystal structures, e.g. I in [15] and II in [16]. There are two orientations of
the TEA cations which are mirror images to each other, when superimposed. They differ mainly in the position of the c( carbon atoms. In most crystal structures of compounds with TEA cations at room temperature the cx carbon atoms are found to be disordered. In the case of (TEA),Bi,Cl,, it was not possible to localize the carbon atoms, which may indicate a more complicated disorder. This can be understood by taking into account the fact that in the sublattice of the big compact B&Cl& ions the TEA cations are arranged in a common space, motions of the cations being probably highly correlated and therefore much more complicated. The disorder of the TEA cations is realized by the reorientation of the cations themselves, by the rotation around the C-N axis (the ethyl group rotation), by the methyl group rotation, or in a combination of some or all of the above-mentioned motions. The NMR studies for TEA salts [17] showed that at room temperature all of the above-mentioned motions are present. On cooling they are consecutively frozen, firstly rotations of the cations around the zi axis, then the ethyl group rotations and, below about 120 K, the rotations of the methyl groups around the 3 axis. The freezing of some of these rotations is reflected in a complex sequence of dielectric anomalies of (TEA),Bi,Cl,, and other compounds with TEA cations [18]. The NMR studies were carried out on (TEA),ZnCl, , (TEA), CoCl, [ 181 and (TEA), SbF, [19]. The analysis of the results obtained based on theoretical values of the second moment of a proton NMR line [17] suggests that the observed phase transitions are associated mainly with the freezing of the reorientational movements of TEA cations (jump of a second moment from about 0.6 to 18 for (TEA)2 SbF,: and from about 2 to 18 for (TEA),CoCl,). In all the crystals studied the contribution of the motions of the anions has to be taken into account, as shown for (TEA)2SbF, [19]. In (TEA),Bi,Cl,,, however, the bulky rigid B&Cl& anions cannot reorientate, and therefore the transitions are presumably associated only with freezing of the motions of the cations. Acknowledgements-This work was supported by the Polish Academy of Sciences within project CPBP 01.12. REFERENCES
0
l210
0
_
-~-_f~-
Fig. 4. Temperature
2‘0
“-
4
dependence of tan S for (TEA),Bi,Cl,, along the b-axis.
1
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