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Single-crystal Raman spectra of [(C2H5)4N]2ZnCl4 and [(CH3)4N]2ZnCl4
Spectrochimia
Acta, Vol. 33.4, pp. 351 to 360. Pergamon Press 1977. Printed in Northern Ireland
Single-crystal
Raman spectra of [(C2H&N],ZnCl, WHd.aN,ZnCb
and
M. SCROCCO Laboratorio di Metodologie Avanzate Inorganiche de1 Consiglio Nazionale delle Ricerche-Roma (Receiued 15 April 1976) Abstract-The single crystal Raman and i.r. spectra of [(C2H5),N12ZnC14 and [(CH3),N]2ZnCl, have been examined and the bands assi,$;ed to the appropriate modes predicted by a factor group analysis for the space group D4,,15 and D2,, respectively. Polarized far-i.r. reflectance spectra, associated with the vibrations of the tetrahedral MX,-’ ion, for oriented single crystal of [(C2H5)4N]2ZnC14 are reported. RESULTS
In this note we report a single crystal analysis of the phonon spectra of two classes of substances: [(C,H,),N],Zn?$ belonging to the space group [(CH,),N],ZnX, (X = P4Jnmc (D4,, 1, and belonging to the space Cl, Br, I), group Pnma (D2,,16). These crystals are of interest because they contain the ZnX,-’ ions in the form of distorted tetrahedra, this site, of D,, symmetry, being readily substituted by a transition metal ion. These doped crystals are useful for single crystal studies of low energy electronic transitions. To this en& the present study completes investigation of the phonon spectra of these crystalline matrices also in the cationic region, results for the anionic region of isomorphous substances being reported in [ 1,2]. EXPERIMENTAL
Large single crystals of (Et,N),ZnCl, were obtained slowly adding an absolute ethanol solution of ZnCl, to an excess of ethanol solution of Et,NCl and allowing a slow evaporation of the solution in a dry box. Crystal of (Me,N)?ZnCl, were grown by evaporation, at room temperature, of aqueous solutions containing the stoichiometric proportions of N(CH,),Cl and ZnCl,. In the Raman experiments a Jarrell-Ash 25-300 spectrometer mounted with a Coherent Radiation ion Argon laser was used. The exciting lines used were the 5145 and 4880 A lines. Crystallographic axes were determined from Weissenberg and procession photographs. The i.r. spectra were recorded with a PerkinElmer 180 apparatus extended to the far i.r. (until 40 cm-‘). Reflectance spectra were recorded on a Beckman-RIIC FS 7RF reflectance module with an angle of incidence of ca. 12”.
(a) [(C,H,),NJ,ZnCl,. The crystal structure of (Et,N),ZnCl, is isomorphous with that reported by STUCKY et al. [3] for (Et,N),CoCl, and NiCl,-’ analogues and assigned as belonging to the space group P4,/nmc (D4,,15). In this approximation, the reported probable positions of atoms in the unit cell are: Zn atom in set 2(b) with DZd symmetry, N atoms in set 4(d) with Czv symmetry and Cl atoms in set S(g) with C, symmetry. The carbon atoms of the cation are disordered between two possible sets of positions. The two orientations possible for tetrahetilammonium ions configurations, and a “trans” arare “swastika” rangement in which the ethyl carbon atoms lie on a mirror plane C, (set 8(g)). The positions of the two hydrogen atom classes of the ethyl group are indeterminate and we have assumed they form two l(h) sets. The mirror planes C, are plane uU. Owing to this structural complexity, the number and classes of Raman and i.r. modes under the selection rules for the primitive unit cell are derived from a factor group analysis [4] and reported in Table 1. The tensor associated with the phonon species belonging to the D,, space group and Raman active (A,, Blgr Bzg, E,), are:
357
E,,X=
... I I .
.
.
e
e; .
E,,Y=
. . _e I
. . .
_e . . I
358
M. SCROCCO Table
1. Factor group analysis of (EtdN),ZnCI, with space group D4,,r5
D4h
ni
T
Al,
13 9 14 9 24 9 14 9 13 24
1
A% B 18 B 2s -% A,, A zu B lu B zu EU
T’
R
2 2 1 3 1
3 1
1 2
1 1
2
3
Table 2. Raman data for (Et4N)2ZnC& as a single crystal with assignments of the vibrational modes
ni’ 12 7 12 8 18 8 12 7 12 18
AI,
Raman inact. Raman Raman Raman inact. ix. inact. inact. i.r.
139 278
390
A,,
B 2.
E,
E,
130 140 (279)
129 134 275 281
388 470 661
389 471 665 898
380 388 468 895
1011
1013 1036
1037 1072
1072 1080 1300 1359 1444
The standard notations [5] of type k(ij)q are used throughout this paper to indicate, in the Raman measurements, the geometrical arrangements of the incident and scattered light polarizations of the incident and scattered propagation directions. The geometries used are: Z(XX) Y; Z( YY)X; X(ZZ) Y Z(YX)Y; Z(XY)X; Z(XZ) Y; Z( YZ)X;
B2,
663
ni =Total number of modes; T= Acoustic modes; T’= Translatory lattice modes; R = Rotatory lattice modes; ni’ = number of internal modes.
AI, +B,,
BI,
110 129
X( YY)Z
1450 1461 1468 2892
2947
2948
2990
vibrational
2993
region
with:
A,,+Bi,=92,96,
X( YZ)Y X( YZ) Y
B,,=94,97, E, =93,171
Table 3. Infrared Sample
enclosed
3026 2997 2986 2957
m vs vs s
1191 1130 1087 1042
vs w s us
2895 *2866 *2760 1480 1473 1468 1460 1409 1380 1358
m w w s us us vs s mw mw
1016 *955 897 890 832 795 792 472 387 291 274
us w w w w vs vs w w vs us
*Combination
bands;
L = lattice
170cm-‘: 171 cm-‘; cm-‘.
The single-crystal i.r. spectra in reflectance brought to light only the vibrations of the ZnCl,-* ion, which fall in the far i.r. Consequently, bands in the mid-i.r. reported in Table 3 have been obtained
spectrum
in Csl discs
2948 2985 2993 3020
3019
ZnBr,-’
The observations in all three directions just described lead to the tentative assignment of the Raman lines reported in Table 2. A parallel study has been done on (Et,N&ZnBr, which shows a different spectrum only in the
1360 1448 1461 1468
1440
of (Et,N),ZnCl, Far i.r. reflectance A 2u
El4
280 124
270 120
69 L
modes.
spectrum
63 L
Single-crystal Raman spectra of [(C2H&N]rZrQ
359
and [(CH,),N12ZnC14
Table 4. Factor group analysis of [(CH,),Nl,ZnCl, complex with space group Dzh16 D 2h
ai
T
A, B Is2 B 2g B 38 AU B lu B2u B 3u
17 13 17 13 13 17 13 17
4 2 4 2 2 3 1 3
T’
R
4’
1 1 1
2 4 2 4 4 2 4 2
11 Raman 7 Raman 11 Raman 7 Raman 7 inact. 11 i.r. 7 i.r. 11 i.r.
ni = Total number of modes; T = Acoustic modes; T’ = Translatory lattice modes; R = Rotatory lattice modes; ni’ = number of internal modes. I 300
I
I
I
200
100
50
Table 5. Raman data for [(CH3),N12ZnC14 as a single crystal with assignment of the vibrational modes
cni'
1?g. 1. Reflectance spectrum of [(CzH&N]rZnCl,. from CsI discs. Figure 1 reports the polarized single-crystal spectra (in reflectance) parallel and perpendicular to c axis which allow the assignment (Table 3) of the observed bands to the two i.r. active modes Ar,(ll,) and E,(I,). (b) [(CH,),N],ZnCI,. The space group of this crystal, reported by MOROSIN and LINGAFEL-~ER where all atoms are in the [6], is D2,,r6 @ma), position 4(c) except: Cl(2), C(3) and C(6) which are in the 8(d) position. The hydrogen atom positions of the methyl group are excluded from this atomic description and in the following we have assumed them to be in position 8(d). The mirror plane C, is the plane uzl.. The predicted Raman and i.r. modes of the crystal primitive unit cell, derived from factor group analysis [4], are presented in Table 4. The Raman active uhonons are associated with the following tensors:
*
.
.
.
e .
e
.
.
B Ig
B%
B%
113 127 274 456 (736) 753 950
115 128 276 459
115 128 276 458
1450 2923 2954 2981 3025
1453
113 127 275 456 (731) 754 950 (955) 1450 2923
A,
753 949
2981 3025
3026
753 949 1453
3026
1412(A,, Bsg), 2813(A,), 2844(A,), associated with combination bands. The i.r. spectrum of powdered samples as CsI discs recorded in the range 3200-2_50cm-’ and single crystal reflectance spectrum recorded in the range 300-50 cm-’ are reported in Table 6. In contrast the far i.r. region, no reflectance spectrum could be observed in the mid-i.r. region. Owing to the poorer quality and smaller size of the crystalline samples, complete polarized reflectance spectra Table 6. Infrared spectrum of (Me4N)2ZnC14 Sample enclosed in Csl discs
The crystal has been lowing geometries: A, Z(XX)Y; Z( YX)Y; Bh B zg Z(XZ)Y; B 3g Z(YZ)Y; The tentative lines is reported also observed
examined Z( YY)X; Z(XY)X; Z(XZ)X; Z(YZ)X;
under
the fol-
Y(ZZ)X Y(XY)X Y(XZ)X Y(ZY)X
assignment of the observed Raman in Table 5. Some weach lines are in the positions: 1174(A,, BZg),
3036 2967 2932 2833 2765 *2598 1489 1455 1422 1294
s m w w w w US s s m
* Combination
*1179 *1129 *lo76 1038 951 917 470 454 292 272
Far i.r. reflectance spectrum
w uw uw w s m UW w s s
bands; L = lattice modes.
272 255 127 120 63 L 48 L
M. SCROCCO
r
jMpLN,lZnC'L
could not be recorded for reflectance spectrum without ported in Fig. 2.
(Me,N),ZnCl,. polarization
The is re-
BIBLIOGRAPHY
[l] I. R. BEATTIE, T. R. GILSON and G. A. OZIN, J. Chem. Sot. (A), 534 (1969). [2] J. T. R. DUNSMUIRand A. P. LANE, J. Chem. Sot. (A), 404 (1971). [3] G. D. STUCKY, J. B. FOLKERS and T. J. KINSTENMACHER, Acta Cryst. 23, 1064 (1967). [4] D. M. ADAMS and D. C. NEWTON. Tables for Factor Group Analysis. Beckman, RIIC, London (1970). [5] T. C. DAMEN, S. P. S. PORTO and B. TELL, Phys. Rev., 142, 570 (1966). [6] B. MOROSIN and E. C. LINGAFELTER,Acra Crysr. 12, 611 (1959).
\ i Ar r\, ::;
I
350
250
150
50
cm“
Fig. 2. Reflectance spectrum of [(CH&N],ZnCI,.
Acta, Vol. 33.4, pp. 351 to 360. Pergamon Press 1977. Printed in Northern Ireland
Single-crystal
Raman spectra of [(C2H&N],ZnCl, WHd.aN,ZnCb
and
M. SCROCCO Laboratorio di Metodologie Avanzate Inorganiche de1 Consiglio Nazionale delle Ricerche-Roma (Receiued 15 April 1976) Abstract-The single crystal Raman and i.r. spectra of [(C2H5),N12ZnC14 and [(CH3),N]2ZnCl, have been examined and the bands assi,$;ed to the appropriate modes predicted by a factor group analysis for the space group D4,,15 and D2,, respectively. Polarized far-i.r. reflectance spectra, associated with the vibrations of the tetrahedral MX,-’ ion, for oriented single crystal of [(C2H5)4N]2ZnC14 are reported. RESULTS
In this note we report a single crystal analysis of the phonon spectra of two classes of substances: [(C,H,),N],Zn?$ belonging to the space group [(CH,),N],ZnX, (X = P4Jnmc (D4,, 1, and belonging to the space Cl, Br, I), group Pnma (D2,,16). These crystals are of interest because they contain the ZnX,-’ ions in the form of distorted tetrahedra, this site, of D,, symmetry, being readily substituted by a transition metal ion. These doped crystals are useful for single crystal studies of low energy electronic transitions. To this en& the present study completes investigation of the phonon spectra of these crystalline matrices also in the cationic region, results for the anionic region of isomorphous substances being reported in [ 1,2]. EXPERIMENTAL
Large single crystals of (Et,N),ZnCl, were obtained slowly adding an absolute ethanol solution of ZnCl, to an excess of ethanol solution of Et,NCl and allowing a slow evaporation of the solution in a dry box. Crystal of (Me,N)?ZnCl, were grown by evaporation, at room temperature, of aqueous solutions containing the stoichiometric proportions of N(CH,),Cl and ZnCl,. In the Raman experiments a Jarrell-Ash 25-300 spectrometer mounted with a Coherent Radiation ion Argon laser was used. The exciting lines used were the 5145 and 4880 A lines. Crystallographic axes were determined from Weissenberg and procession photographs. The i.r. spectra were recorded with a PerkinElmer 180 apparatus extended to the far i.r. (until 40 cm-‘). Reflectance spectra were recorded on a Beckman-RIIC FS 7RF reflectance module with an angle of incidence of ca. 12”.
(a) [(C,H,),NJ,ZnCl,. The crystal structure of (Et,N),ZnCl, is isomorphous with that reported by STUCKY et al. [3] for (Et,N),CoCl, and NiCl,-’ analogues and assigned as belonging to the space group P4,/nmc (D4,,15). In this approximation, the reported probable positions of atoms in the unit cell are: Zn atom in set 2(b) with DZd symmetry, N atoms in set 4(d) with Czv symmetry and Cl atoms in set S(g) with C, symmetry. The carbon atoms of the cation are disordered between two possible sets of positions. The two orientations possible for tetrahetilammonium ions configurations, and a “trans” arare “swastika” rangement in which the ethyl carbon atoms lie on a mirror plane C, (set 8(g)). The positions of the two hydrogen atom classes of the ethyl group are indeterminate and we have assumed they form two l(h) sets. The mirror planes C, are plane uU. Owing to this structural complexity, the number and classes of Raman and i.r. modes under the selection rules for the primitive unit cell are derived from a factor group analysis [4] and reported in Table 1. The tensor associated with the phonon species belonging to the D,, space group and Raman active (A,, Blgr Bzg, E,), are:
357
E,,X=
... I I .
.
.
e
e; .
E,,Y=
. . _e I
. . .
_e . . I
358
M. SCROCCO Table
1. Factor group analysis of (EtdN),ZnCI, with space group D4,,r5
D4h
ni
T
Al,
13 9 14 9 24 9 14 9 13 24
1
A% B 18 B 2s -% A,, A zu B lu B zu EU
T’
R
2 2 1 3 1
3 1
1 2
1 1
2
3
Table 2. Raman data for (Et4N)2ZnC& as a single crystal with assignments of the vibrational modes
ni’ 12 7 12 8 18 8 12 7 12 18
AI,
Raman inact. Raman Raman Raman inact. ix. inact. inact. i.r.
139 278
390
A,,
B 2.
E,
E,
130 140 (279)
129 134 275 281
388 470 661
389 471 665 898
380 388 468 895
1011
1013 1036
1037 1072
1072 1080 1300 1359 1444
The standard notations [5] of type k(ij)q are used throughout this paper to indicate, in the Raman measurements, the geometrical arrangements of the incident and scattered light polarizations of the incident and scattered propagation directions. The geometries used are: Z(XX) Y; Z( YY)X; X(ZZ) Y Z(YX)Y; Z(XY)X; Z(XZ) Y; Z( YZ)X;
B2,
663
ni =Total number of modes; T= Acoustic modes; T’= Translatory lattice modes; R = Rotatory lattice modes; ni’ = number of internal modes.
AI, +B,,
BI,
110 129
X( YY)Z
1450 1461 1468 2892
2947
2948
2990
vibrational
2993
region
with:
A,,+Bi,=92,96,
X( YZ)Y X( YZ) Y
B,,=94,97, E, =93,171
Table 3. Infrared Sample
enclosed
3026 2997 2986 2957
m vs vs s
1191 1130 1087 1042
vs w s us
2895 *2866 *2760 1480 1473 1468 1460 1409 1380 1358
m w w s us us vs s mw mw
1016 *955 897 890 832 795 792 472 387 291 274
us w w w w vs vs w w vs us
*Combination
bands;
L = lattice
170cm-‘: 171 cm-‘; cm-‘.
The single-crystal i.r. spectra in reflectance brought to light only the vibrations of the ZnCl,-* ion, which fall in the far i.r. Consequently, bands in the mid-i.r. reported in Table 3 have been obtained
spectrum
in Csl discs
2948 2985 2993 3020
3019
ZnBr,-’
The observations in all three directions just described lead to the tentative assignment of the Raman lines reported in Table 2. A parallel study has been done on (Et,N&ZnBr, which shows a different spectrum only in the
1360 1448 1461 1468
1440
of (Et,N),ZnCl, Far i.r. reflectance A 2u
El4
280 124
270 120
69 L
modes.
spectrum
63 L
Single-crystal Raman spectra of [(C2H&N]rZrQ
359
and [(CH,),N12ZnC14
Table 4. Factor group analysis of [(CH,),Nl,ZnCl, complex with space group Dzh16 D 2h
ai
T
A, B Is2 B 2g B 38 AU B lu B2u B 3u
17 13 17 13 13 17 13 17
4 2 4 2 2 3 1 3
T’
R
4’
1 1 1
2 4 2 4 4 2 4 2
11 Raman 7 Raman 11 Raman 7 Raman 7 inact. 11 i.r. 7 i.r. 11 i.r.
ni = Total number of modes; T = Acoustic modes; T’ = Translatory lattice modes; R = Rotatory lattice modes; ni’ = number of internal modes. I 300
I
I
I
200
100
50
Table 5. Raman data for [(CH3),N12ZnC14 as a single crystal with assignment of the vibrational modes
cni'
1?g. 1. Reflectance spectrum of [(CzH&N]rZnCl,. from CsI discs. Figure 1 reports the polarized single-crystal spectra (in reflectance) parallel and perpendicular to c axis which allow the assignment (Table 3) of the observed bands to the two i.r. active modes Ar,(ll,) and E,(I,). (b) [(CH,),N],ZnCI,. The space group of this crystal, reported by MOROSIN and LINGAFEL-~ER where all atoms are in the [6], is D2,,r6 @ma), position 4(c) except: Cl(2), C(3) and C(6) which are in the 8(d) position. The hydrogen atom positions of the methyl group are excluded from this atomic description and in the following we have assumed them to be in position 8(d). The mirror plane C, is the plane uzl.. The predicted Raman and i.r. modes of the crystal primitive unit cell, derived from factor group analysis [4], are presented in Table 4. The Raman active uhonons are associated with the following tensors:
*
.
.
.
e .
e
.
.
B Ig
B%
B%
113 127 274 456 (736) 753 950
115 128 276 459
115 128 276 458
1450 2923 2954 2981 3025
1453
113 127 275 456 (731) 754 950 (955) 1450 2923
A,
753 949
2981 3025
3026
753 949 1453
3026
1412(A,, Bsg), 2813(A,), 2844(A,), associated with combination bands. The i.r. spectrum of powdered samples as CsI discs recorded in the range 3200-2_50cm-’ and single crystal reflectance spectrum recorded in the range 300-50 cm-’ are reported in Table 6. In contrast the far i.r. region, no reflectance spectrum could be observed in the mid-i.r. region. Owing to the poorer quality and smaller size of the crystalline samples, complete polarized reflectance spectra Table 6. Infrared spectrum of (Me4N)2ZnC14 Sample enclosed in Csl discs
The crystal has been lowing geometries: A, Z(XX)Y; Z( YX)Y; Bh B zg Z(XZ)Y; B 3g Z(YZ)Y; The tentative lines is reported also observed
examined Z( YY)X; Z(XY)X; Z(XZ)X; Z(YZ)X;
under
the fol-
Y(ZZ)X Y(XY)X Y(XZ)X Y(ZY)X
assignment of the observed Raman in Table 5. Some weach lines are in the positions: 1174(A,, BZg),
3036 2967 2932 2833 2765 *2598 1489 1455 1422 1294
s m w w w w US s s m
* Combination
*1179 *1129 *lo76 1038 951 917 470 454 292 272
Far i.r. reflectance spectrum
w uw uw w s m UW w s s
bands; L = lattice modes.
272 255 127 120 63 L 48 L
M. SCROCCO
r
jMpLN,lZnC'L
could not be recorded for reflectance spectrum without ported in Fig. 2.
(Me,N),ZnCl,. polarization
The is re-
BIBLIOGRAPHY
[l] I. R. BEATTIE, T. R. GILSON and G. A. OZIN, J. Chem. Sot. (A), 534 (1969). [2] J. T. R. DUNSMUIRand A. P. LANE, J. Chem. Sot. (A), 404 (1971). [3] G. D. STUCKY, J. B. FOLKERS and T. J. KINSTENMACHER, Acta Cryst. 23, 1064 (1967). [4] D. M. ADAMS and D. C. NEWTON. Tables for Factor Group Analysis. Beckman, RIIC, London (1970). [5] T. C. DAMEN, S. P. S. PORTO and B. TELL, Phys. Rev., 142, 570 (1966). [6] B. MOROSIN and E. C. LINGAFELTER,Acra Crysr. 12, 611 (1959).
\ i Ar r\, ::;
I
350
250
150
50
cm“
Fig. 2. Reflectance spectrum of [(CH&N],ZnCI,.