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The IR and Raman spectra of Te(OH)6. K2SO4
0020-0891/86$3.00+ 0.00
Infrared Phys. Vol. 26, No. 2, pp. 89-91, 1986
Printed in Great Britain
Pergamon Press Ltd
THE IR AND RAMAN
SPECTRA
OF Te(OH), . K,SO,
K. VISWANATHAN, V. U. NAYAR and G. ARULDHAS Department of Physics, University of Kerala, Kariavattom, Trivandrum 695 581, India (Received 24 September 1985)
Abstract-The IR and Raman spectra of potassium sulphate-tellurate [Te(OH),.K,SO,] have been recorded and analysed. It has been found that the two different anions coexist in the crystal almost independently. The SO, tetrahedron is found to be more distorted than the Te(OH), octahedron.
1. INTRODUCTION
Vibrational spectral studies of compounds containing tellurate have been reported by several authors.““’ Recently, vibrational spectra of different mixed oxides containing the TeO, group were studied and the frequencies corresponding to the TeO, octahedron were identified.(e6’ It is interesting to study the vibrational nature of the Te(OH), group when it is in coexistence with another anion in crystals. The IR and Raman spectra of such a compound, containing two different types of anions [Te(OH), . K,SO& is reported here. 2.
EXPERIMENTAL
The sample was prepared by the method explained by Zilber et al.“’ The Raman spectrum was recorded in a SPEX ‘Ramalog’ double monochromator model 1401. The Raman lines were obtained in the Stoke’s region of the 5145 A line of an Ar+ laser (Spectra Physics Model 165). The IR spectrum was recorded on a Perkin Elmer 283 spectrophotometer, with the sample as KBr pellets. 3.
FACTOR
GROUP
ANALYSIS
The crystal belongs to the triclinic system with space group Pi - C,’ .’ There are two different Ci positions [Te(l) and Te(2)]; all other atoms are in general positions. The Te(OH), octahedra belong to a number of sheets: (i) Sheets parallel to (OOl), c/2 apart, each sheet containing Te atoms of one site only [Te(l)]. The orientation of the octahedra changes from one site to another. As a consequence each sheet is built from octahedra which all have the same orientation, this orientation changes from one sheet to another. (ii) Sheets parallel to (OOl), (b + c)/2 apart, which include Te atoms occupying two sites [Te(l) and Te(2)]. (iii) Sheets parallel to (lOl), (a-b)/2 apart, which also include Te atoms of two sites. The SO, tetrahedra can be described as belonging to the same sheet directions, but alternating with the Te(OH), ones. The environment of the K atoms is octahedral. One of the K atoms is surrounded by three 0 atoms of a Te(2) octahedron and three atoms belonging to an SO, tetrahedron. The environment of the other atom is three 0 atoms of a Te(1) octahedron, one 0 atom of another Te(1) octahedron, one 0 atom of an SO, tetrahedron and one 0 atom of a Te(2) octahedron. The planes (101) and (Oli) contain a Te(OH), octahedron alternating with an SO, tetrahedron.“) The factor group analysis has been done with Te(OH), octahedra sited Ci and SO, at general positions, with the standard correlation method; (‘) 117 normal modes are predicted, which are distributed as follows:
where A, modes are Raman active and A, modes are IR active. 89
K.
90
VISWANATHAN et al.
Table
2
Ob*ervcd
Raman
frequencies and 1hetr assignments TeiOHI,. K-SO. IR
Assignmenr
3042 VW 3000 VW 2x30 VW
iloobr 2300 w
O-H
IIXOM 1203M
IZOOW
J (Te-O-H
II07 M 1086 vs IO7XS I076 S 9X6 VS
1060 Vbr 972 s
of
S
stretching
1
y:(X),)
Y,(SO,)
750
Sh 710Sh 6h6 W
637 s 616
640 vs 600 Sh
i,,SO,
590 w 526 M
585 vs 570 Sh
1,TeO,.
461 vs 450 vs
site group
356 vs 331 vs 329 vs 282 w 247 M 226 M 174w l62M 147M 138M 13ow 122W IISW 108W 104w 101 w 92 w 9ow 81 w 77 W
Factor group c; (Z = 2)
C,
4.
RESULTS
AND
1’)
nnd r,.TeO,
I’.so,
436 s
367 vs 365 vs
Table 1. Correlation of the 0, and Td free-ion groups to the factor erou~ C! through sites C, and C,, respectively
TeO,
654 vs
TeO, asymmetric 350 332 311 259 222
M s s w w
TeO, symmetric
bending bending
r,,TrO, Lattice modes
DISCUSSIONS
on the basis of the characteristic frequencies of the The observed frequencies are interpreted Te(OH), and SO, groups. The Te(OH), group consists of TeO, and hydrogenic vibrations. The octahedral TeO, group has the following vibrational modes: vi, v2 and rz (Raman active) and 12~ and vq (IR active). The vibration vg is inactive in both IR and Raman. The Te(OH), group retains its centre of symmetry in the crystal also (site symmetry C,). Since this group occupies a lower symmetry than the free-ion symmetry, an anisotropic crystal field is produced which removes the degeneracies of the normal modes. From Table 1 it can be seen that the v6 mode, which is inactive in both IR and Raman, has become IR active. The stretching and bending vibrations for compounds containing the TeO, group normally occur in the range of 550-750 and 350-450 cm ‘, respectively. (9)The very strong line observed at 654 cm-’ in Raman is assigned to the symmetric stretching vibration (v, ) of the TeO, group. Due to the strain produced by the crystalline field the inactive modes may also become active. (W The weak line observed at 666 cm ’ in IR may be due to the symmetric stretching of the TeO, group, which is forbidden in 1R. The doubly-degenerate asymmetric bending vibration (vq) of the SO, ion also occurs in the same region, an unambiguous assignment of these vibrations is difficult. The lines observed at 616 and 637 cm-’ may be due to these vibrations. In IR the v2 vibration of TeO,, which is forbidden, may appear only as a weak line. The very strong IR line at 640 cm ’ may therefore be due to the r4 vibration of SO,, which is IR active. The shoulder at 600 cm ’ is tentatively assigned to the v2 vibration of TeO,. The weak
IR and Raman
1
3100
I
2800
I
I
1250
1100
spectra
I
950
of Te(OH),.K,SO,
I
1
I
800
650
500
Wovenumber
Fig.
I. Raman Spectrum
91
(cm-’
I
350
1
200
I 50
)
of Te(OH),.
K?SO,.
Raman lines at 526 and 590 cm-’ and the strong IR band at 585 cm-‘, with a shoulder at 570 cm -‘, are due to the triply-degenerate asymmetric stretching mode (vj). The assignment of the very strong triplet (356, 365 and 376cm- ‘) in Raman to the asymmetric bending mode of TeO, is quite straightforward. However, only a medium-intensity line is observed at 350 cm-’ for this vibration in IR. The very strong doublet 329 and 332 cm-’ (Raman) and the strong lines 311 and 322 cm ’ (IR) are assigned to the triply-degenerate symmetric bending mode. The mode which is inactive in both IR and Raman for the TeO, group is observed as a weak line at 282 cm ’ (Raman). This is in agreement with Wilson’s rule (vg = fi vg). This vibration, which has become IR active in crystal, is observed at 259 cm-‘. The assignment of the internal modes of the SO, group is straightforward, and is given in Table 2. The degeneracies of the v2, v3 and vq modes are lifted in Raman. The very weak lines at 2830, 3000 and 3042 cm ’ in Raman and the broad line at 3 100 cm- ’ in IR may be assigned to the O-H stretching vibration. The in-plane bending vibration of Te-O-H is observed at 1180 and 1203 cm-’ in Raman and at 1200 cm-’ in IR. The identification of the out-of-plane bending vibration could not be achieved as it falls in the internal vibration region of the TeO, and SO, groups. The lines below 250cm-’ are assigned to external modes. The main feature of this structure is the coexistence of two different anions in the same crystal. As splitting due to the interaction between the two anions is not observed, it may be inferred that the anions are existing almost independently. The SO, tetrahedron seems to be more distorted since all of its degenerate modes are split. Acknowledgements-The authors are thankful K. Viswanathan is also thankful to Department support.
to Dr M. Kanakavelu, VSSC, Trivandrum, for recording the IR spectra. of Science and Technology, Government of India, New Delhi. for financial
REFERENCES M. Liegeois Duyckaerts and P. Tarte, Spectrochim. Acta 30A, 1771 (1974). A. F. Commit, H. E. Hoefdraad and G. Blasse, J. inorg. nut/. Chem. 34, 3401 (1972). G. Blasse. J. inorg. nucl. Chem. 37, 1347 (1975). M. Liegeois Duyckaerts. Spectrochim. Acta 31A, 1585 (1975). H. Roller and S. Kemmler Sack, Z. anorg. a&. Chem. 466, 103 (1980). E. J. Barron and I. L. Botto, Z. anovg. allg. Chem. 473, 189 (1981). R. Zilber, A. Durif and M. T. Averbuch-Pouchot, Acra crys/aNogr. 836, 2743 (1980). W. G. Fateley. F. R. Dollish, N. T. MC Devitt and F. F. Bentley, Infrared and Raman Selecrion Rulesfiw Molecular and Lattice Vibrations-The Correlation Method. Wiley, New York (1972). 9. R. Allman and W. Hasse, Inorg. Chem. 15, 804 (1976). 10. S. P. S. Porto and J. F. Scott, Phys. Rec. 157, 716 (1967). I. 2. 3. 4. 5. 6. 7. 8.
Infrared Phys. Vol. 26, No. 2, pp. 89-91, 1986
Printed in Great Britain
Pergamon Press Ltd
THE IR AND RAMAN
SPECTRA
OF Te(OH), . K,SO,
K. VISWANATHAN, V. U. NAYAR and G. ARULDHAS Department of Physics, University of Kerala, Kariavattom, Trivandrum 695 581, India (Received 24 September 1985)
Abstract-The IR and Raman spectra of potassium sulphate-tellurate [Te(OH),.K,SO,] have been recorded and analysed. It has been found that the two different anions coexist in the crystal almost independently. The SO, tetrahedron is found to be more distorted than the Te(OH), octahedron.
1. INTRODUCTION
Vibrational spectral studies of compounds containing tellurate have been reported by several authors.““’ Recently, vibrational spectra of different mixed oxides containing the TeO, group were studied and the frequencies corresponding to the TeO, octahedron were identified.(e6’ It is interesting to study the vibrational nature of the Te(OH), group when it is in coexistence with another anion in crystals. The IR and Raman spectra of such a compound, containing two different types of anions [Te(OH), . K,SO& is reported here. 2.
EXPERIMENTAL
The sample was prepared by the method explained by Zilber et al.“’ The Raman spectrum was recorded in a SPEX ‘Ramalog’ double monochromator model 1401. The Raman lines were obtained in the Stoke’s region of the 5145 A line of an Ar+ laser (Spectra Physics Model 165). The IR spectrum was recorded on a Perkin Elmer 283 spectrophotometer, with the sample as KBr pellets. 3.
FACTOR
GROUP
ANALYSIS
The crystal belongs to the triclinic system with space group Pi - C,’ .’ There are two different Ci positions [Te(l) and Te(2)]; all other atoms are in general positions. The Te(OH), octahedra belong to a number of sheets: (i) Sheets parallel to (OOl), c/2 apart, each sheet containing Te atoms of one site only [Te(l)]. The orientation of the octahedra changes from one site to another. As a consequence each sheet is built from octahedra which all have the same orientation, this orientation changes from one sheet to another. (ii) Sheets parallel to (OOl), (b + c)/2 apart, which include Te atoms occupying two sites [Te(l) and Te(2)]. (iii) Sheets parallel to (lOl), (a-b)/2 apart, which also include Te atoms of two sites. The SO, tetrahedra can be described as belonging to the same sheet directions, but alternating with the Te(OH), ones. The environment of the K atoms is octahedral. One of the K atoms is surrounded by three 0 atoms of a Te(2) octahedron and three atoms belonging to an SO, tetrahedron. The environment of the other atom is three 0 atoms of a Te(1) octahedron, one 0 atom of another Te(1) octahedron, one 0 atom of an SO, tetrahedron and one 0 atom of a Te(2) octahedron. The planes (101) and (Oli) contain a Te(OH), octahedron alternating with an SO, tetrahedron.“) The factor group analysis has been done with Te(OH), octahedra sited Ci and SO, at general positions, with the standard correlation method; (‘) 117 normal modes are predicted, which are distributed as follows:
where A, modes are Raman active and A, modes are IR active. 89
K.
90
VISWANATHAN et al.
Table
2
Ob*ervcd
Raman
frequencies and 1hetr assignments TeiOHI,. K-SO. IR
Assignmenr
3042 VW 3000 VW 2x30 VW
iloobr 2300 w
O-H
IIXOM 1203M
IZOOW
J (Te-O-H
II07 M 1086 vs IO7XS I076 S 9X6 VS
1060 Vbr 972 s
of
S
stretching
1
y:(X),)
Y,(SO,)
750
Sh 710Sh 6h6 W
637 s 616
640 vs 600 Sh
i,,SO,
590 w 526 M
585 vs 570 Sh
1,TeO,.
461 vs 450 vs
site group
356 vs 331 vs 329 vs 282 w 247 M 226 M 174w l62M 147M 138M 13ow 122W IISW 108W 104w 101 w 92 w 9ow 81 w 77 W
Factor group c; (Z = 2)
C,
4.
RESULTS
AND
1’)
nnd r,.TeO,
I’.so,
436 s
367 vs 365 vs
Table 1. Correlation of the 0, and Td free-ion groups to the factor erou~ C! through sites C, and C,, respectively
TeO,
654 vs
TeO, asymmetric 350 332 311 259 222
M s s w w
TeO, symmetric
bending bending
r,,TrO, Lattice modes
DISCUSSIONS
on the basis of the characteristic frequencies of the The observed frequencies are interpreted Te(OH), and SO, groups. The Te(OH), group consists of TeO, and hydrogenic vibrations. The octahedral TeO, group has the following vibrational modes: vi, v2 and rz (Raman active) and 12~ and vq (IR active). The vibration vg is inactive in both IR and Raman. The Te(OH), group retains its centre of symmetry in the crystal also (site symmetry C,). Since this group occupies a lower symmetry than the free-ion symmetry, an anisotropic crystal field is produced which removes the degeneracies of the normal modes. From Table 1 it can be seen that the v6 mode, which is inactive in both IR and Raman, has become IR active. The stretching and bending vibrations for compounds containing the TeO, group normally occur in the range of 550-750 and 350-450 cm ‘, respectively. (9)The very strong line observed at 654 cm-’ in Raman is assigned to the symmetric stretching vibration (v, ) of the TeO, group. Due to the strain produced by the crystalline field the inactive modes may also become active. (W The weak line observed at 666 cm ’ in IR may be due to the symmetric stretching of the TeO, group, which is forbidden in 1R. The doubly-degenerate asymmetric bending vibration (vq) of the SO, ion also occurs in the same region, an unambiguous assignment of these vibrations is difficult. The lines observed at 616 and 637 cm-’ may be due to these vibrations. In IR the v2 vibration of TeO,, which is forbidden, may appear only as a weak line. The very strong IR line at 640 cm ’ may therefore be due to the r4 vibration of SO,, which is IR active. The shoulder at 600 cm ’ is tentatively assigned to the v2 vibration of TeO,. The weak
IR and Raman
1
3100
I
2800
I
I
1250
1100
spectra
I
950
of Te(OH),.K,SO,
I
1
I
800
650
500
Wovenumber
Fig.
I. Raman Spectrum
91
(cm-’
I
350
1
200
I 50
)
of Te(OH),.
K?SO,.
Raman lines at 526 and 590 cm-’ and the strong IR band at 585 cm-‘, with a shoulder at 570 cm -‘, are due to the triply-degenerate asymmetric stretching mode (vj). The assignment of the very strong triplet (356, 365 and 376cm- ‘) in Raman to the asymmetric bending mode of TeO, is quite straightforward. However, only a medium-intensity line is observed at 350 cm-’ for this vibration in IR. The very strong doublet 329 and 332 cm-’ (Raman) and the strong lines 311 and 322 cm ’ (IR) are assigned to the triply-degenerate symmetric bending mode. The mode which is inactive in both IR and Raman for the TeO, group is observed as a weak line at 282 cm ’ (Raman). This is in agreement with Wilson’s rule (vg = fi vg). This vibration, which has become IR active in crystal, is observed at 259 cm-‘. The assignment of the internal modes of the SO, group is straightforward, and is given in Table 2. The degeneracies of the v2, v3 and vq modes are lifted in Raman. The very weak lines at 2830, 3000 and 3042 cm ’ in Raman and the broad line at 3 100 cm- ’ in IR may be assigned to the O-H stretching vibration. The in-plane bending vibration of Te-O-H is observed at 1180 and 1203 cm-’ in Raman and at 1200 cm-’ in IR. The identification of the out-of-plane bending vibration could not be achieved as it falls in the internal vibration region of the TeO, and SO, groups. The lines below 250cm-’ are assigned to external modes. The main feature of this structure is the coexistence of two different anions in the same crystal. As splitting due to the interaction between the two anions is not observed, it may be inferred that the anions are existing almost independently. The SO, tetrahedron seems to be more distorted since all of its degenerate modes are split. Acknowledgements-The authors are thankful K. Viswanathan is also thankful to Department support.
to Dr M. Kanakavelu, VSSC, Trivandrum, for recording the IR spectra. of Science and Technology, Government of India, New Delhi. for financial
REFERENCES M. Liegeois Duyckaerts and P. Tarte, Spectrochim. Acta 30A, 1771 (1974). A. F. Commit, H. E. Hoefdraad and G. Blasse, J. inorg. nut/. Chem. 34, 3401 (1972). G. Blasse. J. inorg. nucl. Chem. 37, 1347 (1975). M. Liegeois Duyckaerts. Spectrochim. Acta 31A, 1585 (1975). H. Roller and S. Kemmler Sack, Z. anorg. a&. Chem. 466, 103 (1980). E. J. Barron and I. L. Botto, Z. anovg. allg. Chem. 473, 189 (1981). R. Zilber, A. Durif and M. T. Averbuch-Pouchot, Acra crys/aNogr. 836, 2743 (1980). W. G. Fateley. F. R. Dollish, N. T. MC Devitt and F. F. Bentley, Infrared and Raman Selecrion Rulesfiw Molecular and Lattice Vibrations-The Correlation Method. Wiley, New York (1972). 9. R. Allman and W. Hasse, Inorg. Chem. 15, 804 (1976). 10. S. P. S. Porto and J. F. Scott, Phys. Rec. 157, 716 (1967). I. 2. 3. 4. 5. 6. 7. 8.