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Vibrational spectrum of Hg2ReO5
SPECTROCHIMICA ACTA PART A
ELSEVIER
Spectrochimica Acta Part A 52 ( 1 9 9 6 ) 4 4 1 - 4 4 4
Vibrational spectrum of HgzReO5 E . J . B a r a n a'*, M . S . S c h r i e w e r - P 6 t t g e n b, W . J e i t s c h k o b ~Ouimica Inorgfinica (QUINOR), Faeultad de Ciencias Exactas, Universidad National de La Plata, C. Correo 962, 1900-La Plata, Argentina b Anorganisch-Chemisches lnstitut der Universitiit Miinster, Wilheim-Klemm-Strasse 8, D-48149 Miinster, Germato' Received 23 May 1995: accepted 26 August 1995
Abstract
The infrared and Raman spectra of the mercury perrhenate of empirical formula Hg2ReO 5 have been recorded and are briefly discussed. The results are consistent with recently reported structural data which show the presence of an infinite polycationic net containing Hg(I), Hg(II) and oxygen atoms, separated by distorted tetrahedral R e O 4 anions. Keywords: Infrared spectrum; Perrhenate vibrations; Raman spectrum
1. Introduction Different mercury oxorhenates were reported some years ago by Priou [1]; however, their structures and spectroscopic properties have not yet been investigated in detail. The recent determination of the structure of one of these materials (Hg2ReO5 [2]), prompted us to also investigate its spectroscopic properties.
ysis and X-ray diffractometry. The infrared spectra were recorded with a Bruker F T I R model 113 v instrument, with the powdered samples dispersed either in KBr or polyethylene pellets. The R a m a n spectra were obtained with a Bruker IFS 66 F T I R instrument provided with the F R A 106 R a m a n accessory. The samples were excited with the 1064 nm light of a N d : Y A G laser.
2. Experimental
3. Results and discussion
Samples of the light yellow c o m p o u n d Hg2ReO5 were prepared by annealing powdered mixtures of mercury(II) oxide and mercury(II) perrhenate in sealed silica tubes, as described earlier [2]. They were characterized by chemical anal* Corresponding author.
3. I. Structural characteristics Hg2ReO5 belongs to the triclinic space group P i (No. 2) with Z = 4. The polymeric structure is built up of 14-membered rings, condensed to puckered two-dimensionally infinite polycationic nets of composition (Hg2 + .2HgO),, separated from each other by R e O 4 anions [2].
0584-8539/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved S S D 1 0584-8539(95)01564-7
442
E.J. Baran et al. ,' Spectrochimica Acta Part A 52 (1996) 441 444
T e-
e-
l-
lObO
860
660
~00 [cm-~]
260
Fig. 1. Infrared spectrum of Hg2ReO 5.
The two structurally different oxygen atoms present in the polycationic layers are three coordinated, conforming to M 3 0 units. Each of these oxygen atoms is bonded to one Hg(I) and two Hg(II) atoms. 3.2. Vibrational spectrum The measured infrared and R a m a n spectra are respectively shown in Figs. 1 and 2. The exact band positions, together with the proposed vibrational assignments are shown in Table 1. As in the crystal lattice the ReO 4 anions are located on C~ sites [2]; the activation of all vibrational modes and the total removal of degeneracies are expected in both spectra [3]. However, despite the fact that the unit cell contains four formula units, the observed spectra are rather simple, pointing to the absence of important correlation field effects. This behavior can probably be explained by the relative "isolation" of the ReO 4 vibrators a m o n g the polycationic layers. It can be observed in the figures that the triply degenerate antisymmetric stretching vibration (v~)
of the ReO 4 ion is clearly resolved in the IR, whereas in the R a m a n spectrum one of its components is seen only as a very weak shoulder. The strongest R a m a n line corresponds, as expected [3,4], to the respective symmetric stretching mode (h), which appears as a very weak band in the infrared spectrum. The straightforward identification of the bending vibrations of the anion is more difficult. In solution, both the symmetric (v2) and the antisymmetric (v4) deformations occur at the same frequency [5]. In the solid state, they often lie very close together [3,6,7] and also an inversion of their relative positions is sometimes observed by comparison of IR and R a m a n data [4]. In the present case, an additional complication arises due to the probable presence of vibrations originating in the polycationic sheets, in the same vibrational range in which these bending modes are expected to lie. Notwithstanding, we have assigned the strong R a m a n line located at 336 cm ' (with a shoulder at its higher frequency side) to one of the expected v2 components. In the R a m a n spectrum of KReO4 this band lies at 335cm ' and in NaReO4 at
E.J. Baran et al. / Spectrochimica Acta Part A 52 (1996) 441 444
334 cm-~ [4]. However, the fact that the IR counterpart of this mode, which lies at the same frequency, appears as a medium intensity band, suggests that the observed bands are not totally " p u r e " v2 modes and are surely mixed to a certain extent with v4 components and O - H g motions. The symmetric bending modes of tetrahedral species are usually seen only as very weak bands in the IR spectra or are completely absent, but present appreciably intensity in the R a m a n spectra [3,4]. The band multiplet in the spectral range between 633 and 490 cm 1 is assigned to stretching vibrations mainly involving the oxygen atoms of the polycationic sheets. For M 3 0 groupings, such as that present in the Hg2ReO5 structure, in-plane stretching modes are expected to lie between 800 and 400 c m - J [8]. Corresponding out-of-plane modes may be located in the region between 350 and 120 c m - 1 [8]. It is interesting to mention that the mercury(II) oxides present strong IR absorptions in the same range (HgO (yellow)= 588, 480 cm 1; H g O ( r e d ) = 573, 475 cm 1) [9].
T nr
443
Table l A s s i g n m e n t o f the v i b r a t i o n a l s p e c t r u m o f H g 2 R e O 5 ( b a n d p o s i t i o n s in c m - ~) Infrared
Raman
Assignment
964 vw
964 vs
v~(ReO4 )
912 vs 887 s 870 s
909 m 895 sh 869 s
v~(ReO4)
633 592 555 521
605 vw 572 w
s w s w
v ( H g ~ O I (see text) 517 w 490 w
336 m
345 s h / 3 3 6 s
v2(ReO 4 )
318 m 305 m 283 w
305 sh 255 w
v4(ReO 4 ) + v ( H g ~ O )
187 s
176 s
v(Hg +
H g +)
Key: m . M e d i u m : sh, s h o u l d e r ; s, s t r o n g ; v, very.
In accordance with the noted expectations, the last band multiplet, located between 320 and 250 c m - ~, undoubtedly includes v4 components of the R e O 4 groups mixed with motions of the H g 3 0 units. Finally, the stretching mode of the H g - H g bonds of the mercurous ions is unambiguously identified at 187 cm ~ in the infrared spectrum and at 176 c m - ~ in the R a m a n spectrum. Besides, this vibration is found at 169 cm-~ in Hg2(NO3) 2 solutions [10]. The observation that most of the corresponding IR and R a m a n bands present identical or nearly identical frequency values is rather interesting, despite the fact that under the factor group Ci, corresponding to the space group P i , the R a m a n active vibrations are all Ag species whereas those active in the infrared are of Ao symmetry. This behavior is the final conclusive evidence for the absence of correlation field effects in the investigated lattice.
Acknowledgements I
1000
I
500
I
[cm-1
Fig. 2. R a m a n s p e c t r u m o f H g 2 R e O 5.
This work was supported by C O N I C E T and CIC-Provincia de Buenos Aires (Argentina) and
444
E.J. Baran et al. / Spectrochimica Acta Part A 52 (1996) 441 444
by t h e D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t a n d the Fondes der Chemischen Industrie (Germany).
References [1] R. Priou, Rev. Chim. Min6r., 15 (1978) 206. [2] M.S. Schriewer-P6ttgen and W. Jeitschko, Z. Anorg. Allg. Chem., 620 (1994) 1855. [3] A. Mfiller, E.J. Baran and R.O. Carter, Struct. Bonding, 26 (1976) 81.
[4] A. Miiller, N. Weinstock and E.J. Baran, An. Asoc. Quim. Argent., 64 (1976) 239. [5] R.H. Busey and O.L. Keller, Jr., J. Chem. Phys., 41 (1984) 215. [6] K. Ulbricht and H. Kriegsmann, Z. Anorg. Allg. Chem., 358 (1968) 193. [7] M.R. Mohamman and W.F. Sherman, J. Phys. C, 14 (1981) 283. [8] I.R. Beattie and T.R. Gilson, J. Chem. Soc. A, (1969) 2322. [9] N.T. McDevitt and W.L. Baun, Spectrochim. Acta, 20 (1964) 799. [10] H. Siebert, Anwendungen der Schwingungsspektroskopie in der Anorganischen Chemie, Springer, Berlin, 1966.
ELSEVIER
Spectrochimica Acta Part A 52 ( 1 9 9 6 ) 4 4 1 - 4 4 4
Vibrational spectrum of HgzReO5 E . J . B a r a n a'*, M . S . S c h r i e w e r - P 6 t t g e n b, W . J e i t s c h k o b ~Ouimica Inorgfinica (QUINOR), Faeultad de Ciencias Exactas, Universidad National de La Plata, C. Correo 962, 1900-La Plata, Argentina b Anorganisch-Chemisches lnstitut der Universitiit Miinster, Wilheim-Klemm-Strasse 8, D-48149 Miinster, Germato' Received 23 May 1995: accepted 26 August 1995
Abstract
The infrared and Raman spectra of the mercury perrhenate of empirical formula Hg2ReO 5 have been recorded and are briefly discussed. The results are consistent with recently reported structural data which show the presence of an infinite polycationic net containing Hg(I), Hg(II) and oxygen atoms, separated by distorted tetrahedral R e O 4 anions. Keywords: Infrared spectrum; Perrhenate vibrations; Raman spectrum
1. Introduction Different mercury oxorhenates were reported some years ago by Priou [1]; however, their structures and spectroscopic properties have not yet been investigated in detail. The recent determination of the structure of one of these materials (Hg2ReO5 [2]), prompted us to also investigate its spectroscopic properties.
ysis and X-ray diffractometry. The infrared spectra were recorded with a Bruker F T I R model 113 v instrument, with the powdered samples dispersed either in KBr or polyethylene pellets. The R a m a n spectra were obtained with a Bruker IFS 66 F T I R instrument provided with the F R A 106 R a m a n accessory. The samples were excited with the 1064 nm light of a N d : Y A G laser.
2. Experimental
3. Results and discussion
Samples of the light yellow c o m p o u n d Hg2ReO5 were prepared by annealing powdered mixtures of mercury(II) oxide and mercury(II) perrhenate in sealed silica tubes, as described earlier [2]. They were characterized by chemical anal* Corresponding author.
3. I. Structural characteristics Hg2ReO5 belongs to the triclinic space group P i (No. 2) with Z = 4. The polymeric structure is built up of 14-membered rings, condensed to puckered two-dimensionally infinite polycationic nets of composition (Hg2 + .2HgO),, separated from each other by R e O 4 anions [2].
0584-8539/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved S S D 1 0584-8539(95)01564-7
442
E.J. Baran et al. ,' Spectrochimica Acta Part A 52 (1996) 441 444
T e-
e-
l-
lObO
860
660
~00 [cm-~]
260
Fig. 1. Infrared spectrum of Hg2ReO 5.
The two structurally different oxygen atoms present in the polycationic layers are three coordinated, conforming to M 3 0 units. Each of these oxygen atoms is bonded to one Hg(I) and two Hg(II) atoms. 3.2. Vibrational spectrum The measured infrared and R a m a n spectra are respectively shown in Figs. 1 and 2. The exact band positions, together with the proposed vibrational assignments are shown in Table 1. As in the crystal lattice the ReO 4 anions are located on C~ sites [2]; the activation of all vibrational modes and the total removal of degeneracies are expected in both spectra [3]. However, despite the fact that the unit cell contains four formula units, the observed spectra are rather simple, pointing to the absence of important correlation field effects. This behavior can probably be explained by the relative "isolation" of the ReO 4 vibrators a m o n g the polycationic layers. It can be observed in the figures that the triply degenerate antisymmetric stretching vibration (v~)
of the ReO 4 ion is clearly resolved in the IR, whereas in the R a m a n spectrum one of its components is seen only as a very weak shoulder. The strongest R a m a n line corresponds, as expected [3,4], to the respective symmetric stretching mode (h), which appears as a very weak band in the infrared spectrum. The straightforward identification of the bending vibrations of the anion is more difficult. In solution, both the symmetric (v2) and the antisymmetric (v4) deformations occur at the same frequency [5]. In the solid state, they often lie very close together [3,6,7] and also an inversion of their relative positions is sometimes observed by comparison of IR and R a m a n data [4]. In the present case, an additional complication arises due to the probable presence of vibrations originating in the polycationic sheets, in the same vibrational range in which these bending modes are expected to lie. Notwithstanding, we have assigned the strong R a m a n line located at 336 cm ' (with a shoulder at its higher frequency side) to one of the expected v2 components. In the R a m a n spectrum of KReO4 this band lies at 335cm ' and in NaReO4 at
E.J. Baran et al. / Spectrochimica Acta Part A 52 (1996) 441 444
334 cm-~ [4]. However, the fact that the IR counterpart of this mode, which lies at the same frequency, appears as a medium intensity band, suggests that the observed bands are not totally " p u r e " v2 modes and are surely mixed to a certain extent with v4 components and O - H g motions. The symmetric bending modes of tetrahedral species are usually seen only as very weak bands in the IR spectra or are completely absent, but present appreciably intensity in the R a m a n spectra [3,4]. The band multiplet in the spectral range between 633 and 490 cm 1 is assigned to stretching vibrations mainly involving the oxygen atoms of the polycationic sheets. For M 3 0 groupings, such as that present in the Hg2ReO5 structure, in-plane stretching modes are expected to lie between 800 and 400 c m - J [8]. Corresponding out-of-plane modes may be located in the region between 350 and 120 c m - 1 [8]. It is interesting to mention that the mercury(II) oxides present strong IR absorptions in the same range (HgO (yellow)= 588, 480 cm 1; H g O ( r e d ) = 573, 475 cm 1) [9].
T nr
443
Table l A s s i g n m e n t o f the v i b r a t i o n a l s p e c t r u m o f H g 2 R e O 5 ( b a n d p o s i t i o n s in c m - ~) Infrared
Raman
Assignment
964 vw
964 vs
v~(ReO4 )
912 vs 887 s 870 s
909 m 895 sh 869 s
v~(ReO4)
633 592 555 521
605 vw 572 w
s w s w
v ( H g ~ O I (see text) 517 w 490 w
336 m
345 s h / 3 3 6 s
v2(ReO 4 )
318 m 305 m 283 w
305 sh 255 w
v4(ReO 4 ) + v ( H g ~ O )
187 s
176 s
v(Hg +
H g +)
Key: m . M e d i u m : sh, s h o u l d e r ; s, s t r o n g ; v, very.
In accordance with the noted expectations, the last band multiplet, located between 320 and 250 c m - ~, undoubtedly includes v4 components of the R e O 4 groups mixed with motions of the H g 3 0 units. Finally, the stretching mode of the H g - H g bonds of the mercurous ions is unambiguously identified at 187 cm ~ in the infrared spectrum and at 176 c m - ~ in the R a m a n spectrum. Besides, this vibration is found at 169 cm-~ in Hg2(NO3) 2 solutions [10]. The observation that most of the corresponding IR and R a m a n bands present identical or nearly identical frequency values is rather interesting, despite the fact that under the factor group Ci, corresponding to the space group P i , the R a m a n active vibrations are all Ag species whereas those active in the infrared are of Ao symmetry. This behavior is the final conclusive evidence for the absence of correlation field effects in the investigated lattice.
Acknowledgements I
1000
I
500
I
[cm-1
Fig. 2. R a m a n s p e c t r u m o f H g 2 R e O 5.
This work was supported by C O N I C E T and CIC-Provincia de Buenos Aires (Argentina) and
444
E.J. Baran et al. / Spectrochimica Acta Part A 52 (1996) 441 444
by t h e D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t a n d the Fondes der Chemischen Industrie (Germany).
References [1] R. Priou, Rev. Chim. Min6r., 15 (1978) 206. [2] M.S. Schriewer-P6ttgen and W. Jeitschko, Z. Anorg. Allg. Chem., 620 (1994) 1855. [3] A. Mfiller, E.J. Baran and R.O. Carter, Struct. Bonding, 26 (1976) 81.
[4] A. Miiller, N. Weinstock and E.J. Baran, An. Asoc. Quim. Argent., 64 (1976) 239. [5] R.H. Busey and O.L. Keller, Jr., J. Chem. Phys., 41 (1984) 215. [6] K. Ulbricht and H. Kriegsmann, Z. Anorg. Allg. Chem., 358 (1968) 193. [7] M.R. Mohamman and W.F. Sherman, J. Phys. C, 14 (1981) 283. [8] I.R. Beattie and T.R. Gilson, J. Chem. Soc. A, (1969) 2322. [9] N.T. McDevitt and W.L. Baun, Spectrochim. Acta, 20 (1964) 799. [10] H. Siebert, Anwendungen der Schwingungsspektroskopie in der Anorganischen Chemie, Springer, Berlin, 1966.