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Vibrational spectra of bis(halomercurio)methanes CH2(HgX)2 (X Cl, Br and I) in poly- and monocrystalline states
Journalof MolecularStructure, ElsevierSciencePublishersB.V.,
143(1986)155-158 Amsterdam -PrintedinTheNetherlands
155
VIBRATIONAL SPECTRA OF BIS(HALOMERCURIO)MBTHANES CH2(HgX)2 (X = Cl, Br AND I) IN POLY- AND MONOCRYSTALLINE STATES* D.K. BREITINGER and W. KRESS Institute of Inorganic Chemistry, University of Erlangen-Numberg, Egerlandstrasse 1, D-8520 Erlangen (F.R.G.)
ABSTRACT
Vibrational spectraofpolycrystalline bis(chloromercurio)methane CH2(HgC1)2 (space group Pnma, Z= 4), and of the deuterated analogue, as representatives of the bis(halomercurio)methanes, arepreliminarily assigned. Low-temperature Raman and IR spectra of CHZ(HgC1)2 reveal correlation splittings between gandu species, andpartly within the sets of gandu modes, as predicted by unit-cell group analysis. Single-crystal Raman studies notonlyconfirm the suggested assignments but are also the only method to unequivocally assign some bands. The limitations oftheapplicability of unit-cellgroupanalysis in the present case are discussed. INTRODUCTION As part of structural [I] and extensive spectrometric (multinuclear NMR, vibrational, UV) [2] investigations of anionomercuriomethanes CH4_n(HgX), (1 =n=4)
thevibrational
spectra of bis(anionomerc-
urio)methanes CH2(HgX)2 (X = Cl, Br and I; CN, SCN and OAc) havebeen studied [31. Raman and IR spectra of powders of the compounds with X = Cl, Br and I, and of deuterated analogues, combined with polarization data for solutions, allow most of the expected and observed fundamentals tobe reliably assigned. Solutions of specific problems and deeper insight into details ofthe spectra are reached with lowtemperature RamanandIR
spectra of polycrystalline samples and with
single-crystal Raman spectra, which will be discussed here. RESULTS AND DISCUSSION Frequencies and preliminary assignments, based partlyonpolarization data for solutions in several solvents, for CH2(HgC1)2 as representative of the series ofbis(halomercurio)methanes,
together with
the corresponding data forCD2(HgC1)2, aregiveninTable
1. Thesedata
for powders under ambient conditions clearlyshowcorrelation * Metallomethanes XIV. For XIII see [51. 0022-2860/86/$03.50 01986 Elsevier 8ciencePublishersB.V.
split-
156 TABLE 1 Vibrational spectra of solid CH2(HgC1)2 and CD2(HgC1)2. CH2 (HgW2
Assignment
Raman
$~~G;;;;$EP1' w(CH2)/w(CD;) p(CH2)/9 (CD2) vas(CHg2) vs(CHg2) vas(HgC1) v,(HgCl) o(CHgC1)
2947 3018 1340 m w s 1006 m 643 512 324 300 { 106 90 73
h(CHg2)
CD2 (HgC1)2
IR
m s m vs s s vs
1335 986 645 633 505 313 297 102 87 76
w s s s m s sh s s sh
Raman
IR
2264 2165 983 809
2260 VW
518 484 324 300 106 90 72
m s m s vw s m s s s vs
978 803 558 520 481 307 280 107 87 78
w w m m m s sh s s s
tings between gerade (g, Raman) and ungerade (u, IR) species of the molecular modes under the symmetry of the unit cell, aspredictedby unit-cell group analysis for CH2(HgC1)2 (Table 2) with known crystal structure (space group Pnma, 2 = 4) [4]. On theotherhand, sets of gandu RamanandIR
the predicted correlation splittings within the
species are onlypartly
spectra (Fig. I). Thus,
in both RamanandIR
observable in low-temperature
the w(CH2) mode shows splitting
spectra, whereas the CH2 stretchinganddeforma-
tion modes do not split. Further, the strongIRbandataround645 (9(CH2) andvas(CHg2))
cm"
shows fourfold splitting, but the Raman coun-
terpart appears as a single band. Finally, the strong Raman band at around 300 cm-1 resolves into three components; simultaneous chlorine isotope effects and correlation couplingleadtoanevenmore
com-
plicated expected structure. Several sets of single-crystal Raman spectraofCH2(HgC1)2 for different arrangements
(90" andO"
scattering) and various orientations
have been measured, but only one set for the orientation a( presented here (Table 3). Firstly,
the bands
)c is
at 3014 cm-l (Big and
B3g spectra, no correlation splitting) and at 2945 cm-l (As and B2g species) can be conclusively assigned totheasymmetricand
symmetric
valence vibrations, respectively, of the CH2 group (cf. Table 2). The assignments of 6(CH2) and w(CH2) are confirmed. The bands at 644 and 512 cm" belongtothe same species Ag and B2g. Since the latter band is clearly vs(CHg2), the former has tobeassigned Table 2); an assignment to 9(CH2) canberuledout. vibrations
to vas(CHg2)
(cf.
The Hg-Cl valence
(vas at 324, vs around 300 ~n'~) show complicated behaviour, caused by superposition of chlorine isotope effects and perisoturbed correlation coupling. The molecules withthreedifferent
157 TABLE 2 16 Correlation diagram for CH2(HgC1)2, Pnma-D2h,
us ICI-21 v’s (CHg2) vs(HgC1) 6 ((X.2) o(CHg2) G(CHgC1) r(CH2) G(CHgC1)
2 = 4. 16
mm2 - C2"
m-C
free molecule
site
Pnma- D2h
S
unit cell Ag
B,g(R)
a, (R, IN
T
z
(RI
B2g(R) B3g(R) R~
>
a2 (R) Au (-)
vas(CHg2) vas(HgC1) T x' "y G(CHgC1) 1 w(CH2)
b, (R, IR)
vas(CH2) Q(CBZ) G(CHgC1)
b2 (R, IR)
BluUR) B2JIR)
Ty, Rx
B3U(IR)
>
tope compositions,
randomly
distributed
in the lattice, no longer
perform the u(HgC1) vibrations in distinctphase relations; thus, in principle, the basis for the unit-cell group analysis approximation is lost. The same is true for the deformation modes G(CHgC1) (105 75 cm-1 range); nevertheless, in-plane (ip, IR
104 and86 cm-11
Fig. 1. Low-temperature IR (left) and Raman spectrum (below) Of CH2 (HgC1j2.
113K
1400
AgandBZg,
600
1000
Raman
302
514
9.4K 308
1400
1000
600
200
158 TABLE 3 Single-crystal Raman spectra of CH2(HgC1)2. Relative intensities for orientation a( Assignment
Frequency
vas(CH2 1 vs(CH2) o(CH2) w(CH2) vas(CHg2) vs(CHg2) vas(HgCI) vs(HgCI) G(CHgC1) ip oop oop ip oop o(CHg2)
3014
and out-of-plane modes
(reference underlined).
a(bb)c
a(ba)c
a(ca)c
a(cb)c
Ag
Big 5
B2g
B3g
0 4 5 10 11 27 16
5 2 0
0 27 1 0 Cl 10
2945 1336 1006 644 512 324 305 299 104 102 90 86 75 (67:)
)c
(oop, BlgandB3g,
102, 90 and 75 cm-l) canbe
distinguished. Finally, the 6(CHg2) mode (AgandB2g, 66 (from another orientation) and 72 cm-l) can be identified. ACKNOWLEDGEMENT One oftheauthors
(D.K.B.) thanks the Ecole des Arts et Manufac-
tures, Chstenay-Malabry, France, and the head of the Laboratoire de Chimie et Physico-chimie Minerales of this school, Dr. NguyenQuy Dao, for a guest professorship has been performed.
during tenure of which
part of this work
Support by the Fonds der Chemischen Industrie,
Frankfurt, F.R.G., is also acknowledged.
REFERENCES 1 D.K. Breitinger, G. Petrikowski, G. Liehr and 2. Naturforsch., 38b(1983)357, and references 2 J. Mink, D.K. Breitinger, 2. Meic and M. Gal, 115(1984)435, and references therein. 3 W. Kress, doctoral thesis, Erlangen (1983). 4 K.P. Jensen, D-K. Breitinger and W. Kress, 2. 36b(l981)188. 5 J. Mink, D.K. Breitinger, W. Kress, W. Morel1 J. Organomet. Chem., in press,
R. Sendelbeck, therein. J. Mol. Struct., Naturforsch., and R. Sendelbeck,
143(1986)155-158 Amsterdam -PrintedinTheNetherlands
155
VIBRATIONAL SPECTRA OF BIS(HALOMERCURIO)MBTHANES CH2(HgX)2 (X = Cl, Br AND I) IN POLY- AND MONOCRYSTALLINE STATES* D.K. BREITINGER and W. KRESS Institute of Inorganic Chemistry, University of Erlangen-Numberg, Egerlandstrasse 1, D-8520 Erlangen (F.R.G.)
ABSTRACT
Vibrational spectraofpolycrystalline bis(chloromercurio)methane CH2(HgC1)2 (space group Pnma, Z= 4), and of the deuterated analogue, as representatives of the bis(halomercurio)methanes, arepreliminarily assigned. Low-temperature Raman and IR spectra of CHZ(HgC1)2 reveal correlation splittings between gandu species, andpartly within the sets of gandu modes, as predicted by unit-cell group analysis. Single-crystal Raman studies notonlyconfirm the suggested assignments but are also the only method to unequivocally assign some bands. The limitations oftheapplicability of unit-cellgroupanalysis in the present case are discussed. INTRODUCTION As part of structural [I] and extensive spectrometric (multinuclear NMR, vibrational, UV) [2] investigations of anionomercuriomethanes CH4_n(HgX), (1 =n=4)
thevibrational
spectra of bis(anionomerc-
urio)methanes CH2(HgX)2 (X = Cl, Br and I; CN, SCN and OAc) havebeen studied [31. Raman and IR spectra of powders of the compounds with X = Cl, Br and I, and of deuterated analogues, combined with polarization data for solutions, allow most of the expected and observed fundamentals tobe reliably assigned. Solutions of specific problems and deeper insight into details ofthe spectra are reached with lowtemperature RamanandIR
spectra of polycrystalline samples and with
single-crystal Raman spectra, which will be discussed here. RESULTS AND DISCUSSION Frequencies and preliminary assignments, based partlyonpolarization data for solutions in several solvents, for CH2(HgC1)2 as representative of the series ofbis(halomercurio)methanes,
together with
the corresponding data forCD2(HgC1)2, aregiveninTable
1. Thesedata
for powders under ambient conditions clearlyshowcorrelation * Metallomethanes XIV. For XIII see [51. 0022-2860/86/$03.50 01986 Elsevier 8ciencePublishersB.V.
split-
156 TABLE 1 Vibrational spectra of solid CH2(HgC1)2 and CD2(HgC1)2. CH2 (HgW2
Assignment
Raman
$~~G;;;;$EP1' w(CH2)/w(CD;) p(CH2)/9 (CD2) vas(CHg2) vs(CHg2) vas(HgC1) v,(HgCl) o(CHgC1)
2947 3018 1340 m w s 1006 m 643 512 324 300 { 106 90 73
h(CHg2)
CD2 (HgC1)2
IR
m s m vs s s vs
1335 986 645 633 505 313 297 102 87 76
w s s s m s sh s s sh
Raman
IR
2264 2165 983 809
2260 VW
518 484 324 300 106 90 72
m s m s vw s m s s s vs
978 803 558 520 481 307 280 107 87 78
w w m m m s sh s s s
tings between gerade (g, Raman) and ungerade (u, IR) species of the molecular modes under the symmetry of the unit cell, aspredictedby unit-cell group analysis for CH2(HgC1)2 (Table 2) with known crystal structure (space group Pnma, 2 = 4) [4]. On theotherhand, sets of gandu RamanandIR
the predicted correlation splittings within the
species are onlypartly
spectra (Fig. I). Thus,
in both RamanandIR
observable in low-temperature
the w(CH2) mode shows splitting
spectra, whereas the CH2 stretchinganddeforma-
tion modes do not split. Further, the strongIRbandataround645 (9(CH2) andvas(CHg2))
cm"
shows fourfold splitting, but the Raman coun-
terpart appears as a single band. Finally, the strong Raman band at around 300 cm-1 resolves into three components; simultaneous chlorine isotope effects and correlation couplingleadtoanevenmore
com-
plicated expected structure. Several sets of single-crystal Raman spectraofCH2(HgC1)2 for different arrangements
(90" andO"
scattering) and various orientations
have been measured, but only one set for the orientation a( presented here (Table 3). Firstly,
the bands
)c is
at 3014 cm-l (Big and
B3g spectra, no correlation splitting) and at 2945 cm-l (As and B2g species) can be conclusively assigned totheasymmetricand
symmetric
valence vibrations, respectively, of the CH2 group (cf. Table 2). The assignments of 6(CH2) and w(CH2) are confirmed. The bands at 644 and 512 cm" belongtothe same species Ag and B2g. Since the latter band is clearly vs(CHg2), the former has tobeassigned Table 2); an assignment to 9(CH2) canberuledout. vibrations
to vas(CHg2)
(cf.
The Hg-Cl valence
(vas at 324, vs around 300 ~n'~) show complicated behaviour, caused by superposition of chlorine isotope effects and perisoturbed correlation coupling. The molecules withthreedifferent
157 TABLE 2 16 Correlation diagram for CH2(HgC1)2, Pnma-D2h,
us ICI-21 v’s (CHg2) vs(HgC1) 6 ((X.2) o(CHg2) G(CHgC1) r(CH2) G(CHgC1)
2 = 4. 16
mm2 - C2"
m-C
free molecule
site
Pnma- D2h
S
unit cell Ag
B,g(R)
a, (R, IN
T
z
(RI
B2g(R) B3g(R) R~
>
a2 (R) Au (-)
vas(CHg2) vas(HgC1) T x' "y G(CHgC1) 1 w(CH2)
b, (R, IR)
vas(CH2) Q(CBZ) G(CHgC1)
b2 (R, IR)
BluUR) B2JIR)
Ty, Rx
B3U(IR)
>
tope compositions,
randomly
distributed
in the lattice, no longer
perform the u(HgC1) vibrations in distinctphase relations; thus, in principle, the basis for the unit-cell group analysis approximation is lost. The same is true for the deformation modes G(CHgC1) (105 75 cm-1 range); nevertheless, in-plane (ip, IR
104 and86 cm-11
Fig. 1. Low-temperature IR (left) and Raman spectrum (below) Of CH2 (HgC1j2.
113K
1400
AgandBZg,
600
1000
Raman
302
514
9.4K 308
1400
1000
600
200
158 TABLE 3 Single-crystal Raman spectra of CH2(HgC1)2. Relative intensities for orientation a( Assignment
Frequency
vas(CH2 1 vs(CH2) o(CH2) w(CH2) vas(CHg2) vs(CHg2) vas(HgCI) vs(HgCI) G(CHgC1) ip oop oop ip oop o(CHg2)
3014
and out-of-plane modes
(reference underlined).
a(bb)c
a(ba)c
a(ca)c
a(cb)c
Ag
Big 5
B2g
B3g
0 4 5 10 11 27 16
5 2 0
0 27 1 0 Cl 10
2945 1336 1006 644 512 324 305 299 104 102 90 86 75 (67:)
)c
(oop, BlgandB3g,
102, 90 and 75 cm-l) canbe
distinguished. Finally, the 6(CHg2) mode (AgandB2g, 66 (from another orientation) and 72 cm-l) can be identified. ACKNOWLEDGEMENT One oftheauthors
(D.K.B.) thanks the Ecole des Arts et Manufac-
tures, Chstenay-Malabry, France, and the head of the Laboratoire de Chimie et Physico-chimie Minerales of this school, Dr. NguyenQuy Dao, for a guest professorship has been performed.
during tenure of which
part of this work
Support by the Fonds der Chemischen Industrie,
Frankfurt, F.R.G., is also acknowledged.
REFERENCES 1 D.K. Breitinger, G. Petrikowski, G. Liehr and 2. Naturforsch., 38b(1983)357, and references 2 J. Mink, D.K. Breitinger, 2. Meic and M. Gal, 115(1984)435, and references therein. 3 W. Kress, doctoral thesis, Erlangen (1983). 4 K.P. Jensen, D-K. Breitinger and W. Kress, 2. 36b(l981)188. 5 J. Mink, D.K. Breitinger, W. Kress, W. Morel1 J. Organomet. Chem., in press,
R. Sendelbeck, therein. J. Mol. Struct., Naturforsch., and R. Sendelbeck,