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Far infrared spectra, vibrational assignment and normal coordinate analysis of the tricyanomethanideion
127 Jo~rrnal of Molecular
Strucrure, 20 (1974) 127-133 IQ Elsevier Scientific Publishing Company, Amsterdam
- Printed
in The Netherlands
FAR INFRARED SPECTRA, VIBRATIONAL ASSIGNMENT AND NORMAL COORDINATE ANALYSIS OF THE TRLCYANOMETHANIDE TON E. MAYER Instittrt flir
Anorganische
trnd Anol_vtische Chetnie,
Uniuersitdt Innsbrttck,
Innsbruck
(Austria)
D. J. GARDINER AND R. E. HESTER Deprrrtment
(Received
of Chemistry,
University
of York, Heslington,
York
(Etrgland)
21 May 1973)
ABSTRACT
Far infrared spectra of the tricyanomethanide ion C(CN)Xin solution and in the solid state have been investigated. The results allow a complete vibrational assrgnment to be made. A normal coordinate analysis has been carried out, the results of whrch are compatible with the existence of some double bond character in the C-C bonds of C(CN),-. INTRODUCTION
Two vibrational studies of the tricyanomethanide ion, C(CN),have been reported, by Long et al. [l], and by Miller and Baer [2]. While both of these studies favour a planar structure with D 9h symmetry and agree on the assignment of the stretching modes, different assignments were proposed for several of the deformation modes. Mdler’s assignment has been favouredin subsequent reports [3, 41, and a normal coordinate analysis has been carried out 131. A value of 4.658 mdyn A-r has been reported for the C-C stretching force constant. Since this force constant appeared to be surprisingly low for a C-C bond which is expected to have partial double bond character [4], we repeated the normal coordinate analysis using both sets of vibrational assignments. We have been unable to reproduce the reported results, and have found that only the assignment given by Long yields a viable solutron. The far infrared spectra presented here reveal previously unobserved infrared bands assignable to carbon skeleton bending modes and lend further support to Long’s original assignment. EXPERIMENTAL
Potassium tricyanomethanide was prepared from dibromomalononitrilepotassium bromide and potassium cyanide [S], and was recrystallised from aceto-
128 nitrite (S.L.R.). The silver salt was prepared by precipitation with silver nitrate. Both salts were dried at 60 “C in a vacuum of IO- 3 torr. Dimethyl sulphoxide was dried over a 4 A molecular sieve before use as a solvent. A nitrogen-filled grove bag was used to handle the solution of KC(CN), in dimethyl sulphoxide. Far in-
frared spectra (50 to 400 cm-“) were obtained from a Grubb-Parsons Cube Interferometer, using standard high density p~~ythene discs to contain the samples. Vaseiine was used far the mulLsi,and dimethy sulphoxide for the sofution spectra,
An X-ray analysis of NaC(CN), showed that the tricyanomethanide ion is nearly planar in the solid state [(El. The slight deviation from planarity was explained in terms of a packing effect [63_ Therefore it seems reasonable to expect planarity for the anion in solution. The planar ion belongs to the point group D,, and gives rise to the following vibrational representation: r vib = 2A~‘(R)~A~‘(inactive)~2A~“(tR)~4~(R~
IR)+E”(R)
where the infrared and Raman activities are shown in parentheses.
A /
cm-’ it so
“8
1 ““I 100
100
““1’1
i’f’
2x4
Fig. 1. Far infrared sgectca of KC(cTN), and AgC(CN), from 50 to 260 cm”. {A340 % wlv KC(CBQ3 h drmethylsulphoxide,0.10 mm spacer; (IS) solid KC&IX)3 in vaseline; (Cl solid AgC(CN)s in vaseline.
129 The far infrared spectra of KC(CN)3
in the sohd state and of KC(CN), in a dimethyl sulphoxide solution are shown in Fig. 1. The solution spectrum shows clearly two distinct maxima at 160 and 176 cm-’ within a very broad absorption band. The solid state spectra are much more complicated and contain several extra absorptions caused by solid state effects. Absorptions corresponding to the bands in solution can be found for solid KC(CN), at 152 and 185 cm-‘, and for solid AgC(CN)3 at 142 and 168 cm-‘. Since these two absorptions appear in solution and in two solids with probably different crystal structures, it seems justified to assign both as fundamental vibrations. These data allow us to differentiate between the two sets of vibrational assignments presented in the literature (Table 1). The absorption in the far infrared TABLE OBSERVED
and AgC(CN)3
1 FIJNDAMEMAL
METHANIDEION
FREQUENCIES
AND
VIBRATIONAL
ASSIGNMENTS
FOR
PLANAR
TRICYAN~-
@ah)
Syrnriielry species
Assignrnenr Long et al [I] (cm-‘)
Assigtmenr
2225 658
222s 657
inactive
inactive
567 ? 217.5 1250
567 404 2175 1250
610 162
608 483 ?
468
Miller
and Boer
(cm- 1)
[2]
at 160 cm-l agrees well with the Raman band at 162 cm-’ found by Long and therefore is assigned as an E’ mode. The other far infrared band at 176 cm-’ can be assigned as the Raman inactive normal mode of AZ” symmetry missing in Long’s assignment. Miller’s assignment of a band at 404 cm-l to this A,” mode was based upon observation of a very weak band in the solid state infrared spectrum and upon observation of a band at 807 cm-’ in the Raman spectrum of the aqueous solution which was assigned as its first overtone. We have reexamined the Raman spectrum under very high gain conditions and found no band of the reported intensity in that region. We suggest therefore that its original observation may have been due to an impurity. Normal coordinate analysis
In the X-ray analysis [6] the three C-C distances were found to be nearly identical (between 1.405 and 1.411 A), but large deviations were observed for the C-N distances (between 1.145 and 1.164 A). It could not be decided, however,
130
Fig. 2. In-plane
internal coordinates
of the trlcyanomethanide
ion.
whether this difference is real and a consequence of coordination, or is just due to wrong corrections. We therefore used an average value of 1.408 8, for the C-C bond length and of 1.153 A for the C-N bond length in the calculations. For the normal coordinate calculations a version of Schachtschneiders computer programmes has been used [7]. This has been described previously [8]. The symmetry coordinates given by Pistorius [9] for the planar symmetrical X(YZ), molecule were used. The in-plane internal coordinates, shown in Fig. 2 are: three C-C bond stretches (d,), three C-N bond stretches (Tr), three C-C-C angle deformations (a,,) and six C-C-N angle deformations (S,j, two of these being associated with each C-C-N angle). The out-of-plane internal coordinates, which have been omitted from Fig. 2 for the sake of clarity, are deformations of the three angles between the C-C bonds and the plane of the molecule (yi), and three out-of-plane C-C-N angle deformations ((li)- These 21 internal coordinates contain six redundancies which are one of the aij and three of the B,j from the in-plane coordinates, and two of the yr from the out-of-plane coordinates. These redundancies have been reported to obscure the meaning of some of the force constants [lo]. However, since the aim of this calculation was to help differentiate between the two reported vibrational assignments rather than to obtain a set of transferable force constants, the redundancies were retained in the calculations. Of the 32 different force constants in the general valence force field, the following 18 were used in the analysis. In-plane force constants: fd - stretching of C-C f, - stretching of C-N f, - bending of C-C-C fa - bending of C-C-N f dd- interaction of C-C f,, - interaction of C-N
in plane in plane with C-C with C-N
(di with dj) (r, with rj)
131 fdr f_ fa, rdl J& &
- interaction of C-C with C-N (di with pi) - interaction of C-C-C with C-C-C - interaction of C-C with adjacent C-C-C - interact‘ Ion of C-C with opposite C-C-C - Interaction of C-C-N with C-C-N (bij with /I,,) - Interaction of C-C with C-C-N (di with fl,,)
Out-of-plane
force constants:
J, - bending of f, - bending of f,, - interaction _fad- interaction f,, - interaction flOY - interaction
C-C, out of plane C-C-N out of plane between two C-C3 bendings between two C-C-N bendings between bendmg of C-C3 and C-C-N between bending of C-C3 and C-C-N
(yi with ai) (ri with aj)
The remaining force constants required to define the full general valence force field [9] were assumed to be negligibly small and fixed at zero in our calculations. Since within the harmonic oscillator approximation no interaction is possible between in-plane and out-of-plane motions, it IS convenient to treat the corresponding force constants separately. Of the 18 force constants used in various attempts to fit the observed frequencies, a restricted selection of nine was dictated by the limited frequency data. It was not possible to obtain a solution with the set of frequencies presented by Miller and Baer (Table l), using any set of values for the force constants listed above-with Long’s set of frequencies a simple diagonal force field also failed to give a satisfactory fit to the observed frequencies. However, a perfect fit was obtained for the in-plane fundamentals, when two interaction constants were incIuded in the iteration. By entering all the different possible combinations of interaction constants in sets of two, together with the four diagonal constants, three solutions were obtained for the in-plane force constants. These are shown in Table 2. It is difficult, with the information on hand, to select from these three sets the best solution. Attempts to differentiate between these solutions by searching for infrared or Raman active combination bands of the inactive Al’ mode with various other normal modes were not successful. However, we feel that the value of the force constant for C-C stretching in set 1 (5.13 mdyn A-l) is too low. From the X-ray analysis [6] it is known that the C-C bond is considerably shortened from its value of 1.47 A in the aliphatic nitriles to 1.408 A consistent with it containing some double bond character. This leav:s us still with two equally likely solutions. The two solutions obtamed for the out-of-plane modes, also shown in Table 2, differ onIy by small contributions from two different interaction constants, f,‘, and f,,. Tt is interesting to note that the value off. in both of these solutions is the same and is an order of magnitude smaller than in XY, systems of Dsh
132 TABLE
2
CALCULATED
VALENCE
In-plane force
FORCE
CONmA?iTS
Set 3 h =760mdyn.&-’ J; = 15.09 mdyn _q- 1 fz = 0 57 erg rad-’ fB = 0.25 erg radm2 f;, = 0.65 mdyn A-’ fdp = 0.76 erg rad- L
6.21 mdyn -9-l 15.85 mdyn -i-l 0.49 erg rad-’ 0.33 erg radm2 0.69 mdyn A-’ 0.27 mdyn A-I
fr = I, = /a = fdd = /= =
force
constnnts Set 2
1
fY = 0.049f0.024 erg rad-’ fa = 0.52f0.08 erg rad-’ f’., = -0.025~0.017 erg rad-2
CALCULATED
ION
for all the in-plane force constants were negligibly small)
Out-of-plane
TABLE
TRICYANOMETHANIDE
Set 2
fd =
5.13 mdyn .a-’ 16.39 mdyn _A-’ 0.56 erg rad-’ 0.42 erg rad-’ 1.23 mdyn -4-l -0.43 erg rad-’
(Errors
set
THE
constants
Set 1 h = I; = f, = fa = faa = fdb, =
FOR
J, = 0 049&0.024 erg radm2 /; = 0.52&0.08 erg radez f,-, = -0.050~0.034 erg radbL
3 FREQUENCIES,
SYhfMETRY
ASSIGNMENTS
AND
APPROXIMATE
DESCRIPTION
OF NORMAL
MODES
Obserued frequenqp (cm - ’ )
Calculated frequency (cm- 1)
2225 657
2225.0 657.0 609.7 (set I) 538.1 (set 2) 472.6 (set 3) 567.0 176.0 2175.0 1243.0 608.0 160.0 478.0
inactive
567 176 (this work) 2175 1243 608 160 (this work) 478
Symmetry
b.1
(Al’)
“2
(A
1’3
(-42’)
I’)
v, (AZ”) “5
642”)
‘-6
W’)
“7
(E’)
8’~ (0 v* ~10
WI @“I
Approximate normal mode v(C-N) 1’ (C-C) G(C-C-N)
rn plane
d(C-C-N) out of plane &C-CA) out of plane v(C-N) @-cl &C-C-N) in plane G(C-C-C) in plane d(C-C-N) out of plane
’ Frequency data from ref. 1.
symmetry [ll]. Table 3 contains the calculated frequencies with an approximate description of the normal modes derived from the potential energy distributions. ACKNOWLEDGEMENT
One of us (E-M.) thanks the Royal Society for a European Exchange Programme Fellowship.
133 REFERENCES 1 D. A. Long, R. A. G. Camngton and R. B. Gravenor, Nurure (Lorrdon), 196 (1962) 371. 2 F. A. Miller and W. K. Baer, Specrrochim. Acru, 19 (1963) 73. 3 G. Nagarajan. lndiun J. Pwe Appl. Phys., 1 (1963) 73. 4 I. H. Enemark and R. H. Holm, fnorg. Chern.. 3 (1964) I4 16. 5 S. Trofimenko, E. L. Little Jr. and H. F. Mower, J. Org. Chem., 27 (1962) 433. 6 P. Andersen, B. Klewe and E. Thorn, Acru C/zenl. Sc~nd., 21 (1967) 1530. 7 J. H. Schachtschneider, Shell Development Company, Tech. Rep.. No. 231-64 and 57-65 (1964) 8 D. J. Gardiner and E. Mayer, J. Mol. Structure, 16 (1973) 173. 9 C. W. F. T. Pistorius, Bull. Sot. Chmr. Be/g., 67 (1958) 566. IO B. Crawford Jr. and J. Overend, J. Mol. Specrrosc.. I2 (1964) 307. 11 L. Beckmann, L. Gutjahr and R. Mecke, Spectrochim. Ado, 21 (1965) 141.
Strucrure, 20 (1974) 127-133 IQ Elsevier Scientific Publishing Company, Amsterdam
- Printed
in The Netherlands
FAR INFRARED SPECTRA, VIBRATIONAL ASSIGNMENT AND NORMAL COORDINATE ANALYSIS OF THE TRLCYANOMETHANIDE TON E. MAYER Instittrt flir
Anorganische
trnd Anol_vtische Chetnie,
Uniuersitdt Innsbrttck,
Innsbruck
(Austria)
D. J. GARDINER AND R. E. HESTER Deprrrtment
(Received
of Chemistry,
University
of York, Heslington,
York
(Etrgland)
21 May 1973)
ABSTRACT
Far infrared spectra of the tricyanomethanide ion C(CN)Xin solution and in the solid state have been investigated. The results allow a complete vibrational assrgnment to be made. A normal coordinate analysis has been carried out, the results of whrch are compatible with the existence of some double bond character in the C-C bonds of C(CN),-. INTRODUCTION
Two vibrational studies of the tricyanomethanide ion, C(CN),have been reported, by Long et al. [l], and by Miller and Baer [2]. While both of these studies favour a planar structure with D 9h symmetry and agree on the assignment of the stretching modes, different assignments were proposed for several of the deformation modes. Mdler’s assignment has been favouredin subsequent reports [3, 41, and a normal coordinate analysis has been carried out 131. A value of 4.658 mdyn A-r has been reported for the C-C stretching force constant. Since this force constant appeared to be surprisingly low for a C-C bond which is expected to have partial double bond character [4], we repeated the normal coordinate analysis using both sets of vibrational assignments. We have been unable to reproduce the reported results, and have found that only the assignment given by Long yields a viable solutron. The far infrared spectra presented here reveal previously unobserved infrared bands assignable to carbon skeleton bending modes and lend further support to Long’s original assignment. EXPERIMENTAL
Potassium tricyanomethanide was prepared from dibromomalononitrilepotassium bromide and potassium cyanide [S], and was recrystallised from aceto-
128 nitrite (S.L.R.). The silver salt was prepared by precipitation with silver nitrate. Both salts were dried at 60 “C in a vacuum of IO- 3 torr. Dimethyl sulphoxide was dried over a 4 A molecular sieve before use as a solvent. A nitrogen-filled grove bag was used to handle the solution of KC(CN), in dimethyl sulphoxide. Far in-
frared spectra (50 to 400 cm-“) were obtained from a Grubb-Parsons Cube Interferometer, using standard high density p~~ythene discs to contain the samples. Vaseiine was used far the mulLsi,and dimethy sulphoxide for the sofution spectra,
An X-ray analysis of NaC(CN), showed that the tricyanomethanide ion is nearly planar in the solid state [(El. The slight deviation from planarity was explained in terms of a packing effect [63_ Therefore it seems reasonable to expect planarity for the anion in solution. The planar ion belongs to the point group D,, and gives rise to the following vibrational representation: r vib = 2A~‘(R)~A~‘(inactive)~2A~“(tR)~4~(R~
IR)+E”(R)
where the infrared and Raman activities are shown in parentheses.
A /
cm-’ it so
“8
1 ““I 100
100
““1’1
i’f’
2x4
Fig. 1. Far infrared sgectca of KC(cTN), and AgC(CN), from 50 to 260 cm”. {A340 % wlv KC(CBQ3 h drmethylsulphoxide,0.10 mm spacer; (IS) solid KC&IX)3 in vaseline; (Cl solid AgC(CN)s in vaseline.
129 The far infrared spectra of KC(CN)3
in the sohd state and of KC(CN), in a dimethyl sulphoxide solution are shown in Fig. 1. The solution spectrum shows clearly two distinct maxima at 160 and 176 cm-’ within a very broad absorption band. The solid state spectra are much more complicated and contain several extra absorptions caused by solid state effects. Absorptions corresponding to the bands in solution can be found for solid KC(CN), at 152 and 185 cm-‘, and for solid AgC(CN)3 at 142 and 168 cm-‘. Since these two absorptions appear in solution and in two solids with probably different crystal structures, it seems justified to assign both as fundamental vibrations. These data allow us to differentiate between the two sets of vibrational assignments presented in the literature (Table 1). The absorption in the far infrared TABLE OBSERVED
and AgC(CN)3
1 FIJNDAMEMAL
METHANIDEION
FREQUENCIES
AND
VIBRATIONAL
ASSIGNMENTS
FOR
PLANAR
TRICYAN~-
@ah)
Syrnriielry species
Assignrnenr Long et al [I] (cm-‘)
Assigtmenr
2225 658
222s 657
inactive
inactive
567 ? 217.5 1250
567 404 2175 1250
610 162
608 483 ?
468
Miller
and Boer
(cm- 1)
[2]
at 160 cm-l agrees well with the Raman band at 162 cm-’ found by Long and therefore is assigned as an E’ mode. The other far infrared band at 176 cm-’ can be assigned as the Raman inactive normal mode of AZ” symmetry missing in Long’s assignment. Miller’s assignment of a band at 404 cm-l to this A,” mode was based upon observation of a very weak band in the solid state infrared spectrum and upon observation of a band at 807 cm-’ in the Raman spectrum of the aqueous solution which was assigned as its first overtone. We have reexamined the Raman spectrum under very high gain conditions and found no band of the reported intensity in that region. We suggest therefore that its original observation may have been due to an impurity. Normal coordinate analysis
In the X-ray analysis [6] the three C-C distances were found to be nearly identical (between 1.405 and 1.411 A), but large deviations were observed for the C-N distances (between 1.145 and 1.164 A). It could not be decided, however,
130
Fig. 2. In-plane
internal coordinates
of the trlcyanomethanide
ion.
whether this difference is real and a consequence of coordination, or is just due to wrong corrections. We therefore used an average value of 1.408 8, for the C-C bond length and of 1.153 A for the C-N bond length in the calculations. For the normal coordinate calculations a version of Schachtschneiders computer programmes has been used [7]. This has been described previously [8]. The symmetry coordinates given by Pistorius [9] for the planar symmetrical X(YZ), molecule were used. The in-plane internal coordinates, shown in Fig. 2 are: three C-C bond stretches (d,), three C-N bond stretches (Tr), three C-C-C angle deformations (a,,) and six C-C-N angle deformations (S,j, two of these being associated with each C-C-N angle). The out-of-plane internal coordinates, which have been omitted from Fig. 2 for the sake of clarity, are deformations of the three angles between the C-C bonds and the plane of the molecule (yi), and three out-of-plane C-C-N angle deformations ((li)- These 21 internal coordinates contain six redundancies which are one of the aij and three of the B,j from the in-plane coordinates, and two of the yr from the out-of-plane coordinates. These redundancies have been reported to obscure the meaning of some of the force constants [lo]. However, since the aim of this calculation was to help differentiate between the two reported vibrational assignments rather than to obtain a set of transferable force constants, the redundancies were retained in the calculations. Of the 32 different force constants in the general valence force field, the following 18 were used in the analysis. In-plane force constants: fd - stretching of C-C f, - stretching of C-N f, - bending of C-C-C fa - bending of C-C-N f dd- interaction of C-C f,, - interaction of C-N
in plane in plane with C-C with C-N
(di with dj) (r, with rj)
131 fdr f_ fa, rdl J& &
- interaction of C-C with C-N (di with pi) - interaction of C-C-C with C-C-C - interaction of C-C with adjacent C-C-C - interact‘ Ion of C-C with opposite C-C-C - Interaction of C-C-N with C-C-N (bij with /I,,) - Interaction of C-C with C-C-N (di with fl,,)
Out-of-plane
force constants:
J, - bending of f, - bending of f,, - interaction _fad- interaction f,, - interaction flOY - interaction
C-C, out of plane C-C-N out of plane between two C-C3 bendings between two C-C-N bendings between bendmg of C-C3 and C-C-N between bending of C-C3 and C-C-N
(yi with ai) (ri with aj)
The remaining force constants required to define the full general valence force field [9] were assumed to be negligibly small and fixed at zero in our calculations. Since within the harmonic oscillator approximation no interaction is possible between in-plane and out-of-plane motions, it IS convenient to treat the corresponding force constants separately. Of the 18 force constants used in various attempts to fit the observed frequencies, a restricted selection of nine was dictated by the limited frequency data. It was not possible to obtain a solution with the set of frequencies presented by Miller and Baer (Table l), using any set of values for the force constants listed above-with Long’s set of frequencies a simple diagonal force field also failed to give a satisfactory fit to the observed frequencies. However, a perfect fit was obtained for the in-plane fundamentals, when two interaction constants were incIuded in the iteration. By entering all the different possible combinations of interaction constants in sets of two, together with the four diagonal constants, three solutions were obtained for the in-plane force constants. These are shown in Table 2. It is difficult, with the information on hand, to select from these three sets the best solution. Attempts to differentiate between these solutions by searching for infrared or Raman active combination bands of the inactive Al’ mode with various other normal modes were not successful. However, we feel that the value of the force constant for C-C stretching in set 1 (5.13 mdyn A-l) is too low. From the X-ray analysis [6] it is known that the C-C bond is considerably shortened from its value of 1.47 A in the aliphatic nitriles to 1.408 A consistent with it containing some double bond character. This leav:s us still with two equally likely solutions. The two solutions obtamed for the out-of-plane modes, also shown in Table 2, differ onIy by small contributions from two different interaction constants, f,‘, and f,,. Tt is interesting to note that the value off. in both of these solutions is the same and is an order of magnitude smaller than in XY, systems of Dsh
132 TABLE
2
CALCULATED
VALENCE
In-plane force
FORCE
CONmA?iTS
Set 3 h =760mdyn.&-’ J; = 15.09 mdyn _q- 1 fz = 0 57 erg rad-’ fB = 0.25 erg radm2 f;, = 0.65 mdyn A-’ fdp = 0.76 erg rad- L
6.21 mdyn -9-l 15.85 mdyn -i-l 0.49 erg rad-’ 0.33 erg radm2 0.69 mdyn A-’ 0.27 mdyn A-I
fr = I, = /a = fdd = /= =
force
constnnts Set 2
1
fY = 0.049f0.024 erg rad-’ fa = 0.52f0.08 erg rad-’ f’., = -0.025~0.017 erg rad-2
CALCULATED
ION
for all the in-plane force constants were negligibly small)
Out-of-plane
TABLE
TRICYANOMETHANIDE
Set 2
fd =
5.13 mdyn .a-’ 16.39 mdyn _A-’ 0.56 erg rad-’ 0.42 erg rad-’ 1.23 mdyn -4-l -0.43 erg rad-’
(Errors
set
THE
constants
Set 1 h = I; = f, = fa = faa = fdb, =
FOR
J, = 0 049&0.024 erg radm2 /; = 0.52&0.08 erg radez f,-, = -0.050~0.034 erg radbL
3 FREQUENCIES,
SYhfMETRY
ASSIGNMENTS
AND
APPROXIMATE
DESCRIPTION
OF NORMAL
MODES
Obserued frequenqp (cm - ’ )
Calculated frequency (cm- 1)
2225 657
2225.0 657.0 609.7 (set I) 538.1 (set 2) 472.6 (set 3) 567.0 176.0 2175.0 1243.0 608.0 160.0 478.0
inactive
567 176 (this work) 2175 1243 608 160 (this work) 478
Symmetry
b.1
(Al’)
“2
(A
1’3
(-42’)
I’)
v, (AZ”) “5
642”)
‘-6
W’)
“7
(E’)
8’~ (0 v* ~10
WI @“I
Approximate normal mode v(C-N) 1’ (C-C) G(C-C-N)
rn plane
d(C-C-N) out of plane &C-CA) out of plane v(C-N) @-cl &C-C-N) in plane G(C-C-C) in plane d(C-C-N) out of plane
’ Frequency data from ref. 1.
symmetry [ll]. Table 3 contains the calculated frequencies with an approximate description of the normal modes derived from the potential energy distributions. ACKNOWLEDGEMENT
One of us (E-M.) thanks the Royal Society for a European Exchange Programme Fellowship.
133 REFERENCES 1 D. A. Long, R. A. G. Camngton and R. B. Gravenor, Nurure (Lorrdon), 196 (1962) 371. 2 F. A. Miller and W. K. Baer, Specrrochim. Acru, 19 (1963) 73. 3 G. Nagarajan. lndiun J. Pwe Appl. Phys., 1 (1963) 73. 4 I. H. Enemark and R. H. Holm, fnorg. Chern.. 3 (1964) I4 16. 5 S. Trofimenko, E. L. Little Jr. and H. F. Mower, J. Org. Chem., 27 (1962) 433. 6 P. Andersen, B. Klewe and E. Thorn, Acru C/zenl. Sc~nd., 21 (1967) 1530. 7 J. H. Schachtschneider, Shell Development Company, Tech. Rep.. No. 231-64 and 57-65 (1964) 8 D. J. Gardiner and E. Mayer, J. Mol. Structure, 16 (1973) 173. 9 C. W. F. T. Pistorius, Bull. Sot. Chmr. Be/g., 67 (1958) 566. IO B. Crawford Jr. and J. Overend, J. Mol. Specrrosc.. I2 (1964) 307. 11 L. Beckmann, L. Gutjahr and R. Mecke, Spectrochim. Ado, 21 (1965) 141.