Vibrational spectra of halophthalonitriles

Article abstract of DOI:10.1016/S1386-1425(97)00236-9

The fundamental vibrational modes of a series of six halophthalonitriles have been studied using Raman and infrared spectroscopy. The vibrational assignment of experimental wave numbers obtained from solid samples was aided using quantum chemical computations. Semi-empirical methods and the local SVWN functional were used to obtain vibrational wave numbers and atomic displacement representations of the fundamental molecular vibrations. The study of a series of molecules with similar structure permits the identification of characteristic wave numbers and the effect of the halosubstitution in the molecular structure.

Full text of DOI:10.1016/S1386-1425(97)00236-9

Spectrochimica Acta Part A 54 (1998) 305–317
Vibrational spectra of halophthalonitriles
a
a,
b
b
Mathew D. Halls , Ricardo Aroca *, Dmitri S. Terekhov , Anna D’Ascanio ,
b
Clifford C. Leznoff
a
Materials and Surface Science Group, Uni6ersity of Windsor, Windsor, ON N9E3P4, Canada
Department of Chemistry, York Uni6ersity, North York, Toronto, ON M3J1P3, Canada
b
Received 18 July 1997; received in revised form 13 September 1997
Abstract
The fundamental vibrational modes of a series of six halophthalonitriles have been studied using Raman and
infrared spectroscopy. The vibrational assignment of experimental wave numbers obtained from solid samples was
aided using quantum chemical computations. Semi-empirical methods and the local SVWN functional were used to
obtain vibrational wave numbers and atomic displacement representations of the fundamental molecular vibrations.
The study of a series of molecules with similar structure permits the identification of characteristic wave numbers and
the effect of the halosubstitution in the molecular structure. © 1998 Elsevier Science B.V. All rights reserved.
Keywords: Raman; Infrared; Vibrations; Substituted phthalonitriles; Assignments; SVWN DFT
1
. Introduction
a vibrational study of novel materials, a series of
six halophthalonitriles, is presented: 3-iodo-
phthalonitrile, 4-iodophthalonitrile, 4,5-diiodo-
phthalonitrile, 4-bromophthalonitrile, 4,5-dibro-
mophthalonitrile and 3,6-dibromophthalonitrile.
Several vibrational studies of different phthaloni-
triles have been carried out [3–7]. However, the
infrared and Raman spectra of the halophthaloni-
triles in this series have not been previously re-
ported. The vibrational assignment of this series
based on the FT-Raman and FT-infrared spectra
is presented here for the first time. Of great assis-
tance in spectral interpretation are quantum
chemical calculations of theoretical harmonic fun-
damentals, atomic displacement representations
and spectral intensities. It has become standard to
perform these calculations using Hartree–Fock
In recent years the synthesis of near infrared
absorbing dyes has been an increasingly active
field. Phthalonitriles (1,2-dicyanobenzenes) are
used as synthetic precursors for large macrocyclic
organic semiconductors, particularly for phthalo-
cyanines [1,2] with strong absorption in the near
infrared region of the spectrum. For the synthesis
of substituted phthalocyanines, halogen substi-
tuted phthalonitriles are used. Vibrational studies
of these precursor molecules are of interest in
their own right and they are extremely valuable
when performing vibrational studies of larger
composite molecular systems. In the present work
*
Corresponding author.
1
386-1425/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.
PII S1386-1425(97)00236-9

3
06
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
(
HF), and the level of theory is largely determined
cording to the procedure of Rasmussen et al. [13],
the 4-nitrophthalonitrile was reduced by 10% pal-
ladium on charcoal in EtOH and hydrogenation
at 415 kPa, to yield 4-aminophthalonitrile. The
product was purified by chromatography on nor-
mal grade silica gel in 84% yield. 4-Aminoph-
thalonitrile was then acidified, cooled and treated
with sodium nitrite. The resulting product was
rapidly filtered by suction filtration and the cool
filtrate was added to a solution of potassium
iodide in water, reacting to produce 4-iodoph-
thalonitrile. The product precipitate was collected
by suction filtration, washed with cold water and
dissolved in benzene. The benzene solution was
by the computational capabilities. Usually HF
based semi-empirical methods, such as AM1 and
PM3, are used due to affordability and some
previous knowledge of relative performance. In
recent years new computational schemes have ar-
rived which are known collectively as density
functional models (DFT). Experience with DFT
models is still relatively limited, however an in-
creasing number of studies are being reported
which show DFT models offer many desirable
features, such as more favorable scaling with re-
spect to system size and better performance than
HF and post-HF (MP2) methods for calculating
frequencies and infrared intensities [8–10]. Pre-
sented in this report are proposed general vibra-
tional assignments based on calculations
performed using the semi-empirical AM1 and
PM3 methods and the DFT SVWN local spin
density functional.
then washed with cold water, 5% NaHCO , sat.
3
Na S O and washed dried over MgSO . Chro-
2
2
3
4
matography on 200 g of normal grade silica gel
with benzene gave 4-iodophthalonitrile in 70%
yield [14].
2
.1.3. 4,5-Diiodophthalonitrile
The synthesis of 4,5-diiodophthalonitrile was
2
2
2
. Experimental
performed starting with phthalimide. To 30%
fuming sulfuric acid was added phthalimide and
iodine. After heating for 24 h the mixture was
cooled over ice and the precipitate was collected
using a funnel and a glass frit. The solids were
washed with water, 2% K CO , sat. Na S O and
.1. Synthesis
.1.1. 3-Iodophthalonitrile
The synthesis of 3-iodophthalonitrile was per-
2
3
2
2
3
formed starting with 3-nitrophthalonitrile which
was prepared using the procedure of Campagna et
al. [11] in 95% yield. 3-Nitrophthalonitrile was
selectively reduced to 3-aminophthalonitrile and
was purified by flash chromatography in 83%
yield. 3-Aminophthalonitrile was then acidified
and treated with sodium nitrite to give the diazo-
nium salt. The diazonium salt solution was added
to a potassium iodide solution in water, resulting
in 3-iodophthalonitrile. The aqueous product 3-
iodophthalonitrile was washed in benzene with
were dried at room temperature. The solids were
extracted with acetone in a Soxhlet extractor for
48 h. The resulting solid was 4,5-diiodophthalic
acid. The 4,5-diiodophthalic acid was filtered
from the acetone and water was added. The solu-
tion was concentrated and cooled to give a precip-
itate of 4,5-diiodophthalimide. Chromatography
on silica gel using CHCl -EtAC as eluent gave an
3
isolated yield of 75%. To concentrated aqueous
ammonia, pure 4,5-diiodophthalimide was added.
This mixture was then stirred and heated to 50–
60°C for 1.5 h, to give a solid intermediate. The
solid was filtered and washed with cold water and
methanol, and was then dried at room tempera-
ture to give 4,5-diiodophthamide in 81%. 4,5-Di-
iodophthamide was then suspended in ice-cooled
dry dioxane and dry pyridine and trifluoroacetic
anhydride was added at 0–5°C. After the addition
the reaction mixture was warmed to room temper-
ature and poured on ice. The product was ex-
5
% NaHCO , sat. Na S O , and cold water. The
3 2 2 3
benzene solution was dried over anhydrous mag-
nesium sulfate, and purified by chromatography
on 200 g of normal grade silica gel in 62% yield
[
12].
2.1.2. 4-Iodophthalonitrile
The synthesis of 4-iodophthalonitrile was per-
formed starting with 4-nitrophthalonitrile. Ac-

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
Fig. 1. FT-IR and FT-Raman spectra of 3-iodophthalonitrile.
Fig. 2. FT-IR and FT-Raman spectra of 4-iodophthalonitrile.
307
tracted with EtOAC. The organic layer was
washed with water, HCl, dilute Na CO and was
then poured into ice water. The resultant mixture
was then extracted with ether and the extract was
washed with H O, 1% NaHCO , 1% NaHSO ,
2
3
dried over MgSO . The product was recrystallized
4
2
3
3
from ethanol to give 4-iodophthalonitrile in 79%
yield [15].
and dried over anhydrous MgSO . Evaporation
4
gave a solid mixture which was separated on a
silica gel column using ethyl acetate–hexane as
eluent to give products 4-bromophthalonitrile
45.2%, 4,5-dibromophthalonitrile 6.7% and 3,6-di-
bromophthalonitrile 7% [17].
2.1.4. 4-Bromophthalonitrile, 4,5-dibromo-
phthalonitrile and 3,6-dibromophthalonitrile
Dibromoisocyanuric acid was prepared by the
procedure of Gottardi [16]. Dibromoisocyanuric
acid was dissolved in 8% fuming sulfuric acid at
room temperature. The solution was cooled in ice
and phthalonitrile (1,2-dicyanobenzene) was
added to solution. The mixture was stirred and
2.2. Infrared and Raman spectra
The infrared spectra of all molecules in this
study were collected from CsI pellets using a

3
08
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
Fig. 3. FT-IR and FT-Raman spectra of 4,5-diiodophthalonitrile.
Fig. 4. FT-IR and FT-Raman spectra of 4-bromophthalonitrile.
Bomem DA3 FTIR spectrometer with far-in-
frared and mid-infrared accessories. A KBr beam
splitter and liquid nitrogen cooled MCT detector
were used to collect the mid-infrared spectra from
FT-Raman spectra were collected from 3400 to
−
1
350 cm
.
2
.3. Computational methods
−
1
4000 to 400 cm . A 6 mm stretched Mylar
pellicle beam splitter and a DTGS detector were
used to collect the far-infrared spectra from 500
to 100 cm . The FT-Raman spectra of the
molecules in this study were collected from solid
capillary using a Bomem Ramspec 150 spec-
trophotometer with an Nd:YAG laser emitting at
Semi-empirical calculations using the AM1 [18]
and the PM3 [19] Hamiltonians have been per-
formed on all molecules in this study. The semi-
empirical computations were performed on a 486
PC using Gaussian92, Revision E.1 [20]. DFT
calculations using the SVWN local spin density
functional Hamiltonian [21,22] with a DN** basis
set (numerical split valence basis set supplemented
by d-type functions on heavy atoms and p-type
−
1
1064.1 nm and a InGaAs detector. The FT-Ra-
man system with a Michelson interferometer is
interfaced to a NEC powermate computer. The

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
309
Fig. 5. FT-IR and FT-Raman spectra of 4,5-dibromophthalonitrile.
Fig. 6. FT-IR and FT-Raman spectra of 3,6-dibromophthalonitrile.
functions on hydrogens) were performed for all
bromo-substituted phthalonitriles in this study.
The DFT calculations were performed on a
RS6000 workstation using Spartan IBM
V.4.1.2GL [23]. All calculations involved first ge-
ometry optimization and subsequent harmonic
frequency calculation at the same level of theory.
phthalonitrile, 4,5-diiodophthalonitrile, 4-bromo-
phthalonitrile, 4,5-dibromophthalonitrile and 3,6-
dibromophthalonitrile. Geometry optimizations at
AM1, PM3 and SVWN levels of theory predict
planar geometries for the molecules considered
here. The molecular series considered here can be
divided into molecules belonging to one of two
symmetry point groups: C or C . Apart from the
s
26
identity element, phthalonitriles of C symmetry
only have the molecular plane as a symmetry
s
3. Results and discussion
element. The C molecules include all singly sub-
s
3
.1. Molecular structure and symmetry
stituted phthalonitriles in this series: 3-iodo-,
4-iodo-, 4-bromo-. Phthalonitriles of C26 sym-
metry have a 2-fold rotational axis and an
The substituted phthalonitriles in this study
correspond to 3-iodophthalonitrile, 4-iodo-

3
10
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
Table 1
Symmetry of vibration, AM1, PM3, SVWN, experimental wavenumbers (cm−1), and band assignments for 4-bromophthalonitrile
4
-Bromo
Nonscaled
Scaled
Observed
Assignment
Mode Sym
AM1 PM3
SVWN
AM1 PM3
SVWN
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
a¦
a%
a%
a%
a¦
a%
a%
a¦
a¦
a%
a%
a¦
a¦
a%
a%
a¦
a%
a¦
a%
a¦
a¦
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
72
123
132
148
234
291
299
377
437
489
0578
592
636
664
718
786
876
893
71
124
126
138
223
270
288
364
404
63
538
557
592
627
662
761
828
66
132
137
149
209
276
280
372
409
430
502
520
591
598
642
729
730
64
110
118
132
208
259
266
336
389
435
514
527
566
591
639
700
780
63
110
113
123
198
240
256
324
360
412
479
496
527
558
589
677
737
771
808
844
887
968
998
1052
1132
1179
1255
1389
1451
1579
1592
2202
2201
2718
2724
2731
65
130
134
147
206
271
276
365
402
422
493
511
581
588
631
717
718
Br wag+CCN wag
CBr bend+CCN bend
CCN wag
155
231
CBr bend+CCN bend
CBr wag+CCN wag
CBr stretch+CCN bend
CBr bend+CCN bend
Ring torsion+CCN wag
CCN torsion+ring torsion+CH wag
Ring deformation
CCN bend
CCN wag+CH wag
CCN wag+CH torsion
CCN bend+ring deformation
CCN bend
CCN torsion+CH wag
Ring deformation
CH torsion
Ring deformation+CCN stretch
CH wag
CH wag
CH bend
CH bend
CH bend
CC stretch+CCN stretch
CC stretch
Ring stretch
CC stretch
CC stretch
267
374
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
439
484
530
590
598
634
717
722
867
908
948
996
811
857
867
939
795
833
853
886
797
843
852
923
936
958
995
841
853
910
1189
1203
1292
1329
368
1444
1570
1652
1750
1771
2560
2560
3167
3169
3181
1088
1121
1182
1272
1325
1410
1560
1630
1774
1789
2474
2473
3054
3061
3069
1080
1112
1192
1226
1247
1378
1411
1479
1578
1617
2295
2301
3135
3157
3170
1058
1071
1150
1183
1217
1285
1397
1470
1558
1576
2278
2278
2819
2820
2831
1062
1094
1172
1205
1226
1355
1387
1454
1552
1590
2257
2263
3082
3105
3117
1079
1110
1180
1211
1269
1381
1396
1474
1553
1583
2233
2241
3034
3074
3105
CC stretch
CC stretch
CN stretch
CN stretch (sym)
CH stretch
CH stretch
CH stretch
additional plane of symmetry. The C26 molecules
include all doubly substituted phthalonitriles in
this series: 4,5-diiodo- 4,5-dibromo-, 3,6-dibromo-
frared and Raman active. For molecules of C26
symmetry, group theory analysis indicates that the
36 fundamental vibrations will reduce as: G=
13a +6a +5b +12b . In the C point group all
.
With 14 atoms composing each structure, each
1
2
1
2
26
molecule has 36 fundamental modes of vibration.
normal vibrations are Raman active and all but
For molecules of C symmetry, the total irre-
the a vibrations are infrared active. A final gen-
s
2
ducible representation of the 36 fundamentals is:
G=25a%+11a¦, where all normal modes are in-
eral comment about the normal vibrations of this
series of molecules is that all phthalonitriles will

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
311
Table 2
Symmetry of vibration, AM1, PM3, SVWN, experimental wavenumbers (cm−1), and band assignments for 4,5-dibromophthaloni-
trile
4
,5-Bromo
Nonscaled
Scaled
AM1
Observed
Assignment
Mode
Sym
AM1
PM3
SVWN
PM3
SVWN
1
2
3
4
5
6
7
8
9
a2
b1
a1
a1
b2
a2
b2
b1
a1
b2
b1
a2
b2
a1
b1
a2
a1
b2
a2
a1
b1
b2
a2
a1
b2
b2
a1
a1
b2
a1
a1
b2
b2
a1
b2
a1
47
101
117
127
143
164
263
280
335
359
422
441
532
583
625
695
703
731
785
894
951
961
980
1207
1281
1322
1357
1454
1549
1646
1742
1765
2560
2560
3161
3164
52
93
125
134
160
178
248
253
326
340
384
412
500
543
579
654
668
706
763
837
938
954
960
1091
1144
1263
1334
1455
1571
1619
1786
1805
2474
2475
3064
3065
45
82
122
131
141
153
239
252
306
332
391
416
480
497
519
636
643
654
721
739
868
876
899
1109
1158
1222
1236
1365
1375
1473
1551
1604
2295
2299
3141
3174
42
89
104
113
127
146
234
249
298
320
376
392
473
519
556
618
626
651
699
796
846
856
872
1074
1140
1176
1208
1294
1379
1465
1550
1571
2278
2279
2814
2816
46
83
111
119
143
158
221
225
290
302
342
367
445
483
515
582
594
629
679
745
835
849
854
971
1018
1124
1187
1295
1399
1441
1589
1607
2202
2202
2727
2728
45
80
120
128
139
151
235
248
301
326
385
409
472
488
510
626
632
643
709
727
853
861
884
1091
1139
1201
1216
1342
1352
1449
1525
1577
2256
2260
3088
3121
CBr+CCN wag
CBr wag
CBr bend+CCN bend
CBr bend+CCN bend
CBr rock+CCN rock
CCN wag+CBr wag
CBr stretch
CBr+CCN wag
CBr stretch+ring deformation
CCN bend+CBr bend
Ring torsion+CH wag
CCN torsion+ring torsion
Ring deformation
CCN bend
CCN wag+CH wag
Ring torsion
Ring deformation
CCN bend
CCN torsion
Ring stretch+CCN stretch
CH wag
Ring deformation
CH wag
CH bend
CH bend
Ring deformation
CC stretch
Ring stretch
CC stretch
CC stretch
CC stretch
146
166
214
242
269
337
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
413
480
494
534
589
627
646
712
723
888
899
915
1119
1146
1220
1267
1324
1336
1466
1529
1566
2237
2237
3013
3087
CC stretch
CN stretch
CN stretch
CH stretch
CH stretch (sym)
have 11 out-of-plane vibrations, 14 stretching vi-
brations and 11 in-plane bending vibrations.
tion, theoretical frequencies and proposed general
assignments for each of these molecules are pre-
sented in Tables 1–6. Frequencies are reported in
wave numbers (cm ). When using computa-
tional methods to predict theoretical normal vi-
brations for relatively complex polyatomics,
scaling strategies are used to bring computed
wave numbers into closer agreement with ob-
served frequencies. For the semi-empirical and
−
1
3.2. Assignment of spectra and effect of
halosubstituent
The structures, FT-Raman and infrared spectra
of halophthalonitriles are shown in Figs. 1–6.
Experimental wave numbers, symmetry of vibra-

3
12
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
Table 3
Symmetry of vibration, AM1, PM3, SVWN, experimental wavenumbers (cm−1), and band assignments for 3,6-dibromophthaloni-
trile
3
,6-Bromo
Nonscaled
Scaled
AM1
Observed
Assignment
Mode
Sym
AM1
PM3
SVWN
PM3
SVWN
1
2
3
4
5
6
7
8
9
a2
b1
b2
a1
a1
b1
a1
a2
b2
a2
b2
b1
b2
a1
a2
a1
b1
b2
a2
b2
a1
b1
a2
a1
b2
b2
a1
a1
b2
a1
a1
b2
b2
a1
b2
a1
65
66
129
131
151
190
230
268
342
387
388
499
526
589
595
670
692
734
833
885
922
976
996
1220
1237
1343
1358
1424
1582
1635
1742
1753
2558
2559
3162
3173
62
68
99
105
140
173
222
247
303
370
370
452
503
531
559
643
646
668
828
855
895
941
994
1119
1126
1295
1338
1406
1579
1641
1755
1824
2476
2477
3058
3072
72
79
122
137
150
177
217
264
310
360
370
432
483
494
566
589
601
653
756
787
840
860
929
1124
1143
1210
1216
1372
1417
1432
1571
1595
2295
2301
3143
3156
57
58
115
116
134
169
205
239
304
345
346
444
468
524
529
596
616
653
742
788
821
868
886
1086
1101
1196
1209
1267
1408
1455
1551
1560
2277
2277
2814
2824
55
61
88
71
77
120
135
147
174
213
259
305
354
364
425
475
485
556
580
591
642
744
774
826
846
914
1106
1124
1189
1195
1349
1394
1409
1545
1568
2257
2262
3090
3104
CCN wag
CBr wag
CCN rock
CCN bend
CBr bend+CCN bend
CCN wag
Ring deformation
CBr wag
CBr bend+CCN bend
CCN torsion+CH torsion
CBr stretch+ring deformation
CCN wag+ring torsion
CBr stretch
94
125
154
197
220
270
330
330
402
447
472
498
572
575
595
737
761
796
838
884
996
1002
1153
1191
1251
1405
1460
1562
1624
2204
2204
2722
2734
147
180
303
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
359
441
478
488
560
577
591
650
734
787
832
847
CCN bend
Ring torsion+CCN wag
Ring deformation+CCN bend
CCN wag
CCN bend
CCN torsion
Ring deformation
Ring deformation
CH wag
CH wag
CH bend
CH bend
Ring deformation
CC stretch
Ring stretch
CC stretch
CC stretch
CC stretch
CC stretch
CN stretch
1127
1144
1152
1204
1270
1395
1445
1556
2236
2236
3064
3107
CN stretch
CH stretch
CH stretch (sym)
DFT methods employed in this work the simplest
limiting scaling strategy was used—homogeneous
scaling [24]. Semi-empirical fundamental frequen-
cies were scaled by a factor of 0.89. The SVWN
local spin functional (Slater exchange functional
for this functional has been reported to be 0.98 by
Wong [9]. This empirical scaling factor was used
to scale the computed SVWN fundamentals in an
effort to increase the agreement between predicted
and observed fundamentals. The average differ-
ence between unscaled frequencies and observed
wave numbers for the semi-empirical AM1 and
PM3 methods were approximately 113 and 80
[
21] with VWN correlation functional [22]) has
been shown to predict fundamental vibrations in
good agreement with experimental data [8,10].
Recently, an empirical vibrational scaling factor
−
1
cm , respectively, across the entire series. The

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
313
Table 4
Symmetry of vibration, AM1, PM3, experimental wavenumbers (cm−1), and band assignments for 3-iodophthalonitrile
3
-Iodo
Nonscaled
AM1
Scaled
AM1
Observed
Assignment
Mode
Sym
PM3
PM3
1
2
3
4
5
6
7
8
9
a¦
a%
a%
a¦
a¦
a%
a%
a¦
a¦
a%
a¦
a%
a¦
a%
a%
a¦
a%
a¦
a¦
a%
a¦
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
59
114
130
157
194
268
290
388
445
474
567
580
652
653
715
805
859
58
107
134
156
184
284
316
369
420
451
541
543
609
622
671
773
831
52
102
116
140
173
238
258
345
396
422
504
516
580
581
637
716
764
52
96
119
139
164
253
281
329
374
401
481
483
542
554
597
688
739
CCN wag+CI wag
CI bend+CCN bend
CCN bend
CCN wag+CI wag
CI wag+CCN wag
CCN bend+CI bend
CI stretch
CCN wag+ring torsion
Ring torsion
Ring deformation
CCN wag+ring torsion
CCN bend
CCN wag+ring torsion
CCN bend+ring deformation
CCN bend+ring deformation
CCN wag+CH wag
CCN stretch+ring deformation
CCN torsion+CH wag
CH wag
Ring deformation
CH torsion
CH bend
CH bend
CH bend
Ring deformation
CC stretch
Ring stretch
CC stretch
CC stretch
CC stretch
CC stretch
135
155
173
241
255
332
389
423
485
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
552
570
617
729
765
876
953
961
839
936
966
780
849
855
897
747
833
860
899
807
822
860
1007
1183
1207
1255
1342
1369
1434
1590
1646
1749
1769
2557
2560
3167
3176
3188
1010
1119
1154
1186
1292
1328
1398
1579
1637
1765
1804
2470
2474
3052
3060
3072
1053
1074
1117
1194
1219
1276
1415
1465
1557
1574
2276
2278
2819
2827
2837
996
1001
1063
1127
1189
1208
1281
1427
1449
1553
1571
2233
2233
2065
3075
3108
1027
1056
1150
1182
1244
1406
1457
1571
1606
2199
2201
2716
2723
2734
CN stretch
CN stretch
CH stretch
CH stretch
CH stretch (sym)
average difference for the SVWN functional was
It is convenient to discuss the vibrational spec-
tra of halophthalonitriles in terms of four charac-
teristic spectral regions: C–H stretching
vibrations, CN stretching region, CꢀC stretching
and ring stretching modes region (1600–1000
−
1
only ca. 27 cm , across the bromo-substituted
phthalonitriles. All vibrational assignments
are based on the respective point group sym-
metry for each molecule. Assignments were
made through visualization of the atomic dis-
placement representations for each vibration,
and matching the predicted normal frequencies
and intensities with experimental Raman and in-
frared data.
−
1
cm ), and out-of-plane C–H vibrations region
−
1
(700–1000 cm ). The vibrational assignment for
the phthalonitrile molecule (1,2-dicyanobenzene),
aided with ab initio computations, has been car-
ried out by Ramirez et al. [7]. The complete

3
14
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
Table 5
Symmetry of vibration, AM1, PM3, experimental wavenumbers (cm−1), and band assignments for 4-iodophthalonitrile
4
-Iodo
Nonscaled
AM1
Scaled
AM1
Observed
Assignment
Mode
Sym
PM3
PM3
1
2
3
4
5
6
7
8
9
0
a¦
a%
a¦
a%
a¦
a%
a%
a¦
a¦
a%
a%
a¦
a¦
a%
a%
a¦
a%
a¦
a%
a¦
a¦
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
a%
68
119
130
131
228
261
274
376
433
487
576
592
632
662
716
787
876
68
124
126
143
221
287
296
364
405
469
541
556
592
639
673
759
832
60
106
116
116
203
233
244
335
385
434
513
527
563
589
637
701
780
61
110
112
127
297
256
263
324
360
417
481
495
527
569
599
676
740
I wag+CCN wag
CI bend+CCN bend
CCN wag
146
231
CI bend+CCN bend
CI wag+CCN wag
CI stretch+CCN bend
CI bend+CCN bend
Ring torsion+CCN wag
CCN torsion+ring torsion+CH wag
Ring deformation
CCN bend
CCN wag+CH wag
CCN wag+CH wag
CCN bend+ring deformation
CCN bend
CCN torsion+CH wag
Ring deformation
CH wag
Ring deformation
CH wag
CH torsion
CH bend
CH bend
CH bend
CC stretch+CCN stretch
CC stretch
Ring stretch
CC stretch
CC stretch
252
377
433
478
529
583
592
629
713
722
752
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
892
942
958
996
865
946
953
994
794
839
853
886
770
842
848
885
836
844
910
1190
1200
1288
1328
1368
1450
1570
1654
1753
1771
2560
2560
3166
3168
3181
1126
1143
1200
1274
1327
1428
1564
1634
1776
1795
2473
2474
3055
3063
3070
1059
1068
1147
1182
1217
1290
1397
1472
1560
1576
2278
2278
2817
2820
2831
1002
1017
1068
1134
1181
1271
1392
1454
1581
1597
2201
2202
2719
2726
2732
1075
1102
1180
1207
1267
1376
1391
1472
1546
1575
2233
2238
2019
3064
3095
CC stretch
CC stretch
CN stretch
CN stretch (sym)
CH stretch
CH stretch
CH stretch
assignments proposed here for the halophthaloni-
triles are in good agreement with the work of
Ramirez et al. [7] with due differences in experi-
mental wave numbers, which depends on the sub-
stituency pattern, and the effect of heavy atom
substituents. The high frequency vibrations of the
CH stretching region and the CN stretching re-
gion are most readily assigned due to the high
amplitude of the normal mode (low mode mixing)
for the corresponding internal coordinate. For the
molecules in this series all CH stretching vibra-
tions were observed. It was of interest to follow
the effect of a change in halosubstituent from
bromine to iodine in the wavenumber value of
fundamentals. For instance, an average downshift
−
1
in wavenumber of 14 cm
is observed for CH
stretching fundamentals upon a change in halo-
substituent from bromine to iodine in analogous
phthalonitriles. This mass effect is illustrated in
Fig. 7.

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
315
Table 6
Symmetry of vibration, AM1, PM3, experimental wavenumbers (cm−1), and band assignments for 4,5-diiodophthalonitrile
4
,5-Iodo
Nonscaled
AM1
Scaled
AM1
Observed
Assignment
Mode
Sym
PM3
PM3
1
2
3
4
5
6
7
8
9
a2
b1
a1
a1
b2
a2
b2
b1
a1
b2
b1
a2
b2
a1
b1
a2
a1
b2
a2
a1
b1
b2
a2
a1
b2
b2
a1
a1
b2
a1
a1
b2
b2
a1
b2
a1
44
74
94
122
123
159
230
270
301
328
414
438
23
582
624
687
705
727
787
891
950
963
994
1205
1273
1320
1360
1468
1555
1648
1749
1765
2560
2560
3163
3165
41
90
95
125
131
154
248
259
342
358
398
413
528
542
576
660
685
39
66
84
109
109
141
205
240
268
292
369
390
465
518
556
612
627
647
701
793
846
857
884
1072
1133
1175
1210
1306
1384
1467
1556
1571
2278
2279
2815
2817
37
80
84
111
116
137
221
231
304
319
354
367
470
482
513
587
610
631
672
767
832
852
925
1070
1105
1131
1189
1306
1369
1470
1587
1589
2201
2202
2715
2716
CI+CCN wag
CI wag
CI bend+CCN bend
CI bend+CCN bend
CI rock+CCN rock
CCN wag+CI wag
CI stretch
CI+CCN wag
CI stretch+ring deformation
CCN bend+CI bend
Ring torsion+CH wag
CCN torsion+ring torsion
Ring deformation
CCN bend
CCN wag+CH wag
Ring torsion
Ring deformation
CCN bend
CCN torsion
Ring stretch+CCN stretch
CH wag
Ring deformation
CH wag
CH bend
CH bend
Ring deformation
CC stretch
Ring stretch
CC stretch
CC stretch
CC stretch
207
255
311
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
403
480
499
528
619
642
710
723
864
885
906
1098
1131
1217
1264
709
755
862
935
957
1039
1203
1242
1271
1336
1468
1538
1652
1783
1786
2474
2475
3051
3052
1322
1453
1523
1557
2232
2232
2991
3072
CC stretch
CN stretch
CN stretch
CH stretch
CH stretch (sym)
Both the symmetric and antisymmetric CN
In the spectral region of the CꢀC stretching
modes, the aromatic ring vibrations overlap with
the C–H bending modes. The ring stretching
modes showed a mass downshift smaller than that
of the CH bending vibrations by a change in
halosubstituent with an average decrease in
stretching vibrations for the 4-substituted ph-
thalonitriles were observed in the experimental
spectra. For 3-iodophthalonitrile and the doubly
substituted phthalonitriles the two modes are acci-
dentally degenerate. Among similarly substituted
phthalonitriles, a change from bromine to iodine
substituent shows an average downshift in ob-
−
1
wavenumber of 7 and 9 cm , respectively.
Out-of-plane wags and torsions and heavy sub-
−
1
−1
served wave numbers of 4 cm . This lessened
effect can be explained by the relative ‘off of the
ring’ location of the CN bonds.
stituent bends show average downshift of 7 cm
with change in halosubstituent. The effect is illus-
trated in Fig. 8. The mass effect was consistently

3
16
M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
observed across all four characteristic spectral
regions, with stretching vibrations being most sen-
sitive. At the same time the electronic effects were
modest as indicated by the permanence of in-
frared intensities with the change in halosub-
perpendicular to the molecular plane is of primary
importance for studies of molecular organization
in thin solid films of materials containing these
molecular moieties. In 1,2-dicyanobenzene [7], the
out-of-plane C–H modes are assigned with wave
−
1
stituent.
A
characteristic infrared intensity
numbers at 885, 928 and 944 cm . In tereph-
−
1
indicates relative invariance in ((v/(Q ), which in
thalonitrile a strong infrared band at 846 cm
i
turn is a qualitative indication of no significant
change in the electronic structure with change in
halosubstituent.
was assigned to the wagging C–H vibration [5]. In
a series of four substituted benzonitriles Green
and Harrison [25] have consistently observed two
C–H out-of-plane vibrations: a weak infrared
−
1
3.3. Out-of-plane C–H 6ibrations
band in the 958–939 cm
region, and a strong
−
1
infrared band in the 842–823 cm
region. Simi-
The identification of the C–H wagging vibra-
tional modes with a dipole moment derivative
lar bands with characteristic wavenumber and
relative intensity in the infrared spectrum were
observed in the series and have been assigned to
the C–H wagging. In the IR spectrum of 4-bro-
−
1
mophthalonitrile a strong band at 853 cm
has
been assigned to the C–H wagging of the two
adjacent C–H bonds. A second out-of-plane C–
−
1
H is observed at 910 cm . In 4,5-dibromoph-
thalonitrile, where the there is no adjacent pair of
C–H bonds, only one wagging mode is observed
−
1
at 915 cm
with strong infrared intensity. In the
infrared spectrum of 3,6-dibromophthalonitrile
the strong band of the wagging mode for the
−
1
adjacent C–H bond is observed at 847 cm . The
infrared spectrum of the 3-iodophthalonitrile a
−
1
strong band at 807 cm
is assigned to the C–H
wag. The high frequency wag is also observed at
−
1
8
60 cm . The 4-iodophthalonitrile follows the
Fig. 7. C–H Stretching vibrations of 4-bromophthalonitrile
and 4-iodophthalonitrile.
pattern observed for the 4-bromophthalonitrile
(
cm
see Fig. 8) with a strong infrared band at 844
−
1
−1
and a weaker out-of-plane at 910 cm
.
Finally, the 4,5-diiodophthalonitrile follows the
template of the corresponding 4,5-dibromo
−
1
derivative and the wagging at 906 cm
is ob-
served. The strong lower wavenumber wag is not
seen.
4
. Conclusions
The infrared and FT-Raman spectra of a series
of six novel halophthalonitriles have been studied.
General assignments of observed fundamental vi-
brations have been proposed for all molecules in
this study, on the basis of quantum chemical
Fig. 8. Out-of-plane C–H region of 4-bromophthalonitrile and
4
-iodophthalonitrile.

M.D. Halls et al. / Spectrochimica Acta Part A 54 (1998) 305–317
317
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computations at the semi-empirical AM1 and
PM3 levels and computations at the SVWN DFT
level. Encouraging results for vibrational proper-
ties were obtained using the DFT methods. The
mass effect of halosubstitution (iodo for bromo)
on fundamental vibrations was observed to be a
downshift in wavenumber with a maximum of 14
cm . The out-of-plane C–H vibrations have
been identified in the infrared spectra of the series
in consideration of their potential as vibrational
probes for molecular organization studies in thin
solid films.
1
[
[
[
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