Structural and vibrational investigation of 2-amino-4-nitropyridine crystal

Article abstract of DOI:10.1016/S0022-2860(97)00009-4

The X-ray structure of 2-amino-4-nitropyridine was determined at room temperature. The crystal belongs to the P2(I)/c space group of the monoclinic system (Z = 4, a = 6.7290(10), b = 10.946(2), c = 9.060(2) A, β = 100.03(3) deg) and is built of layers parallel to the (102) crystallographic plane. The molecules in the layer are joined into centrosymmetric dimers by two N-H···N hydrogen bonds (N···N distance = 3.011(3) A), which form rings of C(i) symmetry. The other N-H bonds of the amino groups are involved in N-H···O hydrogen bonds with the oxygen atoms of the nitro groups (N···O distance = 3.054(3) A). These hydrogen bonds join the dimers into an infinite plane. The powder IR and Raman spectra (4000-80 cm^-1) were measured for normal and deuterated crystals and are discussed with respect to the crystal structure. The N-H stretching vibrations behave as the stretching vibrations of two almost independent hydrogen bonds. Strong A(g)-A(u)-type splitting is observed for the stretching vibrations of the N-H···N type hydrogen bonds.

Full text of DOI:10.1016/S0022-2860(97)00009-4

MOLSTR 9760
Journal of Molecular Structure 415 (1997) 53–63
Structural and vibrational investigation of
2-amino-4-nitropyridine crystal
J. Oszusta, Z. Talika, A. Pietraszkob, M.K. Marchewkab, J. Baranb
aWroclaw University of Economics, 118/120 Komandorska str., 53-345 Wroclaw, Poland
bInstitute of Low Temperature and Structure Research of the Polish Academy of Sciences, 2 Okolna str., 50-950 Wroclaw, Poland
Received 25 November 1996; accepted 23 December 1996
Abstract
The X-ray structure of 2-amino-4-nitropyridine was determined at room temperature. The crystal belongs to the P21/c space
˚
group of the monoclinic system (Z = 4, a = 6.7290(10), b = 10.946(2), c = 9.060(2) A, b = 100.03(3) deg) and is built of layers
…
parallel to the (102) crystallographic plane. The molecules in the layer are joined into centrosymmetric dimers by two N–H
N
…
˚
hydrogen bonds (N N distance = 3.011(3) A), which form rings of Ci symmetry. The other N–H bonds of the amino groups
…
…
˚
are involved in N–H O hydrogen bonds with the oxygen atoms of the nitro groups (N O distance = 3.054(3) A). These
hydrogen bonds join the dimers into an infinite plane. The powder IR and Raman spectra (4000–80 cm−1) were measured for
normal and deuterated crystals and are discussed with respect to the crystal structure. The N–H stretching vibrations behave as
the stretching vibrations of two almost independent hydrogen bonds. Strong Ag–Au-type splitting is observed for the stretching
…
vibrations of the N–H N type hydrogen bonds. ᭧ 1997 Elsevier Science B.V.
Keywords: X-structure; 2-Amino-4-nitropyridine; IR; Raman; Hydrogen bond; Dimers
1. Introduction
such a hydrogen bond arrangement are very interesting
from the point of view of interactions between
hydrogen bonds in the crystal.
2-Amino-4-nitropyridine is interesting because its
compounds with other chemicals may exhibit valuable
physical properties, e.g. ferroelectric, second harmonic
generation (SHG). This paper is devoted to the struc-
tural and vibrational properties of the title compound in
the crystalline state. Unfortunately, the compound can-
not be purchased; therefore we had to synthesize it in
one of our laboratories. The results of the X-ray experi-
ment exclude its application for SHG as the crystal is
centrosymmetric at room temperature. The structure
comprises centrosymmetric dimers containing two
2. Experimental
The title compound was synthesized according to
the procedure elaborated by Talik and Talik [1]; this is
presented in Scheme 1. The crystals were grown from
an aqueous solution and had the shape of pistils. The
deuterated compound was obtained by two-fold
recrystallization from solution in D2O. In this proce-
dure, only the protons of the amino groups can be
replaced by the deuterons.
…
molecules bonded by two identical N–H N hydrogen
bonds forming a ring. The spectroscopic properties of
0022-2860/97/$17.00 Copyright ᭧ 1997 Elsevier Science B.V. All rights reserved
PII S0022-2860(97)00009-4

54
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Scheme 1.
Table 1
Crystal data and structure refinement parameters for 2-amino-4-nitropyridine
Identification code
Empirical formula
Formula weight
Temperature
pyho
C5 H5 N3 O2
139.12
293(2) K
0.71073 A
˚
Wavelength
Crystal system
Space group
Unit cell dimensions
Monoclinic
P2(1)/c
a = 6.7290(10) A, alpha = 90 deg.
˚
˚
b = 10.946(2) A, beta = 110.03(3) deg.
˚
c = 9.060(2) A, gamma = 90 deg.
3
˚
Volume
627.0(2) A
Z
4
Density (calculated)
Absorption coefficient
F(000)
1.474 g cm3 (or Mg m−3
)
0.118 mm−1
288
Crystal size
Theta range for data collection
Index ranges
0.4 × 0.35 × 0.28 mm
3.03–27.05 deg.
− 8 Ͻ = h Ͻ = 8, 0 Ͻ = k Ͻ = 14, − 11 Ͻ = 1 Ͻ = 11
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices (I Ͼ 2j(I))
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
2158
1243 (R(int) = 0.0256)
Full-matrix least-squares on F2
1243/0/112
1.051
R1 = 0.0441, wR2 = 0.0930
R1 = 0.1118, wR2 = 0.1148
0.000(3)
−3
˚
0.134 and − 0.133 e A

55
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table 2
4
2
3
˚
Atomic coordinates ( × 10 ) and equivalent isotropic displacement parameters (A × 10 ) for 2-amino-4-nitropyridine. U(eq) is defined as one
third of the trace of the orthogonalized Uij tensor
x
y
z
U(eq)
C(4)
N(4)
O(1)
O(2)
C(5)
C(6)
N(1)
C(2)
N(2)
C(3)
H(5)
H(6)
H(1)
H(2)
H(3)
2159(3)
1744(2)
1226(2)
1788(2)
1796(2)
2222(2)
653(3)
142(3)
195(2)
778(2)
818(3)
1305(2)
584(28)
−295(26)
1238(30)
561(29)
55(1)
71(1)
94(1)
94(1)
65(1)
63(1)
54(1)
50(1)
71(1)
54(1)
87(8)
70(7)
76(8)
88(8)
58(6)
926(3)
1366(3)
−457(3)
3659(4)
4727(4)
4439(3)
2984(3)
2721(3)
1765(3)
3922(38)
5776(35)
1929(40)
3616(38)
721(31)
862(2)
−219(2)
1252(2)
1308(2)
2168(2)
3361(2)
3753(2)
4960(2)
2940(2)
418(24)
1969(21)
5228(23)
5501(22)
3219(20)
1677(23)
The FTIR spectra were measured as nujol and
hexachlorobutadiene mulls. A Bruker IFS-88 spectro-
meter equipped with an FRA-106 FT-Raman attach-
ment and a diode-pumped Nd:YAG laser with a
power of 150 mW was used for the spectral measure-
ments. Resolution was 2 cm−1 with a weak apodiza-
tion. The Raman spectra above 3200 cm−1 are quite
weak due to detection problems.
The X-ray data were collected at 293 K using a
Kuma-Diffraction KM4 diffractometer (graphite
monochromator, Mo Ka radiation, q/2v scan). The
sample was rhombohedral in shape and measured
0.4 × 0.35 × 0.28 mm3. The unit cell parameters
were determined by the least-squares fit of the setting
angles of 30 reflections in the range 3.03 Ͻ v Ͻ
27.05Њ. Crystallographic data and structure refinement
parameters are listed in Table 1. Three check reflec-
tions, measured after every 50 reflections, showed 1%
variation. The crystal structure was solved by direct
methods (SHELXS-86) [2] and refined by the full-
matrix least-squares method (SHELXL-93) [3]. The
C-bonded H atoms and the N-bonded H atoms were
found from the difference Fourier map and then
refined. The H atoms have a temperature factor of
1.2 × Ueq of the respective bonded heavy atom. The
number of refined parameters was 86. The final
refinement resulted in R(F) = 0.0441 and wR(F2) =
0.0930 with calculated weights w = 1/[a2(FO2 ) +
0.0756P2 + 27.8P], where P = (FO2 + 2Fc2)/3. The
maximum shift was 0.03a and the largest difference
−3
−3
˚
˚
peak and hole were − 0.134 e A and − 0.133 e A .
The final atomic parameters are given in Table 2.
Table 3
2
Anisotropic displacement parameters (A × 103) for 2-amino-4-nitropyridine.The anisotropic displacement factor exponent takes the form:
˚
− 2p2 h2a U11 + + 2hka b U12
2
…
U11
55(1)
U22
60(1)
U33
49(1)
U23
9(1)
15(1)
16(1)
30(1)
4(1)
U13
U12
−8(1)
−16(1)
−18(1)
−7(1)
3(1)
7(1)
1(1)
−1(1)
−7(1)
−2(1)
C(4)
N(4)
O(1)
O(2)
C(5)
C(6)
N(1)
C(2)
N(2)
C(3)
18(1)
18(1)
43(1)
54(1)
34(1)
39(1)
31(1)
24(1)
62(1)
26(1)
70(1)
120(2)
78(1)
74(2)
63(1)
53(1)
51(1)
76(1)
49(1)
78(2)
71(1)
110(2)
50(2)
61(2)
54(1)
53(1)
58(2)
68(2)
61(1)
96(2)
110(1)
77(2)
76(2)
62(1)
51(1)
103(2)
51(1)
1(1)
−3(1)
−3(1)
−11(1)
0(1)

56
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Fig. 1. Projection of the structure along the Y-direction.
Fig. 2. Structure of one layer (projection onto (102) plane). Symmetry code:(a) 1 − x, y, 1 +z; (b) 1 + x, y, z; (c) 1 + x, 1 +y, z; (d) − x, − y, 1 −z (e)
− x, 1 −y, 1 −z; (f) 2 − x, 1 −y, −z; (g) 1 − x, − 0 5 + y, 0 5 −z; (h) 1 − x, 0 5 +y, 0 5 −z; (i) x, 0 5 −y, 0 5 +z; (j) x, 1 5 −y, 0 5 +z.

57
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table
3 contains the anisotropic displacement
Table 4
Bond lengths (A) and angles (deg) for 2-amino-4-nitropyridine
˚
parameters for heavy atoms.
C(4)–C(3)
C(4)–C(5)
C(4)–N(4)
N(4)–O(2)
N(4)–O(1)
C(5)–H(5)
C(5)–C(6)
C(6)–H(6)
C(6)–N(1)
N(1)–C(2)
C(2)–N(2)
C(2)–C(3)
N(2)–H(1)
N(2)–H(2)
1.342(3)
1.369(3)
1.473(3)
1.206(3)
1.219(3)
1.00(3)
3. Results and discussion
3.1. Description of the crystal structure
1.358(3)
0.95(2)
The main features of the crystal structure are the
layers which are parallel to the (102) planes (see
Fig. 1). Two layers are related to each other by the
c-glide plane. The interactions between the layers are
very weak of van der Waals type. Due to this, the crystal
shows strong cleavage properties. The cleavage plane
contains the main cross-section of the optical indi-
catrix. The layer is built of centrosymmetric dimers
1.323(3)
1.333(2)
1.335(3)
1.400(3)
0.81(3)
0.93(3)
…
H(2) N(1i)
2.060(3)
3.011(3)
3.053(3)
2.260(3)
0.93(2)
…
N(2) N(1i)
…
N(2) O(2ii)
(see Fig. 2). Each dimer is formed by two identical
…
H(1) O(2ii)
i
…
…
N(2)–H(2) N(1 ) (i = −x +1; − y + 1; − z) hydrogen
C(3)–H(3)
˚
bonds (N N distance = 3.011(3) A, NHN angle =
i
…
˚
C(3)–C(4)–C(5)
C(3)–C(4)–N(4)
C(5)–C(4)–N(4)
O(2)–N(4)–O(1)
O(2)–N(4)–C(4)
O(1)–N(4)–C(4)
H(5)–C(5)–C(6)
H(5)–C(5)–C(4)
C(6)–C(5)–C(4)
H(6)–C(6)–N(1)
H(6)–C(6)–C(5)
N(1)–C(6)–C(5)
C(6)–N(1)–C(2)
N(1)–C(2)–N(2)
N(1)–C(2)–C(3)
N(2)–C(2)–C(3)
H(1)–N(2)–H(2)
H(1)–N(2)–C(2)
H(2)–N(2)–C(2)
H(3)–C(3)–C(4)
H(3)–C(3)–C(2)
C(4)–C(3)–C(2)
123.0(2)
176.4(13)Њ, H(2) N(1 ) distance = 2.060(3) A)
which make a ring. Similar dimers appear in crystals
of 2-aminopyridine [4] and 2-amino-3-nitropyridine
118.4(2)
118.5(2)
123.7(2)
118.0(2)
118.3(2)
122(2)
…
[5] where the N N distances are 3.071 and 3.009
˚
A, respectively. The other protons of the amino
groups are involved in hydrogen bonds with the oxy-
gen O(2) atoms of nitrate groups of adjacent dimers.
Two dimers joined by the N(2) − H(1) O(2 (ii =
122(2)
115.6(2)
112.5(14)
122.7(14)
124.8(2)
117.9(2)
116.8(2)
121.7(2)
121.4(2)
118(2)
ii
…
…
− x; y + 0.5; − z + 0.5) hydrogen bonds (N
O
˚
distance = 3.054(3) A; NHO angle = 163.8(14)Њ;
ii
…
˚
H(1) O(2 ) distance = 2.260(3) A) are related to
each other by the 21 screw axis. Surprisingly, the
˚
N(4)–O(2) bond (1.205 A), being the proton acceptor
…
in the N(2)–H(1) O(2) hydrogen bond, is shorter
˚
than the second N(4)–O(1) bond (1.220 A) of the
119(2)
121(2)
nitrate group. The lengths of the other bonds and the
values of angles in the pyridine ring are listed in
Table 4. The pyridine ring atoms and the nitrogen
atom of the nitro group are coplanar; the equation of
the plane and the deviations of the atoms from this
plane are listed in Table 5. The N(2) atom deviates
121.8(14)
121.3(14)
116.9(2)
176.4(13)
163.8(13)
…
N(2)–H(2) N(1i)
…
N(2)–H(1) O(2ii)
Symmetry transformations used to generate equivalent atoms: i =
− x + 1; − y + 1; − z; ii = −x; y +0 5; − z + 0 5.
˚
from the pyridyne ring by 0.0129 A. The average
angle between the pyridine ring and the NO2 or
NH2 plane is approx. 4.0Њ or 10Њ, respectively.
modes (39 Ag + 39 Bg) are only Raman-allowed.
The same number of internal modes (39 Au + 39
Bu) are only IR-active. As follows from the correla-
tion diagram (Table 7), each vibration should be split
into Au and Ag modes due to the Ci symmetry of the
3.2. Fundamental mode analysis and selection rules
The formal classification of normal modes for the
title crystal is listed in Table 6. Thus 78 internal

58
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table 5
Table 7
Deviations of the pyridine ring atoms from the plane 2.682X +
0.406Y + 6.564Z = 1.4557 for 2-amino-4-nitropyridine
The correlation diagram for 2-amino-4-nitropyridine crystal
C1
Ci
C2h
Ag
IR
Raman
˚
Atom
Deviation/A
xx, yy, zz, xz
C4
N4
O1
O2
C5
H5
C6
H6
N1
C2
N2
H1
H2
C3
H3
−0.0011
0.0008
0.0801
−0.0693
0.0075
−0.0047
−0.0066
−0.0127
−0.0012
0.0077
0.0129
0.0756
0.1064
−0.0062
−0.0312
Ag
Bg
Au
Bu
xy, zy
A
Y
Au
X, Z
Abbreviations: C1, site group of the molecule in crystal; Ci, site
group of dimer; C2h, factor (unit cell) group of crystal.
of the NH2 group), and the internal modes of the
nitro group and pyridine ring.
In the following discussion, mention will be made
of the IR values of the observed frequencies; the
Raman values are in parentheses.
3.3.1. Vibrations of the NH2 group
dimer (intradimer splitting). In the next step, each
intradimer mode may split into two other components
due to interdimer interactions. It is obvious that the
intradimer coupling should be the most effective.
Therefore, the wavenumbers of bands in the IR spec-
trum should be different from those in the Raman
spectrum. This splitting should be especially big for
The X-ray data show that the amino group is
involved in two hydrogen bonds with the ring nitrogen
and the oxygen of nitro group, respectively. The
lengths of the N–H bonds already indicate that these
two bonds are substantially different. Thus the N(2)–
˚
H(2) bond (0.93 A) involved in the hydrogen bond
…
with the N(1) nitrogen is longer than the N(2)–H(1)
the vibrations of N–H N hydrogen bonds.
˚
bond (0.81 A) creating the hydrogen bond with the
oxygen O(2) of the nitro group. This observation
3.3. Vibrational studies
…
allows us to suggest that the N(2)–H(2) N(1) hydro-
…
gen bond is stronger than the N(2)–H(1) O(2)
The FT-IR and FT-Raman powder spectra (3500–
80 cm−1) of the title crystal and its deuterated analo-
gue are shown in Fig. 3. The band wavenumbers and
proposed assignments are listed in Table 8, where
Wilson’s numbering of benzene ring modes [6] has
been adopted. The observed bands can be con-
veniently divided into those which arise from the
hydrogen bond vibrational modes (or the vibrations
hydrogen bond. Due to this the coupling between
the stretching, vibrations of two N–H bonds in the
NH2 group may be quite weak and can be neglected.
Therefore, instead of the symmetric stretching
(nsNH2) and the asymmetric stretching (naNH2)
vibrations, one should observe two stretching
vibrations of two different hydrogen bonds. This
Table 6
Results of the fundamental modes (k = 0) analysis for 2-amino-4-nitropyridine crystal; space group = P21/c, Z = 4
C2h
N
TA
T
L
I
IR
Raman
Ag
Bg
Au
Bu
45
45
45
45
0
0
1
2
3
3
2
1
3
3
3
3
39
39
39
39
xx,yy,zz,xz
xy,zy
Y
X,Z
Abbreviations: N, total number of modes; TA, acoustic modes; T, translational modes; L, librational modes; I, internal modes including
hydrogen bonds modes; IR, infrared,

59
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table 8
Wavenumbers (cm−1), relative intensities and tentative assignement of bands observed in the powder IR and Raman spectra of 2-amino-4-
nitropyridine and its partly deuterated analogue (ND2)
IR
H
Raman
H
Tentative assignmenta
D
D
3697 vw
3566 vw
3697 vw
3566 vw
3444 sh
3440 vw
3319 vw
…
3442 vs
3314 s
3442 s, 3430 s
3314 m
nNH
O
2 * dNH2
3273 m
3270 w
3266 vw
3227 sh
3150 s
3223 m
3146 m
3121 sh
…
3143 vw
3122 vw
3143 vw
3118 vw
nNH
N
3092 sh
3076 s
3062 sh
3030 s
nCH
nCH
nCH
nCH
20a
20b
2a
3073 m
3063 sh
3032 m
3076 vw
3064 sh
3031 vw
3077 vw
3060 vw
3033 vw
7b
2986 m
2978 m
2977 vw
2950 vw
2938 m
2927 w
2904 w
2902 sh
2890 sh
2872 m
2855 w
2816 w
2780 w
2751 sh
2702 w
2671 sh
2610 w
2902 vw
2809 vw
2906 vw
2873 w
2855 w
2813 w
2782 w
2803 vw
2707 vw
2707 w
2669 sh
2704 vw
2673 vw
2611 vw
2593 sh
2573 vw
2558 sh
2532 sh
…
nND O
2572 m
2553 w
2506 w
2456 vw
2418 vw
2386 vw
2554 vw
2535 w
2506 sh
2469 vw
2455 vw
2448 vw
2449 sh
2403 sh
2375 m
2376 vw
2360 vw
2348 vw
2340 vw
…
nND N
2331 m
2265 sh
2205 vw
2320 m
2291 sh
2266 vw
2224 sh
2292 vw
2266 vw
2195 vw
2156 sh
2118 vw
2116 vw

60
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table 8 Continued
IR
H
Raman
H
Tentative assignmenta
D
D
2091 vw
2069 vw
2047 vw
2043 vw
2033 vw
2034 vw
1990 vw
1930 vw
1924 vw
1901 vw
1900 vw
1874 vw
1844 vw
1824 vw
1902 vw
1900 vw
1818 vw
1807 vw
1767 vw
1750 vw
1649 vs
1750 vw
1651 m
1749 vw
1651 vw
1626 vw
1618 vw
1601 vw
1586 vw
1573 vw
1748 vw
1642 sh
1626 vw
1617 vw
1599 vw
1585 vw
1570 vw
1540 sh
1522 w
dNH2
nCC
1615 s
1594 sh
1618 s
1592 w
8a
8b
1573 vs
1570 vs
1545 sh
1524 vs
1487 m
1466 sh
1442 s
nCC
1524 vs
1487 vs
1522 vw
1487 vw
nasNO2
nCC
1487 vw
19b
19a
14
1442 s
1452 vw
1446 vw
nCC
1404 w
1381 vw
1356 vs
1332 m
1386 sh
1354 vs
1339 s
1384 sh
1353 vs
1337 m
1379 sh
1357 vs
1341 sh
nCC
nsNO2
nCN(O2)
1320 sh
1303 w
1287 s
1306 w
1287 s
1276 sh, 1265 s
1250 sh
1303 sh
1289 w
1275 vw
1301 sh
1288 vw
1266 m
nCN(O2)
dCH
nCN
3
13a
1276 s
dND2
1228 sh
1169 w
1227 sh
1176 w
1161 w
1229 vw
1141 vw
1229 vw
1185 vw
1109 w
1082 m
1113 w
1094 w
1094 vw
1059 vw
996 w
964 w b
952 w
935 w
877 s
830 s
802 w
737 s
1099 m
1069 sh
991 W
rNH2
dCC
993 s
990 m
12
qNH2
gCH
gCH
dNO2
dCC
gCH
qNO2
dCC
952 w
934 w
876 s
955 vw
937 w
875 vw
830 m
793 vw
737 vw
725 vw
693 vw
953 vw
933 vw
876 vw
823 m
791 vw
736 vw
724 vw
690 vw
5
17a
830 sh, 824 vs
802 w
6b
11
737 s
1
4
692 s
690 vs
nCC

61
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Table 8 Continued
IR
H
Raman
H
Tentative assignmenta
D
D
572 vw
561 sh
544 vw
566 m
549 w
566 vw
566 vw
558 sh
526 vw
rNO2
dCC
533 vw a
502 vw
432 vw
412 vw
371 vw
317 vw
227 vw
6a
435 m
412 m
383 m
421 vw
389 vw
250 vw
tNH2
gCC
nCX
402 vw
376 vw
16b
tND2
231 m
213 sh
190 m
101 w
243 vw
190 vw
100 vw
190 w
99 vs
191 w
100 s
tNO2
Abbreviations: vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; b, broad; i, this band occurs at 549 cm−1 in
hexachlorobutadiene.
aWilson’s numbering of benzene ring modes [6]
…
suggestion finds confirmation in the considerably dif-
ferent shapes of bands arising from these two HBs.
The first strong, quite narrow, band appears at the
same wavenumber in the IR and Raman spectra: 3442
of the partly deuterated sample, the N–H O stretch-
ing vibration band is split into two components at
3442 and 3430 cm−1. This could be explained by the
hypothesis that the lower frequency band (3430 cm−1)
(3440) cm−1; after deuteration it moves to 2572 (2573)
arises from the stretching vibration of the N–H
bond of the dimer whose second bond is deuterated
(N–D O). This deuterated bond probably gives rise
O
…
−1
…
cm . This band arises from the N–H O hydrogen
…
bond.
The second strong band occurs at different wave-
numbers in the IR and Raman spectra: 3150
(3143)cm−1. This band is caused by the stretching
to the band observed both in the IR and Raman spectra
at 2535 (2532) cm−1.
The assignment of bands to all possible deforma-
tion vibrations of the amino group is rather difficult.
The data of this paper do not allow problems such as
the coupling between the bending vibrations of two
substantially different N–H bonds to be solved.
Nevertheless, the band at 1649 (1651) cm−1 may be
assigned to the scissoring vibration dNH2. On deutera-
tion it moves to approx. 1250 cm−1 (isotopic ratio shift
= 1.32). The other bending modes of the NH2 group
are strongly coupled with the internal (skeletal)
vibrations of the pyridine ring. Therefore deuteration
causes changes in the wavenumbers and intensities
of many bands, indicated in Table 8. The bands
at 1059 (1069), 964 and 435 (421) cm−1 are
roughly assigned to the rocking (rNH2), wagging
(qNH2) and twisting (tNH2) modes, respectively,
by analogy to the spectra of m-nitroaniline and m-
nitrophenol [7]. In their spectra, the wagging
modes appear at 816 (816) and 904 (904), and
the twisting modes give bands at 510 (512) and
…
vibration of the N–H N hydrogen bond; its width
is broader than the width of the band at 3442 cm−1.
It is consistent with the X-ray data. The difference
between the wavenumbers of the IR (2331 cm−1)
and Raman (2320 cm−1) band arising from the stretch-
…
ing vibration of the N–D N bond is even bigger.
These splittings are caused by the intradimer coupling
resulting from the Au–Ag splitting due to its Ci sym-
metry. This splitting should be bigger for the N–
…
H
N bonds (they are very close and form a ring)
…
than for the N–H O hydrogen bonds, which are
quite far separated. One should notice that there are
more bands than expected in this region. This is
caused by the appearance of some overtones whose
intensities are enhanced by the Fermi resonance.
Relatively strong intensity is shown by the band at
3136 cm−1 which arises from the overtone of the
deformation vibration dNH2.
It is interesting to mention that in the IR spectrum

62
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
Fig. 3. Powder IR and Raman spectra of normal (upper) and deuterated 2-amino-4-nitropyridine. Transmittance scales in regions separated by
broken lines are different.
460 (460) cm−1, respectively, for m-nitroaniline and
m-nitrophenol. The band at 1062 cm−1, assigned to the
rocking mode, was observed only in the IR spectrum
of nitroaniline.
3.3.2. Vibrations of the NO2 group
The asymmetric (naNO2) and symmetric (nsNO2)
vibrations give rise to the bands at 1524 (1522) and
1354 (1353) cm−1 with very strong intensities in the
IR spectrum. The naNO2 band is weak in the Raman
spectrum in comparison to that of the nsNO2 mode,
which reveals particularly strong intensity, probably
The band at 317 cm−1 in the IR spectrum of the
deuterated analogue probably arises from the tND2
mode ((isotopic ratio shift = 1.37).

63
J. Oszust et al./Journal of Molecular Structure 415 (1997) 53–63
as a result of vibronic couplings. A similarly enhanced
Acknowledgements
intensity of this vibration was observed in the Raman
spectrum of m-nitrophenol [7,8] and m-nitroaniline
[9]. The bands at 877 (875), 737 (737), 566 (572)
and 101 (99) cm−1 arise from the scissoring (dNO2),
wagging (qNO2), rocking (rNO2) and twisting
(tNO2) modes, respectively. This is in agreement
with the assignments proposed for several nitro-
benzene and pyridine N-oxide derivatives [7,10].
This research was financially supported by the
Polish State Committee for Scientific Research
(Grant No. 3T09A 00211).
References
[1] Z. Talik, T. Talik, Zeszyty Naukowe Wyzszej Szkoly Ekono-
micznej we Wroclawiu XVIII (1963) 79.
3.3.3. Vibrations of the pyridine ring
[2] G.M. Sheldrick, SHELXS-86, Program for Crystal Solution,
University of Go¨ttingen, Germany, 1986.
[3] G.M. Sheldrick, SHELXS-93, Program for the Refimement
of Crystal Structures, University of Go¨ttingen, Germany,
1993.
[4] M.Chao, E. Schempp, R.D. Rosenstein, Acta Cryst. B31
(1975) 2922.
[5] R. Destro, T. Pilati and M. Simonetta, Acta Cryst. B31 (1975)
2883.
[6] E.B. Wilson, Phys. Rev. 45 (1934) 706.
[7] J. Gierman´ska, G. Wo´jcik, M.M. Szostak, J. Raman Spectrosc.
21 (1990) 479.
[8] K. Kumar, P.R. Carey, J. Chem. Phys. 63 (1975) 3697.
[9] M.M. Szostak, B.J.E. Smith, D.N. Batchelder, in: R.J.H. Clark,
D.A. Long (Eds.), Proceedings of the Eleventh International
Conference on Raman Spectroscopy, London, 1988, Wiley,
Chichester, 1988, p.583.
The assignments of the majority of the pyridine ring
vibrations are relatively straightforward, as similar
bands were observed in the spectra of m-nitroaniline
and m-nitrophenol [7]. There is some difficulty in the
assignment of bands appearing in the regions of
1190–1080 and 560–200 cm−1, where deuteration
changes the number of bands, their wavenumbers
and intensities, and reveals the couplings between
deformation vibrations of the NH2 group and skeletal
vibrations. The bands at 1094 and 1059 cm−1 are not
resolved in the IR spectrum. The other band probably
appears between them, which is clearly seen at 1069
cm−1 in the Raman spectrum of the normal compound.
On deuteration, the band at 1059 (1069) cm−1 arising
from the rNH2 mode disappears, and two new bands
appear there.
[10] P. Plaza, F. Le Guiner, M. Joyeux, Nguyen Quy Dao, J. Zyss,
R. Hierble, J. Mol. Struct. 247 (1991) 363.