Hydrogen bonds and conformational analysis of bis(1-methylisonicotinate) hydrochloride monohydrate by X-ray diffraction, vibrational spectra and B3LYP calculations

Article abstract of DOI:10.1016/j.molstruc.2006.01.033

In the crystal structure of bis(1-methylisonicotinate) hydrochloride monohydrate, (MIN)₂H·Cl·H₂O, 1-methylisonicotinate betaines are hemiprotonated and form a homoconjugated cation through a short asymmetric O·H·O hydrogen bond of length 2.456(3) A?. Water molecules and Cl^- anions are linked alternatively by hydrogen bonds of lengths 3.202(3) and 3.282(2) A? into planar zigzag chains along the [c] direction. The Cl^- anion additionally interacts electrostatically with two positively charged nitrogen atoms of the neighboring MIN molecules. The most stable conformers of (MIN)₂H·Cl·H₂O, (MIN)₂H·Cl, (MIN)₂H·H₂O and (MIN)₂H have been analyzed by the B3LYP/6-31G(d,p) calculations in order to determine the influence of the anion and water molecule on the hydrogen bond in the homoconjugated MIN·H·MIN unit. The FTIR spectrum of (MIN)₂H·Cl·H₂O shows a broad and intense absorption in the 1500-400 cm^-1 region, typical for short hydrogen bonds. The bands at 3416 and 3378 cm^-1 confirm the presence of medium-strong hydrogen bonds between water molecules and Cl^- anions.

Full text of DOI:10.1016/j.molstruc.2006.01.033

Journal of Molecular Structure 794 (2006) 46–53
www.elsevier.com/locate/molstruc
Hydrogen bonds and conformational analysis of bis(1-methylisonicotinate)
hydrochloride monohydrate by X-ray diffraction, vibrational spectra
and B3LYP calculations
*
M. Szafran , A. Katrusiak, Z. Dega-Szafran
´
Faculty of Chemistry, A. Mickiewicz University, ul. Grunwaldzka 6, 60780 Poznan, Poland
Received 14 December 2005; received in revised form 19 January 2006; accepted 19 January 2006
Available online 9 March 2006
Abstract
In the crystal structure of bis(1-methylisonicotinate) hydrochloride monohydrate, (MIN)2H$Cl$H2O, 1-methylisonicotinate betaines are
˚
hemiprotonated and form a homoconjugated cation through a short asymmetric O$H$O hydrogen bond of length 2.456(3) A. Water molecules and
ClK anions are linked alternatively by hydrogen bonds of lengths 3.202(3) and 3.282(2) A into planar zigzag chains along the [c] direction. The
˚
ClK anion additionally interacts electrostatically with two positively charged nitrogen atoms of the neighboring MIN molecules. The most stable
conformers of (MIN)2H$Cl$H2O, (MIN)2H$Cl, (MIN)2H$H2O and (MIN)2H have been analyzed by the B3LYP/6-31G(d,p) calculations in order
to determine the influence of the anion and water molecule on the hydrogen bond in the homoconjugated MIN$H$MIN unit. The FTIR spectrum
of (MIN)2H$Cl$H2O shows a broad and intense absorption in the 1500–400 cmK1 region, typical for short hydrogen bonds. The bands at 3416 and
3378 cmK1 confirm the presence of medium–strong hydrogen bonds between water molecules and ClK anions.
q 2006 Elsevier B.V. All rights reserved.
Keywords: 1-Methylisonicotinate betaine; Hydrogen bond; Electrostatic interactions; X-ray diffraction; DFT calculations; Conformation; FTIR and Raman spectra
1. Introduction
geometries of some of the most stable conformers of
(MIN)2H$Cl, (MIN)2H and their monohydrates are obtained
from the B3LYP/6-31G(d,p) calculations. The aim of this
study is to determine the influence of ClK anion and H2O
molecule on the hydrogen bond in the crystal and in isolated
entities.
Pyridine carboxylic acids (picolinic, nicotinic and isonico-
tinic) on methylation are converted into betaines, homarine
(2-carboxy-1-methylpyridinium inner salt), trigonelline
(3-carboxy-1-methylpyridinium inner salt) and 4-carboxy-
1-methylpyridinium inner salt. The first two betaines, homarine
and trigonelline have been isolated from various plants, seeds
and animal tissues [1–3]. Because of their basic nature they
form 1:1 and 2:1 crystalline complexes with mineral acids
[4–6].
2. Experimental
2.1. Synthesis
4-Carboxy-1-methylpyridinium iodide. A solution of nic-
otinic acid (15 g) in methanol (70 cm3) and methyl iodide (26 g)
was heated at 70 oC in a sealed tube for 40 h. Yellow crystals
were filteredoff and washed with asmallamount of acetone. The
filtrate was evaporated to dryness under reduced pressure and
the solid residue was washed with acetone. Both fractions of the
crystals were combined and recrystallized from methanol, total
yield 61%, m.p. 243 oC; ref. [7], m.p. 189–191 oC.
Previously, we have described the 2:1 complexes of
trigonelline with perchloric [5] and hydrochloric [6] acids,
which crystallize with one water molecule. In this work, we
study the 2:1 complex of 4-carboxy-1-methylpyridinium inner
salt with hydrochloric acid, (MIN)2H$Cl$H2O, which also
crystallizes with water, using X-ray diffraction, FTIR and
Raman spectra. The relative energies and optimized
4-Carboxy-1-methylpyridinium inner salt monohydrate
(betaine). 4-Carboxy-1-methylpyridinium iodide (10 g) was
dissolved in water (20 cm3) in a small canonical flask,
propylene oxide (2.6 g) was added slowly, closed with a cork
and left for 3 days. To remove iodopropanols, the reaction
*
Corresponding author. Tel.: C48 61 829 1320; fax: C48 61 865 8008.
E-mail address: szafran@main.amu.edu.pl (M. Szafran).
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.01.033

M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
47
Table 2
solution was extracted six times with equal volumes of diethyl
ether, than evaporated under reduced pressure to dryness, the
residue was recrystallized from methanol and white crystals
were filtered off, m.p. 291 8C; ref. [7], m.p. 288 8C.
4-Carboxy-1-methylpyridinium chloride. 4-Carboxy-1-
methylpyridinium inner salt monohydrate (betaine) (5 g) was
dissolved in hydrochloric acid, the solution was evaporated to
dryness under reduced pressure, and the white solid residue was
recrystallized from methanol with one drop of hydrochloric
acid, m.p. 226–228 8C; ref. [8], m.p. 265 8C.
Bis(1-methylisonicotinate) hydrochloride monohydrate
was obtained by recrystallization of stoichiometric amounts
of MIN$H2O and MINHCl from a small amount of
methanol, m.p. 215–217 8C. 1H NMR (D2O): d (ppm)Z
4.84 s, NCCH3, 8.87 d, H(2,6), 8.29 d, H (3,5); 13C NMR
(D2O): d (ppm)Z50.9 NCCH3, 148.5 C(2,6), 129.5 C(3,5),
153.8 C(4), 170.9 COO.
Fractional atomic coordinates and equivalent isotropic displacement par-
ameters bis(1-methylisonicotinate) hydrochloride monohydrate. U(eq) is
defined as one-third of the trace of the orthogonalized Uij tensor
Atom
x
y
z
U(eq)
N(1)
0.4834(1)
0.5035(2)
0.4783(2)
0.4322(2)
0.4119(2)
0.4387(2)
0.5131(2)
0.4047(2)
0.3642(1)
0.4229(2)
0.2070(2)
0.1859(2)
0.2110(2)
0.2580(2)
0.2788(2)
0.2532(2)
0.1784(2)
0.2856(2)
0.3261(1)
0.2682(2)
0.6068(2)
0.5866(1)
0.3430
1.3036(5)
1.1493(6)
1.0031(6)
1.0151(5)
1.1752(5)
1.3187(6)
1.4553(6)
0.8538(6)
0.8792(4)
0.7165(5)
0.1833(5)
0.3362(6)
0.4824(6)
0.4724(5)
0.3125(6)
0.1677(6)
0.0252(6)
0.6352(6)
0.6104(4)
0.7719(5)
1.1942(5)
1.2051(1)
0.7500
K0.4315(5)
K0.4617(7)
K0.4195(6)
K0.3420(5)
K0.3134(6)
K0.3590(6)
K0.4754(8)
K0.2944(6)
K0.2144(4)
K0.3260(8)
0.0912(5)
0.1192(7)
0.0763(6)
0.0031(5)
K0.0257(7)
0.0211(7)
0.1385(8)
K0.0447(6)
K0.1228(4)
K0.0041(7)
0.2908(5)
K0.1066(2)
K0.1800
K0.5120
K0.4430
K0.2635
K0.3389
K0.5740
K0.3863
K0.4957
0.1680
0.037(1)
0.042(1)
0.039(1)
0.032(1)
0.039(1)
0.039(1)
0.058(1)
0.044(1)
0.048(1)
0.082(1)
0.036(1)
0.043(1)
0.039(1)
0.032(1)
0.039(1)
0.041(1)
0.056(1)
0.041(1)
0.051(1)
0.085(2)
0.070(1)
0.047(1)
0.0220(50)
0.050
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
O(1)
O(2)
N(10)
C(20)
C(30)
C(40)
C(50)
C(60)
C(70)
C(80)
O(10)
O(20)
O(w)
Cl
2.2. Measurements
FTIR spectra were recorded in Nujol and Fluorolube
suspensions at a 2 cmK1 resolution on a Bruker IFS 113v
spectrometer, which was evacuated to avoid water and CO2.
Each spectrum consists of 250 scans at 31 8C. Raman spectrum
was recorded on a Nicolet Magna 760 spectrometer operating
at the 1064 nm excitation line of an Nd:YAG laser.
H(1)
H(2)
0.5352
1.1415
H(3)
0.4921
0.8964
0.047
H(5)
0.3803
1.1862
0.046
The X-ray diffraction measurements were carried out
using a KUMA-4 CCD diffractometer. The structure was
solved by direct methods with SHELXS-97 [9] program and
H(6)
0.4253
1.4269
0.047
H(71)
H(72)
H(73)
H(20)
H(30)
H(50)
H(60)
H(710)
H(720)
H(730)
H(1w)
H(2w)
0.5301
1.4382
0.075
0.5399
1.4913
0.075
0.4856
1.5418
0.075
0.1540
0.3432
0.051
0.1962
0.5888
0.0965
0.047
Table 1
0.3101
0.3029
K0.770
0.046
Crystal data and structure refinement for bis(1-methylisonicotinate) hydro-
chloride monohydrate
0.2676
0.0600
0.0046
0.049
0.1599
0.0436
0.2341
0.072
0.2053
K0.0626
K0.0097
0.1624
0.072
Empirical formula
Formula weight
Temperature
C14H17ClN2O5
328.75
0.1525
0.0464
0.072
293(2) K
0.6070(30)
0.6030(30)
1.2250(60)
1.0950(30)
0.1880(20) 0.084
0.3370(50) 0.084
˚
Wavelength
0.71073 A
Monoclinic
Cc
Crystal system
Space group
˚
Unit cell dimensions
aZ24.791(5) A
˚
bZ7.8099(16) A
˚
refined by the full-matrix least squares on F2 data using the
SHELLXL-97 [10] program. The crystal data and details
concerning data collection and structure refinement are
given in Table 1. Atomic coordinates and equivalent
displacement parameters are listed in Table 2. Parameters
in the CIF form are available as Electronic Supplementary
Publication from Cambridge Crystallographic Data Centre
(CCDC 273451).
cZ8.1154(16) A
bZ97.26(3)8
3
˚
Volume
1558.7(5) A
Z
4
Calculated density
F(000)
1.401 g/cm3
688
Crystal size
0.3!0.3!0.1 mm
2.74–29.818
q range for data collection
Limiting indices h,k,l
K33%h%32, K10%k%10,
K11%l%8
Reflections collected/unique/[R(int)]
Completeness to qZ29.81
Absolute structure parameter
Data/restraints/parameters
Goodness-of-fit on F2
7482/2601 [R(int)Z0.0436]
91.7%
2.3. Calculations
0.46(15)
2601/7/213
1.181
The calculations were performed using the GAUSSIAN 03
package [11] at the B3LYP [12,13] level of theory in
conjunction with the 6-31G(d,p) [14] basis set.
Final R1/R2 indices [IOs((I)]
R indices (all data)
R1Z0.0478, wR2Z0.1223
R1Z0.0712, wR2Z0.1565
K3
˚
0.547 and K0.683 e A
Largest diff. peak and hole

48
M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
3. Results and discussion
3.1. Molecular parameters
The structure of (MIN)2H$Cl$H2O with the atom numbering
is shown in Fig. 1, the molecular packing in the crystal in Fig. 2
and the environment of the chloride ion in Fig. 3. The bond
lengths, bond angles, and torsion angles are listed in Tables 3
and 4. Two molecules of MIN are bridged by a proton to form a
homoconjugated cationic system with a short, asymmetrical
Fig. 3. The environment of the chlorine ion in bis(1-methylisonicotinate)
hydrochloride monohydrate.
˚
O–H/O hydrogen bond with the O/O distance of 2.456(3) A.
Because the hydrogen bonded MIN molecules are not
symmetrically equivalent, the (MIN)2H cation is similar to the
pseudo-Type A acid salts of carboxylic acids [15], (TRG)2-
H$ClO4$H2O [5], (TRG)2H$Cl$H2O [6] and bis(quinoline
betaine) hydrogen perchlorate [16]. Slightly shorter hydrogen
bonds exist in the Type A acid salts of aromatic monocarboxylic
acids [15] and 2:1 complexes of betaines with mineral acids
[17–19], where proton is in the middle of the bridge. The
(TRG)2H cations are arranged approximately parallel in the
crystal lattice, as shown in Fig. 2. The two carboxy-fragments
participating in the hydrogen bonding are planar, with the
Table 3
˚
Experimental bond lengths (A) and angles (deg) for bis(1-methylisonicotinate)
hydrochloride monohydrate
Bond lengths
N(10)–C(20)
N(1)–C(2)
1.340(6)
1.325(6)
1.462(6)
1.367(6)
1.375(6)
1.377(6)
1.505(6)
1.377(6)
1.279(6)
1.203(6)
1.335(6)
1.347(6)
1.498(6)
1.366(6)
1.376(6)
1.382(6)
1.518(6)
1.373(6)
1.267(6)
1.212(6)
N(10)–C(60)
N(10)–C(70)
C(20)–C(30)
C(30)–C(40)
C(40)–C(50)
C(40)–C(80)
C(50)–C(60)
C(80)–O(10)
C(80)–O(20)
N(1)–C(6)
N(1)–C(7)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(4)–C(8)
C(5)–C(6)
C(8)–O(1)
C(8)–O(2)
Fig. 1. View of bis(1-methylisonicotinate) hydrochloride monohydrate,
Bond angles
C(20)–N(10)–C(60)
C(20)–N(10)–C(70)
C(60)–N(10)–C(70)
N(10)–C(20)–C(30)
C(20)–C(30)–C(40)
C(30)–C(40)–C(50)
C(30)–C(40)–C(80)
C(50)–C(40)–C(80)
C(40)–C(50)–C(60)
N(10)–C(60)–C(50)
O(20)–C(80)–O(10)
O(10)–C(80)–C(40)
O(20)–C(80)–C(40)
(MIN)2H$Cl$H2O, and its atom labeling scheme.
C(2)–N(1)–C(6)
C(2)–N(1)–C(7)
C(6)–N(1)–C(7)
N(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(3)–C(4)–C(8)
C(5)–C(4)–C(8)
C(4)–C(5)–C(6)
N(1)–C(6)–C(5)
O(2)–C(8)–O(1)
O(1)–C(8)–C(4)
O(2)–C(8)–C(4)
Torsion angles
121.0(4)
118.2(4)
120.8(4)
120.7(4)
119.5(4)
118.7(4)
119.3(4)
121.9(4)
119.6(4)
120.4(4)
125.9(5)
114.3(4)
119.8(5)
121.7(4)
119.0(4)
119.3(4)
120.2(4)
120.7(4)
118.6(4)
119.8(4)
121.6(4)
120.1(4)
119.3(4)
127.0(5)
114.3(4)
118.8(5)
N(10)–C(20)–C(30)–C(40)
N(10)–C(60)–C(50)–C(40)
C(20)–N(10)–C(60)–C(50)
C(60)–N(10)–C(20)–C(30)
C(70)–N(10)–C(20)–C(30)
C(70)–N(10)–C(60)–C(50)
C(20)–C(30)–C(40)–C(50)
C(20)–C(30)–C(40)–C(80)
C(30)–C(40)–C(50)–C(60)
C(80)–C(40)–C(50)–C(60)
C(30)–C(40)–C(80)–O(10)
C(50)–C(40)–C(80)–O(10)
C(30)–C(40)–C(80)–O(20)
C(50)–C(40)–C(80)–O(20)
N(1)–C(2)–C(3)–C(4)
N(1)–C(6)–C(5)–C(4)
C(2)–N(1)–C(6)–C(5)
C(6)–N(1)–C(2)–C(3)
C(7)–N(1)–C(2)–C(3)
C(7)–N(1)–C(6)–C(5)
C(2)–C(3)–C(4)–C(5)
C(2)–C(3)–C(4)–C(8)
C(3)–C(4)–C(5)–C(6)
C(8)–C(4)–C(5)–C(6)
C(3)–C(4)–C(8)–O(1)
C(5)–C(4)–C(8)–O(1)
C(3)–C(4)–C(8)–O(2)
C(5)–C(4)–C(8)–O(2)
K1.3(7)
0.6(8)
0.3(8)
1.8(8)
K0.1(7)
0.4(7)
K1.2(8)
0.2(7)
178.4(5)
K178.0(5)
1.9(7)
K179.6(5)
178.5(5)
0.2(7)
K179.5(4)
K1.5(7)
179.8(4)
176.1(4)
K5.3(7)
K0.8(7)
177.8(5)
179.8(4)
K1.2(7)
179.1(5)
K174.7(4)
4.9(6)
Fig. 2. Auto stereogram of the crystal structure of (MIN)2H$Cl$H2O. Hydrogen
bonds linking the water molecules and chloride anions into chains are marked
with the dashed line.
6.5(7)
K173.7(5)

M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
49
Table 4
Hydrogen bonds geometry in bis(1-methylisonicotinate) hydrochloride, its cation and their monohydrates
D–H/A
d(D–H)
d(H/A)
d(D/A)
!(DHA)
1 X-ray
O(1)–H/O(10)
O(1w)–H(1w)/Cl
O(1w)–H(2w)/Cla
B3LYP/6–31G**
2 Linear
1.19(4)
0.87(7)
0.87(7)
1.28(4)
2.38(5)
2.43(6)
2.456(3)
3.202(3)
3.282(2)
171(3)
161
165(5)
O(1)–H/O(10)
1.053
1.450
2.501
174.4
3 Bent
O(1)–H/O(10)
O(w)–H(1w)/Cl
O(w)–H(2w)/O(20)
4 Linear
1.040
0.077
0.974
1.489
2.390
2.033
2.526
2.557
2.971
174.0
170.3
172.8
O(1)–H/O(10)
5 Bent
O(1)–H/O(10)
6 Linear
1.205
1.023
1.137
1.208
1.516
1.289
2.413
2.520
2.425
178.3
164.9
177.5
O(1)–H/O(10)
7 Bent
O(1)–H/O(10)
O(1w)–H(w)/O(20)
8 Linear
1.011
0.982
1.602
1.760
2.596
2.730
166.4
168.9
O(1)–H/O(10)
9 Bent
O(1)–H/O(10)
1.031
1.060
1.484
1.428
2.512
2.485
175.5
174.0
Symmetry code ax, 2Ky, 0.5Cz.
dihedral angle between the O(2)–C(8)–O(1) and O(12)–C(18)–
O(11) moieties being 8.3(5)8, respectively. The dihedral angle
between the planes through the rings is 1.2(3)8 and those
between the rings and the COOK moieties are 3.3(3) and 5.9(3)8,
respectively, for the protonated and unprotonated
1-methylisonicotinates.
and conformations In Fig. 4 the X-ray and the optimized
molecules are compared. Linear and bent types of conformers
can be distinguished. There are three important features that
contribute to the stability of the single molecules investigated
Table 5
˚
Selected distances between the oppositely charge atoms (A) in bis(1-
Each water molecule links two adjacent ClK anions via two
different hydrogen bonds (O(w)–H(1w)/ClK(1) of
methylisonicotinate) hydrochloride monohydrate determined by X-ray diffrac-
tion
K
˚
˚
3.202(3) A) and (O(w)–H(2w)/Cl (1) of 3.282(2) A) form-
ing planar, zigzag chains along the [c] direction (Fig. 2). The
ClK anion additionally interacts via Coulombic attractions
with two close positively charged nitrogen atoms and has close
contacts with some C–H groups (Fig. 3). The shortest contacts
˚
A
Symmetry code
N(1)/Cl
3.519
4.919
5.026
4.914
3.787
4.933
3.703
3.364
5.318
4.110
5.131
5.156
4.068
5.326
4.188
4.922
5.185
4.044
3.869
3.677
3.458
3.392
x, y, z
x, 3Ky, K0.5Cz
x, 2Ky, K0.5Cz
x, y, z
K
C
K
C
0
˚
˚
N(1)/O(1)
N(1)/O(2)
are: Cl /N (1) of 3.517 A, Cl /N (1 )Z4.187 A,
C
C
x, 2Ky, K0.5Cz
x, y, z
˚
˚
O(w)/N (1) of 5.114 A and O(w)/N (1) of 3.400 A
(Table 5). In the crystal each ClK anion and each NC atom
are fourfold coordinated. A prototype of this kind of interaction
has been found in tetramethylammonium halides [20], where
each XK anion is tetrahedrally surrounded by four NC atoms,
and each NC atom by four XK anions. The NC atoms in
(MIN)2H$Cl$H2O are surrounded by two ClK anions and two
water molecules, while ClK anions are surrounded only by two
NC atoms, because the other two contacts are blocked by
two H-bonds with water molecules.
x, 1Cy, z
x, 2Ky, K0.5Cz
x, 2Ky, 0.5Cz
x, 2Ky, K0.5Cz
x, 3Ky, K0.5Cz
x, y, z
N(1)/O(w)
N(1)/O(10)
N(1)/O(20)
N(10)/Cl
x, 2Ky, K0.5Cz
x, 2Ky, K0.5Cz
xK0.5, 1.5Ky, 0.5Cz
xK0.5, K1.5Cy, z
xK0.5, K1.5Cy, z
x, 1Ky, 0.5Cz
x, 1Ky, 0.5Cz
x, K1Cy, z
N(10)/O(1)
N(10)/O(10)
N(10)/O(20)
3.2. B3LYP calculations
x, 1Ky, 0.5Cz
xK0.5, 1.5Ky, K0.5Cz
Table 6 shows the abbreviations of the complexes
investigated, their energies, relative energies, dipole moments
N(10)/O(w)

50
M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
Table 6
Numbers, conformations, energies (Hartree), relative energies (kcal/mol) and dipole moments (m, Debye) of the investigated molecules
Molecule
Method
Type
Energy (Hartree)
Erel.
Dipole
1
2
3
4
5
6
7
8
9
H2O (MIN$H$MIN)CClK
H2O (MIN$H$MIN)CClK
(MIN$H$MIN)CClK$H2O
(MIN$H$MIN)CH
X-ray
Linear
Linear
Bent
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
B3LYP
K1489.565787
K1489.600242
K952.747915
K952.745718
K1029.187396
K1029.187928
K1413.134995
K1413.157021
22.876
0
31.9170
8.1784
0.4505
12.0883
2.1332
13.8815
12.3782
7.7043
Linear
Bent
0
(MIN$H$MIN)C
H
1.38
0.33
0
(MIN$H$MIN)CH2O
(MIN$H$MIN)CH2O
(MIN$H$MIN)CClK
(MIN$H$MIN)CClK
Linear
Bent
13.8
0
Bent
(compared with the gas phase): dipole moment, hydrogen bond
distance and attractive (electrostatic) interactions between the
oppositely charged atoms (the positively charged nitrogen
atoms and anions or water molecules). Bent complexes with
small dipole moments are favored in the gas phase. In the
cation, (MIN$H$MIN)C, and its monohydrates the reverse
trend is observed; more stable are the linear species with
smaller dipole moments. In all linear complexes, the O$H$O
hydrogen bonds are slightly shorter than in the bent ones, but
their energies are slightly higher (Tables 6 and 7). In cations (4
and 5) and their monohydrates (6 and 7), the linear species are
more stable and the O$H$O hydrogen bonds are much shorter
in comparison to the bent ones. As indicated by the data in
Tables 6 and 7, the stability of the optimized complexes is
controlled by the electrostatic attraction between the positively
charged nitrogen atoms NC(1) and NC(10) and ClK anion. In
the bent complexes (3, 9) both NC(1)/ClK and NC(1’)/ClK
spectra varies inversely with the square of the half-width of the
absorption bands. The observed wavenumbers and their
tentative assignments, based on comparison with the spectra
of 4-carboxy-1-methyl-pyridinium chloride [29] and isonico-
tinic acid [30], are listed in Table 8. The frequency plot of the
negative bands in the d2 spectrum versus the Raman
frequencies is linear with unit slope (Fig. 6). Thus the
derivative spectrometry can be used to estimate frequencies
of the narrow bands covered by the broad absorption due to the
stretching and bending OHO vibrations.
4. Conclusions
According to the X-ray data, in the bis(1-methylisonicotinate)
hydrochloride monohydrate, (MIN)2H$Cl$H2O, a pair of
1-methylisonicotinate molecules is joined by a proton to form a
homoconjugated cation, featuring a short and asymmetric
˚
distances are short (between 3.280 and 3.867 A), while in
linear conformers (2, 8) only one distance is short, but the
˚
second is longer than 10 A.
˚
hydrogen bond with the O/O distance equal to 2.456(3) A.
The 1-methylisonicotinate units are not equivalent as a result of
electrostatic interaction with ClK anion and H2O molecule. The
hydrogen bond in the investigated complex is similar to that in
The water molecule has also some effect on the stability of
the conformers investigated. Conformer 6 (linear) is less stable
than 7 (bent) by 0.33 kcal/mol. In 6 the O$H$O hydrogen bond
˚
is shorter by 0.171 A relative to that in 7, but the
C
0
˚
N (1 )/O(w) distance is longer by 8.399 A.
3.3. FTIR and Raman spectra
Fig. 5 shows the FTIR, Raman and second derivative spectra
of (MIN)2H$Cl$H2O. The FTIR spectrum displays a broad and
strong absorption in the 1500–400 cmK1 region, whereas in the
Raman spectrum this feature is absent. A similar broad
absorption appears in the IR spectra of the 2:1 complexes of
other betaines [21] and acid salts of carboxylic acids [22–24].
The broad absorption is typical of compounds with short
H-bonds and arises from the stretching (strong absorption) and
bending (much weaker absorption) vibrations of the O–H
group involved in a short O/O hydrogen bond.
In the FTIR spectrum, the continuous absorption and the
skeletal vibrations overlap, but the latter feature can be
distinguished in the second-derivative spectrum, d2 (Fig. 5b).
In the second-derivative spectra, the minima have the same
wavenumbers as the maxima in the absorbance spectra [25–
28]. The intensity of relative amplitudes of bands in the d2
Fig. 4. Comparison of X-ray (1) and B3LYP (2–9) structures of bis(1-
methylisonicotinate) hydrochloride, its cation and their monohydrates.

M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
51
Table 7
Selected parameters (bond lengths in Angstroms, angles in degrees) for (MIN)2HCl, (MIN)2H and their monohydrates
˚
1
2
3
4
5
6
7
8
9
Linear
Linear
Bend
Linear
Bend
Linear
Bend
Bend
O(1)/O(11)
O(1)–H
O(10)–H
2.456
2.501
2.526
2.413
2.520
2.425
2.596
2.512
1.031
1.484
2.485
1.19
1.28
1.053
1.450
1.040
1.489
1.205
1.208
1.026
1.516
1.137
1.289
1.011
1.602
1.060
1.428
O(1)HO(10)
171
174.4
174.0
178.3
164.9
177.5
166.4
175.5
174.0
C(8)–O(1)
C(80)–O(10)
1.279
1.267
1.203
1.212
1.309
1.271
1.222
1.235
1.310
1.270
1.218
1.245
1.288
1.288
1.226
1.226
1.309
1.266
1.216
1.245
1.296
1.282
1.223
1.229
1.317
1.255
1.214
1.255
1.314
1.265
1.227
1.236
1.304
1.281
1.221
1.235
C(8)–O(2)
C(80)–O(20)
O(1)–C(8)–O(2)
O(10)–C(80)–O(20)
N(1)–C(2)–C(3)–C(4)
N(10)–C(20)–C(30)–C(40)
C(2)–C(3)–C(4)–C(8)
C(20)–C(30)–C(40)–C(80)
C(3)–C(4)–C(8)–O(1)
C(30)–C(40)–C(80)–O(10)
C(3)–C(4)–C(8)–O(2)
C(30)–C(40)–C(80)–O(20)
O(2)–C(8)–O(1)–H
O(20)–C(80)–O(10)–H
N(1)/Cl
125.9
127.7
137.6
0.29
124.4
130.1
124.3
129.5
123.9
126.4
124.8
127.0
K1.3
0.3
128.8
K1.1
2.0
130.1
K0.12
K0.17
K179.7
K179.7
K2.1
129.9
0.5
130.5
K0.07
0.01
129.3
131.8
1.0
129.3
K1.2
K0.8
K0.7
K0.01
179.7
K0.11
175.5
0.96
K1.5
K179.5
179.8
176.1
K174.7
K0.8
6.5
179.8
165.5
34.9
K179.6
K179.7
K1.75
K1.33
178.3
178.1
K178.5
26.2
K177.1
K179.2
2.4
177.6
170.0
33.7
K179.7
K1.4
178.6
26.7
1.04
10.7
K2.1
K0.35
K151.4
K179.9
K167.4
33.2
22.1
K24.5
K180.0
156.9
K11.2
K144.3
174.7
K166.3
18.5
178.4
K143.1
K163.9
K165.1
10.6
177.8
K151.8
K157.7
K165.9
7.8
K179.1
1.33
177.8
178.7
K6.3
K6.4
K5.8
K5.7
2.0
3.19
K88.2
3.694
3.843
3.084
10.050
3.867
3.310
N(10)/Cl
14.057
14.979
3.747
3.280
2.954
4.799
N(1)/OH2
N(10)/OH2
3.715
4.235
5.988
14.387
1.5
1.2
0.9
0.6
0.3
0.0
0.2
0.0
–0.2
8
6
4
2
0
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm–1
)
Fig. 5. Vibrational spectra: (a) FTIR spectra (suspension in Nujol and Fluorolube) of (MIN)2H$Cl$H2O; (b) second derivative FTIR spectrum and (c) Raman
spectrum.

52
M. Szafran et al. / Journal of Molecular Structure 794 (2006) 46–53
Table 8
3500
Vibrational frequencies of 4-carboxy-1-methylpyridinium inner salt mono-
hydrate, MIN$H2O, its hydrochloride, MINH$Cl(t) and bis(1-methylisonico-
tinate) hydrochloride monohydrate, (MIN)2HCl$H2O
3000
2500
2000
1500
1000
500
MIN$H2O
MINH$Cla
(MIN)2HCl$H2O
Raman FTIR
Approximate
assignments
FTIR
FTIR
d2
3436
3422
3413
3377
3249
3161
3122
3111
3095
3070
3050
3018
2983
2949
H2O
H2O
3420
3414
3376
3248
3162
H2O
H2O
H2O
nCH
nCH
3118
3107
3093
3112
3096
nCH
nCH
3100
3080
3053
3098
0
0
500 1000 1500 2000 2500 3000 3500
Raman
nCH3
nCH3
nCH3
nCH3
nCH3
nOH
3038
3050
3019
3048
3020
Fig. 6. Relation between d2 and Raman frequencies for (MIN)2H$Cl$H2O;
n(d2)Z3.0243C0.9980 n(Raman), rZ0.9998.
2959
2949
1712
1643
2668–2214
1710
1712
1645
nCO
1653
1637
1604
1565
1661
1644
nasCOO
nCC
nCC
B3LYP/6-31G(d,p) calculations. Their stability depends on: (i)
dipole moment, (ii) hydrogen bond length, and (iii) attractive
(electrostatic) interactions between the oppositely charged
atoms (the positively charged nitrogen atoms and ClK anions).
The FTIR spectrum of the complex shows a very broad
absorption, typical of such short hydrogen bonds. In the Raman
spectrum only narrow bands are present since the O$H$O
stretching vibration is not active. The frequencies of
the negative bands in the second derivative spectrum agree
well with the Raman frequencies. Derivative spectrometry can
be used to estimate the frequencies of the narrow bands
covered by the broad absorption due to the stretching and
bending OHO vibrations.
1646
1585
1519
1577
1517
1577
1512
1577
1512
1472
1441
1416
1398
1375,
1358
1337
1320,
1305
1291
nCC
nCCCnCN
nCCCnCN
bCH3
bCH3
bOH
1460
1400
1439
1417
1400
1380
1417
1354
1363
bCH3
1315
1304
1320
1288
1324
1317
1324
1316
bCH3
bCH3
1291
1185
1291
1290
nCCCnCO C
bOH
bCH
1257
1245
1207
1192
1140
1131
1075
1060
1042
927
1245
1228
1216
1187
1140
1120
1074
1245
1228
1215
1200
1141
1120
1072
1054
1036
1226
1217
1186
1141
bCH
bCHCnCN
bCH
Acknowledgements
bCHCnCC
bCH
´
Calculations were performed at the Poznan Supercomputing
and Networking Centre.
bCH3CnCN
bCH3CnCN
b Ring
1047
1040
900
881
857
References
878
881
859
881
897
b RingCnCN
b RingCnCN
b RingCnCN
b RingCnCN
tCO2
864
860
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772
762
684
662
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