Hydrogen bonded supramolecular framework in organic acid-base adducts: Crystal structures of five cocrystals/salts assembled from 2-methylquinoline with monocarboxylic acid, dicarboxylic acid, and tricarboxylic acid

Article abstract of DOI:10.1016/j.molstruc.2012.02.048

Studies concentrating on noncovalent weak interactions between the organic base of 2-methylquinoline, and carboxylic acid derivatives have led to an increased understanding of the role 2-methylquinoline has in binding with carboxylic acid derivatives. Her

Full text of DOI:10.1016/j.molstruc.2012.02.048

Journal of Molecular Structure 1017 (2012) 51–59
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Journal of Molecular Structure
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Hydrogen bonded supramolecular framework in organic acid–base adducts:
Crystal Structures of five cocrystals/salts assembled from 2-methylquinoline
with monocarboxylic acid, dicarboxylic acid, and tricarboxylic acid
b
a
a
a
a
a
Shouwen Jin a, , Daqi Wang , Yanfei Huang , Hao Fang , Tianyi Wang , Peixia Fu , Liangliang Ding
⇑
a Tianmu College of ZheJiang A&F University, Lin’An 311300, PR China
b Department of Chemistry, Liaocheng University, Liaocheng 252059, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Studies concentrating on noncovalent weak interactions between the organic base of 2-methylquinoline,
and carboxylic acid derivatives have led to an increased understanding of the role 2-methylquinoline has
in binding with carboxylic acid derivatives. Here anhydrous and hydrous multicomponent organic acid–
base adducts of 2-methylquinoline have been prepared with carboxylic acids that ranged from monocar-
boxylic acid to tricarboxylic acid such as 3,5-dinitrobenzoic acid, 3-hydroxy-2-naphthoic acid, oxalic acid,
fumaric acid, and citric acid.
The five crystalline complexes were characterized by X-ray diffraction analysis, IR, mp, and elemental
analysis. These structures adopted homo or heterosupramolecular synthons or both. Analysis of the crys-
tal packing of 1–5 suggests that there are NAHꢀ ꢀ ꢀO, OAHꢀ ꢀ ꢀN, and OAHꢀ ꢀ ꢀO hydrogen bonds (charge
assisted or neutral) between acid and base components in the studied compounds. Except the classical
hydrogen bonding interactions, the secondary propagating interactions also play an important role in
structure extension. These weak interactions are responsible for the formation of 1D–3D frameworks.
Ó 2012 Elsevier B.V. All rights reserved.
Received 15 December 2011
Received in revised form 8 February 2012
Accepted 8 February 2012
Available online 28 February 2012
Keywords:
Crystal structure
2-Methylquinoline
Carboxylic acids
Hydrogen bonds
Noncovalent interactions
1. Introduction
hydrogen-bonding synthons, and in this regard, the most frequently
used moieties with hydrogen-bonding capability are pyridyl and
Hydrogen bonding plays a crucial role in chemical, catalytic,
and biochemical processes, chemical and crystal engineering, as
well as in supramolecular chemistry [1–3]. During the last few dec-
ades, new types of hydrogen bonding have been found, and all
types of hydrogen bonds have been extensively studied [4,5], with
particular attention to their spectral [6], and structural [7,8]
features.
Carboxylic acids represent one of the most prevalent functional
groups in crystal engineering because they possess a hydrogen
bond donor and acceptor with a geometry that facilitates self-
association through supramolecular homosynthons. Indeed,
carboxylic acids are well-known to self-associate via centrosym-
metric dimer or catemer [9–11]. Furthermore, it is now recognized
that carboxylic acids are ideal candidates for multicomponent
crystals since they form persistent supramolecular heterosynthons
with a number of different N-containing components. It should
be noted that these structures are normally held together by
carboxyl. Strong and specific recognition of the carboxylic acid
group with pyridine (acid-pyridine synthon) is well studied [12–17].
As a pyridyl derivative, besides the methyl group, 2-methyl-
quinoline bears more aromatic
p electrons, which can be a better
unit in creating aromatic stacking interactions. To the best of our
knowledge there are very few reports involving the organic acid–
base adduct concerning the Lewis base of 2-methylquinoline.
Following our previous works of acid–base adducts based on
N-aromatic derivatives and carboxylic acids [18,19], herein we re-
port the synthesis and crystal structure of five supramolecular
complexes assembled through hydrogen bonding interactions be-
tween the carboxylic acid and 2-methylquinoline. In this study,
we got five organic acid–base adducts composed of carboxylic
acids and 2-methylquinoline (Scheme 1), namely 2-methylquino-
line: (3,5-dinitrobenzoic acid): H2O [(HL+)ꢀ ꢀ ꢀ(dnaꢁ)ꢀ ꢀ ꢀH2O, dnaꢁ
=
3,5-dinitrobenzoate, L = 2-methylquinoline] (1), 2-methylquino-
line: (3-hydroxy-2-naphthoic acid) [(HL)+ꢀ ꢀ ꢀ(npaꢁ), npaꢁ = 3-hy-
droxy-2-naphthoate] (2), 2-methylquinoline: (oxalic acid)0.5: H2O
[(HL)+ꢀ ꢀ ꢀ(oa2ꢁ
)
0.5ꢀ ꢀ ꢀH2O, oa2ꢁ = oxalate] (3), 2-methylquinoline:
(fumaric acid)0.5 [(L)ꢀ ꢀ ꢀ(H2fum)0.5, H2fum = fumaric acid] (4), and
2-methylquinoline: (citric acid) [(HL)+ꢀ ꢀ ꢀ(H2ctcꢁ), H2ctcꢁ
dihydrogen citrate] (5) (Scheme 2).
=
⇑
Corresponding author. Tel./fax: +86 571 6374 0010.
E-mail address: Jinsw@zafu.edu.cn (S. Jin).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.02.048

52
S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
NO2
O
HO
O
O
OH
OH
HO
OH
NO2
O
oxalic acid
3,5-dinitrobenzoic acid
3-hydroxy-2-naphthoic acid
O
OH
O
HO
HO
N
OH
HO
OH
O
O
O
2-methylquinoline
fumaric acid
citric acid
Scheme 1. Hydrogen bond synthons discussed in this paper.
O
O
NO2
NO2
N
H
O
O
O
H
N
H
H
H
O
H
1
2
O
H
H
O
O
N
O
H
O
H
N
N
H
O
O
H
N
O
H
O
H
O
3
4
O
OH
O
H
H
H
O
N
O
HO
O
5
Scheme 2. The five superamolecular compounds described in this paper, 1–5.
2.2. Preparation of supramolecular complexes
2. Experimental section
2.2.1. 2-Methylquinoline: (3,5-dinitrobenzoic acid): H2O [(HL+)ꢀ
(dnaꢁ)ꢀH2O] (1)
2.1. Materials and methods
To a methanol solution (2 mL) of 2-methylquinoline (28.6 mg,
0.2 mmol) was added 3,5-dinitrobenzoic acid (42.4 mg, 0.2 mmol)
in 4 mL methanol. The solution was stirred for a few minutes, then
the solution was filtered into a test tube. The solution was left
standing at room temperature for several days, light yellow block
crystals were isolated after slow evaporation of the solution in
All reagents were commercially available and used as received.
The C, H, and N microanalysis were carried out with a Carlo Erba
1106 elemental analyzer. The FT-IR spectra were recorded from
KBr pellets in range 4000–400 cmꢁ1 on a Mattson Alpha-Centauri
spectrometer. Melting points of new compounds were recorded
on an XT-4 thermal apparatus without correction.

S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
53
Table 1
Summary of X-ray crystallographic data for complexes 1–5.
1
2
3
4
5
Formula
Fw
C
17H15N3O7
C21H17NO3
331.36
C11H12NO3
206.22
C12H11NO2
201.22
C16H17NO7
335.31
373.32
T, K
298(2)
298(2)
298(2)
298(2)
298(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
P2(1)/c
12.5912(11)
7.2015(6)
18.8211(16)
90
0.71073
Monoclinic
P2(1)/c
13.0883(12)
6.7662(7)
18.8150(19)
90
0.71073
Monoclinic
P2(1)/c
6.9424(5)
12.1158(12)
11.7782(11)
90
0.71073
Monoclinic
P2(1)/n
7.4968(5)
11.5092(9)
12.6389(10)
90
0.71073
Monoclinic
P2(1)/n
7.5348(8)
12.8294(15)
16.9060(17)
90
a
(°)
b (°)
99.3760(10)
90
1683.8(2)
4
1.473
0.117
93.7310(10)
90
1662.7(3)
4
1.324
0.089
93.0620(10)
90
989.28(15)
4
1.385
0.102
105.7890(10)
90
1049.37(14)
4
1.274
0.087
94.0970(10)
90
1630.1(3)
4
1.366
0.108
c
(°)
V (Å3)
Z
Dcalcd (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
776
696
436
424
704
Crystal size (mm3)
h range (°)
0.48 ꢂ 0.47 ꢂ 0.42
2.52–25.02
ꢁ14 ꢃ h ꢃ 14
ꢁ8 ꢃ k ꢃ 8
ꢁ11 ꢃ l ꢃ 22
8008
0.40 ꢂ 0.38 ꢂ 0.24
2.59–25.02
ꢁ10 ꢃ h ꢃ 15
ꢁ7 ꢃ k ꢃ 7
ꢁ22 ꢃ l ꢃ 22
7895
0.42 ꢂ 0.40 ꢂ 0.30
2.41–25.01
ꢁ8 ꢃ h ꢃ 8
ꢁ14 ꢃ k ꢃ 11
ꢁ13 ꢃ l ꢃ 13
4811
0.47 ꢂ 0.45 ꢂ 0.38
2.44–25.02
ꢁ8 ꢃ h ꢃ 8
ꢁ13 ꢃ k ꢃ 13
ꢁ13 ꢃ l ꢃ 15
5171
0.30 ꢂ 0.21 ꢂ 0.18
2.42–25.01
ꢁ8 ꢃ h ꢃ 8
ꢁ15 ꢃ k ꢃ 10
ꢁ18 ꢃ l ꢃ 20
8053
Limiting indices
Reflections collected
Reflections independent (Rint
)
2972 (0.0377)
1.029
2903 (0.0639)
1.015
1733 (0.0370)
1.046
1847 (0.0437)
0.926
2863 (0.0690)
0.904
Goodness-of-fit on F2
R indices [I > 2
R indices (all data)
Largest diff. peak and hole, e.Åꢁ3
r
I]
0.0619, 0.1624
0.0961, 0.1984
0.379, ꢁ0.331
0.0565, 0.1301
0.1359, 0.1840
0.212, ꢁ0.207
0.0428, 0.1054
0.0785, 0.1344
0.219, ꢁ0.245
0.0466, 0.1222
0.0789, 0.1407
0.226, ꢁ0.146
0.0585, 0.1453
0.0998, 0.1694
0.280, ꢁ0.347
Table 2
Table 3
Hydrogen bond distances and angles in studied structures 1–5.
Selected bond lengths (Å) and angles (°) for 1–5.
1
DAHꢀ ꢀ ꢀA
d(DAH)
(Å)
d(Hꢀ ꢀ ꢀA)
(Å)
d(Dꢀ ꢀ ꢀA)
<(DHA)
(°)
N(1)AC(2)
1.326(4)
1.471(4)
1.246(4)
123.6(3)
N(1)AC(6)
N(3)AC(16)
O(2)AC(11)
1.361(4)
1.458(4)
1.215(4)
(Å)
N(2)AC(14)
O(1)AC(11)
C(2)AN(1)AC(6)
1
O(7)AH(7D)ꢀ ꢀ ꢀO(1)#1 0.85
1.89
1.94
1.77
2.708(4)
2.753(5)
2.628(3)
160.4
160.6
173.2
O(7)AH(7C)ꢀ ꢀ ꢀO(2)
N(1)AH(1)ꢀ ꢀ ꢀO(1)
0.85
0.86
2
N(1)AC(13)
O(1)AC(1)
O(3)AC(4)
O(2)AC(1)AO(1)
1.312(4)
1.302(5)
1.355(5)
123.4(4)
N(1)AC(17)
O(2)AC(1)
C(13)AN(1)AC(17)
1.369(4)
1.231(4)
121.4(3)
2
O(3)AH(3)ꢀ ꢀ ꢀO(2)
0.82
0.86
1.86
1.72
2.592(4)
2.575(3)
147.2
175.2
N(1)AH(1)ꢀ ꢀ ꢀO(1)#1
3
3
O(3)AH(3D)ꢀ ꢀ ꢀO(1)#1 0.85
2.05
2.01
1.81
2.892(3)
2.846(2)
2.619(2)
168.3
168.4
156.7
N(1)AC(2)
O(1)AC(11)
C(2)AN(1)AC(6)
1.324(3)
1.238(3)
122.96(18)
N(1)AC(6)
O(2)AC(11)
O(1)AC(11)AO(2)
1.374(3)
1.259(3)
125.9(2)
O(3)AH(3C)ꢀ ꢀ ꢀO(1)#2 0.85
N(1)AH(1)ꢀ ꢀ ꢀO(2)
4
O(1)AH(1)ꢀ ꢀ ꢀN(1)#2
0.86
0.82
4
1.80
2.603(2)
165.3
N(1)AC(4)
O(1)AC(1)
C(4)AN(1)AC(8)
1.321(3)
1.311(2)
119.93(17)
N(1)AC(8)
O(2)AC(1)
O(2)AC(1)AO(1)
1.383(2)
1.224(3)
124.4(2)
5
O(7)AH(7)ꢀ ꢀ ꢀN(1)#1
O(7)AH(7)ꢀ ꢀ ꢀO(6)
O(5)AH(5)ꢀ ꢀ ꢀO(3)#2
O(2)AH(2)ꢀ ꢀ ꢀO(4)#3
N(1)AH(1)ꢀ ꢀ ꢀO(7)#4
N(1)AH(1)ꢀ ꢀ ꢀO(6)#4
0.82
0.82
0.82
0.82
0.86
0.86
2.24
2.16
1.76
1.76
2.28
2.19
3.016(3)
2.664(3)
2.573(3)
2.572(3)
3.016(3)
2.925(3)
156.9
119.8
168.6
171.4
143.7
143.1
5
N(1)AC(1)
1.337(4)
1.205(3)
1.262(3)
1.316(3)
1.431(3)
118.0(3)
123.0(3)
N(1)AC(5)
O(2)AC(11)
O(4)AC(15)
O(6)AC(16)
C(1)AN(1)AC(5)
O(1)AC(11)AO(2)
O(6)AC(16)AO(5)
1.372(4)
1.319(3)
1.241(3)
1.218(3)
124.7(3)
123.4(3)
125.2(2)
O(1)AC(11)
O(3)AC(15)
O(5)AC(16)
O(7)AC(13)
N(1)AC(1)AC(2)
O(4)AC(15)AO(3)
Symmetry transformations used to generate equivalent atoms for 1: #1 x, y ꢁ 1, z.
Symmetry transformations used to generate equivalent atoms for 2: #1 ꢁx + 1,
ꢁy + 1, ꢁz. Symmetry transformations used to generate equivalent atoms for 3: #1
ꢁx + 1, ꢁy + 1, ꢁz + 1; #2 x + 1, y, z. Symmetry transformations used to generate
equivalent atoms for 4: #2 x, y + 1, z. Symmetry transformations used to generate
equivalent atoms for 5: #1 x + 1/2, ꢁy + 1/2, zꢁ1/2; #2 x + 1, y, z; #3 ꢁx + 3/2, y ꢁ 1/
2, ꢁz + 1/2; #4 x ꢁ 1/2, ꢁy + 1/2, z + 1/2.
air. The crystals were dried in air to give the title compound
[(HL+)ꢀ(dnaꢁ)ꢀH2O] (1), yield 64 mg, 85.72%. m. p. 168–170 °C. Ele-
mental analysis performed on crystals exposed to the atmosphere:
Calc. for C17H15N3O7 (373.32): C, 54.64; H, 4.02; N, 11.25. Found: C,
54.59; H, 3.92; N, 11.16. Infrared spectrum (KBr disk, cmꢁ1):
2.2.2. 2-Methylquinoline : (3-hydroxy-2-naphthoic acid) [(HL)+
ꢀ(npaꢁ)] (2)
3638s(
3064m, 2960m, 1976w, 1836w, 1783w, 1662w, 1606s(
1592m, 1526s( as(NO2)), 1466w, 1374s( m
s(COOꢁ)), 1333s(
m(OH)), 3456s(multiple,
m
as(NH)), 3323s(
m
s(NH)), 3112m,
as(COOꢁ)),
s(NO2)),
m
To a methanol solution (2 mL) of 2-methylquinoline (28.6 mg,
0.2 mmol) was added 3-hydroxy-2-naphthoic acid (36.4 mg,
0.2 mmol) in 8 mL ethanol. Colorless crystals were afforded after
several days of slow evaporation of the solvent. The crystals were
m
m
1250m, 1195m, 1131m, 1079m, 952m, 903m, 853m, 806m, 757m,
726m, 680m, 635m.

54
S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
Fig. 1. The structure of 1, showing the atom-numbering scheme. Displacement
Fig. 3. The structure of 2, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
ellipsoids were drawn at the 30% probability level.
dried in air to give the title compound [(HL)+ꢀ(npaꢁ)] (2), yield:
64 mg, 96.57%. mp 192–194 °C. Elemental analysis: Calc. for
C
21H17NO3 (331.36): C, 76.05; H, 5.13; N, 4.23. Found: C, 76.02; H,
5.06; N, 5.04. Infrared spectrum (KBr disk, cmꢁ1): 3596s(
(OH),
s(NH)), 3028m, 2928m, 1650m, 1616m,
as(COOꢁ)), 1510m, 1480s, 1442m, 1368s( s(COOꢁ)),
m
3460s(
m
as(NH)), 3348s(m
1576s(
m
m
1296m, 1228s, 1180m, 1050m, 1016m, 967m, 882m, 818m, 740m,
688m, 622m.
2.2.3. 2-Methylquinoline: (oxalic acid)0.5: H2O [(HL)+ꢀ(oa2ꢁ
0.5ꢀH2O]
)
(3)
To a methanol solution (2 mL) of 2-methylquinoline (28.6 mg,
0.2 mmol) was added oxalic acid (25.4 mg, 0.2 mmol) in 3 mL eth-
anol. Colorless prisms were afforded after several days of slow
evaporation of the solvent. The crystals were dried in air to give
Fig. 4. The 1D chain structure of 2 running along the b axis direction formed by the
cations via the
p–p interaction, the anions were attached to the chain via NAHꢀ ꢀ ꢀO
the title compound [(HL)+ꢀ(oa2ꢁ
0.5]ꢀH2O (3), yield: 32 mg,
)
hydrogen bonds.
77.59%(Based on L). mp 142–143 °C. Elemental analysis: Calc. for
C
11H12NO3 (206.22): C, 40.09; H, 5.82; N, 6.79. Found: C, 40.02; H,
5.76; N, 6.74. Infrared spectrum (KBr disk, cmꢁ1): 3678s(
(OH)),
3472s( as(NH)), 3384s( s(NH)), 2938m, 1642s, 1587s(
as(COOꢁ)),
1518m, 1401s, 1382s(
s(COOꢁ)), 1284m, 1232s, 1097s, 1036w,
962m, 848m, 792s, 728s, 662m, 614m.
2.2.4. 2-Methylquinoline : (fumaric acid)0.5 [(L)ꢀ(H2fum)0.5] (4)
To a methanol solution (2 mL) of 2-methylquinoline (28.6 mg,
0.2 mmol) was added fumaric acid (24 mg, 0.2 mmol) in 5 mL
methanol. The solution was stirred for 10 min, then the solution
m
m
m
m
m
Fig. 2. 2D corrugated sheet structure of 1 extending parallel to the ab plane.

S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
55
Fig. 7. The structure of 4, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
Fig. 5. The structure of 3, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
collections and reductions were performed using the SMART and
SAINT software [20,21]. The structures were solved by direct meth-
ods, and the non-hydrogen atoms were subjected to anisotropic
refinement by full-matrix least squares on F2 using SHELXTL pack-
age [22]. Hydrogen atom positions for all of the structures were
located in a difference map and refined independently. Further de-
tails of the structural analysis are summarized in Table 1. Selected
bond lengths and angles for complexes 1–5 are listed in Table 2,
the relevant hydrogen bond parameters are provided in Table 3.
was filtered. The solution was left standing at room temperature for
several days, colorless block crystals were isolated after slow
evaporation of the solution in air. The crystals were dried in air to
give the title compound [(L)ꢀ(H2fum)0.5
] (4), yield 34 mg,
84.48%(Based on L). m. p. 188–189 °C. Elemental analysis
performed on crystals exposed to the atmosphere: Calc. for
C
12H11NO2(201.22): C, 71.56; H, 5.47; N, 6.96. Found: C, 71.48; H,
5.44; N, 6.92. Infrared spectrum (KBr disk, cmꢁ1): 3518s(
m
(OH)),
3064m, 2960m, 2492m(broad), 1976w, 1908m(broad), 1836w,
1783w, 1718s(v(C@O)), 1662w, 1596m, 1530m, 1486w, 1333m,
1286s(m(CAO)), 1250m, 1195m, 1131m, 1079m, 952m, 903m,
853m, 806m, 757m, 726m, 692m, 654m, 606m.
3. Results and discussion
3.1. Syntheses and general characterization
2.2.5. 2-Methylquinoline: (citric acid) [(HL)+ꢀðH2ctcꢁ)] (5)
To a methanol solution (2 mL) of 2-methylquinoline (28.6 mg,
0.2 mmol) was added citric acid (42 mg, 0.2 mmol) in 6 mL etha-
nol. Colorless crystals were afforded after several days of slow
evaporation of the solvent. The crystals were dried in air to give
the title compound [(HL)+ꢀ(H2ctcꢁ)] (5), yield: 54 mg, 80.52%. mp
122–123 °C. Elemental analysis: Calc. for C16H17NO7(335.31): C,
57.26; H, 5.07; N, 4.17. Found: C, 57.19; H, 4.94; N, 4.09. Infrared
For the preparation of 1–5, the carboxylic acids were mixed di-
rectly with the 2-methylquinoline in 1:1 ratio in methanol and/or
ethanol solvents, which was allowed to evaporate at ambient
conditions to give the final crystalline products. The molecular
structures and their atom labeling schemes for the five structures
are shown in Figs. 1, 3, 5, 7, and 9, respectively.
The elemental analyses for the five compounds are in good
agreement with their compositions. The infrared spectra of 1–5
are consistent with their chemical formulas determined by
elemental analysis and further confirmed by X-ray diffraction
analysis. The very strong and broad features at 3700–3300 cmꢁ1
arise from OAH or NAH stretching frequencies. Aromatic and
quinoline ring stretching and bending are in the regions of
1500–1630 cmꢁ1 and 600–750 cmꢁ1, respectively. All of the com-
pounds except 4 show the characteristic bands for COOꢁ, and
compounds 4, and 5 display strong IR peaks for COOH groups.
The presence of two broad bands at ca. 2500 cmꢁ1 and
1900 cmꢁ1 in compound 4, characteristic of a neutral OAHꢀ ꢀ ꢀN
spectrum (KBr disk, cmꢁ1): 3624s(
as(NH)), 3346(br, s(NH)), 3060m, 2990m, 2920m, 1964w,
1842w, 1776w, 1735m, 1672vs(v(C@O)), 1604s(
as(COOꢁ)),
1565m, 1522m, 1486s, 1424s, 1392s(
s(COOꢁ)), 1358m, 1300m,
1287s( (CAO)), 1244m, 1198m, 1134m, 1106m, 1054m, 1026m,
m(OH)), 3462s(multiple,
m
m
m
m
m
936m, 853m, 798m, 736m, 676m, 624m.
2.3. X-ray crystallography
Suitable crystals were performed on a Bruker SMART 1000 CCD
diffractometer using Mo radiation (k = 0.71073 Å). Data
K
a
Fig. 6. 2D sheet structure of 3 which was extending on the ac plane.

56
S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
hydrogen-bond interaction, was viewed as evidence for co-crystal
3.3. X-ray structure of 2-methylquinoline: (3-hydroxy-2-naphthoic
formation [23]. Except for the above bands, for 1, the bands at ca.
acid) [(HL)+ꢀ(npaꢁ)] (2)
1526 and 1333 cmꢁ1 were attributed to the
respectively [24].
mas(NO2) and ms(NO2),
Similar to compound 1, the compound 2 is also an organic salt.
In 2 the asymmetric unit is occupied by one anion of 3-hydroxy-2-
naphthoate, and one cation of 2-methylquinolinium (HL)+ (Fig. 3).
The rms deviation of the cation excluding the methyl group is
0.0073 Å. The rms deviation of the benzene ring of the anion is
0.00146 Å. Both planes make dihedral angle of 109.5(3)°. The
CAO bond distance (O(3)AC(4) 1.355(5) Å) is in the range of the
neutral CAO bond distance in the phenol derivatives (1.344
(3) ꢁ 1.357 (3) Å) [29].
IR spectroscopy has also proven to be useful for the recogni-
tion of proton transfer compounds [25]. The most distinct fea-
ture in the IR spectrum of proton transfer compounds is the
presence of strong asymmetrical and symmetrical carboxylate
stretching frequencies at 1550–1610 cmꢁ1 and 1300–1420 cmꢁ1
[26].
3.2. X-ray structure of 2-methylquinoline: (3,5-dinitrobenzoic acid):
In the COOꢁ group, the two CAO bond lengths are significantly
different between O(2)AC(1) (1.231(4) Å) and O(1)AC(1)
H2O [(HL+)ꢀ(dnaꢁ)ꢀH2O] (1)
(1.302(5) Å) (
D is 0.071 Å) The relative large D value is attributed
The compound 1 of the composition [(HL+)ꢀ(dnaꢁ)ꢀH2O] was
prepared by reaction equal mol of 2-methylquinoline and 3,5-dini-
trobenzoic acid, in which the proton of 3,5-dinitrobenzoic acid was
transferred to the ring N atom of the quinoline. This structure is a
solvate. The asymmetric unit of 1 contains one cation of 2-methyl-
quinolinium, an anion of 3,5-dinitrobenzoate, and a water mole-
cule as shown in Fig. 1.
to the fact that the O1 atom involves more strong hydrogen bond
than that of O2 (Table 3). The angle [121.4(3)°] around the proton-
ated N atom (N1) is smaller than the corresponding angle in com-
pound 1 [123.6(3)°], and the saccharate salt of 2-methylquinoline
(123.7(3)°) [30]. This may be due to the difference of the hydrogen
bonding strength in the corresponding compound.
The cations formed a 1D chain along the b axis direction via the
The r.m.s deviations of the aromatic rings in the cation and
the anion from the mean planes of the corresponding rings are
0.0147 Å, and 0.0057 Å, respectively. The dihedral angle between
the benzene ring of the anion and the quinoline ring of the
cation is 113.4°. The carboxylate deviated by 14° from the ben-
zene ring of the anion. The two nitro groups deviated by 172.4°
(for the group N2AO3AO4), and 9.2° (for the group N3AO5AO6)
from the mean plane of the anion benzene ring unit,
respectively.
p–p interaction between the aromatic rings with centroid separa-
tion of 3.394 Å. In the cation chain, the neighboring cations were
antiparallelly arranged, while the third cation is parallel to the first
cation. So does the second cation and the fourth cation. The anions
were bonded to the cation chain through the NAHꢀ ꢀ ꢀO hydrogen
bond between one O atom of the carboxylate and the NH+ of one
cation and CHAO association between the other O atom of the
same carboxylate and the 5-CH of the neighboring cation with
CAO distance of 3.449 Å (Fig. 4). The carboxylate also made an
intramolecular OAHꢀ ꢀ ꢀO contact to form a ring with descriptor of
S11ð6Þ. It is worthy to note that the anions at the same side of the
cation chain were parallel to each other, while the anions at differ-
ent sides of the cation chain intersect at an angle of ca. 60° with
each other.
The CAO distances of COOꢁ of the 3,5-dinitrobenzoate are rang-
ing from 1.215(4) (O(2)AC(11)) to 1.246(4) Å (O(1)AC(11)). The
difference (D is 0.031 Å) in bond distances between O(1)AC(11)
and O(2)AC(11) in the carboxylate group in compound 1 is ex-
pected for ionized carboxyl group. The angle C(2)AN(1)AC(6)
around the protonated N atom is 123.6(3)°, which is similar to
the value in the protonated L [27].
The ionic NAHꢀ ꢀ ꢀO hydrogen bond is formed between the oxy-
gen atom of the carboxylate and the NH+ group (N(1)AH(1)ꢀ ꢀ ꢀO(1),
2.628(3) Å). Two anions formed a dimer via a pair of intermolecu-
lar CHAO associations between the benzene CH and the nitro
group with CAO distance of 3.487 Å. For the presence of such inter-
actions the two anions generated a R22ð8Þ ring motif according to
Bernstein [28].
The parallel anion dimers were stacked along the a axis direc-
tion and joined together via the water molecules by the OAHꢀ ꢀ ꢀO
hydrogen bond between the water molecule and the carboxylate
with OAO separation of 2.708(4) and 2.753(5) Å respectively, and
CHAO interaction between the benzene CH of the anion and the
Ow atom with CAO distance of 3.532 Å to form a 1D ladder struc-
ture. The cations were bonded to the ladders by the NAHꢀ ꢀ ꢀO and
CHAO interactions to form 2D corrugated sheet extending parallel
to the ab plane (Fig. 2). In the sheet the anion ladders and the cat-
ions alternate, the adjacent ladders were not parallel to each other,
and they made an angle of ca 30° with each other, while the third
ladder is parallel to the first ladder, so does the second ladder and
the fourth ladder. The adjacent cations intercalated between the
same pair of anion ladders are antiparallelly arranged, while the
cations intercalated between different pairs of ladders were paral-
lel to each other. The corrugated sheets were further stacked along
3.4. X-ray structure of 2-methylquinoline: (oxalic acid)0.5: H2O
[(HL)+ꢀ(oa2ꢁ
0.5ꢀH2O] (3)
)
The crystal structure of 3 consists of half a dianion of oxalic acid,
one cation of 2-methylquinolinium, and one water molecule in the
asymmetric unit (Fig. 5). The proton of the COOH group has trans-
ferred to the ring N atom of the quinoline moiety. The assignment of
3 as a salt is based on successful refinement of the relevant H atoms
using X-ray data. This is further verified by the CAO distances
[(O(1)AC(11), 1.238(3) Å), O(2)AC(11), 1.259(3) Å with
D = 0.021
Å] in the carboxylate group, which is in the range for the OAC dis-
tances concerning the deprotonated carboxyl groups. In the com-
pound, there is one ion pair with one water molecule, which fits
well with the micro-analysis results.
The CANAC angles of pyridine are very sensitive to protonation
[31,32]. A pyridinium cation always possesses an expanded angle
of CANAC in comparison with the parent pyridine. The hydrogen
atom H(N1), which is deprived from its parent, attaches the nitro-
gen atom. In the cations, the angle C(6)AN(1)AC(2) [122.96(18)°]
is similar to the value in its hydrochloride salt (123.6) [27]. Yet it
is slightly larger than the corresponding CNC angle in the com-
pound 2 (121.4(3)°).
The anions and the water molecules were joined together
through the OAHꢀ ꢀ ꢀO hydrogen bond between the water molecules
(donor) and the carboxylate group (acceptor) with OAO separations
of 2.846(2) Å, and 2.892(3) Å, respectively to form a 1D chain run-
ning along the a axis direction. Herein the anions at adjacent chains
were slipped some distance from each other along the a axis direc-
tion, while the anions at the third chain and the anions at the first
the c axis direction through the O–p interaction between the nitro
group and the benzene ring of the anion with OACg distance of
3.033 Å, and CH3AO interaction between the methyl group of the
cation and the Ow atom with CAO distance of 3.261 Å to form
3D layer network structure.

S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
57
Fig. 8. 2D corrugated sheet structure of 4.
chain were almost in the same line when viewed from the c axis
direction. Such kind of discrete chains were arranged parallelly on
the ac plane. Between the two neighboring chains the cations are
intercalated through the ionic NAH+ꢀ ꢀ ꢀOꢁ hydrogen bond
(N(1)AH(1)ꢀ ꢀ ꢀO(2), 2.619(2) Å) between the NH+ cation and the car-
boxylate and CHAO interactions between the water molecule and
the 4-CH, and 5-CH of the cation with CAO distance of 3.298–
3.417 Å to form a 2D sheet structure extending on the ac plane
(Fig. 6). Here the water molecule acts as bidentate acceptor forming
two CHAO contacts in bifurcate mode. At the same sheet the adja-
cent cations intercalated between the same pair of anion chains
were antiparallelly arranged, while the third cation and the first
cation between the same pair of anion chains were parallelly ar-
ranged. In the sheet there are four-membered O rings composed
by two water molecules and two O atoms of two adjacent oxalates.
Such kind of sheets were further stacked along the b axis direc-
tion via the intersheet CHAO association between 3-CH of the cat-
ion and the carboxylate with CAO distance of 3.524 Å and CH3AO
interactions between the 2-CH3 of the cation and the carboxylate
with CAO distance of 3.556 Å to form a 3D ABAB layer network
structure. Here the third sheet layer has the same projection on
the ac plane as the first sheet layer, so does the second sheet layer
and the fourth sheet layer.
Fig. 9. The structure of 5, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
corresponding value in compounds 1–3, which also conforms our
correct assignment of 4 as a cocrystal.
At each fumaric acid there are bonded two 2-methylquinoline
through the neutral OAHꢀ ꢀ ꢀN hydrogen bond with NAO distance
of 2.603(2) Å, which is considerably less than the sum of the van
der Waals radii for N and O (3.07 Å) [34]. One of the shortest
known OAHꢀ ꢀ ꢀN hydrogen bonds was observed in the crystal
structure of 4-methylpyridine and pentachlorophenol [35] with
the Oꢀ ꢀ ꢀN distance of 2.506 (3) Å at 20 K. Similarly, the title crystal
is also an example of a system with short Oꢀ ꢀ ꢀHꢀ ꢀ ꢀN hydrogen bond
(with the Oꢀ ꢀ ꢀN distance being 2.603(2) Å).
3.5. X-ray structure of 2-methylquinoline: (fumaric acid)0.5
[(L)ꢀ(H2fum)0.5] (4)
Similar to the above compounds, compound 4 was prepared by
reaction of a methanol solution of fumaric acid and 2-methylquin-
oline in 1:1 ratio, which crystallizes as Monoclinic colorless crys-
tals in the centrosymmetric space group P2(1)/n. The asymmetric
unit of 4 consists of one molecule of 2-methylquinoline and half
a molecule of fumaric acid, as shown in Fig. 7.
This is a cocrystal where the COOH groups of fumaric acid are
not ionized by proton transfer to the nitrogen atom (N(1)) of the
2-methylquinoline moieties, which is also confirmed by the bond
distances of O(1)AC(1) (1.311(2) Å) and O(2)AC(1) (1.224(3) Å)
which are typical bond distances for protonated carboxyl groups.
The mean values of the CAC and NAC bond lengths in the ring
of the 2-methylquinoline are 1.394 (3) and 1.352 (2) Å respec-
tively, which are between that of a single bond and a double bond
and agree with those values in the literature [33].
Two 2-methylquinoline and one fumaric acid form a heteroad-
duct. In the heteroadducts there are inversion centers located at
the middle point of the olefinic group in the fumaric acid. So the
two 2-methylquinoline molecules are antiparallelly arranged. Such
kind of heteroadducts were linked together via CHAO associations
between the 7-CH of the 2-methylquinoline and the carbonyl moi-
ety of the fumaric acid with C-O distance of 3.457 Å to form 2D cor-
rugated sheet structure (Fig. 8).
3.6. X-ray structure of2-methylquinoline: (citric acid) [(HL)+ꢀ(H2ctcꢁ)]
(5)
Similar to 1–4, the compound [(HL)+ (H2ctcꢁ)] (5) was also
prepared by reaction of 2-methylquinoline with citric acid in 1:1
ratio, which crystallizes as monoclinic block crystals in the centro-
symmetric space group P2(1)/n. The compound consists of one
The angle of C(4)AN(1)AC(8) [119.93(17)°] is smaller than the
corresponding angle (123.6°) in the protonated L [27], and the

58
S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
Fig. 10. 2D corrugated anionic sheet structure of 5 which is extending along the direction that made an angle of ca. 45° with the ac plane.
2-methylquinolin-1-ium cation, and one dihydrogen citrate anion
(Fig. 9). In 5 the citric acid is singly deprotonated to exhibit valence
number of ꢁ1. The present investigation clearly shows that the
compound is also an organic salt. The proton coming from the car-
boxylic H of the citric acid in compound 5 is on the ring nitrogen
atom, forming an ion pair, which is similar to that of the proton
transfer compound assembled from citric acid and 2,4,6-triamine-
1,3,5-triazine [36]. Unlike the adduct of citric acid and 2,4,6-tri-
amine-1,3,5-triazine [36], in 5 only one terminal COOH carboxyl
group is ionized. And in this case the order of ionization of the citric
acid [37] does not agree with the previous published results that
the central carboxyl group is the first ionized carboxyl group.
As shown in Table 3, all the bond angles and bond distances are
in the normal range. The OAC bond distances of the carboxylate
group were 1.262(3) (O(3)AC(15)), and 1.241(3) Å (O(4)AC(15))
respectively. The difference between the two CAO bonds is
anion and the terminal carboxylate of its adjacent anion with
OAO separation of 2.573(3) Å to form a 1D chain running along
the a axis direction. Two neighboring chains were linked together
via the interchain OAHꢀ ꢀ ꢀO associations between the terminal car-
boxylate group of one chain and the terminal carboxyl group of its
neighboring chain to form a double chain structure. Such double
chains were further combined together via the CH2AO interaction
between the CH2 group of the anion and the carboxylate with CAO
distance of 3.500 Å to form a tetrachain structure running along
the a axis direction. In the tetrachain the middle two chains are al-
most in the same plane, while the outer two chains were protruded
from the plane defined by the middle two chains. Such kinds of
tetrachains were joined together along the c axis direction via
CH2AO interactions with CAO distance of 3.500 Å to form 2D cor-
rugated sheet structure extending along the direction that made an
angle of ca. 45° with the ac plane (Fig. 10). Such kind of sheets were
further stacked along the b axis direction via the intersheet
OAHꢀ ꢀ ꢀO interactions between the terminal carboxyl group of
one sheet layer and the terminal carboxylate group of its neighbor-
ing sheet layer with OAO distance of 2.575(3) Å to form 3D net-
work structure with channels. In the channels there are cations
which is bound to the anion network through NAHꢀ ꢀ ꢀO hydrogen
bond (between the NH+ cation and the carbonyl unit of the middle
carboxyl group in the anion with NAO distance of 2.925(3) Å, and
between the alcohol hydroxyl group of the anion and the same NH+
cation with NAO distance of 3.016(3) Å), CHAO interaction
(between the 8-CH of the cation and the alcohol hydroxyl moiety
with CAO distance of 3.256 Å), and CH3AO interaction (between
the 2-CH3 of the cation and the carboxylate with CAO distance of
3.298 Å) to form 3D network structure with reduced channels.
0.021 Å which is in the range of the reported
D value for organic
salts formed between the carboxylic acid and the N-containing
base [38], which is also expected for ionic CAO bond distances.
The two carboxyl groups both have C@O and CAO bond distances
indicative of an unionized character, in which no Hs transfer has
occurred to the quinoline N atom. The ratio of CAO(long) to C@O
(short) bond distances are 1.0804, and 1.0946, respectively, for
the two carboxyl groups on C(16), and C(11). These values are
characteristic for unionized COOH (ionized COOH groups have a
lower ratio of about 1.030, here it is 1.0169 for the deprotonated
COOH) [39]. It is clear that the
D value in bond lengths of CAO
within the COOH group ( are 0.098, and 0.114 Å) is larger than
D
the one found in the carboxylate group (0.021 Å), which also con-
firms the monoionization of the tricarboxylic acid.
The plane defined by the central hydroxyl and carboxyl groups
is almost perpendicular to the plane of the C atom backbone
(82.7(2)°), yet the dihedral angle between these two planes is
somewhat smaller than what was found for the 1:1 adduct of tri-
methylglycine and citric acid [40].
4. Conclusion
Single crystal X-ray diffraction has enabled the elucidation of
five examples of 2-methylquinoline-carboxylic acid adducts, novel
contributions to the extensive research into the occurrence of
carboxylic acid-quinoline compound motifs in organic salts or
cocrystal. In their place are a series of motifs in which extensive
strong classical NAHꢀ ꢀ ꢀO/OAHꢀ ꢀ ꢀN hydrogen bonds (ionic or
neutral) combine with weaker interactions (CHAO, CH2AO, and
CH3AO). This variety, coupled with the varying geometries and
number of COOH groups of the carboxylic acids employed, has
led to the creation of a range of supramolecular arrays, from 1D
chain structure, to 2D sheet structure, and 3D network structure.
In the compounds 1, 2, 3, and 5, the 2-methylquinolinium
cations function as acceptors for ionic hydrogen bonds that orga-
nize and orient the anions, while in compound 4 2-methylquino-
line fragments function as acceptors for neutral hydrogen bonds.
This phenomenon may be explained by the rule ‘‘strongest donor
The planes of the two end carboxyl groups lie at angles of 16.4
(for C11AO1AO2) and 76.7° (for C15AO3AO4) respectively with
the C atom backbone, and they made a dihedral angle of 74.1° with
each other. The dihydrogen citrate anion assumes a conformation
not previously observed in the solid, with one terminal carboxyl
(C11AO1AO2) and the middle carboxyl group (C16AO5AO6) al-
most perpendicular to each other (the dihedral angle between
the two groups is 88.5°). While another carboxylate group
(C15AO3AO4) and the middle carboxyl group (C11AO1AO2)
intersect at an angle of ca. 149.9° with each other. In this case
the dihedral angle is significantly larger than the corresponding
angle in anhydrous 1:1 cocrystal of citric acid and caffeine
(17.5°) [41].
The anions were connected together by the intermolecular
OAHꢀ ꢀ ꢀO interaction between the middle carboxyl unit of one

S. Jin et al. / Journal of Molecular Structure 1017 (2012) 51–59
59
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fumaric acid has the relatively larger Pka (Pka1) which may led the
D
Pka (between the L and the carboxylic acid) to be out of the range
for salt formation. Although citric acid in 5 has the similar Pka
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possesses O–
p interaction, while there are p–p interactions in
compound 2.
The results presented herein indicate that the strength and
directionality of the N+AHꢀ ꢀ ꢀOꢁ, OAHꢀ ꢀ ꢀO, and OAHꢀ ꢀ ꢀN hydrogen
bonds (ionic or neutral) between carboxylic acids and 2-methyl-
quinoline are sufficient to bring about the formation of binary
organic salts or cocrystals.
5. Supporting information available
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic data center, CCDC
Nos. 851592 for 1, 836676 for 2, 836679 for 3, 835832 for 4, and
841400 for 5. Copies of this information may be obtained free of
charge from the +44(1223)336-033 or Email: deposit@ccdc.cam.a-
c.uk or www: http://www.ccdc.cam.ac.uk.
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Acknowledgements
We gratefully acknowledge the financial support of the Educa-
tion Office Foundation of Zhejiang Province (Project No.
Y201017321) and the financial support of the Zhejiang A & F
University Science Foundation (Project No. 2009FK63).
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