Crystal and molecular structure of eight organic acid-base adducts from 2-methylquinoline and different acids

Article abstract of DOI:10.1016/j.molstruc.2014.05.007

Eight supramolecular complexes with 2-methylquinoline and acidic components as 4-aminobenzoic acid, 2-aminobenzoic acid, salicylic acid, 5-chlorosalicylic acid, 3,5-dinitrosalicylic acid, malic acid, sebacic acid, and 1,5-naphthalenedisulfonic acid were s

Full text of DOI:10.1016/j.molstruc.2014.05.007

Accepted Manuscript
Crystal and molecular structure of eight organic acid-base adducts from 2-meth-
ylquinoline and different acids
Jing Zhang, Lin Tao, Shouwen Jin, Bin Liu, Daqi Wang
PII:
S0022-2860(14)00466-9
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.05.007
MOLSTR 20606
Reference:
Journal of Molecular Structure
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Revised Date:
Accepted Date:
14 February 2014
4 May 2014
5 May 2014
Please cite this article as: J. Zhang, L. Tao, S. Jin, B. Liu, D. Wang, Crystal and molecular structure of eight organic
acid-base adducts from 2-methylquinoline and different acids, Journal of Molecular Structure (2014), doi: http://
dx.doi.org/10.1016/j.molstruc.2014.05.007
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Crystal and molecular structure of eight organic acid-base adducts from
2-methylquinoline and different acids
JingZhanga, Lin Taoa, Shouwen Jina*, Bin Liua*, and Daqi Wangb
aTianmu college ZheJiang A & F University, ZhuJi 311800, P. R. China, Tel & fax:
+86-575-8776-0141. *E-mail: liubin20131031@sohu.com
bDepartment of Chemistry, Liaocheng University, Liaocheng 252059, P. R. China.
Abstract:
Eight supramolecular complexes with 2-methylquinoline and acidic components as
4-aminobenzoic acid, 2-aminobenzoic acid, salicylic acid, 5-chlorosalicylic acid,
3,5-dinitrosalicylic acid, malic acid, sebacic acid, and 1,5-naphthalenedisulfonic acid
were synthesized and characterized by X-ray crystallography, IR, mp, and elemental
analysis. All of the complexes are organic salts except compound 2.
All supramolecular architectures of 1-8 involve extensive classical hydrogen bonds
as well as other noncovalent interactions. The results presented herein indicate that the
strength and directionality of the classical hydrogen bonds (ionic or neutral) between
acidic components and 2-methylquinoline are sufficient to bring about the formation of
binary organic acid-base adducts. The role of weak and strong noncovalent interactions in
the crystal packing is ascertained. These weak interactions combined, the complexes 1-8
displayed 2D-3D framework structure.
Keywords: Crystal structure; 2-methylquinoline; Acids; Hydrogen bonds; Noncovalent
interactions
Introduction
Cocrystal/salt formation is rapidly gaining popularity as a method for the synthesis of
new materials [1]. Important in this regard is the fact that cocrystals/salts provide an
opportunity to synthesize organic solids by design, through the use of supramolecular
1

synthons [2]. Thus, cocrystals/salts can be engineered with the intention to design, or
improve upon, a particular solid-state property of a molecule (e.g. reactivity, dissolution,
mechanical, electrical or optical properties) without affecting its intrinsic structure [3].
The major driving force in cocrystal/salt formation is hydrogen bonding and other
nonbonding interactions [4-8].
Because of the predictable supramolecular properties and the ability to form strong
hydrogen bonds, carboxylic acids were frequently chosen as building blocks for crystal
engineering [9-11]. Numerous heterodimers composed of carboxylic acids and a variety
of N-containing basic building blocks have been documented recently [13-16]. The
hydrogen bonding between hydroxyl groups of carboxylic acids and heterocyclic nitrogen
atoms has been proved to be a useful and powerful organizing force for the formation of
supramolecules. It should be noted that these structures are normally held together by
hydrogen-bonding, and in this regard, the most frequently used moieties with hydrogen
bonding capability are pyridyl and carboxyl. As a pyridyl derivative, besides the methyl
group, 2-methylquinoline bears more aromatic π electrons, which can be a better group 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 [17, 18, 19], herein we report the synthesis and crystal
structure of eight supramolecular complexes assembled through hydrogen bonding
interactions between acidic synthons and 2-methylquinoline. In this study, we got eight
organic acid-base adducts composed of acidic units and 2-methylquinoline (L) (Scheme
1), namely 2-methylquinoline : (4-aminobenzoic acid) [(HL)+ · (4-aba-), 4-aba- =
4-aminobenzoate] (1), 2-methylquinoline : (2-aminobenzoic acid) [(L) · (2-Haba),
2-Haba = 2-aminobenzoic acid] (2), 2-methylquinoline : (salicylic acid) [(HL)+ · (sal-),
sal- = salicylate] (3), 2-methylquinoline : (5-chlorosalicylic acid) [(HL)+ · (csal-), csal-
=
5-chlorosalicylate] (4), 2-methylquinoline
:
(3,5-dinitrosalicylic acid)
[(HL)+ · (3,5-dns-), 3,5-dns- = 3,5-dinitrosalicylate] (5), (2-methylquinoline)2 : (L-malic
acid) [(HL)+ · (L) · (Hmal-), Hmal = L-hydrogenmalate] (6), (2-methylquinoline)2 :
2+
(sebacic acid) [(HL)2 · (seba)2-, seba = sebacate] (7), and (2-methylquinoline)2 :
2

2+
(1,5-naphthalenedisulfonic acid) : 2H2O [(HL)2
· (nsa)2- · 2H2O, nsa =
1,5-naphthalenedisulfonte] (8) (Scheme 2).
H N
2
O
O
NH
2
N
HO
HO
4-aminobenzoic acid
2-methylquinoline
2-aminobenzoic acid
NO
2
HO
HO
HO
O
HO
O
HO
NO
HO
2
Cl
O
5-chlorosalicylic acid
3,5-dinitrosalicylic acid
salicylic acid
O
O
OH
O
OH
HO
HO
OH
O
malic acid
sebacic acid
O
OH
O
S
S
O
HO
O
1,5-naphthalenedisulfonic acid
Scheme 1 Hydrogen bond synthons discussed in this paper.
3

Scheme 2 The eight adducts discussed in this paper.
Experimental Section
Materials and Methods
All reagents were commercially available and used as received. The C, H, N and S
microanalysis were carried out with a Carlo Erba 1106 elemental analyzer. The FT-IR
spectra were recorded from KBr pellets in the range 4000-400 cm-1 on a Mattson
Alpha-Centauri spectrometer. Melting points of new compounds were recorded on an
XT-4 thermal apparatus without correction.
Preparation of supramolecular complexes
a. 2-methylquinoline : (4-aminobenzoic acid) [(HL)+ · (4-aba-)] (1)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
4-aminobenzoic acid (27.4 mg, 0.2 mmol) in 4 mL methanol. The solution was stirred for
10 minutes, then the solution was filtered into a test tube. The solution was left standing
4

at room temperature for several days, light yellow block crystals were isolated after slow
evaporation of the solution in air. The crystals were dried in air to give the title compound
[(HL)+ · (4-aba-)] (1), yield 46 mg, 82.05%. m. p. 159-160°C. Elemental analysis
performed on crystals exposed to the atmosphere: Calc. for C17H16N2O2 (280.32): C,
72.77; H, 5.71; N, 9.99. Found: C, 72.71; H, 5.68; N, 9.92. Infrared spectrum (KBr disc,
cm-1): 3459s(multiple, νas(NH)), 3358s(νs(NH)), 3133m, 3075m, 2976m, 1614m,
1595s(νas(COO-)), 1523m, 1467w, 1409s(νs(COO-)), 1358m, 1304m, 1255m, 1204m,
1128m, 1034m, 984m, 900m, 868m, 787m, 701m, 673m, 623m.
b. 2-methylquinoline : (2-aminobenzoic acid) [(L) · (2-Haba)] (2)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
2-aminobenzoic acid (27.4 mg, 0.2 mmol) in 2 mL methanol. The solution was stirred for
10 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 air. The crystals were dried in air to give the title compound
[(L) · (2-Haba)] (2), yield 39 mg, 69.56%. m. p. 119-120°C. Elemental analysis
performed on crystals exposed to the atmosphere: Calc. for C17H16N2O2 (280.32): C,
72.77; H, 5.71; N, 9.99. Found: C, 72.69; H, 5.65; N, 9.89. Infrared spectrum (KBr disc,
cm-1): 3348s(νas(NH)), 3241s(νs(NH)), 3129m, 3066m, 2954m, 2875m, 2762m, 2486w,
1902w, 1642s(ν(C=O)), 1585m, 1532m, 1486m, 1461m, 1385m, 1371m, 1320m,
1289s(ν(C-O)), 1279m, 1239m, 1163m, 1147m, 936m, 851m, 837m, 772m, 738m, 694m,
626m.
c. 2-methylquinoline : (salicylic acid) [(HL)+ · (sal-)] (3)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
salicylic acid (27.6 mg, 0.2 mmol) in 6 mL ethanol. Colorless crystals were afforded
after several days of slow evaporation of the solvent, yield: 34 mg, 60.43%. mp
139-141°C. Elemental analysis: Calc. for C17H15NO3(281.30): C, 72.52; H, 5.33; N, 4.97.
Found: C, 72.47; H, 5.25; N, 4.88. Infrared spectrum (KBr disc, cm-1): 3599s(ν(OH)),
3486s(multiple, νas(NH)), 3353s(νs(NH)), 3122m, 3081m, 2957m, 2855m, 2761m, 2464w,
1972w, 1624m, 1602s(νas(COO-)), 1533m, 1484w, 1431m, 1379s(νs(COO-)), 1301m,
5

1259m, 1191m, 1127m, 1061m, 977m, 910m, 858m, 806m, 745m, 687m, 636m, 601m.
d. 2-methylquinoline : (5-chlorosalicylic acid) [(HL)+ · (csal-)] (4)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
5-chlorosalicylic acid (34.6 mg, 0.2 mmol) in 8 mL ethanol. Colorless prisms were
afforded after several days of slow evaporation of the solvent, yield: 50 mg, 79.17%. mp
162-163°C. Elemental analysis: Calc. for C17H14ClNO3 (315.74): C, 64.61; H, 4.43; N,
4.43. Found: C, 64.54; H, 4.34; N, 4.39. Infrared spectrum (KBr disc, cm-1): 3614s
(ν(OH)), 3477m(νas(NH)), 3319w(νs(NH)), 3264m, 3194m, 2998m, 2921m, 2865w,
2796w, 1622m, 1586s(νas(COO-)), 1541m, 1489m, 1445m, 1402s(νs(COO-)), 1349m,
1287m, 1229m, 1156m, 1069m, 997m, 943m, 890m, 842m, 786m, 741m, 695m, 657m,
631m, 612m.
e. 2-methylquinoline : (3,5-dinitrosalicylic acid) [(HL)+ · (3,5-dns-)] (5)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
3,5-dinitrosalicylic acid (45.6 mg, 0.2 mmol) in 6 mL methanol. The solution was stirred
for 10 minutes, then the solution was filtered into a test tube. The solution was left
standing at room temperature for several days, yellow block crystals were isolated after
slow evaporation of the solution in air. The crystals were dried in air to give the title
compound [(HL)+ · (3,5-dns-)] (1), yield 56 mg, 75.41%. m. p. 146-148°C. Elemental
analysis performed on crystals exposed to the atmosphere: Calc. for C17H13N3O7 (371.30):
C, 54.94; H, 3.50; N, 11.31. Found: C, 54.89; H, 3.45; N, 11.23. Infrared spectrum (KBr
disc, cm-1): 3615s(ν(OH)), 3456s(multiple, νas(NH)), 3343s(νs(NH)), 3075m, 2989m,
1996w, 1868w, 1783w, 1621m, 1595s(νas(COO-)), 1557m, 1529s(νas(NO2)), 1474w,
1404s(νs(COO-)), 1361m, 1314s(νs(NO2)), 1259m, 1112m, 1063m, 1014m, 955m, 886m,
830m, 798m, 753m, 690m, 643m, 618m.
f. (2-methylquinoline)2 : (L-malic acid) [(HL)+ · (L) · (Hmal-)] (6)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
L-malic acid (13.4 mg, 0.1 mmol) in 8 mL ethanol. Colorless prisms were afforded after
6

several days of slow evaporation of the solvent, yield: 36 mg, 85.62%. mp 82-83°C.
Elemental analysis: Calc. for C24H24N2O5 (420.45): C, 68.50; H, 5.71; N, 6.66. Found: C,
68.45; H, 5.64; N, 6.59. Infrared spectrum (KBr disc, cm-1): 3675s(ν(OH)),
3450s(multiple, νas(NH)), 3358s(νs(NH)), 3140m, 3064m, 2989m, 2952m, 2884m,
2743m, 2493m, 1916w, 1649s(ν(C=O)), 1625m, 1593s(νas(COO-)), 1544m, 1487m,
1431m, 1379s(νs(COO-)), 1322m, 1291s(ν(C-O)), 1243m, 1197m, 1150m, 1001m,
1056m, 1012m, 963m, 905m, 854m, 799m, 741m, 698m, 652m, 615m.
g. (2-methylquinoline)2 : (sebacic acid) [(HL)22+ · (seba)2-] (7)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
sebacic acid (20.2 mg, 0.1 mmol) in 6 mL ethanol. Colorless prisms were afforded after
several days of slow evaporation of the solvent, yield: 60 mg, 61.40% (Based on sebacic
acid). mp 113-115°C. Elemental analysis: Calc. for C30H36N2O4 (488.61): C, 73.68; H,
7.37; N, 5.73. Found: C, 73.59; H, 7.31; N, 5.67. Infrared spectrum (KBr disc, cm-1):
3436s(multiple, νas(NH)), 3345s(νs(NH)), 3116m, 3098m, 3061m, 2935m, 2868m,
1619m, 1585s(νas(COO)), 1541m, 1515m, 1467m, 1383s(νs(COO)), 1295m, 1237m,
1189m, 1093m, 977m, 932m, 898m, 835m, 786m, 741m, 707m, 659m, 617m.
h.
(2-methylquinoline)2
:
(1,5-naphthalenedisulfonic
acid)
:
2H2O
[(HL)22+ · (nsa)2- · 2H2O] (8)
To a methanol solution (2 ml) of 2-methylquinoline (28.6 mg, 0.2 mmol) was added
1,5-naphthalenedisulfonic acid tetrahydrate (36 mg, 0.1 mmol) in 12 mL ethanol.
Colorless prisms were afforded after several days of slow evaporation of the solvent,
yield: 49 mg, 80.24% (Based on 1,5-naphthalenedisulfonic acid tetrahydrate). mp
211-213°C. Elemental analysis: Calc. for C30H30N2O8S2 (610.68): C, 58.95; H, 4.91; N,
4.58; S, 10,48. Found: C, 58.89; H, 4.84; N, 4.53; S, 10.44. Infrared spectrum (KBr disc,
cm-1): 3694s(ν(OH)), 3467s(multiple, νas(NH)), 3381s(νs(NH)), 3144m, 3095m, 3054m,
2994m, 2926m, 2869m, 1625m, 1576m, 1517m, 1469m, 1396m, 1343m, 1262m, 1192m,
1148m, 1073m, 989m, 944m, 875m, 832m, 778m, 739m, 697m, 653m, 616m.
X-ray Crystallography
7

Suitable crystals were performed on a Bruker SMART 1000 CCD diffractometer
using Mo Kαradiation (λ = 0.71073 Å). Data collections and reductions were performed
using the SMART and SAINT software [20-21]. The structures were solved by direct
methods, and the non-hydrogen atoms were subjected to anisotropic refinement by
full-matrix least squares on F2 using SHELXTL package [22]. Hydrogen atom positions
for the eight structures were generated geometrically. Further details of the structural
analysis are summarized in Table 1 and Table 2. Selected bond lengths and angles for the
complexes 1-8 are listed in Table 3, the relevant hydrogen bond parameters are provided
in Table 4.
Table 1 should be inserted here
Table 2 should be inserted here
Results and Discussion
Syntheses and General Characterization
For the preparation of 1-8, the acidic components were mixed directly with
2-methylquinoline in methanol and/or ethanol solvents in 1:1 for the monoacid and 1:2
for the diacid, which was allowed to evaporate at ambient conditions to give the final
crystalline products. The molecular structures and their atom labelling schemes for the
eight structures are shown in Fig. 1, Fig. 3, Fig. 5, Fig. 7, Fig. 9, Fig. 11, Fig. 13, and Fig.
15, respectively.
The elemental analyses for the eight compounds are in good agreement with their
compositions. The infrared spectra of 1-8 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 3700-3200 cm-1 arise from O-H or N-H stretching
frequencies. Aromatic and quinoline ring stretching and bending are in the regions of
1500-1630 cm-1 and 600-750 cm-1, respectively. The intense peak at ca. 1650 cm-1 was
derived from the existence of the C=O stretches, and the band at ca. 1280 cm-1 exhibited
the presence of the C-O stretches of the COOH moieties. The presence of two broad
bands at ca. 2500 cm-1 and 1900 cm-1 in compound 2, characteristic of a neutral O-H···N
hydrogen-bond interaction, was viewed as evidence for co-crystal formation [23]. Except
8

for the above bands, for 5, the bands at ca. 1529 and 1314 cm-1 were attributed to the
νas(NO2) and νs(NO2), respectively [24].
IR spectroscopy has also proven to be useful for the recognition of proton transfer
compounds [25]. The most distinct feature in the IR spectrum of proton transfer
compounds is the presence of strong asymmetrical and symmetrical carboxylate
stretching frequencies at 1550-1610 cm-1 and 1300-1420 cm-1 in all of the adducts except
compounds 2, and 8 [26].
Table 3. should be inserted here.
Table 4. should be inserted here.
X-ray structure of 2-methylquinoline : (4-aminobenzoic acid) [(HL)+ · (4-aba-)] (1)
Fig. 1 should be inserted here
Fig. 2 should be inserted here
Compound 1 was prepared by reacting of a methanol solution of 4-aminobenzoic
acid and 2-methylquinoline in 1 : 1 ratio, which crystallizes as triclinic pale yellow
crystals in the space group P-1. The asymmetric unit of 1 consists of four quarter cations
of 2-methylquinolinium and four quarter anions of 4-aminobenzoate, as shown in Fig. 1.
In the compound, there are four pairs of ion pair with no included solvent molecules,
which is well agreement with the micro-analysis results.
This is a salt where the COOH groups of 4-aminobenzoic acids are ionized by proton
transfer to the nitrogen atoms of the 2-methylquinoline moieties. The C-O bond distances
of the carboxylates are ranged from 1.212(9) Å to 1.307(10) Å with the Δ values of 0.059
Å for O(1)-C(41)-O(2), 0.058 Å for O(3)-C(48)-O(4), 0.095 Å for O(5)-C(55)-O(6), and
0.086 Å for O(7)-C(62)-O(7), respectively. The significant differences of the pair of the
C-O bonds in the same carboxylate are attributed to the different H-bond strength that
these O atoms are involved in (Table 4).
One 2-methylquinolinium cation and one 4-aminobenzoate anion form a heterodimer
through one ionic N+-H···O- hydrogen bonding interaction. Two neighboring
heterodimers were held together by the CH-C(carboxylate) interaction between the 6-CH
of the cation and the π-C of the carboxylate with C-C separation of 3.705 Å to generate a
tetramer. In the tetramer the corresponding anions and the corresponding cations were
9

parallel to each other. Two tetramers were joined together by the CH-π interaction
between the 4-CH of the cation and the aromatic ring of the anion with C-Cg distance of
3.734 Å, and CH-N interaction between the same 4-CH of the cation and the NH2 unit of
the anion with C-N distance of 3.596 Å to form an 8-component aggregate. The
8-component aggregates were linked together by the CH-C interaction between the 6-CH
of the cation and the π-C of the carboxylate with C-C separation of 3.781 Å to form 1D
chain running along the b axis direction (Fig. 2). The 1D chains were further stacked
along the c axis direction via the interchain N-H···O- hydrogen bonding interactions
between the NH2 group at the anion and the carboxylate with N-O distances of
2.878(9)-3.047(8) Å, and CH3-O associations between the 2-CH3 group of the cation and
the carboxylate with C-O distances of 3.539-3.570 Å to form 3D network structure,
herein the neighboring chains were slipped some distances from each other along the b,
and c axis directions, respectively.
X-ray structure of 2-methylquinoline : (2-aminobenzoic acid) [(L) · (2-Haba)] (2)
Fig. 3 should be inserted here
Fig. 4 should be inserted here
The crystal structure of 2 consists of one 2-aminobenzoic acid, and one
2-methylquinoline in the asymmetric unit (Fig. 3). Different from 1, the proton of the
COOH group has not transferred to the ring N atom of the quinoline moiety, thus 2 is an
organic cocrystal. The assignment of 2 as a cocrystal is based on successful refinement of
the relevant H atoms using X-ray data also. This is confirmed by the C-O bond distances
[(O(1)-C(11), 1.327(3) Å), O(2)-C(11), 1.218(3) Å with Δ = 0.109 Å] in the carboxyl
group, which are in the range for the O-C bond distances concerning the protonated
carboxyl groups. In the 2-methylquinoline, the angle C(1)-N(1)-C(5) [118.8(2)°] is
smaller than those in 1 (122.2(8)°, 122.4(7) °, 121.2(7) °, and 125.4(8) °).
Because of the presence of the intramolecular hydrogen bond between the carboxyl
group and the amine group (N(2)-H(2B)···O(2), 2.682(3) Å, 130.3°), it is generally
expected and found that the carboxyl group is essentially coplanar with the benzene ring
[torsion angle C17-C12-C11-O1, 4.22º, C13-C12-C11-O2, 3.64º]. This feature is similar
to that found in 2-aminobenzoic acid [27]. The rms deviation of the quinoline ring
10

excluding the CH3 group is 0.0081 Å. The rms deviation of the benzene ring of the anion
is 0.0041 Å. They make dihedral angle of 72.7° with each other.
One 2-aminobenzoic acid and one 2-methylquinoline were held together by the
O-H···N hydrogen bond between the OH moiety of the carboxyl group and the N group of
the 2-methylquinoline with N-O distance of 2.753(3) Å to form a heterosynthon. Two
heterosynthons were joined together by the CH-O interactions between the O atom of the
carbonyl unit and the 4-, and 5-CH of the 2-methylquinoline with C-O distances of
3.391-3.472 Å to form a dimer. In this dimer the 2-aminobenzoic acids were antiparallely
arranged, so did the 2-methylquinoline molecules. There are no aromatic stacking
interactions between the two antiparallely arranged 2-methylquinoline molecules. The
dimers were further joined together by the N-H···N interaction between the amine group
of the 2-aminobenzoic acid and the ring N of the quinoline with N-N distance of 3.358(3)
Å to form 2D sheet structure extending along the direction that made an angle of ca. 30°
with the ab plane (Fig. 4).
X-ray structure of 2-methylquinoline : (salicylic acid) [(HL)+ · (sal-)] (3)
Fig. 5 should be inserted here
Fig. 6 should be inserted here
Similar to compound 1, the compound 3 is also an organic salt. In 3 the asymmetric
unit is occupied by one monoanion of salicylic acid, and one cation of
2-methylquinolinium (Fig. 5). Compound 3 crystallizes as monoclinic colorless crystals
in the space group P2(1)/c. Here only the proton at COOH of the salicylic acid has
transferred to the N atom of L.
The assignment of 3 as a salt is based on successful refinement of the relevant H
atoms using X-ray data also. This is confirmed by the C-O bond distances [(O(1)-C(11),
1.262(4) Å), O(2)-C(11), 1.256(4) Å with Δ = 0.006 Å] in the carboxylate group, which is
in the range for the O-C distances concerning the deprotonated carboxyl groups. The C-O
bond distance (O(3)-C(13), 1.346(4) Å) is in the range of the neutral C-O bond distance
in the phenol derivatives (1.344 (3) - 1.357 (3) Å) [28]. In the compound, there is one ion
pair without solvent molecules, which fits well with the micro-analysis results.
In the cation, the angle C(5)-N(1)-C(1) [123.9(3)°] is larger than that observed in 2,
11

yet it is in the range of the corresponding value in 1. Because of the presence of the
intramolecular hydrogen bond between the carboxylate group and the phenol group
(O(3)-H(3)···O(2), 2.510(4) Å), it is generally expected and found that the carboxylate
group is essentially coplanar with the benzene ring [torsion angle C13-C12-C11-O1,
179.13º]. This feature is similar to that found in salicylic acid [29], and in the previously
reported structure of proton-transfer compound based on salicylic acid derivatives [30].
The rms deviation of the quinoline ring of the cation is 0.0066 Å. The rms deviation of
the phenyl ring of the anion is 0.0012 Å. They make dihedral angle of 80.6° with each
other, indicating the roughly perpendicular arrangement of both rings.
One cation and one anion were held together by the N+-H···O- hydrogen bond
between one O atom of the carboxylate and the NH+ group with N-O distance of 2.604(3)
Å, and CH3-O association arising from the 2-CH3 of the cation and the same O atom that
is involved in the N+-H···O- hydrogen bond with C-O distance of 3.364 Å to form a
heterodimer. The heterodimers were joined together by the CH-O interaction between the
other O atom of the same carboxylate group and 5-CH of the cation with C-O distance of
3.483 Å to form a tetracomponent aggregate. In this tetracomponent aggregate the two
cations were antiparallely arranged, and the two anions were inversionally located around
the cations. There are no aromatic stacking interactions between the two antiparallely
arranged cations either. The tetracomponent aggregates were further joined together by
the edge to face CH-π interaction between the 4-CH of the cation and the aromatic ring of
the anion with C-Cg distance of 3.614 Å to form a 2D sheet extending parallel to the bc
plane (Fig. 6).
X-ray structure of 2-methylquinoline : (5-chlorosalicylic acid) [(HL)+ · (csal-)] (4)
Fig. 7 should be inserted here
Fig. 8 should be inserted here
Cocrystallization of 2-methylquinoline and 5-chlorosalicylic acid in a 1:1 ratio from
the mixed solution of methanol and ethanol gave single crystals suitable for X-ray
diffraction. Structure determination (Table 1) revealed that 2-methylquinoline and
5-chlorosalicylic acid are present in a 1:1 ratio in the molecular complex 4, and the
12

asymmetric unit is shown in Fig. 7. Like the salt 3, the proton at the carboxyl from the
5-chlorosalicylic acid has been deprotonated and transferred to the ring N atoms of the
2-methylquinoline. Thus 4 is a salt instead of a cocrystal.
The O-C bond distances of the carboxyl group were ranging from 1.248(4) - 1.260(4)
Å. The C-N-C angle at the 2-methylquinolinium cation is 123.1(3)º. Compared with the
above protonated 2-methylquinoline, this angle is similar to the corresponding angles in
the above salts 1, and 3, which also confirms our correct assignment of 4 as a salt. The
usual intramolecular hydrogen bond is found between the phenol group and a carboxyl O
atom [O(3)-H(3)···O(2), 2.523(3) Å], essentially giving coplanarity of the carboxyl group
and the benzene ring [torsion angle C13-C12-C11-O1, 171.03º]. For the presence of this
1
hydrogen bond, compound 4 bears the S1 (6) loop motif. These hydrogen bond
geometries were similar to that found in the salt 3. The rms deviation of the quinoline
ring is 0.0045 Å. The rms deviation of the benzene ring of the anion is 0.01 Å. They
make dihedral angle of 82.1° with each other.
One cation and one anion were held together by N+-H···O- hydrogen bond between
one O atom of the carboxylate and the NH+ group with N-O distance of 2.594(3) Å to
form a heterosynthon. Two heterosynthons were joined together by CH-O interactions
between the other O atom of the same carboxylate and the 4-CH, and 5-CH of the cation
with C-O distances of 3.354-3.446 Å to form a dimer. In this dimer the cations were
antiparallely arranged. And the two anions were inversionally located around the cations.
There are no aromatic stacking interactions between the two antiparallely arranged
cations. Herein the arrangements of the cation and the anion were similar to the
arrangements of the cation and the anion at the salt 3. The dimers were further joined
together by the O-H···Cl hydrogen bond between the phenol group and the Cl atom of the
adjacent dimer with Cl-O distance of 3.166 Å to form a 1D chain running along the
direction that made a dihedral angle of 60° with the ab plane (Fig. 8). The chains were
further stacked along the direction that is perpendicular with its extending direction via
the interchain CH-π association between the 7-CH of the cation and the phenyl ring of the
anion with C-Cg distance of 3.683 Å to form 3D staircase structure. In this case the
adjacent chains were slipped some distance from each other along its extending direction.
13

X-ray structure of 2-methylquinoline : (3,5-dinitrosalicylic acid) [(HL)+ · (3,5-dns-)]
(5)
Fig. 9 should be inserted here
Fig. 10 should be inserted here
Crystallization of 2-methylquinoline and 3,5-dinitrosalicylic acid in a 1:1 ratio from
the methanol gave single crystals suitable for X-ray diffraction. Structure determination
(Table 2) revealed that 2-methylquinoline and 3,5-dinitrosalicylic acid are present in a
1:1 ratio in the molecular complex 5. The crystal structure of 5 consists of one protonated
L, and one monoanion of 3,5-dinitrosalicylic acid in the asymmetric unit (Fig. 9). In 5 the
COOH groups of the 3,5-dinitrosalicylic acids are ionized by proton transfer to the
nitrogen atoms of the 2-methylquinoline moiety, and the phenol group remains
protonated.
The C-O bond distances (1.243(16) and 1.207(16) Å) in the carboxylate
O(1)-C(11)-O(2) are basically not equal with an average value of 1.225 (16) Å (Table 3).
The difference between the two bonds is attributed to the fact that O1 atom is involved in
forming stronger hydrogen bond than that of O2 (Table 4).
Examination of the cationic moiety shows that the atoms C2, C3, C4, C5, C6, C7, C8,
C9, C10, and N1 of the quinolinium ring of the title compound have a good coplanarity
and they form a conjugated plane with average deviation of 0.0118 Å. The benzene ring
of the 3,5-dns- is almost planar with r.m.s. deviation of 0.0156 Å. The dihedral angle
between the aromatic ring of the cation and the benzene ring of the 3,5-dns- is 48.5º. The
torsion angles O4-N2-C14-C15, and O6-N3-C16-C17 are 160.35°, and 177.06°,
respectively. In this regard, both nitro groups are nearly in the same plane as the benzene
ring of the anion, yet the 3-nitro (O4-N2-O5) deviates somewhat more from the plane
than the 5-nitro (O6-N3-O7) group, which is similar with the published results [31].
Since the potentially hydrogen bonding hydroxyl group is present in the ortho position to
the carboxyl group in the anion, it forms the more facile intramolecular hydrogen
bonding. Thus the usual intramolecular hydrogen bond is found between the phenol
group and an O atom of the carboxylate (O(3)-H(3A)···O(2), 2.411(14) Å, 148.0°) which
is similar to the corresponding value (2.409 Å) in proton-transfer compound of
14

[(hmt)+ · [(dnsa)-] [32, 33]. Yet the value is as expected generally smaller than the
distance found for the parent dnsa acid monohydrate [2.566(3) Å] [34], and in the neutral
species found in its adduct. For the presence of the intramolecular hydrogen bond, there
1
also exists hydrogen bonded motif with graphical descriptor of S1 (6).
One anion was bonded to one cation via the N+-H···O- hydrogen bond between the NH+
cation and one O atom of the carboxylate with N-O distance of 2.643(12) Å, and CH-O
association between the 8-CH of the cation and the other O atom of the carboxylate with
C-O separation of 3.454 Å to form a heteroadduct. The heteroadducts were linked
together by the CH-O associations between the 4-, and 5-CH of the cation and one O
atom of the 3-nitro group with C-O distances of 3.473-3.475 Å to form 1D chain running
along the c axis direction. In this case one O atom of the 3-nitro group functioned as a
bifurcate acceptor in generating the CH-O associations. Two neighboring chains were
held together by the interchain CH-O associations between the 3-, and 4-CH of the cation
and one O atom of the 5-nitro group with C-O distances of 3.154-3.212 Å to form 1D
double chain. In this case the O atom of the 5-nitro group also functioned as a bifurcate
acceptor in generating the CH-O associations. The 1D double chains were combined
together by the interchain CH-O associations between the 6-, and 7-CH of the cation and
one O atom of the 3-nitro group and the O atom of the phenol group with C-O distances
of 3.259-3.565 Å to form 2D grid sheet extending along the direction that made an angle
of ca. 30° with the ac plane (Fig. 10). The 2D grid sheets were further stacked along the
direction that is perpendicular with its extending direction via the π-π interaction between
the aromatic ring of the cation and the phenyl ring of the anion with Cg-Cg distance of
3.391 Å, C-π interaction between the carboxyl C atom of the anion and the aromatic ring
of the cation with C-Cg distance of 3.214 Å, and CH-O associations between the 5-, and
6-CH of the cation and the 5-nitro group of the 3,5-dns- with C-O distances of
3.187-3.196 Å to form 3D network structure with reduced channels.
X-ray structure of (2-methylquinoline)2 : (malic acid) [(HL)+ · (L) · (Hmal-)] (6)
Fig. 11 should be inserted here
Fig. 12 should be inserted here
Different from the above compounds, the compound [(HL+) . (L) . (Hmal-)] 6 was
15

prepared by reaction of 2-methylquinoline with L-malic acid in 2:1 ratio, which
crystallizes as monoclinic block crystals in the non-centrosymmetric space group P2(1).
The compound consists of two halves of 2-methylquinolinium cation, two halves of
2-methylquinoline, and two halves of hydrogen L-malate anion (Fig. 11). The present
investigation clearly shows that the compound is also an organic salt. In 6 the L-malic
acid is singly deprotonated to exhibit a valence number of -1.
The O-C bond distances of the carboxylate group (O(1)-C(1)-O(2), and
O(6)-C(5)-O(7)) were ranging from 1.193(9) Å to 1.307 Å, the significant difference
between the two bonds in the same carboxylate are caused by the fact that the two O
atoms are involved in H-bonds with different strength. While the carboxyl group has
typical C=O and C-O bond distances indicative of an unionized character, in which no H
transfer has occurred to the quinoline N atom. The C-N-C angles at the neutral
2-methylquinoline are 118.8(8)°, and 120.7(8)°, respectively. The C-N-C angles at the
2-methylquinolinium are 124.7(8)°, and 122.9(8)°, respectively, which are significantly
larger than the corresponding angles in the 2-methylquinoline. The hydrogen L-malate
anion assumes a conformation that the terminal carboxylate and carboxyl groups are
almost perpendicular to each other (the dihedral angles between the two groups are 97.9º,
and 88.6 º for the anions bearing O1 and O2, O6 and O7 respectively).
At every anion there were bonded a cation (by the ionic N+-H···O- hydrogen bond
between the NH+ cation and the carboxylate with N-O distance of 2.567(9) Å), and a
2-methylquinoline (by the neutral O-H···N hydrogen bond between the alcohol group and
the ring N atom of the 2-methylquinoline with N-O distance of 2.920(9) Å, and CH2-N
association between the CH2 spacer of the anion and the ring N atom of the
2-methylquinoline with C-N distance of 3.457 Å) to form a tricomponent adduct. The
tricomponent adducts were connected together by the O-H···O hydrogen bond between
the COO- and the COOH groups with O-O distance of 2.585(9) Å to form 1D chain
running along the a axis direction. The 1D chains were further combined together by the
CH3-π interactions between the 2-CH3 unit of the cations and the aromatic rings of the
cations with C-Cg distance of 3.594 Å to form 2D sheet extending along the ac plane (Fig.
12). The 2D sheets were further stacked along the b axis direction by the CH3-O
associations between the 2-CH3 group of the cation and the carbonyl group of the
16

carboxyl with C-O distance of 3.445 Å, and CH-O association between the 7-CH of the
cation and the alcohol group with C-O distance of 3.603 Å to form 3D network structure.
X-ray structure of (2-methylquinoline)2 : (sebacic acid) [(HL)22+ · (seba)2-] (7)
Fig. 13 should be inserted here
Fig. 14 should be inserted here
The crystal structure of 7 consists of one cation of 2-methylquinolinium and one half
anion of sebacate in the asymmetric unit (Fig. 13). The salt 7 crystallized as monoclinic
block crystals in the space group C2/c. In the absence of hydrogen bonding and other
electronic perturbations, the C-O bond lengths should be equal because of resonance. The
formation of single or multiple hydrogen bonds at one oxygen atom should cause the
associated C-O bond to lengthen. Herein the O(1)-C(11) (1.190(4) Å) is significantly
shorter than the O(2)-C(11) (1.313(5) Å) which is attributed to the fact that O(2) is
participated in N(1)-H(1)···O(2) hydrogen bond (2.714(4) Å, 164.4°), while O1 has not
any bonding interactions.
Two 2-methylquinolinium and one sebacate formed a tricomponent adduct. At the
tricomponent adduct, every cation was bonded to the same carboxylate by the
hydrogen bond of N(1)-H(1)···O(2) (2.714(4) Å, 164.4°), CH-O association between
the 8-CH of the cation and the carboxylate that was involved in the N(1)-H(1)···O(2)
hydrogen bond with C-O distance of 3.282 Å, and CH3-O association between the
2-CH3 unit of the cation and the other O atom of the same carboxylate with C-O
distance of 3.281 Å. In the tricomponent adduct there existed a symmetry centre
located at the middle point of the C15-C15a bond. The tricomponent adducts were
linked together by the CH-O association between the 4-CH of the cation and the
carboxylate with C-O distance of 3.351 Å to form 1D zigzag chain (Fig. 14). The
chains were further combined together by the interchain CH-O association between
the 4-CH of the cation and the carboxylate with C-O distance of 3.351 Å to form 2D
sheet structure extending at the direction that made an angle of ca. 60° with the ab
plane.
17

X-ray structure of (2-methylquinoline) : (1,5-naphthalenedisulfonic acid) : 2H2O
[(HL)22+ · (nsa)2- · 2H2O] (8)
Fig. 15 should be inserted here
Fig. 16 should be inserted here
Crystallization of 2-methylquinoline and 1,5-naphthalenedisulfonic acid in a 2:1 ratio
gave single crystals suitable for X-ray diffraction. The compound 8 crystallizes as
monoclinic block crystals in the space group P2(1)/n. In the compound 8 the protons of
both SO3H groups were transferred to the N groups of two L molecules. Thus 8 is also an
organic salt. In the asymmetric unit of 8 there existed one cation of HL, and half a
dianion of 1,5-naphthalenedisulfonate, as shown in Fig. 15. The S-O bond distances in
-
the SO3 are ranging from 1.4337(19) to 1.455(2) Å (Δ is 0.0213 Å) which are in the
-
range of the deprotonated SO3 anion (1.435 (2)-1.4599 (17) Å) [28].
At every cation there was bonded a water molecule via the N-H···O hydrogen bond
with N-O distance of 2.700(3) Å. For the water molecule blocked the NH+ group of the
cation, thus there were no direct classical hydrogen bonds between the anion and the
cation. Two cations bonded with the water molecules were attached to the anion by the
-
O-H···O hydrogen bond between the water molecule and the SO3 with Ow-O distance of
2.738(3) Å, and O-H···S hydrogen bond between the same OH unit of the water molecule
-
and the S at the SO3 with O-S separation of 3.799(2) Å to form a five-component
aggregate. In the five-component aggregate there existed an inversion centre at the
gravity centre of the naphthalene ring of the anion. The five-component aggregates were
-
linked together by the CH-O association between the 5-CH of the cation and the SO3
with C-O distance of 3.351 Å to form 1D chain running along the diagonal direction of
the bc plane. The chains were held together by the CH-O interaction between the
aromatic CH of the anion and the water molecule with C-O distance of 3.499 Å to form
2D sheet extending parallel to the bc plane (Fig. 16). The sheets were further stacked
along the a axis direction by the O-H···S hydrogen bond between the water molecule and
-
the SO3 with O-S distance of 3.548(2) Å, O-H···O hydrogen bond between the water
-
molecule and the SO3 with O-O distance of 2.858(3) Å, CH3-O association between the
-
2-CH3 group of the cation and the SO3 with C-O distance of 3.387 Å, CH-O associations
18

-
between the aromatic CH of the cation and the SO3 with C-O distances of 3.527-3.552 Å,
and CH-π interaction between the aromatic CH of the cation and the naphthalene ring of
the anion with C-Cg distance of 3.601 Å to form 3D ABAB layer network structure.
Herein the neighboring sheet layers intersected at an angle of ca. 60° with each other, the
third sheet layer has the same projection on the bc plane as the first sheet layer, so did the
second sheet layer and the fourth sheet layer.
Conclusion
Eight complexes with 2D-3D network structure have been synthesized and
structurally characterized. Despite variations in molecular shape on the acidic
components, there all exist strong inter-molecular hydrogen bonds between the acidic
moieties and the 2-methylquinoline except 8.
All of the complexes are organic salts except compound 2. The reason may be that in
all of the acids used in this manuscript the 2-aminobenzoic acid has the largest Pka(4.95).
In the compounds 1, 3, 4, 5, 6 and 7, the 2-methylquinolinium cations function as
acceptors for ionic hydrogen bonds that organize and orient the anions, while in
compound 2 the 2-methylquinoline fragments function as acceptors for neutral hydrogen
bonds. This study has demonstrated that the N-H···O hydrogen bond is the primary
intermolecular force in a family of structures containing the OH···N2-methylquinoline synthons,
Since the potentially hydrogen bonding phenol group is present in the ortho position to
the carboxyl group in 3, 4, and 5, it forms the more facile intramolecular O-H···O
1
hydrogen bonding with S1 (6) loop motif. The ortho NH2 group to the carboxyl group in
1
2 also generated the S1 (6) ring via the intramolecular N-H···O hydrogen bond. The
C-H···O associations were found in all of the complexes. Two types of secondary C-H···O
associations were observed based upon their geometric preferences, intra- and
inter-substructure interactions. Through an analysis of the metrics displayed by each set
of interactions, it seems that intra- and inter-substructure C-H···O interactions are of equal
structural importance. There are CH3-O interactions in compounds 1, 3, 6, 7 and 8.
Compounds 1, 3, 4 and 8 possesses CH-π interaction. There existed CH3-π association in
6. There are π-π interactions in compound 5. There are CH-N and CH2-N interactions in
compounds 1 and 6, respectively.
19

The results presented herein indicate that the strength and directionality of the
N+-H···O-, O-H···N, O-H···O, O-H···S and N-H···N hydrogen bonds (ionic or neutral)
between the acidic units and 2-methylquinoline are sufficient to bring about the formation
of binary organic salts or cocrystals.
Acknowledgement
We gratefully acknowledge the financial support of the Education Office Foundation
of Zhejiang Province (project No. Y201017321) and the financial support of the Zhejiang
A & F University Science Foundation (project No. 2009FK63).
Supporting Information Available: Crystallographic data for the structural analysis
have been deposited with the Cambridge Crystallographic data center, CCDC Nos.
900184 for 1, 900189 for 2, 917233 for 3, 898475 for 4, 853947 for 5, 882635 for 6,
900185 for 7, and 900183 for 8. Copies of this information may be obtained free of
charge from the +44(1223)336-033 or Email: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk.
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22

Figure captions
Fig. 1 The structure of 1, showing the component of the title compound (for the
crowdedness of the structure the atom-numbering was not labeled). Displacement
ellipsoids were drawn at the 30% probability level.
Fig. 2 1D chain of 1 running along the b axis direction.
Fig. 3 The structure of 2, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 4 2D sheet structure of 2 extending along the direction that made an angle of ca. 30°
with the ab plane.
Fig. 5 The structure of 3, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 6 2D sheet structure of 3 extending parallel to the bc plane.
Fig. 7 The structure of 4, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 8 Packing diagram of 4 showing the 1D chain running along the direction that made
a dihedral angle of 60° with the ab plane.
Fig. 9 The structure of 5, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 10 2D grid sheet structure of 5 extending along the direction that made an angle of
ca. 30° with the ac plane.
Fig. 11 The structure of 6, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 12 2D sheet structure of 6 formed via the CH3-π interactions which was extending
along the ac plane.
23

Fig. 13 The structure of 7, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 14 1D zigzag chain structure of 7 produced by the CH-O association.
Fig. 15 The structure of 8, showing the atom-numbering scheme. Displacement ellipsoids
were drawn at the 30% probability level.
Fig. 16 2D sheet structure of 8 extending parallel to the bc plane.
24

Covering information sheet
Journal name: JOURNAL OF MOLECULAR STRUCTURE
Title: Crystal and molecular structure of eight organic acid-base adducts from
2-methylquinoline and different acids
Corresponding author: Bin Liu
Address: Tianmu college ZheJiang A & F University ZhuJi 311800 P. R. China
Tel & fax: +86-575-8776-0141.
E-mail: liubin20131031@sohu.com
Numbers of pages: 25pp
Figures : 16
Tables: 4
25

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