Structure of four molecular salts assembled from noncovalent associations between carboxylic acids and aromatic bases containing benzimidazole moiety

Article abstract of DOI:10.1016/j.molstruc.2013.01.016

Single crystal X-ray diffraction has enabled the elucidation of four examples of benzimidazole-acid salts, novel contributions to the extensive research into the occurrence of benzimidazole-acid compound motifs in organic salts. In their place are a series of motifs in which extensive strong classical NH?O/OH?O hydrogen bonds (ionic or neutral) combine with other nonconventional weaker interactions. This variety, coupled with the varying geometries and number of acidic groups of the acids employed, has led to the creation of four supramolecular arrays with 3D network structure. All salts were formed in solution and obtained by the slow evaporation technique. The role of weak and strong noncovalent interactions in the crystal packing is analyzed. The results presented herein indicate that the strength and directionality of the NH?O, and OH?O hydrogen bonds (ionic or neutral) between acids and benzimidazole derivatives are sufficient to bring about the formation of organic salts.

Full text of DOI:10.1016/j.molstruc.2013.01.016

Journal of Molecular Structure 1039 (2013) 144–152
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structure of four molecular salts assembled from noncovalent associations
between carboxylic acids and aromatic bases containing benzimidazole moiety
a
a
c
Xingjun Gao b, Shouwen Jin a, , Shanshan Liang , Wei Chen , Daqi Wang
⇑
a Tianmu College of ZheJiang A & F University, Lin’An 311300, PR China
b Faculty of science ZheJiang A & F University, Lin’An 311300, PR China
c Department of Chemistry, Liaocheng University, Liaocheng 252059, PR China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Due to the weak noncovalent interactions, the compounds displayed 3D framework structure.
"
"
"
Four supramolecular compounds
with 3D structure have been
prepared and characterized.
The noncovalent interaction
between benzimidazole moiety and
carboxylic acids have been analyzed.
The NAHꢀ ꢀ ꢀO/OAHꢀ ꢀ ꢀO hydrogen
bond is the primary force in a family
of structures containing the OHꢀ ꢀ ꢀim
synthons.
"
The CHAO associations have also
been discussed.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 May 2012
Received in revised form 11 December 2012
Accepted 7 January 2013
Available online 27 January 2013
Single crystal X-ray diffraction has enabled the elucidation of four examples of benzimidazole-acid salts,
novel contributions to the extensive research into the occurrence of benzimidazole-acid compound
motifs in organic salts. In their place are a series of motifs in which extensive strong classical
NAHꢀ ꢀ ꢀO/OAHꢀ ꢀ ꢀO hydrogen bonds (ionic or neutral) combine with other nonconventional weaker inter-
actions. This variety, coupled with the varying geometries and number of acidic groups of the acids
employed, has led to the creation of four supramolecular arrays with 3D network structure.
All salts were formed in solution and obtained by the slow evaporation technique. The role of weak and
strong noncovalent interactions in the crystal packing is analyzed. The results presented herein indicate
that the strength and directionality of the NAHꢀ ꢀ ꢀO, and OAHꢀ ꢀ ꢀO hydrogen bonds (ionic or neutral)
between acids and benzimidazole derivatives are sufficient to bring about the formation of organic salts.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Crystal structure
3D framework
Hydrogen bonds
Carboxylic acid
Benzimidazole derivatives
1. Introduction
component supermolecules or supramolecular arrays utilizing
noncovalent bonding is a rapidly developing area in supramolecu-
Multicomponent crystals and organic acid_base complexes
have received considerable attention over the past few years
[1,2] not only because of their intriguing structural motifs [3,4]
but also for their useful properties and promising applications as
functional materials [5,6]. The design and construction of multi-
lar synthesis. Thus, the supramolecular synthesis successfully ex-
ploits hydrogen-bonding and other types of noncovalent
interactions, in building supramolecular systems [7]. Of these
interactions hydrogen bond interactions are the most powerful
organizing force for the formation of supermolecules [8–11].
Because of the predictable supramolecular properties and the
ability to form strong and directional hydrogen bonds, carboxylic
acids were frequently chosen as building blocks for crystal
⇑
Corresponding author. Tel./fax: +86 571 6374 6755.
E-mail address: Jinsw@zafu.edu.cn (S. Jin).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.01.016

X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
145
Scheme 1. The building blocks discussed in this paper.
engineering [12–14]. Numerous organic acid_base compounds
from carboxylic acids and a variety of N-containing basic building
blocks have been documented recently [15–19].
sulfosalicylic acid):4H2O [(HL1+)2ꢀ(H2L2)2+ꢀ(5-ssa2ꢁ)2ꢀ4H2O, L2 =
1-(2-(1H-benzimidazol-1-yl)ethyl)-1H-benzimidazole, 5-ssa2ꢁ
=
5-sulfosalicylate] (3), and (benzimidazole):(1,4-cyclohexanedi-
carboxylic acid) [(HL1+)ꢀ(HChdaꢁ), HChdaꢁ = hydrogen 1,4-cycloh-
exanedicarboxylate], (4) (Scheme 2).
Imidazole and its derivatives are ubiquitous in biological and
biochemical structure and function, which attracted special atten-
tion in the construction of some interesting metal–organic frame-
works in recent years [20–25]. And also, great efforts have been
devoted to the development of organic molecular crystals contain-
ing a variety of imidazole architectures [26–28]. Among these
supramolecular architectures, however, only a very few reports de-
scribed the crystals composed of imidazoles [29–33] (e.g., 1,4-
bis[(imidazol-1-yl)methyl]-benzene [29,33], (bis(1-methyl-imida-
zol-2-yl)methyl)-4-nitroimidazol-2-yl)methyl)amine [31], etc.).
Following our previous works of acid–base adducts based on
bis(imidazole) and dicarboxylic acid [34,35], herein we report the
synthesis and crystal structure of four supramolecular compounds
assembled via hydrogen bonding interactions between carboxylic
acids and benzimidazole or its derivative. In this study, we got four
organic compounds composed of carboxylic acids and benzimidaz-
olyl compounds (Scheme 1), namely (benzimidazole):(3,5-dinitro-
2. Experimental section
2.1. Materials and methods
L2 was prepared as described previously [36]. All other 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 range
4000–400 cmꢁ1 on a Mattson Alpha-Centauri spectrometer. Melt-
ing points of new compounds were recorded on an XT-4 thermal
apparatus without correction.
2.2. Preparation of the salts
salicylic acid) [(HL1+)ꢀ(3,5-dnsꢁ), L1 = benzimidazole, 3,5-dnsꢁ
=
2.2.1. (Benzimidazole):(3,5-dinitrosalicylic acid) [(HL1+)ꢀ(3,5-dnsꢁ)]
(1)
Benzimidazole L1 (11.8 mg, 0.1 mmol) was dissolved in 3 mL of
methanol. To this solution was added 3,5-dinitrosalicylic acid
3,5-dinitrosalicylate] (1), (benzimidazole)2:(5-nitrosalicylic acid)
[(HL1)+(L1)ꢀ(5-nsaꢁ), 5-nsaꢁ = 5-nitrosalicylate] (2), (benzimid-
azole):1-(2-(1H-benzimidazol-1-yl)ethyl)-1H-benzimidazole:(5-
Scheme 2. The four compounds described in this paper, 1–4.

146
X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
(22.8 mg, 0.1 mmol) in 6 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,
colorless block crystals were isolated after slow evaporation of
the solution in air. The crystals were dried in air to give the title
compound [(HL1+)ꢀ(3,5-dnsꢁ)] (1), yield 28 mg, 80.86% (Based on
L1). m. p. 182–184 °C. Elemental analysis performed on crystals ex-
posed to the atmosphere: Calc. for C14H10N4O7 (346.26): C, 48.52;
H, 2.88; N, 16.17. Found: C, 48.49; H, 2.83; N, 16.14. Infrared spec-
2.3. X-ray crystallography
Suitable crystals were performed on a Bruker SMART 1000 CCD
diffractometer using MoK
a radiation (k = 0.71073 Å). Data collec-
tions and reductions were performed using the SMART and SAINT
software [37,38]. The structures were solved by direct methods,
and the non-hydrogen atoms were subjected to anisotropic refine-
ment by full-matrix least squares on F2 using SHELXTL package
[39]. Hydrogen atoms for the four structures were set in calculated
positions. Further details of the structural analysis are summarized
in Table 1. Selected bond lengths and angles for compounds 1–4
are listed in Table 2; the relevant hydrogen bond parameters are
provided in Table 3.
trum (KBr disk, cmꢁ1): 3614s (
m
(OH)), 3473s(multiple,
s(NH)), 3128m, 3042m, 2989m, 1994w, 1870w, 1781w,
(C@O)), 1599m, 1532s( as(NO2)), 1472w, 1416m, 1358m,
s(NO2)), 1284s( (CAO)), 1243m, 1126m, 1016m, 944m,
mas(NH)),
3352s(
1642s(
1314s(
m
m
m
m
m
876m, 809m, 754m, 696m, 634m.
3. Results and discussion
2.2.2. (Benzimidazole)2:(5-nitrosalicylic acid) [(HL1)+ꢀ(L1)ꢀ(5-nsaꢁ), 5-
nsaꢁ = 5-nitrosalicylate], (2)
3.1. Syntheses and general characterization
Benzimidazole L1 (11.8 mg, 0.1 mmol) was dissolved in 3 mL of
methanol. To this solution was added 5-nitrosalicylic acid
(18.3 mg, 0.1 mmol) in 9 mL 95% ethanol. Colorless block crystals
were afforded after several days by slow evaporation of the solvent
(yield: 16.0 mg, 76.30%, based on L1). mp 199–201 °C. Elemental
analysis: Calc. for C21H17N5O5 (419.40): C, 60.08; H, 4.05; N,
16.69. Found: C, 60.02; H, 3.97; N, 16.62. Infrared spectrum (KBr
1-(2-(1H-benzimidazol-1-yl)ethyl)-1H-benzimidazole,
and
benzimidazole both have good solubility in common organic sol-
vents, such as CH3OH, C2H5OH, CH3CN, CHCl3, and CH2Cl2. For
the preparation of 1–4, the acids were mixed directly with the base
in methanol and/or ethanol solvents in 1:1 ratio, which was al-
lowed to evaporate at ambient conditions to give the final crystal-
line products. The molecular structures and their atom labeling
schemes for the four structures are shown in Figs. 1, 3, 5 and 7,
respectively.
disk, cmꢁ1): 3664s(
(NH)), 3138m, 3054m, 2996m, 1981w, 1835w, 1766w, 1598s(mas
(COOꢁ)), 1556m, 1524s( s(COOꢁ)),
as(NO2)), 1485w, 1393s(
1358m, 1319s( s(NO2)), 1246m, 1196m, 1137m, 1086m, 1032m,
m(OH)), 3492s(multiple, mas(NH)), 3374s(ms
m
m
m
The elemental analyses for the four compounds are in good
agreement with their compositions. The infrared spectra of 1–4
are consistent with their chemical formulas determined by ele-
mental analysis and further confirmed by X-ray diffraction analy-
sis. The very strong and broad features at 3684–3342 cmꢁ1 arise
from OAH or NAH stretching frequencies. Aromatic and imidazol
ring stretching and bending are in the regions of 1500–
1630 cmꢁ1 and 600–750 cmꢁ1, respectively. Compounds 2–4 show
the characteristic bands for COOꢁ group. Compounds 1, and 4 dis-
play additional strong IR peaks for COOH groups. The bands at ca.
956m, 865m, 779m, 716m, 682m, 635m, 602m.
2.2.3. (Benzimidazole):1-(2-(1H-benzimidazol-1-yl)ethyl)-1H-
benzimidazole:(5-sulfosalicylic acid):4H2O [(HL1+)2ꢀ(H2L2)2+ꢀ(5-
ssa2ꢁ)2ꢀ4H2O, 5-ssa2ꢁ = 5-sulfosalicylate], (3)
1-(2-(1H-benzimidazol-1-yl)ethyl)-1H-benzimidazole
L2
(28 mg, 0.10 mmol), and benzimidazole L1 (11.8 mg, 0.1 mmol)
were dissolved in 7 mL of methanol. To this solution was added
5-sulfosalicylic acid (21.8 mg, 0.1 mmol) in 5 mL ethanol. Colorless
prisms were afforded after several days of slow evaporation of the
solvent, yield: 52 mg, 51.64% (based on L2). mp 152–154 °C. Ele-
mental analysis: Calc. for C44H46N8O16S2 (1007.01): C, 52.43; H,
4.56; N, 11.12; S, 6.35. Found: C, 52.41; H, 4.49; N, 11.05; S, 6.29.
1525 and 1315 cmꢁ1 were attributed to the
respectively [40].
mas(NO2) and ms(NO2),
Infrared spectrum (KBr disk, cmꢁ1): 3682s(
as(NH)), 3359s( s(NH)), 3118m, 3068m, 2986m, 2842m, 2718m,
1997w, 1663w, 1552s(
as(COOꢁ)), 1508m, 1474w, 1399m,
1368s(
s(COOꢁ)), 1233s, 1191m, 1139m, 1082m, 1038w, 956m,
m(OH)), 3468s(multiple,
3.2. X-ray structure of (benzimidazole):(3,5-dinitrobenzoic acid)
m
m
[(HL1+)ꢀ(dnaꢁ)] (1)
m
m
Salt 1 was prepared by reacting of a methanol solution of benz-
imidazole and 3,5-dinitrobenzoic acid in 1:1 ratio, which crystal-
lizes as triclinic colorless crystals in the centrosymmetric space
group P-1. The asymmetric unit of 1 consists of a cation of HL1+,
and one anion of 3,5-dinitrosalicylate, as shown in Fig. 1.
However in this case it is the phenol H that has been deproto-
nated and the COOH group remains protonated. The CAO distance
1.294(7) Å (O(3)AC(10)) concerning the phenolate is similar to the
proton transfer compound bearing the 3,5-dnsꢁ in which only the
phenol group has been deprotonated [41]. The CAO distances
1.221(8) Å (O(1)AC(8)), and 1.305(7) Å (O(2)AC(8)) in the COOH
show characteristic C@O, and CAO distances which are also con-
firming the reliability of adding H atoms experimentally by differ-
ent electron density onto O atoms as mentioned above.
The torsion angles O5AN3AC11AC10, and O6AN4AC13AC14
are 149.33°, and 177.42°, respectively. Similar to the published re-
sults [42], herein the 5-nitro (O6AN4AO7) group is essentially
coplanar with the phenyl ring of the anion, while the 3-nitro
(O5AN3AO4) group is rotated out of the plane.
Since the potentially hydrogen bonding hydroxyl group is pres-
ent in the ortho position to the carboxyl group in the anion, it
forms the more facile intramolecular hydrogen bonding. Thus the
844m, 769m, 714m, 666m, 612w.
2.2.4. (Benzimidazole):(1,4-cyclohexanedicarboxylic acid)
[(HL1+)ꢀ(HChdaꢁ)], (4)
A
solution of 1,4-cyclohexanedicarboxylic acid (17.2 mg,
0.1 mmol) in methanol (2 mL) was added dropwise to a vigorously
stirred solution of benzimidazole L1 (11.8 mg, 0.1 mmol) in meth-
anol (3 mL) over a period of 5 min. 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,
colorless block crystals were isolated after slow evaporation of
the methanol solution in air. The crystals were collected and dried
in air to give the title compound [(HL1+)ꢀ(HChdaꢁ)] (4). (yield:
22 mg, 75.78%). mp 167–168 °C. Elemental analysis: Calc. for
C
15H18N2O4 (290.31): C, 62.00; H, 6.20; N, 9.64. Found: C, 61.93;
H, 6.16; N, 9.57. Infrared spectrum (cmꢁ1): 3684s(
(OH),
s(NH)), 3184m, 3112s, 2974m, 2878m,
as(C@O)), 1629m, 1591s(
as(COOꢁ)), 1552m, 1476m,
s(COOꢁ)), 1342m, 1274s(
s(CAO)),
m
3426s(mas(NH)), 3342s(m
1713s(
m
m
1441m, 1400m, 1380s(
m
m
1228m, 1156m, 1102w, 1085m, 1032m, 978m, 869m, 808m,
771m, 722m, 676m, 645m, 602m.

X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
147
Table 1
Summary of X-ray crystallographic data for complexes 1–4.
1
2
3
4
Formula
Fw
T (K)
C
14H10N4O7
C21H17N5O5
419.40
298(2)
C44H46N8O16S2
1007.01
298(2)
C15H18N2O4
290.31
293(2)
346.26
298(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Triclinic
P-1
0.71073
Triclinic
P-1
0.71073
Triclinic
P-1
0.71073
Orthorhombic
P2(1)2(1)2(1)
5.3285(2)
15.8581(5)
16.3215(6)
90
7.3380(7)
9.6799(11)
10.5201(12)
78.1500(10)
83.2490(10)
88.941(2)
726.25(14)
2
1.583
0.130
356
0.33 ꢂ 0.30 ꢂ 0.18
2.61–25.02
ꢁ8 6 h 6 8
ꢁ11 6 k 6 7
ꢁ12 6 l 6 12
3459
8.9060(8)
9.2819(9)
12.3591(11)
93.7100(10)
101.480(2)
90.4000(10)
998.92(16)
2
1.394
0.103
436
0.43 ꢂ 0.33 ꢂ 0.19
2.68–25.02
ꢁ10 6 h 6 10
ꢁ11 6 k 6 9
ꢁ14 6 l 6 11
4926
7.2760(7)
10.2287(12)
16.7003(19)
73.3520(10)
86.249(2)
70.9100(10)
1124.8(2)
1
1.487
0.202
526
0.40 ꢂ 0.22 ꢂ 0.15
2.55–25.02
ꢁ8 6 h 6 8
ꢁ11 6 k 6 12
ꢁ19 6 l 6 19
5735
a
(°)
b (°)
90
90
c
(°)
V (Å3)
1379.16(8)
4
1.398
0.102
616
Z
Dcalcd (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h Range (°)
0.33 ꢂ 0.19 ꢂ 0.16
2.57–25.02
ꢁ6 6 h 6 4
Limiting indices
ꢁ18 6 k 6 18
ꢁ19 6 l 6 15
4978
Reflections collected
Reflections independent (Rint
)
2402(0.1014)
0.803
3441(0.0351)
1.519
3913(0.0312)
0.888
2393(0.0196)
1.055
Goodness-of-fit on F2
R indices [I > 2
R indices (all data)
Largest diff. peak and hole (eÅꢁ3
r
I]
0.0887, 0.1866
0.2242, 0.2396
0.351, ꢁ0.368
0.1399, 0.4094
0.2038, 0.4523
2.669, ꢁ0.397
0.0524, 0.1158
0.0909, 0.1296
0.352, ꢁ0.265
0.0313, 0.0751
0.0358, 0.0780
0.104, ꢁ0.118
)
Table 2
Table 3
Selected bond lengths (Å) and angles (°) for 1–4.
Hydrogen bond distances and angles in studied structures 1–4.
1
DAHꢀ ꢀ ꢀA
d(DAH)
(Å)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
(°)
N(1)AC(1)
N(2)AC(1)
1.338(8)
1.317(8)
1.472(8)
1.221(8)
1.294(7)
109.5(6)
122.0(7)
N(1)AC(3)
N(2)AC(2)
N(4)AC(13)
O(2)AC(8)
C(1)AN(1)AC(3)
N(2)AC(1)AN(1)
1.374(8)
1.391(8)
1.451(8)
1.305(7)
109.6(6)
108.5(7)
(Å)
(Å)
1
N(3)AC(11)
O(1)AC(8)
O(3)AC(10)
C(1)AN(2)AC(2)
O(1)AC(8)AO(2)
O(2)AH(2A)ꢀ ꢀ ꢀO(3)
N(2)AH(2)ꢀ ꢀ ꢀO(1)#1
N(1)AH(1)ꢀ ꢀ ꢀO(4)#2
N(1)AH(1)ꢀ ꢀ ꢀO(3)#2
0.82
0.86
0.86
0.86
1.68
1.99
2.32
2.04
2.453(6)
2.832(7)
3.052(8)
2.750(7)
155.3
165.5
143.3
139.2
2
2
O(3)AH(3A)ꢀ ꢀ ꢀO(2)
N(4)AH(4)ꢀ ꢀ ꢀO(2)#1
N(4)AH(4)ꢀ ꢀ ꢀO(1)#1
N(2)AH(2)ꢀ ꢀ ꢀN(3)
0.82
0.86
0.86
0.86
1.72
2.60
1.87
1.98
2.462(10)
3.281(11)
2.704(8)
2.825(9)
149.4
136.5
163.4
168.0
N(1)AC(1)
N(2)AC(1)
N(3)AC(8)
N(4)AC(8)
N(5)AC(20)
O(2)AC(15)
C(1)AN(1)AC(3)
C(8)AN(3)AC(10)
N(2)AC(1)AN(1)
O(1)AC(15)AO(2)
1.376(11)
1.299(10)
1.314(10)
1.313(10)
1.434(9)
1.273(10)
106.8(7)
107.5(7)
112.3(7)
125.1(8)
N(1)AC(3)
N(2)AC(2)
N(3)AC(10)
N(4)AC(9)
O(1)AC(15)
O(3)AC(17)
C(1)AN(2)AC(2)
C(8)AN(4)AC(9)
N(4)AC(8)AN(3)
1.385(10)
1.376(9)
1.409(9)
1.397(10)
1.260(11)
1.310(9)
105.5(7)
108.7(7)
111.8(7)
3
O(8)AH(8F)ꢀ ꢀ ꢀO(1)#2
0.85
0.85
1.96
1.96
2.82
2.01
1.96
1.81
1.79
1.82
1.90
2.810(3)
2.810(4)
3.527(2)
2.854(3)
2.805(3)
2.535(3)
2.646(4)
2.638(3)
2.756(3)
179.1
179.0
142.1
171.2
171.1
146.2
175.5
159.0
174.8
O(8)AH(8E)ꢀ ꢀ ꢀO(1)
O(7)AH(7D)ꢀ ꢀ ꢀS(1)#3 0.85
O(7)AH(7D)ꢀ ꢀ ꢀO(6)#3 0.85
O(7)AH(7C)ꢀ ꢀ ꢀO(5)#4 0.85
O(3)AH(3A)ꢀ ꢀ ꢀO(2)
N(4)AH(4)ꢀ ꢀ ꢀO(8)#3
N(3)AH(3)ꢀ ꢀ ꢀO(2)
N(2)AH(2)ꢀ ꢀ ꢀO(7)#5
0.82
0.86
0.86
0.86
3
N(1)AC(1)
N(1)AC(8)
N(2)AC(2)
N(3)AC(11)
N(4)AC(10)
O(2)AC(16)
O(4)AS(1)
1.320(4)
1.458(4)
1.384(4)
1.370(4)
1.382(4)
1.266(4)
1.437(2)
1.453(2)
108.3(2)
125.7(3)
108.6(3)
110.5(3)
123.9(3)
N(1)AC(3)
N(2)AC(1)
N(3)AC(9)
N(4)AC(9)
O(1)AC(16)
O(3)AC(18)
O(5)AS(1)
1.387(4)
1.324(4)
1.304(4)
1.310(4)
1.246(3)
1.349(3)
1.460(2)
1.762(3)
125.9(3)
108.1(3)
107.9(3)
110.8(3)
4
O(1)AH(1)ꢀ ꢀ ꢀO(3)#1
0.82
0.86
1.81
1.82
1.89
2.6195(18)
2.6207(18)
2.7152(18)
169.6
154.5
159.9
N(2)AH(2)ꢀ ꢀ ꢀO(4)#2
N(1)AH(1A)ꢀ ꢀ ꢀO(3)#3 0.86
O(6)AS(1)
S(1)AC(21)
Symmetry transformations used to generate equivalent atoms for 1: #1 ꢁx + 1,
ꢁy + 1, ꢁz + 2; #2 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: #2 ꢁx + 2, ꢁy + 1, ꢁz + 1; #3 x, y ꢁ 1, z; #4 x ꢁ 1, y ꢁ 1, z; #5
x, y + 1, z. Symmetry transformations used to generate equivalent atoms for 4: #1
ꢁx + 1/2, ꢁy + 1, z ꢁ 1/2; #2 x + 1/2, ꢁy + 1/2, ꢁz + 1; #3 ꢁx + 3/2, ꢁy + 1, z ꢁ 1/2.
C(1)AN(1)AC(3)
C(3)AN(1)AC(8)
C(9)AN(3)AC(11)
N(1)AC(1)AN(2)
O(1)AC(16)AO(2)
C(1)AN(1)AC(8)
C(1)AN(2)AC(2)
C(9)AN(4)AC(10)
N(3)AC(9)AN(4)
4
N(1)AC(9)
N(2)AC(9)
O(1)AC(1)
1.320(2)
1.320(2)
1.318(2)
N(1)AC(11)
N(2)AC(10)
O(2)AC(1)
1.392(2)
1.386(2)
1.202(2)
usual intramolecular hydrogen bond is found between the phenol
O(3)AC(2)
1.2721(19)
108.10(14)
123.02(16)
110.87(16)
O(4)AC(2)
C(9)AN(2)AC(10)
O(4)AC(2)AO(3)
1.243(2)
108.53(14)
123.35(16)
OH group and
a
carboxylate
O
atom (O(2)AH(2A)ꢀ ꢀ ꢀO(3),
C(9)AN(1)AC(11)
O(2)AC(1)AO(1)
N(1)AC(9)AN(2)
2.453(6) Å, 155.3°) which is similar to the corresponding value
(2.409 Å) in proton-transfer compound of [(hmt)+ [(dnsa)ꢁ]
[43,44]. Yet the value is as expected generally smaller than the

148
X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
(Fig. 2). The 2D sheets were further stacked along the direction that
is perpendicular with its extending direction through the O–
p
association between the 3-nitro group of the anion and the aro-
matic ring of the cation with OACg distance of 3.186 Å to form
3D ABAB layer network structure. Herein the neighboring sheets
were slipped some distance along its extending direction, while
the third sheet has the same projection as the first sheet on its
extending plane, so does the second sheet and the fourth sheet.
3.3. X-ray structure of (benzimidazole)2:(5-nitrosalicylic acid)
[(HL1)+ꢀ(L1)ꢀ(5-nsaꢁ), 5-nsaꢁ = 5-nitrosalicylate], (2)
Similar to 1, compound 2 was also prepared by reacting of a
methanol solution of benzimidazole and 5-nitrosalicylic acid in
1:1 ratio, which crystallizes as triclinic pale yellow crystals in the
centrosymmetric space group P-1. The asymmetric unit of 2 con-
sists of one protonated L1, one neutral L1, and one 5-nitrosalicylate
anion, as shown in Fig. 3. Compound 2 is also a salt where the
COOH group of one 5-nitrosalicylic acid is deprotonated, which is
confirmed by the pairs of bond distances of O(1)AC(15)
(1.260(11) Å), and O(2)AC(15) (1.273(10) Å) for the carboxylate.
In the solid state, there is consistently hydrogen bond formed
between the NH group, and the 5-nitrosalicylate ion, which is to
be expected [46]. There also exist strong coulombic interactions
between charged cation units of NH+ and the 5-nitrosalicylate
anions.
Because of the presence of the intramolecular hydrogen bond
between the carboxylate group and the phenol group
(O(3)AH(3)ꢀ ꢀ ꢀO(2), 2.462(10) Å,), it is generally expected and
found that the carboxylate group is nearly coplanar with the ben-
zene ring [torsion angle C17AC16AC15AO1, 175.42°]. There exists
a hydrogen bonded S11ð6Þ ring in the anion. This feature is similar to
that found in salicylic acid [47], and in the previously reported
structure of proton-transfer compound based on 5-nsaꢁ [48]. As
expected the OAO separation is in the lower limit of the docu-
mented data [2.489–2.509 Å] [48], but it is somewhat contracted
compared with the nonproton transfer examples (2.547–2.604 Å,
mean: 2.588 Å), as a result of deprotonation. The 5-nitro group also
varies little conformationally [torsion angle C19AC20AN5AO5,
178.41°] compared with the reported torsion angle (175.4–180°)
within this set of compounds [48].
Fig. 1. The structure of 1, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
distance found for the parent dnsa acid monohydrate [2.566(3) Å]
[45], and in the neutral species found in the adduct compound. For
the presence of the intramolecular hydrogen bond, there also exists
hydrogen bonded motif with graphical descriptor of S11ð6Þ.
One anion is bonded to one cation via the bifurcate NAHꢀ ꢀ ꢀO
hydrogen bonds arising from the NH group, the phenolate and
the 3-nitro group with NAO distances of 2.750(7)–3.052(8) Å,
and CHAO contact between the phenyl CH of the benzimidazole
and the same O atom of the 3-nitro group that has a NAHꢀ ꢀ ꢀO asso-
ciation with CAO distance of 3.389 Å to form a heteroadduct. Two
adjacent heteroadducts were combined together by NAHꢀ ꢀ ꢀO
hydrogen bond between the NH moiety and the carbonyl group
of the anion with NAO distance of 2.832(7) Å, and CHAO contact
between the NACHAN of the cation and the OH group of the car-
boxyl unit with CAO distance of 3.066 Å to form a tetracomponent
aggregate. In the tetracomponent aggregate the two cations and
the two anions are symmetrily related. The tetracomponent aggre-
gates were linked together by the CHAO association between the
phenyl CH of the cation and the 5-nitro group of the anion with
CAO distance of 3.256 Å, and OAO association between the 3-nitro
groups with OAO separation of 3.017 Å to form a 1D chain. The 1D
chains were further joined together by the interchain CHAO inter-
action between the phenyl CH of the cation and the 5-NO2 group of
the dnsaꢁ with CAO distance of 3.419 Å to form 2D sheet extend-
ing along the direction that made an angle of 45° with the bc plane
Fig. 2. 2D sheet structure of 1 extending along the direction that made an angle of 45° with the bc plane.

X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
149
Fig. 3. The structure of 2, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
The anion was bonded to the neutral L1 via the bifurcated
NAHꢀ ꢀ ꢀO association between the uncharged NH moiety of L1
and both O atoms of the carboxylate with NAO distances of
2.704(8)–3.281(11) Å, and CHAO contact between the phenyl CH
of L1 and one O atom of the carboxylate with CAO distance of
3.417 Å to form a bicomponent adduct. At the adduct there was
bonded a cation by the NAHꢀ ꢀ ꢀN hydrogen bond with NAN separa-
tion of 2.825(9) Å to produce a tricomponent aggregate. The tri-
component aggregates were linked together by the CHAO
associations to form 1D grid structure. The grids were stacked
along the direction that is perpendicular to its extending direction
Fig. 5. The structure of 3, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
(1.435(2)–1.4599(17) Å) [49]. The OASAO angles in SOꢁ3 are rang-
ing from 111.74(13)°–113.10(13)° with the average value of
112.42° which is in the range of the deprotonated SO3H moiety
also [49]. The phenol group remains unionized which is evidenced
by the C18AO3 bond distance of 1.349(3) Å. The H2L2 cations dis-
play trans conformation.
At the L2 cation there were bonded two water molecules via the
NAHꢀ ꢀ ꢀO hydrogen bond. The 5-sulfosalicylates were bonded with
the L1 cation through the NAHꢀ ꢀ ꢀO association arising from the
carboxylate with NAO distance of 2.638(3) Å. Two L1 cations were
via the p–p interactions between the aromatic rings of the cation
and the anion with CgACg distance of 3.363 Å to form 3D network
structure (Fig. 4). In this regard the adjacent grids were slipped
about half the width of the grid from each other.
3.4. X-ray structure of (benzimidazole):1-(2-(1H-benzimidazol-1-
yl)ethyl)-1H-benzimidazole:(5-sulfosalicylic acid):4H2O [(HL1+)2ꢀ
(H2L2)2+ꢀ(5-ssa2ꢁ)2ꢀ4H2O, 5-ssa2ꢁ = 5-sulfosalicylate], (3)
attached to one L2 cation by the CH–p interaction between the
phenyl CH of the L2 cation and the aromatic ring of the L1 cation
with CACg distance of 3.430 Å to form a seven-component adduct.
In the seven-component adduct there existed an inversion center
located at the middle point of the ethane bridge of the L2 cation.
The seven-component adducts were joined together by the
OAHꢀ ꢀ ꢀO hydrogen bond between the water molecule and the car-
boxylate with OAO separation of 2.810(3) Å, CHAO interaction be-
tween the NACHAN of L1 and the sulfonate with CAO distance of
3.084 Å, CHAO interaction between the NACHAN of L2 and the
The asymmetric unit of 3 consists of one monocation of
benzimidazole, half
a dication of 1-(2-(1H-benzimidazol-1-
yl)ethyl)-1H-benzimidazole, one dianion of 5-ssa2ꢁ, and two water
molecules as shown in Fig. 5. The CAO distances of the COOꢁ of
5-sulfosalicylate are ranging from 1.246(3) (O(1)@C(16)) to
1.266(4) Å (O(2)AC(16)) Å with the
D value of 0.020 Å, which sug-
gests that the carboxylate group is deprotonated. The SAO bond
lengths and the OASAO bond angles in the SOꢁ3 are not perfectly
equivalent, but vary with the environment around the O atoms.
Their values reported in Table 2, indicate relatively little distortion
from a regular pyramid. The S-O distances in SOꢁ3 are ranging from
water molecule with CAO distance of 3.329 Å, and O–p association
between the sulfonate and the aromatic moiety of the L1 with
OACg distance of 3.203 Å to form 2D sheet extending along the
bc plane (Fig. 6). The width of the sheet is ca. two times the length
of the c axis. There are no contacts between the sheets extending at
1.437(2) Å to 1.460(2) Å (
D is 0.023 Å) with the average value of
1.448 Å which is in the range of the deprotonated SO3H moiety
Fig. 4. 3D network structure of 2 formed by the grids via the p–p interactions.

150
X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
Fig. 6. 2D sheet structure of 3 which is extending in the direction that made an angle of ca 45° with the bc plane.
the same plane. The sheets were further stacked along the a axis
direction via the OAHꢀ ꢀ ꢀO hydrogen bonds (between the water
molecules attached to the L2 cation and the sulfonate with OAO
distances of 2.805(3)–2.854(3) Å), OAHꢀ ꢀ ꢀS hydrogen bond (be-
tween the water molecule and the S atom of the sulfonate with
O-S distance of 3.527(2) Å), CHAO associations (between the phe-
nyl CH of the cation, the sulfonate, and the carboxylate unit with
CAO distances of 3.359–3.451 Å), CH2AO interaction (between
the CH2 of the ethane spacer and the sulfonate with CAO distance
of CAO bond distances in the carboxyl group further confirm our
correct assignment of the H atom attached to the carboxyl unit.
Herein the 1,4-cyclohexanedicarboxylic acid molecules adopt chair
conformation with the two carboxyl units in e, e positions,
respectively.
The anions form a 1D wave chain extending along the c axis
direction via the intermolecular COOHꢀ ꢀ ꢀꢁOOC contacts with
OAO distance of 2.6195(18) Å. In the same chain the cyclohexane
rings of adjacent anions are almost perpendicular to each other,
while the cyclohexane ring of the third anion is parallel to the
cyclohexane ring of the first anion, so does the cyclohexane ring
of the second anion and the cyclohexane ring of the fourth anion.
The chains were combined together by the CHAO association be-
tween the CH of the anion and the O atom of the carboxylate that
is not involved in OAHꢀ ꢀ ꢀO hydrogen bond with CAO distance of
3.548 Å to form 2D corrugated sheet extending parallel to the ac
plane. The cations also generated 1D chain running along the a axis
of 3.481 Å), O–
matic ring of L2 with OACg distance of 2.903 Å), and
p
association (between the sulfonate and the aro-
interac-
p–p
tion with CgACg distances of 3.183–3.397 Å to form 3D network
structure.
3.5. X-ray structure of (benzimidazole):(1,4-cyclohexanedicarboxylic
acid) [(HL1+)ꢀ(HChdaꢁ)], (4)
direction via the offset
3.376 Å. The cationic chains were connected to the anionic sheet
p–p association with CgACg distance of
Crystallization of benzimidazole and 1,4-cyclohexanedicarb-
oxylic acid in a 1:1 ratio from the mixed solvent of methanol and
ethanol gave single crystals suitable for X-ray diffraction. In the
compound 4 only one proton of the 1,4-cyclohexanedicarboxylic
acid was transferred to the ring N atom of the L1. Thus 4 is also
an organic salt. In the asymmetric unit of 4 there existed one cation
of L1, and one monoanion of 1,4-cyclohexanedicarboxylic acid, as
shown in Fig. 7.
by the NAHꢀ ꢀ ꢀO hydrogen bond between the NH unit of the cation
and the carboxylate with NAO distance of 2.6207(18) Å, CH2–
p
interaction between the CH2 moiety of the anion and the benz-
imidazole ring of the cation with CACg distance of 3.552 Å
(Fig. 8). In this case the cations in the same chain were parallel
to each other, while the cations at different chains were almost
perpendicular to each other. An alternative reading of this struc-
ture is possible when we emphasize the relative arrangement of
the cations and the anions, i.e., the cations were intercalated be-
tween the anionic sheets to produce 3D ABAB layer network
structure.
The CAO distances of COOꢁ (C(2)AO(3)AO(4)) group of the 1,4-
cyclohexanedicarboxylic acid are ranging from 1.243(2)
(O(4)AC(2)) to 1.2721(19) Å (O(3)AC(2)) with the
D value of
0.0291 Å. The CAO distances of the other COOH (O(1)AC(1)AO(2))
group of the 1,4-cyclohexanedicarboxylic acid are ranging from
1.202(2) (O(2)AC(1)) to 1.318(2) Å (O(1)AC(1)) with the
D value
of 0.116 Å. The differences in bond distances between the two pairs
4. Conclusion
Four organic salts have been prepared and structurally charac-
terized. All four examples involve proton transfer from the carbox-
ylic acids to the N atom of benzimidazole moiety, with subsequent
hydrogen bonding linking the cation and the anion to give 3D
framework structures (3D network structure, and 3D ABAB layer
structure) in all cases. It is worthy to note that both the sulfonic
proton and the carboxyl H are deprotonated for the salt based on
5-sulfosalicylic acid. While for the salt 1, only phenol group has
ionized.
This study has demonstrated that the NAHꢀ ꢀ ꢀO hydrogen bond
Fig. 7. The structure of 4, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
is the primary intermolecular force in a family of structures

X. Gao et al. / Journal of Molecular Structure 1039 (2013) 144–152
151
Fig. 8. The arrangement of the cations and the anions in 4.
[3] (a) D.R. Weyna, T. Shattock, P. Vishweshwar, M.J. Zaworotko, Cryst. Growth
Des. 9 (2009) 1106;
containing the COOHꢀ ꢀ ꢀim synthons. Since the potentially hydro-
gen bonding phenol hydroxyl group is present in the ortho position
to the carboxylate group in 1–3, it forms the more facile intramo-
lecular OAHꢀ ꢀ ꢀO hydrogen bond. Except the classical hydrogen
bonding interactions, the secondary propagating interactions also
play important role in structure extension. All products possess
weak CAHꢀ ꢀ ꢀO associations. Two CAHꢀ ꢀ ꢀO hydrogen bond type
interactions were observed based upon their geometric prefer-
ences, intra- and interchain interactions. From an analysis of the
metrics displayed by each set of interactions, it seems that intra-
and interchain CAHꢀ ꢀ ꢀO interactions are of equal structural impor-
(b) M. Du, Z.H. Zhang, X.J. Zhao, Cryst. Growth Des. 5 (2005) 1247;
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tance. There are
p–p
interactions in compounds 2, 3, and 4. Organic
interactions with the OACg distances in
salts 1, and 3 possess O–
p
the range of 2.903–3.203 Å. These interactions are responsible for
the supramolecular assembly of benzimidazole group and carbox-
ylic acids into salts, with desired connectivities.
In conclusion, we have shown that 3D structures containing
strong hydrogen bond interactions or mixture of strong and weak
hydrogen bond interactions can be constructed and the structure
may be modulated to have nonplanar structure by functional
groups on planar system.
Supporting information available
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic data center, CCDC
Nos. 874224 for 1, 851646 for 2, 851938 for 3, and 867638 for 4.
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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Acknowledgement
We gratefully acknowledge the financial support of the Educa-
tion Office Foundation of Zhejiang Province (Project No.
Y201017321) and the financial support of xinmiao Project of the
Education Office Foundation of Zhejiang Province.
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