Five organic salts assembled from carboxylic acids and bis-imidazole derivatives through collective noncovalent interactions

Article abstract of DOI:10.1016/j.molstruc.2011.08.010

Five multicomponent crystals of bis(imidazole) derivatives have been prepared with 5-nitrosalicylic acid, 5-sulfosalicylic acid, and phthalic acid. The five crystalline forms reported are organic salts of which the crystal structures have all been determi

Full text of DOI:10.1016/j.molstruc.2011.08.010

Journal of Molecular Structure 1004 (2011) 227–236
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Five organic salts assembled from carboxylic acids and bis-imidazole derivatives
through collective noncovalent interactions
b
b
c
Shouwen Jin a, , Jianzhong Guo , Li Liu , 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
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 May 2011
Received in revised form 3 August 2011
Accepted 3 August 2011
Available online 26 August 2011
Five multicomponent crystals of bis(imidazole) derivatives have been prepared with 5-nitrosalicylic acid,
5-sulfosalicylic acid, and phthalic acid. The five crystalline forms reported are organic salts of which the
crystal structures have all been determined by X-ray diffraction. The results presented herein indicate
that the strength and directionality of the NAHꢀ ꢀ ꢀO, OAHꢀ ꢀ ꢀO, and NAHꢀ ꢀ ꢀN hydrogen bonds (ionic or
neutral) between carboxylic acids and ditopic imidazoles are sufficient to bring about the formation of
binary organic salts.
All supramolecular architectures of the organic salts 1–5 involve extensive OAHꢀ ꢀ ꢀO, and NAHꢀ ꢀ ꢀO
hydrogen bonds as well as other noncovalent interactions. The role of weak and strong noncovalent inter-
actions in the crystal packing is ascertained. These noncovalent interactions combined, all the complexes
displayed 3D framework structure.
Keywords:
Crystal structure
3D framework
Hydrogen bonds
Noncovalent interactions
Bis-imidazoles
Ó 2011 Elsevier B.V. All rights reserved.
Carboxylic acids
1. Introduction
formation of supramolecules. Imidazole and its derivatives are
ubiquitous in biological and biochemical structure and function,
Noncovalent interactions between molecules are weak intermo-
lecular contacts that govern the physicochemical properties of
molecular systems in the condensed phase [1]. Noncovalent binding
interactions are nowadays commonly used for the self-assembly of
large supramolecular aggregates in solution [2]. Supramolecular
interactions have attracted considerable attention during the past
few years [3] because the utilization of intermolecular noncovalent
interactions is relied upon for the design and development of func-
tional materials. Noncovalent interactions form the backbone of
supramolecular chemistry and include classical/nonclassical hydro-
gen bond, stacking, electro-static, hydrophobic and charge-transfer
interactions [4]. Of these interactions hydrogen bond interactions
are well-established supramolecular interactions and numerous
crystallographic examples are regularly reported [5,6].
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 engineer-
ing [7–9]. Numerous heterodimers composed of carboxylic acids
and a variety of N-containing basic building blocks have been docu-
mented recently [10–14]. The hydrogen bonding between hydroxyl
group of carboxylic acid and heterocyclic nitrogen atom has
been proved to be a useful and powerful organizing force for the
and great efforts have been devoted to the development of organic
molecular crystals containing a variety of imidazole architectures
[15–17]. Among these supramolecular architectures, however, only
a very few reports described the crystals composed of bis(imidazole)
derivatives [18–22] (e.g., 1,4-bis[(imidazol-1-yl)methyl]-benzene
[18,22], (bis(1-methyl-imidazol-2-yl)methyl)-4-nitroimidazol-2-
yl)methyl)amine [20], etc.).
Following our previous works of acid–base adducts based on
bis(imidazole) and dicarboxylic acid [23–25], herein we report
the synthesis and crystal structure of five supramolecular com-
plexes assembled through noncovalent interactions between car-
boxylic acids and bis(imidazole). In this study, we got five
organic complexes composed of carboxylic acids and symmetric
ditopic bis-imidazol-1-yl compounds (Scheme 1), namely 1-(3-
(1H-benzimidazol-1-yl)propyl)-1H-benzimidazole:(5-nitrosalicyl-
ic acid)2:2MeOH (1) [(H2L1)2+ꢀ(5-nsaꢁ)2ꢀ2MeOH, L1 = 1-(3-(1H-
benzimidazol-1-yl)propyl)-1H-benzimidazole, 5-nsaꢁ = 5-nitrosal-
icylate], 1,5-bis(1-benzimidazolyl)-3-oxapentane:(5-nitrosalicylic
acid)2 (2) [(H2L2)2+ꢀ(5-nsaꢁ)2, L2 = 1,5-bis(1-benzimidazolyl)-
3-oxapentane], bis(N-imidazolyl)methane:(5-sulfosalicylic acid)
(3) [(H2L3)2+ꢀ(5-ssa2ꢁ), L3 = bis(N-imidazolyl)methane, 5-ssa2ꢁ
=
5-sulfosalicylate],
1,4-bis(N-imidazolyl)butane:(5-sulfosalicylic
acid) (4) [(H2L4)2+ꢀ(5-ssa2ꢁ), L4 = 1,4-bis(N-imidazolyl)butane],
and 1,4-bis(N-imidazolyl)butane:(phthalic acid) (5) [(HL4)+ꢀ
(Hptaꢁ), Hptaꢁ = hydrogen phthalate].
⇑
Corresponding author. Tel./fax: +86 571 6374 0010.
E-mail address: jinsw@zafu.edu.cn (S. Jin).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.08.010

228
S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
OH
HO
O
O
HO
HO
O
O
HO
HO
NO2
S
OH
O
O
5-Nitro salicylic acid
5-Sulfosalicylic Acid
Phthalic acid
O
N
N
N
N
N
N
N
N
L1
L2
N
N
N
N
N
N
N
N
L3
L4
Scheme 1. Hydrogen bond synthons discussed in this paper.
209 °C. Elemental analysis: Calc. for C32H28N6O11 (672.60): C,
2. Experimental
57.09; H, 4.16; N, 12.49. Found: C, 56.98; H, 4.09; N, 12.44. Infrared
spectrum (KBr disk, cmꢁ1): 3574s (
m
(OH)), 3486s(multiple,
s(NH)), 3115m, 3054m, 2972m, 2846m, 2724m, 2432w,
2386m, 2231m, 1996w, 1868w, 1783w, 1614m, 1592s(
as(COOꢁ)),
1540s( as(NO2)), 1474w, 1406s( s(NO2)),
s(COOꢁ)), 1358m, 1314s(
mas(NH)),
2.1. Materials and methods
3338s(
m
m
All reagents were commercially available and used as received.
L1–L4 were prepared according to modified procedures of the liter-
atures [26–27]. The C, H, and N micro-analysis 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.
m
m
m
1240m, 1120m, 1013m, 946m, 868m, 806m, 757m, 680m, 637m,
558m.
2.2.3. Bis(N-imidazolyl)methane:(5-sulfosalicylic acid) [(H2L3)2+ꢀ(5-
ssa2ꢁ), 5-ssa2ꢁ = 5-sulfosalicylate], (3)
Bis(N-imidazolyl)methane L3 (30 mg, 0.2 mmol) dissolved in
2 mL of methanol. To this solution was added 5-sulfosalicylic acid
(43.6 mg, 0.2 mmol) in 8 mL ethanol. Colorless prisms were afforded
after several days of slow evaporation of the solvent, yield: 56 mg,
76.43% (based on L3). mp 112–114 °C. Elemental analysis: Calc. for
2.2. Preparation of supramolecular complexes
2.2.1. 1-(3-(1H-benzimidazol-1-yl)propyl)-1H-benzimidazole:(5-
nitrosalicylic acid)2:2MeOH [(H2L1)2+ꢀ(5-nsaꢁ)2ꢀ2MeOH, 5-nsaꢁ = 5-
nitrosalicylate], (1)
C
14H14N4O6S (366.35): C, 45.86; H, 3.82; N, 15.29; S, 8.73. Found:
C, 45.82; H, 3.78; N, 15.22; S, 8.66. Infrared spectrum (KBr disk,
cmꢁ1): 3582s(
(OH)), 3448s(multiple, as(NH)), 3353s( s(NH)),
3213s, 3115w, 3064m, 2960m, 2842m, 2718m, 2468w, 2374m,
2242w, 1996w, 1662w, 1551s(
as(COOꢁ)), 1510m, 1478w, 1395m,
1368s(
s(COOꢁ)), 1234s, 1195m, 1131m, 1087m, 1032w, 936m,
1-(3-(1H-benzimidazol-1-yl)propyl)-1H-benzimidazole
L1
(28 mg, 0.10 mmol) was dissolved in 3 mL methanol. To this solu-
tion was added 5-nitrosalicylic acid (18.3 mg, 0.1 mmol) in 4 mL
methanol. Colorless block crystals were afforded after several days
by slow evaporation of the solvent. yield: 35 mg, 49.53% (based on
L1). mp 196–198 °C. Elemental analysis: Calc. for C33H34N6O12
(706.66): C, 56.04; H, 4.81; N, 11.89. Found: C, 55.96; H, 4.78; N,
m
m
m
m
m
842m, 766m, 714m, 658m, 611w.
11.85. Infrared spectrum (KBr disk, cmꢁ1): 3558s(
3506s(multiple, as(NH)), 3362s( s(NH)), 3290s, 3118m, 3046m,
2960m, 2842m, 2718m, 2448w, 2374m, 2213m, 1976w, 1836w,
1764w, 1586s( as(NO2)), 1486w,
as(COOꢁ)), 1552m, 1526s(
1394s( s(NO2)), 1270m, 1195m,
s(COOꢁ)), 1366m, 1321s(
m(OH)),
2.2.4. 1,4-Bis(N-imidazolyl)butane:(5-sulfosalicylic acid) [(H2L4)2+ꢀ(5-
ssa2ꢁ)] (4)
m
m
m
m
1,4-Bis(N-imidazolyl)butane L4 (19.9 mg, 0.1 mmol) dissolved in
2 mL of ethanol. To this solution was added 5-sulfosalicylic acid
(21.8 mg, 0.1 mmol) in 5 mL methanol. Colorless prisms were affor-
ded after several days of slow evaporation of the solvent, yield:
32 mg, 78.35% (based on L4). mp 106–108 °C. Elemental analysis:
Calc. for C17H20N4O6S (408.43): C, 49.95; H, 4.90; N, 13.71; S, 7.83.
Found: C, 49.92; H, 4.84; N, 13.67; S, 7.78. Infrared spectrum (KBr
m
m
1131m, 1079m, 952m, 903m, 853m, 806m, 760m, 716m, 680m,
637m, 582m.
2.2.2. 1,5-bis(1-benzimidazolyl)-3-oxapentane:(5-nitrosalicylic acid)2
[(H2L2)2+ꢀ(5-nsaꢁ)2, 5-nsaꢁ = 5-nitrosalicylate], (2)
1-(4-(1H-benzimidazol-1-yl)butyl)-1H-benzimidazole
L2
disk, cmꢁ1): 3586s
3373s( s(NH)), 3109m, 3064m, 2972m, 2844m, 2726m, 2428w,
2362m, 2213m, 1976w, 1836w, 1783w, 1626m, 1564s(
as(COOꢁ)),
1513m, 1483w, 1388s(
s(COOꢁ)), 1195m, 1109m, 1045m, 925m,
835m, 757m, 710m, 680m, 626m, 546m.
(m
(OH)), 3472s(multiple,
mas(NH)),
(29 mg, 0.10 mmol) dissolved in 1 mL ethanol. To this solution was
added 5-nitrosalicylic acid (18.3 mg, 0.1 mmol) in 4 mL methanol.
Colorless prisms were afforded after several days of slow evapora-
tion of the solvent, yield: 42 mg, 62.44% (based on L2). mp 206–
m
m
m

S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
229
2.2.5. 1,4-Bis(N-imidazolyl)butane:(phthalic acid) [(HL4)+ꢀ(Hptaꢁ)]
(5)
1,4-Bis(N-imidazolyl)butane L4 (19.9 mg, 0.1 mmol) dissolved
in 2 mL of ethanol. To this solution was added phthalic acid
(17 mg, 0.1 mmol) in 5 mL ethanol. Colorless prisms were afforded
after several days of slow evaporation of the solvent, yield: 29 mg,
81.37% (based on L4). mp 166–168 °C. Elemental analysis: Calc. for
in methanol and/or ethanol solvents, which was allowed to evapo-
rate at ambient conditions to give the final crystalline products.
The molecular structures and their atom labeling schemes for the
four structures are shown in Figs. 1, 3, 5, 7 and 9, respectively.
The elemental analyses for all the compounds are in good agree-
ment with their compositions. The infrared spectra of 1–5 are con-
sistent with their chemical formulas determined by elemental
analysis and further confirmed by X-ray diffraction analysis. The
very strong and broad features at 3600–3300 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. The intense peak at ca. 1713 cmꢁ1
was derived from the existence of the C@O stretches, and the band
at ca. 1286 cmꢁ1 exhibited the presence of the CAO stretches of
the carboxylate for salt 5. The absence of two broad bands at ca.
2500 cmꢁ1 and 1900 cmꢁ1 which is characteristic of a neutral
OAHꢀ ꢀ ꢀN hydrogen-bond interaction was interpreted as a lack of
co-crystal formation in compounds 1–5 [31]. The most distinct fea-
ture in the IR spectrum of proton transfer compounds are the pres-
ence of strong asymmetrical and symmetrical carboxylate
stretching frequencies at 1550–1610 cmꢁ1 and 1300–1420 cmꢁ1
in 1, 2, 3, 4, and 5, respectively [32].
C
18H20N4O4 (356.38): C, 60.61; H, 5.61; N, 15.71. Found: C, 60.56;
H, 5.54; N, 15.68. Infrared spectrum (KBr disk, cmꢁ1):
3560s( (OH)), 3454s(multiple, as(NH)), 3332s( s(NH)), 3140m,
3032m, 2979m, 2926m, 2842m, 2724m, 2610w, 2356m, 2179m,
1998w, 1812w, 1769w, 1713s( as(C@O)), 1676w, 1638m, 1586m,
as(COOꢁ)), 1470m, 1426m, 1376s( s(COOꢁ)), 1304m,
s(CAO)), 1232m, 1196m, 1126m, 1073m, 1020m, 930m,
m
m
m
m
1558s(
1286s(
m
m
m
888m, 802m, 716m, 656m, 614m, 574m, 510m, 464m.
2.3. X-ray crystallography
Suitable crystals were performed on a Bruker SMART 1000 CCD
diffractometer using Mo Ka radiation (k = 0.71073 Å). Data collec-
tions and reductions were performed using the SMART and SAINT
software [28–29]. 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
[30]. Hydrogen atom positions for the two structures were gener-
ated geometrically. Further details of the structural analysis are
summarized in Table 1. Selected bond lengths and angles for com-
plexes 1–5 are listed in Table 2, the relevant hydrogen bond
parameters are provided in Table 3.
3.2. X-ray structure of 1-(3-(1H-benzimidazol-1-yl)propyl)-1H-
benzimidazole:(5-nitrosalicylic acid)2:2MeOH [(H2L1)2+ꢀ(5-nsaꢁ)2
ꢀ2MeOH, 5-nsaꢁ = 5-nitrosalicylate], (1)
Salt 1 was prepared by reacting of a methanol solution of 1-(3-
(1H-benzimidazol-1-yl)propyl)-1H-benzimidazole and 5-nitrosali-
cylic acid in 1: 1 ratio, which crystallizes as monoclinic pale yellow
crystals in the centrosymmetric space group C2/c. The asymmetric
unit of 1 consists of half a dication of L1, one anion of 5-nitrosali-
cylate, and one methanol molecule as shown in Fig. 1. This is a salt
where the COOH groups of 5-nitrosalicylic acids are ionized by pro-
ton transfer to the nitrogen atoms of the 1-(3-(1H-benzimidazol-1-
yl)propyl)-1H-benzimidazole moieties, which is also confirmed by
the bond distances of O(1)AC(10) (1.257(5) Å) and O(2)AC(10)
3. Results and discussion
3.1. Syntheses and general characterization
L1–L4 have good solubility in common organic solvents, such as
CH3OH, C2H5OH, CH3CN, CHCl3, and CH2Cl2. For the preparation of
1–5, the acids were mixed directly with the bases L1–L4 in 1:1 ratio
Table 1
Summary of X-ray crystallographic data for complexes 1–5.
1
2
3
4
5
Formula
Fw
C
33H34N6O12
C32H28N6O11
672.60
C14H14N4O6S
366.35
C17H20N4O6S
408.43
C18H20N4O4
356.38
706.66
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
C2/c
29.596(3)
7.4337(7)
18.3375(17)
90
0.71073
Monoclinic
C2/c
29.602(3)
6.3885(7)
7.8276(7)
90
0.71073
0.71073
Orthorhombic
Pna2(1)
18.5227(16)
9.6884(8)
10.0139(11)
90
0.71073
Orthorhombic
Pna2(1)
13.0059(12)
7.9942(6)
16.7147(16)
90
Orthorhombic
P2(1)2(1)2(1)
9.2099(11)
10.0436(13)
16.7967(16)
90
a
, deg
b, deg
125.864(2)
90
3269.5(5)
4
1.436
0.111
90.8320(10)
90
1480.1(3)
2
1.509
0.116
90
90
1553.7(3)
4
1.566
90
90
1797.0(3)
4
1.510
90
90
1737.9(3)
4
1.362
c
, deg
V, Å3
Z
Dcalcd, Mg/m3
Absorption coefficient, mmꢁ1
F(000)
0.251
760
0.226
856
0.098
752
1480
700
Crystal size, mm3
h range, deg
0.24 ꢂ 0.22 ꢂ 0.20
2.22–25.02
ꢁ34 6 h 6 34
ꢁ8 6 k 6 4
ꢁ21 6 l 6 21
7899
0.40 ꢂ 0.37 ꢂ 0.14
2.60–25.02
ꢁ34 6 h 6 33
ꢁ7 6 k 6 4
ꢁ9 6 l 6 9
3850
0.34 ꢂ 0.20 ꢂ 0.14
2.36–25.02
ꢁ9 6 h 6 10
ꢁ11 6 k 6 11
ꢁ16 6 l 6 19
6475
0.20 ꢂ 0.09 ꢂ 0.07
2.37–25.01
ꢁ14 6 h 6 21
ꢁ11 6 k 6 11
ꢁ11 6 l 6 11
9086
0.40 ꢂ 0.38 ꢂ 0.28
2.82–25.02
ꢁ15 6 h 6 15
ꢁ6 6 k 6 9
ꢁ19 6 l 6 19
8210
Limiting indices
Reflections collected
Reflections independent (Rint
)
2876 (0.0914)
0.884
1868 (0.0425)
1.036
2717 (0.0418)
0.919
3062 (0.0555)
0.971
1592 (0.0357)
1.099
Goodness-of-fit on F2
R indices [I > 2
r
I]
0.0635, 0.1576
0.1306, 0.1916
0.207, ꢁ0.322
0.0698, 0.1794
0.1106, 0.2106
0.657, ꢁ0.251
0.0396, 0.0724
0.0584, 0.0780
0.246, ꢁ0.279
0.0407, 0.0825
0.0560, 0.0886
0.251, ꢁ0.152
0.0345, 0.0809
0.0494, 0.0908
0.177, ꢁ0.160
R indices (all data)
Largest diff. peak and hole, e Åꢁ3

230
S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
electrostatic interactions between charged cation units of NH+ and
the 5-nitrosalicylate anions.
Table 2
Selected bond lengths (Å) and angles (°) for 1–5.
Because of the presence of the intramolecular hydrogen bond
between the carboxylate group and the phenol group
(O(3)AH(3)ꢀ ꢀ ꢀO(2), 2.507(4) Å), it is generally expected and found
that the carboxylate group is essentially coplanar with the benzene
ring [torsion angle C12AC11AC10AO1, 177.85°]. This feature is
similar to that found in salicylic acid [35], and in the previously re-
ported structure of proton-transfer compound based on 5-nsaꢁ
[36]. As expected the OAO separation is essentially in the range
of the documented data [2.489–2.509 Å] [36], but it is slightly con-
tracted 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
C14AC15AN3AO5, 178.68°] compared with the reported data
within this set of compounds (175.4–180°) [36].
1
N(1)AC(3)
N(1)AC(1)
N(2)AC(4)
O(1)AC(10)
1.344(4)
1.477(4)
1.390(4)
1.257(5)
1.339(4)
107.8(3)
126.3(2)
123.9(4)
N(1)AC(5)
N(2)AC(3)
1.395(4)
1.321(4)
1.455(5)
1.266(5)
1.387(6)
125.8(3)
109.0(3)
N(3)AC(15)
O(2)AC(10)
O(6)AC(17)
C(3)AN(1)AC(1)
C(3)AN(2)AC(4)
O(3)AC(12)
C(3)AN(1)AC(5)
C(5)AN(1)AC(1)
O(1)AC(10)AO(2)
2
N(1)AC(3)
N(1)AC(1)
N(2)AC(4)
O(2)AC(10)
O(4)AC(12)
C(3)AN(1)AC(1)
C(3)AN(2)AC(4)
O(2)AC(10)AO(3)
1.313(9)
1.458(9)
1.330(8)
1.256(7)
1.344(7)
121.0(6)
113.4(6)
124.2(6)
N(1)AC(5)
N(2)AC(3)
O(1)AC(2)
O(3)AC(10)
C(3)AN(1)AC(5)
C(5)AN(1)AC(1)
N(2)AC(3)AN(1)
1.399(8)
1.280(8)
1.406(8)
1.257(7)
111.1(6)
127.7(6)
108.3(7)
Two anions were bounded to the cations through the NAHꢀ ꢀ ꢀO
hydrogen bond between the NH+ cation and the carboxylate group
with NAO distance of ca. 2.664(4) Å to form a heteroadduct. At
every carboxylate there was bonded a methanol molecule through
the OAHꢀ ꢀ ꢀO (OAO separation is 2.629(5) Å) hydrogen bond pro-
duced by the same O atom that is involved in the NAHꢀ ꢀ ꢀO hydro-
gen bond. The adjacent heteroadducts were connected together via
two CHAO and one CH2AO associations between the cation and
the NO2 group to form a 1D chain running along the a axis direc-
tion. One CHAO interaction is existed between 2-CH of one benz-
imidazole moiety and one O atom of the nitro group with CAO
distance of 3.463 Å, the other CHAO interaction is between CH of
the benzene ring of another benzimidazole moiety in the same cat-
ion and the remaining O atom of the NO2 group with CAO distance
of 3.369 Å, this O atom also made a CH2AO contact with the pro-
pane spacer of the cation with CAO distance of 3.483 Å. For the
presence of such three interactions there are close joint R22ð8Þ
and R22ð9Þ ring motifs. There are also chains that are antiparallel
to the above chains. These two kinds of chains were combined to-
gether along the b axis direction via the CHAO interaction between
aromatic CH of the anion and the methanol molecule with CAO
distance of 3.266 Å to form a double chain running along the a axis
direction also. Here the two chains were slipped some distance
from each other along the a, and c axis directions, respectively.
Such double chains were further joined together by the CH2AO
interaction between the propane spacer and the carboxylate with
CAO distance of 3.420 Å to form a sheet extending on the ac plane
(Fig. 2). The sheets were further stacked along the b axis direction
by the intersheet CH2AO associations between the propane spacer
and the carboxylate with CAO distance of 3.420 Å to form a 3D net-
work structure.
3
N(1)AC(2)
N(1)AC(1)
N(2)AC(3)
N(3)AC(7)
N(4)AC(5)
O(1)AC(8)
O(3)AC(10)
O(5)AS(1)
C(2)AN(1)AC(4)
C(4)AN(1)AC(1)
C(5)AN(3)AC(7)
C(7)AN(3)AC(1)
N(1)AC(1)AN(3)
N(4)AC(5)AN(3)
1.327(4)
1.437(3)
1.354(4)
1.374(4)
1.306(4)
1.269(4)
1.339(3)
1.443(2)
108.4(2)
125.4(3)
108.6(3)
128.1(3)
111.5(2)
108.4(3)
N(1)AC(4)
N(2)AC(2)
N(3)AC(5)
N(3)AC(1)
N(4)AC(6)
O(2)AC(8)
O(4)AS(1)
O(6)AS(1)
C(2)AN(1)AC(1)
C(2)AN(2)AC(3)
C(5)AN(3)AC(1)
C(5)AN(4)AC(6)
N(2)AC(2)AN(1)
O(2)AC(8)AO(1)
1.374(4)
1.310(4)
1.316(4)
1.455(3)
1.349(4)
1.257(4)
1.443(2)
1.4387(19)
125.9(3)
109.5(3)
123.1(3)
109.5(3)
108.0(3)
123.1(3)
4
N(1)AC(5)
N(1)AC(1)
N(2)AC(6)
N(3)AC(10)
N(4)AC(8)
O(1)AC(11)
O(3)AC(13)
O(5)AS(1)
C(5)AN(1)AC(7)
C(7)AN(1)AC(1)
C(8)AN(3)AC(10)
C(10)AN(3)AC(4)
N(2)AC(5)AN(1)
O(1)AC(11)AO(2)
1.317(4)
1.463(4)
1.361(4)
1.359(4)
1.309(4)
1.229(4)
1.355(3)
1.415(2)
108.6(3)
124.8(3)
107.7(3)
125.6(3)
108.5(3)
124.4(3)
N(1)AC(7)
N(2)AC(5)
N(3)AC(8)
N(3)AC(4)
N(4)AC(9)
O(2)AC(11)
O(4)AS(1)
1.369(4)
1.307(4)
1.314(4)
1.468(4)
1.343(4)
1.282(4)
1.442(3)
1.446(2)
126.6(3)
109.4(3)
126.7(3)
109.0(3)
109.0(3)
O(6)AS(1)
C(5)AN(1)AC(1)
C(5)AN(2)AC(6)
C(8)AN(3)AC(4)
C(8)AN(4)AC(9)
N(4)AC(8)AN(3)
5
N(1)AC(5)
N(1)AC(1)
N(2)AC(6)
N(3)AC(10)
N(4)AC(9)
1.337(4)
1.472(4)
1.363(5)
1.376(4)
1.368(4)
1.289(4)
1.229(4)
107.1(3)
127.0(3)
107.9(3)
125.3(3)
111.4(3)
125.1(3)
N(1)AC(7)
N(2)AC(5)
N(3)AC(8)
N(3)AC(4)
N(4)AC(8)
O(2)AC(11)
O(4)AC(12)
C(5)AN(1)AC(1)
C(5)-N(2)AC(6)
C(8)AN(3)AC(4)
C(8)AN(4)AC(9)
N(3)AC(8)AN(4)
O(3)AC(12)AO(4)
1.367(5)
1.315(4)
1.321(4)
1.466(4)
1.322(4)
1.214(4)
1.274(4)
125.9(3)
105.1(3)
126.8(3)
108.4(3)
109.3(3)
125.2(3)
O(1)AC(11)
O(3)AC(12)
3.3. X-ray structure of 1,5-bis(1-benzimidazolyl)-3-oxapentane:(5-
nitrosalicylic acid)2 [(H2L2)2+ꢀ(5-nsaꢁ)2, 5-nsaꢁ = 5-nitrosalicylate],
(2)
C(5)AN(1)AC(7)
C(7)AN(1)AC(1)
C(8)AN(3)AC(10)
C(10)AN(3)AC(4)
N(2)AC(5)-N(1)
O(2)AC(11)AO(1)
Crystallization of 1,5-bis(1-benzimidazolyl)-3-oxapentane and
5-nitrosalicylic acid in a 1:1 ratio from the mixed solvent of meth-
anol and ethanol gave single crystals suitable for X-ray diffraction.
Structure determination (Table 1) revealed that 1,5-bis(1-benzim-
idazolyl)-3-oxapentane and 5-nitrosalicylic acid are present in a
1:2 ratio in the molecular complex 2. The crystal structure of 2 con-
sists of half a diprotonated L2, and one monoanion of 5-nitrosalicy-
late in the asymmetric unit (Fig. 3). The CAO distances in the
carboxylate are almost equal with each other within the experi-
mental error, indicating that the negative charge was distributed
equally on both O atoms.
(1.266(5) Å) for the carboxylate. L1 is doubly protonated and the
cation with the NH+ groups on the benzimidazole rings in 1 resem-
bles 4,40-H2bipy cation [33]. The protonated L1 cation displays
trans configuration in which the inversion center is located at C(2).
In the compound, there are two pairs of ion pair with two meth-
anol molecules accompanied, which is well agreement with the
micro-analysis results. In the solid state, there is consistently
hydrogen bonds formed between the NH+ group, and the 5-nitro-
salicylate ions, which is to be expected [34]. There also exist strong
The H2L2 adopts a cis configuration with the planes of the two
benzimidazole rings in the same cation inclined by 54.4°. The two
benzimidazole rings formed dihedral angles of 73.7° with the plane

S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
231
Table 3
Hydrogen bond distances and angles in studied structures 1 – 5.
DAHꢀ ꢀ ꢀA
d(DAH) (Å)
d(Hꢀ ꢀ ꢀA) (Å)
d(Dꢀ ꢀ ꢀA) (Å)
\(DHA)[°]
1
N(2)AH(2)ꢀ ꢀ ꢀO(1)#2
O(3)AH(3)ꢀ ꢀ ꢀO(2)
O(6)AH(6)ꢀ ꢀ ꢀO(1)
0.86
0.82
0.82
1.81
1.78
1.81
2.664(4)
2.507(4)
2.629(5)
176.1
147.4
173.3
2
O(4)AH(4)ꢀ ꢀ ꢀO(3)
0.82
0.86
1.76
1.83
2.498(7)
2.674(8)
148.9
165.9
N(2)AH(2)ꢀ ꢀ ꢀO(2)#2
3
O(3)AH(3)ꢀ ꢀ ꢀO(2)
N(4)AH(4)ꢀ ꢀ ꢀO(1)#1
N(2)AH(2)ꢀ ꢀ ꢀO(2)
N(2)AH(2)ꢀ ꢀ ꢀO(1)
0.82
0.86
0.86
0.86
1.74
1.97
2.50
1.94
2.473(3)
2.802(4)
2.957(4)
2.763(3)
148.5
162.8
114.0
161.0
4
O(3)AH(3)ꢀ ꢀ ꢀO(2)
0.82
0.86
0.86
1.76
1.91
1.77
2.493(3)
2.707(3)
2.630(4)
147.1
153.3
173.0
N(4)AH(4)ꢀ ꢀ ꢀO(6)#1
N(2)AH(2C)ꢀ ꢀ ꢀO(2)#2
5
N(4)AH(4)ꢀ ꢀ ꢀN(2)#1
O(1)AH(1)ꢀ ꢀ ꢀO(4)#2
0.86
0.82
1.85
1.95
2.709(4)
2.506(3)
176.7
124.3
Symmetry transformations used to generate equivalent atoms for 1: #1 ꢁ x + 1, y, ꢁz + 3/2; #2 x + 1/2, y + 1/2, z. Symmetry transformations used to generate equivalent
atoms for 2: #2 x, y ꢁ 1, z + 1. Symmetry transformations used to generate equivalent atoms for 3: #1 x, y ꢁ 1, z. Symmetry transformations used to generate equivalent atoms
for 4: #1 x, y ꢁ 1, z ꢁ 1; #2 x, y + 1, z. Symmetry transformations used to generate equivalent atoms for 5: #1 x ꢁ 1, y, z; #2 x ꢁ 1/2, ꢁy + 5/2, z.
defined by the oxapentane spacer, and the benzene ring of the an-
ion made a dihedral angle of 78° with the plane defined by the oxa-
pentane spacer.
At each imidazolium moiety there was bonded an anion by the
hydrogen bond (N(2)AH(2)ꢀ ꢀ ꢀO(2)#2, 2.674(8) Å) between the NH+
cation and one O atom of the carboxylate and CHAO interaction
between the benzene CH of the cation and another O atom of the
carboxylate with CAO distance of 3.464 Å. Due to these two non-
bonding interactions the carboxylate and the imidazole form a
R22ð8Þ ring according to Bernstein et al. [37]. For the presence of
such interactions two anions and one dication form a heteroad-
duct. The heteroadducts were connected together via the CHAO
interactions generated between the NO2 group and the benzene
CH of the cation with CAO distance of 3.488 Å, and CH2AO interac-
tions between the oxapentane spacer and the NO2 group with CAO
distance of 3.460 Å to form a 1D chain running along the b axis
direction. Here one O atom of the NO2 group functioned as bifur-
cate hydrogen bond acceptor to form a R22ð7Þ graph set with the
cation. Such chains were linked together by the interchain OA
p
interactions (between the carboxylate O that bears a CHAO inter-
action with the cation and the benzene ring of the anion with
OACg distance of ca. 3.195 Å) to form a 2D sheet with the thickness
of ca. 11.970 Å that is extending on the bc plane (Fig. 4). Such
sheets were joined together along the a axis direction via the inter-
sheet CHAO interaction (between the OH group and 3-CH of the
anionic benzene ring with CAO distance of 3.515 Å, and between
the CH of the benzimidazole cation and the carboxylate with
CAO distance of 3.420 Å) to form a 3D network structure.
Fig. 1. The structure of 1, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
bond distance (O(3)AC(10), 1.339(3) Å) concerning the phenol
group indicates that there does not exist phenolate ion. The SAO dis-
tances in SOꢁ3 are ranging from 1.4387(19) to 1.443(2) Å which is in
the range of the deprotonated SO3H group (1.435 (2)–1.4599 (17) Å)
[40]. The carboxylate deviated by 8° from the benzene plane of the
anion.
3.4. X-ray structure of bis(N-imidazolyl)methane:(5-sulfosalicylic acid)
The cation displayed cis conformation. One anion is bounded to
the cation through one ionic hydrogen bond (N(4)AH(4)ꢀ ꢀ ꢀO(1)#1,
[(H2L3)2+ꢀ(5-ssa2ꢁ), 5-ssa2ꢁ = 5-sulfosalicylate], (3)
2.802(4) Å), two CHAO associations, and two CHAp interactions to
Different from compounds 1, and 2, in 3 the asymmetric unit is
occupied by one dianion of 5-sulfosalicylic acid and one dication
of bis(N-imidazol-1-ium)methane (H2L3)+ (Fig. 5). Different from
other reported organic salts containing 5-ssaꢁ monoanion [38,39],
here both protons at the SO3H and COOH groups have ionized, and
the phenol OH remains protonized. It is further verified by the
CAO distances of the carboxylate group [O(1)AC(8), 1.269(4) Å;
form a heteroadduct. One O atom of the sulfonyl group forms two
CHAO associations with both of the NACHAN at the same H2L3 cat-
ion in bifurcate fashion with CAO distances of 3.225–3.259 Å. The
CHAp interactions exist between the NACHAN of the cation and
the benzene ring of the anion and between 6-CH of the anion and
the imidazole ring with CACg distance of 3.499 Å. Like 1, and 2,
the usual intramolecular hydrogen bond is found between the phe-
and O(2)AC(8), 1.257(4) Å with the
D
value of 0.012 Å]. The CAO
nol group and
a
carboxylate
O
atom [O(3)AH(3)ꢀ ꢀ ꢀO(2);

232
S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
Fig. 2. 2D sheet structure of 1 extending on the ac plane.
OAO = 2.473(3) Å], essentially giving coplanarity of the carboxylate
group and the benzene ring [torsion angle O(1)AC(8)AC(9)AC(10);
ꢁ174.85(2)°]. This hydrogen bond geometries were similar to the
documented data [40]. For the presence of this hydrogen bond, com-
pound 3 bears the S11ð6Þ loop motif.
The heteroadducts were linked together by the NAHꢀ ꢀ ꢀO, and
CHAO interactions along the b axis direction to form a 1D chain.
The chains were joined together by the interchain CH2AO and
CHAO interactions to form a 2D sheet extending on the ab plane
(Fig. 6). Here the CH2AO interaction is formed between the CH2
bridge of the cation and the sulfonyl group with CAO distance of
3.354 Å. One 5-CH of the bis-imidazole cation formed two CHAO
interactions in bifurcate mode, i.e. one is with the sulfonyl group
with CAO distance of 3.136 Å, the other CHAO interaction involves
the phenol group with the CAO distance of 3.291 Å. While the
other 5-CH of the same cation is involved in only one CHAO inter-
action with the sulfonyl group with CAO distance of 3.461 Å. For
the presence of such hydrogen bonding interactions the close joint
R22ð8Þ and R22ð6Þ motifs were produced. Such sheets were further
Fig. 3. The structure of 2, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
late are ranging from 1.229(4) (O(1)AC(11)) to 1.282(4)
(O(2)AC(11)) Å with the
D value of 0.053 Å, which suggests that
the carboxyl group is deprotonated, while the N atom of N,N0-but-
ylenebis(imidazole) is protonated. The significant difference in
bond distances between O(1)AC(11) and O(2)AC(11) in the car-
boxylate group is contributed to O(2) is involved in forming more
hydrogen bonds than that of O1 (Table 3). The SAO bond lengths
and the OASAO bond angles in the SOꢁ3 are not perfectly equiva-
lent, but vary with the environment around the O atoms. Their val-
ues reported in Table 2, indicate relatively little distortion from a
regular pyramid.
stacked along the c axis direction via CH2AO, and OAp interactions
to form a 3D network structure. Here the CH2 bridge of the cation
formed two CH2AO associations in bifurcate fashion, one is arised
from the sulfonyl group with CAO distance of 2.961 Å, the other is
arised from the phenol group with CAO distance of 3.197 Å. The
OA
p interaction is formed between the phenol group and the
imidazole ring with the OACg distance of 3.158 Å. The OACg dis-
tance is comparable to the documented data (3.12 Å) [41]. In the
3D network structure, the adjacent sheets were slipped some dis-
In the cation, protonation at atoms N2, and N4 leads to an in-
crease in the C5AN2AC6 [109.42°] and C(8)AN(4)AC(9) [109.06°]
angles compared to that observed in the neutral L4 (104.15(4)°),
and this angle is almost equal to the corresponding angle on its
hydrochloride salt (109.08(3)°) [42]. It was found that protonation
of the imidazole ring nitrogen atoms causes no significant change
in conformation of the (H2L4)2+ dication in 4 in comparison to
the corresponding neutral molecule 1-(4-(1H-imidazol-1-yl)bu-
tyl)-1H-imidazole (L4) [42]. The imidazole rings in 4 have trans-
(ap) position in respect to C2AC3 bond (angle C1AC2AC3AC4,
tance from each other along the a, and
respectively.
b axis directions,
3.5. X-ray structure of 1,4-bis(N-imidazolyl)butane:(5-sulfosalicylic
acid) [(H2L4)2+ꢀ(5-ssa2ꢁ)] (4)
Similar to the salt 3, the asymmetric unit of 4 consists of one
dication of N,N0-butylenebis(imidazole) and one dianion of 5-ssa2ꢁ
,
as shown in Fig. 7. The CAO distances of the COOꢁ of 5-sulfosalicy-

S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
233
Fig. 4. 2D sheet structure of 2 that is extending on the bc 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 on the ab plane.
178.3°), which is different from the corresponding 1,10-(1,4-but-
anediyl)bis(imidazolium) dihydrochloride [42]. The two imidazole
rings in the same cation make a dihedral angle of 167.6° with each
other. The imidazolium rings (N1, N2, C5, C6, C7, and N3, N4, C8,
C9, C10) form dihedral angles of 90.1° and 101.4° with the plane
defined by the C atoms of the A(CH2)4A aliphatic linker in the
(H2L4)2+ cation. Compared with 3, the carboxylate deviated by only
1.3° from the phenyl ring plane of the 5-sulfosalicylate.
The anions and the cations were connected together by the
NAHꢀ ꢀ ꢀO hydrogen bonds to form a 1D chain running along the b
axis direction. The NAHꢀ ꢀ ꢀO hydrogen bonds are formed between
the imidazolium and the carboxylate group (N(2)AH(2C)ꢀ ꢀ ꢀO(2)#2,
2.630(4) Å, 173.0°, #2 x, y + 1, z) and the sulfonyl moiety
(N(4)AH(4)ꢀ ꢀ ꢀO(6)#1, 2.707(3) Å, 153.3°, #1 x, y ꢁ 1, z ꢁ 1). Adja-
cent chains were held together by the interchain CHAO (between
the NACHAN of the cation and the sulfonyl group with CAO

234
S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
interaction between 5-CH of the imidazole and the carboxylate
with CAO distance of 3.229 Å, and CH2AO interaction between
the butane spacer and the sulfonyl group with CAO distance of
3.235 Å to form a double sheet structure. The double sheets were
connected together by the CHAO (between the NACHAN of the
cation and the sulfonyl group with CAO distance of 3.093 Å),
NAHꢀ ꢀ ꢀO (between the NH+ cation and the SOꢁ3 group with NAO
distance of 3.162 Å), CH2AO (between the butane spacer and the
phenol group with CAO distance of 3.305 Å), and CHA
p interac-
tions (between the NACHAN of the cation and the benzene ring
of the anion with CACg distance of 3.661 Å) to form a 3D ABAB
layer network structure. Here the adjacent double sheets were ex-
tended along different directions and made an angle of ca. 30° with
each other, yet the third double sheet has the same project on the
bc plane as the first double sheet, so did the second double sheet
and the fourth double sheet.
3.6. X-ray structure of 1,4-bis(N-imidazolyl)butane:(phthalic acid)
[(HL4)+ꢀ(Hptaꢁ)] (5)
Fig. 7. The structure of 4, showing the atom-numbering scheme. Displacement
ellipsoids were drawn at the 30% probability level.
he asymmetric unit of 5 consists of one monocation of N,N0-but-
ylenebis(imidazole), and one monoanion of phthalic acid, which is
shown in Fig. 9. Different from the above adducts, here only one N
atom of the 1-(4-(1H-imidazol-1-yl)-butyl)-1H-imidazole is pro-
tonated by the phthalic acid. Thus only one proton of the phthalic
acid is deprotonated to maintain the charge neutrality. In the com-
pound, there is one pair of ion pair with no included solvent mole-
cules. In the cation, protonation at the atom N4 leads to an
increase in the C(8)AN(4)AC(9) [108.38°] angle compared to that
observed in the neutral L4 (104.15(4)°), and this angle is slightly
smaller than the corresponding angle in 4 and its hydrochloride salt
(109.08(3)°) [42].
distance of 3.250 Å), CH2AO (between the butane spacer and the
carboxylate group with CAO distance of 3.544 Å), OA
the phenol group of the anion and the imidazole ring with OACg
distance of 2.967 Å), and interactions (between two imidazole
p (between
pAp
rings with CgACg separation of 3.373 Å). Here the OACg distance is
significantly shorter than the OACg distance in 3. Under these
interactions the chains were combined together to form a 2D sheet
extending along the bc plane (Fig. 8). The two adjacent sheets were
joined together along the a axis direction via the intersheet CHAO
Fig. 8. 2D sheet structure of the salt 4 which is viewed along the a axis direction.
Fig. 9. The structure of 5, showing the atom-numbering scheme. Displacement ellipsoids were drawn at the 30% probability level.

S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
235
Fig. 10. 3D ABAB layer structure of the salt 5.
Similar to 4, protonation of the imidazole ring N atoms causes no
significant change in conformation of (HL4)+ in 5 in comparison to
the corresponding neutral molecule L4 [42]. Different from the salt
of 1,10-(1,4-butanediyl)bis(imidazolium) dihydrochloride [42], the
imidazole rings in 5 have trans-(ap) position in respect to C2AC3
bond (angle C1AC2AC3AC4, 179.46°).
aration of 2.506(3) Å to form a 2D sheet extending on the ab plane.
The cations also formed a 1D chain running along the a axis direc-
tion through the NAHꢀ ꢀ ꢀN hydrogen bond between the NH+ group
and the unprotonated imidazole N atom with NAN separation of
2.709(4) Å. Two adjacent chains were combined together by the
CHAp, and pAp interactions between the protonated imidazole
The two imidazole rings have a dihedral angle of 15.3°. The two
imidazolium rings (N1, N2, C5, C6, C7; and N3, N4, C8, C9, C10)
make dihedral angles of 36.6°, and 51.9 (3)° with the plane defined
by the C atoms of the A(CH2)4A aliphatic linker in the HL4 cation,
respectively. The dihedral angles are significantly smaller than
those in 4, which may be attributed to the different hydrogen
bonding strength existed in the two compounds. The carboxylates
deviated by 43° (O(1)AC(11)AO(2)), and 125.4° (O3AC12AO4)
from the phenyl ring plane of the phthalate, respectively, which
is different from the reported adduct of phthalate in which the car-
boxylates are almost coplanar with the phenyl ring [43].
moieties and the unprotonated imidazole moieties to form a
cationic double chain. There are no NAHꢀ ꢀ ꢀO, and OAHꢀ ꢀ ꢀN hydro-
gen bonds between the cations and the anions.
The cationic double chains were intercalated between the anion
sheets through the CHAO, CH2AO, and CHAp interactions to form
a 3D ABAB layer network structure (Fig. 10). The double chains
were linked with the first sheet layer through CHAO interactions
that include the CHAO interaction between 2-CH of the unproto-
nated imidazole unit and the carboxylate with CAO distance of
3.536 Å, the CHAO interaction between 4-CH of the protonated
imidazole unit and the C@O of the COOH with CAO distance of
3.201 Å, and the CHAO interaction between 5-CH of the protonated
imidazole and the COOꢁ with CAO distance of 3.226 Å. There are
also CH2AO associations generated between the butane CH2 of
the cation and the C@O of the first anionic sheet with CAO distance
of 3.498 Å.
The cationic double chains were connected with the second an-
ionic sheet layer through CHAO interactions that include the
CHAO interaction between 2-CH of the protonated imidazole unit
and the carboxylate with CAO distance of 3.181 Å, the CHAO inter-
action between 4-CH of the unprotonated imidazole unit and the
COOꢁ with CAO distance of 3.522 Å, and the CHAO interaction be-
tween 5-CH of the unprotonated imidazole unit and the COOꢁ
group with CAO distance of 3.211 Å. There are CH2AO associations
generated between the butane spacer of the cation and the carbox-
ylate of the second anionic sheet with CAO distance of 3.463 Å.
There are also CH2AO associations produced between the butane
bridge of the cation and the phenol group of the second anionic
It is clear that the difference in bond lengths of CAO within
the carboxyl group (0.075 Å) is much greater than the one found
in the phthalate anions (0.045 Å). Also the average distance for
CAO (1.251 Å) in the phthalate is less than the single bond CAO
(1.289(4) Å) and greater than the double bond C@O (1.214(4) Å)
in the carboxyl group of the phthalic acid. This supports our
correct assignment of the phthalate anions. So the negative
charge in COꢁ2 group is localized on O(4) atom. Whereas the cor-
0
responding distances for COꢁ2 ꢀ ꢀ ꢀHOOC (O(1)AC(11), 1.289(4) ÅA)
support the existence of non-ionic acid moieties indicating
co-crystal formation.
The anions formed a 1D chain along the b axis direction via the
CHAO interactions between the benzene CH of one anion and the
carbonyl group of its neighboring anion with CAO distance of
3.493 Å. In the chain the anions were arranged in head to tail fash-
ion. The COOH groups on the adjacent chains were directed toward
opposite directions, i.e. at one chain the carboxyl is directed to the
+b axis direction, while the carboxyl on its neighboring chain is di-
rected to the ꢁb axis direction. So did the COOꢁ groups. The chains
arranged in such a fashion on the ab plane alternatively and they
are joined together by the interchain OAHꢀ ꢀ ꢀO hydrogen bond be-
tween the COOH group and the carboxylate group with OAO sep-
sheet with CAO distance of 3.557 Å. There also exist CHAp interac-
tions between 2-CH of the protonated imidazole and the anionic
benzene ring of the second sheet layer with CACg distance of
3.618 Å. Obviously these interactions contribute to the formation
and stabilization of the final 3D structure.

236
S. Jin et al. / Journal of Molecular Structure 1004 (2011) 227–236
4. Conclusion
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Acknowledgements
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 Uni-
versity Science Foundation (Project No. 2009FK63).