Network formation of bis(2-benzimidazylmethyl)amine in salts with carboxylic acids: The structures based on the interplay of strong and weak intermolecular interactions

Article abstract of DOI:10.1021/cg2006748

Six new organic salts containing flexible and polydentate bis(2-benzimidazylmethyl)amine (BBMA) and a variety of carboxylic acids, including benzoic acid (HBA), p-nitrobenzoic acid (4-NHBA), 3,5-dinitrobenzoic acid (3,5-DiNHBA), terephthalic acid (H₂

Full text of DOI:10.1021/cg2006748

ARTICLE
pubs.acs.org/crystal
Network Formation of Bis(2-benzimidazylmethyl)amine in Salts with
Carboxylic Acids: The Structures Based on the Interplay of Strong and
Weak Intermolecular Interactions
Baoming Ji,*,† Dongsheng Deng,† Ning Ma,† Shaobin Miao,† Liguo Ji,†,‡ Peng Liu,†,§ and Xianfei Li†,#
†College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang 471022, P. R. China
‡College of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao 266555, P. R. China
§Department of Chemistry, Zhengzhou University, Zhengzhou 450052, P. R. China
#Northwest Agriculture and Forest University, Yangling 712100, P. R. China
ABSTRACT: Six new organic salts containing flexible and
polydentate bis(2-benzimidazylmethyl)amine (BBMA) and a
variety of carboxylic acids, including benzoic acid (HBA),
p-nitrobenzoic acid (4-NHBA), 3,5-dinitrobenzoic acid (3,5-
DiNHBA), terephthalic acid (H2TPA), trimesic acid (H3T-
MA), and pyromellitic acid (H4PMA), formulated as (HB-
BMA) (HBA) (BA) (1), (HBBMA) (4-NBA) (4-NHBA) (2),
3
3
3
3
(H2BBMA) (3,5-DiNBA)2 (3), (H2BBMA) (TPA) (H2-
3
3
3
TPA)0.5 DMF (4), (H2BBMA) (H2TMA)2 DMF (5), and (H2BBMA) (H2PMA) (6), have been synthesized. The salts were
3
3
3
3
characterized by elemental analysis, IR, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction, to
understand how variations in their molecular structures and intermolecular interactions influence their supramolecular assemblies. Proton
transfer from the COOH to benzimidazole N acceptor (BimN) occurred in the six organic salts (1ꢀ6), leading to the ionic heterosynthon
VI in all structures. Competition and cooperation between COOH, COOꢀ, BimNH+, BimN, -NH2 -, and -NH- functional groups for the
+
observed hydrogen bond synthons are examined in the six structures. To the best of our knowledge, there are no systematic studies on
hydrogen bond competition and interplay when the above six H-bonded donors or acceptors are present in the same crystal structure. It is
noted that CꢀH O hydrogen bonds increase the dimensionality of the supramolecular architectures of the six salts (from one-
3 3 3
dimensional (1-D) to two-dimensional (2-D) in 1; from 1-D to three-dimensional (3-D) in 2, from zero-dimensional (0-D) to 3-D in 3,
from 2-D to 3-D in 5, from 1-D to 2-D in 6).
’ INTRODUCTION
synthons12 between common functional groups is a first step
toward crystal engineering. Strong and specific recognition of the
carboxylic acid group with pyridine (acid-pyridine synthon) is
well studied.13ꢀ18 However, the recognition pattern between the
carboxylic acid group and imidazole (acid-imidazole synthon)
remains less well-explored.
Multicomponent crystals and acidꢀbase complexes have
received considerable attention over the past few years1,2 not
only because of their intriguing structural motifs3,4 but also for
their useful properties and promising applications as func-
tional materials.5,6 An advantage in fabricating cocrystals or
salts is that a number of closely related X-ray crystal structures
may be determined to understand the relationship among
intermolecular forces, molecular shapes, and crystal struc-
tures, which represents the fundamental aspect in supramo-
lecular chemistry.7,8
Carboxylic acids represent one of the most prevalent func-
tional groups in crystal engineering because they possess a
hydrogen bond donor and acceptor with a geometry that
facilitates self-association through supramolecular homosyn-
thons. Indeed, carboxylic acids are well-known to self-associate
via centrosymmetric dimer (I) or catemer (II).9ꢀ11 Further-
more, it is now recognized that carboxylic acids are ideal
candidates for multicomponent crystals since they form persis-
tent supramolecular heterosynthons with a number of different
complementary functional groups such as aromatic nitrogen,
phosphonyls, and sulfonyls. The identification of supramolecular
Recently, we and others have made efforts to use organic salts
as molecular building blocks to control molecular packing in
crystalline materials.19ꢀ25 In this regard, a series of salts formed
by imidazoles with carboxylic acids were chosen to investigate its
supramolecular synthons and provided the experimental data to
validate the work toward the a priori prediction of organic salt
crystal structures.19ꢀ25 A survey of the Cambridge Structural
Database (CSD) indicates that 79% of complexes that contain
both imidazole and carboxyl groups generate imidazolium-
carboxylate supramolecular heterosynthons rather than carbox-
yl or imidazole supramolecular homosynthons.19 Moreover,
there is a mix of neutral OꢀH
N and ionic N+ꢀH
Oꢀ
3 3 3
3 3 3
Received: May 28, 2011
Revised:
August 2, 2011
Published: August 03, 2011
r
2011 American Chemical Society
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Crystal Growth & Design
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Scheme 1. Supramolecular Homosynthons (I, II, and III) and Heterosynthons (IV, V, and VI, VII, VIII, IX, X, XI)
Scheme 2. Two-Step Protonation Processes of BBMA
acid-imidazole synthons in these crystal structures. All these
findings indicate that there is indeed a strong competition
between the anion and the neutral molecule toward recognition
in the available receptors. For the polybenzimidazole, except for
homosynthons III, there are five variants of the acid-imidazole
heterosynthon in crystal structures: neutral, one-point (IV, V,
XI); and ionic, single-point (VI, VIII), as depicted in Scheme 1.
The carboxylic acid OH donor is localized on the acid group, and
benzimidazole N or amino N is the acceptor in neutral synthons
(IV, V, XI). When there is a sufficient pKa difference between the
COOH and benzimidazole groups, proton transfer will occur to
attempted to isolate different degrees of protonated receptors
of BBMA at different experimental conditions to study the
recognition pattern of anion vs cation. In this contribution, we
will present a systematic investigation on such organic salts of
BBMA and demonstrate the reliable supramolecular syn-
thons. Indeed, proton transfer from carboxyl to benzimida-
zole is found, and crystallization of BBMA with various
carboxylic acids (see Scheme 3) produce ordered lattices by
supramolecular synthons II, III, IV, V, VI, VII, VIII, IX, X,
and XI. A schematic representation of H-bonding synthons
related to this work is summarized in Scheme 1.
give an ionic hydrogen bond N+ꢀH Oꢀ, which can exist as a
3 3 3
single interaction, (VI) and (VIII). The transfer from neutral to
’ EXPERIMENTAL SECTION
ionic hydrogen bond as a continuum of intermediate NꢀH
O
3 3 3
bond states has ever been noted.19ꢀ23,26ꢀ29 The issue of whether
the acid-imidazole synthon is neutral or ionic is more than a
physical and structural chemistry problem, thanks to the legal and
patent implications of pharmaceutical cocrystals and salts.30
On the other hand, compared to tris(2-benzimidazyl-
methyl)amine, the bis(2-benzimidazylmethyl)amine is a more
flexible molecule, and thus conformational changes will lead
to a changeable array of intermolecular interactions based on
the binding sites, which probably results in a variety of
crystalline architectures with desirable connectivity and me-
trics. Meanwhile, it is noted that the BBMA can exhibit two-
step proton-transfer processes to give protonated species,
HBBMA+, H2BBMA2+ (i), and H2BBMA2+ (ii), as shown in
Scheme 2. These species exhibit a diverse directionality
intrinsic to the BBMA system and construct multidimensional
network structures. At this juncture, as a case study we have
Materials and General Procedures. Starting materials and
solvents for synthesis were purchased commercially and used as
received. The ligand BBMA was prepared according to reported
procedures.31 IR spectra were recorded as KBr pellets on a Nicolet
Magna 750 FTꢀIR spectrometer in the 4000ꢀ400 cmꢀ1 region.
Elemental analyses for C, H, and N were performed on a Flash 1112
elemental analyzer. Powder X-ray diffraction (PXRD) patterns were
recorded using a Rigaku D/Max-IIIA diffractometer from 2° to 60° with
a step size of 0.02° and a scan speed of 0.3 s preset time. Thermogravi-
metric analyses were carried out on a SDT Q600 analyzer. A platinum
pan was used for heating the sample, and the analyses were carried out in
nitrogen at a heating rate of 10 °C/min in the temperature range
25ꢀ700 °C.
General Procedure for the Preparation of the Compounds
(1ꢀ6). A mixture of the bis(2-benzimidazylmethyl)amine and aromatic
acid in a molar ratio of 1:2 was heated with gentle stirring at 60ꢀ80 °C
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Crystal Growth & Design
ARTICLE
Scheme 3. Molecular Components Used in This Work
unit cell parameters were determined by a least-squares fit of 2θ values,
and intensity data were measured on a Bruker SMART APEX II CCD
diffractometer equipped with graphite-monochromatized MoꢀKR ra-
diation (λ = 0.71073 Å) at room temperature. The intensities were
corrected for Lorentz and polarization effects as well as for empirical
absorption based on a multiscan technique. The structures were solved
by direct methods and refined by full-matrix least-squares
(SHELXTLꢀ97)32,33 with anisotropic thermal parameters for all non-
H atoms. The H atoms were introduced in calculated positions and
refined with fixed geometry with respect to their carrier atoms. Details of
crystal data, data collection, and refinement parameters are given in
Table 1.
’ RESULTS AND DISCUSSION
for 1 h in DMF and then cooled to room temperature. The undissolved
materials were removed by filtration. The filtrate was set aside to
crystallize. After one week, the single crystals suitable for X-ray analysis
were obtained.
IR Spectral Studies. Compared with the IR spectra of
organic salts 1ꢀ6, it was found that the asymmetric CdO
stretches for 1, 2, 3, 4, 5, and 6 occur at 1541, 1560, 1541, 1547,
1547, and 1578 cmꢀ1, while the symmetric CdO stretches for
1, 2, 3, 4, 5, and 6 appear at 1369, 1341, 1343, 1374, 1371, and
1361 cmꢀ1, respectively. The positions of these stretches clearly
show the presence of carboxylate groups. It is pointed out that
the IR spectra of 4 and 5 also display the CdO stretching
vibration of DMF at 1677.6 cmꢀ1, indicating the presence of
DMF. This can be further confirmed by the crystal structure
analyses of 4 and 5.
Description of Structures. In DMF, cocrystallization of
BBMA with each of the acid coformers (Scheme 3) led to salt
solid forms (1ꢀ6) as confirmed by single crystal X-ray
diffraction experiments. In all cases, the 1:2 or 1:1 (cation/
anion) stoichiometry expected30 from the ratio of hydrogen
bond donors to acceptors was found in the salts. It must be
pointed out that crystals suitable for single crystal X-ray
diffraction experiments could not be grown when BBMA was
cocrystallized with phthalic acid or isophthalic acid. In addi-
tion, as a consequence of the low solubility of the base and acid
species in other organic solvents such as methanol, acetone,
acetonitrile, benzene, and toluene, the combination of them
only led to the formation of a lot of precipitates. The crystal-
lographic data for the novel crystal structures are reported in
Table 1, and the hydrogen bond parameters for all solid forms
are given in Table 2.
(HBBMA) (BA) (HBA) (1), the yield was 86% based on the
3
3
BBMA. Mp: 253.0ꢀ255.0 °C. Anal. Calcd. for C30H27N5O4: C,
69.08; H, 5.22; N, 13.43 (%). Found: C, 68.99; H, 5.27; N, 13.31 (%).
IR: 3300 (w), 1727 (s), 1667 (w), 1627 (w), 1593 (m), 1541 (s),
1514(m), 1448 (m), 1369(vs), 1312 (m), 1300 (m),1270 (m), 1151
(m), 1116 (w), 1050 (m), 1017 (w), 1003 (w), 948 (w), 903 (m), 802
(m), 752 (s), 740 (s), 713 (vs), 690 (m), 668 (s) cmꢀ1
.
(HBBMA) (4-NBA) (4-NHBA) (2), the yield was 77% based on
3
3
the BBMA. Mp: 195.0ꢀ197.0 °C. Anal. Calcd. for C30H25N7O8: C,
58.92; H, 4.12; N, 16.03 (%). Found: C, 58.79; H, 4.20; N, 16.15 (%).
IR: 3431 (w), 3293 (w), 3047 (m), 2923.7 (m), 2869 (m), 2742 (m),
1725 (s), 1628 (m), 1560 (vs), 1519 (s), 1488 (w), 1456 (m), 1375
(m), 1341 (vs), 1316 (s), 1149 (w), 1103 (w), 1059 (w), 1004 (w),
967 (w), 882 (m), 859 (w), 797 (m), 751 (s), 723 (s), 620 (w),
476(w) cmꢀ1
.
(H2BBMA) (3,5-DiNBA)2 (3): the yield was 82% based on the
3
BBMA. Mp: 201.0ꢀ203.0 °C. Anal. Calcd. for C30H23N9O12: C, 51.36;
H, 3.30; N, 17.97 (%). Found: C, 51.41; H, 3.19; N, 18.05 (%).IR: 3434
(w), 3162 (w), 3113 (w), 3064 (w), 1625 (m), 1541 (vs), 1458 (m),
1446 (m), 1387 (m), 1343 (vs), 1275 (w), 1221 (m), 1124 (w), 1071
(m), 954 (w), 920 (w), 877 (w), 844 (w), 789 (w), 766 (m), 750 (m),
729 (s), 715 (s), 644 (w), 610 (m), 558 (w), 527 (w) cmꢀ1
.
(H2BBMA) (TPA) (H2TPA)0.5 DMF (4), the yield was 76%
3
3
3
based on the BBMA. Mp: 247.0ꢀ249.2 °C. Anal. Calcd. for
C31H31N6O7: C, 62.10; H, 5.21; N, 14.02 (%). Found: C, 62.31; H,
5.07; N, 13.92 (%). IR: 3305 (m), 3071 (m), 1722 (s), 1679(s), 1625
(m), 1610 (m), 1547 (s), 1440 (m), 1402 (m), 1374 (m), 1256 (s), 1210
(s), 1168 (s), 1107 (m), 1017 (w), 981 (w), 932 (w), 890 (w), 802 (w),
Salt of Bis(2-benzimidazylmethyl)amine Benzoic Acid
(1:2) (1). The structure has the space group P2(1)/c with one
monoprotonated HBBMA+ cation, one benzoate anion (BA),
and one HBA within the asymmetric unit. The carboxylic acid
proton is transferred to the benzimidazole nitrogen. In the crystal
structure, the HBBMA+ cations are bridged by benzoate anions
via NꢀH O hydrogen bonds (synthon VI: N O =
756 (s), 700 (w), 680 (s), 669 (s), 617 (m), 536 (w), 421 (m) cmꢀ1
.
(H2BBMA) (H2TMA)2 DMF (5): the yield was 63% based on the
3
3
BBMA. Mp: 245.8ꢀ247.2 °C. Anal. Calcd. for C37H34N6O13: C, 57.66;
H, 4.45; N, 10.90 (%). Found: C, 57.81; H, 4.60; N, 10.72 (%). IR: 3384
(m), 3064 (m), 2609 (m), 1721 (s), 1678 (s), 1628 (m), 1607 (m), 1545
(s), 1440 (m), 1409 (m), 1371 (m), 1257 (s), 1208 (s), 1170 (s), 1104
(m), 1012 (w), 989 (w), 936 (w), 893 (w), 800 (w), 749 (s), 699 (w),
3 3 3
3 3 3
2.637(3) Å; synthon VII: N O = 2.863(2) and 2.761(2) Å;
3 3 3
synthon X: N O = 3.292(2) Å) to form a one-dimensional
3 3 3
(1-D) chain, as shown in Figure 1a. Along the hydrogen-bonded
1-D chain, each HBA is anchored to benzimidazole N atom via
OꢀH N bonds (synthon IV: O N = 2.559(3) Å). The
682 (s), 667 (s), 619 (m), 530 (w), 409 (m) cmꢀ1
.
(H2BBMA) (H2PMA) (6): the yield was 75% based on the
3 3 3
3 3 3
3
neighboring hydrogen-bonded chains are held together via
BBMA. Mp: 229.0ꢀ232.0 °C. Calcd. for C26H21N5O8: C, 58.76;
H, 3.98; N, 13.18 (%). Found: C, 58.91; H, 4.10; N, 12.95 (%). IR:
3373 (w), 3068 (m), 2922 (m), 2755(m), 2632 (m), 2515 (m), 1729
(s), 1624 (m), 1578 (s), 1461 (vs), 1405 (s), 1361 (vs), 1293 (m),
1223 (m), 1142 (s), 1092 (m), 1014 (m), 890 (m), 763 (m), 752 (m),
additional CꢀH O interactions to form a two-dimensional
3 3 3
(2-D) layer (C O = 3.348(4) and 3.395(3) Å, respectively), as
3 3 3
shown in Figure 1b.
Salt of Bis(2-benzimidazylmethyl)amine 4-Nitrobenzoic
Acid (1:2) (2). Bis(2-benzimidazylmethyl)amine with 4-nitrobe-
zoic acid form 1:2 salt 2 through the monoproton transfer in the
space group P2(1)/c. The asymmetric unit of 2 contains one
680 (m), 615 (m) cmꢀ1
.
X-ray Crystallographic Measurements. Suitable single crystals
of 1ꢀ6 were selected and mounted in air onto thin glass fibers. Accurate
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Crystal Growth & Design
ARTICLE
Table 1. Crystallographic and Experimental Data for Organic Salts 1ꢀ6
organic salts
1
2
3
4
5
6
CCDC number
formula
M
820586
C30H27N5O4
521.57
820587
C30H25N7O8
611.57
820591
C30H23N9O12
701.57
orthorhombic
P2(1)/c
8.5018(11)
28.411(4)
12.7009(16)
90
820588
820589
C37H34N6O13
770.70
820590
C31H31N6O7
599.62
C26H22N5O8
532.49
crystal system
space group
a/Å
monoclinic
P2(1)/c
17.5925(19)
9.5612(11)
16.7805(19)
90
monoclinic
P2(1)/c
18.793(3)
9.4762(15)
16.807(3)
90
triclinic
triclinic
P1
triclinic
P1
P1
10.1284(12)
11.7095(14)
14.5623(17)
72.0820(10)
70.2570(10)
69.1370(10)
1484.1(3)
2
8.583(2)
13.886(3)
14.780(4)
83.222(3)
88.057(3)
89.200(3)
1748.2(7)
2
7.431(2)
8.113(2)
10.178(3)
101.341(4)
90.255(4)
103.227(4)
584.9(3)
1
b/Å
c/Å
R/°
β/°
γ/°
volume/Å3
111.7930(10)
90
107.759(2)
90
90
90
2620.8(5)
4
2850.5(8)
4
3067.9
4
Z
Dcalc/g cmꢀ3
μ/mmꢀ1
T/K
1.322
1.425
1.519
1.342
1.464
1.512
0.090
0.106
0.121
0.097
0.113
0.115
296(2)
291(2)
20622
291(2)
22387
296(2
291(2)
13032
293(2)
3803
reflns collected
unique reflns
R1(I > 2σ)
wR2(I > 2σ)
15707
11380
4878
5303
5712
5483
6436
2110
0.0470
0.0433
0.0411
0.1066
0.0575
0.0662
0.0516
0.1123
0.1074
0.1561
0.1759
0.1136
deprotonated 4-nitrobenzoate anion (4-NBA), one 4-NHBA,
bonding regardless of possessing the potential to act as hydrogen
bond acceptors. The results indicate that the strong hydrogen
bond-directed network in this salt is in such a way as to match the
strongest donor and the strongest acceptor first. Meanwhile, it
must be pointed out that all N atoms in the H2BBMA2+ (ii)
cations participate in hydrogen bonding. Further analysis of the
crystal packing reveals that the 0-D six-component aggregates are
and one HBBMA+ cation. As observed in 1, the HBBMA+ cations
are bridged by 4-nitrobenzoate anions via NꢀH
O hydro-
3 3 3
O = 2.656(2) Å; synthon VII:
gen bonds (synthon VI: N
3 3 3
N
O = 2.811(2) and 2.9062(19) Å) to form a 1-D chain, as
shown in Figure 2a. Along the hydrogen-bonded 1-D chain,
3 3 3
each 4-NHBA is anchored to benzimidazole N atom via Oꢀ
H
N bonds (synthon IV: O
N = 2.561(2) Å). In addition,
further connected by weak CꢀH O hydrogen bonds between
3 3 3
3 3 3
3 3 3
3,5-DiNBA anions and H2BBMA2+ (ii) cations, leading to a 3-D
network, as depicted in Figure 3b.
the 4-NHBA molecules also function as a bridge to link the
adjacent 1-D chains via NꢀH O bonds (synthon XI:
3 3 3
O = 2.980(2) Å), resulting in a 2-D layer, as shown in
N
Salt of Bis(2-benzimidazylmethyl)amine Terephthalic
Acid (1:2) (4). Bis(2-benzimidazylmethyl)amine and terephtha-
lic acid afforded a crystalline organic salt 4, in a 1:2 ratio, which
has a 3-D framework with 1-D channels that are filled with DMF
molecules. In the asymmetric unit of 4, there are one di-
deprotonated terephthalate anion (TPA), half of one H2TPA
molecule, one H2BBMA2+ (i), and one DMF molecule. Synthons
II, V, VI, and VII can be formed in the supramolecular assembly
of 4, as shown in Figure 4a. In 4, two carboxylic groups in each
H2TPA and two carboxylate groups in each TPA anion take part
in different hydrogen-bonding modes. First, each ꢀCOOH
group of a H2PA not only connects the adjacent ꢀCOOꢀ
3 3 3
Figure 2b. Moreover, the layers are connected by weak Cꢀ
H
O hydrogen bonds between 4-NBA anions and HBBMA+
cations, forming a three-dimensional (3-D) network, as de-
picted in Figure 2c.
3 3 3
Salt of Bis(2-benzimidazylmethyl)amine 3,5-Dinitroben-
zoic Acid (1:2) (3). Bis(2-benzimidazylmethyl)amine and 3,5-
dinitrobenzoic acid afforded a crystalline organic salt 3, in a 1:2
ratio, which has a 3-D framework. In the asymmetric unit of 3,
there are two 3,5-DiNBA anions and one H2BBMA2+ (ii).
Synthons III, VI, VII, VIII, and IX can be formed in the
supramolecular assembly of 3. Two H2BBMA2+ (ii) cations are
connected in a head-to-head pattern via two NꢀH N hydro-
3 3 3
group of the terephthalate anion via OꢀH
O hydrogen
O = 2.456(2) Å) but also links
3 3 3
gen bonds (synthon III: N N = 2.808(2) Å), creating a
3 3 3
bonds to give synthon II (O
3 3 3
centrosymmetric dimer. This structure is different from that
observed in 1 and 2, maybe due to the different protonated sites
of bis(2-benzimidazylmethyl)amine. In 1 and 2, the site only
situates the benzimidazole N atoms, while in 3, one site is one
benzimidazole N atom, and the other one is amine N atom. As
depicted in Figure 3a, each dimer links four 3,5-DiNBA anions
the adjacent H2BBMA2+ (i) via NꢀH
O hydrogen bonds
3 3 3
(synthon VII: N
O = 2.674(3) Å). Second, one ꢀCOOꢀ
3 3 3
group of a PA anion connects the adjacent H2TPA and
H2BBMA2+, forming one OꢀH
O and one NꢀH
O
3 3 3
3 3 3
hydrogen bond, respectively, synthon VI: N O = 2.692(3) Å.
3 3 3
The other one connects the neighboring H2BBMA2+ (i) via
through the formation of NꢀH O hydrogen bonds between
3 3 3
the 3,5-DiNBA anion and H2BBMA2+ (ii) cation (synthon VI:
NꢀH
O hydrogen bond (synthon VI: N
O = 2.550(3);
3 3 3
3 3 3
synthon VII: N
O = 2.734(3) Å). As a result, these
N
O = 2.667(2) Å; synthon VII: N O = 2.742(2) Å;
3 3 3
3 3 3
3 3 3
hydrogen bonds extend the acidꢀbase subunits to form a
synthon VIII: N O = 2.561(2) Å; synthon IX: N O =
2.755(2) Å), leading to a 0-D six-component aggregate. It should
be noted that no nitro groups are involved in strong hydrogen
3 3 3
3 3 3
3-D framework with 1-D channels that are occupied by DMF
molecules. Furthermore, CꢀH
O hydrogen bond is
3 3 3
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Crystal Growth & Design
ARTICLE
Table 2. Geometrical Parameters of Hydrogen Bonds
salts
DꢀH
A
H
A (Å)
D
A (Å)
DꢀH A (deg)
symmetry codes
3 3 3
3 3 3
1.99
3 3 3
3 3 3
1
N1ꢀH1 O4
2.846(2)
3.105(3)
2.863(2)
2.637(3)
3.292(2)
2.560(3)
3.160(2)
2.8111(18)
2.980(2)
2.656(2)
2.9062(19)
2.5614(19)
2.808(2)
2.667(2)
2.775(2)
2.561(2)
2.742(2)
2.734(2)
2.674(3)
2.550(2)
2.691(2)
2.456(2)
2.991(4)
2.199(3)
2.889(3)
2.690(3)
2.383(3)
2.843(3)
2.708(3)
2.590(3)
2.594(3)
2.633(3)
2.612(3)
2.651(10)
2.688(12)
2.738(10)
2.688(10)
2.385(3)
171.3
117.9
169.7
165.3
139.8
165.9
119.7
171.4
144.6
170.7
167.9
167.9
175.7
167.8
163.7
168.2
148.7
149.4
165.6
152.9
171.8
162.9
114.0
121.3
145.8
175.9
161.3
156.4
169.6
149.6
168.6
147.4
164.4
170.2
173.3
160.7
177.5
172.8
ꢀx + 1, y + 1/2, ꢀz + 1/2
ꢀx + 1, y + 1/2, ꢀz + 1/2
ꢀx + 1, y + 1/2, ꢀz + 1/2
x + 1, ꢀy, ꢀz + 1
ꢀx + 1, y + 1/2, ꢀz + 1/2
x, y + 1, z
3 3 3
N1ꢀH1 O3
2.61
2.01
1.80
2.59
1.76
2.64
1.96
2.19
1.80
2.06
1.75
1.95
1.82
1.88
1.67
1.97
1.96
1.83
1.75
1.84
1.66
2.54
2.67
2.14
1.83
2.56
2.03
1.86
1.85
1.78
1.91
1.81
1.80
1.83
1.91
1.83
1.57
3 3 3
N3ꢀH3 O4
3 3 3
N4ꢀH4A O3
3 3 3
N5ꢀH5A O4
3 3 3
O2ꢀH2 N2
3 3 3
2
N5ꢀH5D O2
x, y ꢀ 1, z
x, y ꢀ 1, z
x, ꢀy + 1/2, z + 1/2
x, ꢀy + 3/2, z + 1/2
x, y ꢀ 1, z
ꢀx, y ꢀ 1/2, ꢀz + 1/2
ꢀx + 1, ꢀy + 1, ꢀz + 1
ꢀx + 1, ꢀy + 1, ꢀz
ꢀx + 1, ꢀy + 1, ꢀz
3 3 3
N5ꢀH5D O1
3 3 3
N3ꢀH3D O6
3 3 3
N2ꢀH2D O2
3 3 3
N1ꢀH1D O1
3 3 3
O5ꢀH5C N4
3 3 3
3
4
5
N5ꢀH5D N1
3 3 3
N4ꢀH4D O7
3 3 3
N3ꢀH3A O8
3 3 3
N3ꢀH3B O2
3 3 3
N2ꢀH2D O8
ꢀx + 1, ꢀy + 1, ꢀz
ꢀx, ꢀy, ꢀz + 1
3 3 3
N1ꢀH1 O2
3 3 3
N2ꢀH2 O5
3 3 3
N4ꢀH4A O1
3 3 3
N5ꢀH5A O3
x, y, z-1
3 3 3
O6ꢀH6 O4
x, y, z-1
3 3 3
N5ꢀH5D O12
ꢀx + 1, ꢀy + 1, ꢀz + 1
ꢀx + 2, ꢀy + 1, ꢀz + 1
ꢀx + 2, ꢀy + 1, ꢀz + 1
3 3 3
N5ꢀH5D O130
3 3 3
N5ꢀH5D O8
3 3 3
N4ꢀH4D O2
3 3 3
N3ꢀH3D O10
x + 1, y, z ꢀ 1
3 3 3
N2ꢀH2D O3
ꢀx + 2, ꢀy, ꢀz + 1
x, y, z ꢀ 1
3 3 3
N1ꢀH1D O9
3 3 3
O11ꢀH11 O9
x ꢀ 1, y, z
3 3
O7ꢀH7 O1
ꢀx + 1, ꢀy + 1, ꢀz + 1
x ꢀ 1, y, z
3 3
O6ꢀH6 O2
3 3 3
O4ꢀH4 O10
ꢀx + 1, ꢀy, ꢀz + 2
ꢀx + 1, ꢀy + 1, ꢀz + 1
x + 1, y + 1, z + 1
x + 1, y + 1, z + 1
ꢀx + 1, -y + 1, -z + 1
-x+1, -y, -z+1
3 3 3
6
N1ꢀH1 O1
3 3 3
N2ꢀH2 O3
3 3 3
N4ꢀH4A O1
3 3 3
N5ꢀH5 O3
3 3 3
O4ꢀH4 O2
3 3 3
observed in the structure, which further consolidates the
crystal packing.
synthon II: O
O = 2.633(3) Å), as well as one OꢀH
O
3 3 3
3 3 3
hydrogen bond (synthon II: O
O = 2.594(3) Å). Second,
3 3 3
unlike the ꢀCOOꢀ group, one of two ꢀCOOH groups links
Salt of Bis(2-benzimidazylmethyl)amine Trimesic Acid
(1:2) (5). Trimesic acid crystallizes readily with 0.5 equiv of
bis(2-benzimidazylmethyl)amine, yielding organic salts 5. The
asymmetric unit of 5 consists of two mono-deprotonated
trimesic acid anions, one diprotonated bis(2-benzimidazyl-
methyl)amine cation, and one DMF molecule. Analysis of the
intermolecular interactions reveals that trimesic acid does not
introduce a typical extended honeycomb topology;34 two
carboxylic groups and one carboxylate group in each H2TMA
anion are involved in different hydrogen-bonding modes. First,
one ꢀCOOꢀ group in a trimesic acid unit connects one
adjacent H2BBMA2+ (i) cation and two neighboring H2TMA
two adjacent H2BBMA2+ (i) cations and one neighboring
H2TMA anion, creating one OꢀH
N and one OꢀH
O
3 3 3
3 3 3
hydrogen bond (synthon VII: N
O = 2.889(4) Å, synthon
3 3 3
II: O
O = 2.611(3) Å). Finally, the other one ꢀCOOH
3 3 3
group links adjacent H2TMA anion to construct one OꢀH
O
3 3 3
hydrogen bond (synthon II: O O = 2.590(3) Å). These
3 3 3
synthons are depicted in Figure 5a. As a consequence, these
hydrogen bonds extend the acidꢀbase subunits to develop a 2-D
layer structure in the bc-plane, as shown in Figure 5b. It is
interesting to note that, with this assembly, each layer contains
two 2-D sheets, which are furnished with trimesic acid anion
anions, forming one bifurcated N+ꢀH
Oꢀ and one Oꢀ
through the formation of OꢀH O hydrogen bond, as de-
3 3 3
3 3 3
3 3 3
H
O hydrogen bond (synthon VI: N
O = 2.690(3) Å,
picted in Figure 5c. Furthermore, via bifurcated CꢀH
O
3 3 3
3 3 3
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Crystal Growth & Design
ARTICLE
Figure 1. View of 1. (a) View down the b axis, 1-D infinite chain. (b) Viewed along the b axis, 2-D layered structure. The broken lines represent the
hydrogen bonds [NꢀH O (red), OꢀH N (red), CꢀH O (blue)].
3 3 3
3 3 3
3 3 3
Figure 2. View of 2. (a) View down the b axis, 1-D infinite chain. (b) View along the b axis, 2-D layered structure. (c) View of 3-D arrangement. The
broken lines represent the hydrogen bonds [NꢀH O (red), OꢀH N (red), CꢀH O (blue)].
3 3 3
3 3 3
3 3 3
interactions with H2BBMA2+ (i) cation, the solvents (DMF) are
captured to locate in the interlayer of the framework and function
as a bridge to connect the neighboring layer, resulting in a 3-D
network as depicted in Figure 5d.
Salt of Bis(2-benzimidazylmethyl)amine Pyromellitic
Acid (1:1) (6). Crystallization of bis(2-benzimidazyl-
methyl)amine with 1,2,4,5-tetracarboxylic acid produced a
proton-transfer organic salt, 6, in the space group P1. The
asymmetric unit of 6 contains one di-deprotonated H2PMA
anion and one diprotonated H2BBMA (i) cation. With respect
to the tetracarboxylate component, two of the four carboxylic
acids are deprotonated and hydrogen-bond with diprotonated
H2BBMA (i) cation forming two N+ꢀH
Oꢀ hydrogen
3 3 3
O = 2.651(10) and
bonds, resulting in synthon VI (N
3 3 3
2.688(10) Å), while the remaining two COOH moieties are
oriented longitudinally (z-axis) facilitating the H-bonding
(synthon V: N
promotes the 1-D polar tapes along the crystallographic c-
O = 2.688(10) and 2.738(10) Å) that
3 3 3
axis, as shown in Figure 6a. These 1-D polar tapes are further
linked through the formation of CꢀH
O interactions,
3 3 3
leading to 2-D sheets as depicted in Figure 6b. Two kinds of
intramolecular hydrogen bonds are observed in this assembly;
namely, one is formed between one ꢀCOOH and one
ꢀCOOꢀ group situated at an ortho position to each other,
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Crystal Growth & Design
ARTICLE
Figure 3. View of 3. (a) View of 0-D six-component aggregate. (b) View of 3-D arrangement. The broken lines represent the hydrogen bonds
[NꢀH O (red), CꢀH O (blue)].
3 3 3
3 3 3
Figure 4. View of 4. (a) View of the synthons II, V, VI, and VII. (b) 3-D arrangement with 1-D channels viewed along the a axis (DMF molecules are
omitted for clarity). The broken lines represent the hydrogen bonds [NꢀH O (red), OꢀH N (red), CꢀH O (blue)].
3 3 3
3 3 3
3 3 3
and the other one is generated between an adjacent pair of N
atoms of H2BBMA (i). Because these hydrogen bonds con-
solidate the molecular geometry, the two ꢀCOOH groups
and two ꢀCOOꢀ groups of H2PMA anion are almost coplanar
with the torsional angles being 3.81°, 3.81°, 7.78°, and 7.78°,
respectively, and each the benzimidazole ring is also planar
within 0.01 Å of deviations and the dihedral angles between
them are 3.65°. Moreover, it is interesting to observe that the
formed in the six structures; (4) as is observed in previous
studies,19ꢀ25 the ionic hydrogen bonds of salts 1ꢀ6 also have
smaller N
O distances (2.67ꢀ2.68) than the interactions
3 3 3
for the neutral bond (>2.88 Å) (Table 2); (5) the formation of
O hydrogen bonds influences molecular packing in
CꢀH
3 3 3
1ꢀ3, 5, and 6.
In the six salts, the site of protonation (on BBMA) or
deprotonation (of organic acid) is variable and thus provide
unique opportunities for the discovery of new synthons. As a
result, new synthons VIII, IX, and XI were first found in the acid-
imdazole system. In the crystal structure, whether the COOH
and imidazole group is neutral or ionized was ascertained by
CꢀO, CdO bond distances and CꢀNꢀC, CꢀN+ꢀC angles.
For example, bond distances of 1.30, 1.20 Å and angles of
117ꢀ118° indicate a neutral synthon, whereas an intermediate
distance of 1.25 Å and a slightly obtuse angle of 120ꢀ121° mean
an ionized imidazole state. The CꢀO distance parameter is
restated as Δr < 0.03 Å for ionic COOꢀ and Δr > 0.08 Å for
neutral COOH.
2-D sheets stack with notable aromatic π
π interactions
3 3 3
with the distance being ca. 3.30 Å, which generates 3-D layers,
as illustrated in Figure 6c.
Structural Features and Synthon Evaluation. Variation of
the carboxylic acid elements along with flexible and polyden-
tate bis(2-benzimidazylmethyl)amine compound is envisioned
to produce ionic N+ꢀH
Oꢀ hydrogen bond as well as
3 3 3
weaker CꢀH
O and aromatic π
π interactions. A sys-
3 3 3
3 3 3
tematic comparison of these intermolecular interactions in the
six salts reveals the following characteristics: (1) all NH
functions in the protonated bis(2-benzimidazylmethyl)amine
serve as H-bond donors to anions; (2) proton transfer from the
carboxylic acid to BimN is present in all cases, leading to form
single-point ionic synthons (VI and VIII); (3) as a conse-
quence of competition and cooperation between COOH,
In the six salts, the formation of CꢀH O hydrogen bonds
3 3 3
can influence molecular packing. This is not surprising since we
examined all intermolecular contacts between CꢀH protons on
six crystallographically unique bis(2-benzimidazylmethyl)amine
cations and neighboring oxygen atoms. Most of these interac-
COOꢀ, BimNH+, BimN, -NH2 -, and -NH- functional groups,
+
other synthons, such as III, IV, V, VII, IX, X, and XI, can be
tions had H O distances less than 2.72 Å (the sum of the van
3 3 3
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Crystal Growth & Design
ARTICLE
Figure 5. View of 5. (a) View of the synthons II, VI, and VII. (b) 2-D layer structure, H2BBMA2+ (i) cations connecting two carboxylate sheets (DMF
molecules are omitted for clarity). (c) 2-D sheets are formed with trimesic acid anion. (d) 3-D arrangement. The broken lines represent the hydrogen
bonds [NꢀH O (red), OꢀH N (red), CꢀH O (blue)].
3 3 3
3 3 3
3 3 3
der Waals radii for hydrogen (1.20 Å) and oxygen (1.52 Å)) and
respectively, where the decomposition of the framework starts.
For 1, the weight loss of 46.75% from 170 to 243 °C (calcd
46.6%) corresponds to the loss of one BA anion and one HBA
molecule per formula. The second weight loss of 35.8% (calcd
for 53.3%) can be detected from 256 to 490 °C, which is
attributed to partial decomposition of HBBMA cations. In
compound 2, two mass loss steps were observed. A mass loss of
53.9% (calcd for 54.7%) over the range 248ꢀ390 °C corre-
sponded to the loss of 1 equiv of 4-NBA anions and 1 equiv of
4-NHBA molecules. However, the latter mass losses of 20.2%
corresponded to partial decomposition of HBBMA cations.
Salt 3 displays the same thermogravimetric properties as 1 and
2. Two mass loss steps were also observed. A mass loss of
58.2% (calcd for 60.5%) over the range 262ꢀ470 °C corre-
sponded to the loss of approximately 2 equiv of 3,5-diNBA
anions. The second mass losses of 8.3% corresponded to partial
decomposition of HBBMA cations. In 4, the first mass losses
represented the loss of approximately 1 equiv of DMF (calcd:
12.2%, found: 12.3%). The second mass losses of 41.9% (calcd
for 41.6%), over the range 258ꢀ590 °C, corresponded to the
loss of approximately 1.5 equiv of TPA anions. In 5, the first
mass losses represented the loss of approximately 1 equiv of
DMF (calcd: 9.5%, found: 9.9%). The second mass losses of
54.9% (calcd for 54.5%), over the range 315ꢀ410 °C, corre-
sponded to the loss of approximately 2 equiv of H2TMA
anions. The last mass loss represented the partial decomposi-
tion of H2BBMA (i) cations. In 6, two mass loss steps were
observed. A mass loss of 15% over the range 280ꢀ360 °C
CꢀH O angles greater than 90°. The H O distances rather
3 3 3
3 3 3
than the C
O distances were examined because most of the
3 3 3
CꢀH
O interactions were bent instead of linear. The
3 3 3
H
O bond lengths ranged between 2.29 and 2.60 Å with
3 3 3
an average length of 2.51 Å. The CꢀH
O bond angles
3 3 3
ranged between 118 and 172° with an average angle of 147°.
The CꢀH O hydrogen bond parameters for salts 1ꢀ6 are
3 3 3
given in Table 3. The fact that most of the CꢀH
O
3 3 3
interactions deviated significantly from linearity is not surpris-
ing, considering that formation of stronger N+ꢀH
Oꢀ
3 3 3
hydrogen bonds is one of the principal organizational forces
involved in determining the orientation of bis(2-benzimida-
zylmethyl)amine cations during crystal packing. Meanwhile, it
is noted that the bis(2-benzimidazylmethyl)amine cations
generally form CꢀH
O interactions between layers in-
stead of within layers. One reason the cations may twist out of
the layers in these structures is to maximize the number of
3 3 3
CꢀH O contacts that form. Consequently, fewer CꢀH
O
3 3 3
3 3 3
interactions would occur if the cations were coplanar with the
layers in these structures. The structural analyses demonstrate
that the formation of weak CꢀH O hydrogen bonds controls
3 3 3
the dimensionality of the H-bonding.
Thermal Stability and Powder X-ray Diffraction. To study
the stability of 1ꢀ6, thermogravimetric analyses (TGA) of
these salts were performed (Figure 7). The TGA curves of 1
and 4 indicate that pyrolysis occurs at ca. 170 °C, while 2, 3, 5,
and 6 are more stable up to 248, 262, 287, and 280 °C,
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Crystal Growth & Design
ARTICLE
Figure 6. View of 6. (a) View down the c axis, 1-D infinite chain. (b) View of 2-D sheet. (c) Three dimensional stacking of neighboring sheets. The
broken lines represent the hydrogen bonds [NꢀH O (red), NꢀH N (red), OꢀH O (red), CꢀH O (blue), π π (blue)].
3 3 3
3 3 3
3 3 3
3 3 3
3 3 3
Table 3. Geometrical Parameters of CꢀH O Hydrogen Bonds (Å, °) for 1ꢀ6
3 3 3
DꢀH
A
H
A (Å)
D
A (Å)
DꢀH A (deg)
symmetry codes
3 3 3
3 3 3
2.60
3 3 3
3 3 3
1
2
C1ꢀH1 O4
3.395(3)
3.348(4)
3.490(3)
3.384(2)
3.318(2)
3.389(3)
3.500(3)
3.034(2)
3.317(2)
3.218(2)
3.374(4)
3.273(6)
3.377(3)
3.228(8)
3.329(4)
3.374(8)
3.338(14)
3.311(15)
3.059(11)
3.252(16)
3.158(15)
140
144
170
143
140
163
170
120
147
172
142
135
142
152
144
167
160
148
115
154
118
x, 1/2 ꢀ y, 1/2 + z
x, 3/2 ꢀ y, 1/2 + z
1 ꢀ x, ꢀy, 1 ꢀ z
ꢀx, 1 ꢀ y, 1 ꢀ z
ꢀx, ꢀy, ꢀz
1 + x, 3/2 ꢀ y, ꢀ1/2 + z
1 ꢀ x, 1 ꢀ y, ꢀz
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
ꢀx, 1 ꢀ y, 1 ꢀ z
1 + x, y, z
3 3 3
C6ꢀH6 O1
2.55
2.57
2.56
2.55
2.49
2.58
2.43
2.46
2.29
2.59
2.52
2.60
2.38
2.49
2.46
2.45
2.48
2.52
2.39
2.58
3 3 3
C4ꢀH4 O7
3 3 3
C9ꢀH9B O1
3 3 3
C13ꢀH13 O6
3 3 3
3
C3ꢀH3C O4
3 3 3
C5ꢀH5 O9
3 3 3
C8ꢀH8A O1
3 3 3
C9ꢀH9A O2
3 3 3
C27ꢀH27 O2
3 3 3
4
5
6
C5ꢀH5 O4
ꢀx, ꢀy, 2 ꢀ z
ꢀ1 + x, y, z
3 3 3
C8ꢀH8B O7
3 3 3
C18ꢀH18 O6
ꢀx, 1 ꢀ y, 1 ꢀ z
2 ꢀ x, ꢀy, 1 ꢀ z
1 + x, y, ꢀ1 + z
2 ꢀ x, 1 ꢀ y, 1 ꢀ z
3 ꢀ x, 2 ꢀ y, 1 ꢀ z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
1 + x, 1 + y, 1 + z
ꢀ1 + x, y, 1 + z
1 ꢀ x, 1 ꢀ y, 1 ꢀ z
3 3 3
C5ꢀH5 O13
3 3 3
C8ꢀH8A O110
3 3 3
C12ꢀH12 O13
3 3 3
C8ꢀH8 O4
3 3 3
C10ꢀH10 O2
3 3 3
C13ꢀH13A O1
3 3 3
C16ꢀH16 O4
3 3 3
C21ꢀH21A O1
3 3 3
corresponded to the partial loss of H2PMA anions. The last
mass loss represented the partial decomposition of H2PMA
anions and H2BBMA (i) cations.
The identity of the single-crystal sample and as-synthesized
bulk material has also been confirmed by a comparison of the
simulated and experimental powder X-ray diffraction (PXRD)
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Crystal Growth & Design
ARTICLE
diversification. Further studies on such flexible building blocks
are desirable to understand the crystal engineering of ionic
hydrogen-bonded solids, and related exploration on this per-
spective is underway.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: lyhxxjbm@126.com.
’ ACKNOWLEDGMENT
We are grateful to the Natural Science Foundation of China
(Grant No. 20872057; 21072089) and the Natural Science
Foundation of Henan Province (No. 082300420040) for the
financial support.
Figure 7. TGA curves of 1ꢀ6.
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patterns. As shown in Figure 8, the PXRD patterns of 1ꢀ6 are
almost the same as that simulated from the single-crystal data,
revealing the phase purity of the bulk samples.
’ CONCLUSIONS
In the present contribution for molecular tectonics, we
describe the supramolecular synthesis and rational analysis of
six binary salts based on carboxylic acids and polydentate bis-
(2-benzimidazylmethyl)amine ligand. It is evident that the poly-
carboxylic acids have robust and ionic hydrogen-bonding do-
nors/acceptors to fulfill the diversiform motifs. This work also
demonstrates that bis(2-benzimidazylmethyl)amine is an excel-
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3 3 3
gen bond is successfully applied in the design of supramolecular
structures between carboxylic acids and bis(2-benzimidazyl-
methyl)amine. Meanwhile, the formation of weak CꢀH
O
3 3 3
increases the dimensionality of the supramolecular architectures.
Additionally, the relative orientation and the nature of the
different carboxylic acids also have a significant effect on forming
the final diverse networks from 2-D in 1 to 3-D in 2ꢀ6.
Therefore, the results presented here reveal that assemblies for
such supramolecular systems are variable, and subtle differences
of the building components will account for their structural
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