Anion-controlled dimerized rectangular, herringbone and tape building blocks by L-shaped diamide-substituted pyridinium salts via N-H...O and C-H...O hydrogen bonding

Article abstract of DOI:10.1039/c2ce25695a

A series of 1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium salts with different anions (PF₆^- (1), OTf^- (2), BPh ₄^- (3) and Br^- (4)) have been synthesized and characterized by single crystal X-ray diffraction. The results demonstrate that the unparallel diamide-substituted pyridinium salts form a dimerized rectangular building block and a 2-D rectangular structure via N-H...O and C-H...O hydrogen bonding (PF₆^- (1) and OTf ^- (2), respectively), a 2-D sheet structure (BPh₄ ^- (3)) via N-H...O hydrogen bonding catemers and a 2-D plate structure via N-H...O and C-H...O hydrogen bonding catemers (Br ^- (4)). The effects on the hydrogen bonding motifs, building blocks and structures by the four anion species with different hydrogen bonding acceptor abilities, sizes and shapes have been discussed.

Full text of DOI:10.1039/c2ce25695a

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PAPER
Anion-controlled dimerized rectangular, herringbone and tape building blocks
…
…
by L-shaped diamide-substituted pyridinium salts via N–H O and C–H O
hydrogen bonding{
Wei-Liang Li, An-Kai Wu and Kwang-Ming Lee*
Received 6th May 2012, Accepted 30th June 2012
DOI: 10.1039/c2ce25695a
2
A series of 1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium salts with different anions (PF6 (1),
2
OTf2 (2), BPh4 (3) and Br2 (4)) have been synthesized and characterized by single crystal X-ray
diffraction. The results demonstrate that the unparallel diamide-substituted pyridinium salts form a
…
…
dimerized rectangular building block and a 2-D rectangular structure via N–H O and C–H
2
O
2
hydrogen bonding (PF6 (1) and OTf2 (2), respectively), a 2-D sheet structure (BPh4 (3)) via
…
…
…
N–H O hydrogen bonding catemers and a 2-D plate structure via N–H O and C–H O hydrogen
bonding catemers (Br2 (4)). The effects on the hydrogen bonding motifs, building blocks and
structures by the four anion species with different hydrogen bonding acceptor abilities, sizes and
shapes have been discussed.
blocks and crystal structures. Recently, we reported two series of
Introduction
pyridinium salts with N-acetamido and 3-ethyl acetate38 or
3-amide39 functional group pyridinium salts. Here, we report a
series of 1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium salts
…
The self-assembly of well defined structures by N–H O and C–
…
H
O hydrogen bonding1–6 has received much attention due to its
importance in crystal engineering,7–18 biological structures19–27
and material sciences.28–33 Although the hydrogen bonding dimer
with PF6 (1), OTf2 (2), BPh4 (3) and Br2 (4) anions. The
L-shaped cations could form well-defined building blocks via
different supramolecular synthons. In particular, when the anions
are weak hydrogen bonding acceptors, such as PF62 (1) and OTf2
(2), a dimerized rectangular building block is formed by two
L-shaped cations in a head-to-tail manner. The rectangular
building blocks consequently formed a two dimensional (2-D)
2
2
…
…
or catemer motifs of N–H O and C–H O interactions are
relatively well known, how to efficiently control these motifs to
form reliable building blocks and consequently lead to well
defined crystal structures is still one of the major challenges in
crystal engineering. This challenge should be greater in ionic
crystal structures because anions have a great variety of shapes,
sizes, charges and hydrogen bonding acceptor abilities and
play important roles in biological structures, supramolecular
chemistry and crystal engineering.34–36 The primary amide group
…
rectangular structure via an N–H O hydrogen bonding dimer
…
motif and C–H
O hydrogen bonding in the orthogonal
direction. With the biggest anion BPh42, a 2-D herringbone sheet
…
structure is formed via an N–H O hydrogen bonding dimer and
…
(–C(LO)NH2) with intermolecular N–H O hydrogen bonding is
anti-oriented catemer motifs. However, the Br2 anions possess
a well known supramolecular synthon in neutral crystal engineer-
ing. Generally, there are four possible amide hydrogen bonding
motifs, including the simple dimer, the syn- and anti-oriented
strong hydrogen bonding acceptor abilities to all the N–H atoms
…
of the amide groups and suppress the N–H O dimer motif,
…
resulting in a 1-D tape building block via a syn-oriented N–H
…
O
…
hydrogen bonding N–H O catemers and a dimer–catemer mixed
and C–H O hydrogen bonding catemer and consequently a 2-D
…
motif.37 We are interested in the ionic crystal structures of
N-acetamide substituted 3- or 4-amide pyridinium salts with
different anions because the L-shaped cationic moiety possess
non-coplanar diamide groups which could restrict the orientations
of the hydrogen bonding motifs formed by acetamide, amide and
plate structure via the C–H O hydrogen bonding in the
orthogonal direction. This study will help clarify how the amide
motifs and the packing structures of the diamide-substituted
cationic molecules are affected by different anion species and it
provides useful information for the application of these motifs in
the field of crystal engineering.
… …
the ring C–H groups via N–H O and/or C–H O hydrogen
bonding. In addition, we are also interested in the roles that
…
C–H X hydrogen bonding and the anions play in the building
Experimental
Department of Chemistry, National Kaohsiung Normal University, 62
Shen-Shung Road, Kaohsiung 824, Taiwan. E-mail: kmlee@nknu.edu.tw;
Fax: +886-7-6051083; Tel: +886-7-7172930 ext 7119
{ CCDC reference numbers 879092–879095. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c2ce25695a
General materials and methods
The 1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium bromide
salt (4) was synthesized first by the reaction of isonicotinamide
6072 | CrystEngComm, 2012, 14, 6072–6078
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Table 1 Crystal data and structure refinement for salts 1 to 4
1
2
3
4
Empirical formula
Formula weight
Crystal system
T/K
C8H10F6N3O2P
325.16
Monoclinic
100
P21/c
8.8952(8)
12.8953(12)
11.1052(10)
90
96.686(2)
90
C9H10F3N3O5S
329.26
Monoclinic
100
P 21/n
11.6815(4)
12.4142(5)
18.5652(7)
90
100.7840(10)
90
C32H30BN3O2
499.40
Orthorhombic
296
Pbca
9.8176(5)
17.2416(7)
30.5102(14)
90
90
90
C8H10BrN3O2
260.10
Monoclinic
100
Cc
5.03600(10)
28.8208(7)
6.9016(2)
90
109.0290(10)
90
Space group
˚
a/A
˚
b/A
˚
c/A
a (u)
b (u)
c (u)
3
˚
V/A
1265.2(2)
4
1.707
2644.71(17)
8
1.654
5164.5(4)
8
1.285
946.97(4)
4
1.824
Z
Dc/g cm23
m/mm21
h/deg
0.298
0.308
0.080
4.318
2.31 to 26.49
211 to 11
215 to 16
213 to 8
10 317
1.91 to 26.44
26 to 14
215 to 15
223 to 23
20 963
1.33 to 26.41
212 to 12
215 to 21
238 to 31
40 108
2.83 to 26.38
26 to 5
236 to 36
28 to 7
3519
Range h
Range k
Range l
reflns collected
unique reflns
Data/restraints/parameters
R1, wR2 [I . 2s(I)]
R1, wR2 (all data)
GOF
2606
5447
5121
1625
2606/0/181
0.0356, 0.0887
0.0494, 0.0954
1.037
5447/0/379
0.0350, 0.0815
0.0483, 0.0880
1.024
1.33 to 26.41
0.0442, 0.1297
0.0667, 0.1711
1.092
1625/2/128
0.0464, 0.1194
0.0487, 0.1331
1.115
CCDC number
879092
879093
879094
879095
with 2-bromoacetamide. The PF62, OTf2 and BPh4 salts were
obtained via a reaction of salt 4 with the AgPF6, AgOTf and
NaBPh4 salts, respectively.
(0.1013 g) from a H2O (1 ml)–MeOH (20 ml) solution via the
vapour diffusion of diethyl ether. 1H-NMR (300 MHz, d6-
DMSO, ppm): 9.11–9.09 (d, 2H, 3J = 6.3 Hz, –N–CH–CH), 8.66,
8.28 (s, 1H, –N–CH–CH–CO–NH2), 8.43–8.41 (d, 2H, 3J =
6.6 Hz, –N–CH–CH), 8.05, 7.74 (s, 1H, –N–CH2–CO–NH2),
5.43 (s, 2H, –N–CH2–CO–NH2).
2
1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium hexafluoro-
phosphate (1). A solution of salt 4 (0.4841 g, 2.24 mmol) in
deionized water (25 mL) was added to a 25 mL H2O solution of
AgPF6 (0.5903 g, 4.84 mmol). The resultant solution was filtered
and the product collected with a yield of 0.4297 g (59%), mp
166–168u. Column-shaped crystals suitable for single crystal
X-ray diffraction were obtained by recrystallizing the product
1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium trifluoro-
methanesulfonate (2). A solution of salt 4 (1.0012 g, 4.64 mmol)
in deionized water (25 mL) was added to a 25 mL H2O solution
of AgOTf (1.2406 g, 4.83 mmol). The resultant solution was
Scheme 1 The L-shaped pyridinium cations form (i) rectangular building blocks and 2-D rectangular structures with the PF6 (1) and OTf2 (2)
anions, (ii) a 2-D herringbone sheet structure with the BPh42 (3) anion and (iii) a 1-D tape building block and 2-D interdigitated plate structure with the
Br2 (4) anion.
2
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Table 2 Hydrogen bonds of the salts 1–4 reported in this study
…
…
˚
A (A)
…
˚
A (A)
…
/D–H A (u)
˚
D–H (A)
D–H
A
H
D
symmetry operation for A
1
…
N1–H1A F2
0.88
0.88
0.88
0.88
0.95
0.95
0.95
0.99
0.99
0.95
0.88
0.88
2.31
2.31
2.59
2.18
2.66
2.65
2.45
2.32
2.55
2.18
2.10
2.14
3.008(2)
3.086(2)
3.139(2)
3.016(2)
3.534(2)
3.405(2)
3.389(2)
3.301(2)
3.148(2)
3.060(2)
2.945(2)
2.982(2)
2a
2.920(2)
2.882(2)
3.020(2)
3.003(2)
3.258(2)
3.211(2)
3.315(2)
3.016(2)
3.136(2)
3.477(2)
3.175(2)
2b
2.967(2)
2.964(2)
3.026(2)
3.000(2)
3.144(2)
3.406(2)
3.300(2)
3.318(2)
3.375(2)
3.101(2)
3
136.9(1)
146.4(1)
121.7(1)
158.8(1)
152.7(1)
137.0(1)
169.8(1)
172.0(1)
119.0(1)
152.7(1)
161.1(1)
161.2(1)
1 2 x, 1/2 + y, 3/2 2 z
1 2 x, 1/2 + y, 3/2 2 z
1 2 x, 2y, 1 2 z
1 2 x, 2y, 1 2 z
1 2 x, 2y, 1 2 z
x, 1/2 2 y, 21/2 + z
x, 1/2 2 y, 21/2 + z
x, 1/2 2 y, 21/2 + z
2 2 x, 1/2 + y, 3/2 2 z
2 2 x, 1/2 + y, 3/2 2 z
2 2 x, 2y, 1 2 z
…
N1–H1A F3
…
N3–H3A F1
…
N3H3A F4
…
C7–H7 F3
…
C8–H8 F5
…
C8–H8 F6
…
C2–H2B F2
…
C2–H2A O2
C4–H4 O2
…
…
N3–H3B O1
…
N1–H1B O1
2 2 x, 1 2 y, 1 2 z
…
N1–H1B O21
0.88
0.88
0.88
0.88
0.99
0.99
0.99
0.95
0.95
0.95
0.95
2.05
2.07
2.15
2.15
2.57
2.50
2.67
2.13
2.20
2.63
2.39
170.4(1)
152.3(1)
171.2(1)
164.1(1)
122.9(1)
128.1(1)
126.6(1)
155.5(1)
167.3(1)
149.2(1)
139.4(1)
1 + x, y, z
K + x, 3/2 2 y, 21/2 + z
1 + x, 21 + y, z
…
N1–H1A O23
…
…
N3–H3B O21
N3–H3A O4
3/2 2 x, 21/2 + y, 1/2 2 z
K + x, 1/2 2 y, 1/2 + z
3/2 2 x, 1/2 + y, 1/2 2 z
3/2 2 x, 21/2 + y, 3/2 2 z
3/2 2 x, 1/2 + y, 1/2 2 z
3/2 2 x, 21/2 + y, 1/2 2 z
3/2 2 x, 21/2 + y, 3/2 2 z
3/2 2 x, 21/2 + y, 3/2 2 z
…
C2–H2A F3
…
C2–H2B O2
…
C2–H2A O24
…
C4–H4 O2
…
…
C7–H7 O4
C8–H8 F6
…
C8–H8 O24
…
N21–H21B O1
0.88
0.88
0.88
0.88
0.99
0.99
0.95
0.95
0.95
0.95
2.11
2.15
2.17
2.13
2.56
2.45
2.59
2.43
2.60
2.34
165.0(1)
154.1(1)
165.1(1)
169.7(1)
118.0(1)
163.6(1)
155.4(1)
131.8(1)
139.1(1)
136.8(1)
21 + x, y, z
x, y, z
21 + x, 1 + y, z
2x, 2 2 y, 1 2 z
K 2 x, 21/2 + y, 1/2 2 z
2x, 1 2 y, 2z
2x, 1 2 y, 2z
2x, 1 2 y, 2z
2x, 2 2 y, 1 2 z
K 2 x, 21/2 + y, 1/2 2 z
…
N21–H21A O3
…
N23–H23B O1
…
…
N23–H23A O25
C22–H22B O22
…
C22–H22A O3
…
C24–H24 F2
…
C24–H24 O5
…
…
C25–H25 O25
C28–H28 O22
…
N1–H1A O1
0.88
0.88
0.99
0.99
0.99
0.95
0.95
2.39
2.01
2.66
2.68
2.70
2.69
2.76
2.996(2)
2.869(2)
2.481
3.591(2)
3.417(2)
2.40
126.5(1)
166.4(1)
132.52
129.5(1)
153.4(1)
139.7
1/2 + x, y, 3/2 2 z
2x, 2y, 1 2 z
…
N3–H3B O2
…
C2–H2A centroid3
1/2 + x, 1/2 2 y, 1 2 z
1 2 x, 2y, 1 2 z
1 2 x, 2y, 1 2 z
1/2 + x, 1/2 2 y, 1 2 z
1 2 x, 2y, 1 2 z
…
C2–H2B C22
…
C2–H2B C23
…
…
C4–H4 centroid1
C8–H8 centroid2
2.61
4
152.7
…
N1–H1A Br1
0.88
0.88
0.88
0.88
0.99
0.99
0.95
0.95
2.87
2.58
2.04
2.52
2.81
2.12
2.53
2.84
3.511(9)
3.432(8)
2.894(9)
3.388(6)
3.554(7)
3.04(1)
3.42(1)
3.72(1)
131.3(6)
164.6(6)
163.2(4)
169.1(4)
132.5(4)
153.6(4)
156.7(5)
155.5(6)
21 + x, 2 1 + y, z
x, 21 + y, z
21 + x, y, z
21/2 + x, 21/2 + y, z
21 + x, 1 2 y, 21/2 + z
21 + x, y, z
…
N1–H1B Br1
…
N3–H3A O2
…
…
N3–H3B Br1
C2–H2A Br1
…
C2–H2B O1
…
C7–H7 O2
21/2 + x, 1/2 2 y, 1/2 + z
21 + x, 1 2 y, 1/2 + z
…
C8–H8 Br1
filtered and the product collected with a yield of 0.9153 g (60%),
mp 195–197u. Column-shaped crystals suitable for single crystal
X-ray diffraction were obtained by recrystallizing the product
(0.1173 g) from a MeOH (3 ml) solution via the vapour diffusion of
diethyl ether. 1H-NMR (300 MHz, d6-DMSO, ppm): 9.11–9.08 (d,
of NaBPh4 (0.7895 g, 4.84 mmol). The resultant solution was
filtered and the product collected with a yield of 1.9784 g (85%),
mp 200u (decomposed). Column-shaped crystals suitable for
single crystal X-ray diffraction were obtained by recrystallizing
the product (0.1024 g) from an ACN (5 ml) solution via the
vapour diffusion of diethyl ether. 1H-NMR (300 MHz, d6-
DMSO, ppm): 9.10–9.08 (d, 2H, 3J = 6.20 Hz, –N–CH–CH),
8.66, 8.28 (s, 1H, –N–CH–CH–CO–NH2), 8.42–8.40 (d, 2H, 3J =
6.14 Hz, –N–CH–CH), 8.05, 7.74 (s, 1H, –N–CH2–CO–NH2) ,
3
2H, J = 6.90 Hz, –N–CH–CH), 8.66, 8.28 (s, 1H, –N–CH–CH–
3
CO–NH2), 8.42–8.40 (d, 2H, J = 6.53 Hz, –N–CH–CH), 8.05,
7.74 (s, 1H, –N–CH2–CO–NH2), 5.43 (s, 2H, –N–CH2–CO–NH2).
3
1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium tetraphenyl-
borate (3). A solution of salt 4 (1.0042 g, 4.66 mmol) in
deionized water (25 mL) was added to a 25 mL aqueous solution
7.16 (s, 8H, –B–CH–CH–CH) , 6.94–6.89 (t, 8H, J = 7.24 Hz,
–B–CH–CH–CH) , 6.80–6.75 (t, 4H, 3J = 7.19 Hz, –B–CH–CH–
CH), 5.42 (s, 2H, –N–CH2–CO–NH2).
6074 | CrystEngComm, 2012, 14, 6072–6078
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2
Fig. 1 (a) ORTEP drawing of the 1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium cation moiety of the PF6 salt (1) with atomic numbering. (b)
…
Side views of the pyridinium rings, with a view along the C3–C6 N2–C2 direction, and the h1 and h2 torsional angles of the four salts. h1 is the
torsional angle between the acetamide plane (C2–(C2LO1)–N1) and the pyridinium plane. h2 is the torsional angle between the acetamide plane and the
amide plane (C6–(C3LO2)–N3).
1-(2-amino-2-oxoethyl)-4-carbamoylpyridin-1-ium bromide (4).
A solution of isonicotinamide (2.0498 g, 16.78 mmol) and
2-bromoacetamide (2.3940 g, 25.60 mmol) was refluxed in
acetonitrile for 3 h. After cooling, the white-yellow precipitated
powder was collected and recrystallized from an H2O–methanol
(1 : 3) solution via layering with diethyl ether to give the product
4 with a yield of 3.498 g (80%), mp 247–249u. Column-shaped
crystals suitable for single crystal X-ray diffraction were
obtained by recrystallizing the product (0.1103 g) from a H2O
(1 ml)–methanol (3 ml) mixed solution via the vapour diffusion
of diethyl ether. 1H-NMR (300 MHz, d6-DMSO, ppm): 9.12–
atoms were refined with anisotropic thermal parameters. For the
H-atoms, a riding model was employed. The details of the crystal
parameters, data collection and structure refinements are
summarized in Table 1.
Computational methods
All the calculations were performed using the Gaussian-09 suite
of programs.40
Results and discussion
3
9.10 (d, 2H, J = 6.21 Hz, –N–CH–CH), 8.69, 8.29 (s, 1H, –N–
For the convenience of their description and discussion, all the
types of building blocks, 2-D structures and hydrogen bonding
motifs formed by salts 1 to 4 are depicted in Scheme 1. All the
intermolecular hydrogen bonds of salts 1 to 4 are listed in
Table 2. All of the cationic moieties, 1-(2-amino-2-oxoethyl)-4-
carbamoylpyridin-1-ium of salts 1 to 4, exhibit L-shaped
structures (Fig. 1). Due to the steric hindrance of the methylene
group, the acetamide plane is not coplanar with the pyridinium
plane and they adopt torsional angles of 63–107u (h1). In
addition, the torsional angles between the two amide planes in
the four salts are in the range of 24 to 87u (h2).
CH–CH–CO–NH2), 8.43–8.41 (d, 2H, 3J = 6.23 Hz, –N–CH–
CH), 8.08, 7.75(s, 1H, –N–CH2–CO–NH2), 5.45 (s, 2H, –N–
CH2–CO–NH2).
X-Ray crystallographic analyses and computational methods
Single-crystal X-ray diffraction data was collected with Mo–K
˚
radiation (l = 0.71073 A) in W and v scan modes using a Bruker
APEX-II diffractometer equipped with a CCD array detector
and graphite monochromator. All the structures were solved by
the direct method and refined (based on F2 using all the
independent data) using full-matrix least-squares methods
(Bruker SHELXTL 97). The crystal of 4 is a racemic twin and
the obtained Flack parameter is 0.41(2). The non-hydrogen
In the crystal structure of the PF62 salt (1), the torsional angle
(h1) between the acetamide plane and the pyridinium ring is 81u.
Two L-shaped cations are bonded to each other in a head-to-tail
…
manner via N3–H3A O2 hydrogen bonding to form
a
2
Fig. 2 The hydrogen bonding motifs and packing of the PF6 salt (1). (a) The dimerized rectangular building block via N3–N3B O1 hydrogen
…
…
bonding. (b) Each 1-D rectangle bonds to adjacent 1-D rectangles along the c-axis via bifurcate C–H O hydrogen bonding and results in a 2-D
2
…
…
rectangular structure. (c) The PF6 anions are located between the rectangles and form N–H F and C–H F hydrogen bonds. The detailed hydrogen
bonding data is listed in Table 2.
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Fig. 3 The hydrogen bonding motifs and packing of the OTf2 salt (2). (a) The dimerized rectangular building block via N3–N3B O21 hydrogen
…
…
bonding. Each neighboring rectangle links to each other to form an amide dimer motif via N–H O (N1–H1B O21) hydrogen bonding and results in
…
…
a 1-D rectangular structure. (b) Each 1-D rectangle bonds to adjacent 1-D rectangles along the c-axis via bifurcate C–H O hydrogen bonding and
results in a 2-D rectangular structure. (c) The OTf2 anions are located between the rectangles and form N–H O, C–H O and C–H F hydrogen
…
…
…
bonds. The detailed hydrogen bonding data is listed in Table 2.
centrosymmetric dimerized rectangular motif (Fig. 2(a)). The
acetamide groups of each neighboring rectangle link to each
…
other to form an amide dimer motif via a N–H O (N1–
…
H1B O2) hydrogen bond and results in a one dimensional (1-
D) rectangular structure along the b-axis (Fig. 2 (a)). Each 1-D
rectangular structure bonds to an adjacent one along the c-axis
…
via bifurcate C–H O hydrogen bonding and results in a 2-D
2
rectangular structure (Fig. 2(b)). The PF6 anions are located
…
between the 2-D rectangular structure and form four N–H F–P
…
and four C–H F–P hydrogen bonds (Fig. 2(c) and Table 2).
In the crystal structure of the OTf2 salt (2), there are two
crystallographically distinct cationic moieties in the unit cell,
which possess only slightly different torsion angles (h2) between
the two amide planes (62 and 286u for cations 2a and 2b
2
respectively). Like the PF6 salt (1), the L-shaped cationic
moiety forms a centrosymmetric dimerized rectangular motif, a
…
1-D rectangular structure via bifurcate C–H O hydrogen
bonding (Fig. 3a) and consequently a 2-D rectangular structure
(Fig. 3b). The OTf2 anions are also located between the 2-D grid
…
…
structures and they form two N–H OLS, two C–H OLS and
two C–H F hydrogen bonds (Fig. 3(c) and Table 2).
…
2
The crystal structure of the BPh4 salt (3) shows a 2-D
herringbone sheet structure via two conventional types of N–
…
H
O amide motifs: the cyclic dimer and anti-orientated catemer
2
motifs (Fig. 4 (a) and Table 2). The BPh4 anions are located
…
between the sheets and form four C–H
…
hydrogen bonds,
… …
including two Cring–H
…
(C4–H4 R1 and C8–H8 R2) and
… …
two C–H
(C2–H2A R3 and C2–H2B C23 and C26)
…
hydrogen bonds, which are shown in Fig. 4 (b). The C–H
p
hydrogen bonds are similar to our previous report39 and the
reported BPh4 salt.41
2
In the crystal structure of the Br2 salt (4), both the h1 and h2
torsion angles are apparently smaller than those of salts 1 to 3.
The h1 angle is 63u and moreover, the h2 angle is only 24u, which
shows that the two amide groups are closer to parallel rather
than perpendicular to each other. Fig. 5(a) depicts the 1-D tape
motif formed via the two types of hydrogen bonding catemers,
Fig. 4 The hydrogen bonding motifs and packing structure of the
2
… …
one is a conventional N–H O (N3–H3A O2) amide catemer
BPh4 salt (3). (a) The herringbone sheet structure formed by the N–
…
…
with amide groups of nicotinamide and the other is
a
H
O dimer and catemer motifs. (b) The formation of the C–H
2
p
…
unconventional C–H O (C2–H2B O1) catemer. In fact, this
…
interactions by the cations and BPh4 anions. The detailed hydrogen
bonding data is listed in Table 2.
…
C–H O catemer was commonly observed in the 3-positional
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isomers of the 1-(2-amino-2-oxoethyl)-3-carbamoylpyridin-1-
ium salts.39 The tapes are connected to each other via orthogonal
…
…
directional C–H O (C7–H7 O2) hydrogen bonding and form
an interdigitated plate structure (Fig. 5(b)). The Br2 anions are
located between the interdigitated plates and form five hydrogen
…
…
…
bonds, including three N–H O (N1–H1A Br, N2–H1B Br
…
…
…
and N3–H3B Br) and two C–H OLC (C2–H2A Br and C8–
H8 Br) hydrogen bonds, which are shown in Fig. 5(a).
…
To estimate the degree of deformation of the cation moieties in
the crystal packing, single point energy calculations of the
cationic moieties of the four salts were carried out, on data
obtained directly from the crystal structure of salts 1 to 4, at the
RB3LYP level using the 6-311G(d,p) basis set to give the total
energies. The results are given in Table 3 with the energies
2
normalized to the lowest energy BPh4 salt (3). These results
Fig. 5 Hydrogen bonding motifs and packing structure of the Br2 salt
…
show that the stronger the hydrogen bonding acceptor property
of the anion species, the higher degree of deformation the in the
structure. Therefore, on the basis of the crystal structures and
single point energies of salts 1 to 4, we think the building blocks
and structures of the four salts are mainly affected by the sizes
and hydrogen bonding acceptor abilities of the anion species and
the following conclusions can be drawn: (a) the diamide
pyridinium salts may aggregate convergently to form a dimerized
(4). (a) The 1-D tape building block formed by one N–H O and one C–
…
H
O catemer motif. (b) Each neighboring 1-D tape links to each other
…
via C7–H7 O2 hydrogen bonding and results in a 2-D interdigitated
plate structure. The detailed hydrogen bonding data is listed in Table 2.
2
rectangle (PF6 (1) and OTf2 (2)) or divergently to form an
Table 3 Calculated energies for the salts 1–4
infinite 2-D herringbone sheet (BPh42 (3)) and 1-D tape building
blocks (Br2 (4)). (b) The dimerized rectangle is a reliable
building block when the anion species are smaller and have weak
Erel (kcal mol21
)
h2
a
Salts
Ecalc (Hartrees)
1
2625.3875049
2625.3879241
2625.3871031
2625.3902354
2625.386552
1.71
1.45
1.97
0
69
62
286
87
2a
2b
3
2
hydrogen bonding acceptor abilities. (c) Although the BPh4
anion has the weakest hydrogen bonding acceptor ability, this is
the largest anion and is mismatched in size with the cationic
moiety. This spatial requirement causes the cationic moiety to
form the loose herringbone sheet structure. In contrast, as they
possess the strongest hydrogen bonding acceptor ability, the Br2
anions dominate and bond to three of the four N–H atoms and
block the amide dimer motif which is formed in salts 1 to 3. In
addition, the Br2 anion causes the cationic moiety to adopt a
relatively high energy conformation to enable the maximum
4
2.31
24
a
2
Relative to the energy of BPh4 salt 3.
…
…
amount of N–H Br or C–H Br hydrogen bonding.
It would be useful to give structural comparisons of the four
salts reported in this study with other two series of previously
reported L-shaped salts.38,39 Fig. 6 and 7 show the two types of
analogous dimerized rectangular structures as well as the three
types of analogous sheet structures formed by these three
different L-shaped pyridinium salts. We think that both the
two types of structure could be considered as reliable motifs for
the acetamide-substituted L-shaped pyridinium cations when the
Fig. 6 (a) The dimerized rectangular structures of salts 1 and 2 reported
in this study. (b) The analogous structures formed by the 1-(2-amino-2-
oxoethyl)-3-carbamoylpyridin-1-ium diamide pyridinium triflate salt.
Fig. 7 Three analogous sheet structures formed by three different L-shaped pyridinium salts.
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anion species are weak hydrogen bonding acceptors. In addition,
…
it is worth pointing out the importance of the C–H O hydrogen
…
bonding because it could serve as an alternative to the N–H
hydrogen bonding within the two types of structure.
O
Conclusions
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2
2
BPh4 (3) and Br2 (4) anions. The L-shaped cations can form a
dimerized rectangle, a herringbone sheet or a tape structure via
…
…
N–H O and/or C–H O hydrogen bonding, controlled by the
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…
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…
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Acknowledgements
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This work was supported by the National Science Council of
Taiwan, Republic of China (NSC-100-2113-M-017-001) and
National Kaohsiung Normal University. We are grateful to the
National Center for High-performance Computing for the
computer time and facilities.
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