Study of supramolecular frameworks having aliphatic dicarboxylic acids, N,N′-bis(salicyl)ethylenediamine and N,N′-bis(salicyl) butylenediamine

Article abstract of DOI:10.1016/j.molstruc.2014.04.064

The reaction of bases (L₁ and L₂) (where L ₁ = N,N′-bis(salicyl)ethylenediamine, L₂ = N,N′-bis(salicyl)butylenediamine) with dicarboxylic acids [adipic acid (1,6-Hexanedioic acid, AA), pimelic acid (1,7-Heptaned

Full text of DOI:10.1016/j.molstruc.2014.04.064

Journal of Molecular Structure xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Study of supramolecular frameworks having aliphatic dicarboxylic acids,
N,N0-bis(salicyl)ethylenediamine and N,N0-bis(salicyl)butylenediamine
b
Nidhi Goel a, , Naresh Kumar
⇑
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India
b Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee 247 667, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Six new salts of dicarboxylic acids
with N,N0-
bis(salicyl)alkylenediamines.
Detailed X-ray crystallographic study
for salts.
Comparison of solid and gaseous
phase structure for salts.
Curve fitting analysis between
experimental and theoretical values.
ꢀ
ꢀ
ꢀ
a r t i c l e i n f o
a b s t r a c t
The reaction of bases (L1 and L2) (where L1 = N,N0-bis(salicyl)ethylenediamine, L2 = N,N0-bis(salicyl)buty-
lenediamine) with dicarboxylic acids [adipic acid (1,6-Hexanedioic acid, AA), pimelic acid (1,7-Hepta-
nedioic acid, PA) and suberic acid (1,8-Octanedioic acid, SUA] yielded the corresponding six new ionic
salts viz., [1/2L1H+ꢁ1/2AAꢂꢁ1/2AA] (1), [2 ꢃ 1/2L1H+ꢁPA2ꢂꢁCHCl3] (2) [1/2L1H+ꢁ1/2SUAꢂ] (3), [1/2L2H+ꢁ1/
2AAꢂꢁ2CH3OH] (4), [1/2L2H+ꢁ1/2PAꢂ] (5) and [1/2L2H+ꢁ1/2SUAꢂ] (6), respectively. Theses salts were char-
acterized by elemental analysis, FT-IR, NMR, X-ray crystallography, and theoretically by means of Gauss-
ian 09. The X-ray crystallographic studies revealed that the proton transfer occurred from acid to base. It
also demonstrated that different type of hydrogen bond interactions between cations and anions were
responsible for the supramolecular frameworks. The optimized structures of these salts were calculated
in terms of the density functional theory. The curve fitting analysis between experimental and simulated
data of structural parameters was done, and found statistically close. The orientation of molecules was
remained same in both the gas and solid phases. The thermal studies of these salts were investigated
by TG–DTG.
Article history:
Received 23 January 2014
Received in revised form 19 April 2014
Accepted 19 April 2014
Available online xxxx
Keywords:
N,N0-bis(salicyl)ethylenediamine
N,N0-bis(salicyl)butylenediamine
Dicarboxylic acids
Hydrogen bond interactions
Density functional theory
Supramolecular framework
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
Noncovalent interactions are responsible for the designing of
supramolecular frameworks, where the molecules interact with
Supramolecular chemistry is an expanding area of research for
the creation of new cocrystals, ionic salts and molecular com-
plexes, which exhibits the structural novelty and diversity [1–6].
each other, and form a highly ordered crystalline materials [7–
13]. Among the various noncovalent interactions, hydrogen bond
is the most important, and intensively studied in the structural
chemistry as well as in biology due to its strength, high degree of
directionality, and participation in construction of robust supramo-
lecular synthons [14–19]. In this context, Etter gave a guideline
⇑
Corresponding author. Tel.: +91 09412841504.
E-mail address: nidhigoel.iitr@gmail.com (N. Goel).
http://dx.doi.org/10.1016/j.molstruc.2014.04.064
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
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2
N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
regarding the hydrogen-bond interactions, ‘‘the best donor in the
molecule preferentially interacts with the best acceptor in the sys-
tem, the second best donor–acceptor group hydrogen bond next,
and so on’’ [20]. The carboxylic acids are the most popular func-
tional groups, and play a significant role in forming the directional
and robust synthons [21,22]. It is well known that the carboxylic
acids have both hydrogen bond donor and acceptor groups that
are self-associated through OAHꢁ ꢁ ꢁO hydrogen bonds, and are
involved in the formation of supramolecular homosynthons, while
on the other side the same functional group has been extensively
used as a strong hydrogen bond donor to a variety of nitrogen con-
taining hydrogen bond acceptors, and is resulted in the formation
of supramolecular heterosynthons. Due to these attractive features,
carboxylic acids have been used for cocrystallization by several
workers [23–31], but their use in cocrystallization with N,N0-
bis(salicyl)ethylenediamine (L1) and N,N0-bis(salicyl)butylenedi-
amine (L2) as one component are not yet reported. These bases
are important organic compounds, and may be used for assembling
the diverse architectures in the area of supramolecular chemistry
as molecular building blocks control the molecular packing in crys-
talline materials due to presence of donor and acceptor functional
groups. The purpose of this work is to cocrystallize the selected
dicarboxylic acids with bases (L1 and L2), and also see the effect
of increasing carbon chain in acids and bases on the supramolecu-
lar frameworks and hydrogen bond interaction energy of these
salts. This paper reports the syntheses, crystal structures, theoret-
ical, thermal studies of newly constructed ionic salts, and also
presents the significant role of these bases in the formation of
well-designed and long-range structures.
borohydride (1.52 g, 40.0 mmol) was added slowly at 45 °C. The
reaction mixture was refluxed for 6 h at 60 °C. The precipitate
obtained by addition of water, was filtered, and recrystallized from
methanol at 4 °C in 79.3% (0.24 g, 0.79 mmol) yield. Anal. Calcd. (%)
for C18H24N2O2 (300.18): C, 71.97; H, 8.04; N, 9.33; Found: C,
71.67; H, 7.94; N, 9.11. FT-IR (KBr, cmꢂ1): 3519, 3439, 3033,
2937, 2815, 2083, 1899, 1779, 1651, 1602, 1449, 1273, 1169,
939, 753, 617, 504. 1H NMR (DMSO-d6, ppm) d: 2.59 (s, 4H, CH2,
Benzylic), 3.40 (m, 4H, CH2, aliphatic), 3.90 (m, 4H, CH2, aliphatic),
6.71–6.77 (m, 4H, CH, Ar), 7.06–7.14 (m, 4H, CH, Ar), 12.04 (s, br,
2H, NH).
Synthesis of salt 1
Salt 1 was prepared by mixing L1 (0.27 g, 1.0 mmol) and AA
(0.15 g, 1.0 mmol) in an acetonitrile-methanol mixture (v/v%, 1:4,
10 ml). The resulting solution was stirred for 6 h, and filtered
through Celite. The filtrate was evaporated until dryness under
vacuum, and the white solid obtained was redissolved in methanol.
The colorless crystals of 1 in 72.5% (0.41 g, 0.72 mmol) yields, suit-
able for X-ray data collection were obtained by slow evaporation of
solvent at room temperature. Anal. Calcd. (%) for C28H40N2O10
(564.62): C, 59.56; H, 7.13; N, 4.96. Found: C, 59.12; H, 7.01; N,
4.73. FT-IR (KBr, cmꢂ1): 3669, 3332, 3077, 2951, 2869, 2671,
2292, 1686, 1426, 1365, 1272, 1127, 1029, 926, 739, 677, 519. 1H
NMR (DMSO-d6, ppm) d: 12.14 (s, br, 4H, NH2), 6.10–6.74 (m, 8H,
CH, Ar L1), 3.21 (t, 4H, CH2, aliphatic L1), 2.34 (s, 4H, CH2, Benzylic
L1), 2.12 (m, 4H, CH2, AA2ꢂ), 1.37 (t, 4H, CH2, AA2ꢂ).
Synthesis of salt 2
Salt 2 was obtained by the same procedure as outlined above for
1 using PA (0.16 g, 1.0 mmol) in chloroform–methanol mixture (v/
v%, 1:4, 10 ml) with 69.8% (0.68 g, 0.69 mmol) yields. Anal. Calcd.
(%) for C47H65N4O12Cl3 (984.40): C, 57.34; H, 6.65; N, 5.69; Found:
C, 57.07; H, 6.55; N, 5.49. FT-IR (KBr, cmꢂ1): 3643, 3324, 2949,
2411, 2269, 2161, 1933, 1697, 1567, 1412, 1354, 1139, 1033,
922, 739, 697, 526. 1H NMR (DMSO-d6, ppm) d: 12.37 (s, br, 4H,
NH2), 6.07–6.62 (m, 8H, CH, Ar L1), 3.19 (t, 4H, CH2, aliphatic L1),
2.31 (s, 4H, CH2, Benzylic L1), 2.17 (t, 4H, CH2, PA2ꢂ), 1.55 (m, 4H,
CH2, PA2ꢂ), 1.29 (m, 2H, CH2, PA2ꢂ).
Experimental section
Materials
All manipulations were performed in air using commercial
grade solvents. N,N0-bis(salicyl)ethylenediamine (L1) and N,N0-
bis(salicylidene)butylenediamine were prepared by the known
procedure [32,33]. Adipic acid (1,6-Hexanedioic acid, AA), pimelic
acid (1,7-Heptanedioic acid, PA) and suberic acid (1,8-Octanedioic
acid, SUA) were purchased from Aldrich Chemical Company, USA.
Synthesis of N,N0-bis(salicyl)butylenediamine and salts
Synthesis of salt 3
The same procedure was applied on salt 3 as outlined above for
1 using SUA (0.17 g, 1.0 mmol) with 77.7% (0.35 g, 0.78 mmol)
yields. Anal. Calcd. (%) for C24H34N2O6 (446.54): C, 64.55; H, 7.67;
N, 6.27. Found: C, 63.87; H, 7.56; N, 6.53. FT-IR (KBr, cmꢂ1):
3659, 3337, 2945, 2845, 2759, 2617, 2259, 2049, 1611, 1529,
1455, 1377, 1256, 1109, 1057, 931, 841, 791, 529. 1H NMR
(DMSO-d6, ppm) d: 12.21 (s, br, 4H, NH2), 5.99–6.59 (m, 8H, CH,
Ar L1), 3.18 (t, 4H, CH2, aliphatic L1), 2.29 (s, 4H, CH2, Benzylic
The salts 1–6, were synthesized by the stoichiometric combina-
tion of L1, L2 and dicarboxylic acids (AA/PA/SUA) as shown in
Schemes 1 and 2.
Synthesis of N,N0-bis(salicyl)butylenediamine (L2)
N,N0-bis(salicylidene)butylenediamine (5.93 g, 20.0 mmol) was
dissolved in 50.0 ml of methanol. Then to this solution, sodium
Scheme 1. General method for preparation of salts 1–3.
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N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
3
Scheme 2. General method for preparation of salts 4–6.
L1), 2.16 (t, 4H, CH2, SUA2ꢂ), 1.54 (t, 4H, CH2, SUA2ꢂ), 1.28 (m, 4H,
CH2, SUA2ꢂ).
3.81 (m, 4H, CH2, aliphatic L2), 3.33 (m, 4H, CH2, aliphatic L2),
2.51 (s, 4H, CH2, Benzylic L2), 2.18 (t, 4H, CH2, PA2ꢂ), 1.61 (m, 4H,
CH2, PA2ꢂ), 1.33 (m, 2H, CH2, PA2ꢂ).
Synthesis of salt 4
Salt 4 was obtained by the same procedure as outlined above for
1 using L2 (0.30 g, 1.0 mmol) and AA (0.15 g, 1.0 mmol) with 77.8%
Synthesis of salt 6
Salt 6 was obtained by the same procedure as outlined above for
4 using SUA (0.17 g, 1.0 mmol) with 72.9% (0.35 g, 0.73 mmol)
yields. Anal. Calcd. (%) for C26H38N2O6 (474.58): C, 65.80; H, 8.06;
N, 5.90. Found: C, 65.33; H, 7.95; N, 5.69. FT-IR (KBr, cmꢂ1):
3788, 3320, 3032, 2941, 2863, 2604, 2543, 2360, 1610, 1541,
1430, 1253, 1121, 1004, 795, 682. 1H NMR (DMSO-d6, ppm) d:
12.23 (s, br, 4H, NH2), 7.02–7.07 (m, 4H, CH, Ar L2), 6.66–6.73 (m,
4H, CH, Ar L2), 3.84 (m, 4H, CH2, aliphatic L2), 3.35 (m, 4H, CH2,
aliphatic L2), 2.53 (s, 4H, CH2, Benzylic L2), 2.18 (t, 4H, CH2, SUA2ꢂ),
1.57 (t, 4H, CH2, SUA2ꢂ), 1.31 (m, 4H, CH2, SUA2ꢂ).
(0.40 g, 0.78 mmol) yields. Anal. Calcd. (%) for
C26H42N2O8
(510.62): C, 61.15; H, 8.28; N, 5.48; Found: C, 60.91; H, 8.23; N,
5.36. FT-IR (KBr, cmꢂ1): 3545, 3326, 2957, 2663, 2561, 1623,
1541, 1419, 1279, 1112, 1039, 927, 749, 611. 1H NMR (DMSO-d6,
ppm) d: 12.33 (s, br, 4H, NH2), 7.03–7.11 (m, 4H, CH, Ar L2),
6.69–6.74 (m, 4H, CH, Ar L2), 3.84 (m, 4H, CH2, aliphatic L2), 3.37
(m, 4H, CH2, aliphatic L2), 2.54 (s, 4H, CH2, Benzylic L2), 2.13 (m,
4H, CH2, AA2ꢂ), 1.41 (t, 4H, CH2, AA2ꢂ).
Synthesis of salt 5
Salt 5 was obtained by the same procedure as outlined above for
4 using PA (0.16 g, 1.0 mmol) with 69.3% (0.32 g, 0.69 mmol)
yields. Anal. Calcd. (%) for C25H36N2O6 (460.56): C, 65.19; H, 7.87;
N, 6.08. Found: C, 64.92; H, 7.69; N, 5.89. FT-IR (KBr, cmꢂ1):
3589, 3330, 2940, 2869, 2700, 2556, 1621, 1504, 1408, 1123,
1065, 922, 790, 673. 1H NMR (DMSO-d6, ppm) d: 12.19 (s, br, 4H,
NH2), 7.04–7.09 (m, 4H, CH, Ar L2), 6.64–6.71 (m, 4H, CH, Ar L2),
Instrumentation
Crystallized salts were carefully dried under vacuum for several
hours prior to elemental analysis on Elementar Vario EL III ana-
lyzer. FT-IR spectra were obtained on a Thermo Nikolet Nexus
FT-IR spectrometer in KBr pellets. 1H NMR spectra were recorded
on Bruker-D-Avance 500 MHz spectrometer with Fourier trans-
form technique using TMS as internal standard. Thermogravimetry
Table 1
Crystallographic data and structure refinement parameters for salts 1–6.
Salt 1
28H40N2O10
564.62
296(2)
Triclinic
Pꢂ1
Salt 2
Salt 3
Salt 4
Salt 5
Salt 6
Empirical formula
Formula weight
Temprature
Crystal system
Space group
a (Å)
C
C24H33N2O6Cl3
551.87
296(2)
Monoclinic
C 2/c
22.825(4)
13.896(4)
19.379(5)
90.00
114.92(17)
90.00
5574(2)
8
1.315
0.368
C24H34N2O6
446.53
296(2)
Triclinic
Pꢂ1
C26H42N2O8
510.62
296(2)
Monoclinic
P21/c
8.547(14)
22.146(4)
7.355(13)
90.00
100.00(9)
90.00
1371.2(4)
2
1.237
0.091
C25H36N2O6
460.56
296(2)
Monoclinic
C 2/c
18.518(6)
9.396(3)
13.959(5)
90.00
91.81(2)
90.00
2427.5(13)
4
1.260
0.090
C26H38N2O6
474.58
296(2)
Monoclinic
C 2/c
18.455(17)
9.179(7)
15.271(12)
90.00
95.28(7)
90.00
2576.3(4)
4
1.224
0.086
8.528(5)
8.914(5)
9.704(6)
73.91(3)
88.95(3)
79.12(3)
695.67(7)
1
1.348
0.102
302
0.3 ꢃ 0.24 ꢃ 0.19
2.19–30.68
4249
3548
4249/0/186
0.920
5.824(3)
7.679(5)
13.744(8)
97.26(3)
98.18(3)
101.16(3)
589.3(6)
1
b (Å)
c (Å)
a
(0)
b (0)
c
(0)
V (Å3)
Z
DCalc (g/cm3)
1.258
0.090
240.0
0.21 ꢃ 0.18 ꢃ 0.14
2.74–28.59
2744
1406
2744/0/146
0.828
l
(Mo K
F(000)
Crystal size
a
) (cmꢂ1
)
2320.0
552
992
1024
0.27 ꢃ 0.21 ꢃ 0.16
1.77–28.37
6893
4650
6893/0/318
2.097
0.29 ꢃ 0.23 ꢃ 0.17
2.96–28.36
3329
2365
3329/0/166
1.400
0.31 ꢃ 0.27 ꢃ 0.21
2.20–28.36
2984
1663
2984/0/151
1.060
0.26 ꢃ 0.19 ꢃ 0.13
2.68–28.43
3179
1559
3179/0/155
1.141
Theta range for data collection (o)
No. of measured reflections
No. of observed reflections
Data/restraints/parameters
Goodness-of-fit
a
Final R indices[I > 2(I) R1
0.0383
0.1177
0.0971
0.1953
0.0715
0.1647
0.0738
0.2172
0.0768
0.1925
0.0813
0.1943
b
wR2
P
P
||Fo|ꢂ|Fc||/ |Fo|.
P
a
R1
=
P
b
wR2 = { [w (F2oꢂF2c)2]/ w (Fo2)2.
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4
N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 2
and derivative thermogravimetry (TG–DTG) were carried out at
10 °C/min (mass 0.055 g) under a nitrogen atmosphere (flow rate
of 200 ml/min) on PerkinElmer’s (Pyris Diamond) (Woodland,
California, USA) thermogravimetric analyzer.
Noncovalent interactions for salts 1–6 (Å and °).
DAHꢁ ꢁ ꢁA
Salt 1
d(DAH)
d(HAA)
d(DAA)
h(DHA)i
N1AH1Aꢁ ꢁ ꢁO3
N1AH1Bꢁ ꢁ ꢁO4
O1AH1ꢁ ꢁ ꢁO5
O2AH2Aꢁ ꢁ ꢁO4
C10AH10Aꢁ ꢁ ꢁO2
0.900
0.900
0.820
0.970
0.970
0.970
1.921 (9)
1.848(7)
1.894(9)
1.608(27)
2.814(10)
3.474(53)
2.820(13)
2.659(11)
2.696(13)
2.533(12)
3.620(16)
3.808(10)
177.3
156.0
165.6
175.9
141.0
102.7
X-ray diffraction data
Single crystal X-ray diffraction data were collected at 100 K on a
Bruker Kappa four circle-CCD diffractometer using graphite mono-
chromated Mo K
a
radiation (k = 0.71070 Å). Empirical absorption
C7AH7Bꢁ ꢁ ꢁ
p
corrections were applied in the reduction of data Lorentz and
polarization corrections [34]. The SHELXTL program was used for
the structure solution, refinement and data output [35,36]. Non-
hydrogen atoms were refined anisotropically, while the hydrogen
atoms were placed in geometrically calculated positions by using
a riding model. Images and hydrogen bonding interactions were
created with DIAMOND and MERCURY softwares [37,38]. The crys-
tallographic data and the selected hydrogen bond distances are
given in Tables 1 and 2, respectively.
Salt 2
N1AH1Bꢁ ꢁ ꢁO6
N1AH1Cꢁ ꢁ ꢁO3
N2AH2Bꢁ ꢁ ꢁO5
N2AH2Bꢁ ꢁ ꢁO6
N2AH2Cꢁ ꢁ ꢁO4
O1AH1ꢁ ꢁ ꢁO5
0.900
0.900
0.900
0.900
0.900
0.821
0.821
0.929
0.970
0.970
0.930
0.970
0.970
1.881(29)
1.846(28)
2.759(30)
1.906(25)
2.412(46)
1.759(38)
2.310(92)
2.650(38)
2.643(27)
2.569(24)
2.528(29)
2.883(89)
2.864(70)
2.743(42)
2.675(38)
3.492(37)
2.789(35)
3.049(49)
2.561(51)
3.021(91)
3.280(61)
3.316(44)
3.287(42)
3.387(46)
3.389(74)
3.331(61)
159.8
152.2
139.4
166.3
127.9
164.8
145.1
125.6
126.8
130.8
153.7
123.5
121.8
O2AH2Aꢁ ꢁ ꢁO4
C2AH2ꢁ ꢁ ꢁO5
C8AH8Aꢁ ꢁ ꢁO3
C8AH8Bꢁ ꢁ ꢁO6
C13AH13ꢁ ꢁ ꢁO5
C15AH15ꢁ ꢁ ꢁO4
C16AH16Bꢁ ꢁ ꢁO4
Computational and statistical analysis
Geometry optimization of the different ionic salts was done by
Gaussian 09 program at B3LYP/6-311G++(d,p) basis set [39–41].
The input for the simulation was Z-matrix generalized by Gauss-
view 5.0 that was also used for visualizing the molecules with opti-
mized geometries. ChemCraft, version 1.5 software was used for
comparing the optimized structure with the crystallographic one.
The experimental and simulated values for bond lengths and bond
angles were statistically tested for significance in MATLAB R2010a
toolbox that is used for measuring the potency and direction of a
linear association between two variables.
Salt 3
N1AH1Aꢁ ꢁ ꢁO2
N1AH1Aꢁ ꢁ ꢁO3
N1AH1Bꢁ ꢁ ꢁO3
O1AH1ꢁ ꢁ ꢁO2
C5AH5ꢁ ꢁ ꢁO3
C8AH8Aꢁ ꢁ ꢁO3
C8AH8Bꢁ ꢁ ꢁO2
C8AH8Bꢁ ꢁ ꢁO3
0.899
0.899
0.900
0.819
0.930
0.970
0.969
0.969
0.969
1.831(23)
2.548(34)
1.796(33)
1.808(27)
2.601(32)
2.818(31)
2.933(27)
2.908(37)
3.259(16)
2.677(34)
3.336(42)
2.693(42)
2.573(38)
3.269(47)
3.489(43)
3.559(38)
3.631(48)
4.123(38)
155.6
146.6
174.3
154.6
129.2
127.0
123.3
132.2
149.4
C10AH10Aꢁ ꢁ ꢁ
Salt 4
p
N1AH1Aꢁ ꢁ ꢁO2
N1AH1Aꢁ ꢁ ꢁO3
N1AH1Bꢁ ꢁ ꢁO2
O4AH4ꢁ ꢁ ꢁO1
C4AH4Aꢁ ꢁ ꢁO4
C5AH5ꢁ ꢁ ꢁO3
0.900
0.900
0.900
0.820
0.931
0.930
0.930
0.970
0.970
0.970
0.960
1.810(8)
2.816(5)
2.087(2)
2.888(9)
3.162(9)
3.469(9)
3.401(18)
2.933(6)
2.532(9)
3.116(8)
3.082(6)
2.709
3.461
2.860
3.395
3.833
4.148
3.957
3.592
3.317
3.657
3.526
176.8
129.7
143.2
121.9
130.5
131.8
120.6
126.2
138.0
116.8
109.9
Results and discussions
Infrared and NMR spectroscopy
As compared to free carboxylic acids (1673 and 1737 cmꢂ1), the
C@O stretching bands appear in the range 1592 and 1650 cmꢂ1 for
salts 1–6. The NH stretching vibration is normally observed at
3500–3400 cmꢂ1, which is shifted to lower wavenumber (Tables
S1 and S2). The shifting towards lower frequency is due to the
hydrogen bonded noncovalent interactions between ANH protons
donor and carboxylate anion acceptor [42–44]. The presence of
hydrogen bond interactions in the solution for 1–6 was confirmed
by the prominent downfield chemical shift in the 1H NMR spectra
of each case with respect to the free ligand.
C5AH5ꢁ ꢁ ꢁO4
C7AH7Aꢁ ꢁ ꢁO3
C9AH9Aꢁ ꢁ ꢁO2
C9AH9Bꢁ ꢁ ꢁO2
C13AH13Bꢁ ꢁ ꢁO1
Salt 5
N1AH1Aꢁ ꢁ ꢁO2
N1AH1Bꢁ ꢁ ꢁO3
O1AH1ꢁ ꢁ ꢁO3
0.900
0.900
0.820
0.970
1.949(4)
1.898(2)
1.815(6)
3.250(3)
2.715
2.765
2.631
4.217
142.0
161.0
173.2
174.9
C8AH8Bꢁ ꢁ ꢁ
p
Salt 6
N1AH1Aꢁ ꢁ ꢁO3
N1AH1Bꢁ ꢁ ꢁO2
N1AH1Bꢁ ꢁ ꢁO3
O1AH1ꢁ ꢁ ꢁO1
O1AH1ꢁ ꢁ ꢁO2
C2AH2ꢁ ꢁ ꢁO2
0.899
0.900
0.900
0.819
0.819
0.970
0.970
0.970
0.970
2.748(4)
1.872(2)
2.643(7)
2.855(3)
1.860(3)
2.765(6)
2.923(10)
2.647(8)
3.541(10)
3.112
2.759
3.112
3.261
2.653
3.396
3.591
3.235
4.477
125.5
168.2
132.3
112.8
162.8
125.8
126.9
123.3
162.7
Structure description of salts 1–6
Salt 1 is crystallized in the triclinic system with space group
Pꢂ1. An asymmetric unit consists of half molecule of protonated
C9AH9Aꢁ ꢁ ꢁO2
C11AH11Aꢁ ꢁ ꢁO1
base (L1H22+), half molecule of deprotonated adipate ion (AA2ꢂ
)
C8AH8Aꢁ ꢁ ꢁ
p
and half molecule of neutral adipic acid (AA). In 1, the acidic hydro-
gen of the carboxyl group on adipic acid was transferred to the
nitrogen atom of base as shown in Fig. 1. The protonated nitrogen
(N1) shows the strong hydrogen bonding with the oxygen atoms
(O3, O4) of adipic acid and adipate anion via NAHꢁ ꢁ ꢁO
[N1AH1Aꢁ ꢁ ꢁO3, 1.921 (9) Å; N1AH1Bꢁ ꢁ ꢁO4, 1.848(7) Å] intermo-
lecular interactions. The crystal packing also shows other OAHꢁ ꢁ ꢁO
[O1AH1ꢁ ꢁ ꢁO5, 1.894(9) Å; O2AH2Aꢁ ꢁ ꢁO4, 1.608(27) Å], CAHꢁ ꢁ ꢁO
molecule. The presence of different noncovalent interactions is
resulted in the creation of three dimensional host–guest supramo-
lecular framework along ‘a’ axis (Fig. 2).
The salt 2 with two half molecules of protonated base (L1H22+),
one molecule of pimelate ion (PA2ꢂ) and one molecule of chloro-
form in asymmetric unit crystallizes in monoclinic system with
space group C 2/c as shown in Fig. 3. The protonated nitrogen
atoms (N1, N2) of bases present the strong hydrogen bonding
with the oxygen atoms (O3, O4, O5, O6) of pimelate ion via
NAHꢁ ꢁ ꢁO [N1AH1Bꢁ ꢁ ꢁO6, 1.881(29) Å; N1AH1Cꢁ ꢁ ꢁO3, 1.846(28) Å;
[C10AH10Aꢁ ꢁ ꢁO2, 2.814(10) Å] and CAHꢁ ꢁ ꢁ
p
[C7AH7Bꢁ ꢁ ꢁ
p,
3.474(53) Å] noncovalent interactions (Fig. S1). All hydrogen
bonded interactions are in good agreement with the reported val-
ues [45,28]. These interactions are involved in the formation of a
cavity through protonated bases and adipate anions for the accom-
modation of neutral adipic acid, where adipic acid acts as a guest
N2AH2Bꢁ ꢁ ꢁO5,
2.759(30) Å;
N2AH2Bꢁ ꢁ ꢁO6,
1.906(25) Å;
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N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
5
Fig. 1. Molecular structure of salt 1. Color code: C, yellow; H, orange; O, red; N,
blue. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
Fig. 2. Three dimensional host–guest supramolecular framework in 1. Color code:
protonated base, orange; adipate ion, pink; adipic acid, blue. (For interpretation of
the references to colour in this figure legend, the reader is referred to the web
version of this article.)
N2AH2Cꢁ ꢁ ꢁO4, 2.412(46) Å] intermolecular interactions. Other
noncovalent interactions such as OAHꢁ ꢁ ꢁO [O1AH1ꢁ ꢁ ꢁO5,
1.759(38) Å; O2AH2Aꢁꢁ ꢁO4, 2.310(92) Å] and CAHꢁ ꢁꢁO [C2AH2ꢁ ꢁꢁO5,
2.650(38) Å; C8AH8Aꢁ ꢁ ꢁO3, 2.643(27) Å; C8AH8Bꢁꢁ ꢁO6, 2.569(24) Å;
C13AH13ꢁ ꢁ ꢁO5,
2.528(29) Å;
C15AH15ꢁ ꢁ ꢁO4,
2.883(89) Å;
the different NAHꢁ ꢁ ꢁO [N1AH1Aꢁ ꢁ ꢁO2, 1.831(23) Å; N1AH1Aꢁ ꢁ ꢁO3,
2.548(34) Å; N1AH1Bꢁ ꢁ ꢁO3, 1.796(33) Å], OAHꢁ ꢁ ꢁO [O1AH1ꢁ ꢁ ꢁO1,
1.808(27) Å], CAHꢁ ꢁ ꢁO [C5AH5ꢁ ꢁ ꢁO3, 2.601(32) Å; C8AH8Aꢁ ꢁ ꢁO3,
C16AH16Bꢁ ꢁ ꢁO4, 2.864(70) Å] are also present (Fig. S2a). According
to Fig. S2b, the chloroform molecule is bonded with the pimelate
ion through very weak Cl2ꢁ ꢁ ꢁO4, 3.043(23) Å noncovalent interac-
tion [46,47]. Due to the presence of various noncovalent interac-
tions, these acids and bases with solvent molecules provide the
mat like perspective view along the ‘c’ axis (Fig. 4).
The cocrystallization of base (L1) with suberic acid give salt 3. It
crystallizes in triclinic system with space group Pꢂ1, and contains
half molecule of protonated base (L1H22+) and half molecule of
suberate anion (Fig. 5). As shown in Fig. S3, one molecule of cat-
ionic base holds the three molecules of suberate anions through
2.818(31) Å;
2.908(37) Å] and CAHꢁ ꢁ ꢁ
C8AH8Bꢁ ꢁ ꢁO2,
2.933(27) Å;
C8AH8Bꢁ ꢁ ꢁO3,
p
[C10AH10Aꢁ ꢁ ꢁ
p, 3.259(16) Å] noncova-
lent interactions [48]. Various hydrogen bonded interactions
between protonated bases and suberate anions give the three
dimensional ladder like packing view along the ‘a’ axis with three
different types of peudocavities (Fig. 6).
Salt 4 is crystallized in the monoclinic system with space group
P21/c. An asymmetric unit consists of half molecule of protonated
base (L2H22+), half molecule of deprotonated adipate ion (AA2ꢂ) and
Fig. 3. Molecular structure of salt 2. Color code: C, yellow; H, orange; O, red; N, blue. (For interpretation of the references to colour in this figure legend, the reader is referred
to the web version of this article.)
Please cite this article in press as: N. Goel, N. Kumar, J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.04.064

6
N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 4. Three dimensional mat like perspective view in 2. Color code: protonated bases, red and blue; pimelate ion, green; CHCl3, yellow. (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Molecular structure of salt 3. Color code: C, yellow; H, orange; O, red; N,
blue. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
two molecules of methanol solvent. In 4, the acidic hydrogen of the
carboxyl group on adipic acid was transferred to the nitrogen atom
of base as shown in Fig. 7. According to Fig. 8(a), the phenolic oxy-
gen (O1) and phenyl CAH of protonated base (L2H22+) are hydrogen
Fig. 6. Ladder like packing view with three different types of cavities in 3. Color
code: protonated base, green; suberate ions, purple. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
bonded with the oxygen (O4) of methanol via O4AH4ꢁ ꢁ ꢁO1,
2.888(9) Å;
C4AH4Aꢁ ꢁ ꢁO4,
3.162(9) Å
and
C5AH5ꢁ ꢁ ꢁO4,
3.401(18) Å noncovalent interactions, respectively. The CAH of
methanol is also noncovalently bonded with the oxygen atom
(O1) of L2H22+ through C13AH13Bꢁ ꢁ ꢁO1, 3.082(6) Å intermolecular
interaction. All these interactions are resulted in the creation of
square shaped pseudocavity of size 3.7 Å through L2H22+ and meth-
anol molecules for the accommodation of guests (adipate ions).
Adipate ions are resided in the cavity with the help of NAHꢁ ꢁ ꢁO
[N1AH1AꢁꢁꢁO2, 1.810(8) Å; N1AH1AꢁꢁꢁO3, 2.816(5) Å; N1AH1BꢁꢁꢁO2,
2.087(2) Å] and CAHꢁ ꢁ ꢁO [C5AH5ꢁ ꢁ ꢁO3, 3.469(9) Å; C7AH7Aꢁ ꢁ ꢁO3,
2.933(6) Å; C9AH9Aꢁ ꢁ ꢁO2, 2.532(9) Å; C9AH9Bꢁ ꢁ ꢁO2, 3.116(8) Å]
intermolecular interactions (Fig. 8(b)). Three dimensional
host–guest supramolecular framework is formed along ‘c’ axis with
the help of these noncovalent interactions (Fig. 8c and d) [7].
The salt 5 with half molecule of protonated base (L2H22+) and
half molecule of pimelate ion (PA2ꢂ) in asymmetric unit crystal-
lizes in monoclinic system with space group C 2/c as shown in
Fig. 9. The two molecules of L2H22+ interact with each other via
C8AH8Bꢁ ꢁ ꢁ
p, 3.250(3) Å intermolecular interactions, and form a
rectangular shaped cavity of size 1.4 Å for the insertion of pimalate
ion (Fig. 10(a)). Guest ions are accommodated in the cavity with
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N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
7
Fig. 7. Molecular structure of salt 4. Color code: C, yellow; H, orange; O, red; N,
blue. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
Fig. 9. Molecular structure of salt 5. Color code: C, yellow; H, orange; O, red; N,
blue. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
the help of NAHꢁ ꢁ ꢁO [N1AH1Aꢁ ꢁ ꢁO2, 1.949(4) Å; N1AH1Bꢁ ꢁ ꢁO3,
1.898(2) Å] hydrogen bond interactions (Fig. 10(b)). Other nonco-
valent interaction O1AH1ꢁ ꢁ ꢁO3, 1.815(6) Å is also present between
cation and anion (Fig. S4). All these interactions provide the mat
like host–guest supramolecular organic framework with and with-
out guests along the ‘c’ axis (Fig. 10c and d). The crystallographic
packing view of this salt is similar to salt 4.
Salt 6 crystallizes in monoclinic system with space group C 2/c,
which contains half molecule of protonated base (L2H22+) and half
molecule of suberate ion (SUA2ꢂ) as shown in Fig. 11. According
to Fig. 12(a), six molecules of L2H22+ are hydrogen bonded to each
other through O1AH1ꢁ ꢁ ꢁO1, 2.855(3) Å and C8AH8Aꢁ ꢁ ꢁ
p,
3.541(10) Å noncovalent interactions, and form a spider shaped
cavity of size 3.3 Å for the insertion of suberate ions as a guest.
Two molecules of SUA2ꢂ are accommodated in the cavity via
NAHꢁ ꢁ ꢁO [N1AH1Aꢁ ꢁ ꢁO3, 2.748(4) Å; N1AH1Bꢁ ꢁ ꢁO2, 1.872(2) Å;
N1AH1Bꢁ ꢁ ꢁO3, 2.643(7) Å], OAHꢁ ꢁ ꢁO [O1AH1ꢁ ꢁ ꢁO2, 1.860(3) Å]
and CAHꢁ ꢁ ꢁO [C2AH2ꢁ ꢁ ꢁO2, 2.765(6) Å; C9AH9Aꢁ ꢁ ꢁO2, 2.923(10) Å;
C11AH11Aꢁ ꢁ ꢁO1,
2.647(8) Å]
intermolecular
interactions
Fig. 8. (a) Square shaped cavity, (b) adipate ions in a cavity, (c) three dimensional host framework, and (d) three dimensional host–guest perspective view in 4. Color code:
protonated base, orange; adipate ion, pink; CH3OH, green. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)
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8
N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
Fig. 10. (a) Rectangular shaped cavity, (b) pimalate ions in a cavity, (c) three dimensional host framework, and (d) three dimensional host–guest supramolecular architecture
in 5. Color code: protonated base, green; pimalate ion, pink. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this
article.)
surface. The single point energy calculations were performed for
recording the zero point corrected total energies of various species.
The optimized structures of salts 1–6 at B3LYP/6-311G++(d,p) basis
set are shown in Fig. 13. In addition to the characterization of these
salts, the gas phase geometries, harmonic vibrational frequencies,
and binding energies of these salts were also computed. The com-
parisons between experimental and simulated structural parame-
ters such as bond lengths and bond angles are listed in Tables S3
and S4.
The hydrogen bond interaction energies were determined
according to the following equation [8,9]
D
E ¼ Esalt ꢂ ðEacid þ EbaseÞ
where Esalt, Eacid and Ebase are the zero point corrected total energies
of salt, acid and base, calculated at B3LYP/6-311G++(d,p) level of
theory. We have removed the solvent and neutral molecules to
check the relative stability. The trend observed for the hydrogen
bond interaction energy is given in Table 3. DFT calculation shows
that the hydrogen bond interaction energy decreases due to
increase the carbon chain of both acids and bases i.e., CH2 group
is increased stepwise in each acid and base. This is because of +I
effect, which makes the bond weak due to lengthening of the bond.
Hence, the force constant becomes lower, and the energy decreases.
Along with this, the negligible difference in the energy of the opti-
mized structures and crystal structures of salts 1–6, suggests that
the orientation and interaction remain almost same in both the
gas and solid phases (Table S5). From the statistical analysis, it is
found that the value of correlation coefficient (R) for bond lengths
are 0.966, 0.985, 0.944, 0.978, 0.946 and 0.964, while its values
for bond angles are 0.989, 0.976, 0.959, 0.952, 0.974 and 0.981,
respectively, in salts 1–6. From this, it is clear that the theoretical
(DFT) values are statistically closed to actual experimental (XRD)
values. The plots for curve fitting analysis are given in Figs. S5-S8.
Fig. 11. Molecular structure of salt 6. Color code: C, yellow; H, orange; O, red; N,
blue. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
(Fig. 12(b)). A similar hydrogen bonding motif is also present in salt
3. Various hydrogen bonded interactions between protonated
bases and suberate anions give the three dimensional supramolec-
ular motif view along the ‘c’ axis (Fig. 12c and d).
DFT and statistical analysis
The optimized geometry of salts 1–6 showed the positive har-
monic vibrational frequencies, which suggested that the optimized
structures were the global minimum on the potential energy
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N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
9
Fig. 12. (a) Spider shaped cavity, (b) suberate ions in a cavity, (c) three dimensional host framework, and (d) three dimensional host–guest view in 6. Color code: protonated
base, cyan; suberate ion, green. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 13. Optimized geometry of salts 1–6. Color code: C, pink; H, red; O, green; N, yellow. (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
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10
N. Goel, N. Kumar / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 3
statistical analysis, it is found that the theoretically calculated
Hydrogen bond interaction energy of salts 1–6.
structural parameters are in line with the crystallographic data
for salts 1–6. The structural analysis reveals that the N,N0-bis(sali-
cyl)ethylenediamine and N,N0-bis(salicyl)butylenediamine are
excellent building blocks, which are responsible for the creation
of entirely different three dimensional packing views. The diversity
in supramolecular structures may be due to the difference in the
carbon chain of carboxylic acids, bases, type of interactions and
the orientation of the molecules in three dimensional spaces. From
the three dimensional packing diagrams, it is cleared that the cav-
ities with different shapes and size are created as the carbon chain
increases in bases i.e., in salts 1–3, there is no cavity but salts 4–6
have square to rectangular to spider shaped cavities. So the synthe-
sis of these salts with pre-determined connectivity and topology
will offer a path towards the design of materials with pre-deter-
mined bulk properties. Theoretical studies suggest that structures
are same in both the gas and solid phases, and hydrogen bond
interaction energy largely depends on the number of carbon chain
i.e., hydrogen bond interaction energy decreases on increasing the
chain length. Thermal study shows that all synthesized salts are
stable at room temperature, and decompose at high temperature.
S. no.
Salts
Hydrogen bond interaction
energy (kcal/mol)
1
2
3
4
5
6
Salt 1
Salt 2
Salt 3
Salt 4
Salt 5
Salt 6
30.48
28.17
25.75
29.76
26.82
24.49
Table 4
TG–DTG data of salts 1–6 under a nitrogen atmosphere.
S. no.
Salts
TG
DTG
Ti/°C
Tf/°C
a
Peak temp./°C
1
2
Salt 1
Salt 2
157
329
151
215
198
134
355
294
213
214
423
174
369
347
207
437
429
352
24.3
72.9
20.9
77.4
98.7
12.1
86.6
98.4
98.6
194 °C
377 °C
121 °C
253 °C
324 °C
160 °C
379 °C
367 °C
341 °C
3
4
Salt 3
Salt 4
5
6
Salt 5
Salt 6
Acknowledgments
Authors gratefully acknowledge CSIR, New Delhi, India, for
financial assistance in form of PDF to NG, SRF to NK and IITR for
instrumental facilities.
Thermal analysis
The thermal stability of salts 1–6 is demonstrated by TG–DTG.
The thermoanalytical data are listed in Table 4, and the TGA–
DTG curves are shown in Figs. S9 and S10. The thermograms clearly
indicate that these salts are stable up to 100 °C but at higher tem-
peratures, curves show irregular pattern. The thermal decomposi-
tion of salt 1 occurs in two steps. The first weight loss (24.3%) in the
temperature range of 157 and 214 °C (DTG peak at 194 °C) corre-
sponds to the release of neutral adipic acid. The second weight loss
(72.9%) is observed in between 329 and 423 °C (DTG peak at
377 °C). It may be due to the release of protonated base and adi-
pate ion. Salt 2 also undergoes two stages decomposition. The first
stage (20.9% mass loss) corresponds to DTG peak at 121 °C. In this
step chloroform (151–174 °C) leaves out. In the second stage (215–
369 °C), both cation and anion are released (77.4% mass loss),
which shows DTG peak at 253 °C. The thermal decomposition of
salt 3 at temperature range 198–347 °C predicts the weight loss
of 98.7% with the DTG peak at 324 °C due to the release of both
protonated base and suberate ion. In salt 4, first weight loss of
12.1% in between 134 and 207 °C (DTG peak at 160 °C) corresponds
to the release of two methanol molecules. The second weight loss
(86.6%) is observed in between 355 and 437 °C (DTG peak at
379 °C), and it may be due to the release of protonated base and
adipate ion. Salt 5 undergoes one step decomposition with the loss
of 98.4% in total mass, corresponds to DTG peak at 367 °C. In this
step both cation and anion (294–429 °C) leaves out. The thermal
decomposition of salt 6 (213–352 °C) shows the weight loss of
98.6% with the DTG peak at 341 °C due to the release of both pro-
tonated base and suberate ion.
Appendix A. Supplementary material
CCDC numbers 956403-956405 and 969961-969963 contain
the supplementary crystallographic data (CIF) for this article. These
data can be obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223 336 033; E-
mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Additional figures (Figs. S1–S10) and DFT calculations (Tables
S1–S5) are available in PDF formats. Supplementary data associ-
ated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.molstruc.2014.04.064.
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