N-(thiazol-2-yl)benzamide derivatives as a new series of supramolecular gelators: Role of methyl functionality and S?O interaction

Article abstract of DOI:10.1016/j.jssc.2019.121027

A new series of N-(thiazol-2-yl) benzamide derivatives were synthesized, characterized and investigated for their gelation behavior with the aim to elucidate the role of methyl functionality and multiple non-covalent interactions on gelation/non-gelation

Full text of DOI:10.1016/j.jssc.2019.121027

Journal Pre-proof
N-(thiazol-2-yl)benzamide derivatives as a new series of supramolecular gelators:
Role of methyl functionality and S⋯O interaction
Priyanka Yadav, Amar Ballabh
PII:
S0022-4596(19)30532-8
DOI:
https://doi.org/10.1016/j.jssc.2019.121027
YJSSC 121027
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 22 September 2019
Revised Date: 19 October 2019
Accepted Date: 22 October 2019
Please cite this article as: P. Yadav, A. Ballabh, N-(thiazol-2-yl)benzamide derivatives as a new series
of supramolecular gelators: Role of methyl functionality and S⋯O interaction, Journal of Solid State
Chemistry (2019), doi: https://doi.org/10.1016/j.jssc.2019.121027.
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N-(thiazol-2-yl)benzamide derivatives as a new series of
supramolecular gelators: role of methyl functionality and S…O
interaction
Priyanka Yadav and Amar Ballabh*
TABLE OF CONTENTS (TOC)
H
N
N
O
S
XEROGEL
CRYSTAL

N-(thiazol-2-yl)benzamide derivatives as a new
series of supramolecular gelators: role of methyl
functionality and S…O interaction
Priyanka Yadav and Amar Ballabh*
Department of Chemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda,
Vadodara-390002 Gujarat (India)
ABSTRACT
A new series of N-(thiazol-2-yl) benzamide derivatives were synthesized, characterized and
investigated for their gelation behavior with the aim to elucidate the role of methyl functionality
and multiple non-covalent interactions on gelation/non-gelation behavior using Crystal
engineering approach. Interestingly, two amides, namely, 3-methyl-N-(thiazol-2-yl) benzamide
(1c) and 3-methyl-N-(5-methylthiazol-2-yl) benzamide (3c) displayed gelation behavior towards
ethanol/water and methanol/water mixture with good stability and low minimum gelator
concentration (MGC). The single crystal structure of gelator (1c) displayed the helical assembly
driven by π-π interaction along with cyclic N-H…N and S…O interaction, whereas single crystal
structure of gelator (3c) displayed 2D hydrogen bonded network without any π-π interaction.
KEYWORDS: Crystal engineering, supramolecular gelators, S…O interaction, helical
architecture, thiazole amide derivatives
1

INTRODUCTION
2-aminothiazole and its derivatives, a simple heterocyclic compound, with huge biological
implication are at the forefront of research and development since many decades.1 Surprisingly,
the use of 2-aminothiazole as structural motif for crystal engineering and supramolecular
assembly is not addressed to its fullest.2,3 In our quest for new supramolecular gelators, we
serendipitously discovered 2-aminothiazole as a versatile structural motif for design and
synthesis of new Low Molecular Weight gelators (LMWGs).4-8 LMWGs are special class of
supramolecular materials capable of immobilizing solvent (water, organic or mixture) through
weak non-covalent interactions such as hydrogen bonding, π-π, van der Waals forces, etc. In last
two decades, design, synthesis and application of new LMWGs have gained considerable interest
due to its potential applications in various areas of research ranging from material science to bio-
medical applications.9-15 Even though, most of the LMWGs were discovered serendipitously
but crystal engineering approach proved to be a reliable tool for designing new LMWGs.16,17
Recently, we found series of compounds, which can be classified as LMWGs based on 2-
aminothiazole capable of immobilizing water18 and organic solvents.19,20 Our studies on aliphatic
amides of 2-aminothiazole displayed many interesting properties such as dependence of gelation
behaviour on the position of methyl functionality on 2-aminothiazole as well as number of
methylene group in the aliphatic backbone, i.e., even number of methylene groups (-CH2)
displayed gelation, whereas odd number of –CH2 group was found to be deterrent to gelation
behaviour.19
Inspired by our success with 2-aminothiazole based LMWGs (salts, amides, metal complex),
we decided to design new series of compounds containing the 2-aminothiazole moiety, amide
linkage and aromatic backbone (Chart 1). These set of compounds may provide an opportunity
2

to study the role of π- π interaction in inducing supramolecular gelation along with other weak
non-covalent interactions such as (methyl) C-H... π, (methyl) C-H...N, (methyl) C-H...S (Scheme
1). Our studies on 2-aminothiazole based LMWGs displayed frequent occurrence of
intermolecular cyclic N-H...N interaction and intramolecular (amide) O…..S (thiazole)
interactions (Scheme IA). Surprisingly, S…O interaction is rarely explored as supramolecular
glue in crystal engineering related studies21 as compared with its prevalence in biological
system.22-26
In the present study, series of thiazole based amide having aromatic backbone were
synthesized and characterized by various physicochemical methods. The effect of position of
methyl functionality (thiazole moiety and benzene ring) on crystalline packing and gelation
behavior was evaluated. Out of 12 compounds synthesized two (1c and 3c) displayed excellent
gelation behavior towards ethanol/water and methanol/water mixture (1:1). The single crystal
structure of two gelators (1c and 3c) and non-gelators (1b, 1d, 3b and 3d) were compared to
understand the cause of gelation/ non-gelation behavior based on hydrogen bonding pattern and
synergistic effect of other weak non-covalent interaction such as S…O, C-H…π, π…π, etc.
3

X
O
C
N
R
Y
N
S
H
1a,X=H,Y=H,R=H
2a,X=CH3,Y=H,R=H
1b,X=H,Y=H,R=2-CH3
1c,X=H,Y=H,R=3-CH3
1d,X=H,Y=H,R=4-CH3
2b,X=CH3,Y=H,R=2-CH3
2c,X=CH3,Y=H,R=3-CH3
2d,X=CH3,Y=H,R=4-CH3
3a,X=H,Y=CH3,R=H
3b,X=H,Y=CH3,R=2-CH3
3c,X=H,Y=CH3,R=3-CH3
3d,X=H,Y=CH3,R=4-CH3
Chart I: List of N-(thiazol-2-yl)benzamide derivatives synthesized in the present study
Scheme 1: Probable supramolecular synthons in amides and thiazole containing amides
4

Experimental Section
Materials and physical measurements
2-Aminothiazole (97%), 2-Amino-5-methylthiazole (98%), 2-Amino-4-methylthiazole (98%),
benzoic acid (97%), 2-toluicacid (98%), 3-toluic acid (98%), 4-toluicacid (99%) (All Chemical
were purchased from Aldrich) were used as received. The other chemicals were of the highest
commercial grade available and were used without further purification. The solvents used for the
preparation of gels were reagent grade. All solvents used in the synthesis were purified, dried
and distilled as required. FTIR Spectra were recorded on a Perkin Elmer –RX FTIR instrument.
Solid samples were recorded as an intimate mixture with powdered KBr. Microanalysis was
1
performed on Perkin Elmer elemental analyzer (Series II, 2400). The H- NMR spectra were
1
measured by using a Bruker AVANCE, 400MHZ for H-NMR with TMS as internal standard.
Morphologies of all reported gel materials were investigated using Scanning Electron
Microscopy (SEM) (JEOL JSM5610 LV microscope). For SEM study, the gel samples were
dried at room temperature (25°C) to obtain xerogel, followed by recording the micrographs.
Single crystal X-ray study was carried out on Single Crystal X-ray diffractometer (Xcalibur,
EOS, Gemini diffractometer). All structures were solved and refined using the Olex227 software
and ShelXL28 refinement package Graphics are generated using MERCURY 3.9. All structures
are solved by direct methods and refined in a routine manner. In all cases, non-hydrogen atoms
are treated anisotropically. Whenever possible, the hydrogen atoms are located on a difference
Fourier map and refined. In other cases, the hydrogen atoms are geometrically fixed.
Rheological study: Sample 1a and 1c were subjected to rheological study by amplitude sweep
methods using TA instruments (Model- ARES G2) at 25°C. Rheometer has parallel plate
geometry with a plate diameter of 50 mm maintained at a gap of 1mm. The gel samples were
5

subjected to frequency variation of 10 rad/s. The storage (G’) and loss modulus (G’’) of the
samples were evaluated with respect to oscillation strain (in %).
Gelation Study
A weighted amount of potential gelator and a measured volume of selected pure organic
solvent were placed into a test tube, and the system was heated in oil or water bath until all solid
materials were dissolved. The solution was cooled to room temperature and finally, the test tube
was turned upside down to observe if the solution inside could still flow. A positive test is
obtained if the flow test is negative. Systems in which only solution remained until the end of the
tests are referred as solutions (S). Systems that are clear solutions when they are hot but
precipitation or crystallization occurs when they are cooled down to room temperature are
denoted by P (precipitation) and R (recrystallization), respectively. Temperatures of gel-to-sol
transition (Tgel) were determined by using a conventional “falling ball” method. In a typical Tgel
measurement experiment, a small glass ball (63mg) was carefully placed on the top of the gel
sample in a test tube. The tube was slowly heated in a thermostated oil bath until the ball fell to
the bottom of the test tube. The temperature at which the ball touched the bottom of the test tube
was recorded as gel-sol transition temperature (Tgel) for a given gelator-solvent system.
Synthetic procedure
Synthesis method of N-(thiazol-2-yl) benzamide derivatives
Oxalyl chloride (2 mL, 20 mmol) was added slowly to a solution of monocarboxylic acids (2
mmol) in dry dichloromethane (10 mL) under a nitrogen atmosphere with continuous stirring and
reaction mixture was kept for 12 hours under inert atmosphere. Excess oxalyl chloride and
solvent were removed by distillation under reduced pressure. The acid chloride obtained was
6

dissolved in dry dichloromethane (10 mL) and subsequently, added to the 2-aminothiazole (2
mmol) and triethylamine (0.3ml, 2.15mmol) mixture in a RB flask. The mixture was stirred
under a nitrogen atmosphere for more than 12 hours .The reaction mixture was then added to
dilute hydrochloric acid (5%), and extracted with chloroform. The product obtained after
removing chloroform was further purified by repeated crystallization from ethanol.
Synthesis and Characterization: All the synthesized compounds were characterized various
physicochemical studies. The IR studies of compounds 1a-1d, 2a-2d and 3a-3d showed amide I
(C=O) stretching peak in the range of 1611-1688 cm-1 and N-H stretching frequency in the range
of 3452-3182 cm-1 (see supporting information). All the compounds were further characterized
by 1H NMR spectroscopy and elemental analysis.
RESULTS AND DISCUSSION
Gel Formation and morphology studies
All the synthesized compounds were subjected to gelation test in various solvents with varied
polarity ranging from highly polar solvents such as water, ethanol, methanol, etc. to very less
polar solvents such as toluene and n-octadecane (See supporting information Table S1). Out of
12 synthesized compounds only two (1c and 3c) turned out to be good gelator for ethanol/water
(1:1) and methanol/water (1:1) mixture. 1c and 3c showed quite low minimum gel concentration
(MGC) for the gelation of methanol/water and ethanol/water mixture (Table S1).
A graph of Tgel versus concentration of gelator molecules in wt % (w/v) showed a gradual
increase in Tgel up to a certain concentration of gelator then plateau was observed (Figure
1).Understandably, the increase in gelator concentration improves the self-aggregation and
stability of supramolecular assembly but not beyond certain critical concentration. The nature of
7

the graph for Tgel versus concentration of gelator is frequently observed for supramolecular
gelators.
1C
80
75
3C
70
65
60
1
2
3
4
5
conc.(wt%)
Figure 1: Sol-to-gel transition temperature (Tgel) versus change in concentration (wt % w/v)
graph for gelator 1c and 3c in ethanol/water mixture
To study the morphology of gelator fibres a detailed SEM analysis was carried out on xerogel
(dried gel) of 1c and 3c obtained from ethanol/water (1:1) gel (Figure 2). SEM image of xerogel
of 1c displayed highly crossed linked twisted fibres. However, the xerogel of 3c showed a well-
defined independent assembly of rod like morphology. Presumably, such loose collections of
crystalline tubes immobilize solvents, resulting in a weak gel (high MGC). Understandably,
highly cross linked network of fibres in 1c would be capable of hardening a solvent easily than a
bundle of rods, which lacks a junction point and or/cross linking (3c).
8

Figure 2: SEM images of xerogel of (A)1c and (B) 3c from 1:1 ethanol/water mixture
A
The gel made from the gelators 1c and 3c were further characterized by rheological experiments.
The magnitude of the storage modulus (G’) was found to be an order of magnitude higher that
the loss modulus (G”) for both the gel samples. This represents the true behaviour of the
viscoelastic gel materials (Figure 3).
10 µM
50 µM
A
B
30000
45000
30000
G'
20000
G'
G"
G"
15000
10000
0.00 0.01 0.02 0.03 0.04 0.05
oscillation strain(%)
0.00
0.05
0.10
oscillation strain(%)
Figure 3: Rheological studies of the gel formed from A) 1c and B) 3c in ethanol/water
mixture (1:1)
Single crystal X-ray studies of compounds (1b-1d and 3b-3d)
2-methyl-N-(thiazol-2-yl) benzamide (1b): 1b crystallizes in the orthorhombic space group
Pccn. Asymmetric unit of 1b contains one molecule of 2-methyl-N-(thiazol-2-yl) benzamide.
Two molecules of 1b are strongly hydrogen-bonded with each other through cyclic N-H.....N
(thiazole) (N....N =2.951 Å, ∠N-H.....N=175.930) and N-H...N (thiazole) (N....N=2.951 Å, ∠N-
9

H...N =175.930) interactions, along with the intramolecular bond between the carbonyl oxygen
atom and the thiazole sulphur atom (O....S=2.719Å), resulting in a zero-dimensional (0D)
network. The 0D network extends to 1D through the bifurcated short contacts between the
benzene ring i.e. C-H.....
=150.02°). Interestingly, C-H…
H…Centroid (Cg) = 2.825 Å,
π
(C…
π
=3.722 Å,
∠C-H…π =158.01°; C…π =3.753Å, ∠C-H…π
π
interaction was observed between two thiazole ring (C-
∠
C-H…Cg= 132.8 °C) which propagates packing of 1b to two-
dimensional network (2D). (Figure 4A). A critical examination of the crystal structures suggests
the overall twisted packing (Figure 4B).
A
B
Figure 4: View of A) hydrogen bonded helical network of 1b in ball and sticks model and B)
Space fill model
3-methyl-N-(thiazol-2-yl) benzamide (1c): 1c crystallizes in the triclinic space group
P-1. The asymmetric unit of 1c contains two molecules of 3-methyl-N-(thiazol-2-yl) benzamide.
The two molecules of 1c are hydrogen-bonded with each other through cyclic N-
H.....N(thiazole)(N....N =2.927 Å, ∠N-H.....N=150.02°) and N-H...N (thiazole) (N....N= 3.008
10

Å,
∠
N-H.....N=151.79° ) interactions. The hydrogen bonded assembly of four molecules of 1c
interaction (Centroid….Centroid=
were held together with C-H…O interaction and two
π…π
3.893Å) between thiazole molecule and benzene ring. The assembly of 4 molecules were
extended to 1D network through S…S (S....S =3.461Å) interaction. Surprisingly, non-bonded
interaction S…S interaction is not reported in the crystal engineering of organic molecules to the
best of our knowledge. Interestingly, the self-assembly of 1c displayed double helical structure
(Figure 5).
B
A
Figure 5: view of A) hydrogen bonded double helical network of 1c in ball and sticks model
and B) Space fill model
4-methyl-N-(thiazol-2-yl) benzamide (1d): 1d crystallizes in the triclinic space group P-1.
The asymmetric unit of 1d contains two molecules of 4-methyl-N-(thiazole-2-yl) benzamide.
The two molecules of 1d are held together by cyclic N-H.....N(thiazole) (N....N =2.955 Å,
∠N-
H.....N=155.91°) and N-H...N (thiazole) (N....N=2.934 Å, N-H.....N=166.84°) interactions,
∠
11

along with the intramolecular bond between oxygen atom and sulphur atom(O....S=2.668Å),
resulting in a 0D network. Various short contacts such as C-H.....S (C....S =3.884 Å,
∠C-
H.....S=171.840) and C-H.....N (C....N =3.428Å, C-H.....N=150.940) interactions propagates the
∠
0D network into 1D hydrogen bonded twisted structure (Figure 6A), While C-
C-H.....C= 133.390) interactions propagates, leading to 2D hydrogen
H.....π(C....C=3.841Å, ∠
bonded network (Figure 6B).
A
B
Figure 6: view of hydrogen bonded network of 1d, resulting twisted structure A) space fill
model and B) ball and sticks model
2-methyl-N-(5-methylthiazol-2-yl) benzamide (3b): 3b crystallizes in the triclinic space
group P-1. One molecule of 3b was found in the asymmetric unit of 3b. The two molecules of
3b are held together by strong supramolecular synthon N-H…N (N....N =2.871Å,
∠N-
H.....N=155.910) interactions, along with the intramolecular bond between the carbonyl oxygen
12

atom and the thiazole sulphur atom (O....S=2.769Å), resulting in a 0D network. 0D network of
3b is retained by multiple C-H…O interaction between two molecules of 3b. The 0D network
extends to 1D network through C-H…O (C....O =3.484 Å, ∠C-H.....O=145.06°)interaction
between two molecules of 3b one above and one below the plane A weak van der Waals
interaction between the C-H...C is also observed in the crystal structure leading to overall 2D
network having twisted hydrogen bonded network (Figure 7).
B
A
Figure 7: view of A) hydrogen bonded network of 3b in ball and sticks model and B) Space fill
model
3-methyl-N-(5-methylthiazol-2-yl) benzamide (3c): 3c crystallizes in the monoclinic space
group P 21/c. The two molecules of 3c are held together by strong supramolecular synthon N-
H…N (N....N =2.934Å,
∠
N-H.....N=177.080) interactions, along with the intramolecular bond
between the carbonyl oxygen atom and the thiazole sulphur atom (O....S=2.684Å), resulting in a
0D network. The 0D network extends to 2D network through C-H…O (C....O =3.544 Å,
∠
C-
13

H.....O=154.53°) interaction and weak van der Waals interaction between the C-H...C (C....C
=3.672 Å,
∠
C-H.....C=178.15°), C-H...C (C....C =3.544 Å,
∠C-H.....C=151.50°) (Figure 8) .
B
A
Figure 8: view of A) hydrogen bonded network of 3c in ball and sticks model and B) Space fill
model
4-methyl-N-(5-methylthiazol-2-yl) benzamide (3d): 3d crystallizes in the monoclinic space
group I 2/a. The asymmetric unit of 3d contains one molecules of 4-methyl-N-(5-methylthiazol-
2-yl) benzamide. The two molecules of 3d are bonded through hydrogen bonding
supramolecular synthons with each other i.e. cyclic N-H.....N(thiazole) (N....N =3.996 Å,
∠N-
H.....N=148.97°) and N-H...N (thiazole) (N....N=2.991Å, N-H.....N=149.51°) interactions,
∠
along with the intramolecular bond between the carbonyl oxygen atom and the thiazole sulphur
atom(O....S=2.696 Å), resulting in a 0D network. 0D network of 3d extends to 2D through
various short contacts such as (methyl)C-H.....
C-H.....O (C....O =3.312Å, C-H.....O= 132.80 °). Even though, the self-assembly of 3d did not
propagated in twisted manner but it showed consecutive double turn conformation (Figure 9).
π (centroid…C-=3.657 Å, ∠C-H.....C=159.55°),
∠
14

Figure 9: view of hydrogen bonded twisted network of 3d in capped stick model
A critical analysis of weaker interactions (Table 1 and supporting information Table S3 and
Figure S1) clearly shows the presence of robust cyclic (amide) N-H...N (thiazole)
supramolecular synthon leading to 0-D hydrogen bonded network in all the crystal structures
(Scheme 1, synthon A). None of the structure displayed the presence of amide-amide linkage,
suggested the preference of cyclic N-H…N interaction over amide-amide supramolecular
synthon (Scheme 1, synthon B and C). However, intramolecular O....S interaction was found in
all the crystal structures of thiazole amide, with or without a methyl functional group, leading to
restricted C-C bond rotation between thiazole moiety and amide functional group. To understand
the effect of position of methyl group on benzene ring as well as thiazole moiety, we carry out
measurement of angles between the planes passing through the aromatic and thiazole ring. We
observed the drastic variation in angles between two planes (plane passing through aromatic ring
and thiazole ring) for the two series of compounds i.e. 1b-1d and 3b-3d, ranging from 8.78° to
88.67°. Understandably, such change in angles may be attributed to close proximity of methyl
group to thiazole amide dimer (see supporting information Table S4 and Figure S2).
15

Table 1: Critical analysis of non-bonded interactions present in single crystal X-ray structures
1b
1c
1d
3b
3c
3d
Bond
length
(A0)
Bond
angle
Bond
length
Bond
angle
Bond
length
Bond
angle
Bond
length
Bond
angle
Bond
length
Bond
angle
Bond
length
Bond
angle
(0)
(A0)
(0)
(A0)
(0)
(A0)
2.769
2.871
2.871
(0)
(A0)
2.683
2.935
2.935
(0)
(A0)
2.696
3.996
2.991
(0)
O……S
Cyclic
2.719
2.951
2.951
3.722
3.753
2.675
2.668
175.93
175.93
158.01
150.02
2.927 150.02 2.955
3.008 151.79 2.934
155.91
166.84
155.91
155.91
173.39
173.39
148.97
149.51
N-H….N
C-H.....π
C-H.....π
(methyl)C-
H.....O
2.683 126.71
3.439
140.25
3.555
157.42
π....π
S....S
3.391
3.461
3.884
3.428
C-H.....S
C-H.....N
171.84
150.94
(methyl)C-
H.....π
3.575
3.575
147.50
147.50
3.685
3.578
171.06
145.49
(methyl)C-
H.....π
As ortho position of methyl group on phenyl ring brought the maximum change in angle
between the planes passing through aromatic and thiazole ring, i.e. 1b (59.84°) and 3b (88.67°),
whereas the para position of methyl group to phenyl ring brought the least deviation in the angles
between the planes, especially in the series of compounds, 3b-3d. It is difficult to make a
comment on the series of compounds (1b-1d) as 1c and 1d both contain two molecules each in
asymmetric unit with drastically different angle between the planes passing through the aromatic
and thiazole ring.
16

Scheme 2: Schematic representation of a plausible mechanism of gelation (1c and 3c) and non-
gelation (2c).
Interestingly, the series containing methyl group at meta position of phenyl ring (1c and 3c)
turned out to be hydrogelator. Compound 1c turned out to be an excellent gelator for
alcohol/water mixture, whereas compound 3c was found to be a weak gelator of solvent mixture,
suggesting the position of methyl group on the thiazole moiety play a crucial role in gelation
process (Scheme 2). Understandably, the suitable position of methyl groups (on thiazole moiety
and phenyl ring) facilitate the formation of extended hydrogen bonding network through
multiple weak non-covalent interactions such as C-H…O, C-H…N, etc. The series of 4-
methylthiazole amide having phenyl ring with ortho, meta and para –CH3 group turned out to be
non-gelator for the solvent studied (Scheme2). Furthermore, the good gelation property of 1c in
water/ethanol and water/methanol mixture (based on its single crystal structure) may be
attributed to the presence of multiple weak non-covalent interactions such as C-H…O, π…π,
17

S…S along with cyclic N-H…N and S…O interactions, which are invariably present in all the
crystal structures (gelator and non-gelators). On the other hand, the single crystal structure of
weak gelator 3c also contains multiple weak interactions such as two C-H…π and one C-H…O
interactions. Comparative analysis of weak non-bonded interactions present in gelators (1c and
3c) suggests greater number of auxiliary non-bonded contacts than non-gelators molecules (1b,
1d, 3b and 3d). This prompted us to propose that along with N-H…N (cyclic dimeric
supramolecular synthons) and S…O (intramolecular ) interactions multiple weak non-bonded
contacts play a crucial role in controlling the overall supramolecular assembly.
The single crystal structure of thiazole amide displayed plethora of weak non-bonded
interactions such as C-H…π, C-H…O, C-H…N, C-H…S, S…S, etc., suggested more detailed
research is required before we can choose the robust supramolecular synthons for designing a
new material with interesting properties especially in thiazole based compounds.
CONCLUSIONS
A new series of LMOGs based on thiazole amide moiety decorated with aromatic ring was
designed and synthesized using the concept of crystal engineering. Out of 12 amides synthesized
two molecules namely 1c and 3c turned out to be good gelling agent for ethanol/water (1:1) and
methanol/water (1:1) mixture. Some interesting facts were observed in the single crystal
structure of gelator/non-gelator. All the structure show the recurrence of two supramolecular
synthons i.e. N-H...N (cyclic) and intramolecular S…O interaction. The single crystal structure
of gelator (1c) displayed the presence of
interactions, whereas gelator 3c structure displayed presence of multiple C-H…O interactions
along with S…O and N-H…N interactions (absence of interaction). The intramolecular
π-π interaction along with S…O and N-H…N
π-π
18

S…O interaction seems to bestow rigidity and planarity to the structures and cyclic N-H…N
interaction makes 0-D supramolecular assembly. Surprisingly, the additional interaction or
π…π
C-H…O interaction proved to be crucial factor in inducing the gelation properties in these series
of compounds. The present studies open an avenue to design a new set of LMWGs based on
present design strategy of thiazole derivatives-amide linker-benzene derivatives to any
heterocyclic compounds-hydrogen bonding linker-aromatic backbone. Furthermore, these
studies show how crystal engineering approach may help in designing and understanding the
supramolecular assembly of new LMWGs. We believe the weak S…O interaction observed in
thiazole based compounds need to be strengthen further before it can be used as reliable
designing tool in crystal engineering.
ASSOCIATED CONTENT
Supporting Information. Physicochemical data of compounds 1a-1d, 2a-2d and 3c-3d, gelation
study table, crystallographic parameter table of 1b(CCDC No. 958804), 1c (CCDC No.
972288), 1d(CCDC No. 964475), 3b(CCDC No. 994091) , 3c ( CCDC NO. 1890271) and
3d(CCDC No. 994092), ORTEP diagram and table of hydrogen bonds with symmetry
operation (1b-1d and 3b-3d), table containing inter-planar angles between aromatic ring and
thiazole moiety in the crystal structures ( 1b-1d and 3b-3d). 1H NMR and IR spectra of
compounds 1a-1d, 2a-2d and 3a-3d.
19

AUTHOR INFORMATION
Corresponding Author
Fax: +91-265-2795569. Tel: +91-265-2795552. E-mail: bamar.chem@gmail.com/
amar.ballabh-chem@msubaroda.ac.in
Author Contributions
The manuscript was written through contributions of all authors. All authors have given
approval to the final version of the manuscript.
ACKNOWLEDGMENT
Authors would like to acknowledge the DST-PURSE program funding for the Single Crystal X-
ray Diffractometer at Faculty of Science, The Maharaja Sayajirao University of Baroda,
Vadodara and NMR facility to DST-FIST (Phase I) program of Department of Chemistry,
Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara. AB would like
also like to acknowledge The Head, Department of Chemistry, Faculty of Science, M. S.
University of Baroda for moral support and providing infrastructural facility. Solvay Research
and Innovation Centre (R &I), Vadodara is gratefully acknowledge for their help in Rheological
characterization of gel samples.
ABBREVIATIONS
MGC Minimum Gelator Concentration, LMWG Low Molecular Weight Gelator, Tgel gel-sol
transition temperature
20

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Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: