3-(benzo[d]thiazol-2-YL)phenol and 4-(benzo[d]thiazol-2-YL)phenol: Crystal Structure Determination, DFT Calculations and Visualizing Intermolecular Interactions Using Hirshfeld Surface Analysis

Article abstract of DOI:10.1080/15421406.2015.1107812

This article describes the synthesis and X-ray crystal structure analysis of 3-(benzo[d]thiazol-2-yl) phenol (I) and 4-(benzo[d]thiazol-2-yl)phenol (II), crystallized in centrosymmetric triclinic and orthorhombic space groups respectively. The packing in

Full text of DOI:10.1080/15421406.2015.1107812

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
3-(benzo[d]thiazol-2-YL)phenol and 4-
(benzo[d]thiazol-2-YL)phenol: Crystal Structure
Determination, DFT Calculations and Visualizing
Intermolecular Interactions Using Hirshfeld
Surface Analysis
R. K. Mudsainiyan & A. K. Jassal
To cite this article: R. K. Mudsainiyan & A. K. Jassal (2016) 3-(benzo[d]thiazol-2-YL)phenol
and 4-(benzo[d]thiazol-2-YL)phenol: Crystal Structure Determination, DFT Calculations and
Visualizing Intermolecular Interactions Using Hirshfeld Surface Analysis, Molecular Crystals and
Liquid Crystals, 629:1, 120-134, DOI: 10.1080/15421406.2015.1107812
To link to this article: http://dx.doi.org/10.1080/15421406.2015.1107812
Published online: 16 Jun 2016.
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Date: 20 June 2016, At: 16:04

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
-(benzo[d]thiazol--YL)phenol and -(benzo[d]thiazol--YL)
phenol: Crystal structure determination, DFT calculations and
visualizing intermolecular interactions using Hirshfeld surface
analysis
R. K. Mudsainiyan and A. K. Jassal
Department of Chemistry, Centre for Advanced Studies-I, Guru Nanak Dev University, Amritsar, India
ABSTRACT
KEYWORDS
Centrosymmetric;
This article describes the synthesis and X-ray crystal structure analy-
sis of 3-(benzo[d]thiazol-2-yl) phenol (I) and 4-(benzo[d]thiazol-2-
yl)phenol (II), crystallized in centrosymmetric triclinic and orthorhom-
bic space groups respectively. The packing in the unit cell of these two
positional isomers are different resulting difference in various types of
intermolecular interactions (C-H …S, O-H …Ow and O-H …N) connect
the molecules into 2D frameworks. Due to presence of lattice water
in compound (I), H-bonding interactions are strong and melting point
of (I) is comparatively higher than (II). The DFT optimized molecular
geometries in (I) and (II) agree closely with those obtained from crys-
tallographic studies.
D-fingerprint plot; hirshfeld
surface; positional isomers;
space group; two-dimensi-
onal framework
GRAPHICAL ABSTRACT
The compounds (I) and (II) have been crystallized in centrosym-
metric space groups. The DFT optimized molecular geometries in
both compounds agree closely with those obtained from the crys-
tallographic studies. An interplay of O-H …Ow and O-H …N type
strong hydrogen bonds and C-H …S type weak interactions connect
the molecules of (I) and (II) into 2D framework. Hirshfeld surface
analysis of (I) indicates that the H …H and H …π contacts can
account for 47.4% and 18.7%, respectively, of the Hirshfeld surface
area, whereas the corresponding fraction in (II) is 36.5% and 29.5%,
respectively.
CONTACT R. K. Mudsainiyan
mudsainiyanrk@gmail.com
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
Supplemental data for this article can be accessed at http://dx.doi.org/./...
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
121
1. Introduction
In the past decants, various sulfur and nitrogen-containing heterocyclic compounds and their
derivatives have been occur predominately in nature appreciable to their stability and ease of
generating new compounds [1–8]. These compounds exhibit pronounced biological activities,
fluorescence properties, various applications in organic electroluminescent devices, biosen-
sors, detection of metal ions, etc. [9–16]. Intermolecular interactions due to particular hydro-
gen bonds are key factors for the construction of molecular assemblies of neutral organic
molecules with donor and acceptor functionalities [17]. Many of the synthon observed in
supramolecular chemistry involve strong hydrogen bonds, which provide the requisite robust-
ness and reproducibility to create a variety of solid-state architectures described as layers, rods,
tapes, ribbons, channels, helices, and sheets [18]. The intermolecular hydrogen bonding inter-
actions can help to stabilize crystal packing in the unit cell of each system. In addition to these
relatively strong hydrogen bonds like O-H …Ow and O-H …N, weak hydrogen bonding inter-
actions such as C-H …S are also important in the description of self-assembly process. The
influence of these weak interactions can be evaluated by comparing their structural features
as well as the interplay of hydrogen bonds in building possible supramolecular aggregation
in closely related compounds. Single-crystal X-ray diffractometry is the method of choice for
determination of crystal structure of molecular compounds but an intrinsic limitation of this
approach is the requirement to grow single crystals of appropriate size and good quality that
make them amenable to structure analysis.
A comparison of the torsion angles between mean planes of the benzene and thiol rings
in the crystals with the DFT theoretical calculations have also been performed. The inclusion
of weak intermolecular hydrogen bonding interactions from crystallographic data compared
with Hirshfeld surface analysis for both compounds. Hirshfeld surface analysis has been used
to visualize the molecular shapes employing 3D molecular surface contours and 2D finger-
print plots. Molecular orbital diagrams provide visual representations of the top level molec-
ular orbital surfaces in each compound. This idea prompted us to investigate the structural
features of benzothiazole derivatives using X-ray powder diffraction and to analyze the role of
O-H …Ow and O-H …N hydrogen bonds in building possible supramolecular architecture.
The compound (II) is already solved in same space group [19] but we tried to solve it in better
way and detail of crystal structure is given along with comparison of two positional isomers
(I) and (II). The results of crystal structural study of compounds (I) and (II) are reported here
along with the DFT calculations to study the molecular geometry. The intermolecular inter-
actions and their percentage in each compound can be obtained by using Crystal Explorer 3.1
[20].
2. Experimental
2.1. Synthesis of 3-(benzo[d]thiazol-2-yl)phenol (I) and 4-(benzo[d]thiazol-2-yl)
phenol (II) (Scheme 1)
2-aminobenzenethiol (0.125g, 1 mmol) was dissolved in dry methanol (10 mL). 3-
hydroxybenzaldehyde for (I) and 4-hydroxybenzaldehyde for (II) were dissolved in dry
methanol (10 mL) separately. Both solutions of 2-aminobenzenethiol and hydroxybenzalde-
hyde were mixed slowly and refluxed for 2 h in a round-bottomed flask. The completion of
reaction was monitored by TLC. After refluxing, filtered the solution mixture and transferred

122
R.K. MUDSAINIYAN AND A.K. JASSAL
Scheme . Synthesis of -(benzo[d]thiazol--yl)phenol (I) and -(benzo[d]thiazol--yl)phenol (II)
to a 25mL conical flask for slow evaporation at room temperature. Yellowish crystals were
separated out by filtration and dried well.
Compound (I), M.p. 183 ºC. Anal. Calcd for C26H20N2O3S2 (I) (%): C, 66.08; H, 4.27;
N, 5.93; S, 13.57; Found: C, 66.06; H, 4.29; N, 5.91; S, 13.52. MS (DMSO): m/z 548.06
[M+DMSO-2]+, 476.05 [M-3]+. IR (cm−1) selected bonds: IR (cm−1) selected bonds: ν(-
OH) = 3738 b, ν(C-Haromatic) = 3045 w, ν (C = N) = 1654 w, ν (C = C) = 1595 sh, ν (C-S)
= 793 sh.
Compound (II), M.p. 176 ºC. Anal. Calcd for C13H9NOS(II) (%): C, 68.70; H, 3.99; N, 6.16;
S, 14.11; Found: C, 68.76; H, 3.97; N, 6.14; S, 14.12. MS (DMSO): m/z, 227.12 [M+, 100%],
228.12 [M+1]+ ion, 229.12 [M+2]+ ion, 226.10 [M-1]+ ion. IR (cm−1) selected bonds: ν(-
OH) = 3657 b, ν(C-Haromatic) = 2930 w, ν (C = N) = 1620 w, ν (C = C) = 1576 sh, ν (C-S)
= 711 sh. (b = broad, sh = sharp, w = weak).
2.2. Physical measurements
All the starting reagents of analytical grade were used without further purification. C, H, N ele-
mental analyses were obtained with a CHNS-O analyzer flesh-EA-1112 series. The IR spectra
of compounds (I) and (II) were recorded on Perkin ELMER FTIR spectrometer in the range
4000–400 cm−1. Single crystal structural X-ray diffraction was carried out on a Bruker’s Apex-
II CCD diffractometer using Mo Kα (λ = 0.71069) at room temperature. Molecular Hirshfeld
surfaces calculations of compounds (I) and (II) were performed by using the Crystal Explorer
˚
3.1. The 3D dnorm surfaces are mapped over a fixed color scale of –1.25 (red) to 1.52 A (blue),
˚
Shape index mapped in the color range of –1.0 to 1.0 A and Curvedness in the range of –4.0
˚
˚
to 0.4 A . The 2D fingerprint plots displayed by using the standard 0.58–2.7 A view, with
the de and di distance scales displayed on the graph axes. DFT calculations were performed
by using Gaussian 03 (G03) and optimized structures were visualized by gauss view. Mass
spectra of compounds were recorded on Bruker compass microTOF-Q11.
2.3. X-ray crystallography
The crystals of compounds (I) and (II) were grown by slow evaporation in dry methanol.
X-ray data of both the compounds were collected on a Bruker’s Apex-II CCD diffractome-
ter using Mo Kα (λ = 0.71069) at room temperature. The data were corrected for Lorentz
and polarization effects and empirical absorption corrections were applied using SADABS
from Bruker. A total of 13875 reflections were measured out of which 3964 were independent

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
123
Figure . ORTEP showing molecular structures of compounds (I) and (II) (with % probability).
Figure . Showing packing diagrams within unit cells of compounds (I) and (II).
for compound (I) and 13856 reflections were measured out of which 3393 were independent
for compound (II). The structures of (I) and (II) were solved by direct methods in triclinic
P-1 and orthorhombic Pbca space groups, respectively, using SIR-92 [21] and refined by full-
matrix least squares refinement methods [22] based on F2, using SHELX-97. The protons of
the -OH groups of both compounds and lattice water molecule of compound (I) were located
from the difference Fourier synthesis and were refined isotropically with Uiso values 1.2 times
that of their carrier oxygen atoms. All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were fixed geometrically with their Uiso values 1.2 times of the phenylene
carbons. Geometry of this complex and hydrogen bonding interactions were calculated using
Figure . (a) Showing tetrahedral geometry around lattice water in compound (I) alongb axis, (b) π-π inter-
actions beetween pheny rings, phenyl and thiol rings in ab plane [centroid (C-C) … centroid (C-C) =
˚
˚
. A , centroid (C-N-C-C-S) … centroid (C-C) = . A ].

124
R.K. MUDSAINIYAN AND A.K. JASSAL
Figure . H-bonded network of compound (II) in bc plane. π-π interactions are missing but weak CH-π
interactions are observed in this compound.
PARST programme [23]. All the drawings of complexes were made using ORTEP [24] and
MERCURY [25] programs. All calculations were performed using Wingx package [26]. Struc-
ture refinement data of compounds (I) and (II) are given in Table 1 and important H-bonding
interactions are shown in Table 2.
Figure . Molecular Hirshfeld dnorm surfaces, shape index and curvedness of compounds (I) and (II), where
˚
de Surfaces have been mapped between de . and . A .

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
125
Table . Crystal data and structure refinement for compounds (I) and (II).
Identification code
(I)
(II)
Empirical formula
Formula weight
Temperature
CHNOS
.
CHNOS
.
() K
() K
˚
˚
Wavelength
. A
. A
Crystal system
Space group
Unit cell dimensions
Triclinic
P –
Orthorhombic
Pbca
˚
˚
˚
a = .() A , α = .()°.
a = .() A , α = °.
˚
b = .() A , β =
b = .() A , β = °.
.()°.
˚
˚
c = .() A , γ =
c = .() A , γ = °.
.()°.
˚
˚
Volume
Z
.() A 
.() A 


Density (calculated)
Absorption coefficient
F()
Crystal size
Theta range for data collection
Index ranges
. Mg/m
. mm-

. Mg/m
. mm-

. × . × . mm
. × . × . mm
. to .°.
. to .°.
−< = h< = , −< = k< =
, −< = l< = 

−< = h< = , −< = k< =
, −< = l< = 

Reflections collected
Independent reflections
Completeness to theta = .°
Absorption correction
Max. and min. transmission
Refinement method
 [R(int) = .]
 [R(int) = .]
.%
.%
Semi-empirical from equivalents
. and .
Full-matrix least-squares on F
 /  / 
Semi-empirical from equivalents
. and .
Full-matrix least-squares on F
 /  / 
Data / restraints / parameters
Goodness-of-fit on F
.
.
Final R indices [I>sigma(I)]
R indices (all data)
Largest diff. peak and hole
CCDC number
R = ., wR = .
R = ., wR = .
R = ., wR = .
R = ., wR = .
˚
˚
. and −. e. A -
. and −. e. A -
1034985
1034986
Table . Showing important H-bonding interactions in compounds (I) and (II).
Compound (I)
X-H …Y
X …Y
Y …H
X-H …Y
C-H …S
C-H …OW
C-H …S
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.
.
.
.()
.











O-HA …OW
C-H …OW
C-H …OW
OW-HW …N
OW-HW …N
C-H …OW
C-H …OW
O-HA …O
()-x+,-y+,-z
.
.()
.()
.
.
.()
()-x+,-y+,-z
()x-,+y,+z
()x-,+y,+z+
Compound (II)
X-H …Y
X …Y
.()
.()
.()
.()
Y …H
.
.
.
.()
.
X-H …Y




C-H …S
C-H …O
C-H …N
O-H …N
C-H …O
() -x+,+y-/,-z+/+
.()
() -x+,+y+/,-z+/+

() -x+/+,-y+,+z-/

126
R.K. MUDSAINIYAN AND A.K. JASSAL
Figure . D fingerprint plot of compounds (I) and (II), where areas of different intermolecular contacts are
clearly shown; de and di are the distances to the nearest atom centre exterior and interior to the surface.
2.4. Hirshfeld surface calculations
A Hirshfeld surface analysis [27,28] is a technique used to visualize intermolecular interac-
tions and give rise to 3D molecular surface contours. The Hirshfeld surfaces in the crystal
structure of particular compound (which may be organic molecule or inorganic metal com-
plex) are constructed on the basis of electron distribution calculated as the sum of electron
densities of spherical atom. The 2D fingerprint plots have also been used to examine molec-
ular shapes and give the exact percentage of all important intermolecular contacts which are
valuable in the exploration of the packing modes [29]. Distances from points on the surface
to a nucleus (atom) inside (di) and outside (de), the mean surface are determined by the dif-
fering vdW radii of atoms, whereby the contact distances di and de can be normalized (dnorm).
Therefore, intermolecular interactions (short, moderate, long) in a crystal structure resulting
from hydrogen bond donors/acceptors can be visually represented by Hirshfeld surfaces. The
value of dnorm is –ve or +ve when intermolecular contacts are shorter or longer than van der
Waals radii, respectively. The 2-D fingerprint plots summarize the nature and type of inter-
molecular contacts experienced by the molecules in the crystal. For an each crystal structure,
Figure . Relative contributions to the Hirshfeld surface area for the various intermolecular contacts (H …H,
O …H, C …H, S …H, N …H, C …C, S …S, C …N, C …S and C …O) in compounds (I) and (II).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
127
the Hirshfeld surfaces as well as fingerprint plots are unique, and the number of unique Hir-
shfeld surfaces depends on the number of crystallographically independent molecules in the
corresponding asymmetric unit [30,31].
2.5. Density function theory (DFT) calculations
DFT calculations can be performed by using Gaussian 03 package [32] with 6-31G basis set for
all atoms at B3LYP level. These calculations can give rise to the shape of molecular geometries
o
o
˚
with minimum energies, bond distances ( A ), bond angles ( ), torsion angles ( ) and HOMO-
LUMO values etc. The crystal structures of positional isomers are different due to difference in
rational design of packing arrangement and intermolecular interactions. Diagrams of molec-
ular orbitals of compounds (I) and (II) are visualized using “gauss view” [33,34].
3. Results and discussion
3.1. Crystal structure of 3-(benzo[d]thiazol-2-yl)phenol (I)
The compound (I) is solved in centrosymmetric triclinic space group P −1. In the molecular
structure of this compound two molecules of3-(benzo[d]thiazol-2-yl) phenol and one lattice
water molecule is present (Fig. 1). The packing diagram of complex (I) shows arrangement
of molecules within unit cell (Fig. 2a). The dihedral angles between thiol ring and phenyl
o
o
ring in both molecules of compound (I) are 7.54(10) and 4.33(10) . The phenyl ring is
twisted from the benzothiazole moiety about the C …C bond, torsion angle C6-C1-C7-S1 is
–172.35 o, C2-C1-C7-N1 is –172.62 o for first molecule and torsion angle C19-C14-C20-S2
is –175.29 o, C15-C14-C20-N2 is –175.60 o for other molecule of compound (I). The impor-
tant H-bonding interactions are present between lattice water and molecular unit forming H-
bonded tetrahedral geometry as shown in Fig. 3a, along b axis [O1-H1A …O1W = 1.78(3)
#
#
#
˚
˚
˚
A , O1W-H12W …N1 = 2.00(3) A , O1W-H11W …N2 1 = 2.01(2) A , O2-H2A …O1 3
#
#
#
˚
= 1.95(3) A , (where : -x+2,-y+1,-z; 1: -x+1,-y+1,-z; 3: x-1,+y,+z+1)]. The π-π inter-
actions between pheny rings, phenyl and thiol rings in ab plane [centroid C1-C6) … centroid
˚
˚
(C8-C13) = 3.856 A , centroid (C7-N1-C8-C13-S1) … centroid (C1-C6) = 3.897 A ] form-
ing extended 1-D chain (Fig. 3b). These are intra and intermolecular interactions and detail
of exact percentage of these interactions are explained by Hirshfeld surface analysis.
3.2. Crystal structure of 4-(benzo[d]thiazol-2-yl)phenol (II)
The compound (II) is solved in centrosymmetric orthorhombic space group Pbca. In the
molecular structure of this compound, only 4-(benzo[d]thiazol-2-yl) phenol is present
(Fig. 1). The packing diagram of complex (II) shows arrangement of molecules within unit
cell (Fig. 2b). The phenyl ring is not planar with benzothiazole moiety and 18.37(6) o dihedral
angle is observed between these two rings. The phenyl ring is twisted from the benzothiazole
moiety about the C …C bond, torsion angle C2-C1-C7-S1 is 160.16 o and C6-C1-C7-N1 is
o
163.30 . The important H-bonding interactions are observed between proton of hydroxyl
#
˚
(–OH) group and nitrogen atom of pyridyl ring with distance of O1-H1 …N1 = 1.93(2) A ,
where #: -x+1,+y+1/2,-z+1/2+1. These are intra and intermolecular interactions and detail
of these interactions are explained by Hirshfeld surface analysis. A comparison of title struc-
ture and those of early reported thiazole derivatives reveal no significant difference observed

128
R.K. MUDSAINIYAN AND A.K. JASSAL
Figure . Showing optimized structures of compounds (I) and (II) and their energies after optimization (in
Kcal/mol).
either in bond length and bond angles. This compound is already reported in literature [19],
but we tried to refine in better way along with weak and strong H-bonded networks reported
here. The crystal structure shows H-bonded extended network in bc plane through weak CH-
π interactions (Fig. 4).
3.3. IR spectroscopy
The experimental result for the C, H, N, S analysis are in good agreement with those cal-
culated for compounds (I) and (II) formed in the reaction. As shown in Figure S1 (SI), the
broad band at 3738 cm−1 in compound (I) is due to stretching vibrations of –OH group. Weak
Figure . Showing HOMO-LUMO values and energy gap (ꢀE value) for compounds (I) and (II).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
129
˚
Table . Comparison of selected experimental and calculated geometric parameters (bond lengths ( A ),
and bond angles (°)) for compound (I).
Compound (I)
Experimental
Theoretical
Deviation
C-C
C-C
C-C
.
.
.
.
.
.
− .
− .
.
C-C
C-C
C-C
C-C
C-O
C-N
.
.
.
.
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
.
C-S
C-C
C-C
C-N
C-C
C-C
C-C
C-C
C-S
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
− .
− .
.
.
.
− .
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-O
C-C-O
C-C-C
C-C-N
C-C-S
N-C-S
C-C-C
C-C-N
C-C-N
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-S
C-C-S
C-N-C
C-S-C
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
− .
.
− .
.
.
− .
.
− .
− .
− .
− .
.
.
.
− .
− .
.
.
− .
− .
− .
.
− .
.
absorption bands at 3045 and 1654 cm−1 are due to stretching vibrations of aromatic –CH
and –C = N groups respectively. The sharp peaks observed at 1595 cm−1 and 793 are due to
vibrations in –C = C and –C-S groups, respectively. In Figure S2 (SI), IR spectrum of com-
pound (II) shows, the broad band at 3657 cm−1 is due to stretching vibrations of –OH group.
Weak absorption bands at 2930 and 1620 cm−1 are due to stretching vibrations of aromatic
–CH and –C = N groups, respectively. The sharp peaks observed at 1576 cm−1 and 711 are
due to vibrations in –C = C and –C-S groups respectively. The mass spectra (Figures S3-S4)
of the compounds (I) and (II) support their formation. For compound (I), the peak of high
intensity is observed at 548.06 corresponds to the molecular ion and two molecules of DMSO
(dimethyl sulphoxide) solvent. Another peak at 476.05 corresponds to the molecular ion peak.
In mass spectrum of compound (II), the base peak at 227.12 corresponds to the molecular ion
peak.

130
R.K. MUDSAINIYAN AND A.K. JASSAL
Table . Comparison of selected experimental and calculated geometric parameters (Torsion angles (°)) for
compound (I).
Compound (I)
Experimental
Theoretical
Deviation
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-N
C-C-C-S
.
.
.
− .
− .
.
.
.
− .
− .
− .
.
.
− .
.
.
.
.
.
.
C-C-C-N
C-C-C-S
.
.
− .
− .
.
− .
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-O
C-C-C-C
O-C-C-C
C-C-N-C
S-C-N-C
C-C-S-C
N-C-S-C
C-C-C-C
N-C-C-C
C-C-C-C
C-C-C-S
N-C-C-C
N-C-C-S
C-C-N-C
C-C-N-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-S
C-C-S-C
C-C-S-C
.
− .
− .
.
.
− .
− .
− .
.
− .
− .
− .
.
− .
− .
.
− .
− .
.
− .
− .
− .
.
− .
.
.
− .
− .
.
.
.
− .
− .
− .
− .
.
.
.
− .
− .
− .
− .
− .
.
− .
− .
.
− .
− .
.
.
.
.
.
.
.
− .
− .
.
− .
.
− .
− .
− .
.
.
− .
− .
− .
− .
− .
− .
.
3.4. Hirshfeld surface calculations
A Hirshfeld surface analysis [27] was performed to visualize the different intermolecular inter-
actions in crystal structures employing 3D molecular surface contours. The Hirshfeld sur-
faces in the crystal structure of organic compounds are constructed on the basis of calculated
electron distribution as the sum of spherical atom electron densities. Some properties can be
mapped on Hirshfeld surface: like de = the distance from the Hirshfeld surface to the nearest
nucleus outside the surface, di = the corresponding distance to the nearest nucleus inside the
surface, dnorm = a normalized contact distance, the sum of these two (di and de) normalized
by the van der Waals radii quantities. Where atoms make intermolecular contacts closer than
the sum of their van der Waals radii, these contacts will be highlighted in red on the dnorm
surface. Longer contacts are blue, and contacts around the sum of van der Waals radii are
white [28]. Moreover, 2D fingerprint plots (introduced by Spackman and McKinnon) [29,31]
which clearly identify each type of intermolecular interactions produced. They not only indi-
cate which intermolecular interactions are present, but also the relative area of the surface
corresponding to each kind of interaction.
The 2D fingerprint plots have also been used to examine molecular shapes and give the
exact percentage of all important intermolecular contacts. Many applications in the recent
past demonstrated that this analysis can be very valuable in the exploration of the packing
modes and intermolecular contacts [28–31]. The Shape index is the measurement of “which

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
131
˚
Table . Comparison of selected experimental and calculated geometric parameters (bond lengths ( A ),
and bond angles (°)) for compound (II).
Compound (II)
Experimental
Theoretical
Deviation
C-C
C-C
C-C
.
.
.
.
.
.
− .
− .
.
C-C
C-C
C-C
C-C
C-O
C-N
C-S
C-C
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
− .
− .
− .
− .
.
C-C
C-N
.
.
.
.
C-C
C-C
C-C
C-C
C-S
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
− .
.
− .
− .
.
.
.
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-O
C-C-O
C-C-C
C-C-N
C-C-S
N-C-S
C-C-C
C-C-N
C-C-N
C-C-C
C-C-C
C-C-C
C-C-C
C-C-C
C-C-S
C-C-S
C-N-C
C-S-C
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
− .
− .
− .
− .
− .
− .
.
.
.
− .
.
.
.
− .
− .
− .
.
− .
.
shape”, the red triangles on Shape index represent concave regions indicating atoms of the
π …π stacked molecule above them, and the blue triangles represent convex regions indi-
cating the atoms of the molecule inside these surfaces. The Curvedness conveys the similar
information as Shape index, which is the measurement of “how much shape”. The 3D dnorm
˚
surfaces are mapped over a fixed color scale of −0.628 (red) to 1.424 A (blue), Shape index
˚
˚
mapped in the color range of −1.0 to 1.0 A and Curvedness in the range of −4.0 to 0.4 A.
˚
The 2D fingerprint plots displayed by using the standard 0.58-2.7 A view, with the de and
di distance scales displayed on the graph axes. The two larger red regions on the bottom left
and upper left of the dnorm surfaces are correspond to the significant O-H …O and O-H …N
type hydrogen bond interactions, which represent the closest intermolecular interactions in
compounds (I) and (II). The large flat region delineated by a blue outline on the Curvedness
surfaces indicating π …π stacking in compound (I) and CH … π interactions in compound

132
R.K. MUDSAINIYAN AND A.K. JASSAL
Table . Comparison of selected experimental and calculated geometric parameters (Torsion angles (°)) for
compound (II).
Compound (II)
Experimental
Theoretical
Deviation
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-N
C-C-C-S
− .
− .
− .
− .
− .
− .
− .
− .
.
.
− .
− .
.
− .
− .
.
− .
− .
.
.
− .
− .
− .
− .
− .
.
.
− .
− .
.
.
.
.
.
C-C-C-N
C-C-C-S
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-O
C-C-C-C
O-C-C-C
C-C-N-C
S-C-N-C
C-C-S-C
N-C-S-C
C-C-C-C
N-C-C-C
C-C-C-C
C-C-C-S
N-C-C-C
N-C-C-S
C-C-N-C
C-C-N-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-C
C-C-C-S
C-C-S-C
C-C-S-C
.
− .
.
.
.
.
.
− .
.
− .
− .
.
.
.
.
− .
− .
.
− .
− .
.
.
− .
.
− .
− .
− .
.
.
.
.
− .
− .
− .
− .
.
− .
.
− .
.
.
.
− .
− .
− .
− .
.
− .
− .
.
.
.
.
− .
.
− .
− .
.
− .
.
− .
.
.
.
− .
(II) (Fig. 5). The 2D fingerprint plot of compound (I) shows sharp spikes of O …H interac-
tions towards inner side and other sharp spikes of N …H interactions towards outer side but
spikes of O …H interactions in compound (II) are less prominent. The proportion of inter-
molecular interactions calculated by 2D fingerprint plot (Fig. 6, Figures S5–S6) were found to
be 47.4%, 18.7%, 9.0%, 7.2%, 7.0%, and 4.7% for H-H, C-H, O-H, C-H, N-H, and C-S con-
tacts to the total Hirshfeld surfaces for compound (I) whereas 36.5%, 29.5%, 8.9%, 4.0%, 6.5%,
and 3.6% for H-H, C-H, O-H, C-H, N-H, and C-S contacts to the total Hirshfeld surfaces for
compound (II) (Fig. 7).
Table . Chemical reactivity indices for compounds (I) and (II).
Codes
(I)
(II)
HOMO (eV)
LUMO (eV)
ꢀE (eV)
− .
− .
.
− .
− .
.
μ (eV)#
− .
− .
η (eV)##
.
.
ω (eV)###
.
.
# μ = (EHOMO + ELUMO) /, ## η = (ELUMO - EHOMO) /, ### ω = μ/η.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
133
3.5. DFT calculations
A density functional theory (DFT) geometry calculation have been done with GAUSSIAN-
03 program package employing the B3LYP (Becke three parameter Lee-Yang–Parr) exchange
correlation functional and the 6-31 G(d) basis set was performed [33,34] on compounds (I)
and (II). Diagram of molecular orbital is visualized using “gauss view” [34]. No solvent correc-
tions were made with these calculations. Starting geometries were taken from X-ray refine-
ment data. The optimized geometric results in the free molecule state are, therefore, com-
pared to those in the crystalline state and energies after optimization (in Kcal/mol) of both
compounds are also shown in Fig. 8. In addition, a comparison of strong and weak inter-
molecular hydrogen bond interactions have been included in a discussion of the structural
aspects. Optimized structure of compounds (I) and (II) were compared with those obtained
o
˚
from X-ray diffraction analysis studies. In both cases, the bond distances ( A ) and angles ( ) of
optimized (theoretical) data are similar to the structural (experimental) data and there is neg-
ligible deviation in them but there are significant differences in the torsion angles ( Tables 3–6).
The HOMO-LUMO values and their energy gaps (ꢀE) of compounds (I) and (II) are given
in Fig. 9.
In the compound (I), the highest occupied molecular orbital (HOMO) is localized over the
smaller regions of phenyl and thiazolyl rings and oxygen atom of –OH group whereas lowest
unoccupied molecular orbital (LUMO) is most distributed mainly over the nitrogen, sulfur
atoms and some carbon atoms of aromatic rings except the –OH group.
In the compound (II), the HOMO is localized all over the molecule including –OH group
whereas LUMO is most distributed mainly over small regions of the nitrogen, sulfur atoms,
some carbon atoms of aromatic rings and oxygen of –OH group. Larger the HOMO-LUMO
energy gap, more stable and less reactive molecule is formed. ꢀE value of (I) is 4.381 eV
and compound (II) is 4.327 eV, so (I) is more stable and less reactive than (II). On the basis
of molecular orbitals, the values of chemical hardness (η), electronic chemical potential (μ),
global electrophilicity index (ω) etc. of compounds can be calculated [35,36]. Global elec-
trophilicity index (ω), introduced by Parr [37], and measures the propensity or capacity of a
species to accept electrons. Chemical reactivity indices for compounds (I) and (II) are given
in Table 7 which shows that chemical hardness of compound (I) is comparatively high than
(II). The results of μ, though are not so conclusive for (I) and (II). Compound (I) is nucle-
ophilic and presence of lattice or coordinated water molecules (in aqueous medium) increases
nucleophilicity of particular compound.
4. Conclusion
The compounds (I) and (II) have been crystallized in centrosymmetric triclinic and
orthorhombic space groups respectively. These two positional isomers are differ in packing
arrangement in unit cell, inter and intramolecular H-bonding interactions. The DFT opti-
mized molecular geometries in compounds (I) and (II) agree closely with those obtained from
the crystallographic studies. The HOMO-LUMO gap in (I) is higher than (II) which indicate
the greater stability, hardness and lesser reactivity of (I) as compare to (II). The melting point
of (I) is higher than (II) because of lattice water leads to stability by strong H-bonding inter-
actions and increases the nucleophilicity of this compound in aqueous medium which is also
confirmed by DFT calculations. An interplay of O-H …Ow and O-H …N type strong hydro-
gen bonds and C-H …S type weak interactions connect the molecules of (I) and (II) into 2D
framework. Hirshfeld surface analysis of (I) indicate that the H …H and H …π contacts can

134
R.K. MUDSAINIYAN AND A.K. JASSAL
account for 47.4% and 18.7%, respectively, of the total Hirshfeld surface area, whereas the
corresponding fraction in (II) is 36.5% and 29.5%, respectively.
Acknowledgements
RK Mudsainiyan gratefully acknowledges UGC-BSR for financial assistance. AK Jassal thanks DST for
INSPIRE fellowship.
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