6 Molecular and Crystal Structures of Polymorphic …
255
synthesised from sulphamethoxazole by 2-hydroxy-1-naphtalaldehyde was found
to crystallise in five polymorphic forms in the same methanol solution. The five
forms (I–V) are orange, although the colour of one form has been reported as dark.
Table 6.9 lists their crystallographic parameters. All forms were analysed at room
temperature. The IV- and V-forms consist of two independent molecules.
Figure 6.20 shows the molecular geometries of the five forms. All the molecules
form π-conjugation between the central phenyl and naphthalene rings, which was
confirmed by the nearly planar conformation between these two units and the azomethine unit. The conjugation between these units can also be characterised by the
bond lengths, indicating a significant contribution from the quinoidal structure. A
major structural difference in the molecular structures of the five forms was found
in the conformation of the sulphonamide unit, which is largely bent and almost
perpendicular to the azomethine group in all forms.
Figure 6.21 depicts the molecular arrangements of the five polymorphs. The basic
structural element in the crystal structures of these polymorphic forms is a π–π
stacked molecular pair. In addition, hydrogen bonding plays an important role in
forming the 3D structures. In the I-form, the stacked pairs are aligned nearly parallel
to form a 1D arrangement with slight slipping along the long molecular axis. This
1D arrangement aligns in a herringbone-like manner through weak intermolecular
interactions to form a 3D structure. In the II-form, the stacked units assemble with
neighbouring stacked units similar to puzzle pieces to form 2D molecular sheets,
which align along the a-axis to form a 3D crystal structure. The molecules in the
III-form also form a stacked pair similar to that in the II-form. This stacked unit
further arranges in a translational operation to form 2D-like molecular sheets, which
align along the c-axis to form a 3D crystal structure. In both the IV- and V-forms, two
Table 6.9 Crystallographic parameters of the five polymorphs of 1-[(E)-({4-[(5-methyl-1,2oxazol-3-yl)sulphamoyl]phenyl}imino)methyl]naphthalen-2-olate
Polymorph
I
II
III
IV
V
Space group
P2 1 /c
C2/c
P-1
P-1
P-1
Z
4
8
2
4
4
a/Å
12.1116 (18) 27.545 (2)
8.3554 (7)
7.4491 (16)
10.9669 (5)
b/Å
11.2257 (15) 12.0217 (10) 10.0022 (8)
14.2402 (11) 11.6578 (6)
c/Å
14.8557 (18) 13.7703 (10) 12.7955 (10) 18.3131 (16) 15.8105 (8)
α/°
90
90
67.259 (5)
87.191 (6)
90.949 (2)
β/°
94.573 (5)
118.646 (4)
80.749 (4)
84.895 (5)
106.494 (1)
γ/°
90
90
86.833 (4)
77.080 (5)
94.680 (2)
V /Å 3
2013.4 (5)
4001.7 (6)
973.37 (14)
1885.1 (13)
1930.06 (17)
d/g/cm 3
1.344
1.353
1.39
1.436
1.402
Refcode
ZULGEU01
ZULGEU02
ZULGEU03
ZULGEU04
ZULGEU05
References
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)
255
synthesised from sulphamethoxazole by 2-hydroxy-1-naphtalaldehyde was found
to crystallise in five polymorphic forms in the same methanol solution. The five
forms (I–V) are orange, although the colour of one form has been reported as dark.
Table 6.9 lists their crystallographic parameters. All forms were analysed at room
temperature. The IV- and V-forms consist of two independent molecules.
Figure 6.20 shows the molecular geometries of the five forms. All the molecules
form π-conjugation between the central phenyl and naphthalene rings, which was
confirmed by the nearly planar conformation between these two units and the azomethine unit. The conjugation between these units can also be characterised by the
bond lengths, indicating a significant contribution from the quinoidal structure. A
major structural difference in the molecular structures of the five forms was found
in the conformation of the sulphonamide unit, which is largely bent and almost
perpendicular to the azomethine group in all forms.
Figure 6.21 depicts the molecular arrangements of the five polymorphs. The basic
structural element in the crystal structures of these polymorphic forms is a π–π
stacked molecular pair. In addition, hydrogen bonding plays an important role in
forming the 3D structures. In the I-form, the stacked pairs are aligned nearly parallel
to form a 1D arrangement with slight slipping along the long molecular axis. This
1D arrangement aligns in a herringbone-like manner through weak intermolecular
interactions to form a 3D structure. In the II-form, the stacked units assemble with
neighbouring stacked units similar to puzzle pieces to form 2D molecular sheets,
which align along the a-axis to form a 3D crystal structure. The molecules in the
III-form also form a stacked pair similar to that in the II-form. This stacked unit
further arranges in a translational operation to form 2D-like molecular sheets, which
align along the c-axis to form a 3D crystal structure. In both the IV- and V-forms, two
Table 6.9 Crystallographic parameters of the five polymorphs of 1-[(E)-({4-[(5-methyl-1,2oxazol-3-yl)sulphamoyl]phenyl}imino)methyl]naphthalen-2-olate
Polymorph
I
II
III
IV
V
Space group
P2 1 /c
C2/c
P-1
P-1
P-1
Z
4
8
2
4
4
a/Å
12.1116 (18) 27.545 (2)
8.3554 (7)
7.4491 (16)
10.9669 (5)
b/Å
11.2257 (15) 12.0217 (10) 10.0022 (8)
14.2402 (11) 11.6578 (6)
c/Å
14.8557 (18) 13.7703 (10) 12.7955 (10) 18.3131 (16) 15.8105 (8)
α/°
90
90
67.259 (5)
87.191 (6)
90.949 (2)
β/°
94.573 (5)
118.646 (4)
80.749 (4)
84.895 (5)
106.494 (1)
γ/°
90
90
86.833 (4)
77.080 (5)
94.680 (2)
V /Å 3
2013.4 (5)
4001.7 (6)
973.37 (14)
1885.1 (13)
1930.06 (17)
d/g/cm 3
1.344
1.353
1.39
1.436
1.402
Refcode
ZULGEU01
ZULGEU02
ZULGEU03
ZULGEU04
ZULGEU05
References
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)
Tahir et al.
(2015)