Liquid crystal behavior of Ag(I) complexes based on a series of mesogenic 1,3,4-thiadiazole ligands

Article abstract of DOI:10.1080/15421406.2020.1860624

2-(4-Alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH₂) _n H, n = 1–8) (6a–h) (as a series of 1,3,4-thiadiazole derivatives) and their silver(I) complexes: bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) complexes (alkoxy: O(CH₂) _n H, n = 1–8) (7a–h) were prepared and characterized with different techniques: microelemental analysis, FTIR, UV–Vis, ¹H NMR, ¹³C NMR and mass (for the organic compounds) spectra, in addition to the molar conductivity measurements (for Ag(I) complexes). Liquid crystal behavior of the two series of compounds was evaluated using polarized light optical microscopy (POM). The study revealed that both series are enantiotropic liquid crystalline materials (exhibiting wide mesomorpic temperature ranges) with different behavior and properties. 6a–f displayed only nematic mesophase upon heating and cooling, while 6g and 6h exhibited both of SmC and nematic mesophases upon heating and cooling. Upon complexation of 1,3,4-thiadiazoles (6a–h) to silver(I), the liquid crystal behavior and properties are significantly changed (different mesophases, and lower mesophase and clearing temperatures). However, 7b–h exhibited SmA mesophase upon heating and cooling, while 7a shows no mesomorphic properties (simply melted to isotropic liquid).

Full text of DOI:10.1080/15421406.2020.1860624

Molecular Crystals and Liquid Crystals
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Liquid crystal behavior of Ag(I) complexes based
on a series of mesogenic 1,3,4-thiadiazole ligands
Ivan Hameed R. Tomi, Ahmed Jasim M. Al-Karawi, Al-Ameen Bariz OmarAli &
Dhafir T. A. Al- Heetimi
To cite this article: Ivan Hameed R. Tomi, Ahmed Jasim M. Al-Karawi, Al-Ameen Bariz
OmarAli & Dhafir T. A. Al- Heetimi (2021): Liquid crystal behavior of Ag(I) complexes based on
a series of mesogenic 1,3,4-thiadiazole ligands, Molecular Crystals and Liquid Crystals, DOI:
10.1080/15421406.2020.1860624
To link to this article: https://doi.org/10.1080/15421406.2020.1860624
Published online: 25 Jun 2021.
Submit your article to this journal
Article views: 15
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gmcl20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/10.1080/15421406.2020.1860624
Liquid crystal behavior of Ag(I) complexes based on a
series of mesogenic 1,3,4-thiadiazole ligands
Ivan Hameed R. Tomia, Ahmed Jasim M. Al-Karawia, Al-Ameen Bariz OmarAlia, and
Dhafir T. A. Al- Heetimib
b
aMustansiriya University, College of Science, Department of Chemistry, Baghdad, Iraq; College of
Education for Pure Science Ibn Alhaitham, Department of Chemistry, University of Baghdad,
Baghdad, Iraq
KEYWORDS
ABSTRACT
Mesogens;
2-(4-Alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2)nH,
n ¼ 1–8) (6a–h) (as a series of 1,3,4-thiadiazole derivatives) and their
silver(I) complexes: bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-
silver(I) complexes (alkoxy: O(CH2)nH, n ¼ 1–8) (7a–h) were prepared
and characterized with different techniques: microelemental analysis,
FTIR, UV–Vis, 1H NMR, 13C NMR and mass (for the organic com-
pounds) spectra, in addition to the molar conductivity measurements
(for Ag(I) complexes). Liquid crystal behavior of the two series of
compounds was evaluated using polarized light optical microscopy
(POM). The study revealed that both series are enantiotropic liquid
crystalline materials (exhibiting wide mesomorpic temperature
ranges) with different behavior and properties. 6a–f displayed only
nematic mesophase upon heating and cooling, while 6g and 6h
exhibited both of SmC and nematic mesophases upon heating and
cooling. Upon complexation of 1,3,4-thiadiazoles (6a–h) to silver(I),
the liquid crystal behavior and properties are significantly changed
(different mesophases, and lower mesophase and clearing tempera-
tures). However, 7b–h exhibited SmA mesophase upon heating and
cooling, while 7a shows no mesomorphic properties (simply melted
to isotropic liquid).
Metallomesogens; 1,3,4-
Thiadiazoles; Silver(I)
complexes; Liquid
cystalline materials
Introduction
Hydrophobic materials are a class of compounds with a low affinity to water (water
repellents). The hydrophobicity of such materials is mainly due to the presence of one
or more of hydrocarbon chains. These materials have shown some remarkable applica-
tions in several fields, such as chemistry, biology and material science [1–3].
Among various classes of organic compounds, heterocyclic derivatives have received
special interest due to their versatile applications in different fields. These compounds
have been already used as pharmaceutical drugs due to their high efficacy against a
wide range of bacterial and fungal strains [4–8]. Furthermore, the heterocyclic com-
pounds have many other industrial applications, such as corrosion inhibitors,
CONTACT Ivan Hameed R. Tomi
ahmedalkarawi@uomustansiriyah.edu.iq
Baghdad, P.O. Box 46010, Iraq
ivanhrtomy@uomustansiriyah.edu.iq; Ahmed Jasim M. Al-Karawi
Mustansiriya University, College of Science, Department of Chemistry,
ß 2020 Taylor & Francis Group, LLC

2
I. H. R. TOMI ET AL.
surfactants, sanitizers, antioxidants, dyestuff [9,10]. The presence of oxygen, nitrogen
and/or sulfur as hetroatoms gave these compounds high capability for electron-donating
which related to being used as organic chelate ligands [11–13].
The fascinating applications (especially in medicine and industry) of mesogens and
metallomesogens are majorly contributed in the expansion of this field by attracting the
attention of the researches around the world. Due to that and since 1888 (first observa-
tion of a liquid-crystalline birefringent medium), thousands of researchers are so inter-
ested in designing materials with liquid crystal properties. In the ten recent years, a
numerous number of articles have been reported, describing the liquid crystal properties
of a wide range of organic derivatives [14–28] and metal-containing materials especially
with aluminum [29], nickel [30], zinc [31,32], palladium [33,34], silver [35–40], iridium
[41], platinum [34,42–44], and gold [45,46], as well as some lanthanide ions [47–49].
The most characteristic of metallomesogens is that the fundamental properties of the
metal ions (magnetism, electrical conductivity, carrier mobility, etc.) can be combined
with the liquid crystalline properties.
Silver(I) complexes based on different organic derivatives have shown some fascinat-
ing liquid crystal properties. In 2004, Ching K. Lee et al. [36] prepared a homologous
series of silver(I) complexes based on a serious of 1-alkylimidazole (ID) compounds (R-
ID, R ¼ CnH2nþ1, where n ¼ 10, 12, 14, 16 and 18). The X-ray crystal structure of [Ag
(C12H25-ID)2]. NO3 displayed that the Ag center is two-coordinate, adopting a U-shaped
conformation with bilayer packing. All of these compounds (except for n ¼ 10) exhib-
ited liquid crystalline properties with smectic A (SmA) mesophase, while, in 2010,
ꢀ
ꢀ
Marıa Jose Mayoral et al. [37] reported the synthesis of a series of Ag(I) complexes sup-
ported by 3,5-bis(4-alkyloxyphenyl)pyrazole (Py) compounds with the general formula:
[Ag (R-Py)2]. X (R ¼ CnH2nþ1, where n ¼ 12, 14, 16 and 18; X ¼ CH3-p-C6H4SO3-(PTS),
CF3SO3-(OTf)) as metallomesogens. Beside the liquid crystalline properties, these com-
pounds displayed photoluminescence properties in the solid state, in the mesophase and
in solution. Recently, we prepared three series of silver(I) complexes based on symmet-
rical azines ([Ag2(SA)(NO3)2], SA: 1,2-bis[4-(n-alkoxy)benzylidene] hydrazine (where,
n-alkoxy: O(CH2)nH, n ¼ 1–10 or 12)) [38], asymmetrical azines ([Ag2(AA)(NO3)2],
AA:
[1-(4-(n-alkoxy))-2-(40-dodecyloxy)benzylidene]hydrazine
(where
n-alkoxy:
O(CH2)nH, n ¼ 1–8)) [39] and pyrazoles ([Ag (PY)2].NO3, PY: 3,5-bis[4-(n-alkoxy)-
phenyl]-1H-pyrazole (where, n-alkoxy: O(CH2)nH, n ¼ 6–10)) [40] as photoluminescent
materials. Some of these complexes showed some remarkable liquid crystal properties.
We report herein the synthesis and liquid crystal behavior of a series of 1,3,4-thiadia-
zoles and their silver (I) complexes.
Experimental
Physical measurements
Varian Cary 100 Conc. spectrophotometer was used to record the electronic spectra of
the prepared compounds in the region (200–800 nm) for (1 ꢀ 10ꢁ4 M) in dichlorome-
thane (DCM) at room temperature. Elemental analyses (C, H and N) were carried out
by using a EuroEA 3000 Elemental Analyzer, while Ag was measured using a 7300 V
ICP-OES PerkinElmer-Optima Spectrometer. Mass spectra were recorded using a

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
MS-SCI Shimadzu QP 1000EX spectrometer. Infrared spectra were obtained in the
region (4000–600 cmꢁ1) by using a 8400S-FT–IR Shimadzu spectrophotometer. 1H
NMR and 13C NMR spectra were performed in DMSO for precursors (1, 2, 3 and 5),
1
and CDCl3 for ligands (6a–h) and complexes (7a–h) using a Bruker 300 MHz for H
NMR and 75 MHz for 13C NMR spectrometer. PW-BK5000R microscope supplied with
HS-400 (KER3100-08S) heating stage was used to obtain the liquid crystal mesophases
of 1,3,4-thiadiazoles and their silver(I) complexes. Molar conductivity of Ag(I) com-
plexes in acetone (1 ꢀ 10ꢁ3 M) was measured at 25 Cꢂ using a WTW 82362-Weilheim
digital conductometer.
Materials
The reagents used in this work were purchased from Aldrich Co. (Germany) and used
as it is, without further purification: 1-iodomethane (98%), 1-bromoethane (99%), 1-
bromopropane (99%), 1-bromobutane (98%), 1-bromopentane (99%), 1-bromohexane
(99%), 1-bromoheptane (99%), 1-bromooctane (99%), p-toluic acid (98%), hydrazine
hydrate (80%), phosphorus pentasulfide (99%), aluminum chloride (98%), potassium
permanganate (99%). Methyl 4-methylbenzoate (1) and p-toluic hydrazide (2) were pre-
pared following the synthetic procedure described in our previous work [23].
Synthesis of 4-methoxy-N0-(4-methylbenzoyl)benzohydrazide (3)
The synthetic procedure of this compound was slightly modified from that described in
the literatures [23,50]. To a solution of p-toluic hydrazide (18 g, 120 mmol) in anhyd-
rous pyridine (100 mL), 4-methoxybenzoyl chloride (20.5 g, 120 mmol) was added drop-
wise at ꢁ5 ꢂC. The reaction mixture was kept overnight at room temperature, and then
poured into cold aqueous solution of HCl (10%, 250 mL) to give a pale yellow micro-
crystalline solid. This solid was boiled in water for 15 min to remove the unreacted
materials, and the remaining solid was collected by filtration. The final solid was recrys-
tallized from ethanol to give the desired product. Yield (91%); m.p.¼ 210–212 ꢂC. FTIR
(t/cmꢁ1): 3207 (w, t(N–H)), 3151 (w, t(N–H)), 2943 (w, tas(C–H) of CH3 group), 2845
(w, ts(C–H) of CH3 group), 1614 (m, t(C ¼ O)), 1593, 1558 and 1512 (s,m,m, t(C ¼ C)
1
aromatic), 1251 (s, t(C–O)). H NMR (d/ppm): 2.35 (3H, s, CH3), 3.68 (3H, s, OCH3),
6.88–6.91 (2H, d, J ¼ 8.8 Hz, aromatic protons), 7.15–7.18 (2H, d, J ¼ 8.0 Hz, aromatic
protons), 7.60–7.63 (2H, d, J ¼ 8.0 Hz, aromatic protons), 7.75–7.78 (2H, d, J ¼ 8.8 Hz,
aromatic protons), 10.17 (1H, s, NH), 10.20 (1H, s, NH). 13C NMR (d/ppm): 20.09
(CH3), 55.86 (OCH3), 114.19 ((C–H) aromatic), 125.22 ((C) aromatic), 129.48 ((C–H)
aromatic), 130.32 ((C–H) aromatic), 142.25 ((C–CH3) aromatic), 162.47 ((C–OCH3)
aromatic), 165.80 (C ¼ O), 166.24 (C ¼ O). Mass spect. (m/z): 284.
Synthesis of 2-(4-methoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (4 5 6a)
The title compound was prepared by the previously reported procedure [23,51].
Compound 3 (25 g, 87 mmol) and phosphorous pentasulfide (24.9 g, 87 mmol) were dis-
solved in anhydrous pyridine (150 mL), and the reaction mixture was heated under

4
I. H. R. TOMI ET AL.
reflux for 24 h. The mixture was then poured into cold water (500 mL) and a precipitate
deposited. This precipitate was collected by filtration, washed thoroughly with water
and finally recrystallized from ethyl acetate to give the desired product in pure form.
Yield (87%); m.p.¼ 209–210 ꢂC. FTIR (t/cmꢁ1): 3066 (w, t(C–H) aromatic), 2964 (w,
tas(C–H) of CH3 group), 2837 (w, ts(C–H) of CH3 group), 1602 (m, t(C ¼ N)), 1577
ꢃ
and 1516 (w,s, t(C ¼ C) aromatic), 1255 (s, t(C–O)). UV–Vis (k/nm): 232 (n–r ), 326
1
ꢃ
(p–p ). H NMR (d/ppm): 2.40 (3H, s, CH3), 3.86 (3H, s, OCH3), 6.96–6.99 (2H, d,
J ¼ 8.7 Hz, aromatic protons), 7.26–7.28 (2H, d, J ¼ 7.9 Hz, aromatic protons), 7.85–7.88
(2H, d, J ¼ 8.0 Hz, aromatic protons), 7.91–7.94 (2H, d, J ¼ 8.7 Hz, aromatic protons).
13C NMR (d/ppm): 21.50 (CH3), 63.80 (OCH3), 114.49 ((C–H) aromatic), 122.94 ((C)
aromatic), 127.57 ((C) aromatic), 127.73 ((C–H) aromatic), 129.40 ((C–H) aromatic),
129.79 ((C–H) aromatic), 141.33 ((C–CH3) aromatic), 161.80 ((C–OCH3) aromatic),
167.44 (C ¼ N), 167.47 (C ¼ N). Mass spect. (m/z): 282.
Synthesis of 4-(5-(p-tolyl)-1,3,4-thiadiazol-2-yl)phenol (5)
This compound was prepared following the procedure described in our previous work
[23]. Anhydrous aluminum chloride (1.00 g, 7.5 mmol) was added to a solution of com-
pound 4 ¼ 6a (0.68 g, 2.4 mmol) in dry benzene (25 mL), and the reaction mixture was
heated by reflux for 24 h. After evaporation of the solvent and pouring the residue into
cold water, an off-white microcrystalline solid was formed. The obtained solid was col-
lected by filtration, and then dissolved in an aqueous solution of potassium hydroxide
(10%, 30 mL). The solution was filtered, and the filtrate was neutralized with HCl
(10%). The precipitate formed was washed thoroughly with water and dried under vac-
uum. The final solid was recrystallized from ethanol to obtain compound 5. Yield
(81%); m.p.¼ 221–223 ꢂC. FTIR (t/cmꢁ1): 3045 (w, t(C–H) aromatic), 2966 (w,
tas(C–H) of CH3 group), 2850 (w, ts(C–H) of CH3 group), 1608 (m, t(C ¼ N)), 1583
1
and 1523 (m,w, t(C ¼ C) aromatic), 1244 (s, t(C–O)). H NMR (d/ppm): 2.18 (3H, s,
CH3), 6.77–6.79 (2H, d, J ¼ 8.65 Hz, aromatic protons), 7.13–7.16 (2H, d, J ¼ 8.17 Hz,
aromatic protons), 7.64–7.66 (4H, d, J ¼ 8.43 Hz, aromatic protons), 10.09 (1H, s, OH).
13C NMR (d/ppm): 21.44 (CH3), 116.65 ((C–H) aromatic), 121.04 ((C) aromatic),
127.46 ((C) aromatic), 127.81 ((C–H) aromatic), 129.84 ((C–H) aromatic), 130.37
((C–H) aromatic), 141.57 ((C–CH3) aromatic), 160.85 ((C–OH) aromatic), 166.88
(C ¼ N), 167.84 (C ¼ N). Mass spect. (m/z): 268.
Synthesis of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6a–h)
(general procedure)
These compounds were prepared based on the synthetic procedure described in our
previous work [23]. To a mixture of compound 5 (2.68 g, 10 mmol) and anhydrous
potassium carbonate (1.38 g, 10 mmol) in acetone (50 mL), n-alkyl bromide (11 mmol)
was added. The reaction mixture was refluxed for 12 h and then left to cool at room
temperature. The crude product was then poured into cold water, and the solid formed
was collected by filtration. This solid was washed with aqueous solution of potassium

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
hydroxide (5%), then with water several times, and finally recrystallized from
ethyl acetate.
2-(4-Methoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6a), see compound 4
2-(4-Ethoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6b)
Yield (85%). FTIR (t/cmꢁ1): 3080 (w, t(C–H) aromatic), 2982 (w, tas(C–H) of CH3
group), 2929 (w-m, tas(C–H) of CH2 group), 2866 (w, ts(C–H) of CH3 group), 2825
(w-m, ts(C–H) of CH2 group), 1605 (m, t(C ¼ N)), 1573 and 1518 (s,m, t(C ¼ C) aro-
1
ꢃ
ꢃ
matic), 1251 (s, t(C–O)). UV–Vis (k/nm): 231 (n–r ), 324 (p–p ). H NMR (d/ppm):
1.41-1.45 (3H, t, -OCH2CH3), 2.42 (3H, s, CH3), 4.02-4.06 (2H, q, -OCH2CH3), 6.97-
7.00 (2H, d, J ¼ 8.73 Hz, aromatic protons), 7.25–7.27 (2H, d, J ¼ 7.91 Hz, aromatic pro-
tons), 7.88–7.90 (2H, d, J ¼ 7.95 Hz, aromatic protons), 7.92–7.95 (2H, d, J ¼ 8.75 Hz,
aromatic protons). 13C NMR (d/ppm): 14.73 (-OCH2CH3), 21.16 (CH3), 63.74
(-OCH2CH3), 114.99 ((C–H) aromatic), 122.80 ((C) aromatic), 127.61 ((C) aromatic),
127.65 ((C–H) aromatic), 129.43 ((C–H) aromatic), 129.81 ((C–H) aromatic), 141.34
((C–CH3) aromatic), 161.26 ((C–OCH2) aromatic), 167.41 (C ¼ N), 167.57 (C ¼ N).
Mass spectrum (m/z): 296.
2-(4-Propyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6c)
Yield (84%). FTIR (t/cmꢁ1): 3066 (w, t(C–H) aromatic), 2964 (w, tas(C–H) of CH3
group), 2931 (m, tas(C–H) of CH2 group), 2866 (w, ts(C–H) of CH3 group), 2826 (w-
m, ts(C–H) of CH2 group), 1602 (m, t(C ¼ N)), 1575 and 1516 (s,m, t(C ¼ C)aromatic),
1
ꢃ
ꢃ
1255 (s, t(C–O)). UV–Vis (k/nm): 230 (n–r ), 325 (p–p ). H NMR (d/ppm): 1.04-1.09
(3H, t, -OCH2CH2CH3), 1.88-1.90 (2H, m, -OCH2CH2CH3), 2.42 (3H, s, CH3), 3.97-
4.01 (2H, t, -OCH2CH2CH3), 6.95–6.97 (2H, d, J ¼ 8.74 Hz, aromatic protons),
7.26–7.27 (2H, d, J ¼ 7.91 Hz, aromatic protons), 7.85–7.87 (2H, d, J ¼ 7.93 Hz, aromatic
protons), 7.89–7.91 (2H, d, J ¼ 8.75 Hz, aromatic protons). 13C NMR (d/ppm): 10.49
(-OCH2CH2CH3), 21.52 (-OCH2CH2CH3), 22.50 (CH3), 69.73 (-OCH2CH2CH3), 115.02
((C–H) aromatic), 122.75 ((C) aromatic), 127.60 ((C) aromatic), 127.65 ((C–H) aro-
matic), 129.42 ((C–H) aromatic), 129.81 ((C–H) aromatic), 141.33 ((C–CH3) aromatic),
161.47 ((C–OCH2) aromatic), 167.39 (C ¼ N), 167.59 (C ¼ N). Mass spectrum
(m/z): 310.
2-(4-Butyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6d)
Yield (88%). FTIR (t/cmꢁ1): 3068 (w, t(C–H) aromatic), 2953 (w, tas(C–H) of CH3
group), 2935 (m, tas(C–H) of CH2 group), 2868 (w, ts(C–H) of CH3 group), 2852 (w,
ts(C–H) of CH2 group), 1600 (m, t(C ¼ N)), 1578 and 1514 (s,m, t(C ¼ C)aromatic),
1
ꢃ
ꢃ
1251 (s, t(C–O)). UV–Vis (k/nm): 229 (n–r ), 322 (p–p ). H NMR (d/ppm): 0.96-1.02
(3H, t, -OCH2(CH2)2CH3), 1.48-1.61 (2H, m, -OCH2CH2CH2CH3), 1.82-1.85 (2H, m,
-OCH2CH2CH2CH3), 2.41 (3H, s, CH3), 3.97-4.05 (2H, t, -OCH2CH2CH2CH3),
6.97–6.99 (2H, d, J ¼ 8.77 Hz, aromatic protons), 7.27–7.30 (2H, d, J ¼ 7.92 Hz, aromatic
protons), 7.86–7.88 (2H, d, J ¼ 7.90 Hz, aromatic protons), 7.91–7.93 (2H, d, J ¼ 8.76 Hz,
aromatic protons). 13C NMR (d/ppm): 13.86 (-OCH2(CH2)2CH3), 19.23

6
I. H. R. TOMI ET AL.
(-OCH2CH2CH2CH3),
21.54
(CH3),
31.54
(-OCH2CH2CH2CH3),
67.95
(-OCH2(CH2)2CH3), 115.00 ((C–H) aromatic), 122.72 ((C) aromatic), 127.64 ((C) aro-
matic), 127.77 ((C–H) aromatic), 129.42 ((C–H) aromatic), 129.82 ((C–H) aromatic),
141.34 ((C–CH3) aromatic), 161.31 ((C–OCH2) aromatic), 167.40 (C ¼ N), 167.56
(C ¼ N). Mass spectrum (m/z): 324.
2-(4-Pentyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6e)
Yield (89%). FTIR (t/cmꢁ1): 3067 (w, t(C–H) aromatic), 2958 (w, tas(C–H) of CH3
group), 2930 (m, tas(C–H) of CH2 group), 2870 (w, ts(C–H) of CH3 group), 2858 (m,
ts(C–H) of CH2 group), 1602 (m, t(C ¼ N)), 1575 and 1518 (s,m, t(C ¼ C)aromatic),
1
ꢃ
ꢃ
1253 (s, t(C–O)). UV–Vis (k/nm): 231 (n–r ), 325 (p–p ). H NMR (d/ppm): 0.88-0.96
(3H, t, -OCH2(CH2)3CH3), 1.42-1.57 (4H, m, -OCH2CH2(CH2)2CH3), 1.81-1.84 (2H,
m, -OCH2CH2(CH2)2CH3), 2.42 (3H, s, CH3), 3.98-4.03 (2H, t, -OCH2(CH2)3CH3),
6.95–6.98 (2H, d, J ¼ 8.74 Hz, aromatic protons), 7.26–7.28 (2H, d, J ¼ 7.94 Hz, aromatic
protons), 7.84–7.87 (2H, d, J ¼ 7.96 Hz, aromatic protons), 7.92–7.94 (2H, d, J ¼ 8.73 Hz,
aromatic protons). 13C NMR (d/ppm): 14.05 (-OCH2(CH2)3CH3), 21.53
(-OCH2(CH2)2CH2CH3), 22.57 (CH3), 29.13 (-OCH2CH2CH2CH2CH3), 31.58
(-OCH2CH2(CH2)2CH3), 68.28 (-OCH2(CH2)3CH3), 114.96 ((C–H) aromatic), 122.72
((C) aromatic), 127.77 ((C) aromatic), 128.03 ((C–H) aromatic), 129.37 ((C–H) aro-
matic), 129.82 ((C–H) aromatic), 141.33 ((C–CH3) aromatic), 161.33 ((C–OCH2) aro-
matic), 167.40 (C ¼ N), 167.61 (C ¼ N). Mass spectrum (m/z): 338.
2-(4-Hexyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6f)
Yield (80%). FTIR (t/cmꢁ1): 3064 (w, t(C–H) aromatic), 2961 (w, tas(C–H) of CH3
group), 2933 (m, tas(C–H) of CH2 group), 2862 (w, ts(C–H) of CH3 group), 2851 (m,
ts(C–H) of CH2 group), 1601 (m, t(C ¼ N)), 1575 and 1516 (s,m, t(C ¼ C) aromatic),
1
ꢃ
ꢃ
1256 (s, t(C–O)). UV–Vis (k/nm): 230 (n–r ), 324 (p–p ). H NMR (d/ppm): 0.89-0.95
(3H, t, -OCH2(CH2)4CH3), 1.40-1.59 (6H, m, -OCH2CH2(CH2)3CH3), 1.78-1.82 (2H,
m, -OCH2CH2(CH2)3CH3), 2.40 (3H, s, CH3), 3.98-4.02 (2H, t, -OCH2(CH2)4CH3),
6.95–6.97 (2H, d, J ¼ 8.79 Hz, aromatic protons), 7.23–7.25 (2H, d, J ¼ 7.96 Hz, aromatic
protons), 7.84–7.86 (2H, d, J ¼ 7.92 Hz, aromatic protons), 7.95–7.97 (2H, d, J ¼ 8.76 Hz,
aromatic protons). 13C NMR (d/ppm): 14.08 (-OCH2(CH2)4CH3), 21.55
(-OCH2(CH2)3CH2CH3), 22.62 (CH3), 28.84 (-OCH2(CH2)2CH2CH2CH3), 29.13
(-OCH2CH2CH2(CH2)2CH3), 31.62 (-OCH2CH2(CH2)3CH3), 68.31 (-OCH2(CH2)4CH3)
114.99 ((C–H) aromatic), 122.76 ((C) aromatic), 127.81 ((C) aromatic), 128.13 ((C–H)
aromatic), 129.41 ((C–H) aromatic), 129.87 ((C–H) aromatic), 141.30 ((C–CH3) aro-
matic), 161.46 ((C–OCH2) aromatic), 167.44 (C ¼ N), 167.62 (C ¼ N). Mass spectrum
(m/z): 352.
2-(4-Heptyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6g)
Yield (83%). FTIR (t/cmꢁ1): 3060 (w, t(C–H) aromatic), 2962 (w, tas(C–H) of CH3
group), 2927 (m, tas(C–H) of CH2 group), 2852 (w, ts(C–H) of CH3 group), 2847 (m,
ts(C–H) of CH2 group), 1603 (m, t(C ¼ N)), 1575 and 1518 (s,m, t(C ¼ C)aromatic),
1
ꢃ
ꢃ
1259 (s, t(C–O)). UV–Vis (k/nm): 230 (n–r ), 322 (p–p ). H NMR (d/ppm): 0.87-0.96

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
(3H, t, -OCH2(CH2)5CH3), 1.45-1.62 (8H, m, -OCH2CH2(CH2)4CH3), 1.76-1.79 (2H,
m, -OCH2CH2(CH2)4CH3), 2.41 (3H, s, CH3), 3.99-4.05 (2H, t, -OCH2(CH2)5CH3),
6.96–6.99 (2H, d, J ¼ 8.76 Hz, aromatic protons), 7.26–7.29 (2H, d, J ¼ 7.99 Hz, aromatic
protons), 7.85–7.88 (2H, d, J ¼ 7.94 Hz, aromatic protons), 7.93–7.95 (2H, d, J ¼ 8.79 Hz,
aromatic protons). 13C NMR (d/ppm): 14.03 (-OCH2(CH2)5CH3), 21.54
(-OCH2(CH2)4CH2CH3), 22.57 (CH3), 28.59 (-OCH2(CH2)3CH2CH2CH3), 29.77
(-OCH2(CH2)2CH2(CH2)2CH3),
29.17
(-OCH2CH2CH2(CH2)3CH3),
31.65
(-OCH2CH2(CH2)4CH3), 68.37 (-OCH2(CH2)5CH3) 114.83 ((C–H) aromatic), 122.83
((C) aromatic), 127.90 ((C) aromatic), 128.10 ((C–H) aromatic), 129.38 ((C–H) aro-
matic), 129.81 ((C–H) aromatic), 141.35 ((C–CH3) aromatic), 161.37 ((C–OCH2) aro-
matic), 167.56 (C ¼ N), 167.67 (C ¼ N). Mass spectrum (m/z): 366.
2-(4-Octyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole (6h)
Yield (90%). FTIR (t/cmꢁ1): 3072 (w, t(C–H) aromatic), 2972 (w, tas(C–H) of CH3
group), 2928 (m, tas(C–H) of CH2 group), 2853 (w, ts(C–H) of CH3 group), 2835 (m,
ts(C–H) of CH2 group), 1604 (m, t(C ¼ N)), 1576 and 1516 (s,m, t(C ¼ C)aromatic),
1
ꢃ
ꢃ
1257 (s, t(C–O)). UV–Vis (k/nm): 229 (n–r ), 325 (p–p ). H NMR (d/ppm): 0.87-0.91
(3H, t, -OCH2(CH2)6CH3), 1.37-1.59 (10H, m, -OCH2CH2(CH2)5CH3), 1.78-1.81 (2H,
m, -OCH2CH2(CH2)5CH3), 2.43 (3H, s, CH3), 4.00-4.04 (2H, t, -OCH2(CH2)6CH3),
6.97–6.99 (2H, d, J ¼ 8.69 Hz, aromatic protons), 7.28–7.30 (2H, d, J ¼ 7.81 Hz, aromatic
protons), 7.87–7.90 (2H, d, J ¼ 7.97 Hz, aromatic protons), 7.91–7.94 (2H, d, J ¼ 8.75 Hz,
aromatic protons). 13C NMR (d/ppm): 14.29 (-OCH2(CH2)6CH3), 21.66
(OCH2(CH2)5CH2CH3), 22.34 (CH3), 26.28 (-OCH2(CH2)4CH2CH2CH3) 28.69
(-OCH2(CH2)3CH2(CH2)2CH3),
29.42
(-OCH2(CH2)2CH2(CH2)3CH3),
29.62
(-OCH2CH2CH2(CH2)4CH3), 31.44 (-OCH2CH2(CH2)5CH3), 68.41 (-OCH2(CH2)6CH3)
114.75 ((C–H) aromatic), 122.73 ((C) aromatic), 127.95 ((C) aromatic), 128.23 ((C–H)
aromatic), 129.43 ((C–H) aromatic), 129.99 ((C–H) aromatic), 149.72 ((C–CH3) aro-
matic), 161.39 ((C–OCH2) aromatic), 167.59 (C ¼ N), 167.73 (C ¼ N). Mass spectrum
(m/z): 380.
Synthesis of bis(1,3,4-thiadiazole)-silver(I) complexes (7a–h) (general procedure)
To a solution of appropriate 1,3,4-thiadiazole compound (2.36 mmol) in DCM (50 ml),
AgNO3 (0.2 g, 1.18 mmol) was added as a solid. The reaction mixture was stirred at
room temperature in the absence of light, and under inert conditions until all the
AgNO3 solid disappeared. The solvent was removed under vacuum, and the residue was
dissolved in DCM. A colorless solid was appeared after the addition of hexane. This
solid was collected by filtration, washed subsequently with water and hexane, and finally
dried in vacuum.
Bis[2-(4-methoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7a)
Yield (75%). Elemental analysis (%) calc.: C 52.3, N 9.5, H 3.8, Ag 14.7; found: C 52.1,
N 9.4, H 3.6, Ag 14.4. Molar conductivity (K): 69 S.cm2.molꢁ1. FTIR (t/cmꢁ1): 3059 (w,
t(C–H) aromatic), 2948 (w, tas(C–H) of CH3 group), 2826 (w, ts(C–H) of CH3 group),

8
I. H. R. TOMI ET AL.
1614 (m, t(C ¼ N)), 1598 and 1510 (w,s, t(C ¼ C) aromatic), 1253 (s, t(C–O)). UV–Vis
1
ꢃ
ꢃ
(k/nm): 234 (n–r ), 330 (p–p ). H NMR (d/ppm): 2.43 (6H, s, 2 ꢀ CH3), 3.89 (6H, s,
2 ꢀ OCH3), 7.00–7.03 (4H, d, J ¼ 8.71 Hz, aromatic protons), 7.29–7.32 (4H, d,
J ¼ 7.47 Hz, aromatic protons), 7.87–7.90 (4H, d, J ¼ 8.10 Hz, aromatic protons),
7.93–7.96 (4H, d, J ¼ 8.50 Hz, aromatic protons). 13C NMR (d/ppm): 21.02 (CH3), 55.00
(OCH3), 114.29 ((C–H) aromatic), 123.01 ((C) aromatic), 127.28 ((C) aromatic), 127.89
((C–H) aromatic), 128.96 ((C–H) aromatic), 129.40 ((C–H) aromatic), 143.51 ((C–CH3)
aromatic), 160.89 ((C–OCH3) aromatic), 167.14 (C ¼ N), 167.39 (C ¼ N).
Bis[2-(4-ethoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7b)
Yield (74%). Elemental analysis (%) calc.: C 53.6, N 9.2, H 4.2, Ag 14.1; found: C 53.3,
N 9.0, H 4.1, Ag 13.9. Molar conductivity (K): 70 S.cm2.molꢁ1. FTIR (t/cmꢁ1):, 3068
(w, t(C–H) aromatic), 2955 (w, tas(C–H) of CH3 group), 2931 (w-m, tas(C–H) of CH2
group), 2853 (w, ts(C–H) of CH3 group), 2839 (w-m, ts(C–H) of CH2 group), 1613 (m,
t(C ¼ N)), 1599 and 1512 (s,m, t(C ¼ C) aromatic), 1250 (s, t(C–O)). UV–Vis (k/nm):
1
ꢃ
ꢃ
229 (n–r ), 322 (p–p ). H NMR (d/ppm): 1.44-1.48 (6H, t, 2ꢀ(-OCH2CH3)), 2.43
(6H, s, 2 ꢀ CH3), 4.08-4.12 (4H, q, 2ꢀ(-OCH2CH3)), 6.98-7.01 (4H, d, J ¼ 8.51 Hz, aro-
matic protons), 7.29–7.31 (4H, d, J ¼ 7.34 Hz, aromatic protons), 7.86–7.89 (4H, d,
J ¼ 7.72 Hz, aromatic protons), 7.91–7.94 (4H, d, J ¼ 8.41 Hz, aromatic protons). 13C
NMR (d/ppm): 14.59 (-OCH2CH3), 20.14 (CH3), 63.99 (-OCH2CH3), 114.62 ((C–H)
aromatic), 121.89 ((C) aromatic), 126.46 ((C) aromatic), 127.45 ((C–H) aromatic),
128.56 ((C–H) aromatic), 129.97 ((C–H) aromatic), 142.09 ((C–CH3) aromatic), 162.07
((C–OCH2) aromatic), 167.32 (C ¼ N), 167.88 (C ¼ N).
Bis[2-(4-propyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7c)
Yield (72%). Elemental analysis (%) calc.: C 54.7, N 8.9, H 4.6, Ag 13.6; found: C 54.5,
N 8.8, H 4.3, Ag 13.2. Molar conductivity (K): 69 S.cm2.molꢁ1. FTIR (t/cmꢁ1):, 3061
(w, t(C–H) aromatic), 2959 (w, tas(C–H) of CH3 group), 2933 (m, tas(C–H) of CH2
group), 2855 (w, ts(C–H) of CH3 group), 2834 (w-m, ts(C–H) of CH2 group), 1611 (m,
t(C ¼ N)), 1600 and 1510 (s,m, t(C ¼ C)aromatic), 1254 (s, t(C–O)). UV–Vis (k/nm):
228 (n–r ), 322 (p–p ). 1H NMR (d/ppm): 1.03-1.09 (6H, t, 2ꢀ(-OCH2CH2CH3)),
1.81-1.88 (4H, m, 2ꢀ(-OCH2CH2CH3)), 2.42 (6H, s, 2 ꢀ CH3), 3.97-4.01 (4H, t, 2ꢀ(-
OCH2CH2CH3)), 6.97–7.00 (4H, d, J ¼ 8.53 Hz, aromatic protons), 7.28–7.30 (4H, d,
J ¼ 7.94 Hz, aromatic protons), 7.86–7.89 (4H, d, J ¼ 7.89 Hz, aromatic protons),
7.91–7.94 (4H, d, J ¼ 8.58 Hz, aromatic protons). 13C NMR (d/ppm): 9.98
(-OCH2CH2CH3), 21.02 (-OCH2CH2CH3), 22.99 (CH3), 69.27 (-OCH2CH2CH3), 114.60
((C–H) aromatic), 121.97 ((C) aromatic), 124.94 ((C) aromatic), 127.27 ((C–H) aro-
matic), 128.94 ((C–H) aromatic), 129.38 ((C–H) aromatic), 141.06 ((C–CH3) aromatic),
161.68 ((C–OCH2) aromatic), 168.03 (C ¼ N), 168.34 (C ¼ N).
ꢃ
ꢃ
Bis[2-(4-butyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7d)
Yield (71%). Elemental analysis (%) calc.: C 55.7, N 8.6, H 4.9, Ag 13.2; found: C 55.6,
N 8.4, H 4.7, Ag 13.0. Molar conductivity (K): 67 S.cm2.molꢁ1. FTIR (t/cmꢁ1):, 3065
(w, t(C–H) aromatic), 2951 (w, tas(C–H) of CH3 group), 2938 (m, tas(C–H) of CH2

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
group), 2857 (w, ts(C–H) of CH3 group), 2853 (w, ts(C–H) of CH2 group), 1612 (m,
t(C ¼ N)), 1601 and 1512 (s,m, t(C ¼ C)aromatic), 1254 (s, t(C–O)). UV–Vis (k/nm):
1
ꢃ
ꢃ
m,
234 (n–r ), 331 (p–p ). H NMR (d/ppm): 0.97-1.02 (6H, t, 2ꢀ(-OCH2(CH2)2CH3)),
1.48-1.58
(4H,
2ꢀ(-OCH2CH2CH2CH3)),
1.76-1.85
(4H,
m,
2ꢀ(-
OCH2CH2CH2CH3)), 2.42 (6H, s, 2 ꢀ CH3), 4.01-4.05 (4H, t, 2ꢀ(-OCH2CH2CH2CH3)),
6.97–6.99 (4H, d, J ¼ 8.53 Hz, aromatic protons), 7.27–7.30 (4H, d, J ¼ 7.64 Hz, aromatic
protons), 7.87–7.89 (4H, d, J ¼ 8.08 Hz, aromatic protons), 7.91–7.94 (4H, d, J ¼ 8.58 Hz,
aromatic protons). 13C NMR (d/ppm): 13.33 (-OCH2(CH2)2CH3), 18.72
(-OCH2CH2CH2CH3),
21.01
(CH3),
30.70
(-OCH2CH2CH2CH3),
67.46
(-OCH2(CH2)2CH3), 114.53 ((C–H) aromatic), 122.59 ((C) aromatic), 127.27 ((C) aro-
matic), 128.91 ((C–H) aromatic), 129.31 ((C–H) aromatic), 129.66 ((C–H) aromatic),
140.84 ((C–CH3) aromatic), 161.82 ((C–OCH2) aromatic), 167.77 (C ¼ N),
169.01 (C ¼ N).
Bis[2-(4-pentyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7e)
Yield (69%). Elemental analysis (%) calc.: C 56.7, N 8.3, H 5.2, Ag 12.7; found: C 56.5,
N 8.0, H 5.0, Ag 12.4. Molar conductivity (K): 68 S.cm2.molꢁ1. FTIR (t/cmꢁ1):, 3063
(w, t(C–H) aromatic), 2952 (w, tas(C–H) of CH3 group), 2937 (m, tas(C–H) of
CH2 group), 2874 (w, ts(C–H) of CH3 group), 2858 (m, ts(C–H) of CH2 group),
1613 (m, t(C ¼ N)), 1597 and 1515 (s,m, t(C ¼ C)aromatic), 1255 (s, t(C–O)).
UV–Vis (k/nm): 229 (n–r ), 323 (p–p ). 1H NMR (d/ppm): 0.89-0.95 (6H, t,
2ꢀ(-OCH2(CH2)3CH3)), 1.43-1.58 (8H, m, 2ꢀ(-OCH2CH2(CH2)2CH3)), 1.82-1.87
(4H, m, 2ꢀ(-OCH2CH2(CH2)2CH3)), 2.41 (6H, s, 2 ꢀ CH3), 3.99-4.05 (4H, t,
2ꢀ(-OCH2(CH2)3CH3)), 6.97–7.00 (4H, d, J ¼ 8.62 Hz, aromatic protons),
7.27–7.29 (4H, d, J ¼ 7.91 Hz, aromatic protons), 7.86–7.89 (4H, d, J ¼ 7.92 Hz,
aromatic protons), 7.93–7.96 (4H, d, J ¼ 8.69 Hz, aromatic protons). 13C NMR
(d/ppm): 13.53 (-OCH2(CH2)3CH3), 21.01 (-OCH2(CH2)2CH2CH3), 22.09 (CH3), 28.63
(-OCH2CH2CH2CH2CH3), 31.06 (-OCH2CH2(CH2)2CH3), 67.78 (-OCH2(CH2)3CH3),
114.52 ((C–H) aromatic), 122.49 ((C) aromatic), 127.77 ((C) aromatic), 128.91 ((C–H)
aromatic), 129.31 ((C–H) aromatic), 129.99 ((C–H) aromatic), 140.93 ((C–CH3) aro-
matic), 162.02 ((C–OCH2) aromatic), 167.62 (C ¼ N), 167.83 (C ¼ N).
ꢃ
ꢃ
Bis[2-(4-hexyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7f)
Yield (68%). Elemental analysis (%) calc.: C 57.7, N 8.0, H 5.5, Ag 12.3; found: C 57.5,
N 7.9, H 5.4, Ag 12.0. Molar conductivity (K): 67 S.cm2.molꢁ1. FTIR (t/cmꢁ1):, 3065
(w, t(C–H) aromatic), 2967 (w, tas(C–H) of CH3 group), 2942 (m, tas(C–H) of CH2
group), 2861 (w, ts(C–H) of CH3 group), 2855 (m, ts(C–H) of CH2 group), 1612 (m,
t(C ¼ N)), 1599 and 1511 (s,m, t(C ¼ C)aromatic), 1253 (s, t(C–O)). UV–Vis (k/nm): 229
1
ꢃ
ꢃ
(n–r ), 329 (p–p ). H NMR (d/ppm): 0.87-0.93 (6H, t, 2ꢀ(-OCH2(CH2)4CH3)), 1.42-1.61
(12H, m, 2ꢀ(-OCH2CH2(CH2)3CH3)), 1.76-1.84 (4H, m, 2ꢀ(-OCH2CH2(CH2)3CH3)), 2.42
(6H, s, 2 ꢀ CH3), 3.99-4.04 (4H, t, 2ꢀ(-OCH2(CH2)4CH3)), 6.98–7.01 (4H, d, J¼ 8.82 Hz,
aromatic protons), 7.25–7.28 (4H, d, J¼ 7.82 Hz, aromatic protons), 7.85–7.87 (4H, d,
J¼ 7.88 Hz, aromatic protons), 7.98–8.01 (4H, d, J ¼ 8.79 Hz, aromatic protons). 13C
NMR (d/ppm): 13.52 (-OCH2(CH2)4CH3), 21.04 (-OCH2(CH2)3CH2CH3), 21.94

10
I. H. R. TOMI ET AL.
(CH3), 27.66 (-OCH2(CH2)2CH2CH2CH3), 28.34 (-OCH2CH2CH2(CH2)2CH3), 31.99
(-OCH2CH2(CH2)3CH3), 67.80 (-OCH2(CH2)4CH3), 114.64 ((C–H) aromatic), 122.31
((C) aromatic), 127.24 ((C) aromatic), 128.87 ((C–H) aromatic), 129.43 ((C–H) aro-
matic), 130.03 ((C–H) aromatic), 141.06 ((C–CH3) aromatic), 161.11 ((C–OCH2) aro-
matic), 168.01 (C ¼ N), 168.72 (C ¼ N).
Bis[2-(4-heptyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7g)
Yield (65%). Elemental analysis (%) calc.: C 58.5, N 7.8, H 5.8, Ag 12.0; found: C 58.4,
N 7.7, H 5.6, Ag 11.7. Molar conductivity (K): 66 S.cm2.molꢁ1. FTIR (t/cmꢁ1):,
3063 (w, t(C–H) aromatic), 2968 (w, tas(C–H) of CH3 group), 2939 (m, tas(C–H)
of CH2 group), 2855 (w, ts(C–H) of CH3 group), 2841 (m, ts(C–H) of CH2
group), 1614 (m, t(C ¼ N)), 1600 and 1510 (s,m, t(C ¼ C)aromatic), 1254 (s,
t(C–O)). UV–Vis (k/nm): 231 (n–r ), 328 (p–p ). 1H NMR (d/ppm): 0.87-0.96
(6H, t, 2ꢀ(-OCH2(CH2)5CH3)), 1.45-1.62 (16H, m, 2ꢀ(-OCH2CH2(CH2)4CH3)),
1.76-1.79 (4H, m, 2ꢀ(-OCH2CH2(CH2)4CH3)), 2.41 (6H, s, 2 ꢀ CH3), 3.99-4.05
(4H, t, 2ꢀ(-OCH2(CH2)5CH3)), 6.96–6.99 (4H, d, J ¼ 8.76 Hz, aromatic protons),
7.26–7.29 (4H, d, J ¼ 7.99 Hz, aromatic protons), 7.86–7.89 (4H, d, J ¼ 7.91 Hz,
aromatic protons), 7.92–7.94 (4H, d, J ¼ 8.81 Hz, aromatic protons). 13C NMR
(d/ppm): 13.51 (-OCH2(CH2)5CH3), 21.04 (-OCH2(CH2)4CH2CH3), 21.94
(CH3), 27.66 (-OCH2(CH2)3CH2CH2CH3), 28.34 (-OCH2(CH2)2CH2(CH2)2CH3),
ꢃ
ꢃ
29.88
(-OCH2CH2CH2(CH2)3CH3), 31.91 (-OCH2CH2(CH2)4CH3), 67.80
(-OCH2(CH2)5CH3), 114.64 ((C–H) aromatic), 119.87 ((C) aromatic), 127.27 ((C)
aromatic), 128.87 ((C–H) aromatic), 129.44 ((C–H) aromatic), 130.07 ((C–H) aro-
matic), 141.06 ((C–CH3) aromatic), 161.12 ((C–OCH2) aromatic), 167.99 (C ¼ N),
168.62 (C ¼ N).
Bis[2-(4-octyloxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole] silver(I) nitrate (7h)
Yield (63%). Elemental analysis (%) calc.: C 59.4, N 7.5, H 6.1, Ag 11.6; found: C 59.3,
N 7.2, H 6.2, Ag 11.8. Molar conductivity (K): 66 S.cm2.molꢁ1. FTIR (t/cmꢁ1):,
3069 (w, t(C–H) aromatic), 2970 (w, tas(C–H) of CH3 group), 2941 (m, tas(C–H) of
CH2 group), 2855 (w, ts(C–H) of CH3 group), 2838 (m, ts(C–H) of CH2 group), 1612
(m, t(C ¼ N)), 1599 and 1513 (s,m, t(C ¼ C)aromatic), 1254 (s, t(C–O)). UV–Vis
(k/nm): 230 (n–r ), 323 (p–p ). 1H NMR (d/ppm): 0.85-0.90 (6H, t,
2ꢀ(-OCH2(CH2)6CH3)), 1.40-1.60 (20H, m, 2ꢀ(-OCH2CH2(CH2)5CH3)), 1.79-1.83
(4H, m, 2ꢀ(-OCH2CH2(CH2)5CH3)), 2.41 (6H, s, 2 ꢀ CH3), 3.98-4.02 (4H, t,
2ꢀ(-OCH2(CH2)6CH3)), 6.99–7.02 (2H, d, J ¼ 8.73 Hz, aromatic protons),
7.29–7.31 (2H, d, J ¼ 7.88 Hz, aromatic protons), 7.89–7.92 (2H, d, J ¼ 7.96 Hz, aro-
matic protons), 7.93–7.96 (2H, d, J ¼ 8.82 Hz, aromatic protons). 13C NMR
(d/ppm): 13.61 (-OCH2(CH2)6CH3), 21.02 (OCH2(CH2)5CH2CH3), 22.17 (CH3),
25.51 (-OCH2(CH2)4CH2CH2CH3) 28.66 (-OCH2(CH2)3CH2(CH2)2CH3), 28.74
ꢃ
ꢃ
(-OCH2(CH2)2CH2(CH2)3CH3),
28.85
(-OCH2CH2CH2(CH2)4CH3),
31.32
(-OCH2CH2(CH2)5CH3), 67.80 (-OCH2(CH2)6CH3), 114.55 ((C–H) aromatic),
122.12 ((C) aromatic), 127.07 ((C) aromatic), 128.92 ((C–H) aromatic), 129.43

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
Scheme 1. Synthetic diagram for the preparation of compounds. Reactions and reagents: (i) metha-
nol, H2SO4; (ii) ethanol, NH2NH2.H2O; (iii) pyridine, 0 ꢂC; (iv) P2S5, pyridine; (v) AlCl3, benzene; (vi) RBr,
acetone; (vii) AgNO3, CH2Cl2.
((C–H) aromatic), 129.34 ((C–H) aromatic), 140.92 ((C–CH3) aromatic), 161.04
((C–OCH2), 167.77 (C ¼ N), 168.32 (C ¼ N).
Result and discussion
Synthesis and characterization of the compounds
A
series of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2)nH,
n ¼ 1–8) (6a–h) was prepared through several successive steps starting from p-toluic
acid, while bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) complexes

12
I. H. R. TOMI ET AL.
(alkoxy: O(CH2)nH, n ¼ 1–8) (7a–h) were prepared by the stirring of a corresponding
1,3,4-thiadiazole compound with silver nitrate in DCM, in the absence of light, and
under inert and ambient conditions. Scheme 1 shows the synthetic diagram of the pre-
pared compound.
Various techniques were used to identify the mesogens (6a–h) and metallomesogens
1
(7a–h): microelemental analysis, FTIR, UV–Vis, H NMR, 13C NMR and mass (for the
organic compounds) spectra, in addition to the molar conductivity measurements (for
Ag(I) complexes). The details of these data are illustrated in the experimental part.
Microelemental analyses (C, H and N) data show the good agreement of the actual
and the proposed formulas.
In general, some characteristic bands belong to C–H, C ¼ C, C ¼ N and C–O func-
tional groups [52] are observed in the FTIR spectra of 6a–h. The FTIR spectra of silver(I)
complexes (7a–h) displayed almost, the same bands that detected in the spectra of their
corresponding ligands (1,3,4-thiadiazole compounds) but with slight changes either in
their appearance or positions. For example, the band due to the stretching vibration of
C ¼ N group that observed in the spectra of 1,3,4-thiadiazole compounds (6a–h), were
found to be slightly shifted to higher frequencies in the spectra of the corresponding
Ag(I) complexes(7a–h). This gives an evidence that the binding of a thiadiazole molecule
(organic ligand) to the silver(I) ion takes place through the N atom of the C ¼ N group.
Shifting the stretching vibration of a C ¼ N group to higher frequencies upon coordin-
ation to a metal ion is already detected and reported earlier [53–56].
Several signals belonging to the various proton and carbon nuclei are observed in the
1H NMR and 13C NMR spectra of 1,3,4-thiadiazole compounds (for instance see Fig. 1a).
In the spectra of Ag(I) complexes, some of these signals are found to be shifted, either to
a lower or higher chemical shift, for example see Fig. 1b. The details of these signals and
their assignment for all the prepared compounds are depicted in the experimental part.
UV–Vis spectra of 1,3,4-thiadiazoles (6a–h) displayed two absorption peaks at the
ꢃ
ranges: (229–232 nm) and (322–326 nm). The first peak is attributed to the n–r transi-
tion, while the second one is assigned to p–p transition. However, the spectra show no
ꢃ
ꢃ
ꢃ
peak related to the n–p transition band which may be hidden by p–p band. Upon
coordination of the prepared 1,3,4-thiadiazole compounds to Ag(I) ion, the n–r and
p–p were found to be shifted either to higher or lower wavernumbers. Moreover, the
band due to the charge transfer (CT) transition in all complexes was located either
ꢃ
ꢃ
ꢃ
merged or slightly separated from the strong p–p band. No d-d transitions are
appeared in all the spectra of silver(I) complexes because of the filled d–orbitals of silver
atom [57]. The details of the UV–Vis spectral data are listed in the experimental part.
The molar conductivity values of silver(I) complexes (7a–h) in acetone (1 ꢀ 10ꢁ3M)
are in the range (66–70) S. cm2. molꢁ1, confirming their (1:1) electrolytic nature [58].
The data provided by FTIR, UV–Vis, NMR (1H and 13C NMR) spectra, conductivity
measurements and microelemental analysis, revealed the monodentate behavior of 1,3,4-thia-
diazole compounds toward silver(I). Two molecules of 1,3,4-thiadiazoles are binding to the
Ag atom through the N atom, produced a linear-mononuclear complex with the general
formula [Ag (L)2]. NO3 (where L: 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole derivative).
Almost of the prepared thiadiazole complexes that investigated so far confirmed that the
binding of thiadiazole ligand to a metal ion is took place through N atoms [59–62].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
13
Figure 1. 1H NMR spectra of 6c (a) and 7c (b).

14
I. H. R. TOMI ET AL.
Table 1. Phase transitions and their temperatures for the prepared compounds obtained by POM.
Phase transitions (T / ꢂC)
First heating
Phase transitions (T / ꢂC)
First cooling
Compound
6a
n
1
Cr-N (154.0)
N-I (216.0)
Cr-N (141.0)
N-I (224.0)
Cr-N (146.0)
N-I (200.0)
Cr-N (138.0)
N-I (204.0)
Cr-N (122.0)
N-I (192.0)
Cr-N (117.0)
I-N (214.0)
N-Cr (138.0)
I-N (220.0)
N-Cr (125.0)
I-N (198.0)
N-Cr (122.0)
I-N (198.0)
N-Cr (110.0)
I-N (191.0)
N-Cr (106.0)
I-N (191.0)
N-Cr (98.0)
I-N (183.0)
6b
6c
6d
6e
6f
2
3
4
5
6
7
N-I (196.0)
6g
Cr-SmC (113.0)
SmC-N (121.0)
N-I (186.0)
Cr-SmC (110.0)
SmC-N (134.0)
N-I (183.0)
Cr-I (204.00)
Cr-SmA (147.0)
SmA-I (210.0)
Cr-SmA (133.0)
SmA-I (185.0)
Cr-SmA (127.0)
SmA-I (191.0)
Cr-SmA (125.0)
SmA-I (181.0)
Cr-SmA (112.0)
SmA-I (186.0)
Cr-SmA (107.0)
SmA-I (178.0)
Cr-SmA (113.0)
SmA-I (180.0)
N-SmC (118.0)
SmC-Cr (96.0)
I-N (181.0)
6h
8
N-SmC (129.0)
SmC-Cr (93.0)
I-Cr (200.00)
I-SmA (207.0)
SmA-Cr (55.0)
I-SmA (181.0)
SmA-Cr (68.0)
I-SmA (188.0)
SmA-Cr (59.0)
I-SmA (179.0)
SmA-Cr (66.0)
I-SmA (182.0)
SmA-Cr (96.0)
I-SmA (172.0)
SmA-Cr (94.0)
I-SmA (177.0)
SmA-Cr (92.0)
7a
7b
1
2
7c
7d
7e
7f
3
4
5
6
7
8
7g
7h
Cr—crystalline solid, SmA—smectic A mesophase, SmC—smectic C mesophase, N—nematic mesophase, I—isotropic
liquid, n—alkyl chain length.
Liquid crystalline behavior of the prepared compounds
Liquid crystalline behavior of the prepared compounds was evaluated using polarized
light optical microscopy (POM) technique. The studies showed in general that all the
compounds of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2)nH,
n ¼ 1–8) (6a–h) and bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) com-
plexes (alkoxy: O(CH2)nH, n ¼ 2–8) (7 b–h) are mesomorphic materials displaying enan-
tiotropic liquid crystal properties, while 7a (n ¼ 1) shows no mesomorphic properties
(simply melted to isotropic liquid). The details of the mesophase transitions are depicted
in Table 1, and examples of optical micrographs of these compounds are illustrated in
Fig. 2.
It can be clearly seen from Table 1 that compounds 6a–h displayed only nematic
mesophase upon heating and cooling, which was attributed from the typical thread-like
texture, droplet-like texture or schlieren-like texture, while 6g and 6h showed both of
SmC and nematic mesophases upon heating and cooling. SmC mesophase was identified
by the schlieren-like texture, while nematic mesophase assigned from the typical thread-
like texture, droplet-like texture or schlieren-like texture. These results are quite similar
to that obtained by Jie Han et al. [63].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
15
Figure 2. Optical micrographs (magnification:ꢀ300) of (a) the nematic droplet-like texture obtained
for 6f, at 120 ꢂC upon cooling; (b) the nematic thread-like texture observed for 6g, at 176 ꢂC upon
cooling; (c) the schlieren nematic texture detected for 6e, at 183 ꢂC upon heating; (d) the smectic C
texture exhibited by 6g, at 117 ꢂC upon heating, (e) the fan-shape texture shown by 7e, at 131 ꢂC
upon cooling; (f) the fan-shape texture observed for 7g, at 113 ꢂC upon cooling.

16
I. H. R. TOMI ET AL.
Figure 3. Clearing temperature (Tc) as a function of alkyl chain length for 1,3,4-thiadiazoles series
(black line) and silver(I) complexes series (red line).
Upon complexation of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles to silver(I),
the liquid crystal behavior and properties are appreciably changed. In this context,
silver(I) complexes 7 b–h exhibit SmA mesophase upon heating and cooling, while
7a shows no mesomorphic properties (simply melted to isotropic liquid). This differ-
ence may be due to the different stereochemical structure of the two series
of compounds.
In general, the length of hydrocarbon chain might have variable effects on the clear-
ing temperature of a mesogen or metallomesogen. So, as the chain length of a com-
pound increases, the van der Waals interactions increase and this would increase the
clearing point. On the other hand, the flexibility of the hydrocarbon chain may disrupt
the lateral core–core interactions, and consequently reduces the clearing point of a com-
pound. The clearing temperatures of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles
(alkoxy: O(CH2)nH, n ¼ 1–8) (6a–h) and bis(2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thia-
diazole)-silver(I) complexes (alkoxy: O(CH2)nH, n ¼ 1–8) (7a–h) are found to be
decreased with increasing the chain length, see Fig. 3 (the odd-even effect in both series
can be clearly seen from this figure). Therefore, this indicates that the melting process
seems to be governed by the random motion of hydrocarbon chains, and is less affected
by the van der Waals interactions between chains [14,38,64]. Moreover, the clearing
temperature of silver(I) complexes series (7a–h) were found to be lower than that of the
corresponding 1,3,4-thiadiazoles series (6a–h). This may be due to the following reason:
the structure of 1,3,4-thiadiazole compounds (6a–h) show only one tail of hydrocarbon
chain, while the structure of silver(I) complexes (7a–h) displayed two tails.
Consequently, the disruption of the lateral core–core interactions by flexibility of the
alkyl chains would be more pronounced in silver(I) complexes.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
17
Conclusions
Reaction of 2-(4-alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazoles (alkoxy: O(CH2)nH,
n ¼ 1–8) (6a–h) (as a series of 1,3,4-thiadiazole derivatives) with silver nitrate at room
temperature, in the absence of light, and under inert conditions produced a series of
organic-inorganic hybrids with two tails of hydrophobic hydrocarbon chains: bis(2-(4-
alkoxyphenyl)-5-(p-tolyl)-1,3,4-thiadiazole)-silver(I) complexes (alkoxy: O(CH2)nH,
n ¼ 1–8) (7a–h). Both series are confirmed as liquid crystalline materials with different
behavior and properties (different mesophases, and different melting and clearing tem-
peratures). The prepared1,3,4-thiadiazoles behave as mesogens (6a–f) show only nematic
mesophase upon heating and cooling, while 6g and 6h display SmC and nematic meso-
phases upon heating and cooling. On the other hand, the silver(I) complexes behave as
metallomesogens exhibiting SmA mesophase upon heating and cooling, except 7a which
shows no mesomorphic properties (simply melted to isotropic liquid).
Acknowledgments
Our special thanks to Mustansiriyah University/Baghdad, Iraq (https://uomustansiriyah.edu.iq)
for support and access to facilities. We indebted to the Arab Science of Technology Foundation
(ASTF) group for support.
References
[1] A. Ramamoorthy, Thermotropic Liquid Crystals: recent Advances (Springer, Dordrecht,
2007).
[2] J. W. Steed, and J. L. Atwood, Supramolecular Chemistry (John Wiley & Sons, Wiltshire,
2009)
[3] A. Mu€ller et al., Chemistry 20 (22), 6659 (2014). doi:10.1002/chem.201402216
[4] P. N. Kalaria, S. C. Karad, and D. K. Raval, Eur. J. Med. Chem. 158, 917 (2018). doi:10.
1016/j.ejmech.2018.08.040
[5] M. Rbaa et al., Chem. Data Collect. 24, 100306 (2019). doi:10.1016/j.cdc.2019.100306
[6] Y. Mi et al., Carbohydr. Polym. 249, 116847 (2020). doi:10.1016/j.carbpol.2020.116847
[7] P. Zoumpoulakis et al., Bioorg. Med. Chem. 20 (4), 1569 (2012). doi:10.1016/j.bmc.2011.
12.031
[8] Q. Wu et al., Bioorg. Med. Chem. Lett. 30 (10), 127113 (2020). doi:10.1016/j.bmcl.2020.
127113
[9] E. A. Yaqo et al., J. Mol. Struct. 1202, 127356 (2020). doi:10.1016/j.molstruc.2019.127356
[10] M. Abdallah et al., Chem. Data Collect. 28, 100407 (2020). doi:10.1016/j.cdc.2020.100407
[11] C. Fliedel et al., Coord. Chem. Rev. 394, 65 (2019). doi:10.1016/j.ccr.2019.05.003
[12] R. Thapa, and S. M. Kilyanek, J. Organomet. Chem. 901, 120937 (2019). doi:10.1016/j.jor-
ganchem.2019.120937
[13] T. Scattolin et al., Polyhedron. 154, 382 (2018). doi:10.1016/j.poly.2018.08.007
[14] A. J. Hammood et al., Mol. Cryst. Liq. Cryst. 648 (1), 114 (2017). doi:10.1080/15421406.
2017.1301872
[15] A. J. M. Al-Karawi et al., Liq. Cryst.1 (2020). doi:10.1080/02678292.2020.1786175
[16] A. A. Awad et al., J. Chem. Res. 43 (1-2), 67 (2019). doi:10.1177/1747519819840715
[17] I. H. R. Tomi, J. Saudi Chem. Soc. 16 (2), 153 (2012). doi:10.1016/j.jscs.2010.12.002
[18] I. H. R. Tomi et al., Tetrahedron. 72 (29), 4390 (2016). doi:10.1016/j.tet.2016.06.013
[19] I. H. R. Tomi, D. T. A. Al-Heetimi, and H. J. Jaffer, J. Mol. Struct. 1141, 176 (2017). doi:
10.1016/j.molstruc.2017.03.105

18
I. H. R. TOMI ET AL.
[20] I. H. R. Tomi, M. M. A. R. Al-Obaidy, and A. H. R. Al-Daraji, Liq. Cryst. 44 (4), 603
(2017). doi:10.1080/02678292.2016.1225837
[21] M. M. A. R. Al-Obaidy, I. H. R. Tomi, and H. J. Jaffer, Liq. Cryst. 44 (7), 1131 (2017).
doi:10.1080/02678292.2016.1264013
[22] H. J. Abboud, S. J. Lafta, and I. H. R. Tomi, Liq. Cryst. 44 (14-15), 2230 (2017). doi:10.
1080/02678292.2017.1360953
[23] H. J. Jaffer, Y. A. Aldhaif, and I. H. R. Tomi, Mol. Cryst. Liq. Cryst. 643 (1), 199 (2017).
doi:10.1080/15421406.2016.1266881
[24] G. Q. Ali, and I. H. R. Tomi, Liq. Cryst. 45 (3), 421 (2018). doi:10.1080/02678292.2017.
1338767
[25] I. H. R. Tomi, H. J. Jaffer, and Y. A. Aldhaif, Phase Transit. 91 (4), 434 (2018). doi:10.
1080/01411594.2017.1408806
[26] G. Q. Ali, and I. H. R. Tomi, Soft Mater. 16 (2), 94 (2018). doi:10.1080/1539445X.2018.
1424639
[27] G. Q. Ali, and I. H. R. Tomi, J. Dispers. Sci. Technol. 40 (8), 1093 (2019). doi:10.1080/
01932691.2018.1496832
[28] N. M. Abdulnabi et al., ChemistrySelect. 5 (28), 8740 (2020). doi:10.1002/slct.202001857
[29] F. Camerel et al., Adv. Mater. 20 (18), 3462 (2008). doi:10.1002/adma.200800059
[30] M.-H. Qi, and G.-F. Liu, J. Mater. Chem. 13 (10), 2479 (2003). doi:10.1039/b302308g
[31] D. Pucci et al., Eur. J. Inorg. Chem. 2009 (28), 4274 (2009). doi:10.1002/ejic.200900536
[32] E. Cavero et al., J. Am. Chem. Soc. 129 (37), 11608 (2007). doi:10.1021/ja073639c
[33] M. Micutz, I. Pasuk, and M. Ili¸s, J. Mol. Liq. 243, 151 (2017). doi:10.1016/j.molliq.2017.08.
013
[34] M. Ili¸s et al., Polyhedron. 69, 31 (2014). doi:10.1016/j.poly.2013.11.015
[35] M. Middha, R. Kumar, and K. Raina, Liq. Cryst. 43 (7), 1002 (2016). doi:10.1080/
02678292.2016.1155772
[36] C. K. Lee et al., Dalton Trans. (8), 1120 (2004). doi:10.1039/b314367h
[37] M. J. Mayoral et al., New J. Chem. 34 (12), 2766 (2010). doi:10.1039/b9nj00753a
[38] A. J. M. Al-Karawi, Liq. Cryst. 44 (14-15), 2285 (2017). doi:10.1080/02678292.2017.
1371799
[39] A. J. M. Al-Karawi et al., J. Mol. Struct. 1168, 92 (2018). doi:10.1016/j.molstruc.2018.05.023
[40] A. J. M. Al-Karawi et al., Liq. Cryst. 45 (11), 1603 (2018). doi:10.1080/02678292.2018.
1446553
[41] C. O. Rossi et al., Liq. Cryst. 44 (5), 880 (2017). doi:10.1080/02678292.2016.1254294
[42] M. Krikorian et al., Liq. Cryst. 43 (12), 1709 (2016). doi:10.1080/02678292.2016.1200679
[43] M. Krikorian, S. Liu, and T. M. Swager, J. Am. Chem. Soc. 136 (8), 2952 (2014). doi:10.
1021/ja4114352
[44] Y.-T. Tsai et al., Org. Electron. 15 (1), 311 (2014). doi:10.1016/j.orgel.2013.11.025
[45] S. Coco et al., Dalton Trans. (48), 6894 (2008). doi:10.1039/b811482j
ꢀ
[46] J. Arias, M. Bardajı, and P. Espinet, Inorg. Chem. 47 (9), 3559 (2008). doi:10.1021/
ic701831v
[47] B. Yao, Y. Cong, and B. Zhang, Liq. Cryst. 43 (9), 1190 (2016). doi:10.1080/02678292.
2016.1162860
[48] A. Escande et al., Chem. Eur. J. 13 (31), 8696 (2007). doi:10.1002/chem.200700560
[49] Y. G. Galyametdinov et al., Adv. Mater. 20 (2), 252 (2008). doi:10.1002/adma.200701714
[50] A. Prajapati, and V. Modi, Phase Transit. 83 (8), 634 (2010). doi:10.1080/01411594.2010.
505341
[51] H.-M. Kuo et al., Tetrahedron. 68 (36), 7331 (2012). doi:10.1016/j.tet.2012.06.092
[52] R. Silverstein et al., Spectrophotometric Identification of Organic Compounds (Willy, New
York, 2014).
[53] M. A. Ali et al., polyhedron. 30 (2), 299 (2011). doi:10.1016/j.poly.2010.10.027
ꢀ
[54] P. Souza, A. I. Matesanz, and V. Fernandez, J. Chem. Soc., Dalton Trans. (14), 3011
(1996). doi:10.1039/DT9960003011

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
19
[55] A.-A. B. OmarAli et al., Acta. Crystallogr. C. Struct. Chem. 76 (Pt 5), 476 (2020). doi:10.
1107/S2053229620004994
[56] A.-A. B. OmarAli et al., J.Mol. Struct. 1217, 1 (2020).
[57] A. B. P. Lever, Inorganic Electronic Spectroscopy (Elesvier Publishing, New York, 1968).
[58] W. J. Geary, Coord. Chem. Rev. 7 (1), 81 (1971). doi:10.1016/S0010-8545(00)80009-0
[59] S. Demir et al., J. Coord. Chem. 72 (18), 3071 (2019). doi:10.1080/00958972.2019.1685089
[60] Q. Zhang et al., Jnl. Chinese Chemical Soc. 57 (5A), 992 (2010). doi:10.1002/jccs.
201000138
[61] M. Maekawa et al., Inorg. Chim. Acta. 290 (2), 153 (1999). doi:10.1016/S0020-
1693(99)00122-X
[62] L. M. T. Frija, A. J. L. Pombeiro, and M. N. Kopylovich, Coord. Chem. Rev. 308 (1), 32
(2016). doi:10.1016/j.ccr.2015.10.003
[63] J. Han et al., Liq. Cryst. 36 (2), 157 (2009). doi:10.1080/02678290902752124
[64] J. W. Goodby et al., Handbook of Liquid Crystals (Wiley-VCH, Weinheim, 2014).