Manganese(II) catalyzed synthesis of bis(N-cyclohexylthiourea) derived from thiosemicarbazide: Structural characterization, fluorescence, cyclic voltammetry, Hirshfeld surface analysis and DFT calculation

Article abstract of DOI:10.1016/j.molstruc.2021.131060

A new compound bis(N-cyclohexylthiourea) (H₂chth) has been synthesized and characterized with the aid of elemental analyses, IR, NMR and single crystal X-ray diffraction data. Compound H₂chth crystallizes in triclinic system with space group P-1. During the course of reaction, the cyclohexyl isothiocynate moiety of the substituted thiosemicarbazide undergoes tautomerization and rearrangement into the corresponding carbothioamide moiety in the presence of manganese(II) acetate. The interaction of H₂chth with different metal ions in methanol solution is studied and it shows interesting red shifts with Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ ions which suggests that compound H₂chth may be a useful probe for sensing of these metal ions. Cyclic voltammetric studies of H₂chth and its interaction with different metal ions exhibit complete irreversible redox behavior. Compound H₂chth exhibits emission at 27322 cm^?1 upon excitation at 37037 cm^?1. The emission spectra of different metal ions with H₂chth exhibit less intense emissions as compared to the free H₂chth. The structure of compound H₂chth is stabilized via intermolecular N-H···S and C-H···S hydrogen bonding. The geometry of the compound H₂chth has been optimized using the B3LYP density functional theory method and the results are compared with the X-ray diffraction data. The calculated geometrical parameters corroborate with the experimental data. Frontier molecular orbital analysis suggests that compound H₂chth is soft and highly reactive. Hirshfeld surface map and 2D finger print plot were used to explore the intermolecular interactions of H₂chth.

Full text of DOI:10.1016/j.molstruc.2021.131060

Journal of Molecular Structure 1246 (2021) 131060
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Manganese(II) catalyzed synthesis of bis(N-cyclohexylthiourea) derived
from thiosemicarbazide: Structural characterization, fluorescence,
cyclic voltammetry, Hirshfeld surface analysis and DFT calculation
S. Jaiswala, M.K. Gonda, M.K. Bhartya,∗, B. Maitia, S. Krishnamoorthia, R.J. Butcherb
a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
b Department of Chemistry, Howard University, 525 College Street NW, Washington, DC 20059, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A new compound bis(N-cyclohexylthiourea) (H2chth) has been synthesized and characterized with the
aid of elemental analyses, IR, NMR and single crystal X-ray diffraction data. Compound H2chth crys-
tallizes in triclinic system with space group P-1. During the course of reaction, the cyclohexyl isothio-
cynate moiety of the substituted thiosemicarbazide undergoes tautomerization and rearrangement into
the corresponding carbothioamide moiety in the presence of manganese(II) acetate. The interaction of
H2chth with different metal ions in methanol solution is studied and it shows interesting red shifts with
Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ ions which suggests that compound H2chth may be a useful
probe for sensing of these metal ions. Cyclic voltammetric studies of H2chth and its interaction with dif-
ferent metal ions exhibit complete irreversible redox behavior. Compound H2chth exhibits emission at
27322 cm−1 upon excitation at 37037 cm−1. The emission spectra of different metal ions with H2chth
exhibit less intense emissions as compared to the free H2chth. The structure of compound H2chth is sta-
bilized via intermolecular N-H···S and C-H···S hydrogen bonding. The geometry of the compound H2chth
has been optimized using the B3LYP density functional theory method and the results are compared
with the X-ray diffraction data. The calculated geometrical parameters corroborate with the experimen-
tal data. Frontier molecular orbital analysis suggests that compound H2chth is soft and highly reactive.
Hirshfeld surface map and 2D finger print plot were used to explore the intermolecular interactions of
H2chth.
Received 22 February 2021
Revised 30 June 2021
Accepted 5 July 2021
Available online 20 July 2021
Keywards:
Bis(N-cyclohexylthiourea)
Crystal structure
photoluminescence and electrochemical
behaviour
Hirshfeld surface analysis and DFT
calculation
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
thiourea are important compounds which possess biological activ-
ity, act as corrosion inhibitors, antioxidant and are the main com-
Nitrogen-sulfur containing ligands have been of great interest to
researchers and play an important role in the synthesis of biologi-
cally active compounds [1-6]. This is due to their potential biolog-
ical activities viz. anticancer, antibacterial, antifungal, antiamoebic
and insecticidal and also for their therapeutic uses [7-16]. A vari-
ety of nitrogen and sulphur containing ligands are known which
include thiourea, thiosemicarbazide, thiosemicarbozones and N-
acyl-N’-thioaroylhydrazides. A number of thiosemicarbazides and
their derivatives have been synthesized and characterized by vari-
ous physicochemical techniques and used as intermediate for the
syntheses of five membered nitrogen-sulfur or nitrogen-oxygen
ponent of the polymers [19]. They are used as analytical reagents,
especially for the determination of metal ions in the presence of
various metal ions [20,21]. Acyl/aryl thiourea derivatives are well
known for a wide range of biological activities such as bacterici-
dal, fungicidal, insecticidal and possess regulating activity for plant
growth [22-24]. Due to the presence of S, N and O donor atoms,
the versatility and interesting behaviour of thiourea as building
blocks in polydentate ligands for metals have become a research
topic of interest in the last few years. It has been reported that
acylthiourea ligands behave as monodentate or bidentate bonding
through sulphur and oxygen donor atoms [25]. These hard and soft
donor atoms provide a multitude of bonding possibilities [26,27]. A
number of thiourea derivatives have been reported to form com-
plexes with 3d metal ions [28]. In view of the above, we have
synthesized a new compound bis(N-cyclohexylthiourea) (H2chth)
and characterized by various physicochemical techniques and sin-
gle crystal X-ray diffraction data.
ꢀ
heterocyclic compounds [17,18]. Thiourea and N, N -disubstituted
∗
Corresponding author.
E-mail addresses: mkbharty@bhu.ac.in, manoj_vns2005@yahoo.co.in (M.K.
Bharty).
https://doi.org/10.1016/j.molstruc.2021.131060
0022-2860/© 2021 Elsevier B.V. All rights reserved.

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
2. Experimental
Journal of Molecular Structure 1246 (2021) 131060
against all data by full matrix least-square on F2 using anisotropic
displacement parameters for all non-hydrogen atoms. All of the
hydrogen atoms were included in the refinement at geometrically
ideal positions and refined with riding model [29]. The MERCURY
package and ORTEP-3 for windows program were used for gener-
ating the structures [30,31].
2.1. Chemicals and starting materials
Commercial reagents were used without further purification.
Cyclohexyl isothiocynate was purchased from Sigma Aldrich. Other
chemicals were of reagent grade and used as received without fur-
ther purification. All the synthetic manipulations were carried out
in open atmosphere and at room temperature. The solvents were
dried and distilled before use following the standard procedure.
2.4. Quantum Chemical Calculation
Density Functional Theory (DFT) calculations were performed
using the B3LYP functional [32]. The 6-31G∗∗ basis set was used for
all atoms. The geometry optimization and frequency calculation (to
verify genuine minimum energy structures) were performed using
Gaussian 09 program package [33].
2.2. Physical measurements
The carbon, hydrogen and nitrogen contents were determined
on an Elementar Vario EL III Carlo Erba 1108 instrument. Infrared
spectra were recorded in the 400-4000 cm−1 region as KBr pel-
lets on a Varian Excalibur 3100 FT-IR spectrophotometer. 1H and
13C NMR spectra were recorded in DMSO-d6 on a JEOL JNM-
ECZ500R/S1 FT-NMR spectrometer using TMS as an internal refer-
ence. Electronic spectra were recorded at 10−4 M solution in MeOH
on a SIMADZU 1700 UV-Vis spectrophotometer. The fluorescent
data were collected at room temperature on “Agilent Technolo-
gies Cary Eclipse” Fluorescence Spectrophotometer in MeOH. Elec-
tro chemical studies were performed on Metrohm (Netherlands)
Instrument (Autolab PGSTAT204) attached with NOVA 1.11 software
at room temperature under N2 atomsphere. A three electrode, one
compartment cell with solid Pt electrode as a working electrode,
platinum wire as counter electrode and Ag/AgCl as reference elec-
trode was used. Thermogravimetric analysis (TG-DTA) of H2chth
was done using a Perkin Elmer-STA 6000 thermal analyzer, TA in-
struments under a nitrogen atmosphere with heating rate of 10°C
2.5. Synthesis of 1-hydroxy benzoyl-4-cyclohexyl-3-thiosemicarbazide
(H2hbchth)
4-Hydroxy benzoic acid hydrazide was prepared by refluxing
ethyl-4-hydroxybenzoate (3.0 g, 20 mmol) and hydrazine hydrate
(1.2 mL, 20 mmol) for 5 h at 80°C. White solid obtained after
cooling the reaction mixture was washed with ether and dried in
vacuo. To the ethanol suspension of 4-hydroxy benzoic acid hy-
drazide, cyclohexyl isothiocynate (2.54 mL, 20 mmol) added drop-
wise and the reaction mixture was stirred for 4 h. The light yel-
low solid of 1-hydroxy benzoyl-4-cyclohexyl-3-thiosemicarbazide
obtained upon cooling was filtered off, washed with ether and
dried in vacuo. Yield: 72%. M.p. 195°C. Anal. Calc. for C14 H19 N3O2S
(293.00): C, 57.3; H, 6.48; N, 14.33. Found: C, 56.01; H, 6.19; N,
15.32. IR (KBr, cm−1): v(-OH) 3420, v(-NH) 3212, 3112, v(-CH aro-
matic ring) 3007, v(-CH cyclohexyl ring) 3112, v(-C=O) 1673, v(-
N-N) 1169, v(-C=S) 984. 1H NMR (DMSO-d6, 500 MHz; δ ppm)
10.30, 9.35 (2H,-NH), 7.77-7.80 (4H, aromatic protons), 4.25 (1H,
OH), 1.22-1.28 (cyclohexyl protons). 13C NMR (DMSO-d6, 500 MHz;
δ ppm) 180.89 (C=S), 162.04 (C=O), 114.91-131.49 (aromatic ring
carbons), 14.40-32.60 (cyclohexyl ring carbons).
min−1
.
2.3. Crystal structure determination
Crystals suitable for X-ray analysis of bis(N-cyclohexylthiourea)
(H2chth) was grown at room temperature. The Crystal data were
collected on an oxford Gemini diffractometer equipped with a
CryAlis CCD software using a graphite mono-chromated Mo Kα
2.6. Synthesis of bis(N-cyclohexylthiourea) (H2chth)
˚
(λ =0.71073A) radiation source at 293 K. A multi scan absorption
A
methanol solution (20 mL) of Mn(OAc)2·4H2O (0.122 g,
correction was solved by direct methods (SHELXL-08) and refined
0.5 mmol) was added to the methanol suspension of 1-hydroxy
Scheme 1. Synthesis of bis(N-cyclohexylthiourea) (H2chth)
2

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
NH), 1.23-1.33 (cyclohexyl protons). 13C NMR ((DMSO-d6, 500 MHz;
δ ppm): 165.36 (C=S), 23.52-38.83 (cyclohexyl ring carbons).
benzoyl-4-cyclohexyl-3-thiosemicarbazide (0.293 g, 1 mmol) and
stirred for 4 h. White solid was obtained, filtered off and washed
with ether. A methanol solution of o-phen (0.099 g, 0.5 mmol) was
added to methanol suspension of above solid and stirred for 1 h. A
clear solution was obtained, filtered off and kept for crystallization.
White crystals of H2chth, suitable for X-ray analysis, were obtained
by slow evaporation of the above solution over a period of 10 days.
Yield 60 %. M.p. 220°C. Anal. Found: C, 53.80; H, 7.90; N, 17.40 %.
Anal. Calc. for C14 H26N4S2 (314.51): C, 53.50; H, 8.2; N, 17.83 %. IR
(KBr, v, cm−1): 3245, 3144 v(NH), 1446 v(C-N), 1168 v(N-N); 984
v(C=S). 1H NMR (DMSO-d6, 500 MHz; δ ppm): 10.30, 8.87 (s, 4H,
3. Result and discussion
The
intermediate
1-hydroxy
benzoyl-4-cyclohexyl-3-
thiosemicarbazide (H2hbchth) reacts with Mn(OAc)2•4H2O
and forms white precipitate in methanol solution. The above
precipitate was dissolved in methanol solution of o-phen to
yield bis(N-cyclohexylthiourea) (H2chth). We have synthesized
H2chth from 1-hydroxy benzoyl-4-cyclohexyl-3-thiosemicarbazide
Scheme 2. Plausible mechanism for synthesis of the bis(N-cyclohexylthiourea)
3

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Scheme 3. Protonated and deprotonated form of bis(N-cyclohexylthiourea) (H2chth)
Fig. 1. A: UV-vis. absorption spectra of H2chth and interaction with various metal ions at 10−4 M (A) B: UV-vis. absorption spectra of H2chth and interaction with metal
ions shows d-d transitions
Fig. 3. Thermogram of bis(N-cyclohexylthiourea) (H2chth)
Fig. 2. Emission spectra of H2chth with various metal ions in MeOH solution at
due to the stretching modes (cm−1) of OH (3420), NH (3212,
room temperature
3112), C=O (1673), N-N (1169) and C=S (984). Two bands ob-
(H2hbchth) assisted by Mn(II) acetate at room temperature with
the product yield of 60%. During the course of reaction, the
cyclohexyl isothiocynate moiety of the intermediate undergoes
tautomerization and rearrangement into the corresponding car-
bothioamide moiety in the presence of manganese(II) acetate.
This method is different from the reported earlier synthesis of
other similar bis(N-acylthiourea) [34]. The schemes 1 and 2 depict
the formation of compound H2chth and its plausible mechanism,
respectively. The compound H2chth is air stable, non-hygroscopic
crystalline solid. It is soluble in common organic solvents and can
be kept at room temperature over a prolonged period without
any sign of decomposition. The present route is relatively safer
involving less hazardous chemicals that can be easily handled. The
compound H2chth melts at 220 °C. Thus, the new route employed
for the synthesis of above compound does not only impart good
yield but is also adequate for growing their single crystals.
served at 3007 and 2939 cm−1 due to CH stretching vibrations
of aromatic and cyclohexyl rings. The IR spectrum of H2chth
shows absorption due to stretching modes of NH (3245, 3144),
C-N (1446), N-N (1168) and C=S (984). The absence of ν(C=O)
band together with the appearance of one new band for ν(C-
N) at 1446 cm−1 in the IR spectrum of the H2chth suggests
the conversion of thiosemicarbazide to bis(N-cyclohexylthiourea).
Thus, it is clear from the IR data that the intermediate 1-hydroxy
benzoyl-4-cyclohexyl-3-thiosemicarbazide converted to the corre-
sponding bis(N-cyclohexylthiourea). A band observed at 3007 cm−1
due to CH stretching vibrations of aromatic ring in intermedi-
ate H2hbchth which is absent in the spectrum H2chth. Compound
H2chth showed two absorptions bands at 2853 and 2931 cm−1 due
to CH stretching vibrations of cyclohexyl ring. The HCH scissoring
vibrations observed in the region 1534–1446 cm−1 are due to cy-
clohexyl ring.
3.1. IR spectra
3.2. NMR spectra
The IR spectrum of the intermediate 1-hydroxy benzoyl-4-
The 1H NMR spectrum of intermediate 1-hydroxy benzoyl-4-
cyclohexyl-3-thiosemicarbazide (H2hbchth) shows absorption band
cyclohexyl-3-thiosemicarbazide (H2hbchth) exhibits three signals
4

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Fig. 4. ORTEP diagram of bis(N-cyclohexylthiourea) (H2chth) with atomic numbering scheme
(ꢀ =8750 L M−1 cm−1) may be assigned to n→π∗ transition which
is attributed to the HNCS moiety. The electronic spectra of H2chth
with different metal ions show two bands in the range of 38910-
37735 cm−1 which may be assigned to the intraligand/charge
transfer transitions (Fig. 1A & 1B). Upon excitation at 37037 cm−1
compound H2chth exhibits maximum emission at 27322 cm−1
,
(Fig. 2). Emission spectra of Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+
Cd2+ and Hg2+ ions with H2chth exhibit a slightly lower lumines-
cent property as compared to the free H2chth with respect to in-
,
tensity and energy. Metal ions Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+
,
Cd2+ and Hg2+ with H2chth, upon excitation at 37037 cm−1, ex-
hibit emission maxima at 27397, 27322, 31152, 31847, 31250, 27247,
27472 and 27322 cm−1, respectively. Thus compound H2chth and
its interaction with different metal ions show Stokes shift of 9640,
9715, 5885, 5190, 5787, 9790, 9565 and 9715 cm−1, respectively
and emit blue light. The emission spectra suggest that metal ions
with H2chth exhibit less intense emission as compared to free
H2chth. The compound H2chth possesses two dissociable protons
and is supposed to furnish its deprotonated form with higher ex-
tent of conjugation and thereby high extent of luminescence. Upon
the addition of a particular metal ion to the H2chth solution the
same is expected to compete for the lone pairs of the H2chth.
Consequently, the complex species is expected to get formed in
the solution. This phenomenon might be diminishing the extent
of equilibrium A and prospective the same towards left hand side
i.e. equilibrium B (scheme 3). In other words, upon the addition of
metal ions the prospective of equilibrium A is diminished and is
favoured towards the left hand side i.e. equilibrium B which ulti-
mately leads to decrease in luminescence behaviour of LH2 (proto-
nated form of compound).
Fig. 5. Showing cyclic voltammogram of bis(N-cyclohexylthiourea) (H2chth)
at δ 10.30, 9.95 and 9.35 ppm for the amide, thioamide and NH
protons attached with cyclohexyl ring, respectively. Aromatic pro-
tons appear as multiplet between δ 6.82-7.80 ppm. One signal ob-
served at 4.23 ppm due to OH proton. Cyclohexyl ring protons ap-
pear in the region of 1.22-1.28 ppm. The 13C NMR spectrum of
H2hbchth shows several signals for various carbon atoms out of
which the signals at δ 180.89 and 162.04 ppm are due to >C=S
and >C=O, carbons, respectively. The signals appearing between δ
114.91-131.49 ppm are due to aromatic carbons. Cyclohexyl ring
carbons appear in the region of 14.40-32.60 ppm. The 1H NMR
spectrum of H2chth shows two signals at 10.30 and 8.87 ppm due
to the thioamide NH protons and one NH proton attached to the
cyclohexyl ring, respectively. Cyclohexyl ring protons appear in the
region of 1.23-1.33 ppm. The 13C NMR spectrum of H2chth shows
a signal at δ 165.6 ppm due to C=S carbon. The cyclohexyl ring
carbons appear in the range δ 14.40-32.60 ppm. Disappearance of
C=O signal in 13C NMR spectrum of H2chth (present at 162.04
ppm in the intermediate H2hbchth) suggests the conversion of
thiosemicarbazide moiety to the corresponding N-acylthioura moi-
ety.
3.4. Cation Interaction Behaviour
UV-Vis absorption spectra were recorded in 10−4 M methanol
solution. The absorption spectral band observed for compound
H2chth at 38610 cm−1 may be assigned to n → π∗ transition due
to the presence of HNCS moiety (Fig. 1A). Addition of 1.0 equiv-
alent each of Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ Cd2+ and Hg2+
metal ion as their acetate salts respectively to the 10−4 M so-
lution of H2chth produced UV-vis. spectral changes. We detected
the colour change and new d-d absorption bands upon addition
of different metal(II) acetates due to coordination between metal
ion and thioamide sulfur atom (Fig. 1B). The above observation
clearly proves the sensitivity of H2chth towards the above men-
tioned transition metal ions via coordination between metals and
3.3. Electronic absorption and Emission spectra
The electronic spectra of H2chth and interaction with different
metal ions are recorded in methanol of 10−4 M solution. Com-
pound H2chth displays one high intensity band at 38610 cm−1
5

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
15015 cm−1, and it is the characteristic of octahedral Ni(II) com-
thioamide sulfur atom. Upon addition of chromium acetate solu-
tion the colour changed to light green and two new bands were
observed at 17123 and 22727cm−1 due to d-d transitions whereas
upon addition of manganese(II) acetate solution, the ions did not
show any significant colour change and an absorption band was
observed at 38314 cm−1 (Fig. 1B). These values are close to the
absorption maxima reported in their metal complexes with sim-
ilar ligands [35]. Cobalt, nickel, copper and mercury acetate gave
light pink, light green, light blue and light yellow colour, respec-
tively in methanol solution of H2chth, while zinc and cadmium
acetate did not show any significant colour change in the solu-
tion. Upon addition of cobalt acetate solution the colour changed
to light pink and a new band was observed at 19230 cm−1. This
plex assigned to the 3A2g→ T1g (P) and 3T1g(P) (ν2) transitions
3
[35] (Fig. 1B), respectively. Upon addition of copper(II) acetate so-
lution the colour changed to light blue and absorption band at
14100 cm−1 for Cu-H2chth may be assigned to the envelope of the
2T2g
→
2Eg transitions indicating an octahedral geometry for the
Cu(II) complex [35, 36]. This study suggests that Co2+, Cu2+, Mn2+
and Ni2+ ions showed significant red shift in UV-visible spectra,
hence compound H2chth may be a good probe for sensing these
metal ions in the solution. The high energy absorption maxima in
the range of 38910-33898 cm−1 can be attributed to the HNCS
moiety. It is noteworthy that free H2chth showed one band at
38610 cm−1 due to the presence of HNCS moiety while upon addi-
tion of metal ions the former band either disappeared or its inten-
sity decreased. It also suggests the interaction of metal ions with
HNCS moiety present in the H2chth.
band can be assigned to the 4T1g(F) → A2g(F) (ν2) transition, sug-
4
gesting a distorted octahedral geometry for the complex (Fig. 1B).
Nickel-H2chth solution gives two absorption bands at 25000 and
Fig. 6. A: Cyclic voltammogram of Mn-H2chth at 140 mVs−1 scan rate B: Cyclic voltammogram of Co-H2chth at 140 mVs−1 scan rate C: Cyclic voltammogram of Ni-H2chth
at 140 mVs−1 scan rate D: Cyclic voltammogram of Cu-H2chth at 140 mVs−1 scan rate E: Cyclic voltammogram of Zn-H2chth at 140 mVs−1 scan rate F: Cyclic voltammogram
of Cd-H2chth at 140 mVs−1 scan rate
6

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Table 1
Table 2
˚
Crystallographic data, structure solution and refinement for H2chth.
Bond length (A) and angles (°) for H2chth
˚
Parameters
H2chth
14H26N4S2
Bond length (A)
Cal
Bond angle (°)
Cal
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C
S(1)-C(7)
S(2)-C(8)
N(1)-C(7)
N(1)-C(1)
N(2)-C(7)
N(2)-N(3)
N(3)-C(8)
N(4)-C(8)
1.695(3)
1.696
1.696
1.331
1.468
1.387
1.390
1.387
1.331
C(7)-N(1)-C(1)
N(1)-C(7)-S(1)
S(1)-C(7)-N(2)
N(3)-N(2)-C(7)
N(4)-C(8)-N(3)
C(8)-N(4)-C(9)
C(10)-C(9)-N(4)
C(2)-C(1)-N(1)
124.8(2)
124.7 (2)
118.03(19)
119.5(2)
117.2(2)
125.2 (2)
111.8(2)
111.8(2)
126.4
126.2
117.8
120.6
115.9
126.4
111.0
111.0
314.51
1.695(3)
1.323(3)
1.467(3)
1.374(3)
1.396(3)
1.369(3)
1.327(3)
Triclinic
P-1
100(2)
˚
λ, Mo Kα (A)
0.71073
˚
a (A)
6.1344(3)
10.0305(5)
13.7249(6)
85.736(2)
80.569(2)
89.352(2)
831.88(7)
2
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
Table 3
˚
Hydrogen bonds parameter for H2chth (A and °)
3
˚
V, (A )
Z
D-H...A
d(D-H)
d(H...A)
d(D...A)
<(DHA)
(g/cm3)
1.256
N(2)-H(2C)...S(1)#1
N(3)-H(3N)...S(2)#2
C(2)-H(2A)...S(2)#3
C(10)-H(10A)...S(1)#4
N(2)-H(2C)...S(1)#1
N(3)-H(3N)...S(2)#2
C(2)-H(2A)...S(2)#3
C(10)-H(10A…S(1)#4
0.87(4)
0.93(3)
0.99
2.51(4)
2.41(3)
2.89
3.371(2)
2.336(2)
3.727(3)
3.701(3)
3.371(2)
3.336(2)
3.727(3)
3.701(3)
174(3)
174(3)
142.6
142.2
174(3)
174(3)
142.6
142.2
ρ
calcd
μ (mm−1
)
0.317
F(000)
Crystal size(mm3)
340
0.99
2.87
? x ? x ?
2.442 to 28.318
-8 ≤ h ≤ 8,
-10 ≤ k ≤ 13,
-18 ≤ l ≤ 18
10194
0.87(4)
0.93(3)
0.99
2.51(4)
2.41(3)
2.89
θ range for data collections(°)
Index ranges
0.99
2.87
No. of reflections collected
No. of independent reflections(Rint
No. of data/restrains/parameters
Goodness-of-fit on F2
Symmetry transformations used to generate equivalent atoms: #1 -x,-y,-
)
4087
z+1 #2 -x,-y+1,-z+1 #3 -x+1,-y+1,-z+1 #4 -x+1,-y,-z+1
4087 / 0 / 189
1.101
b
R1a, wR2 [(I>2σ(I)]
0.0898, 0.2451
0.1024, 0.3287
2.362, -0.994
b
R1a, wR2 (all data)
˚
ported phenyl thiosemicarbazide [1.685(5) A] and phenylthiourea
Largest difference in peak /hole
derivatives [40,41]. Thus, the carbon sulfur bond length has a dou-
ble bond character [37,42]. The C7-N2 and C7-N1 bond length
−3
˚
(e.A
)
a
R1 = ꢁ||Fo| – |Fc||ꢁ|Fo|.,
˚
in the thiourea moiety are 1.374(3) and 1.323 (3) A, respectively.
R2 = [ꢁw (|F2o| – |F2c|)2/ꢁw|F2o|2]1/2
b
These values differ from the thiosemicarbazide moiety 1.326(2)
˚
and 1.316(3) A but are very similar to other reported thiosemicar-
˚
bazide compounds 1.373(3), 1.320(3) A [43,44]. In the solid state,
3.5. Thermal analysis of bis(N-cyclohexylthiourea) (H2chth)
the structure of the compound H2chth is stabilized by N-H···S in-
termolecular hydrogen bonding (N2-H2C•••S1 & N3-H3N•••S2) oc-
curring between the NH hydrogen of thioamide group and sulfur
atoms of other unit of the thioamide group leading to the for-
mation of a supramolecular architecture (supplementary figure 3).
In addition, the structure is further stabilized by C-H···S hydrogen
bonding (C2-H2A•••S2 & C10-H10A•••S1) between the CH hydro-
gen of cyclohexyl rings and sulfur atoms of thioamide group (sup-
plementary figure 3).
The thermal property of compound H2chth was studied by TGA
in the temperature range 30-700°C under the nitrogen atmosphere.
The thermogravimetric analysis of H2chth shows that it starts de-
composing at 150°C and thermogram exihibits two distinct de-
compositions step in the range of 140-340 and 340-600°C (Fig. 3).
The major weight loss of 52.86 % (obs.50.76 %) in the tempera-
ture range of 140-340°C due to loss of two molecules of cyclohexyl
ring. The second minor weight loss may be due to the loss of two
molecules of HNCS moiety (Calcd. weight loss 37.57%; obs. 32.85%).
At higher temperature remaining organic moiety finally converted
into the gaseous products. The corresponding endothermic peak in
the DTA was obtained at 194°C. This study suggests that H2chth
is almost stable upto its melting temperature of 220 °C and starts
decomposing thereafter.
3.7. Electrochemical characterization
The electrochemical behavior of the compound H2chth was
studied using cyclic voltammetry and is depicted in Fig. 5. The
cyclic voltammograms were recorded in 10−3 M H2chth solution
in CH3CN at a platinum electrode using 0.1M TBAP as supporting
electrolyte. Compound H2chth exhibited only one cathodic peak at
0.190 V (scan rate 0.140 V.s−1) due to the reduction of carbon sul-
fur double bond (thione form) into carbon sulfur single bond (thiol
form). Upon addition of metal ions to the acetonitrile solution of
H2chth, the cathodic peak shifted to the positive potential due to
the complexation (Fig. 6A-6F). Various transition metal ions such
Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ with H2chth exhibit an-
odic and cathodic peaks at 0.998 and 0.143 V for Mn2+, 0.994 and
0.084 V for Co2+, 0.989 and 0.094 V for Ni2+, 0.958 and 0.129 V
for Cu2+, 0.994 and 0.070 V for Zn2+ and at 0.989 and 0.050 V for
Cd2+ ions (scan rate 0.140 V.s−1), respectively. All anodic peaks ob-
served in the cyclic voltammograms of the metal ions with H2chth
might be assigned to the irreversible oxidation of metal ions (M2+
to M3+). Similarly, all the cathodic peaks might be assigned to the
irreversible reduction of thione to thiol form as discussed earlier.
The slight positive shift observed in the presence of metal ions
may be due to the complexation. On scanning with higher scan
3.6. Crystal structure description of bis(N-cyclohexylthiourea)
(H2chth)
The molecular structure of compound H2chth has been deter-
mined by single crystal X-ray diffraction data. The details of data
collection, structure solution and refinement are listed in Table 1.
ORTEP diagram for H2chth with atom numbering scheme have
shown in Fig. 4. Selected bond lengths and angles are given in
Table 2. Weak intermolecular hydrogen bonding interactions are
listed in Table 3. The compound H2chth crystallizes in triclinic sys-
tem with space group P-1 but discrete molecules are located on
the twofold axes, out of the symmetry centres. Therefore, H2chth
has lower C2 symmetry as shown in Fig. 4. The dihedral angle be-
tween two cyclohexyl ring is found to be 49.37° indicating that
rings are tilted with respect to each other. The C7-S1 bond length
˚
is shorter [1.695(3) A] in H2chth molecule than other reported
˚
compounds [1.753(5) A] [37-39], but similar to that in other re-
7

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Fig. 7. Optimized structure of H2chth
rates the cathodic peak potential slightly shifted and anodic peak
current increased which indicates that the process is completely ir-
reversible [45-47]. We have also performed the cyclic voltammetric
studies of Cr3+ and Hg2+ ions with compound H2chth which show
no significant changes in to the cathodic peak of H2chth and no
anodic peak is observed in the interaction of metal ions with com-
pound (Supplementary figures 1 & 2).
3.8. DFT calculation
3.8.1. Geometry optimization
The geometry optimization of compound H2chth has been car-
ried out to understand bonding. The structure obtained from ge-
ometry optimization confirms the formation of H2chth as deter-
mined by X-ray diffraction analysis. Structure of H2chth optimized
by DFT is shown in Fig. 7 and calculated bond lengths and an-
gles from DFT are given in Table 2. The slight disagreement in
the bond lengths is due to the fact that the DFT calculations are
done for an isolated molecule in gaseous phase while the X-ray
crystallographic data were obtained from crystal lattice of com-
plex molecules. The computed geometrical parameters using DFT
(specifically, B3LYP) corroborates X-ray crystallography data as can
be seen from Table 2.
Fig. 8. Frontier molecular orbitals of H2chth
3.8.2. Frontier molecular orbital analysis
The most important frontier molecular orbitals (FMOs) such as
highest occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) analysis of a molecule is very useful.
HOMO and LUMO analysis determines reactivity, optical polariz-
ability, chemical hardness-softness and also determines the charge
transfer capability of a molecule. A molecule with smaller energy
gap between HOMO and LUMO orbitals is more reactive, highly po-
larizable or soft [48]. The shapes and energy levels of the HOMO
and LUMO of H2chth are displayed in Fig. 8. It indicates that HOMO
of H2chth is having dominant electron density on the S atoms of
the thioamide group while LUMO is more likely on both the ni-
trogen and sulphur atoms of the H2chth. HOMO is of π-type and
LUMO is of π∗ type. Hence, for H2chth HOMU-LUMO transition is
going to be of π→π∗ transition. The energy gap between HOMO
and LUMO for H2chth is 5.4842 eV [49,50]. The small energy gap
indicates that this compound is soft and highly reactive and can
serve as better target for photophysical studies and electronics ap-
plications [51,52].
Fig. 9. Hirshfeld surface of H2chth showing weak intermolecular interactions plot-
ted over dnorm
surface. Two middle red spots represent hydrogen bond N-H···S
with donor S atom from neighbouring molecule and H atom as ac-
ceptor (H→S type). On the other hand, extreme two red spots rep-
resent S···H-C interactions with S donor atom to neighbouring H
atom as acceptor (S→H type). 2D fingerprint plot of the Hirshfeld
surface is depicted in Fig. 10 a-d. The S···H interactions appeared as
scattered spikes in the 2D fingerprint plots with overall Hirshfeld
surfaces of 9.6 % (H→S) + 13.9% (S→H) = 23.5%.
3.8.3. Hirshfeld surface analysis
Hirshfeld surfaces showing weak intermolecular interactions
present in crystal structure are plotted over dnorm (Fig. 9) for
H2chth from its crystal structure (cif file). To compute Hirshfeld
surface we have used Crystal Explorer 17.5 suits of program [53].
From the Fig. 10, it is discernible that there two types of H-bonding
interactions N-H···S and S···H-C through red spot over the dnorm
8

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Fig. 10. Atom-atom interactions and their contribution to the Hirshfeld surface: (a) all interactions surface (b) all S•••H interaction surface (c) contribution from H→S and
(d) contribution from S→H
4. Conclusions
and C-H···S hydrogen bonding. Frontier molecular orbitals analysis
reveals that compound H2chth is soft and highly reactive.
In this paper we report the synthesis, structure, fluores-
cence and electrochemical behaviour of
cyclohexylthiourea) (H2chth). The compound was synthesized
using 1-hydroxy benzoyl-4-cyclohexyl-3-thiosemicarbazide,
a compound bis(N-
Credit author statement
Shubham Jaiswal: Development and design of methodology,
writing the original draft, and Data curation.
Mannu Kumar Gond: Data curation, Writing – review, and edit-
ing.
Mn(OAc)2·4H2O and o-phen in two steps. The compound is
characterised by various physicochemical methods. During the
course of reaction, the cyclohexyl isothiocynate moiety of the
intermediate substituted thiosemicarbazide undergoes tautomer-
ization and rearrangement into the corresponding carbothioamide
in the presence of manganese(II) acetate. In the UV-Vis absorp-
tion spectrum of the compound a band observed at 38610 cm−1
which may be assigned to n→π∗ transition due to the presence
Biswajit Maiti: Data curation, Software (DFT calculation).
S. Krishnamoorthi: Data curation, Writing – review, and edit-
ing.
Ray J Butcher: Data curation, Software (X-ray single-crystal
analysis).
of HNCS moiety. Upon excitation at 37037 cm−1
, the H2chth
Manoj Kumar Bharty: Conceptualization, Formal analysis,
Funding acquisition, Investigation, Resources, Software, Supervi-
sion, Validation, Roles/ writing original draft, Writing – review and
editing.
exhibits maximum emission at 27322 cm−1 which indicates that
the compound may be used as fluorescent active material. The
sensing behaviour of the compound with different metal ions
in methanol solution are studied and it showed interesting red
shifts with Co2+, Cu2+, Ni2+ and Mn2+ ions which suggested that
H2chth may be useful in the sensing of these metal ions in solu-
tion. The emission spectra of metal ions with H2chth exhibit less
intense emission as compared to free H2chth. Cyclic voltammetric
analysis of the H2chth and its interaction with different metal
ions (H2chth-M) exhibit complete irreversible redox behaviour.
The thermal degradation of the compound, as analysed by TG-DTA
method, showed that compound H2chth is almost stable upto 220
°C and starts decomposing thereafter and finally remaining organic
moiety converted into the gaseous products at higher temperature.
The structure of H2chth is stabilized via intermolecular N-H···S
Declaration of Competing interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgements
Dr M. K. Bharty thanks the Science and Engineering Research
Board, India for the award of a Project (No. SB/EMEQ-150/2014).
9

S. Jaiswal, M.K. Gond, M.K. Bharty et al.
Journal of Molecular Structure 1246 (2021) 131060
Supplementary materials
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