Mercury (II) sensing via cyclization of a dithioamide into a benzimidazole derivative: A structural and spectroscopic study

Article abstract of DOI:10.1016/j.ica.2020.119680

An o-phenylenediamine-derived dithioamide L was found to sense Hg(II) in the UV–visible via Hg(II)-mediated cyclization leading to a new benzimidazole derivative (L′). Both L and L′ have been characterized by single-crystal X-ray crystallography. The stru

Full text of DOI:10.1016/j.ica.2020.119680

InorganicaChimicaActa510(2020)119680
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Research paper
Mercury (II) sensing via cyclization of a dithioamide into a benzimidazole
derivative: A structural and spectroscopic study
Adenike O. Fasiku, Matthew T. Fortunato, Indranil Chakraborty⁎, Konstantinos Kavallieratos⁎
Department of Chemistry and Biochemistry and Biomolecular Sciences Institute, Florida International University, Miami, FL 33199, United States
A R T I C L E I N F O
A B S T R A C T
Dedicated to the memory of Professor Tara P.
Dasgupta.
An o-phenylenediamine-derived dithioamide L was found to sense Hg(II) in the UV–visible via Hg(II)-mediated
cyclization leading to a new benzimidazole derivative (L′). Both L and L′ have been characterized by single-
crystal X-ray crystallography. The structure of L reveals relatively strong intramolecular H-bonding interactions
of NeH...S type. The extended structure is consolidated by several classical hydrogen bonding interactions. For
L′, analysis of the packing pattern reveals few non-classical H-bonding contacts. Spectroscopic studies by FT-IR,
UV–Visible, 1H-and 13C NMR support the single-crystal X-ray crystallography results and confirm the formation
of the new benzimidazole derivative. UV–Vis titrations suggest and NMR confirms that the cyclization reaction
occurs via an initial formation of a Hg(II) complex, which is too transient to be fully characterized. As this
reaction is Hg(II)-mediated, dithioamide L acts as a selective Hg(II) sensor as shown by UV–Visible titrations and
a selectivity study against Pb(II), Cd(II), Ca(II), Zn(II), Ag(I), and Cr(III): For Hg(II), but not for other metals, a
distinct color change from yellow to pink is observed with corresponding UV–Vis spectroscopic changes and an
isosbestic point at 270 nm.
Keywords:
Benzimidazole synthesis
Mercury sensor
Thioamide
Mercury-catalyzed cyclization
1. Introduction
wide range of applications in pharmaceutical industries, benzimidazole
derivatives are considered as an important class of heterocyclic com-
Mercury is a pollutant arising from both natural and anthropogenic
sources mainly through medicinal and industrial applications. The very
toxic organic forms of mercury have some lipophilicity and can pass
through the blood brain barrier, thus causing short-term and long-term
detrimental effects to human brain, and also to lungs and kidneys [1].
Hg(II) is an environmentally mobile form of Hg and can be transformed
into more toxic organic forms. Hence, developing methods to sense
both Hg(II) and organic mercury in the environment is of great im-
portance. Over the years, various detection methods for mercury in the
environment have been widely studied including atomic absorption,
fluorescence sensing, electrochemical sensing and colorimetric methods
[2]. Low-cost colorimetric and fluorescence sensors offer the potential
for high sensitivity and selectivity for detection of Hg(II) in environ-
ment [3–8].
pounds. One of the most common examples of existence of benzimi-
dazole derivative in nature is N-ribosyl-dimethylbenzimidazole, which
binds the Cobalt center axially in Vitamin B12 [13]. Based on their
biological evaluations, several benzimidazole derivatives have also find
their place as anti-microbial, anti-hypertensive, anti-viral and anti-ulcer
agents within clinical settings [14–19]. In recent times the prevailing
antimicrobial resistance is an alarming issue worldwide, especially as a
sizeable number of multi drug resistant (MDR) pathogens have been
found to render the action of some crucial antimicrobial agents (like β-
lactam-based antibiotics, vancomycin, quinolones etc.) ineffective. This
situation has triggered various research groups to develop smart ways
of designing antibacterial agents to alleviate the resistance mechanisms
inherent to these MDR pathogens. Due to structural similarity with
purines, there is a considerable research interest to develop anti-
microbial agents based on benzimidazole ligand frameworks. Although
the direct synthetic methodology for preparation of benzimidazoles
which involves ortho-di- aryl amine and an aldehyde are well known,
this procedure often leads to several undesirable side products. Various
metal-based catalysts, namely Cu, Co, Ru, Pd, Zn and Rh are known to
afford much cleaner and sustainable results [20–24]. Mercury has also
been reported as a catalyst that mediates these cyclization reactions
Our group has been engaged in developing sulfonamide and car-
boxamide-based extractants for sequestration and sensing of toxic me-
tals ions, such as Pb(II) [9–11] and f-elements [12]. As we were
studying the Hg(II) complexation properties of dithioamide (L) with
HgCl2/Hg(CH3COO)2 we noticed that no Hg(II) complex with L could
be isolated from the reaction, but instead a new benzimidazole deri-
vative (L′) was formed via Hg(II)-mediated cyclization. Owing to their
⁎ Corresponding authors.
E-mail address: kavallie@fiu.edu (K. Kavallieratos).
https://doi.org/10.1016/j.ica.2020.119680
Received 17 December 2019; Received in revised form 7 April 2020; Accepted 15 April 2020
Availableonline18April2020
0020-1693/©2020ElsevierB.V.Allrightsreserved.

A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
[6,25,26]. For instance, Su et al. developed a microwave- assisted
technique for a HgCl2-mediated synthesis of benzimidazole by inter-
molecular cyclization using triethylamine [27]. Wang et al. synthesized
polysubstituted benzimidazoles from ortho-di-arylcarboxamides
After 5 h, the reaction contained a pink solution with a black pre-
cipitate, which was filtered off by gravity filtration. The volatiles were
evaporated under reduced pressure, and the pink residue was dissolved
in methylene chloride and subjected to a silica gel column chromato-
graphy using methylene chloride as the mobile phase. The fraction
containing the pink band was collected, dried under reduced pressure,
and the resulting purple powder was recrystallized in CH2Cl2/hexanes,
washed with hexanes, and dried under vacuum. Yield (based on HgCl2):
0.025 g, (0.08 mmol, 66.6%); FT-IR (cm−1): 1587, 1446, 1313, 1309,
1267, 1164, 1033; 1H NMR (600 MHz, CDCl3) δ 7.95 (d, J = 7.8 Hz,
1H), 7.68 (dd, J = 14.6, 7.3 Hz, 4H), 7.53 (d, J = 7.4 Hz, 1H), 7.42 (t,
J = 7.7 Hz, 1H), 7.39 (d, J = 8.2 Hz, 1H), 7.34 – 7.27 (m, 6H); 13C
NMR (101 MHz, MeOD) δ 209.63 (s), 145.70 (s), 143.82 (s), 137.90 (s),
135.47 (s), 131.34 (s), 130.88 (s), 130.61 (s), 130.15 (s), 129.76 (s),
126.12 (s), 126.00 (s), 120.59 (s), 118.17 (s), 113.79 (s); Anal. Calc. for
through
electrophilic
activation
of
amides
with
tri-
fluoromethanesulfonic anhydride and 2-chloropyridine [28].
Herein, we are exploiting the capability of Hg(II) to catalyze the
cyclization reaction of o-phenylenediamine-derived diamides to benzi-
midazoles to report a unique sensing method for Hg(II), which is rea-
sonably selective against several competing metals. Furthermore, we
have shown the utility of this Hg(II)-mediated reaction for a facile
synthesis of a new fully characterized benzimidazole thioamide deri-
vative, which is not straightforward by other conventional synthetic
pathways.
2. Experimental
C20H14N2S·1/6CH2Cl2 (%): C 73.72, H 4.40, N 8.53. Found (%): C
73.83, H 4.43, N 8.53.
2.1. Materials and methods
2.4. X-ray crystallography
All chemicals and materials were purchased from Fisher Scientific
or Sigma-Aldrich. All chemicals were standard reagent grade and were
used without further purification except for toluene, which was distilled
from CaH2 before use. NMR spectra were recorded on either a 400-MHz
Bruker Avance or a 600-MHz Bruker Avance NMR spectrometer. The
UV–Visible spectra were recorded on a CARY 100 Bio UV–Visible
spectrophotometer. X-ray diffraction studies were carried out on a
Bruker D8 Quest with PHOTON 100 detector. The diamide precursor
(N,N′-(1,2-phenylene)dibenzamide) of L was synthesized by a mod-
ification of a previously-reported procedure [29] and was found spec-
troscopically identical to the reported compound [30]. The dithioamide
ligand L has been previously reported [31], yet we have now synthe-
sized it by a different method [32] and report its NMR characterization
and X-ray structure.
The isolated L and L′ were dissolved in methylene chloride and the
solutions were layered carefully with hexanes. Yellow crystals of the
dithioamide were formed after several days. Light purple crystals of the
benzimidazole derivative were formed within a week. X-ray structure
determination experimental details are summarized in Table 1. The
non-H atoms are located through intrinsic phasing using SHELXT [33]
integrated in the Olex2 graphical user interface [34]. H-atoms are in-
cluded in calculated positions riding on the C atoms to which they
bonded, with CeH = 0.93 Å and Uiso(H) = 1.2Ueq(C). The NeH
hydrogen atoms are located within the difference map.
3. Results and discussion
3.1. Synthesis
2.2. Synthesis of N,N′-(1,2-phenylene)dibenzothioamide (L)
The dithioamide L [31] was synthesized in two steps (Scheme 1)
from commercially available o-phenylenediamine and benzoyl chloride
in DMF [29] to give initially the diamide, which was subsequently re-
acted [32] with Lawesson’s Reagent in dry toluene to give a yellow
product, which was characterized by FT-IR, 1H/13C NMR, and X-ray
crystallography. Even though L is known [31], the report is not easily
accessible, and its X-ray structure is also reported here for the first time.
The benzimidazole thioamide derivative L′ was synthesized by a Hg
(II)-mediated cyclization reaction after reflux in CH3OH using 1.2 eq. of
HgCl2 or Hg(OAc)2. In a reaction similar to ours, Wang et al. have
successfully synthesized different polysubstituted benzimidazoles from
ortho-di-arylcarboxamides using trifluoromethanesulfonic anhydride
and 2-chloropyridine as the reaction mediator [28]. Su et al. have also
used a microwave-assisted Hg(II)-mediated cyclization to synthesize
benzimidazoles using HgCl2 and triethylamine [27]. Our reported cy-
clization reaction has now resulted to a new thioamide-benzimidazole
derivative, and we also provide evidence -for the first time for this type
of reactions- on the formation of a transient Hg(II)-L dithioamide
complex. The reaction was carried out by dropwise addition of HgX2
(X = Cl− or CH3COO−) in methanol to a stirring solution of ligand and
DIPEA in methanol. The transient Hg(II) complex was formed im-
mediately as a yellow powder and filtered, while the pink filtrate was
dried in vacuo and recrystallized to obtain the cyclized product. The
stability of the isolated transient Hg(II) complex both in solution and in
solid state is poor, yet we were able to record the UV–Vis, FT-IR (Figs.
S1 and S2), and 1H NMR spectra (Fig. 7) immediately after synthesis,
which already show the transient complex being transformed gradually
to the cyclized benzimidazole product. As our group focuses on the
complexation and sensing of mercury by sulfonamides and thioamides,
this mercury-mediated cyclization reaction was further exploited for Hg
(II)-selective sensing. For synthesis in a larger scale, we found out that
N,N′-(1,2-phenylene)dibenzamide (0.506 g (1.60 mmol) was dis-
solved in distilled dry toluene (100 mL). To this solution, 1.424 g
(3.52 mmol, 2.2 eq.) of 2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithia-di-
phosphetane-2,4-disulfide (Lawesson’s Reagent) was added. The reac-
tion mixture was then heated to reflux under nitrogen with constant
stirring. After 30 min, the solution turned yellow. After 12 h, the vo-
latiles were evaporated to dryness. A small volume of dichloromethane
was used to dissolve the residue, which was subjected to silica gel
column chromatography with hexane/ethyl acetate (7:3) as the eluent.
The yellow-band eluted fraction was dried in vacuo and dissolved in a
small volume of dichloromethane. Dropwise addition of hexanes and
cooling at 4 °C gave a crystalline yellow precipitate, which was filtered,
washed with hexanes, and dried under vacuum. Yield: 0.244
g
(0.70 mmol, 43.8%); FT-IR (cm−1): 3263, 1508, 1444, 1361, 1216,
987, 921; 1H NMR (600 MHz, CDCl3) δ 9.38 (s, 2H), 7.86 (d,
J = 7.7 Hz, 4H), 7.64 – 7.60 (m, 2H), 7.56 – 7.51 (m, 2H), 7.48 (t,
J = 7.4 Hz, 2H), 7.39 (t, J = 7.7 Hz, 4H); 13C NMR (101 MHz, CDCl3) δ
200.04 (s), 141.05 (s), 134.85 (s), 131.87 (s), 129.18 (s), 128.68 (s),
127.95 (s), 127.08 (s).
2.3. Synthesis of Phenyl(2-phenyl-1H-benzimidazol-1-yl)methanethione
(L′)
N,N′-(1,2-phenylene)dibenzothioamide (L) (0.041 g, 0.12 mmol)
was dissolved in methanol (20 mL) in a round-bottom flask. 42 µL
(0.264 mmol) of N.N′-diisopropylethylamine (DIPEA) was added and
the solution was left to stir for 5 min. A solution of HgCl2 (0.032 g,
0.12 mmol) or Hg(OAc)2 (0.038 g, 0.12 mmol) in methanol (5 mL) was
added dropwise to the stirring solution of L. A pale yellow precipitate
immediately formed. The reaction mixture was then heated to reflux.
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A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
Table 1
Experimental details for X-ray structure determination.
(L)
(L′)
Crystal data
Chemical formula
C
20H16N2S2
C20H14N2S
314.39
Mr
348.47
Crystal system, space group
Temperature (K)
a, b, c (Å)
Triclinic, P1
Triclinic, P1
293
273
8.7208 (4), 10.0905 (5), 11.4131 (5)
8.9989 (7), 9.8812 (8), 9.9587 (8)
α, β, γ (°)
66.506 (1), 72.172 (1), 89.016 (1)
111.313 (2), 97.350 (2), 98.663 (2)
V (Å3)
870.49 (7)
799.35 (11)
Z
2
2
Radiation type
Mo Kα
Mo Kα
µ (mm−1
)
0.31
0.20
Crystal size (mm)
Data collection
0.30 × 0.25 × 0.20
0.15 × 0.10 × 0.08
Diffractometer
Bruker D8 Quest with PHOTON 100 detector
Multi-scan
Bruker D8 Quest with PHOTON 100 detector
Multi-scan
Absorption correction
SADABS2016/2 (Bruker, 2016/2) was used for absorption
correction. wR2(int) was 0.0430 before and 0.0379 after
correction. The Ratio of minimum to maximum transmission is
0.9450. The λ/2 correction factor is Not present.
0.705, 0.746
SADABS2016/2 (Bruker, 2016/2) was used for absorption
correction. wR2(int) was 0.0598 before and 0.0480 after
correction. The Ratio of minimum to maximum transmission is
0.8939. The λ/2 correction factor is not present.
0.650, 0.745
T
min, Tmax
No. of measured, independent and
observed [I > 2σ(I)] reflections
Rint
17250, 4321, 3533
10067, 2726, 2003
0.020
0.668
0.031
0.589
(sin θ/λ)max (Å−1
)
Refinement
R[F2 > 2σ(F2)], wR(F2), S
No. of reflections
0.037, 0.102, 1.04
0.048, 0.135, 1.05
4321
2726
No. of parameters
225
208
H-atom treatment
H-atoms treated by a mixture of independent and constrained
H-atom parameters constrained
refinement
Δρmax, Δρmin (e Å−3
)
0.26, −0.37
0.32, −0.48
refluxing the reaction mixture for 5 h gives higher yields (up to 66.6%)
for the formation of the benzimidazole derivative (L′) (Scheme 1). For
growing suitable crystals for X-ray diffraction: Methylene chloride so-
lutions of reaction mixtures of HgCl2 and L were layered with hexanes.
The solution color turned initially yellow, and eventually pink, with a
black precipitate settled at the bottom of the tubes. This is presumably
due to demetallation of the transient Hg(II)-L species, with the black
precipitate being HgS (Scheme 2).
3.2. FT-IR studies
The infrared spectrum of the new benzimidazole derivative (L′) is
characterized by the presence of three distinct bands at 1585, 1309, and
1162 cm−1 (Fig. 1). These bands are attributed to the stretching vi-
brations of the C]N, CeN and C]S respectively. Strong and medium
intensity bands at 1600–1400 cm−1 correspond to the C]N and C]C
stretching vibrations. Disappearance of the band corresponding to NeH
Scheme 1. Synthesis of N,N′-(1,2-phenylene)dibenzothioamide (L) and Phenyl(2-phenyl-1H-benzo[d]imidazole-1-yl)methanethione (L′).
3

A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
Scheme 2. Proposed mechanism of Hg(II)-catalyzed cyclization reaction
transforming L into L′.
Fig. 2. UV–Vis spectra of i) L (0.1 mM) in MeOH, ii) isolated L′ (0.1 mM) in
MeOH and iii) reaction mixture after addition of HgCl2 (1 eq., 0.1 mM) to L in
MeOH, after standing for 24 h.
Fig. 1. FT-IR spectra of the dithioamide ligand (L) and the cyclized benzimi-
dazole (L′).
stretching vibrations in the 3300–3000 cm−1 region of the ligand (L)
Fig. 3. UV–Vis titration of L (0.02 mM) and DIPEA (2.2 eq.) in CH3OH after
gradual addition of HgCl2 (0.5 mM) at constant L and DIPEA concentration.
v
spectra and the appearance of a new (C]N) band of medium intensity
at 1585 cm−1 for L′ indicates formation of the benzimidazole ring. In
v
addition, shifts to lower frequency are observed for the (C]S) from
1216 cm−1, in L to 1162 cm−1 in L′. A shift for the (CeN) band is also
observed from 1365 cm−1, in L to 1309 cm−1 in L′, which is also
consistent with the formation of the benzimidazole.
benzimidazole. Very similar spectra were obtained after the addition of
Hg(OAc)2 (Fig. S3 in Supporting Information section). The ratio
changes observed in the titration plot (Fig. 3) produced a linear func-
tion for a Hg(II) concentration up to 10.63 μM. The detection limit was
calculated to be 0.69 μM (see Supporting Information), with a 1.08 μM
to 10.63 μM dynamic range. It is notable that the spectra of i) isolated
benzimidazole product ii) the reaction mixture after 24 h, and iii) the
titration spectra after Hg(II) addition, are virtually identical. This ob-
servation is consistent with the hypothesis that the UV–Vis sensing of
Hg(II) is a direct result of the Hg(II)-mediated cyclization reaction.
Selectivity for Hg(II) sensing by L compares favorably vs. various
other metals, including Cd(II), Pb(II), Zn(II), Ca(II), Ag(I), and Cr(III). 1
equivalent of these metals (added as chloride salts) was added to so-
lutions of L (0.1 mM) and 2.2 eq of DIPEA and the solutions were left to
stand for 24 h. The UV–Vis spectra were collected and are shown in
Fig. 4 (for Cd(II), Pb(II), Zn(II), and Hg(II)), and in Fig. 5 (for Ca(II), Ag
(I), Cr(III) and Hg(II)). Only for mercury addition the new benzimida-
zole bands at 286 nm and 328 nm appear prominently. Pb(II) and Cd
3.3. UV–Visible sensing studies - titrations
The formation of the new benzimidazole derivative L′ was also
confirmed by UV–Vis spectroscopy. The absorption spectra of L and
isolated L′ were recorded in 0.1 mM MeOH solutions using a quartz
cuvette of 1 cm path length (Fig. 2). Response to Hg(II) addition was
monitored by gradual addition of various amounts of Hg(II)
(0.005–1.600 mL of 0.5 mM HgCl2) to solutions of L (0.02 mM) and
DIPEA (0.044 mM) in MeOH (at constant concentration of L and
DIPEA). A 10 min interval was used before each reading to ensure the
reaction is under thermodynamic control. The UV–Vis spectra of di-
thioamide L in MeOH solution shows an absorption band at 248 nm.
Addition of Hg(II) resulted in a red shift and a gradual disappearance of
this absorption band (Fig. 3) with two new bands appearing at 286 nm
and 328 nm, an observation consistent with formation of the
4

A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
(II), show some increases in absorption (Fig. 4), which are more con-
sistent with complex formation, rather than benzimidazole formation,
while Zn(II), Ca(II), Ag(I) and Cr(III) show no interference (Figs. 4 and
5).
3.4. NMR spectroscopy
The 1H NMR spectrum of benzimidazole L′ differs significantly from
the spectrum of dithioamide
L (Fig. 6). There is a multiplet
at δ 7.34–7.27 which is assigned to the phenyl protons. The NeH re-
sonance for L at δ 9.38 is no longer present at L′. The ortho-aryl protons
of L assigned as d and e (δ 7.62 and 7.53), both split into d and g (δ 7.95
and 7.39) and e, f (δ 7.53 and 7.42), for L′ (Fig. 6). Fig. 7 depicts the 1H
NMR spectrum of L after addition of HgCl2 (1.2 eq.), in comparison
with the spectra of L (3.2 mM) and L with DIPEA (7.0 mM) (bottom, top
and middle respectively). After Hg(II) addition the formation of a new
species is clearly indicated, with chemical shifts at 8.06, 7.45, and
7.28 ppm, which are substantially different than the benzimidazole L′.
Resonances for the deprotonated ligand are still prominent, however,
indicating that the formation of the transient Hg(II) complex (Scheme
2) is a slow step in the process.
Fig. 4. UV–Vis spectra of L (0.1 mM) before and after addition of chloride salts
of Zn(II), Pb(II), Cd(II), or Hg(II) (1 eq.) in MeOH after standing for 24 h.
3.5. Single crystal X-ray crystallography
Crystal data, data collection and structure refinement details are
summarized in Table 1. The dithioamide compound L was solved and
refined in a Triclinic, P-1 space group, with a full molecule in the
asymmetric unit (as shown in Fig. 8). The phenyl group of the o-phe-
nylenediamine motif (constituted by C1, C2, C3, C4, C5, C6 atoms) is
satisfactorily planar with mean deviation of 0.11 (3) Å. The two other
dangling phenyl groups constituted by C8, C9, C10, C11, C12, C13 and
C15, C16, C17, C18, C19, C20 atoms show excellent planarity (mean
deviation, 0.003 (2) Å). The dihedral angles between the two planes
constituted by these two phenyl rings with the phenyl ring of the o-
phenylenediamime motif are 55.8 and 82.8° respectively. The asym-
metric unit displays an intramolecular H-bonding interaction of NeH…
S, type involving an S atom associated with a thioamide and an amide
NeH, that is a part of another thioamide. Examination of the packing
pattern for L (Fig. 9) revealed that its extended structure is consolidated
by several classical H-bonding interactions (N1eH1eS2, with HeS,
2.39 Å; N2eH2eS1, with HeS, 2.67 Åi; C5eH5eS1, with HeS, 2.87 Å;
C9eH9eS1, with HeS, 2.65 Å; C16eH16eS2, with HeS, 2.74 Å;
Symmetry code: (i) −x + 1, −y + 2, −z + 1). The cyclized
Fig. 5. UV–Vis spectra of L (0.1 mM) before and after addition of chloride salts
of Ca(II), Ag(I), Cr(III), and Hg(II) (1 eq.) in MeOH, after standing for 24 h.
Fig. 6. 1H NMR spectra of di-thioamide (L) and the cyclized benzimidazole product (L′) in CDCl3.
5

A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
Fig. 7. 1H NMR spectra of L (3.2 mM) (top) in comparison with L + DIPEA (2.2 eq.) (middle) and the reaction mixture after addition of HgCl2 (1.2 eq.) showing the
transient Hg(II)-L complex formation at 8.06, 7.45, and 7.28 ppm (bottom).
Fig. 9. Packing pattern of L along a axis. The dotted lines indicate both intra-
and inter-molecular H-bonding interactions.
Fig. 8. ORTEP representation (50% probability ellipsoids) for the X-ray crystal
structure of dithioamide L, with atom labeling scheme, showing an NeH…S
intramolecular hydrogen bonding interaction.
benzimidazole L′ (Fig. 10) was obtained from compound L through a
mercury (II) mediated cyclization process (vide infra). The benzimida-
zole fragment (constituted by C1, C2, C3, C4, C5, C6, C7, N2, N1 atoms)
in this compound is satisfactorily planar with mean deviation of 0.017
(3) Å. The conjoining phenyl ring (constituted by C8, C9, C10, C11,
C12, C13 atoms) shows excellent planarity (mean deviation, 0.005 (3)
Å) and the dihedral angle between this plane and the benzimidazole
fragment is 43.0°. The other phenyl ring (constituted by C15, C16, C17,
C18, C19, C20 atoms) is also highly planar (mean deviation, 0.004 (3)
Å) and the dihedral angle between this plane and the plane of benzi-
midazole ring is 72.7°. In case of L′, its extended structure (Fig. 11) is
consolidated
by
few
non-classical
H-bonding
interactions
(C16eH16eN1, with HeN, 2.54 Å; C19eH19eN2, with HeN, 2.61 Åi;
C20eH20eS1, with HeS, 2.76 Å; Symmetry code: (i) x, y, z − 1).
Fig. 10. ORTEP representation (50% probability ellipsoids) for the X-ray crystal
structure of benzimidazole L′, with atom labeling scheme.
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A.O. Fasiku, et al.
InorganicaChimicaActa510(2020)119680
Fig. 11. Packing pattern of L′ along b axis. The dotted lines indicate intermolecular H-bonding interactions.
4. Conclusion
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(2015) 372459, , https://doi.org/10.1155/2015/372459.
In conclusion we have reported selective Hg(II) sensing via Hg(II)-
mediated cyclization of a dithioamide, leading to a new benzimidazole
derivative. Both the dithioamide and benzimidazole compounds were
fully characterized by X-ray crystallography. The Hg(II)-mediated cy-
clization is presumed to occur via the formation of a transient Hg(II)
thioamide species, which was characterized tentatively by 1H NMR. We
expect to continue this study in the future with detailed selectivity
studies under competitive conditions in the presence of more compli-
cated metal mixtures and also perform similar studies with substituted
derivatives, such as N,N′-(4,5-dimethyl-1,2-phenylene)dibenzothioa-
mide.
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Declaration of Competing Interest
[10] R.J. Alvarado, J.M. Rosenberg, A. Andreu, J.C. Bryan, W.-Z. Chen, T. Ren,
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The authors declare that they have no known competing financial
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Acknowledgements
We would like to thank Mr. Omar Fernandez, Mr. Yatfung Chiu, Ms.
Maria Fabiola Alvarado-Yepes, and Ms. Naivys Rodriguez for synthetic
assistance, and an anonymous reviewer for constructive comments and
suggestions. This research project was supported by the US Department
of Energy Minority Serving Institution Partnership Program (MSIPP)
managed by the Savannah River National Laboratory under SRNS
contract BOA No: 541, TOA No. 0000332972 and 0000403067 to FIU.
MTF was supported with a scholarship from Nuclear Energy University
Programs, Office of Nuclear Energy, US Dept. of Energy, under the DE-
NE 0008365 cooperative agreement with FIU.
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Appendix A. Supplementary data
Supplementary data including X-ray crystal data for N,N’-(1,2-phe-
nylene)dibenzothioamide (L): CCDC 1848353, and Phenyl(2-phenyl-
1H-benzimidazol-1-yl)methanethione (L′): CCDC 1848354 and addi-
tional experimental details to this article can be found online at https://
doi.org/10.1016/j.ica.2020.119680.
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