Physicochemical and X-ray crystallographic properties of the first rhenium compound of benzophenone thiosemicarbazone (bptsc), fac-[Re(CO)3(κ2-Nim,S-bptsc)Cl]

Article abstract of DOI:10.1016/j.molstruc.2021.130135

fac-[Re(CO)₃(κ²-N_im,S-bptsc)Cl] (2), isolated from the reaction between Re(CO)₅Cl and benzophenone thiosemicarbazone, bptsc, (1) in refluxing toluene in air, is the first Re compound of 1 and is the second Re(CO

Full text of DOI:10.1016/j.molstruc.2021.130135

Journal of Molecular Structure 1235 (2021) 130135
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Physicochemical and X-ray crystallographic properties of the first
rhenium compound of benzophenone thiosemicarbazone (bptsc),
2
fac-[Re(CO) (κ -N ,S-bptsc)Cl]
3
im
a,∗
a
a
b
Mohammed Bakir , Mark A.W. Lawrence , Junior Johnson , Colin McMillen
a
Department of Chemistry, University of the West Indies, Mona Kingston 7, Jamaica, West Indies
b
Department of Chemistry, Clemson University, 379 Hunter Laboratories, Clemson, SC29634-0973, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
2
fac-[Re(CO)3(κ -Nim,S-bptsc)Cl] (2), isolated from the reaction between Re(CO)5Cl and benzophenone
thiosemicarbazone, bptsc, (1) in refluxing toluene in air, is the first Re compound of 1 and is the second
Received 13 December 2020
Revised 12 February 2021
Accepted 16 February 2021
Available online 25 February 2021
2
Re(CO)3Cl compound of κ -Nim,S-coordinated ligand (im = imine). The authenticity of 2 was established
from the results of its elemental composition, spectroscopic measurements, and X-ray crystallographic
analysis. Single crystals of 2 grown from DMF are in the monoclinic space group P21/c. The asymmetric
unit of 2 revealed pseudo-octahedral coordination about Re. Two carbonyl C atoms, an imine N atom and
a thione S atom occupy the equatorial sites and the axial sites are occupied by a carbonyl C atom and a
Keywords:
Rhenium
Benzophenone thiosemicarbazone
X-ray crystallography
Spectroscopy
2
–
Cl atom. The κ -N,S-coordination of 1 to Re forms a semi-planar five-membered [Re-N-N C-S] metallo-
cyclic ring. The extended structure disclosed stacks of molecules interlocked via a web of N–H···X (X = Cl
or O), S···S and C–H···π interactions. DFT calculations divulged facile delocalization of electron density
in the molecule and interatomic distances and angles in good agreement with the solid state structure.
Electrochemical measurements on 2 in CH3CN and DMF revealed sequential irreversible electron trans-
fers pointing to structural changes due to electrochemically induced thione-thiol tautomerization of the
thioamide moiety. Plausible mechanisms for the oxidative and reductive electrochemical decomposition
of 1 and 2 are reported. The proposed mechanisms are in good agreement with those reported in the
literature for closely related compounds.
DFT calculations
Electrochemistry
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
nomical [1], and medicinal [9,17] application of 1 were investigated
and revealed interesting antiflatoxigenic [1], anti-fungal [12] and
antitumor [9,11,12,17] properties. The chelating properties of ben-
zophenone thiosemicarbazones account in part for their environ-
mental, and biological applications.
Benzophenone thiosemicarbazone, bptsc, (1) (see Scheme 1)
and its derivatives have attracted research interest for their con-
venient synthesis [1,2], physicochemical properties [3–8] and im-
plications in many important processes [1,7,9–12]. The non-linear
optical (NLO) behavior of 1 revealed efficient semiconducting prop-
erties [13,14]. The NLO activity of 1 is due in part to the donor-
accepting capacity of the benzophenone to thiosemicarbazone. The
thione (C=S) moiety enhances the second harmonic generation
Although physicochemical properties and biological implica-
tions of variety of metal compounds of 1 were reported, there has
been no report on the chemistry of 1 with high- or low-valent
rhenium compounds. This study describes the synthesis, spectro-
scopic, solid state structure, DFT calculations and electrochemical
2
(
SHG) efficiency. Catalytic Suzuki-Miyaura C–C and C–N cross cou-
properties of the first rhenium compound of 1, fac-[Re(CO) (κ -
3
pling reactions were induced by an orthometallated Pd-complex
of 1 and closely related complexes [7]. Benzophenone thiosemicar-
bazones were utilized as sensitive analytical reagents for the detec-
tion and determination of trace amounts of hazardous metal ions
such as Cd(II) and Hg(II) in drinking water [10,15,16]. The agro-
Nim,S-bptsc)Cl] (2) (see Scheme 1). This is in continuation of
our efforts to explore the chemistry of hydrazonic compounds of
the type [R R C=N–NH-(C=X)nY] (R and R2 = aryl, heterocyclic;
1
2
1
n = 0 or 1 with Y = alkyl, aryl or heterocyclic (hydrazone); n = 1
with Y = NH or NR R and X = O (semicarbazone) and X = S
2
1 2
(
thiosemicarbazone) [18–21]. Our interest in the chemistry of hy-
drazonic compounds stems from their diverse reactivity patterns,
∗
Corresponding author.
E-mail address: mohammed.bakir@uwimona.edu.jm (M. Bakir).
https://doi.org/10.1016/j.molstruc.2021.130135
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
2
Scheme 1. Representations of bptsc (1) and fac-[Re(CO)3(κ -Nim,S-bptsc)Cl] (2).
rich physicochemical properties, and molecular sensing and cat-
alytic behavior.
Electrochemical measurements were performed with the use of
a DigiIvy DY2312 potentiostat, under an argon atmosphere at room
temperature, and were uncorrected for junction potential. A stan-
dard three electrode cell setup was employed, using a glassy car-
bon working electrode (diameter = 3 mm), Ag wire quasi-reference
2. Experimental
2
.1. Reagents
electrode (QRE) and Pt wire as an auxiliary electrode; against
+
which Fe(Cp) /Fe(Cp)2 couple appeared at E1/2 = +0.65 V in DMF
2
Re(CO) Cl was purchased from Strem Chemicals, Inc.; ben-
and E1/2 = +0.48 V in CH CN. Solvents used in the electrochemical
5
3
zophenone (bp) and thiosemicarbazide (tsc) were purchased from
Sigma-Aldrich. All other reagents were obtained from commercial
sources and used as received. 1 was prepared from the acid cat-
alyzed condensation of benzophenone (bp) with thiosemicarbazide
experiments were dried using standard procedures [22].
2
.4. DFT calculations
(
tsc) in refluxing acidified ethanol in air as described in the litera-
Density functional theory (DFT) calculations were carried out
ture [1]. Anal. Calcd. for C14 H13N O (%): C, 65.85; H, 5.13; N, 16.46.
Found: C, 65.80; H, 5.00; N, 16.78. Selected IR (KBr disk, cm 1):
3
on 2 in the gas phase and in DMF using the GAMESS software
package1 [23,24]. The structure was optimized in the gas phase as
−
v(NH ) 3430, 3345 (s), v(N–H) 3257 (broad), v(C=N) + v(C=C) 1610
2
indicated by the absence of imaginary frequencies in the Hessian,
using PW91X/SBKJC [25,26] with the common polarization and
spherical coordinates. Solvent optimization in DMF was carried out
and 1477, v(C=S) + v(N–C-N) 1083, 1070, v(C=S) 846. UV–visible /
−
1
−1
M ) in CH CN: 315 (16,200), in DMF: 319
nm (ε ± 300 / cm
3
(
17,700). 1H NMR (δ, ppm) in DMSO-d : 8.67 (s, 1H, NH), 8.40 (s,
6
using the SMD solvation method [27]. The GAMESS input file was
generated using MacMolPlt 7.72 [28], and the output file viewed
2
H, NH ), 7.67–7.63 (m, 5H, aromatic) and 7.42–7.34 (m, 5H, aro-
2
matic). 13C NMR (δ, ppm): 177.7, 149.1, 136.3, 131.2, 130.0, 129.8,
using the same. The bond angles and lengths of the optimized
structure (see Supplemental Table 1) are comparable to those ob-
tained from X-ray structural analysis suggesting that the basis sets
employed are satisfactory. The SBKJC basis set results was initially
compared to those obtained using the improved model core poten-
tials with scalar relativistic effects (PW91X/IMCP-SR2) [29,30]. This
basis set provided comparable FMO to the SBKJC basis set, albeit
with different energies (as was expected, see supporting informa-
tion). The PW91X/SBKJC level of theory was adopted since it gave
reasonable values relative to the experimental values without the
computational expense.
1
29.7, 128.3, 128.2, 127.6.
2
2
.2. Synthesis of fac-[Re(CO) (κ -Nim, S-bptsc)Cl] (2)
3
A mixture of Re(CO) Cl (160 mg, 0.39 mmol), 1 (99 mg,
5
0
.39 mmol), and toluene (30 mL) was refluxed for 4 h. Slow evap-
oration of the mixture gave a yellow powder that was filtered
off, washed with CH CN and dried. Yield 190 mg (87%). Anal.
3
Calcd. for C17 H13ClN O ReS (%): C, 36.39; H, 2.34; N, 7.49. Found:
C, 36.56; H, 2.13; N, 7.22. Selected IR (KBr disk, cm 1): v(NH2)
3
3
−
3
436, 3264 (s), v(NH) 3180 (s), v(C=N) 1614, v(C≡O) 1887, 1945,
and 2026 (vs), v(C=N) + v(C=C) 1698, 1614, 1563, 1556 and 1428,
v(C=S) + v(N–C-N) 1176 and 1170 and v(C=S) 798. UV-visible /nm
2
2
.5. Crystal structure of fac-[Re(CO) (κ -Nim, S-bptsc)Cl] (2)
3
ε ± 300/ M cm ) in DMF: 319 (11,950), 356 sh (5600). 1H NMR
−
1
−1
(
(
Single crystals of 2 were grown from DMF when allowed to
δ, ppm) in DMSO-d : 11.65 (s, 1H), 9.26 (s, 1H), 8.26 (s, 1H), 7.60–
6
.41 (m, 10 H). 13C NMR (δ, ppm): 196.8, 193.9, 190.6, 179.8, 169.2,
stand in air for several days. X-ray diffraction data were collected
on a yellow columnar crystal. A Bruker D8 Venture diffractome-
7
140.3, 134.3, 131.7, 130.2, 129.5, 129.1, 128.4, 128.3, 127.5.
˚
ter having a Mo (λ = 0.71073 A) microfocus source and a Photon
2
.3. Physical measurements
100 detector were used for data collection. Data were processed
and corrected for absorption using multi-scan techniques (SAD-
ABS). The structure was solved by intrinsic phasing (SHELXT), and
Electronic absorption spectra were recorded on
a HP8543
diode array spectrometer. Solution 1H and 13C NMR spectra were
recorded on a Bruker ACE 500-MHz Fourier-transform spectrom-
eter and referenced to the residual protons in the incompletely
deuterated solvent. Infrared spectra were recorded as KBr pellets
on a Bruker Vector 22 FT-IR Spectrometer.
1
GAMESS: an open-sourcegeneral ab initio quantum chemistry package. https://
www.msg.chem.iastate.edu/gamess/index.html
2
MacMolPlt: an open-source molecular builder and visualization tool for
GAMESS. http://brettbode.github.io/wxmacmolplt/
2

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
Table 1
2
ported for variety of fac-[Re(CO) (κ -L-L)Cl] (L-L = N,N-bidentate
3
2
Crystal data and structure refinement for fac-[Re(CO)3(κ -Nim,S-bptsc)Cl] (2).
ligand) [33–35]. Comparison of the spectrum of 2 with that of 1
shows changes in the combined ν(C=N) + ν(C=C) between 1650
Empirical formula
C17 H13 ClN3O3ReS
−1
–
1400 cm , combined ν(C=S) + ν(N–C-N) between 1200 – 1000
F. W. (g/mol)
561.01
cm 1, and ν(C=S) between 850 – 800 cm [36] (see experimental
−
-1
Temperature (K)
Crystal system
173(2)
2
Monoclinic
section) consistent with κ -N,S-coordination of 1.
Space group
a ( A˚ )
b ( A˚ )
c ( A˚ )
β (°)
P21/c
1H and 13C NMR measurements on DMSO-d6 solutions of 1 and
6.5396(7)
2
2
confirmed the κ -N ,S-coordination of 1 to fac-Re(CO) Cl moi-
im
3
17.9807(18)
ety via the S atom of the thioimide, and the N atom of the imine
(C=N) group. This is evident from the downfield shift of the amide
(NH) proton as well as the thione (C=S) and imine (C=N) C reso-
nances of 2 compared to 1 (see experimental section). The down-
field shift of the NH proton points to the increase in its acidity due
16.1311(16)
97.573(4)
Volume ( A˚ 3
)
1880.3(3)
Z
4
D(calcd)(g/cm3)
μ, mm−1
1.982
6.737
2
to κ -Nim,S-coordination of 1 to Re. The significant downfield shift
F(000)
1072
Crystal size (mm)
θ range,°
0.03 × 0.03 × 0.19
of the imine (C=N) C atom confirms the imine coordination of 1.
2.60 to 25.50
13
In the C NMR spectrum of 2, the thione (C=S) and imine (C=N)
Reflections collected
Indep. Reflections
Limiting indices
Goodness of fit (S)
No. of parameters
R indices (I>2σ(I))
40,273
C resonances appeared at 179.8 and 169.2 ppm, while in 1 these
resonances appeared at 177.7 and 149.1 ppm. The slight downfield
shift of the thioamide (C=S) C resonance and significant downfield
shift of the imine (C=N) C resonance of 2 compared to 1 point to
3490 [R(int) = 0.0518]
−7←h→7, −21←k→21; −19←l→19
1.279
244
R1a = 0.0488, wR2 = 0.1011
R1a = 0.0536, wR2 = 0.1028
2.446 and −3.418
b
†
stronger binding of the imine N atom to fac-Re(CO) Cl moiety. The
3
b
R indices (all data)
Largest diff. peak and hole (e. A˚ 3
terminal amino (NH ) protons of 2 are not equivalent, appeared at
2
)
9
.24 and 8.25 ppm upfield from the 11.65 ppm of the thioamide
CCDC No.
1,986,270
NH proton resonance. In the case of 1, the terminal amine protons
†
a
R1 = S||Fo| – [Fc||/S|Fo| and wR2 = {S[w(Fo – Fc2)2]/S[wFo2] }1/2.
b
2
2
are equivalent, appeared as a singlet at 8.40 ppm upfield from the
8
.67 ppm singlet of the thioamide NH proton. The aromatic pro-
tons of 2 coalesce pointing to higher symmetry due to binding of
to Re compared to the aromatic protons of 1.
refined by full matrix least squares on F2 (SHELXL) [31]. All non-
1
hydrogen atoms were refined anisotropically. H atoms attached to
C atoms were refined in calculated positions using riding models.
H atoms attached to N atoms were located from difference elec-
tron density maps and their positions refined. In the final refine-
3.2. Solid state structure
˚
−3
ment cycle, seven peaks greater than 1 e A appeared in the dif-
ference map. Six of these surround Re and can be attributed to
Crystals of 2 grown from DMF are in the centrosymmetric mon-
oclinic space group P2 /c. The asymmetric unit of 2 is shown in
1
˚
residual effects of absorption. One peak was at 1.997 A from C16
Fig. 1. The coordination about Re is pseudo-octahedral with an
imine N atom, a thione S atom and two carbonyl C atoms occupy
the equatorial positions, and the axial positions are occupied by a
carbonyl C atom and a Cl atom.
and has no chemical significance. Cell parameters and other crys-
tallographic information are given in Table 1 and the supporting
crystallographic files (CIF) (Table 2).
Deviation from idealized octahedral geometry is due to κ2-
Nim,S-binding of 1. This is evident from the N1-Re1-S1, N1-Re1-Cl1
and C2-Re1-Cl1 bond angles of 79.98(19)°, 79.05(19)° and 174.7(3)°,
3
. Results and discussion
2
3
.1. Synthesis and characterization
respectively. The κ -Nim,S-binding of 1 to Re forms a virtually pla-
nar five-membered [-Re1-N3-N2-C4-S1-] metallocyclic ring as ev-
ident from the Re1-S1-C5-N2 and C5-N2-N1-Re1 dihedral angles
of +5.0(8) and +8.0(10)°, respectively. The thiosemicarbazone C5-
N1-N2-C4 moiety with dihedral angle of +171.4(8)° is nearly pla-
nar. The phenyl rings are neither co-planar to each other nor to
the thiosemicarbazone backbone as evident from C11-C4-C21-C22,
C21-C4-C11-C12 and N1-C4-C11-C12 dihedral angles of −52.9(1),
+127.9(9) and −51.4(12)°. The C=S bond distance of 1.698(9) A
Following a procedure similar to those reported for the syn-
thesis of variety of fac-Re(CO) Cl compounds of α-diimine, di-
3
2
-pyridyl ketone hydrazonic compounds and closely related lig-
2
ands, fac-[Re(CO) (κ -Nim,S-bptsc)Cl] (2) was isolated in good yield
3
(
87%) from the reaction between Re(CO) Cl and 1 in refluxing
5
toluene in air [21,32]. The identity of 2 was established from the
results of its elemental analysis and a number of spectroscopic
measurements, and confirmed from the results of single crystal X-
ray crystallography. In the infrared spectra of 2, peaks appeared
˚
˚
˚
is of the same order as the 1.6866(17) A and 1.680(1) A of
uncoordinated 1 and H2htp [1-(1–2-hydroxyphenyl)ethylidene)-4-
phenylthiosemicarbazone], respectively [30]. The Re1-N1 and Re1-
in the ν(NH ), ν(NH), ν(CH), ν(C≡O), combine ν(C=N) + ν(C=C),
2
combined ν(C=S) + ν(N-C-N) and ν(C=S) (see experimental sec-
S1 bond lengths of 2.228(7) and 2.470(2) A are similar to the
˚
˚
tion) consistent with the coordination of 1 to fac-Re(CO) Cl. Three
2.242(3) and 2.467(1) A bond distances reported for the imine (Re-
3
2
peaks appeared in the carbonyl ν(C≡O) region similar to those re-
N) and thione (Re-S) coordinated H2htp in fac-[Re(CO) (κ -Nim,S-
3
Table 2
Hydrogen bond distances ( A˚ ) and angles (°) for 2.
D-H···A
d(D-H)
d(H···A)
d(D···A)
<(DHA)
Symmetry Transformation
N3-H3A···Cl1
N3-H3B···O1
N2-H2···Cl1
0.90(7)
0.84(7)
0.84(7)
2.48(8)
2.29(8)
2.39(8)
3.308(9)
3.122(11)
3.138(7)
152(9)
167(11)
148(9)
x-1, y, z
-x + 1, -y, -z + 1
x-1, y, z
Non-covalent interactions
S···S
D(S···S) = 3.385 A˚
C22-H22···π
d(C-H···centroid) = 3.051 A˚
<C-H···centroid = 145.04°
3

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
Fig. 1. A view of the structure of 2 with displacement ellipsoids drawn at the 30%
probability level. H atoms are shown as isotropic spheres of arbitrary radius.
Fig. 3. Packing of molecules in 2, viewed along the a-axis. N–H···O, N–H···Cl,
C–H···Cl, and S···S interactions are shown as blue dashed lines.
1
H2htp)(κ -S-H2htpi)Cl] (H2htpi is the thiolate-iminium zwitteri-
onic H2htp) [37]. The Re1-S1 bond length in 2 is slightly shorter
˚
1
than the 2.536(1) A Re-S distance of monodentate coordinated κ -
spectra of 2. The calculated ν(C≡O) appeared at 2013, 1941, and
2
1
S-H2htpi in fac-[Re(CO) (κ -N ,S-H2htp)(κ -S-H2htpi)Cl]. The av-
erage Re-C bond distance of 1.913(10) A is normal and of the same
–1
3
im
1921 cm while the infrared spectra showed three peaks at 2026,
˚
945, and 1887 cm–1. The slight variation between the calculated
1
2
order as those reported for fac-[Re(CO) (κ -N,N-L-L)Cl] compounds
3
and experimental values are due to solid state effect. The bond
lengths and angles are of the same order as those obtained from
X-ray structural analysis (see supplementary Table S1). The fron-
tier MOs of the LUMO are scattered across the phenyl rings, fac-
Re(CO)3 and hydrazone backbone and the LUMO(+) MOs are scat-
tered over a phenyl ring, hydrazone backbone and the carbonyl
groups in the gas phase. The solvated model shows the LUMO
MOs involve the phenyl rings and the hydrazone backbone while
the LUMO+1 MOs scatter across the hydrazone backbone, and fac-
[
37–39].
Classical hydrogen bonds of the type N–H···X (X=O or Cl) and
non-covalent S···S interaction, and C–H···π interactions link adja-
cent molecules in the extended structure (see Table 3, Fig. 2). The
packing of molecules revealed stacks of 2 linked via a web of non-
covalent interactions (see Fig. 3). The bond distances and angles of
the classical hydrogen bonds are normal and similar to those re-
ported for variety of N–H···X hydrogen bonds [39].
Re(CO) . The key feature in the electronic spectrum of 2 is the
3
∗
3
.3. DFT calculations
overlap between π-π transition of the ligand with the MLCT tran-
sition at ~ 300 nm (Fig. S1). A shoulder due to MLCT transtion at ~
356 nm is partially resolved from the ligand transition. TDHF anal-
ysis of the singlet excited states consists primarily of transitions
from the HOMO to LUMO+n (n = 1 to 10) of which the HOMO
to LUMO+4 and +5 are the most intense (with oscillator strengths
Fig. 4 shows the frontier molecular orbitals of 2 in the gas
phase and in DMF. The calculated ν(NH ) appeared at 3400 and
2
3
295 cm–1 while ν(NH) appeared at 3014 cm–1. These values are
similar to the 3436, 3264 and 3180 cm–1 observed in the infrared
Fig. 2. Intermolecular interactions in 2. Classical hydrogen bonds are shown on the left (blue dashed contacts) and C–H···π interactions are shown on the right (magenta
dashed contacts)
4

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
Fig. 4. DFT optimized structures in the gas phase (PW91X/SBKJC, shadowed images) and in DMF (PW91X/SBKJC/SMD) for 2.
Re→NHC=S moieties are masked by DMF (see Supporting informa-
tion). The MLCT transition due to the carbonyl moieties, observed
at 319 nm (in DMF) is predicted to occur at 290 nm. The ~ 30 nm
difference between the observed and the calculated bands is the
result of TDHF singlet excited states being calculated in the gas
∗
phase. It is known that the π orbitals of carbonyl will interact
with the polar solvent which will lower the orbital energies.
3
.4. Electrochemical properties
Electrochemical measurements on 1 and 2 in CH CN and DMF
3
were investigated using voltammetric techniques. Fig. 5 shows
cyclic voltammograms of 1 and 2 measured in CH CN.
3
The voltammograms display irreversible redox processes on
oxidatively and reductively initiated scans signifying structural
changes following electronic transfer. Reductively initiated scan on
1
(Fig. 5a) shows irreversible reductions at Ep,c = –1.65, –2.10 and
–
2.50 V followed by electrochemically generated product waves at
Ep,a = +0.02, +0.60 V due to the oxidation of the reductively gen-
erated product waves (see Scheme 2) along with an irreversible
oxidation at Ep,a = +1.20 V. On oxidatively initiated scan (Fig. 5a),
the reductively generated product waves disappeared and oxida-
tively generated product waves appeared at Ep,c = +0.35, +0.04
and –0.42 V. The electrochemical signature of 1 in DMF is sim-
ilar to that observed in CH CN along with additional oxidation
3
waves appeared between Ep,a = +1.30 to +2.00 V (see Figure S4).
The results point to facile electrochemical decomposition of 1 in
CH CN and DMF. The voltammograms of 1 are similar to those
3
of di-2-heteroaromatic hydrazonic compounds that include di-2-
pyridyl ketone hydrazones, di-2-pyridyl ketone thiosemicarbazone
and di-2-thienyl ketone thiosemicarbazone. Plausible mechanisms
for the oxidative and reductive decomposition of 1 are shown in
Scheme 2.
n
Fig. 5. Cyclic voltammograms of CH3CN solutions containing 0.1 M [ Bu4N]PF6 of
1
4 mM 1 (a) and 12 mM 2 (b) at a glassy carbon working electrode (dia = 3.0 mm)
vs Ag.
of 0.2719 and 0.2493, respectively). The frontier MOs suggest that
The voltammogram of 2 measured in CH CN on reductively
3
∗
the observed transitions are indeed π-π transition of the ligand
initiated scan (Fig. 5b) displays a series of a closely spaced irre-
versible reductions at Ep,c = –1.30, –1.55, –1.80, –2.00 V and an
irreversible reduction at Ep,c = –2.40 V. The voltammogram also
mixed with MLCT of Re. The two most intense singlet transitions
predicted to occur at 251 and 252 nm due to Re→phenyl and
5

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
Scheme 2. Plausible mechanisms for the redox decomposition of 1.
[C-S]2 , [C=N] → [C–N] and [C–N] → [C–N] . The oxidation
−
.−
.−
2−
shows irreversible oxidations at Ep,a = +1.40 and +1.85 V and elec-
trochemically generated product waves between Ep,c = +0.30 and
I/II
wave at E
p,a
= +1.40 V is assigned to Re as it fall in the same
I/II
+
1.20 V. The closely spaced reduction waves observed between
range as those of Re oxidation in fac-[Re(CO) (L-L)Cl] complexes
3
Ep,c = −1.20 to −2.20 V hints to delocalization of electrons and
mixed metal-ligand reductions. This is consistent with DFT cal-
culations that show facile delocalization of electron density be-
tween the HOMO-LUMO orbitals. Comparison of the reduction po-
tentials of 2 with those of thiones that include benzimidazole-2-
thione and its derivatives suggests the first reduction wave is due
[21,33]. The multi-electronic oxidation at Ep,a = +1.85 V is due to
−
the 2e /2H O decomposition of the 1,1-diphenylmethanimine moi-
2
ety [N=C(Ph) ] to benzophenone. This is similar to those reported
2
for the oxidation of heteroaromatic ketone hydrazonic compounds.
When DMF was used in place of CH CN similar electrochemical
3
behavior was observed (see supplementary Figure S4). Plausible
mechanisms for the electrochemical decomposition of 2 are shown
in Scheme 3. The proposed mechanisms are consistent with the
observed redox transformations and are similar to those reported
for closely related redox transformations in the literature.
.
−
to [C=S] → [C-S] [40]. The reduction wave at Ep,c = –1.55 V
is assigned to ReI/0 as it falls in the same region as those ob-
served for fac-[Re(CO) (L-L)Cl] complexes [33,41]. The other reduc-
3
tion waves are ligand-based and can be assigned to [C-S].
−
→
6

M. Bakir, M.A.W. Lawrence, J. Johnson et al.
Journal of Molecular Structure 1235 (2021) 130135
Scheme 3. Plausible mechanisms for the electrochemical decomposition of 2.
4
. Conclusion
lographic measurements; M. B., M. A. W. L. and C. M. analyzed
data; M. B. and M. A. W. L wrote the paper and M. B., M.A. W.
L. and C. M. edited the manuscript.
2
fac-[Re(CO) (κ -Nim,S-bptsc)Cl] isolated from the reaction be-
3
tween Re(CO) Cl and 1 in toluene displays interesting physico-
5
chemical properties. The solid state structure shows the coordina-
tion of the thione (C–S) S atom and imine (C–N) N atom of the
thioamide group of 1 to Re. The extended structure of 2 shows
a network of non-covalent interactions. DFT calculations reveled
facile HOMO-LUMO electron transfer. Electrochemical measure-
Declaration of Competing Interest
None.
Acknowledgement
ments on 1 and 2 in DMF and CH CN show sequential irreversible
3
The authors express their gratitude to Ms. Shannen Lorraine,
Ms. Toni Johnson, and Dr. P. Maragh for their assistance. We are
also grateful to The University of the West Indies Mona for finan-
cial support.
electronic transfers consistent with their electrochemical decom-
position. Due to the facile synthesis of hydrazonic compounds, di-
verse coordination patterns, rich physicochemical properties and
applications in various chemical and biological processes, studies
are in progress in our laboratory to explore their coordination be-
havior and molecular sensing and catalytic applications.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130135.
Credit author statement
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