Spectroscopic, electrochemical and X-ray crystallographic properties of a novel palladium(II) complex of thioamide deprotonated di-2-pyridyl ketone thiosemicarbazone (dpktsc-H)?

Article abstract of DOI:10.1080/00958972.2017.1374379

The reaction between di-2-pyridyl ketone thiosemicarbazone (dpktsc) and PdCl₂(CH₃CN)₂, generated in situ from the reaction between PdCl₂ and CH₃CN, gave the unprecedented [Pd₂Cl₃(κ⁵-N_py,N_im,S,N_py,N_am-dpktsc-H)]·2CH₃CN (1) complex (py = pyridine, im = imine and am = amide). The identity of 1 was confirmed via its elemental analysis and spectroscopic properties. Infrared and ¹H-NMR spectra confirmed the coordination of (dpktsc-H)^? to the palladium ions. The electronic absorption spectra measured in dmso and dmf and density functional theory (DFT) calculations revealed metal-to-ligand charge-transfer (MLCT), d–d and intra-ligand charge-transfer (ILCT) electronic transitions. X-ray structural analysis on a crystal of [Pd₂Cl₃(κ⁵-N_py,N_im,S,N_py,N_am-dpktsc-H)]·H₂O (2) grown from dmf solution of 1 confirmed its formulation and showed the solid-state structure contains a web of molecules locked via a network of non-covalent interactions. Electrochemical measurements on 1 in dmf revealed metal- and ligand-based redox processes. In contrast to the electrochemical decomposition of uncoordinated dpktsc, coordinated (dpktsc-H)^? in 1 does not undergo electrochemical decomposition. Electrochemical titrations of 1 with p-toluenesulfonic acid monohydrate (p-TSOH) revealed electro-catalytic proton reduction. Over-potential (η) of 180?mV for the H₂ evolution was observed and is comparable to several molecular electro-catalysts for proton reduction. Controlled-potential electrolysis confirmed the electro-catalytic proton reduction by the Pd-complex. Electrochemical reactions of CO₂ in the presence of 1 exhibited a proton dependence, and metal- and ligand-based electrochemical reaction.

Full text of DOI:10.1080/00958972.2017.1374379

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Spectroscopic, electrochemical and X-ray
crystallographic properties of a novel palladium(II)
complex of thioamide deprotonated di-2-pyridyl
-
ketone thiosemicarbazone (dpktsc-H)
Mohammed Bakir, Mark A. W. Lawrence, Marhoun Ferhat & Rebecca R.
Conry
To cite this article: Mohammed Bakir, Mark A. W. Lawrence, Marhoun Ferhat & Rebecca R.
Conry (2017): Spectroscopic, electrochemical and X-ray crystallographic properties of a novel
-
palladium(II) complex of thioamide deprotonated di-2-pyridyl ketone thiosemicarbazone (dpktsc-H) ,
Journal of Coordination Chemistry, DOI: 10.1080/00958972.2017.1374379
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1374379
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Date: 02 September 2017, At: 03:08

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2017.1374379
Spectroscopic, electrochemical and X-ray crystallographic properties of a
novel palladium(II) complex of thioamide deprotonated di-2-pyridyl ketone
-
thiosemicarbazone (dpktsc-H)
MOHAMMED BAKIR*†, MARK A. W. LAWRENCE†, MARHOUN FERHAT‡ and REBECCA R. CONRY§
†
Department of Chemistry and ‡Department of Physics, The University of the West Indies-Mona Campus,
Kingston 7-Jamaica, W. I.
Department of Chemistry, Colby College, Waterville, ME 04901-8857, USA
§
The reaction between di-2-pyridyl ketone thiosemicarbazone (dpktsc) and PdCl (CH CN) ,
2
3
2
generated in situ from the reaction between PdCl and CH CN, gave the unprecedented
2
3
5
[
Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)]·2CH CN (1) complex (py = pyridine, im = imine and
2
3
py im
py am
3
am = amide). The identity of 1 was confirmed via its elemental analysis and spectroscopic
1
-
properties. Infrared and H-NMR spectra confirmed the coordination of (dpktsc-H) to the
palladium ions. The electronic absorption spectra measured in dmso and dmf and density
functional theory (DFT) calculations revealed metal-to-ligand charge-transfer (MLCT), d-d and
intra-ligand charge-transfer (ILCT) electronic transitions. X-ray structural analysis on a crystal of
5
[
Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)]·H O (2) grown from dmf solution of 1 confirmed the
2
3
py im
py am
2
formulation and showed that the solid-state structure contains a web of molecules locked via a
network of non-covalent interactions. Electrochemical measurements on 1 in dmf revealed
metal- and ligand-based redox processes. In contrast to the electrochemical decomposition of
-
uncoordinated dpktsc, coordinated (dpktsc-H) in 1 does not undergo electrochemical
decomposition. Electrochemical titrations of 1 with p-toluenesulfonic acid monohydrate
(p-TSOH) revealed electro-catalytic proton reduction. Over-potential (η) of 180 mV for the H2
evolution was observed and is comparable to several molecular electro-catalysts for proton
reduction. Controlled-potential electrolysis confirmed the electro-catalytic proton reduction by
*
Corresponding author. Email: mohammed.bakir@uwimona.edu.jm
1

the Pd-complex. Electrochemical reactions of CO in the presence of 1 exhibited a proton
2
dependence and a metal- and ligand-based electrochemical reaction.
Keywords: Palladium; Di-2-pyridyl ketone thiosemicarbazone; Proton and CO reduction;
2
Electrochemistry; X-ray crystallography
1
. Introduction
Hydrazonic ligands of the type R,R’C=N-NH-(C=X) -Y (R, or R’ = H, alkyl, aryl, or
n
heterocyclic ring; X = O or S; n = 0 or 1 and Y = R, R’, or NRR’) such as hydrazones,
semicarbazones, thiosemicarbazones, etc. and their metal complexes have attracted research
activities for their intriguing physico-chemical properties and applications in several areas
[1-16]. Hydrazonic ligands coordinate to metal ions in various binding modes depending on the
hydrazonic [C=N-NH-(C(X) )] backbone, the identity and oxidation state of the metal, and the
n
reaction conditions [3, 4, 9, 16-21]. Upon coordination to metal ions, the acidity of the
hydrazonic (NH) proton increases in part due to the delocalization of electron density about the
metallocyclic ring(s) [19, 20, 22-26]. This makes the hydrazonic nitrogen atom susceptible to
electrophilic attack. Hydrazonic derivatives are widely used as sensitive analytical reagents for
the detection and determination of trace amounts of environmental and biological substrates,
such as the determination of copper(II) concentrations in drinking water [27, 28]. They have also
been employed as highly selective and efficient metal-based catalysts for C-X (where X = C, O
or N) cross-coupling reactions [3-8], such as the Suzuki–Miyaura cross-coupling reaction of aryl
halides with organoboronic acids and the Mizoroki-Heck cross-coupling reaction of aryl halides
with olefins [29]. Hydrazonic derivatives and their metal compounds have also demonstrated
potential in the treatment of various diseases such as tuberculosis [9], cancer [10-13, 30], iron-
overload, hypertension, etc. [12, 13, 31, 32]. Most notably, di-2-pyridyl ketone
thiosemicarbazones and their metal complexes show potent anti-proliferative activity against
lung and pancreatic cancer [30, 33]. The therapeutic properties of hydrazonic ligands are due in
part to their excellent chelating properties, hence depriving cells from essential metal ion
nutrients leading to cell death. Di-2-pyridyl ketone thiosemicarbazones coordinate to metal
2
3
4
5
moieties in  -N ,N -, -N ,N -S,  -N ,N -S, N , or  -N ,N -S, N N -coordination
py py
py im
py im
py
py im
py, am
modes to form a range of mononuclear and polynuclear metal complexes.
2

The development of the chemistry of palladium complexes with thiosemicarbazone
ligands stems from the potential of these complexes to be an alternative to cisplatin
chemotherapeutic agents owing to their effectiveness toward cell lines resistant to cisplatin, their
good anti-mycobacterial effect, and their observed anti-proliferative effect on human breast
cancer [10, 12, 13, 18]. Although palladium complexes of hydrazonic derivatives have been
extensively studied, the chemistry of palladium with di-2-pyridyl ketone hydrazonic derivatives
is scarce. To our knowledge, only three reports appeared in the literature, those are the synthesis
and characterization of [PdCl (N ,N -dpk)], [PdCl (N ,N -dpk.HX)] (X = OH, OMe or OEt)
2
py py
2
py py
and [Pd(N ,O,N -dpkO,OH) ](ClO ) [34], and the spectrophotometric determination and
py
py
2
4 2
II
extraction of Pd with di-2-pyridyl ketone hydrazones [35, 36].
As a part of an on-going research program that focusses on the chemistry of
heteroaromatic ketones and their hydrazonic derivatives, we have reported a series of studies on
the synthesis, spectroscopic, electrochemical and X-ray structural analysis of di-2-pyridyl ketone
hydrazonic derivatives and their metal compounds including the molecular sensing properties of
di-2-pyridyl ketone thiosemicarbazone and its reactions with [Re(CO) Cl] and [Mn(CO) Br]
5
5
[19, 20, 23, 24, 37-43]. Spectroscopic measurements on di-2-pyridyl ketone derivatives have
shown a high sensitivity of the (thio)amide (NH) proton to solvent, temperature and metal ion
identity allowing the use of these species as sensitive analytical regents for the detection and
determination of trace amounts of various substrates [19, 20, 22-25, 37, 41]. Electrochemical
measurements on di-2-pyridyl ketone hydrazonic ligands typically show irreversible redox
transformations leading to electrochemical decomposition following the first electronic reduction
[19, 22, 37, 43-45]. In this report, we describe the synthesis plus the spectroscopic, structural,
and electrochemical properties of {µ-[(N’-2-pyridin-2-ylmethylene)carbamohydrazonothiolate]-
3
N ,N ,S-palladium(II)chlorido,  N ,N -palladiumdichlorido}.solvate and [Pd Cl ( -
2
5
py im
py am
2
3
N ,N ,S,N ,N -dpktsc-H)].solvate (solvate = CH CN or H O).
py im
py am
3
2
2
2
. Experimental
.1. Reagents
The ligand dpktsc was prepared following a literature procedure, from the reaction between di-2-
pyridyl ketone (dpk) and thiosemicarbazide (ts) in refluxing acidified alcoholic solution [22].
PdCl was purchased from BDH, Ltd., dpk and ts were obtained from Sigma-Aldrich and all
2
3

other reagents were obtained from either BDH or Sigma-Aldrich sources and used as received.
Solvents used in spectroscopic and electrochemical measurements were analytical grade and
were deoxygenated prior to use.
2
.2. Physical measurements
Electronic absorption spectra were measured using an HP-8452A Photodiode Array
Spectrophotometer. Baseline corrections for pure solvents were recorded prior to measurements.
1
Solution H NMR spectra were measured using a Bruker ACE 500-MHz Fourier-transform
spectrometer and were referenced internally to the residual protons of the incompletely
deuterated solvent. Infrared spectra were recorded on a Bruker Vector 22 FT-IR spectrometer
with an ATR accessory. Electrochemical measurements were performed under an argon or
nitrogen atmosphere using a conventional three-electrode configuration consisting of a glassy
carbon (diameter = 3 mm) working electrode, a Pt wire auxiliary electrode and a Ag wire quasi-
reference electrode using either a Princeton Applied Research (PAR) Model 173 or a BAS
Epsilon C3 potentiostat/galvanostat. Measurements were performed in solutions containing
n
0
.1 M [ Bu N]PF (TBAH) electrolyte. A Bruker SMART CCD area-detector diffractometer
4
6
with Mo-K radiation and a graphite monochromator was used for data collection and the
α
SHELXTL software package version 5.1 [46, 47] and PLATON for Windows [48] were used for
structure solution. Density Functional Theory (DFT) calculations were conducted using the
computational package Atomistix Toolkit (ATK-DFT) [49-51]. Geometry optimization and
electronic structure calculations were performed using the generalized gradient approximation
(GGA) of Perdew-Burke-Ernzerhof (PBE) to represent the exchange correlation energy [52].
Double-zeta- polarized basis sets of local numerical orbitals were employed for all atoms and the
electrostatic potentials were determined on a real-space grid with mesh cutoff energy of 150 Ry.
Analysis of the vibrational modes confirmed that the optimized geometry corresponded to the
true minimum since all those modes were found to be positive (no imaginary frequency).
Comparison of bond lengths and angles after the structural relaxation of the atoms within the
molecule were close to those obtained from the X-ray measurements. The calculations were
5
performed on an isolated [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)] species in the gas phase, so a
2
3
py im
py am
reasonable amount of variation in bond distances and angles is expected compared to the solid-
4

state structure. GC experiments were performed on an HP (Agilent) 5890 series II instrument
-1
with an ECD detector (40 C isothermal; 1.0 mL min flow rate; He carrier gas).
2
.3. Analytical procedures
MEDAC LTD., Department of Chemistry, Brunel University, and Uxbridge - United Kingdom
performed elemental microanalyses.
5
2
.4. Preparation of [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)]·2CH CN (1)
2
3
py im
py am
3
A mixture of PdCl (100 mg, 0.56 mmol) and CH CN (100 mL) was stirred at room temperature
2
3
for 18 h. The resulting yellow solution was filtered and dpktsc (150 mg, 0.58 mmol) dissolved in
CH CN (25 mL) was added to the filtrate, turning the reaction mixture deep red. After stirring
3
the mixture at room temperature for 3 h, all but about 25 mL of the solvent was distilled away
under reduced pressure. The resulting red precipitate was filtered off, washed with acetonitrile
then hexanes and dried in air to yield 150 mg (82%). Anal. Calc. for C H Cl N Pd S
1
6
16
3
7
2
5
(
Pd Cl ((η -N,N,S,N,N-dpktsc-H)·2CH CN) (%): C, 29.22; H, 2.45; N, 14.90. Found: C, 29.50;
2 3 3
-1
H, 2.22; N, 14.76. IR (ATR, neat/cm ): ν(N-H of NH ) 3612, 3528, 3441, ν(C-H) 3100-2900,
2
-1
-1
ν(C=C and C=N) 1637, 1614, 1610, and ν(C-S) 694. UV-vis (/nm,  ± 200/ M cm ): dmf 478
(6800), 434 (6160), 375 (22780), 352 (20450) and 303 (25,640); dmso 476 (7930), 432 (7890),
1
3
8
75 (28940), 354 (27670), and 311 (29315). H-NMR (d -dmso): 8.78 (1 H, d, J = 4.8 Hz, H24),
6
.61 (1H, d, J = 4.8 Hz, H14), 8.03 (2H, overlapped triplet, H23 and H13), 7.77 (1H, d, J = 7.2,
H21), 7.60 (2H, overlapped triplet, H12 and H22), 7.12 (1H, d, J = 8, H11), 5.97 (2H, broad
singlet, NH2).
2
.5. X-ray crystallography
3
Crystals of {µ-[(N’-2-pyridin-2-ylmethylene)carbamohydrazonothiolate]- N ,N ,S-
py im
2
5
palladium(II)chlorido, N ,N -palladiumdichlorido}.aqua, [Pd Cl ( -N ,N ,S,N ,N -
py am
2
3
py im
py am
dpktsc-H]·H O (2) were grown from a dmf solution of 1 when left to stand several days at room
2
temperature open to air. A single crystal was selected, coated with Paratone-N oil, coaxed onto
the end of a glass fiber, and placed in the cold stream on the goniometer. A Bruker SMART
CCD area-detector diffractometer with Mo-K radiation and a graphite monochromator was used
α
for data collection. A Bruker AXS, APEXS v2015.9-0 and the Bruker AXS Inc. 2015, SAINT
5

v8.35A were used for cell refinement and data reduction, respectively (see CIF file). The
SHELXS-97 and SHELXL-2014/7 were used for structure solution and refinement, and
PLATON software version 240413 were used for structure analysis [46-48]. All non-hydrogen
atoms and hydrogen atoms of H O were refined anisotropically. Hydrogen atoms except those of
2
H O were assigned by assuming idealized geometry with N-H and C-H bond distances of 0.88
2
and 0.95 Å, respectively. The positions of H1OA and H2OB were located from Fourier
difference maps, and were then fixed and allowed to ride on O1. During the course of structure
refinement a region of electron density at a non-bonding distance to the Pd-dimer was located
and assigned to a lattice H O. All hydrogen atoms except H’s of lattice water were assigned by
2
assuming idealized geometries. Crystallographic information for 2 is given in table 1 and details
of the data collection and structural solution are provided in the supporting crystallographic files
(CIF). The atomic coordinates and equivalent isotropic displacement parameters are given in
table S1.
2
.6. Controlled-potential electrolysis (CPE)
Controlled-potential electrolysis (CPE) measurements for the production of hydrogen were
conducted at –0.45 V on unstirred solutions for 20 min in a sealed two-chambered H-cell
separated by a fine frit, where one chamber held the working and reference electrodes in 10 mL
n
of 0.8 mM of complex in 0.1 M [ BuN ]PF (supporting electrolyte) with 19 mM p-TSOH and
4
6
the second chamber held the auxiliary electrode in 5 mL of the solvent with the supporting
electrolyte. A glassy carbon plate (contact area ~2 cm × 1 cm × 3 mm) and a Pt wire were used
as the working and auxiliary electrodes, respectively, with a Ag wire as the reference electrode.
The solution was purged with N for 20 minutes and then sealed under an N atmosphere before
2
2
the start of each electrolysis experiment. The amount of H evolved was calculated based on the
2
charge accumulated from the catalyst solution during CPE minus charge from the same solution
but without catalyst [53]. After electrolysis, 50 µL of the headspace was injected into the gas
chromatograph (GC).
6

3
3
. Results and discussion
.1. Synthesis and spectroscopic properties of [Pd Cl ( -N ,N ,S,N ,N -dpktsc-
5
2
3
py im
py am
H]·2CH CN (1)
3
When PdCl (CH CN) , generated in situ from the reaction between CH CN and PdCl , was
2
3
2
3
2
allowed to react with dpktsc at room temperature, a facile reaction occurred to give 1 in good
yield (scheme 1). The isolated complex formulated as {µ-[(N’-2-pyridin-2-
3
2
ylmethylene)carbamohydrazonothiolate]- N ,N ,S-palladium(II)chlorido, N ,N -
py im
py am
5
palladiumdichlorido}.bis-acetonitrile, [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H].2CH CN, 1 is the
2
3
py im
py am
3
5
-
first reported Pd-complex of  -(dpktsc-H) and is only the third example of coordinated
5
-
(
 -dpktsc-H) to our knowledge. The other such reported complexes include the trinuclear
Cu(II) complex, [Cu (DpyEtsc) (NO ) (H O) ]·H O (DpyEtsc = di-2-pyridyl ketone
3
2
3 4
2
2
2
N(4)ethylthiosemicarbazone) [21] and the dinuclear rhenium carbonyl compounds
Re (CO) X(dpktsc)] (X = Cl or Br) [54]. In these complexes the thiosemicarbazone anion
[
2
6
3
coordinates to one metal center in a  -N ,N ,S-coordination mode to form two fused five-
py im
2
membered metallocyclic rings and is bound in an  -N ,N -coordination mode to the other
py am
metal center forming fused five- and six-membered metallocyclic rings.
Scheme 1. The reaction of dpktsc with PdCl in CH CN.
2
3
The identity of 1 was established from the results of its elemental analysis and spectroscopic
1
properties. The H-NMR spectrum of 1 in d -dmso revealed a series of resonances in the
6
aromatic and amine regions between 10.0-5.0, consistent with the coordination thioamide
deprotonated dpktsc (see Experimental section). This is evident from the absence of the amide
7

NH proton which appears at 13.00 ppm in the spectrum of dpktsc. A peak appeared at ~2.10 ppm
when the sample was prepared at room temperature, which is consistent with the presence of
–
1
CH CN. The infrared spectrum of 1 contains peaks between 2900-4000 cm due to the ν(N-H)
3
–
and ν(C-H) of coordinated (dpktsc-H) and solvated CH CN. The ν(C=N) for coordinated
3
–
–1
–1
(
dpktsc-H) is observed at 1635 cm , which is shifted to higher frequency by 23 cm compared
to the free ligand. Additional changes in the pyridyl ν(C=N) and ν(C=C) stretches are present,
consistent with the coordination of the imine and pyridyl nitrogen atoms. Similarly, peak shifts in
–
1
the ν(N-N-C=S), ν(N-N), ν(C-N) region between 1400-700 cm point to the coordination of the
-1
amide nitrogen and sulfur atoms. The ν(CH ) of CH CN appeared at 2965 cm . The N-H out-of-
3
3
–
1
plane bending vibrations observed between 700-600 cm in the free ligand are no longer present
in the spectrum of the metal complex, confirming deprotonation of the thioamide proton. The
electronic absorption spectra of 1 measured in protophilic solvents (dmso or dmf) show low-
-1
-1
energy electronic transitions between 400-600 nm with molar absorptivities < 10,000 M cm
along with highly intense electronic transitions in the ultraviolet region < 400 nm (figure 1). The
low-energy electronic transitions are possibly mixed Pd-N, Pd-S metal-to-ligand charge-transfer
along with d-d transitions and the high-energy electronic transitions are intra-ligand charge-
-
transfer →* and n→* transitions for (dpktsc-H) of which the lowest-energy peak is red-
-
shifted compared to uncoordinated (dpktsc-H) [22]. DFT calculations showed the electrons in
2
the HOMO are located primarily on the  -N ,N -PdCl fragment with some involvement of
py am
2
the thioamide deprotonated nitrogen atom and the sulfur atom of the hydrazone backbone. The
3
LUMO is delocalized over the  -N ,N ,S-PdCl fragment as well as the ligand backbone
py im
(figure 2). The combination of metal centers and the ligand backbone in both the HOMO and
LUMO are consistent with the assignment of the electronic transitions.
3
.2. Structural analysis
After 1 was allowed to stand in dmf for several days, crystals of 2 were isolated. A view of the
5
solid-state structure of 2 revealed well separated [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)] and
2
3
py im
py am
–
5
H O molecules and (dpktsc-H) coordinated in a  -N ,N ,S,N ,N - fashion (figure 3). Thus,
2
py im
py am
the deprotonated bridging dpktsc ligand is coordinated to the Pd(II) ion with one chloride in a
3
-N ,N ,S-coordination mode through a nitrogen atom of a pyridyl ring, and the imine
py im
nitrogen and sulfur atoms of the thiosemicarbazone backbone, forming fused two five–
8

membered metallocyclic rings with Pd in a distorted square planar geometry. This distortion is
seen in the > 90 Cl-Pd-X (X = N or S) bond angles and is due to the constraints associated with
3
-N,N,S coordination of the ligand. Simultaneously (dpktsc-H) is coordinated to the Pd(II) ion
–
2
bearing two chlorides in a  -N ,N -cordination mode through the nitrogen atom of the other
py am
pyridyl ring and the nitrogen atom of deprotonated thioamide in a six-membered metallocyclic
ring containing Pd in a pseudo-square planar geometry. This coordination mode is similar to that
reported previously for trinuclear copper and dinuclear rhenium carbonyl complexes with dpk
ligand derivatives [21, 54]. The bond distances and angles in 2 (table 2) are similar to those
5
–
reported for Cu- and Re-complexes of  -N ,N ,S,N ,N -coordinated (dpktsc-H) and Pd-,
py im
py am
and Mn-complexes containing similar bonds [9, 55-58].
The extended structure of 2 (figure S2) contains stacks of 2 locked via a web of classical
hydrogen bonds of the type X···H-Y (X = Cl, N or O) and non-classical hydrogen bonds of the
type X···H-C along with Pd···Pd and Pd···H-C bond interactions (table 3 and figure 4). When two
molecules are aligned parallel to but rotated by ~180 from one another, the chlorine atoms on
the Pd ions bearing only one chloride ligand appear to interact weakly with the Pd on the other
molecule, giving a short Pd-Pd distance of 3.421 Å, and indicating a potential weak Pd···Pd
interaction. One chlorine atom of the Pd ion with two chloride ligands appears to weakly bind to
an adjacent Pd in a PdCl unit, a hydrogen atom of NH , and a hydrogen atom of H O forming
2
2
2
trifurcated bonds of the type Cl···Pd and Cl···H-N, Cl···H-O; while the other chloride forms a
hydrogen bond with H O of the type Cl···H-O. Classical hydrogen bonds of the type Cl···H-O
2
and non-classical hydrogen bond of the type Cl···H-C lock the various stacks in the extended
structure.
3
.3. Electrochemical properties of 1
The electrochemical properties of 1 measured in dmf were investigated using voltammetric
techniques. Cyclic voltammograms of 1 and dpktsc on reductively and oxidatively initiated scans
are shown in figure 5. In the voltammograms of 1 two closely spaced irreversible reductions
occur at –0.25 and –0.40 V followed by a quasi-reversible reduction at E = –0.77 V (E =
1
/2
p,c


0.84 and E = –0.70 V), quasi-reversible reductions at E = –1.27 V (E = –1.30 and E =
p,a 1/2 p,c p,a
1.20 V), an irreversible reduction at E = –1.90 V plus multi-electron irreversible oxidations
p,c
between E = +1.23 and E = +1.83 V. Square wave voltammograms measured between 0.00
p,a
p,a
9

and –2.00 V and 0.00 and +2.00 V confirmed the observed redox processes. Scan rate variations
and scan reversals between 0.00 and –0.50 V and between 0.00 and –1.00 V showed no sign of
reversibility for the reduction waves between 0.00 and –0.50 V, and confirmed the quasi-
reversibility of the reduction wave between –0.50 and –1.00 V. The reduction waves between
II
I
I
0
0
.00 and –1.00 V are metal-based due to Pd →Pd and Pd →Pd . The more negative metal-based
3
reduction waves are assigned to the  -N,N,S-PdCl moiety and the more positive metal-based
2
reduction waves are assigned to the  -N,N-PdCl moiety because of the greater electron-
2
–
–
II
I
I
0
donating character of S compared to Cl . The assigned Pd →Pd and Pd →Pd are similar to
those of PdCl (CH CN) measured under similar conditions. The more negative reductions
2
3
2
between –1.00 and –2.00 V are ligand-based and assigned to the imine (C=N) reductions. On a
reductive scan between –0.50 and –2.50 V (figure S3) a multi-electron reduction occurs at E =
p,c
–
2.40 V. In the free ligand reduction waves appeared at E = –1.30, –1.78 and –2.20 V. The
p,c
ligand-based reductions in 1 appeared at more negative potentials compared to the free ligand,
–
suggesting an enhanced electron density on coordinated (dpktsc-H) . The reductively generated
product waves observed at +0.45 and +0.95 V on reductively initiated scans in the
voltammogram of dpktsc (figure 5c) are absent from the voltammograms of 1, pointing to the
–
absence of electrochemical decomposition of coordinated (dpktsc-H) . The oxidative wave
observed at E = +1.23 V is ligand-based as it appeared at nearly the same potential as seen for
p,a
II
IV
the free ligand. The oxidation observed at E = +1.83 V is assigned to the Pd →Pd oxidation.
p,a
-
The voltammograms for 1 showed no sign of the 2Cl to Cl oxidation, implying the absence of
2
-
Cl labilization upon reduction.
On oxidatively-initiated scans, electrochemical signatures similar to those observed on
reductively-initiated scans were observed, except that there is a slight increase in the reductive
current appeared on the metal-based redox processes. This might be due to the possible oxidation
II
IV
of residual water in dmf on the Pd →Pd oxidation and subsequent reduction of the
+
II
I
I
0
electrochemically-generated H on the Pd →Pd and Pd →Pd reductions. This was confirmed
when electrochemical titrations of 1 with p-TSOH were conducted. Cyclic voltammograms of 1
in the absence and presence of increasing amounts of p-TSOH are shown in figure 6. These
voltammograms show an increase in the cathodic current (i ) in the metal-based reductions
p,c
-
(
between –0.3 and –0.8 V) and again the absence of the 2Cl to Cl oxidation. The peak current
2
(
i ) on the first reduction wave is scan rate dependent and the plot of i vs √[p-TSOH] is linear
p,c
p,c
1
0

†
[
59, 60] and an over-potential of 180 mV for H evolution were observed [59-62]. The electro-
2
catalytic behavior of the complex toward proton reduction was investigated by controlled
potential electrolysis (CPE) in the presence of p-TSOH. A turnover number (TON) of ~ 1.3 × 103
which corresponds to 65 moles of hydrogen per mole of catalyst per minute was calculated after
2
0 minutes. These values are comparable those reported by Vos et al. in their photo-catalytic
experiments involving Pd(II) complexes [63].
The electrochemical reactions of 1 in the presence of CO with and without a proton
2
source (H O or p-TSOH) were explored (figure 6). On reductively-initiated scans, cyclic
2
voltammograms of 1 measured in the absence and presence of CO (figure 7a) showed current
2
I/0
enhancement at Pd and ligand-based reductions followed by a reductively generated product
wave at E = +0.36 V. On oxidatively-initiated scans in the presence of CO (figure 7b), a
p,a
2
II/I
significant current increase appeared for the Pd wave, a slight current increase was seen for the
I/0
Pd wave and a slight decrease in current occurred for the ligand-based reduction compared to
reductively-initiated scans in the presence of CO . When the electrochemical cell containing CO
2
2
was purged with N , the voltammogram of 1 in the absence of CO was restored. These results
2
2
I/0
suggest a non-covalent interaction of CO with Pd and ligand and proton dependence of the
2
electrochemical reactions of 1 with CO . These results were further confirmed when the
2
electrochemical reactions of 1 with CO were explored in the presence of H O and p-TsOH
2
2
(figure 7c and d). The voltamograms show p-TsOH has a significant influence on the
electrochemical reactions of CO with 1 (figure 7d) for both the metal- and ligand-based
2
reductions while H O showed only a slight influence in the electrochemical reaction at the ligand
2
(
figure 7c). When the electrochemical cell was purged with N , the current for the ligand-based
2
reduction decreased (figure 7e), confirming the non-covalent interaction between CO and the
2
complex. Although a plausible pathway for the electrochemical reactions of CO at the metal
2
center may involve two electrons to form CO or HCOOH in the absence and presence of
p-TSOH, the electrochemical reactions of CO at the ligand in the absence of a proton source
2
•
may involve a single electron reduction to form the CO radical anion that may dimerize to form
2
†
η
cat/2 = E°H+ – 0.059 × (pK
a
) – Ecat/2
(1)
+
where ηcat/2 is overpotential at the catalytic half-wave potential, E°H+ (–0.92 V vs Fc /Fc) is the reduction potential of
= 2.6 in DMF, and Ecat/2 is the Pd+2/0 couple vs Fc /Fc [61].
+
p-TSOH, pK
a
1
1

oxalate [64]. Detailed analysis of the mechanistic pathways for the electrochemical reactions of
CO with 1 remain to be explored.
2
Due to the rich reactivity patterns, physical properties of hydrazonic ligands and their
metal complexes studies are in progress in our laboratory to develop novel metal-based
hydrazonic compounds for potential chemical and biological applications.
4
. Conclusion
-
The first dinuclear palladium complex (1) of (dpktsc-H) is generated from the facile reaction
between PdCl (CH CN) and dpktsc in CH CN. Spectroscopic and elemental analysis results
2
3
2
3
-
established the coordination of (dpktsc-H) to Pd Cl and X-ray structural analysis confirmed the
2
3
5
identity of [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H]. Electrochemical measurements disclosed
2
3
py im
py am
+
metal- and ligand-based redox processes as well as the elctro-catalytic reduction of H and CO
2
-
in dmf. Coordinated (dpktsc-H) is stable to redox transformations. Electro-catalytic proton
reduction using 1 gave overpotential comparable to those reported for several molecular proton
electro-catalysts.
Supplementary material
5
CCDC no. 1544002 contain the supplementary crystallographic data for [Pd Cl ( -
2
3
N ,N ,S,N ,N -dpktsc-H)]·H O. The data can be obtained free of charge from the Cambridge
py im
py am
2
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Other supplementary
data associated with this article are also provided.
Acknowledgements
The authors acknowledge the University of the West Indies for financial support; the United
States National Science Foundation and Colby College for support of the X-ray diffraction
facility at Colby College and would like to express their gratitude to Ms. Toni Johnson and
Ms. Shannen Lorraine.
References
[
1]
2]
P. Madan, V.D. Barhate. J. Chem. Pharm. Res., 7, 1113 (2015).
[
S.A. Reddy, P.V. Raman, A.V. Reddy. J. Chem. Pharm. Res., 7, 146 (2015).
1
2

[3]
[4]
[5]
[6]
P. Anitha, R. Manikandan, P. Viswanathamurthi. J. Coord. Chem., 68, 3537 (2015).
J. Dutta, S. Bhattacharya. J. Indian Chem. Soc., 91, 663 (2014).
L. Lu, P. Chellan, G.S. Smith, X. Zhang, H. Yan, J. Mao. Tetrahedron, 70, 5980 (2014).
L.C. Matsinha, J. Mao, S.F. Mapolie, G.S. Smith. Eur. J. Inorg. Chem., 2015, 4088
(2015).
[
7]
8]
P.K. Suganthy, R.N. Prabhu, V.S. Sridevi. Inorg. Chem. Commun., 44, 67 (2014).
A.-C. Tenchiu, I.-K. Ventouri, G. Ntasi, D. Palles, G. Kokotos, D. Kovala-Demertzi, I.D.
Kostas. Inorg. Chim. Acta, 435, 142 (2015).
[
[
[
[
[
9]
R. Arancibia, C. Quintana, C. Biot, M.E. Medina, S. Carrere-Kremer, L. Kremer, A.H.
Klahn. Inorg. Chem. Commun., Klahn, 55, 139 (2015).
10] A. Dobrova, S. Platzer, F. Bacher, M.N.M. Milunovic, A. Dobrov, G. Spengler, E.A.
Enyedy, G. Novitchi, V.B. Arion. Dalton Trans., 45, 13427 (2016).
11] W. Hernandez, J. Paz, F. Carrasco, A. Vaisberg, E. Spodine, J. Manzur, L. Hennig, J.
Sieler, S. Blaurock, L. Beyer. Bioinorg. Chem. Appl., 1-2 (2015).
12] M. Jagadeesh, M. Lavanya, S.K. Kalangi, Y. Sarala, C. Ramachandraiah, A. Varada
Reddy. Spectrochim. Acta, Part A, 135, 180 (2015).
[13] A.I. Matesanz, P. Albacete, P. Souza. Polyhedron, 109, 161 (2016).
[14] B.K. Dey, P. Paul, S. Bhattacharya. J. Indian Chem. Soc., 91, 359 (2014).
[15] J. Martinez, E.M. Cabaleiro-Lago, J.M. Ortigueira, M.T. Pereira, P. Frieiro, F. Lucio,
J.M. Vila. Inorg. Chim. Acta, 449, 20 (2016).
[
16] A.I. Matesanz, C. Hernandez, P. Souza. J. Organomet. Chem., 751, 374 (2014).
17] J.M. Vila, M.T. Pereira, J.M. Ortigueira, M. Grana, D. Lata, A. Suarez, J.J. Fernandez, A.
Fernandez, M. Lopez-Torres, H. Adams. J. Chem. Soc., Dalton Trans., 4193 (1999).
18] W. Hernández, J. Paz, A. Vaisberg, E. Spodine, R. Richter, L. Beyer. Bioinorg. Chem.
Appl., 2008, 690952 (2008).
[
[
[
[
[
[
[
[
19] M. Bakir, M.A.W. Lawrence, S. McBean. Spectrochim. Acta, Part A, 146, 323 (2015).
20] M. Bakir, M.A.W. Lawrence, M. Singh-Wilmot. J. Coord. Chem., 60, 2385 (2007).
21] S. Renjusha, K. Laly, M.R.P. Kurup. Asian J. Chem., 28, 864 (2016).
22] M. Bakir, O. Brown. J. Mol. Struct., 1006, 402 (2011).
23] M. Bakir, R.R. Conry, O. Green, W.H. Mulder. J. Coord. Chem., 61, 3066 (2008).
24] M. Bakir, O. Green, C. Gyles, B. Mangaro, R. Porter. Talanta, 62, 781 (2004).
1
3

[
[
[
[
25] M. Bakir, C. Gyles. J. Mol. Struct., 753, 35 (2005).
26] M. Bakir, C. Gyles. J. Mol. Struct., 833, 161 (2007).
27] P. Puangploy, S. Smanmoo, W. Surareungchai. Sens. Actuators, B, 193, 679 (2014).
28] M.E.V. Suarez Iha, S.O. Pehkonen, M.R. Hoffmann. Environ. Sci. Technol., 28, 2080
(1994).
[
29] T. Mino, Y. Shirae, Y. Sasai, M. Sakamoto, T. Fujita. J. Org. Chem., 71, 6834 (2006).
30] D.B. Lovejoy, D.M. Sharp, N. Seebacher, P. Obeidy, T. Prichard, C. Stefani, M.T. Basha,
P.C. Sharpe, P.J. Jansson, D.S. Kalinowski, P.V. Bernhardt, D.R. Richardson. J. Med.
Chem., 55, 7230 (2012).
[
[
31] P.V. Bernhardt, J. Mattsson, D.R. Richardson. Inorg. Chem., 45, 752 (2006).
32] Z. Debebe, T. Ammosova, D. Breuer, D.B. Lovejoy, D.S. Kalinowski, P.K. Karla, K.
Kumar, M. Jerebtsova, P. Ray, F. Kashanchi, V.R. Gordeuk, D.R. Richardson, S. Nekhai.
Mol. Pharmacol., 79, 185 (2011).
[
[
33] P.J. Jansson, D.S. Kalinowski, D.J.R. Lane, Z. Kovacevic, N.A. Seebacher, L. Fouani, S.
Sahni, A.M. Merlot, D.R. Richardson. Pharmacol. Res., 100, 255 (2015).
34] G. Annibale, L. Canovese, L. Cattalini, G. Natile, M. Biagini-Cingi, A.-M. Manotti-
Lanfredi, A. Tiripicchio. J. Chem. Soc., Dalton Trans., 2280 (1981).
[
[
[
[
35] E. Kavlentis. Microchim. Acta, 90, 251 (1986).
36] T. Nakanishi, M. Otomo. Anal. Sci., 1, 161 (1985).
37] M. Bakir, M.A.W. Lawrence, P.N. Nelson, R.R. Conry. Electrochim. Acta, 212, 1010
(2016).
[
[
[
[
[
[
[
38] M. Bakir. J. Electroanal. Chem., 466, 60 (1999).
39] M. Bakir. Acta Crystallogr., Sect. C, C57, 1154 (2001).
40] M. Bakir, K. Abdur-Rashid. Transition Met. Chem., 24, 384 (1999).
41] M. Bakir, R. Conry, D. Thomas. J. Coord. Chem., 67, 249 (2014).
42] M. Bakir, C. Gyles. J. Mol. Struct., 918, 138 (2009).
43] M. Bakir, C. McDermot, T. Johnson. J. Mol. Struct., 1040, 221 (2013).
44] A.D. Özel, Z. Durmuş, I. Yılmaz, A. Çukurovalı, E. Kılıç. Acta Chim. Slov., 56, 797
(2009).
[45] M.R.D. Reddy, A.R.G. Prasad, Y.N. Spoorthy, L.R.K.R. Ravindranath. Anal. Bioanal.
Electrochem., 5, 740 (2013).
1
4

[
[
[
46] G. Sheldrick. Acta Crystallogr., Sect. A, 64, 112 (2008).
47] G.M. Sheldrick. SHELXL 2014/7, University of Gottngen, Germany (2014).
48] A.L. Spek, PLATON - A Multipurpose Crystallographic Tool, Utrecht University,
Utrecht, The Netherlands (2003).
[49] Atomistix ToolKit, 2016.4; QuantumWise A/S.
[50] M. Brandbyge, J.-L. Mozos, P. Ordejón, J. Taylor, K. Stokbro. Phys. Rev., B 65, 165401
(2002).
[51] J.M. Soler, E. Artacho, J.D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal.
J. Phys. Condens. Matter, 14, 2745 (2002).
[52] J.P. Perdew, K. Burke, M. Ernzerhof. Phys. Rev. Lett., 77, 3865 (1996).
[53] T. Fang, L.-Z. Fu, L.-L. Zhou, S.-Z. Zhan, S. Chen. Electrochim. Acta, 178, 368 (2015).
[54] G. Pereiras-Gabián, E.M. Vázquez-López, H. Braband, U. Abram. Inorg. Chem., 44, 834
(2005).
[
55] R.A. Begum, D. Powell, K. Bowman-James. Inorg. Chem., 45, 964 (2006).
56] M.A.W. Lawrence, Y.A. Jackson, W.H. Mulder, P.M. Björemark, M. Håkansson. Aust. J.
Chem., 68, 731 (2015).
[
[
[
[
[
[
[
57] C.-Y. Duan, B.-M. Wu, T.C.W. Mak. J. Chem. Soc., Dalton Trans., 3485 (1996).
58] V. Philip, V. Suni, M.R.P. Kurup, M. Nethaji. Spectrochim. Acta, Part A, 64, 171 (2006).
59] X. Hu, B.S. Brunschwig, J.C. Peters. J. Am. Chem. Soc., 129, 8988 (2007).
60] J.-M. Savéant. Chem. Rev., 108, 2348 (2008).
61] E.S. Wiedner, R.M. Bullock. J. Am. Chem. Soc., 138, 8309 (2016).
62] G.A.N. Felton, R.S. Glass, D.L. Lichtenberger, D.H. Evans. Inorg. Chem., 45, 9181
(2006).
[63] G. Singh Bindra, M. Schulz, A. Paul, R. Groarke, S. Soman, J.L. Inglis, W.R. Browne,
M.G. Pfeffer, S. Rau, B.J. MacLean, M.T. Pryce, J.G. Vos. Dalton Trans., 41, 13050
(2012).
[64] E.E. Benson, C.P. Kubiak, A.J. Sathrum, J.M. Smieja. Chem. Soc. Rev., 38, 89 (2009).
1
5

Figure 1. Electronic absorption spectra for 1 measured in dmf (solid line) and dmso (dotted line).
1
6

5
Figure 2. DFT energy level diagram for [Pd Cl ( -N ,N ,S,N ,N -dpktsc-H)]. HOMO and
2
3
py im
py am
LUMO levels are depicted together with their relative isosurfaces.
1
7

Figure 3. View of the molecular structure of 2. The thermal ellipsoids are drawn at the 30%
probability level.
1
8

a
b
Figure 4. Views of the hydrogen bonds in the extended structure of 2.
1
9

Figure 5. Cyclic voltammograms of 6 mM (1) (a): reductively initiated scans and (b): oxidatively
initiated scans) and 8 mM dpktsc (c) and (d) measured in dmf on a glassy carbon working
n
electrode (dia = 3.0 mm) vs Ag. Supporting electrolyte = 0.1 M [ Bu N]PF , scan rate =
4
6
-1
4
00 mV s .
2
0

Figure 6. Cyclic voltammogram of 5 mM (1) in dmf at a glassy carbon working electrode (dia =
.0 mm) vs Ag in the presence of p-TSOH: (a) 0 (b) 7.68 (c) 15.4 (d) 21.8 (e) 29.3, and
3
n
-1
(f) 39.8 mM. Supporting electrolyte = 0.1 M [ Bu N]PF , scan rate = 400 mV s .
4 6
2
1

Figure 7. Cyclic voltammograms of 6 mM (1) with reductively-initiated scans in dmf at a glassy
carbon working electrode (dia = 3.0 mm) vs Ag, (a) N (solid line) vs CO (broken line)
2
2
atmospheres, (b) reductively-initiated scan (solid line) vs oxidatively-initiated scan (broken line)
in N atmosphere, (c) N (solid line) vs CO and 15 L of H O (broken line) atmospheres (d) N
2
2
2
2
2
(
solid line) vs 14 mM p-TSOH and CO (broken line) atmospheres, and (e) N (solid line) vs
2
2
1
4 mM p-TSOH in N (broken line) atmospheres.
2
2
2

Table 1. Crystal data and structure refinement for 2.
5
Identification code
Empirical formula
Formula weight
[Pd Cl ( N ,N ,S,N ,N -dpktsc-H]·H O
2
3
py im
py am
2
C H Cl N Pd S
1
2
12
3
5
2
593.48
173(2)
0.71073
Temperature (K)
Wavelength (Å)
Crystal system, space group
Monoclinic, P2(1)/c
Unit cell dimensions
a (Å)
b (Å)
c (Å)
9.3239(9)
24.141(2)
8.3116(8)
105.4770(10)

()
Volume (Å3)
Z, Calculated density (g cm )
1803.0(3)
4, 2.186
-3
-1
Absorption coefficient (mm )
F(000)
2.565
1144
Crystal size (mm)
0.14 × 0.09 × 0.07
1.69 to 29.42

range for data collection ()
Range of h, k, l
−12/12, −32/31, −11/11
Reflections collected / unique
Completeness to  = 25.00 (%)
Absorption correction
16732 / 4603 [R(int) = 0.0462]
100
Multi-scan
0.8506
Ratio of minimum to maximum
Apparent transmission
Refinement method
Full-matrix least-squares on F2
4603 / 2 / 225
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2 (I)]
R indices (all data)
1.018
R
1
= 0.0319, wR = 0.0694
2
R = 0.0474, wR = 0.0754
1
2
−
3
Largest diff. peak and hole (eÅ )
CCDC no.
1.154 and –0.670
1544002
2
3

Table 2. Bond lengths [Å] and angles [°] for 2.
Bond lengths
Pd(1)-N(3)
Pd(1)-S(1)
Pd(2)-N(2)
Pd(2)-Cl(3)
S(1)-C(2)
1.962(3)
2.2612(11)
2.030(3)
2.2890(11)
1.739(4)
1.319(5)
1.373(4)
Pd(1)-N(1)
Pd(1)-Cl(1)
Pd(2)-N(4)
Pd(2)-Cl(2)
C(1)-N(3)
C(2)-N(4)
2.051(3)
2.3014(10)
2.056(3)
2.2966(10)
1.305(4)
1.358(5)
C(2)-N(5)
N(4)-N(3)
Bond angles
N(3)-Pd(1)-N(1)
N(1)-Pd(1)-S(1)
N(1)-Pd(1)-Cl(1)
N(2)-Pd(2)-N(4)
N(4)-Pd(2)-Cl(3)
N(4)-Pd(2)-Cl(2)
C(2)-S(1)-Pd(1)
C(2)-N(4)-Pd(2)
80.56(12)
165.87(8)
97.81(9)
84.63(12)
171.75(9)
92.95(9)
95.34(13)
124.7(2)
N(3)-Pd(1)-S(1)
N(3)-Pd(1)-Cl(1)
S(1)-Pd(1)-Cl(1)
N(2)-Pd(2)-Cl(3)
N(2)-Pd(2)-Cl(2)
Cl(3)-Pd(2)-Cl(2)
C(2)-N(4)-N(3)
N(3)-N(4)-Pd(2)
85.41(9)
178.33(9)
96.23(4)
92.57(10)
177.56(10)
89.87(4)
113.2(3)
110.9(2)
2
4

Table 3. Classical (H..A < r(A) + 2.000 Å and <DHA > 110°) , non-classical hydrogen
and non-covalent bonds (Å) and angles (°) for 2.
D-H…A
d(D-H)
d(H..A)
d(D..A)
<DHA
Classical hydrogen bonds
N5-H1A…Cl3#1
N5-H1B…O1#2
O1-H1OB…. Cl1#3
O1-H1OA…Cl2#4
O1-H1OA…Cl3#4
0.88
2.44
3.315(3)
2.759(5)
3.203(4)
3.216(4)
3.556(4)
171.4
0.88
1.90
163.1
0.85(2)
0.85(2)
0.85(2)
2.41(2)
2.58(4)
2.78(2)
156(4)
133(4)
152(4)
Non-classical hydrogen bonds
C11-H11…Cl1
C14-H14…Cl2#4
C22-H22…Cl1#5
C24-H24…O1#6
C12-H12…Cl2#3
0.95
0.95
0.95
0.95
0.95
2.89
2.74
2.66
2.59
2.94
3.448(5)
3.509(4)
3.551(4)
3.325(6)
3.867(4)
118.9
138.6
156.2
134.0
164.0
Non-covalent bonds
Pd1…Pd1#7
Pd1…Cl1#7
3.421
3.585
#
1
#2
Symmetry transformations used to generate equivalent atoms: x, -y+1/2, z-1/2; x+1,
#
3
#4
#5
#6
#7
y, z-1; -x+1, -y+1, -z+1; x-1, y, z; -x+1, y-1/2, -z+1/2; x, y, z-1; -x+1, -y+1, -z
2
5

Graphical abstract
2
6