Novel rhenium(V) nitride complexes with dithiocarbimate ligands – A synchrotron X-ray and DFT structural investigation

Article abstract of DOI:10.1016/j.ica.2017.11.023

The application of rhenium complexes as therapeutic agents in nuclear medicine has propelled research into the chemistry of these compounds. In our effort to develop and investigate new therapeutic radiopharmaceuticals based on the complexes of rhenium we

Full text of DOI:10.1016/j.ica.2017.11.023

Inorganica Chimica Acta 475 (2018) 142–149
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Inorganica Chimica Acta
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Novel rhenium(V) nitride complexes with dithiocarbimate ligands – A
synchrotron X-ray and DFT structural investigation
Joanne Perils a,b,1, Fernando Cortezon-Tamarit c,1, Navaratnarajah Kuganathan d,1, Gabriele Kociok-Köhn c,
Jonathan R. Dilworth b, , Sofia I. Pascu c,
⇑
⇑
a School of Chemistry, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg 3209, South Africa
b Department of Chemistry, University of Oxford, Chemistry Research Laboratory, South Parks Road, Oxford OX1 3TA, UK
c Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
d Department of Materials, Imperial College London, Royal School of Mines, Exhibition Road, London SW7 2AZ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 July 2017
Received in revised form 7 November 2017
Accepted 13 November 2017
Available online 21 November 2017
The application of rhenium complexes as therapeutic agents in nuclear medicine has propelled research
into the chemistry of these compounds. In our effort to develop and investigate new therapeutic radio-
pharmaceuticals based on the complexes of rhenium we have investigated the nitride core, [ReN]2+. This
work looks at the behavior of sulfonamide based dithiocarbimates towards the rhenium(V) nitride core.
The aim here was to prepare anionic complexes with aromatic as well as fluorescent aromatic groups in
the sulfonamide substituent located on the dithiocarbimate backbone. We envisaged that the polar sul-
fonamide and dianionic charge would confer solubility in water. Here we report the reactions of the
dithiocarbimate ligands towards the rhenium(V) precursors: [ReNCl2(PPh3)2] and [ReNCl2(PMe2Ph)3].
These reactions proceeded with bis-substitution by the dithiocarbimate ligand, resulting in the formation
of a dianionic rhenium(V) complex, of the type [ReN(S-S)2]2ꢀ, where (S-S) denotes the sulfonamide-
tagged dithiocarbimato unit. Spectroscopic characterization data, as well as the synchrotron X-ray
diffraction structure of the metal complex with the phenyl sulfonamide backbone shed light into the
structural features of this interesting class of ligands and opens up opportunities for further studies in
molecular imaging and therapeutic arenas.
This paper is dedicated to Professor Ionel
Haiduc on the occasion of his 80th birthday.
Keywords:
Rhenium(V) nitrides
Sulfonamide
Dithiocarbimates
Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
cancer patients [1]. The research area has been reviewed: the chap-
ters in Comprehensive Coordination Chemistry on Technetium by
Despite significant progress made in the development of diag-
nostic radioisotopes for medical imaging techniques such as single
photon emitted computed tomography (SPECT) or positron emis-
sion tomography (PET), the availability of therapeutic radioisotopes
with matching radiochemistry, half-lives and wide accessibility at
reasonable costs remains the holy-grail for applications in nuclear
medicine, particularly for oncology. The development of rhenium
compounds as therapeutic radiopharmaceuticals remains a matter
of interest for chemists and nuclear imaging specialists both in aca-
demic and in clinical settings.
Alberto [2] and Rhenium by Abram, [3] are detailed. Extensive
reviews have covered the recent chemistry aspects of both
186/188Re and 99mTc chemistry across a whole range of available
oxidation states and coordination numbers in aqueous and non-
aqueous media [4,5]. Our recent book Chapter also gives an over-
view of the development of the coordination chemistry of Tc and
Re relevant to nuclear medicine with an emphasis on key ligand
systems and imaging agents [4].
The strong
p-donating characteristics of the trianionic nitride-
group make a major contribution to the stability of high oxidation
state Tc and Re nitrides. The presence of an additional negative
charge on ‘‘nitride” compared to ‘‘oxo” opens up a series of com-
plexes with different co-ligands, or overall charges, to those of
the ubiquitous Re-oxo complexes. Tc or Re nitride syntheses were
first carried out by Chatt et al. who showed that [ReNCl2(PPh3)2]
and [ReNCl2(PMe2Ph)3] could be synthesized using hydrazine or
azide as the source of nitride [6,7]. This work was extended to
99Tc and 99mTc: Baldas and co-workers reported extensively on
To date, the most widespread use of rhenium complexes in
major clinical applications is that involving ReHEDP (hydrox-
yethane bisphosphonate) for uses in bone targeting in terminal
⇑
Corresponding authors.
E-mail addresses: jon.dilworth@chem.ox.ac.uk (J.R. Dilworth), s.pascu@bath.ac.
uk (S.I. Pascu).
1
These authors contributed equally to the work.
https://doi.org/10.1016/j.ica.2017.11.023
0020-1693/Ó 2017 Elsevier B.V. All rights reserved.

J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
143
nitride complexes and proposed that the nitride core could be used
in 99mTc based radiopharmaceuticals [8–14]. The paramagnetic Tc
(VI) species [TcNCl4]ꢀ emerges from the reaction between pertech-
netate and azide in acid solution. Its substitution and redox chem-
istry (by the same synthetic route) was applied to the synthesis of
[ReNCl4]ꢀ [15]. The coordination chemistries and spectroscopic
properties of the [TcN]2+ and [ReN]2+ cores were highlighted by
Abram et al. and some representative examples of this work are
shown in Fig. 1 (A–C) [16–18,15,19]. In the nitride complexes
research space, Duatti and co-workers showed that neutral dithio-
carbamato-Tc nitrides act as promising heart imaging agents. Par-
ticularly, the bis(N-ethoxy, N-ethyl dithiocarbamato)nitrido
technetium(V), TcNOET (Fig. 1, compound D) entered clinical trials
despite the fact that myocardial tissue retention remains unclear
[20–22].
A
B
Scheme 1. Proposed resonance forms for dithiocarbimate-based ligands.
The hydrazine derivative MeSCSNMeNH2 and its variants led to
the formation of both [TcN]2+ and [ReN]2+ cores directly from the
corresponding tetroxometallates in high yields [23,24]. No inter-
mediates could be isolated with the Tc core but the [ReO
(NHNMeCSSMe)2]+ species emerged from the reaction of [ReO4]ꢀ
with the N-methylated hydrazine in the presence of HCl, followed
by addition of a dithiocarbimate (dtc) to give [ReN(dtc)2] [25]. To
incorporate the nitride core, it is of interest to synthesize com-
plexes with a mixed ligand system analogous to a [3 + 2] systems,
which have been shown to be effective for oxo complexes. The
same approach for the nitrides gives mixtures of compounds, how-
ever, it has been shown that the stereochemistry and stoichiome-
try of the Tc or Re nitride cores can be controlled using
Scheme 2. General synthesis for dithiocarbimate ligands studied hereby.
the sulfonamide substituent. This will enable observation of the
behavior of these complexes at the cellular level. To date, the only
related rhenium compounds reported in the literature are neutral
and involve the diethyldithiocarbamate ligand [36,37].
A measure of water solubility is a prerequisite for metal com-
plexes to be used in biomedical applications. A commonly adopted
approach is to add polar groups containing carboxylate, hydroxy or
sulfonate groups to the ligand backbone. Here, we have adopted an
alternate approach by using sulfonyl substituted dithiocarbimate
ligands. Dithiocarbimate ligands have been relatively little studied
and there have been just a couple of X-ray structures reported of Re
complexes, readily prepared from sulfonamides and CS2 in the
presence of a base [38,39]. They have two possible resonance forms
as shown in Scheme 1. In form B, one negative charge resides on a
sulfonyl oxygen giving a charged group closely related to the sul-
fonic acids (RSOꢀ3 ). We anticipate that such complexes could be
water-soluble and this would be enhanced by a negative charge
on the complex.
tridentate SNS or PNP donors. In the case of PNP ligands, the
p-
acceptor P donors favor a trans geometry [26]. The halide ligands
are placed in a cis position and they can readily be substituted by
bidentate monoanionic or dianionic ligands [27]. This control level
can be achieved with bidentate nitrogen ligands (i.e. bipy, phenan-
throline) that allow the isolation of the cyanonitrido complexes
[28]. The use of bulky thiolate ligands demonstrated stabilizing
effect on the rhenium nitride, arylimido and nitrile cores [29].
The structure of the Re dichloride (compound E) and the catio-
nic dithiocarbamate derivative bis[(dimethoxypropylphosphanyl)
ethyl]ethoxyethylamine
N,N0-bis(ethoxyethyl)dithiocarbamato
The substituents on the sulfonyl backbone of the ligands, methyl,
phenyl, tolyl and naphthyl groups, have been carefully chosen in the
work reported hereby to improve kinetic stabilities and modulate
the lipophilicities. To enhance the understanding of the behavior
of these compounds in cells across a range of conditions and concen-
tration domains, a fluorescent ligand tag (e.g. naphthyl based) is
desirable as it would allow the monitoring of the in vitro behavior
of the compound. The design and synthesis of a series of ligands
and of their novel complexes are here reported. Currently there
are no reports in the literature regarding X-ray structures of Re com-
plexes with this ligand. New species were characterized in solution
and in the solid state, and their UV–Vis spectroscopy behavior in
solution was investigated. The fluorescence spectra of a new naph-
thyl-tagged ligand and investigations into its corresponding Re(V)
complex are also reported. A stability study of the tolyl complex,
[ReN(SDTC2)2]2ꢀ, in the presence of water over a period of 6 h was
also conducted showing promising kinetic stability compatible with
its intended pre-clinical aims. The complex proved to be stable in the
presence of H2O, with the UV–Vis spectra showing little change over
this period.
nitrido technetium(V), Tc-N-DBDOC (compound F which shows
promise as a cardiac imaging agent in vivo) are shown in Fig. 1
[30]. A choice of bidentate ligands with bioorthogonal functional-
ization can lead to conjugation to a range of biomolecules as well
as hig kinetic stabilities [31–35].
Rhenium has two beta-emitting radioisotopes, 186Re and 188Re,
and through careful ligand design these can be encapsulated and
then targeted to cancer cells where the beta-radiation emitted
destroys the cancer cells. Both of these species are reactor-produced
radioisotopes which are attractive for a variety of therapeutic appli-
cations. Thus far, Re-186 is unavailable from a generator system, and
must therefore be directly produced in a nuclear reactor. However,
Re-188 can be eluted as perrhenate from an alumina-based
188W/188Re generator, and although it has a much shorter half-life
of 16.9 h, this is still compatible with most in vivo imaging and ther-
apy requirements as it emits a beta-particle with a much higher
energy (2.12 MeV and a 155 keV gamma photon, 15%) which would
be also suitable for the coupled SPECT imaging.
To date, the majority of research into rhenium based therapeu-
tic agents design has centered around the rhenium(V) oxo core.
Our approach in this study was to investigate the coordination of
a series of sulfonyl-dithiocarbimate ligands to the rhenium(V)
nitride, [Re„N]2+ core. This work focuses on the synthesis and
coordination behavior of sulfonamide based dithiocarbimates
(Scheme 2, SDTC 1–4) towards the rhenium(V) nitride core. The
aim here is to functionalize the dithiocarbimate backbone by incor-
porating both fluorescent and non-fluorescent aromatic groups in
2. Results and discussions
The synthesis of the sulfonamide dithiocarbimate ligands was
adapted from literature procedures [36,37] and successfully
employed for all starting materials with alkylic and arylic back-
bones. The addition of carbon disulfide to the sulfonamides in a

144
J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
basic medium yielded the dianionic dithiocarbimate ligands as
potassium salts (Scheme 2).
[STDC1]2ꢀ and [ReN(STDC1)2]2ꢀ also support the assignments
made for the experimental IR spectra (ESI). The shapes and energies
for the frontier orbitals for the [STDC1]2ꢀ and [ReN(STDC1)2]2ꢀ
(DFT-calculated, Fig. 6) are also given. These are of interest to
explore in the context of the fact that UV–Vis spectroscopy of the
Re(V) compound could be observed experimentally and showed
strong absorption bands in the 250–350 nm region of the spec-
trum. Encouraged by these calculations the involvement of such
frontier orbitals in the transitions responsible for fluorescence
emission spectra was also evaluated. Whilst for the simple com-
plexes bearing the [SDTC1]–[SDTC3] anionic ligands the fluores-
cence was rather weak, the fluorescence emission spectrum of
the potassium salt of the SDTC4 free ligand was observed (Fig. 2
and ESI). Interestingly, the fluorescence emission quenching upon
metallation with Re(V) and the formation of the [ReN(SDTC4)2]2ꢀ
complex dianion occurred in CH3CN solutions (ESI). This loss of flu-
orescence emission may well be as a result of non-radiative path-
ways due to the dynamic equilibria between canonical forms A/B
(shown in Scheme 1) of the coordinating ligand becoming involved
in solutions. Also, the presence of traces of paramagnetic rhenium
species forming in aerated solution during the analysis could not
be fully discounted at first, therefore the kinetic stability tests in
aqueous environment were carried out: spectroscopic evaluations
of compounds of this class showed a remarkable kinetic stability in
water media (Fig. 3B). The complex [ReN(SDTC2)2]2ꢀ proved to be
stable in CH3CN:H2O with the UV–Vis spectra showing little
change over this period. Taking the shape and energies of
HOMO-LUMO calculated by DFT for SDTC1 and [ReN(SDTC1)2]2ꢀ
in the simplified gas phase models (using a wide variety of basis
sets and conditions, ESI), it is feasible to assume that these frontiers
orbitals are involved in the observed electronic absorption bands
and in the occurrence of fluorescence [51]. The higher energy gap
between the HOMO and LUMO orbitals in the complex compared
to the ligand can indicate that the metal-to-ligand charge transfer
associated to the fluorescence process is not as favored resulting
in a quenching of the fluorescence intensity. Furthermore, the stabil-
ity study of the tolyl complex, [ReN(SDTC2)2]2ꢀ monitored in an
organic solvent (CH3CN) in the presence of water over a period of
6 h was also conducted showing promising kinetic stability compat-
ible with its intended pre-clinical aims. Longer term we are inter-
ested in setting the foundations for the Re(V) radiochemistry
labelling which requires aqueous conditions. As such, prior to
engaging in extensive ‘hot’ experiments using 186/188Re we have
been establishing the ‘cold’ chemistry protocols hereby, and fluores-
cence spectroscopy proved to be a helpful tool in assessing the nec-
essary compatibility and kinetic stability in aqueous solutions.
A significant fluorescence emission was observed for the dian-
ionic ligand with the naphthyl backbone (denoted SDTC4) with
excitation and emission in the UV region of the spectrum (Fig. 1).
Interestingly, the excitation and emission spectra also showed
peaks of lower intensity in the NIR region (650–700 nm). The fluo-
rescence emission in this region is especially attractive for biomed-
ical imaging as interference from tissue autofluorescence in vitro
and in vivo substantially decreases in the NIR.
The reaction of the ligands with rhenium nitride precursors
results in bis-substitution of the dithiocarbimate ligand, and in
the formation of a dianionic rhenium(V) complex of the type
[ReN(SS)2]2ꢀ (Scheme 3).
The desired complexes featuring the [ReN]2+ (Re(V)) core were
obtained either from the [ReNCl2(PPh3)2] or [ReNCl2(PPhMe2)3]
by refluxing in methanol with the ligands and adding PPh4Br to
generate the counter-ion. The negative ESI TOF mass spectra
obtained for the [ReN(SDTC3)2]2ꢀ complex show peaks for the pro-
tonated complex, [M+H]ꢀ, but also for the dianionic species, m/z
corresponding to [M]2ꢀ. The ESI TOF results obtained for the com-
plex [ReN(SDTC4)2]2ꢀ, however, only showed the dianionic species
[M]2ꢀ (see ESI).
Furthermore, the UV–vis spectra of the prepared rhenium com-
plexes are summarized in Fig. 3(A) as well as the corresponding
stability test in aqueous media for [ReN(SDTC4)2][PPh4]2 is given
in Fig. 3(B). The absorption maxima is maintained at ca. 270–
280 nm and in the case of SDTC4, the bands above 300 nm are
not observed in the complex.
Interestingly, a search in the literature confirmed that the
reported X-ray crystal structures for rhenium nitride complexes
with bidentate S-donor ligands are scarce (vide infra). Among these,
only a handful display a square pyramidal geometry like the com-
pounds described herein. Other examples including those with
additional phosphine ligands and adopting a pseudo-octahedral
geometry [40–42] or multimetallic complexes [43–49] are outside
the scope of this discussion and consequently not included here.
The closest examples to the complexes prepared in this work
are depicted in Fig. 4. In all examples, the Re-N nitride distances
are practically identical while the Re-S distances vary more with
the type of ligands. The dithiolate derivative, II [15], presents the
shorter Re-S distances followed by the complexes containing
dithiocarbimate ligands, I [50] and [ReN(SDTC1)2][PPh4]2. The
longer distances found are consistent with the likely occurrence
of the canonical form B in Scheme 1. The complex with dithioimi-
dophosphinato ligands, IV [19], presents the longest Re-S distances
with values around 2.4 Å (Fig. 4). The ORTEP representation of the
[ReN(SDTC1)2][PPh4]2 complex acquired using synchrotron X-ray
radiation is represented in Fig. 5 and a summary of the most rep-
resentative structural parameters is listed in Table 1.
3. Conclusions and outlook
Additionally we carried out investigation by DFT calculations on
the binding of the anionic ligands to the [ReN]2+ core. For the
model ligand SDTC1, and the corresponding dianionic complex,
gas phase DFT optimizations using a variety of basis sets under
Gaussian platforms were employed. In each case, as expected for
these bonding models, there are delocalized bonding throughout
which appeared to be favored for both the experimental structure
and the model compounds. The optimized (Fig. 6, Table 2 and ESI)
geometries are in agreement with the findings from X-ray diffrac-
tion studies on [ReN(SDTC1)2][PPh4]2 and other literature data
[15,19,50] and Figs. 4 and 5.
Key structural data for the experimental structure, species mod-
elled as well as the partial charge distributions estimated are also
given in the Supporting Information.
Molecular parameters are in agreement with those resulting
from the X-ray structural data and the calculated IR spectra
The synthesis of new ligands and their [ReN]2+ core-tagged
complexes was described herein. The characterization data in solu-
tion and in the solid state as well as the crystal structure of the
metal complex [ReN(SDTC1)2](PPh4)2 are given. This compound is
representative of the series and incorporates the phenyl sulfon-
amide backbone: its geometry was discussed and compared to
DFT level gas-phase calculations. Additional highlights are the fact
that the free dianionic ligand SDTC4 isolated as a potassium salt is
fluorescent in wet solvents, however, it is clear that quenching has
taken place upon its coordination to the Re(V) centre. New coordi-
nation chemistry of Re(V) in wet organic solvents was developed
hereby and opens up the possibility of generating complexes
including the [S(O)2N] moiety known for playing a role in the
selective reductive trapping of related compounds in hypoxic cells
and tissues: further work in this context is currently in progress in
our laboratories.

J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
145
Fig. 1. Representative examples of complexes exhibiting TcN and ReN cores.
Scheme 3. General procedure for the preparation of [ReN(SDTC)2][PPh4]2 complexes anions. The two [PPh4]+ counterions were omitted in the scheme shown above.
1.2
Emission (exc = 287 nm)
Excitation (em = 352 nm)
1
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 2. Normalized excitation (black line) and emission (orange line) spectra of compound [SDTC4]K2 in CH3CN/H2O. (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
4.1. General procedure for sulfonamide dithiocarbimate synthesis
4. Experimental section
Ligands SDTC1 to SDTC4 as dipotassium salts were prepared fol-
lowing literature procedures [36,37]. Generally, carbon disulfide
(1 eq.) and KOH (1 eq.) were added to the sulfonamide starting
material (1 eq.) dissolved in DMF. The reaction was stirred at 0 °C
for 2 h and a second equivalent of KOH added and the mixture
The rhenium precursors [ReNCl2(PPh3)2], and [ReNCl2(PMe2-
Ph)3] were prepared according to literature procedures [7,52].
These complexes were fully characterized and used in further reac-
tions to give the desired metallic sulfonamide-based
dithiocarbimates.

146
J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
B)
A)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.9
0.25 h
0.5 h
1 h
2 h
4 h
ReN(SDTC1)
ReN(SDTC2)
0.8
ReN(SDTC3)
ReN(SDTC4)
0.7
6 h
0.6
0.5
0.4
240
290
340
390
440
490
250
275
300
Wavelength (nm)
Wavelength (nm)
Fig. 3. A) UV–vis spectra of Re nitride complexes in CH3CN (10 mM conc); B) Stability tests of [ReN(SDTC2)2][PPh4]2 by UV–Vis spectroscopy in aqueous CH3CN (ca. 1:1
CH3CN:H2O, 10 mM).
Fig. 4. Distances (Å) and angles (italics, °) of ReN complexes including S donor ligands in a square pyramidal geometry. Hydrogen atoms have been omitted for clarity.
further stirred for 1 h. The removal of the solvent resulted in the
precipitation of the dithiocarbimate salts as pale yellow solids.
Dipotassium (phenylsulfonyl)carbonimidodithioate (SDTC1):
Yield: 51%. Anal. Calc. for C7H5S3O2NK2ꢁ2H2O: C, 24.3; H, 2.6, N,
4.0%. Found: C, 24.1; H, 2.4; N, 3.9%. 1H NMR (d6-DMSO): d 7.28–
2.4; N, 3.7%. Found: C, 34.5; H, 2.6; N, 3.3%. 1H NMR (d6-DMSO):
d 8.40 (s, 1H), 8.15–8.04 (m, 2H), 8.01 (d, J = 7.5 Hz, 1H), 7.88 (d,
J = 8.6 Hz, 1H), 7.71–7.59 (m, 2H). IR (cmꢀ1): 1273 (
mCN), 1264
(mSO2ass), 1144 (mSO2sym), 971 (mCS2).
7.34 (m, 3H); 7.65–7.72 (m, 2H). IR (cmꢀ1): 1263 (
SO2ass); 1132 ( SO2sym); 978 ( CS2).
Dipotassium (tosyl)carbonimidodithioate (SDTC2): Yield:
mCN); 1253
(m
m
m
4.2. General procedure for the synthesis of sulfonamide
dithiocarbimate rhenium nitride complexes
94%. Anal. Calc. for C8H7S3O2NK2ꢁ3H2O: C, 25.4; H, 3.5; N, 3.7%.
Found: C, 25.1; H, 2.9; N, 3.7%. 1H NMR (d6-DMSO): d 7.57 (d, J =
8.0 Hz, 2H); 7.06 (d, J = 8.0 Hz, 2H); 2.26 (s, CH3). IR (cmꢀ1): 1267
ReNCl2(PPh3)2 (0.120 g, 0.151 mmol) was added to [SDTC1]K2
(0.164 g, 0.530 mmol) in methanol (50 mL) and the resulting solu-
tion was heated under reflux for a period of 4 h. To the orange/
brown solution obtained, PPh4Br (0.128 g, 0.305 mmol) was added
in 3 mL of methanol. The solution was filtered, the solvent
removed under vacuum, and the residue re-dissolved in 25 mL of
dichloromethane. This solution was washed with H2O and the
organic layer dried over MgSO4. The addition of an excess of diethyl
(
m
CN); 1256 (
Dipotassium (methyl)carbonimidodithioate (SDTC3): Yield:
60%. 1H NMR (d6-DMSO): d 2.98 (s, 3H). IR (cmꢀ1): 1287 (
CN);
1265 ( SO2ass); 1187 ( SO2sym); 960 ( CS2).
Dipotassium (naphthylsulfonyl)carbonimidodithioate
(SDTC4): Yield 83%. Anal. Calc. for C11H7S3O2NK2ꢁH2O: C, 35.0; H,
mSO2ass); 1136 (mSO2sym); 973 (mCS2).
m
m
m
m

J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
147
Fig. 5. Synchrotron X-ray diffraction data (k = 0.69110 Å); molecular structure of complex [ReN(SDTC1)]2 [PPh4]2. Ellipsoids shown at the 50% level. PPh+4 counter-cations and
hydrogen atoms have been omitted for clarity.
Table 1
for C62H50S6O4P2N3Re: C, 55.5; H, 3.8; N, 3.1. Found: C, 55.2; H,
3.8; N, 3.1%.
Selected bond lengths and angles for the complex [ReN(SDTC1)2][PPh4]2.
Alternatively, this rhenium complex was prepared starting from
ReNCl2(PMe2Ph)3 precursor and following the same experimental
protocol. The same product was obtained. Yield: 90%. Anal. Calc.
for C62H50S6O4P2N3ReꢁH2O: C, 54.8; H, 3.9; N, 3.1%. Found: C,
54.4; H, 3.8; N, 3.0%.
[ReN(SDTC2)2](PPh4)2: The complex was prepared following
the general procedure, from ReNCl2(PPh3)2, yield: 57%. From
ReNCl2(PMe2Ph)3, yield: 45%. Anal. Calc. for C64H54S6O4P2N3Re: C,
56.1; H, 4.0; N, 3.1. Found: C, 56.3; H, 3.9; N, 2.8%.
[ReN(SDTC3)2](PPh4)2: The complex was prepared following
the general procedure from ReNCl2(PPh3)2, yield: 57%. From
ReNCl2(PMe2Ph)3, yield: 45%. Anal. Calc. for C52H46S6O4P2N3-
Reꢁ4H2O: C, 48.4; H, 4.2; N, 3.3; S, 14.9%. Found: C, 48.1; H, 3.9;
N, 3.6; S, 15.2%.
Bond
Bond length (Å)
Angle
Bond angles (°)
Re1-N1
Re1-S1
Re1-S2
Re1-S4
Re1-S5
N2-C1
N3-C8
S1-C1
1.655(5)
2.373(1)
2.393(1)
2.368(1)
2.393(1)
1.282(6)
1.280(6)
1.750(5)
1.758(4)
1.754(5)
1.764(4)
N1-Re1-S1
N1-Re1-S2
N1-Re1-S4
N1-Re1-S5
S1-Re1-S2
S4-Re1-S5
S2-Re1-S4
S1-Re1-S5
S1-C1-S2
108.2(2)
108.4(2)
106.1(2)
105.4(2)
72.86(4)
72.98(4)
145.48(5)
146.27(5)
107.5(3)
107.2(3)
121.5(4)
121.9(4)
S2-C1
S4-C8
S5-C8
S4-C8-S5
C1-N2-S3
C8-N3-S6
ether yielded yellow precipitates, which in each case was washed
with diethyl ether and dried under vacuum.
[ReN(SDTC4)2](PPh4)2 complex was isolated in a yield lower
than 10% and characterized by mass spectrometry, IR, UV–Vis
and fluorescence spectroscopies.
[ReN(SDTC1)2](PPh4)2: The complex was prepared following
the general procedure from ReNCl2(PPh3)2, yield: 45%. Anal. Calc.
4.3. Crystal structure determination
Crystals suitable for X-ray crystallography were obtained from
the slow evaporation of a methanol solution of the complex at
room temperature. The crystals were isolated by filtration, and a
(a)
HOMO
HOMO
419.63 kJ/mol
156.69 kJ/mol
LUMO
LUMO
462.96 kJ/mol
269.82 kJ/mol
(b)
Fig. 6. DFT calculated energies and shapes of selected frontier orbitals (HOMO and LUMO) for (a) [(SDTC1)]2ꢀ and (b) [ReN(SDTC1)2]2ꢀ. Additional frontiers orbitals and their
energies are given in ESI. Structures optimized in the gas phase using the exchange correlation functional PBEPBE LANL2TZ/631G** basis set.

148
J. Perils et al. / Inorganica Chimica Acta 475 (2018) 142–149
Table 2
DFT Calculated bond lengths and angles for the anion complex [ReN(SDTC1)2]2ꢀ using the PBEPBE exchange correlation function and two different basis sets. Additional
conditions surveyed are given in ESI.
Bond
Bond length (Å)
Angle
Bond angles (°)
LANL2TZ/6-31G**
aug-cc-PVTZ pp/6-31G**
LANL2TZ/6-31G**
aug-cc-PVTZ pp/6-31G**
Re1-N1
Re1-S1
Re1-S2
Re1-S4
Re1-S5
N2-C1
N3-C8
S1-C1
1.669
2.421
2.426
2.424
2.419
1.324
1.323
1.775
1.771
1.772
1.776
1.665
2.411
2.415
2.417
2.412
1.325
1.325
1.774
1.769
1.769
1.774
N1-Re1-S1
N1-Re1-S2
N1-Re1-S4
N1-Re1-S5
S1-Re1-S2
S4-Re1-S5
S2-Re1-S4
S1-Re1-S5
S1-C1-S2
107.17
106.74
106.88
107.20
72.62
107.32
106.95
106.82
107.32
72.65
72.67
72.63
146.38
145.62
108.08
107.94
123.38
146.24
145.35
107.65
107.65
122.80
S2-C1
S4-C8
S5-C8
S4-C8-S5
C1-N2-S3
specimen crystal was selected under an inert atmosphere, covered
with polyfluoroether and mounted on the end of a glass fibre.
Crystallographic data for [ReN(SDTC1)2](PPh4)2 were collected
at the SRS Daresbury Radiation Source. The crystal structure was
deposited at the Cambridge Crystallographic Data Centre. The data
have been assigned to the deposition numbers: CCDC 1561939
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Acknowledgements
STFC is thanked for funding this work via access to synchrotron
facilities. Dr John Warren is thanked for assistance with data col-
lection. Mass spectrometry EPSRC service at Swansea is thanked
for support, as is the Imperial College EPSRC Supercomputing Facil-
ity. The ERC Consolidator Grant O2Sense to S.I.P. and EPSRC CDT
and CSCT Centre at Bath University are thanked for financial
support.
The asymmetric unit consists of 1.5 Re-complex molecules and
three PPh+4 cationic species as counterions. One generally well-
ordered formula unit is 2(C24H20P)(C14H10 N3O4ReS6). The Re com-
plex with Re2 (as labelled) centre is located on a special position (a
centre of inversion), with Re2 and N2 disordered over two sites
which were refined with 50% occupation. One tosyl-group in the
complex (bound to Re1) shows disorder over two sites in the ratio
54:46. Three out of four phenyl groups attached to P3 are disor-
dered over two sites and were modelled with geometric
constraints.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at https://doi.org/10.1016/j.ica.2017.11.023.
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