Syntheses and reactivity of 'sulfur rich' Re(III) and Tc(III) complexes containing trithioperoxybenzoate, dithiobenzoate and dithiocarbamate ligands

Article abstract of DOI:10.1039/b503938j

Reduction-substitution reactions of [M(O)C1₄]^- (M = Re, ⁹⁹Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS₂)^- in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M^III(R-PhCS₃)₂(R-PhCS₂) (M = Re; Re1-9; M = ⁹⁹Tc; Tc1-9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS₃)₂(4-Me-PhCS₂), Re2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d⁴ trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(V) to Re(III and oxidation of dithiobenzoate to trithioperoxybenzoate. M2-9 complexes contain a substitution-inert [M(R-PhCS₃)₂] ⁺ moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M ^III(R-PhCS₃)₂(Et₂NCS₂) (M = Re; Re10-18; M = ⁹⁹Tc; Tc10-18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS₃)₂(Et₂NCS₂), Re10 and ⁹⁹Tc(PhCS₃)₂(Et₂NCS ₂), Tc10. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503938j

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F U L L P A P E R
Syntheses and reactivity of ‘sulfur rich’ Re(III) and Tc(III)
complexes containing trithioperoxybenzoate, dithiobenzoate
and dithiocarbamate ligands
Nicolas Lepareur,a Franck Me´vellec,a Nicolas Noiret,a Fiorenzo Refosco,b Francesco Tisato,*b
Marina Porchiab and Giuliano Bandolic
a Ecole Nationale Supe´rieure de Chimie de Rennes, UMR CNRS 6052, Synthe`ses et Activations
de Biomole´cules, Institut de Chimie de Rennes, Rennes, France.
E-mail: nicolas.noiret@ensc-rennes.fr
b ICIS-CNR, C-so Stati Uniti 4, 35127, Padova, Italy. E-mail: tisato@icis.cnr.it
c Dipartimento di Scienze Farmaceutiche, Universita` di Padova, Via Marzolo 5, 35131, Padova,
Italy. E-mail: giuliano.bandoli@unipd.it
Received 18th March 2005, Accepted 30th June 2005
First published as an Advance Article on the web 19th July 2005
Reduction–substitution reactions of [M(O)Cl4]− (M = Re, 99Tc) precursors with an excess of substituted
dithiobenzoate ligands (R-PhCS2)− in dichloromethane/methanol mixtures afford a series of six-coordinated neutral
mixed-ligand complexes of the type MIII(R-PhCS3)2(R-PhCS2) (M = Re; Re1–9; M = 99Tc; Tc1–9). The coordination
sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement,
as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS3)2(4-Me-PhCS2), Re2. These compounds show
sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d4 trigonal prismatic
configurations. The red-ox processes involve reduction of the metal from Re(V) to Re(III) and oxidation of
dithiobenzoate to trithioperoxybenzoate. M2–9 complexes contain a substitution-inert [M(R-PhCS3)2]+ moiety
including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The
latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class
of mixed ligand complexes of the type MIII(R-PhCS3)2(Et2NCS2) (M = Re; Re10–18; M = 99Tc; Tc10–18), which
retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds
Re(PhCS3)2(Et2NCS2), Re10 and 99Tc(PhCS3)2(Et2NCS2), Tc10.
induced oxidation of the ligand and formation of sulfur enriched
Introduction
trithioperoxybenzoate (PhCS3)− adducts. The resulting six-
188Re (t1 = 17 h; Ebmax = 2.1 MeV) offers advantageous
coordinated neutral compound M(PhCS3)2(PhCS2) contain two
2
nuclear properties for targeted radiotherapy.1 The chemical
similarity with its second-row congener technetium2 allows one
to take advantage of the huge efforts made in the last two
decades in diagnosis with 99mTc, and to try to transfer this
knowledge straight to rhenium based therapeutic analogues. In
this connection, a step ahead has been recently provided by the
introduction of 188W/188Re generators,3 theoretically identical
to the widely used 99Mo/99mTc generators, which ensure the
availability of carrier free amounts of [188ReO4]− for research
purposes and preliminary phases of clinical trials.
oxidised dithiobenzoate and one dithiobenzoate unit.8,9
Preparation of the above mentioned ‘sulfur rich’ complexes
at carrier free level starting from generator eluted [99mTcO4]−
and [188ReO4]− confirmed the possibility of stabilising M(III)
ions in extremely dilute conditions.10 The concomitant pres-
ence of several sulfur atoms and phenyl groups imparts a
lipophilic character to these molecules, a property which can
be profitably used for applications in nuclear medicine. For
example, M(PhCS3)2(PhCS2) (M = 99mTc, 188Re) was recently
investigated for the treatment of hepatocellular carcinoma in
animal models. Indeed, this ‘sulfur rich’ radiopharmaceutical
is able to label efficiently lipiodol, and the resulting mixture
has shown elevated uptake and retention in the hepatic tissue
of animal models.11 Moreover, with the aim of finding suitable
radiopharmaceuticals in the differentiation of infection versus
inflammation, 99mTc(PhCS3)2(PhCS2) complexes have shown
high yield and selective in vitro labelling of lymphocytes in whole
blood.12
The promising biological properties of M(PhCS3)2(PhCS2)
agents prompted us to prepare a series of related M(III)
complexes to validate the surprising synthetic pathway which
resulted in the mixed bis-trithioperoxybenzoate dithiobenzoato
coordination sphere. In addition, possible fine tuning of the
lipophilic–hydrophilic balance of the resulting complexes might
eventually improve their biological properties. Hence, we have
prepared a series of substituted dithiobenzoato compounds of
general formula M(R-PhCS3)2(R-PhCS2), M2–9, and charac-
terised them both in the solid state and in solution by con-
ventional physicochemical techniques. All of these compounds,
Most of the rhenium based therapeutic agents proposed so
far comprise the monooxo-Re(V) core surrounded by a series of
tetra-dentate ligands including N2S2-diamino-dithiolate, N2S2-
diamido-dithiolate, N3S-triamido-monothiolate frameworks, or
by bis-bidentate S2-dimercaptosuccinate chelates.1,4,5 More re-
cently, examples of low valent Re(I) species based on the
organometallic [188Re(CO)3]+ moiety and bifunctional ligand
systems comprising bis[imidazol-2-yl]methylamine or iminodi-
acetic acid conjugates have been proposed for the labelling of
biomolecules with high specific activity.6
In this context, much less explored so far is the possibility
of stabilising 188Re agents having the metal in intermediate
oxidation states. Only very recently, sulfur donor ligands in-
cluding tris(2-mercaptoethyl)amine7 or dithiobenzoates8 have
proven to be efficient chelates to seek Re(III) and Tc(III) ions. The
former tripodal ligand is utilised in conjunction with isocyanides
or monophosphines to stabilise the so called ‘4 + 1’ system
in a trigonal bipyramidal arrangement,7 and dithiobenzoates
(PhCS2)− give unexpected mixed ligand complexes after metal
2 8 6 6
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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including the unsubstituted analogs M(PhCS3)2(PhCS2), M1,
undergo substitution of the unique dithiobenzoate for dithiocar-
bamate without affecting the geometry of the substitution-inert
[M(R-PhCS3)2]+ moieties. Hence, an additional series of mixed
bis-trithioperoxybenzoate dithiocarbamate complexes M(R-
PhCS3)2(Et2NCS2), M10–18, have been prepared and X-ray au-
thenticated. The effect of the various substituents incorporated
in the aromatic ring has been analysed by means of several
techniques including cyclovoltammetry, UV-vis and NMR spec-
troscopy. Kinetic and thermodynamic stability measurements in
biological media of selected compounds are in progress.
Re(4-MePhCS3)2(4-MePhCS2) (Re2). Yield 53% (0.068 g).
Elemental analysis: molecular formula C24H21S8Re. Found:
%C = 38.83, %H = 2.76, %S = 34.05; Calc. for [Re(4-
MePhCS3)2(4-MePhCS2)]: %C = 38.33, %H = 2.81, %S = 34.10.
Mp = 168 ◦C. Rf (PE/CH2Cl2 7/3) = 0.79. IR (KBr disk) (cm−1):
1598 (s), 1501 (w), 1408 (w), 1309 (m), 1262 (s), 1220 (w), 1179
(s), 1096 (s), 1015 (s, mC–S), 950 (m), 910 (w), 879 (w), 812 (s), 706
(w), 544 (m, mS–S), 447 (m), 399 (m, mRe–S ). 1H NMR (400.13 MHz,
CDCl3, SiMe4): dH 2.42 (s, 3H, CH3), 2.59 (s, 6H, CH3), 7.15 (d,
J = 8.4 Hz, 2H, Haromatic), 7.30 (d, J = 8.4 Hz, 4H, Haromatic),
7.59 (d, J = 8.1 Hz, 2H, Haromatic), 7.94 (d, J = 8.1 Hz, 4H,
Haromatic). 13C NMR (100.67 MHz, CDCl3, SiMe4): dC 21.6 and
30.10 (OCH3), 125.2 128.6 129.3 and 132.3 (CHaromatic), 133.0
and 141.2 (C–CH3), 144.5 (C–CS3), 144.9 (C–CS2), 234.2 (CS3),
238.6 (CS2).
Experimental
CAUTION! 99Tc is a weak b-emitter (Eb = 0.292 MeV, t1/2
=
2.12 × 105 years). All manipulations were carried out in lab-
oratories approved for low-level radioactivity using monitored
hoods and glove-boxes. When handled in milligram amounts,
99Tc does not present a serious health hazard since common lab-
oratory glassware provides adequate shielding. Bremsstrahlung
is not a significant problem due to the low-energy of the b-
particles. However, normal radiation safety procedures must
be used at all times, especially with solid samples, to prevent
contamination and inhalation.
Re(4-EtPhCS3)2(4-EtPhCS2) (Re3). Yield 70% (0.095 g). El-
emental analysis: molecular formula C27H27S8Re. Found: %C =
40.83, %H = 3.43, %S = 32.05; Calc. for [Re(4-EtPhCS3)2(4-
EtPhCS2)]: %C = 40.84, %H = 3.43, %S = 32.30. Mp = 164 ◦C.
Rf (PE/CH2Cl2 7/3) = 0.76. IR (KBr disk) (cm−1): 1595 (s), 1449
(w), 1413 (w), 1273 (m), 1240 (s), 1179 (s), 1054 (m), 1008 (s, mC–S),
964 (s), 905 (s), 832 (s), 768 (w), 593 (w), 561 (m, mS–S), 465 (w),
438 (w), 408 (w), 385 (m, mRe–S ). 1H NMR (400.13 MHz, CDCl3,
SiMe4): dH 1.20 (t, J = 7.6 Hz, 3H, CH3), 1.28 (t, J = 7.6 Hz, 6H,
CH3), 2.70 (q, J = 7.4 Hz, 2H, CH2), 2.84 (q, J = 7.6 Hz, 4H,
CH2), 7.18 (d, J = 8.4 Hz, 2H, Haromatic), 7.32 (d, J = 8.4 Hz, 4H,
Haromatic), 7.61 (d, J = 8.4 Hz, 2H, Haromatic), 7.96 (d, J = 8.1 Hz,
4H, Haromatic). 13C NMR (100.67 MHz, CDCl3, SiMe4): dC 14.2
and 16.1 (CH3), 28.9 and 29.2 (CH2),125.3 127.4 128.1 and 132.4
(CHaromatic), 133.2 141.4 150.7 and 151.0 (Caromatic), 234.2 (CS3),
238.5 (CS2).
Dichloromethane and petroleum ether (PE) (bp 30–60 ◦C)
were purified according to the methods reported in the
literature.13 Methanol was used as received. Diethyldithiocarba-
mate sodium salt (Nadedc) was purchased from Aldrich (Saint
Quentin Fallavier, France). Dithiobenzoate sodium (Nadtb)
or piperidinium (Pipdtb) salts were prepared as described
previously.14 [ReOCl4][NBu4]15 and [99TcOCl4][NBu4]16 were syn-
thesised according to literature methods.
Re(2-EtPhCS3)2(2-EtPhCS2) (Re4). Yield 62% (0.084 g). El-
emental analysis: molecular formula C27H27S8Re. Found: %C =
40.81, %H = 3.43, %S = 31.95; Calc. for [Re(2-EtPhCS3)2(2-
EtPhCS2)]: %C = 40.84, %H = 3.43, %S = 32.30. Mp = 170 ◦C.
Rf (PE/CH2Cl2 7/3) = 0.70. IR (KBr disk) (cm−1): 1476 (m),
1458 (m), 1441 (s), 1371 (w), 1259 (w), 1190 (w), 1160 (w), 1119
(w), 1057 (w), 1000 (s, mC–S), 943 (m), 913 (w), 751 (s), 544 (s,
Carbon, hydrogen and oxygen analysis were performed by
I.C.S.N. (Gif sur Yvette, France) on a Carlo Erba elemental anal-
yser Model-1106 or by C.R.M.P.O (Rennes, France) on a Ther-
moFinnigan elemental analyser Flash EA1112 CHNS/O. FT
IR spectra were recorded on a Nicolet 510P Fourier-transform
spectrometer in the range 4000–400 cm−1 in KBr mixtures
using a Spectra-Tech diffuse-reflectance collector accessory for
technetium compounds or on a Mattson 3030 Fourier-transform
spectrometer in the range 4000–400 cm−1 in KBr pellets for
1
mS–S), 454 (m), 399 (m, mRe–S ). H NMR (400.13 MHz, CDCl3,
SiMe4): dH 1.19 (t, J = 7.5 Hz, 3H, CH3), 1.24 (t, J = 7.5 Hz,
6H, CH3), 2.77 (q, J = 7.6 Hz, 2H, CH2), 3.00 (q, J = 7.5 Hz, 4H,
CH2), 7.19 (m, 2H, Haromatic), 7.25 (m, 2H, Haromatic), 7.36 (m, 4H,
Haromatic), 7.44 (m, 4H, Haromatic). 13C NMR (100.67 MHz, CDCl3,
SiMe4): dC 16.2 (CH3), 26.8 (CH2), 125.4 128.4 129.7 131.4 125.7
129.1 130.9 and 131.8 (CHaromatic), 134.0 141.7 143.9 and 145.5
(Caromatic), 235.4 (CS3), 243.9 (CS2).
1
rhenium compounds. H and 13C NMR spectra were collected
in CDCl3 on a BRUKER ARX 400 (rhenium compounds)
and on a BRUKER AC 300 (technetium compounds), using
SiMe4 as internal reference. Cyclic voltammetry measurements
were performed on a BAS (Bioanalytical System Inc.) CV-
1B cyclic voltammograph at 293 K under an atmosphere
of nitrogen by using a conventional three-electrode cell. A
platinum-disk electrode (area ca. 10−3 cm2) was used as the
working electrode, a platinum wire as the counter electrode,
and a silver wire as a quasi-reference electrode. Controlled
potential coulometries were performed using an Amel model
721 integrator, in an H-shaped cell containing, in arm 1, a
platinum gauze working electrode and an Ag/Ag+ reference
isolated inside a salt bridge by a medium-glass frit and, in arm
2, an auxiliary platinum-foil electrode. The UV-Vis spectra were
recorded in dichloromethane on a Spectronic Unicam UV500
UV-Visible spectrometer equipped with Vision 32 software.
Spectra were recorded in the region from 190 to 780 nm using
10−4 to 10−6 M solutions. The magnitude of the absorption
coefficients was between 103 and 105 cm−1 M−1. UV-vis data of
bis-trithioperoxybenzoate dithiobenzoate complexes have been
analysed in detail in a separate contribution.17 Thin layer chro-
matography was performed on silica gel F254S plates (Merck).
Re(4-MeOPhCS3)2(4-MeOPhCS2)
(Re5). Yield
54%
(0.074 g). Elemental analysis: molecular formula C24H21O3S8Re.
Found: %C = 36.03, %H = 2.64, %S = 31.96; Calc. for
[Re(4-MeOPhCS3)2(4-MeOPhCS2)]: %C = 36.03, %H = 2.65,
%S = 32.06. Mp = 170 ◦C. Rf (PE/CH2Cl2 7/3) = 0.25. IR
(KBr disk) (cm−1): 1592 (s), 1564 (w), 1501 (m), 1452 (w), 1305
(m), 1259 (s), 1169 (s), 1116 (w), 1027 (s, mC–S), 992 (w), 948 (w),
912 (w), 883 (w), 827 (s), 805 (w), 733 (w), 631 (w), 593 (m, mS–S),
545 (w), 398 (m, mRe–S ). 1H NMR (400.13 MHz, CDCl3, SiMe4):
dH 3.83 (s, 3H, OCH3), 3.92 (s, 6H, OCH3), 6.84 (d, J = 8.9 Hz,
2H, Haromatic), 6.98 (d, J = 8.9 Hz, 4H, Haromatic), 7.67 (d, J =
9.2 Hz, 2H, Haromatic), 8.06 (d, J = 6.7 Hz, 4H, Haromatic). 13C NMR
(100.67 MHz, CDCl3, SiMe4): dC 55.9 and 56.0 (OCH3), 113.2
113.9 127.4 128.9 (CHaromatic), 134.2 (C–CS3), 137.6 (C–CS2),
164.5 and 165.0 (C–OCH3), 233.4 (CS3), 237.1 (CS2).
Re(3-MeOPhCS3)2(3-MeOPhCS2)
(Re6). Yield
65%
(0.089 g). Elemental analysis: molecular formula C24H21O3S8Re.
Found: %C = 36.11, %H = 2.63, %S = 31.71; Calc. for
[Re(3-MeOPhCS3)2(3-MeOPhCS2)]: %C = 36.03, %H = 2.65,
%S = 32.06. Mp = 178 ◦C. Rf (PE/CH2Cl2 7/3) = 0.19. IR
(KBr disk) (cm−1): 1593 (w), 1570 (s), 1476 (m), 1425 (m), 1321
(w), 1286 (m), 1261 (s), 1200 (w), 1162 (w), 1098 (s), 1050 (s),
Synthesis of rhenium complexes
Bis-trithioperoxybenzoato dithiobenzoato complexes Re(R-
PhCS3)2(R-PhCS2) were synthesised according to the procedure
utilised for the unsubstituted complex with R = H (Re1).8
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
2 8 6 7

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1017 (s, mC–S), 978 (w), 948 (w), 866 (m), 803 (s), 678 (s), 564 (m,
mS–S), 395 (m, mRe–S ). H NMR (400.13 MHz, CDCl3, SiMe4):
Procedure (b). To a MeOH solution (5 mL) containing
[ReOCl4][NBu4] (0.15 g, 0.265 mmol), the pertinent dithioben-
zoate sodium salt (5 equivalents) and the diethyldithiocarbamate
sodium salt (5 equivalents), in MeOH (5 mL) were added
dropwise and the solution was stirred at room temperature for
2 h. The precipitate was filtered off, washed several times with
MeOH or EtOH, loaded onto a silica chromatography column
and eluted with a mixture of petroleum ether and CH2Cl2 (8 :
2, v/v). The brown-green band was collected, and after removal
of the solvent by evaporation under vacuum, an olive green
solid was obtained: this powder was dissolved in a mixture of
petroleum ether and CH2Cl2 (1 : 1, v/v) and after 3 days, crystals
were collected.
1
dH 3.79 (s, 3H, OCH3), 3.91 (s, 6H, OCH3), 6.91 (m, 3H,
Haromatic), 7.20 (m, 1H, Haromatic), 7.29 (m, 3H, Haromatic), 7.41
(t, J = 7.9 Hz,1H, Haromatic), 7.58 (m,4H, Haromatic).13C NMR
(100.67 MHz, CDCl3, SiMe4): dC 55.8 and 56.0 (OCH3), 116.8
119.9 125.2 129.5 (CHaromatic), 136.4 (C–CS3), 144.4 (C–CS2),
159.0 and 159.4 (C–OCH3), 234.0 (CS3), 238.6 (CS2).
Re(2-MeOPhCS3)2(2-MeOPhCS2)
(Re7). Yield
59%
(0.080 g). Elemental analysis: molecular formula C24H21O3S8Re.
Found: %C = 36.10, %H = 2.59, %S = 32.00; Calc. for
[Re(2-MeOPhCS3)2(2-MeOPhCS2)]: %C = 36.03, %H = 2.65,
%S = 32.06. Mp = 180 ◦C. Rf (PE/CH2Cl2 7/3) = 0.22. IR
(KBr disk) (cm−1): 1589 (m), 1568 (w), 1480 (s), 1458 (s), 1429
(m), 1284 (m), 1250 (s), 1164 (m), 1097 (s), 1047 (w), 1012 (s,
mC–S), 944 (w), 913 (w), 878 (w), 801 (s), 752 (s), 648 (w), 568 (w,
mS–S), 383 (w, mRe–S ). 1H NMR (400.13 MHz, CDCl3, SiMe4): dH
3.84 (s, 3H, OCH3), 3.93 (s, 6H, OCH3), 6.88 (d, J = 8.4 Hz,
1H, Haromatic), 6.95 (t, J = 7.1 Hz, 1H, Haromatic), 7.11 (m, 4H,
Haromatic), 7.22 (d, J = 7.1 Hz, 1H, Haromatic), 7.35 (t, J = 8.4 Hz,
2H, Haromatic), 7.79 (dd, J = 8.1 Hz and J = 1.8 Hz, 1H, Haromatic),
7.91 (dd, J = 7.6 Hz and J = 1.5 Hz, 2H, Haromatic). 13C NMR
(100.67 MHz, CDCl3, SiMe4): dC 55.8 and 56.4 (OCH3), 111.2
111.9 119.7 120.9 126.1 128.6 (CHaromatic), 133.8 (C–CS3), 134.5
(C–CS2), 157.1 and 158.4 (C–OCH3), 229.4 (CS3), 234.6 (CS2).
Re(PhCS3)2(Et2NCS2) (Re10). Procedure (a) yield 75%
(0.090 g). Procedure (b) yield 50% (0.025 g). Elemental analysis:
molecular formula C19H20NReS8. Found: %C = 32.44, %H =
2.87, %S = 36.41; Calc. for [Re(PhCS3)2(Et2NCS2)]: %C = 32.35,
%H = 2.86, %S = 36.36. Mp = 165 ◦C. Rf (PE/CH2Cl2 7/3) =
0.50. IR (KBr disk) (cm−1): 1504 (s), 1482 (m), 1454 (m), 1440
(s), 1377 (w), 1354 (w), 1300 (w), 1275 (m), 1241 (m), 1208 (m),
1179 (w), 1078 (w), 1028 (w), 1001 (s), 990 (s, mC–S), 908 (m),
1
755 (s), 687 (s), 544(s, mS–S), 454 (m), 399 (m, mRe–S ). H NMR
(400.13 MHz, CDCl3, SiMe4): dH 1.19 (t, J = 7.1 Hz, 6H, CH3),
3.60 (m, 4H, CH2), 7.31 (t, J = 8.1 Hz, 2H, Haromatic), 7.53 (t, J =
8.1 Hz, 4H, Haromatic), 8.07 (d, J = 8.6 Hz, 4H, Haromatic). 13C NMR
(100.67 MHz, CDCl3, SiMe4): dC 12.8 (CH3), 44.4 (CH2), 128.1
132.4 and 132.8 (CHaromatic), 134.9 (C–CS3), 204.5 (NCS2), 233.4
(CS3). UV/Vis (CH2Cl2): kmax 639, 483, 398 and 301.
The following complexes were synthesised using a one-pot
procedure (b).
Re(4-FPhCS3)2(4-FPhCS2) (Re8). Yield 77% (0.100 g). Ele-
mental analysis: molecular formula C21H12F3S8Re. Found: %C =
33.12, %H = 1.63, %S = 30.70. Calc. for [Re(4-FPhCS3)2(4-
FPhCS2)]: %C = 33.00, %H = 1.60, %S = 33.60. Mp = 120 ◦C. Rf
(PE/CH2Cl2 7/3) = 0.67. IR (KBr disk) (cm−1): 1591 (m), 1499
(s), 1407 (w), 1304 (w), 1280 (w), 1265 (w), 1237 (s), 1156 (m),
1008 (s, mC–S), 1001 (s, mC–S), 834 (m), 807 (w), 578 (w), 547 (w), 547
(s, mS–S), 454 (m), 399 (m, mRe–S ). 1H NMR (400.13 MHz, CDCl3,
SiMe4): dH 7.00 (t, J = 8.6 Hz, 2H, Haromatic), 7.15 (t, J = 8.5 Hz,
4H, Haromatic), 7.64 (dd, J = 5.3 and 8.9 Hz, 2H, Haromatic), 8.00
(dd, J = 5.3 and 8.9 Hz, 4H, Haromatic). 13C NMR (100.67 MHz,
CDCl3, SiMe4): dC 114.9 (d, J = 22.2 Hz, CHaromatic), 115.5 (d,
J = 21.2 Hz, CHaromatic), 127.3 (d, J = 9.1 Hz, CHaromatic), 131.3
(C–CS3), 131.4 (C–CS2), 134.0 (d, J = 8.1 Hz, CHaromatic), 139.7,
142.0 142.2 and 142.5 (C–F), 232.6 (CS3), 244.4 (CS2).
Re(4-MePhCS3)2(Et2NCS2) (Re11). Yield 56% (0.070 g).
Elemental analysis: molecular formula C21H24NReS8·C2H5OH.
Found: %C = 35.66, %H = 3.86, %S = 31.66; Calc. for [Re(4-
MePhCS3)2(Et2NCS2)]·C2H5OH: %C = 35.45, %H = 3.88, %S =
32.92. Mp = 178 ◦C. Rf (PE/CH2Cl2 7/3) = 0.43. IR (KBr disk)
(cm−1): 1599 (w), 1506 (m), 1435 (w), 1353 (w), 1261 (s), 1209 (w),
1181 (w), 1096 (s), 1019 (s, mC–S), 912 (w), 867 (w), 802 (s), 703 (w),
662 (w), 544 (w, mS–S), 475 (w), 475 (w), 399 (m, mRe–S ). 1H NMR
(400.13 MHz, CDCl3, SiMe4): dH 1.10 (t, 3H, EtOH), 1.19 (t, J =
7.1 Hz, 6H, CH3), 2.62 (s, 6H, CH3), 3.40 (q, 2H, EtOH), 3.59
(m, 4H), 7.32 (dd, J = 8.6 Hz and J = 0.6 Hz, 4H, Haromatic), 7.97
(d, J = 8.2 Hz, 4H, Haromatic). 13C NMR (100.67 MHz, CDCl3,
SiMe4): dC 13.2 (CH3), 21.5 (OCH3), 44.7 (CH2), 129.0 and 132.7
(CHaromatic), 133.0 (C–CH3), 144.1 (C–CS3), 206.9 (NCS2), 233.9
(CS3). UV/Vis (CH2Cl2): kmax 639, 484, 400 and 326.
Re(3-FPhCS3)2(3-FPhCS2) (Re9). Yield 48% (0.063 g). Ele-
mental analysis: molecular formula C21H12F3S8Re. Found: %C =
33.01, %H = 1.58, %S = 30.57. Calc.for [Re(3-FPhCS3)2(3-
FPhCS2)]: %C = 33.00, %H = 1.60, %S = 33.60. Mp = 125 ◦C.
Rf (PE/CH2Cl2 7/3) = 0.70. IR (KBr disk) (cm−1): 1581 (w),
1479 (m), 1433 (m), 1249 (s), 1158 (w), 1136 (w), 1026 (m, mC–S),
1001 (w), 963 (s), 869 (m), 824 (w), 809 (m), 786 (s), 690 (m), 672
(s), 563 (w, mS–S), 521 (w), 372 (w, mRe–S ). 1H NMR (400.13 MHz,
CDCl3, SiMe4): dH 7.07 (td, J = 8.1 and 2,6 Hz, 3H, Haromatic), 7.36
Re(4-EtPhCS3)2(Et2NCS2) (Re12). Yield 54% (0.070 g).
Mp = 152 ◦C. Rf (PE/CH2Cl2 7/3) = 0.43. IR (KBr disk) (cm−1):
1601 (m), 1557 (m), 1506 (w), 1456 (m), 1412 (w), 1381 (w), 1353
(w), 1262 (s), 1209 (m), 1171 (m), 1096 (s), 1022 (s, mC–S), 929 (w),
882 (s), 802 (s), 764 (m), 702 (w), 646 (w), 616 (w), 555 (w, mS–S),
473 (w), 406 (m, mRe–S ).1H NMR (400.13 MHz, CDCl3, SiMe4):
dH 1.19 (t, J = 7.1 Hz, 6H, CH3), 1.30 (t, J = 7.6 Hz, 6H, CH3),
2.87 (q, J = 7.8 Hz, 4H, CH2), 2.59 (qd, J = 7.1 Hz and J =
2.7 Hz, 4H, CH2), 7.35 (d, J = 8.3 Hz, 4H, Haromatic), 8.00 (d, J =
8.3 Hz, 4H, Haromatic). 13C NMR (100.67 MHz, CDCl3, SiMe4):
dC 13.2 and 16.3 (CH3), 28.8 and 44.7 (CH2), 127.9 and 132.8
(CHaromatic), 133.1 and 150.3 (Caromatic), 204.9 (NCS2), 233.9 (CS3).
UV/Vis (CH2Cl2): kmax 639, 485, 402 and 323.
(m, 2H, Haromatic), 7.49 (m, 3H, Haromatic), 7.80 (m, 4H, Haromatic). 13
C
NMR (100.67 MHz, CDCl3, SiMe4): dC 115.3 122.0 and 124.4
(CHaromatic), 131.2 and 137.3 (C–CS2), 161.9 and 164.4 (C–F),
229.3 (CS3), 242.3 (CS2).
Bis-trithioperoxybenzoato diethyldithiocarbamato Re(R-
PhCS3)2(Et2NCS2) were prepared as detailed below using two
different procedures.
Procedure (a). To a CH2Cl2 solution (5 mL) containing Re1
(0.05 g, 0.070 mmol), diethyldithiocarbamate sodium salt (5
equivalents) dissolved in methanol (5 mL) was added dropwise
and the solution stirred at room temperature for 2 h. The solvent
was removed by evaporation under vacuum and the residue
loaded onto a silica chromatography column and eluted with a
mixture of petroleum ether and CH2Cl2 (8 : 2, v/v). The brown-
green band was collected, and, after removal of the solvent by
evaporation under vacuum, an olive green solid was obtained:
this powder was dissolved in a mixture of petroleum ether and
CH2Cl2 (1 : 1, v/v) and after 3 days, crystals were collected.
Re(2-EtPhCS3)2(Et2NCS2) (Re13). Yield 54% (0.048 g).
Mp = 209 ◦C. Rf (PE/CH2Cl2 7/3) = 0.48. IR (KBr disk) (cm−1):
1505 (s), 1478 (m), 1435 (s), 1354 (m), 1272 (s), 1209 (w), 1188
(w), 1148 (m), 1118 (w), 1077 (m), 1012 (s, mC–S), 944 (w), 913 (w),
852 (w), 785 (w), 752 (s), 648 (w), 578 (m, mS–S), 560 (w), 466 (w),
1
399 (m, mRe–S ). H NMR (400.13 MHz, CDCl3, SiMe4): dH 1.18
(t, J = 7.1 Hz, 6H, CH3), 1.25 (t, J = 7.5 Hz, 6H, CH3), 2.81 (q,
J = 7.5 Hz, 4H, CH2), 3.50–3.66 (m, 4H, CH2), 7.29–7.40 (m, 4H,
Haromatic), 7.43–7.50 (m, 4H, Haromatic). 13C NMR (100.67 MHz,
CDCl3, SiMe4): dC 13.1 (CH3), 16.6 (CH3), 26.9 (CH2),
2 8 6 8
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5

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44.8 (CH2), 125.9 129.7 130.9 and 132.8 (CHaromatic), 134.7 and
144.5 (Caromatic), 204.7 (NCS2), 235.6 (CS3). UV/Vis (CH2Cl2):
kmax 603, 464, 388 and 287.
(cm−1): 1600 (m), 1579 (s), 1501 (s), 1484 (s), 1471 (s), 1432
(s), 1379 (w), 1358 (w), 1270 (s), 1258 (s), 1209 (m), 1148 (s),
1078 (w), 1011 (w), 1000 (m, mC–S), 985 (s, mC–S), 872 (s), 808 (s),
779 (s), 673 (m), 576 (w), 524 (w, mS–S), 458 (w), 405 (w, mRe–S ).
1H NMR (400.13 MHz, CDCl3, SiMe4): dH 1.20 (t, J = 7.4 Hz,
6H, CH3), 3.60 (qd, J = 7.2 Hz and J = 3.0 Hz, 4H, CH2), 7.02
(td, J = 8.4 Hz and J = 2.6 Hz, 2H, Haromatic), 7.49 (qd, J =
Re(4-MeOPhCS3)2(Et2NCS2) (Re14). Yield 55% (0.072 g).
Elemental analysis: molecular formula C21H24NO2ReS8·
C2H5OH. Found: %C = 33.81, %H = 3.616, %S = 31.41;
Calc. for [Re(4-MeOPhCS3)2(Et2NCS2)]·C2H5OH: %C = 34.05,
%H = 3.73, %S = 31.62. Mp = 181 ◦C. Rf (PE/CH2Cl2 7/3) =
0.17. IR (KBr disk) (cm−1): 1594 (s), 1567 (w), 1504 (s), 1455 (m),
1434 (m), 1354 (w), 1300 (m), 1259 (s), 1173 (s), 1095 (m), 1025
(s, mC–S), 991 (w), 911 (w), 830 (m), 803 (m), 632 (w), 592 (m, mS–S),
545 (w), 480 (w), 399 (m, mRe–S ).1H NMR (400.13 MHz, CDCl3,
SiMe4): dH 1.11 (t, 3H, EtOH), 1.19 (t, J = 7.0 Hz, 6H, CH3),
3.42 (q, 2H, EtOH), 3.60 (q, J = 7.3 Hz, 4H, CH2), 3.93 (s, 6H,
5.7 Hz and J = 2.5 Hz, 2H, Haromatic), 7.83 (m, 4H, Haromatic). 13
C
NMR (100.67 MHz, CDCl3, SiMe4): dC 13.2 (CH3), 44.8 (CH2),
119.8 128.3 128.8 129.8 and 130.1 (CHaromatic), 136.6 (C–CS3),
162.1(C–F), 204.5 (NCS2), 231.4 (CS3). UV/Vis (CH2Cl2): kmax
649, 486, 401 and 299.
Synthesis of technetium complexes
OCH3), 7.01 (d, J = 9.0 Hz, 4H), 8.08 (d, J = 9.0 Hz, 4H). 13
C
Bis-trithioperoxybenzoato dithiobenzoato complexes Tc(R-
PhCS3)2(R-PhCS2) were synthesised according to the proce-
dure utilised for the unsubstituted Tc(PhCS3)2(PhCS2) complex
(Tc1).9
NMR (100.67 MHz, CDCl3, SiMe4): dC 13.3 (CH3), 44.7 (CH2),
56.1 (OCH3), 113.8 and 128.9 (CHaromatic), 134.7 (C–CS3), 164.4
(C–OCH3), 205.1 (NCS2), 233.4 (CS3). UV/Vis (CH2Cl2): kmax
640, 487, 407 and 343.
99Tc(4-MePhCS3)2(4-MePhCS2) (Tc2). Yield 92% (0.100 g).
Rf (PE/CH2Cl2 7/3) = 0.79. IR (Nujol mull) (cm−1): 1600 (s),
1563 (m), 1544 (m), 1450 (s), 1377 (s), 1309 (w), 1279 (w), 1264
(m), 1205 (w), 1176 (s), 1018 (m, mC–S), 948 (w), 889 (m), 815 (s),
768 (m), 758 (w), 637 (w), 620 (w), 549 (w, mS–S), 503 (w), 464 (m,
Re(3-MeOPhCS3)2(Et2NCS2) (Re15). Yield 66% (0.086 g).
Elemental analysis: molecular formula C21H24NO2ReS8·
C2H5OH. Found: %C = 34.21, %H = 3.97, %S = 30.19; Calc. for
[Re(3-MeOPhCS3)2(Et2NCS2)]·C2H5OH: %C = 34.05, %H =
3.73, %S = 31.62. Mp = 92 ◦C. Rf (PE/CH2Cl2 7/3) = 0.13.
IR (KBr disk) (cm−1): 1591 (m), 1573 (m), 1504 (m), 1456 (m),
1424 (m), 1377 (w), 1353 (w), 1319 (w), 1285 (m), 1261 (s), 1197
(w), 1161 (w), 1149 (w), 1095 (m), 1047 (s), 1019 (s, mC–S), 979
(w), 950 (w), 925 (w), 866 (w), 848 (w), 790 (w), 774 (m), 680 (s),
560 (m, mS–S).1H NMR (400.13 MHz, CDCl3, SiMe4): dH 1.12 (t,
3H, EtOH), 1.20 (t, J = 7.1 Hz, 6H, CH3), 3.42 (q, 2H, EtOH),
3.60 (q, J = 7.0 Hz, 4H, CH2), 3.93 (s, 6H, OCH3), 6.87 (td, J =
8.2 Hz and J = 2.5 Hz, 2H, Haromatic), 7.43 (t, J = 8.2 Hz, 2H,
Haromatic), 7.63 (m,4H, Haromatic).13C NMR (100.67 MHz, CDCl3,
SiMe4): dC 13.2 (CH3), 44.7 (CH2), 56.0 (OCH3), 117.5 119.4
125.7 129.3 (CHaromatic), 136.3 (C–CS3), 159.3 (C–OCH3), 205.6
(NCS2), 233.6 (CS3). UV/Vis (CH2Cl2): kmax 640, 484, 401 and
300.
1
mTc–S ). H NMR (300.13 MHz, CDCl3, SiMe4): dH 2.33 (s, 3H,
CH3), 2.45 (s, 6H, CH3), 7.11 (d, J = 8.2 Hz, 2H, Haromatic), 7.25
(d, J = 8.0 Hz, 4H, Haromatic), 7.78 (d, J = 8.2 Hz, 2H, Haromatic),
7.97 (d, J = 8.1 Hz, 4H, Haromatic). NMR (75.48 MHz, CDCl3,
SiMe4): dC 22.0 (CH3), 124.9 129.3 129.8 and 136.1 (CHaromatic),
140.1 and 144.0 (Caromatic), 227.1 (CS3), 236.0 (CS2).
99Tc(4-EtPhCS3)2(4-EtPhCS2) (Tc3). Yield 92% (0.132 g). Rf
(PE/CH2Cl2 7/3) = 0.76. IR (Nujol mull) (cm−1): 1599 (s), 1461
(s), 1414 (w), 1376 (s), 1267 (s), 1232 (w), 1179 (s), 1130 (m),
1050 (w), 999 (s, mC–S), 964 (w), 950 (w), 910 (w), 832 (s), 769
(w), 669 (m), 593 (w), 569 (w), 553 (w, mS–S), 461 (m, mTc–S ), 440
1
(w). H NMR (300.13 MHz, CDCl3, SiMe4): dH 1.19 (t, J =
7.6 Hz, 3H, CH3), 1.27 (t, J = 7.6 Hz, 6H, CH3), 2.63 (q, J =
7.9 Hz, 2H, CH2), 2.73 (q, J = 7.6, 4H, CH2), 7.14 (d, J =
8.6 Hz, 2H, Haromatic), 7.27 (d, J = 8.2 Hz, 4H, Haromatic), 7.80 (d,
Re(2-MeOPhCS3)2(Et2NCS2) (Re16). Yield 37% (0.048 g).
Elemental analysis: molecular formula C21H24NO2ReS8. Found:
%C = 33.01, %H = 3.20, %S = 33.40; Calc. for [Re(2-
MeOPhCS3)2(Et2NCS2)]: %C = 32.96, %H = 3.16, %S = 33.52.
Mp = 190 ◦C. Rf (PE/CH2Cl2 7/3) = 0.20. IR (KBr disk) (cm−1):
1590 (w), 1505 (w), 1481 (w), 1456 (w), 1434 (w), 1261 (s), 1096
(s), 1077 (m), 1047 (m), 1019 (s, mC–S), 912 (w), 880 (w), 802 (s),
749 (m), 668 (w), 566 (w, mS–S), 460 (m), 409 (w, mRe–S ). 1H NMR
(400.13 MHz, CDCl3, SiMe4): dH H 1.18 (t, J = 7.1 Hz, 6H, CH3),
3.59 (qd, J = 6.9 Hz, 4H, CH2), 3.94 (s, 6H, OCH3), 7.11 (d, J =
8.4 Hz, 2H, Haromatic), 7.16 (t, J = 7.4 Hz, 2H, Haromatic), 7.32 (m,
2H, Haromatic), 7.93 (dd, J = 7.8 Hz and J = 1.8 Hz, 2H, Haromatic).
13C NMR (100.67 MHz, CDCl3, SiMe4): dC 13.2 (CH3), 44.7
(CH2), 56.4 (OCH3), 111.1 120.8 125.8 and 133.5 (CHaromatic),
134.4 (C–CS3), 157.6 (C–OCH3), 205.5 (NCS2), 230.3 (CS3).
UV/Vis (CH2Cl2): kmax 629, 480, 395 and 293.
J = 8.4 Hz, 2H, Haromatic), 7.99 (d, J = 8.4 Hz, 4H, Haromatic). 13
C
NMR (75.48 MHz, CDCl3, SiMe4): dC 15.7 and 15.8 (CH3), 29.3
and 29.4 (CH2), 125.0 128.1 128.7 and 129.9 (CHaromatic), 136.3
and 150.2 (Caromatic), 227.2 (CS3), 236.0 (CS2).
99Tc(2-EtPhCS3)2(2-EtPhCS2) (Tc4). Yield 59% (0.055 g).
Rf (PE/CH2Cl2 7/3) = 0.70. IR (Nujol mull) (cm−1): 1459 (s),
1376 (s), 1258 (m), 1224 (w), 1188 (w), 1160 (w), 1120 (m), 1073
(m), 999 (s, mC–S), 945 (m), 910 (w), 881 (w), 864 (w), 754 (s),
670 (m), 648 (m), 577 (w), 551 (w, mS–S), 491 (w), 465 (m, mTc–S ).
1H NMR (300.13 MHz, CDCl3, SiMe4): dH 1.18 (t, J = 5.8 Hz,
3H, CH3), 1.22 (t, J = 7.6 Hz, 6H, CH3), 2.71 (q, J = 7.5 Hz,
4H, CH2), 2.93 (q, J = 7.4 Hz, 2H, CH2), 7.16 (m, 2H, Haromatic),
7.31 (m, 3H, Haromatic), 7.41 (m, 7H, Haromatic). NMR (75.48 MHz,
CDCl3, SiMe4): dC 16.1 and 19.2 (CH3), 26.5 and 29.7 (CH2),
125.6 127.6 128.9 129.3 129.6 129.7 130.7 and 130.8 (CHaromatic),
131.0 136.6 140.8 and 142.1 (Caromatic), 229.1 (CS3), 242.6 (CS2).
Re(4-FPhCS3)2(Et2NCS2) (Re17). Yield 12% (0.015 g).
Mp = 163 ◦C. Rf (PE/CH2Cl2 7/3) = 0.45. IR (KBr disk) (cm−1):
1592 (s), 1576 (w), 1558 (w), 1539 (w), 1499 (s), 1455 (w), 1435
(m), 1377 (w), 1353 (m), 1297 (w), 1264 (s), 1234 (s), 1211 (w),
1156 (s), 1098 (m), 1077 (m), 1045 (w), 1011 (s, mC–S), 954 (w),
913 (w), 888 (w), 829 (s), 805 (s), 632 (w), 587 (m), 542 (m), 428
99Tc(4-MeOPhCS3)2(4-MeOPhCS2) (Tc5). Yield 92%
(0.140 g). Rf (PE/CH2Cl2 7/3) = 0.25. IR (Nujol mull) (cm−1):
1595 (s), 1560 (w), 1542 (w), 1506 (m), 1469 (s), 1377 (s), 1305
(m), 1264 (s), 1237 (w), 1168 (s), 1074 (m), 1029 (s, mC–S), 949 (w),
829 (m), 739 (w), 668 (s), 594 (w, mS–S), 549 (w), 456 (m, mTc–S ).
1H NMR (300.13 MHz, CDCl3, SiMe4): dH 3.82 (s, 3H, CH3),
3.89 (s, 6H, CH3), 6.80 (d, J = 7.7 Hz, 2H, Haromatic), 6.93 (d,
J = 7.7 Hz, 4H, Haromatic), 7.87 (d, J = 8.5 Hz, 2H, Haromatic), 8.08
(d, J = 7.5 Hz, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3,
SiMe4): dC 56.1 (OCH3), 113.8 114.4 127.1 131.8 (CHaromatic),
132.1 (C–CS3), 137.0 (C–CS2), 163.9 and 164.4 (C–OCH3),
226.2 (CS3), 234.2 (CS2).
1
(w, mRe–S ). H NMR (400.13 MHz, CDCl3, SiMe4): dH 1.20 (t,
J = 7.1 Hz, 6H, CH3), 3.60 (qd, J = 7.1 Hz and J = 2.0 Hz,
4H, CH2), 7.22 (t, J = 8.4 Hz, 4H, Haromatic), 8.08 (dd, J = 8.6Hz
and J = 5.3 Hz, 4H, Haromatic). 13C NMR (100.67 MHz, CDCl3,
SiMe4): dC 13.2 (CH3), 44.7 (CH2), 115.5 and 134.6 (CHaromatic),
131.6 (C–CS3), 166.7 (C–F), 204.6 (NCS2), 232.2 (CS3).
Re(3-FPhCS3)2(Et2NCS2) (Re18). Yield 38% (0.048 g).
Mp = 207 ◦C. Rf (PE/CH2Cl2 7/3) = 0.47. IR (KBr disk)
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
2 8 6 9

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99Tc(3-MeOPhCS3)2(3-MeOPhCS2) (Tc6). Yield 59%
(0.060 g). Rf (PE/CH2Cl2 7/3) = 0.19. IR (Nujol mull) (cm−1):
1596 (s), 1572 (s), 1488 (m), 1478 (m), 1427 (m), 1377 (m), 1323
(m), 1286 (s), 1263 (s), 1195 (w), 1163 (w), 1053 (m), 1020 (m),
1003 (m, mC–S), 978 (m), 947 (w), 870 (s), 806 (w), 786 (s), 681
1148 (m), 1074 (w), 1001 (m), 999 (s, mC–S), 904 (s), 756 (s), 731
(m), 683 (s). H NMR (300 MHz, CDCl3, SiMe4): dH 1.17 (t,
1
J = 7.2 Hz, 6H, CH3), 3.66 (m, 4H, CH2), 7.46 (m, 6H, Haromatic),
8.10 (m, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3, SiMe4): dC
12.6 (CH3), 44.5 (CH2), 128.6 129.5 and 132.2 (CHaromatic), 138.2
(Caromatic), 200.0 (NCS2), 225.7 (CS3). UV/Vis (CH2Cl2): kmax 525,
401 and 313.
99Tc(4-MePhCS3)2(Et2NCS2) (Tc11). Yield 55% (0.012 g).
Rf (PE/CH2Cl2 7/3) = 0.43. IR (Nujol mull) (cm−1): 1597 (m),
1560 (w), 1509 (s), 1458 (s), 1376 (s), 1354 (w), 1277 (s), 1231
(w), 1210 (m), 1180 (s), 1148 (m), 1076 (w), 1016 (s, mC–S), 949
(w), 907 (m), 812 (s), 735 (m), 669 (w), 637 (w), 585 (w), 546 (m,
mS–S), 483 (w), 444 (m, mTc–S ).1H NMR (300 MHz, CDCl3, SiMe4):
dH 1.17 (t, J = 7.2 Hz, 6H, CH3), 2.46 (s, 6H, CH3), 3.65 (q, J =
7.3 Hz, 4H, CH2), 7.26 (d, J = 4.0 Hz, 4H, Haromatic), 8.01 (d, J =
8.3 Hz, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3, SiMe4):
dC 13.1 and 21.9 (CH3), 44.9 (CH2), 129.9 and 131.4 (CHaromatic),
143.3 and 148.2 (Caromatic), 195.9 (NCS2), 224.7 (CS3). UV/Vis
(CH2Cl2): kmax 526, 394 and 323.
99Tc(4-EtPhCS3)2(Et2NCS2) (Tc12). Yield 66% (0.025 g). Rf
(PE/CH2Cl2 7/3) = 0.43. IR (Nujol mull) (cm−1): 1458 (s), 1376
(m), 1271 (m), 1179 (w), 1119 (s), 978 (m, mC–S), 899 (s), 826
(w), 668 (m), 592 (w), 544 (w, mS–S), 461 (m, mTc–S ).1H NMR
(300.13 MHz, CDCl3, SiMe4): dH 1.17 (t, J = 7.2 Hz, 6H, CH3),
1.28 (t, J = 7.6 Hz, 6H, CH3), 2.75 (q, J = 7.5 Hz, 4H, CH2),
3.65 (qd, J = 7.2 Hz and J = 2.7 Hz, 4H, CH2), 7.28 (d, J =
8.5 Hz, 4H, Haromatic), 8.03 (d, J = 8.3 Hz, 4H, Haromatic). 13C NMR
(75.48 MHz, CDCl3, SiMe4): dC 13.1 and 15.9 (CH3), 29.2 and
44.9 (CH2), 128.5 and 130.0 (CHaromatic), 136.4 and 149.5 (Caromatic),
200.4 (NCS2), 226.2 (CS3). UV/Vis (CH2Cl2): kmax 526, 398 and
324.
99Tc(4-MeOPhCS3)2(Et2NCS2) (Tc14). Yield 73% (0.028 g).
Rf (PE/CH2Cl2 7/3) = 0.17. IR (Nujol mull) (cm−1): 1594 (m),
1559 (w), 1542 (w), 1506 (m), 1458 (s), 1418 (m), 1376 (s), 1302
(m), 1266 (s), 1200 (m), 1167 (s), 1118 (w), 1096 (s), 980 (m, mC–S),
944 (w), 917 (w), 831 (m), 789 (w), 739 (w), 668 (m), 592 (w, mS–S),
473 (m), 460 (m, mTc–S ). 1H NMR (300.13 MHz, CDCl3, SiMe4):
dH 1.17 (t, J = 7.4 Hz, 6H, CH3), 3.62–3.90 (m, 4H, CH2), 3.99 (s,
6H, CH3), 6.96 (dd, J = 8.4 Hz, 4H, Haromatic), 8.12 (d, J = 8.6 Hz,
4H, Haromatic). 13C NMR (75.48 MHz, CDCl3, SiMe4): dC 13.0
(CH3), 44.8 (CH2), 56.1 (OCH3), 114.3 and 131.8 (CHaromatic),
129.3 (C–CS3), 163.6 (C–OCH3), 195.2 (NCS2), 225.4 (CS3).
UV/Vis (CH2Cl2): kmax 530, 413 and 351.
1
(s), 568 (m), 465 (m, mTc–S ). H NMR (300.13 MHz, CDCl3,
SiMe4): dH 3.80 (s, 3H, CH3), 3.90 (s, 6H, CH3), 7.01 (m, 3H,
Haromatic), 7.24 (t, J = 8.0 Hz, 1H, Haromatic), 7.36 (t, J = 7.9 Hz,
2H, Haromatic), 7.40 (t, J = 2.3 Hz, 1H, Haromatic), 7.49 (dq, J = 7.6
and 0.7 Hz, 1H, Haromatic), 7.59–7.64 (m, 4H, Haromatic). 13C NMR
(75.48 MHz, CDCl3, SiMe4): dC 30.2 and 56.1 (OCH3), 114.4
119.4 122.7 and 130.1 (CHaromatic), 141.5 and 159.9 (Caromatic),
227.1 (CS3), 236.1 (CS2).
99Tc(2-MeOPhCS3)2(2-MeOPhCS2) (Tc7). Yield 94%
(0.066 g). Rf (PE/CH2Cl2 7/3) = 0.22. IR (Nujol mull) (cm−1):
1592 (m), 1569 (w), 1460 (s), 1376 (s), 1285 (m), 1246 (s),
1162 (m), 1110 (s), 1020 (s, mC–S), 975 (w), 944 (w), 785 (w),
753 (s), 668 (m), 649 (w), 571 (w, mS–S), 467 (s, mTc–S ).1H NMR
(300.13 MHz, CDCl3, SiMe4): dH 3.84 (s, 3H, CH3), 3.92 (s, 6H,
CH3), 6.89 (t, J = 7.8 Hz, 2H, Haromatic), 6.95 (t, J = 8.0 Hz,
2H, Haromatic), 7.03 (t, J = 7.8 Hz, 1H, Haromatic), 7.10 (t, J =
7.3 Hz, 1H, Haromatic), 7.29 (t, J = 7.3 Hz, 2H, Haromatic), 7.43 (t,
J = 7.4 Hz, 1H, Haromatic), 7.97 (dd, J = 7.7 and 1.5 Hz, 1H,
Haromatic), 8.01 (dd, J = 5.3 and 1.8 Hz, 2H, Haromatic). 13C NMR
(75.48 MHz, CDCl3, SiMe4): dC 55.9 and 56.5 (OCH3), 111.9
112.6 120.4 121.4 129.4 and 131.4 (CHaromatic), 133.4 (C–CS3),
135.6 (C–CS2), 155.6 and 168.2 (C–OCH3), 222.3 (CS3), 232.5
(CS2).
99Tc(4-FPhCS3)2(4-FPhCS2) (Tc8). Yield 86% (0.080 g). Rf
(PE/CH2Cl2 7/3) = 0.67. IR (Nujol mull) (cm−1): 1592 (s), 1499
(s), 1458 (s), 1407 (w), 1376 (m), 1261 (m), 1239 (s), 1156 (s),
1003 (s, mC–S), 948 (w, mas C–S), 908 (s), 835 (s), 807 (w), 588 (m), 546
(m, mS–S), 472 (m, mTc–S ). 1H NMR (300.13 MHz, CDCl3, SiMe4):
dH 7.02 (dd, J = 8.6 Hz, 2H, Haromatic), 7.16 (dd, J = 6.5 Hz,
4H, Haromatic), 7.88 (dd, J = 8.9 and 5.3 Hz, 2H, Haromatic), 8.09
(dd, J = 6.9 and 5.2 Hz, 4H, Haromatic). 13C NMR (75.48 MHz,
CDCl3, SiMe4): dC 115.3 115.9 126.7 and 131.4 (CHaromatic), 134.3
and 138.8 (C–CS2), 165.6 and 166.2 (C–F), 225.3 (CS3), 234.2
(CS2).
99Tc(3-FPhCS3)2(3-FPhCS2) (Tc9). Yield 57% (0.035 g). Rf
(PE/CH2Cl2 7/3) = 0.70. IR (Nujol mull) (cm−1): 1578 (s), 1559
(w), 1544 (m), 1508 (m), 1465 (s), 1376 (s), 1340 (w), 1284 (w),
1148 (w), 1097 (s), 984 (m, mC–S), 949 (m), 879 (s), 829 (m), 806
(m), 787 (m), 675 (s), 524 (w, mS–S), 471 (s, mTc–S ), 461 (s). 1H NMR
(300.13 MHz, CDCl3, SiMe4): dH 7.11–7.22 (m, 3H, Haromatic),
7.32 (qd, J = 8.2 and 2.5 Hz, 1H, Haromatic), 7.44 (qd, J = 8.2 and
2.4 Hz, 2H, Haromatic), 7.55 (dt, J = 9.6 and 2.3 Hz, 1H, Haromatic),
7.65 (d, J = 8.3, 1H, Haromatic), 7.81 (m, 4H, Haromatic). 13C NMR
(75.48 MHz, CDCl3, SiMe4): dC 111.6 116.7 119.7 and 125.7
(CHaromatic), 130.2 and 130.8 (C–CS2), 161.2 and 164.4 (C–F),
225.4, (CS3), 234.8 (CS2).
99Tc(3-MeOPhCS3)2(Et2NCS2) (Tc15). Yield 23% (0.006 g).
Rf (PE/CH2Cl2 7/3) = 0.13. IR (Nujol mull) (cm−1): 1593 (w),
1576 (w), 1489 (m), 1458 (s), 1376 (s), 1285 (s), 1269 (s), 1120
(s), 1075 (s), 1020 (m), 967 (s, mC–S), 911 (m), 787 (m), 741 (w),
668 (w), 542 (m), 470 (s, mTc–S ). 1H NMR (300.13 MHz, CDCl3,
SiMe4): dH 1.17 (t, J = 7.2 Hz, 6H, CH3), 3.66 (m, 4H, CH2), 3.92
(s, 6H, CH3), 7.00 (m, 2H, Haromatic), 7.36 (m, 2H, Haromatic), 7.51–
7.55 (m, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3, SiMe4):
dC 13.1 (CH3), 44.9 (CH2), 56.1 (OCH3), 114.7 118.7 122.8 and
129.9 (CHaromatic), 139.6 and 159.9 (Caromatic), 200.4 (NCS2), 225.9
(CS3). UV/Vis (CH2Cl2): kmax 526 and 385.
Bis-trithioperoxybenzoato diethyldithiocarbamato Tc(R-
PhCS3)2(Et2NCS2) were prepared as detailed below.
To a CH2Cl2 solution (5 mL) containing the relevant Tc(R-
PhCS3)2(R-PhCS2) compound (0.050 mmol), diethyldithiocar-
bamate sodium salt (5 equivalents) dissolved in methanol (5 mL)
was added dropwise and the solution stirred at room tempera-
ture for 2 h. The solvent was removed by evaporation under
vacuum and the residue loaded onto a silica chromatography
column and eluted with a mixture of petroleum ether and
CH2Cl2 (8 : 2, v/v). The pink band was collected, and, after
removal of the solvent by evaporation under vacuum, a pink
solid was obtained. Crystals suitable for X-ray diffraction studies
were grown from a petroleum ether/CH2Cl2/EtOH (1 : 1 : 1)
mixture.
99Tc(4-FPhCS3)2(Et2NCS2) (Tc17). Yield 89% (0.025 g). Rf
(PE/CH2Cl2 7/3) = 0.45. IR (Nujol mull) (cm−1): 1592 (s), 1560
(w), 1499 (s), 1458 (s), 1406 (w), 1376 (s), 1297 (w), 1273 (m),
1237 (s), 1157 (s), 1077 (w), 1011 (m, mC–S), 913 (w), 830 (s), 806
1
(m), 608 (w), 588 (m), 544 (m, mS–S), 472 (m, mTc–S ). H NMR
(300.13 MHz, CDCl3, SiMe4): dH 1.18 (t, J = 7.1 Hz, 6H, CH3),
3.66 (m, 4H, CH2), 7.16 (dd, J = 8.5 Hz, 4H, Haromatic), 8.12 (dd,
J = 8.6 and 5.3 Hz, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3,
SiMe4): dC 13.1 (CH3), 44.9 (CH2), 116.2 and 131.84 (CHaromatic),
129.1 (C–CS3), 165.9 (C–F), 200.3 (NCS2), 224.5 (CS3). UV/Vis
(CH2Cl2): kmax 526, 403 and 312.
99Tc(3-FPhCS3)2(Et2NCS2) (Tc18). Yield 50% (0.006 g). Rf
(PE/CH2Cl2 7/3) = 0.47. IR (Nujol mull) (cm−1): 1579 (m),
99Tc(PhCS3)2(Et2NCS2) (Tc10). Yield 66% (0.033 g). Rf
(PE/CH2Cl2 7/3) = 0.50. IR (Nujol mull) 504 (s), 1499 (m),
1458 (m), 1440 (m), 1376 (w), 1274 (m), 1207 (m), 1180 (w),
2 8 7 0
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5

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1559 (w), 1542 (w), 1522 (w), 1498 (m), 1458 (s), 1436 (w), 1376
(m), 1266 (m), 1209 (w), 1146 (w), 1099 (s), 985 (m, mC–S), 948
(w), 916 (w), 869 (w), 808 (w), 769 (m), 679 (m), 669 (m), 471
dichloromethane/methanol solutions gave mixed neutral bis-
trithioperoxy/dithiobenzoato MIII(R-PhCS3)2(R-PhCS2) com-
plexes M1–9 in moderate (for Re) to high (for Tc) yields. As
described previously, the reaction took place through reduction
of the metal centre and oxidation of the dithiobenzoate ligand
to trithiobenzoate.8,9 The insertion of electron-donating sub-
stituents at the dithiobenzoate fragment did not significantly
modify the reaction profile nor the recovered yields. The
unique dithiobenzoate ligand was found to be labile, irrespective
of the substituent incorporated on the phenyl ring. Hence,
reactions of these M(R-PhCS3)2(R-PhCS2) complexes with an
excess of diethyldithiocarbamate (Et2NCS2)− afforded another
class of mixed neutral bis-trithioperoxybenzoato dithiocar-
bamato M(R-PhCS3)2(Et2NCS2) compounds M10–18. In the
case of rhenium, formation of mixed ligand Re(R-PhCS3)2-
(Et2NCS2) compounds also could be achieved using a direct
procedure by mixing [ReOCl4]− with an excess of both dithioben-
zoate and dithiocarbamate ligands in methanol. In the case of
technetium, such a simplified reaction pathway does not work,
and mixtures of unsubstituted and dithiocarbamate-substituted
compounds were collected along with several uncharacterised
impurities.
Thin layer chromatography performed on silica gel plates
indicated that: i) isostructural technetium and rhenium com-
pounds showed identical Rf values (see Experimental section),
ii) compounds bearing alkyl substituted and fluoro-substituted
phenyl groups are the most lipophilic of the series with Rf
values in the 0.67–0.79 range, while methoxy substituents gave
rise to less lipophilic species (Rf in the 0.19–0.25 range),
iii) dithiocarbamate containing M10–18 compounds displayed
less lipophilic character than the corresponding dithiobenzoate
containing M1–9 compounds.
1
(m, mTc–S ). H NMR (300.13 MHz, CDCl3, SiMe4): dH 1.18 (t,
J = 7.2 Hz, 6H, CH3), 3.65 (m, 4H, CH2), 7.16 (t, J = 8.2 Hz,
2H, Haromatic), 7.44 (q, J = 8.2 Hz, 2H, Haromatic), 7.86 (t, J =
7.1 Hz, 4H, Haromatic). 13C NMR (75.48 MHz, CDCl3, SiMe4): dC
13.1 (CH3), 45.0 (CH2), 116.7 119.1 125.9 and 130.5 (CHaromatic),
140.0 (C–CS2), 164.4 (C–F), 200.2 (NCS2), 223.9 (CS3). UV/Vis
(CH2Cl2): kmax 529, 403, and 312.
Determination of the structures
The X-ray data collections of Re2, Re10 and Tc10·EtOH were
performed at room temperature with a Nicolet R3m/V four-
circle diffractometer on single crystals mounted in a thin walled
glass capillary, with graphite monochromated Mo-Ka radiation
˚
(k = 0.71073 A). The positions of the heavier atoms were
determined by Patterson function and subsequent Fourier-
difference syntheses revealed the positions of the other non-
hydrogen atoms. Solution of the structures was performed
with SHELXTL NT18 and refined by full-matrix least-squares
methods on F2. After some cycles of refinement, performed with
the SHELXL-97 program,19 in Tc10 an EtOH molecule afflicted
with high thermal motion appeared, and its atoms were refined
isotropically. In Re10 the carbon atoms C(6) and C(7) of an
ethyl group were each disordered over two positions. The site
occupancy factors of the disordered atoms were refined and the
multiplicity resulted ca. 2/3 : 1/3. All non-H atoms were refined
anisotropically, while H atoms were placed geometrically and
allowed to ride on their attached atoms with isotropic thermal
parameters according to the atoms to which they were attached.
As a common feature, in all determinations the methyl H atoms
were not apparent from the difference map and they were not
included in the refinement procedure. In the final difference maps
Characterization
−3
˚
˚
some peaks (up to 1.9 e A , 0.88 A from Re in Re10) were
considered to be noise. Crystal data, summary of data collection
and structure refinement are collected in Table 1.
CCDC reference numbers 264127–264129.
See http://dx.doi.org/10.1039/b503938j for crystallographic
data in CIF or other electronic format.
Elemental analysis of rhenium compounds, as shown in the
Experimental section, are in good agreement with the proposed
formulation. The IR spectra of all of the complexes show no
retention of the monooxo–metal stretching vibration, but exhibit
absorptions typical of coordinated trithio- and dithio-benzoate
or dithiocarbamate ligands at ca. 1590, 1000, 550 and 400 cm−1.
NMR spectra show profiles characteristic of diamagnetic
species, which are in agreement with the low spin d4 electron
configuration typical of trigonal prismatic M(III) compounds
(vide infra). In detail, 1H NMR spectra of M(R-PhCS3)2(R-
PhCS2) show two set of A2B2 (phenyl para-substituted deriva-
tives M2, M3, M5 and M8), or ABCE (phenyl meta-substituted
M6 and M9) or ABCD (phenyl ortho-substituted M4 and M7)
Results and discussion
Synthesis
As sketched in Scheme 1, reduction–substitution reactions of
labile [MOCl4]− precursors with an excess of dithiobenzoate
(PhCS2)− or substituted dithiobenzoates (R-PhCS2)− ligands in
Table 1 Crystal data and details of data collection for Re2, Re10 and Tc10·EtOH
Re2
Re10
Tc10·EtOH
Empirical formula
M
C24H21ReS8
752.09
C19H20NReS8
705.04
Orthorhombic; Pca21 (No. 29)
12.503(3)
10.546(2)
19.355(4)
90
90
90
2552.1(9)
4; 1.835
0.71073; 54.2
2343
C21H26NOTcS8
662.91
Triclinic; P1 (No. 2)
¯
¯
Crystal system; space group
Triclinic; P1 (No. 2)
5.984(1)
12.106(2)
20.618(4)
101.61(3)
92.87(3)
94.22(3)
1455.9(5)
2; 1.716
0.71073; 47.6
5083
˚
a/A
9.913(2)
10.414(2)
14.912(3)
109.94(3)
90.39(3)
108.16(3)
1364.0(5)
2; 1.614
0.71073; 11.6
5035
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z, Dcalcd/Mg m−3
−1
˚
k/A; l/cm
Reflns collected
Reflns obsd (I > 2r(I))
2702
0.048
0.091
0.810
2039
0.055
0.142
1.013
4918
0.052
0.135
1.191
R1a (obsd reflns)
wR2b (obsd reflns)
GOFc on F2
−3
˚
˚
˚
˚
0.92 (0.98 A far from Tc)
Largest peak/e A
1.07 (1.15 A far from Re)
1.88 (0.90 A far from Re)
2
2
2
a R1 = RꢀFo| − |Fc||/R|Fo|. b wR2 = [Rw(Fo − Fc2)2/Rw(Fo2)2]1/2
.
c GOF = [Rw(|Fo | − |Fc |)2]/(Nobsd − Nparams)]1/2
.
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
2 8 7 1

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Scheme 1
aryl protons (relative integration 2 : 1), and two set of aliphatic
protons (relative integration 2 : 1) for alkyl substituted phenyl
ligands (M2–7 species), indicating the existence of different coor-
dinating trithioperoxybenzoate and dithiobenzoate phenyl rings.
This feature is confirmed by the occurrence of two dithiocarboxy
signals in the 222–244 ppm region in the corresponding 13C
spectra. On the other hand, M(R-PhCS3)2(Et2NCS2) complexes,
M10–18, exhibit a unique set of aryl protons (those arising from
the two magnetically equivalent trithioperoxybenzoate phenyl
rings) along with the signals of the dithiocarbamate residue.
According to the different nature of the trithioperoxybenzoate
and dithiocarbamate fragments two dithiocarboxy signals are
still observed in the 13C spectra in the 196–235 ppm region.
The dithiocarbamate carboxy signal falls consistently around
205 ppm in the rhenium complexes, while it is more shielded
(196–200 ppm) in the technetium analogs.
The cyclic voltammetric data of selected Re and Tc com-
pounds are reported in Table 2. As depicted in the voltammo-
gram shown in Fig. 1, two-reversible one-electron oxidations and
one reversible cathodic wave are observed for the representative
Tc(PhCS3)2(Et2NCS2) (Tc10) compound.
The oxidations are assigned by coulombmetric experiments
to the formation of Tc(IV) and Tc(V), respectively, presumably
accessing the 5d3 and 5d2 systems, whereas the reduction is
assigned to the Tc(III)/Tc(II) couple. As expected on the basis
of previous investigations on isostructural technetium and
Table 2 Cyclic voltammetric data for some Re(III) and Tc(III) complexes recorded at 200 mV s−1, referenced to the Fc/Fc+ couple
Compound
M = Re
Redox couple
M = Tc
M(PhCS3)2(PhCS2)
M1
+0.580
−1.090
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
M(III)/M(IV)
M(IV)/M(V)
M(III)/M(II)
+0.894
+1.362a
−0.556
+0.300
+0.775
−1.056
+0.450
+0.950a
−0.944
+0.480
+0.955a
−0.945
+0.194
+0.756
M(4-MeOPhCS3)2(4-MeOPhCS2)
M(3-MeOPhCS3)2(3-MeOPhCS2)
M(4-FPhCS3)2(4-FPhCS2)
M(PhCS3)2(Et2NCS2)
M5
+0.225
+0.587
−1.320a
c
M6
c
M8
+0.275
+0.637b
−1.412a
+0.050
+0.362
−1.412a
−0.005
+0.455
−1.468a
+0.110
+0.530
−1.370a
M10
M14
M15
−1.125
c
M(4-MeOPhCS3)2(Et2NCS2)
M(3-MeOPhCS3)2(Et2NCS2)
c
c
c
a Irreversible process (by changing the potential scan speed from 50 to 400 mV s−1 the corresponding anodic wave is never observed). b Anodic process
followed by chemical reaction. c Adsorption process on the electrode surface.
2 8 7 2
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5

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Fig. 1 Cyclic voltammogram of 99Tc(PhCS3)2(Et2NCS2) (Tc10) in the
−1.5 to +1.5 V region, 0.2 V cm−1, Ag wire quasi-reference electrode:
3.5 × 10−3 M complex, 0.1 M [Bu4N][ClO4] in dry and degassed CH2Cl2.
rhenium systems,2 rhenium complexes are generally easier to
oxidise and more difficult to reduce than the corresponding
technetium species. In addition, for rhenium complexes, the
reduction process is irreversible. The insertion of electron donor
substituents on the dithiobenzoate phenyl framework, which
increases the electron density at the metal centre, makes the
resulting M(R-PhCS3)2(R-PhCS2) complexes easier to oxidise by
300–600 mV and more difficult to reduce by 230–500 mV than
the corresponding unsubstituted phenyl derivatives M1. Analo-
gously, the substitution of the diethyldithiocarbamate for the
dithiobenzoate fragment in M(PhCS3)2(Et2NCS2) derivatives
(M10) produces easier oxidation and more difficult reduction
processes compared to the dithiobenzoato analogues M1. Such
effects are magnified in the technetium compounds. For example,
in Tc10 the Tc(III)/Tc(IV) and Tc(III)/Tc(II) processes occur at
more negative values by 700 and 570 mV, respectively, compared
to those observed in Tc1, while the corresponding Re(III)/Re(IV)
and Re(III)/Re(II) processes occur at more negative values by 530
and 320 mV for Re10 compared to Re1.
Red-ox potentials exhibited by the M(III)/M(II)
and M(III)/M(IV) couples in M10 compounds resemble those
reported for analogous ‘sulfur rich’ mixed-ligand complexes
[M(9S3)(SSS)]+ (M = Tc, Re; 9S3 = 1,4,7-trithiacyclononane;
SSS = SCH2CH2SCH2CH2S).20 For example, in the rhenium
complex [Re(9S3)(SSS)]+ oxidation to Re(IV) is reported to
occur at +0.015 V and reduction to Re(II) at −1.350 V, values
to be compared with +0.050 and −1.412 V detected for the
corresponding couples in Re10.
Electronic spectra of both dithiobenzoate containing M(R-
PhCS3)2(R-PhCS2) M1–9 and dithiocarbamate contain-
ing M(R-PhCS3)2(Et2NCS2) M10–18 compounds are dominated
by three different absorption bands: those occurring beyond
550 nm (e ca. 1000 M−1 cm−1) are attributed to d–d spectral tran-
sitions and are responsible for the green colour of the rhenium
compounds. Pink-violet technetium complexes show red-shifted
shoulders at 650–660 nm (Fig. 2, top spectra). Absorptions in
the 480–400 nm (for Re) and 530–400 nm (for Tc) ranges (e ca.
104 M−1 cm−1) are assigned to charge transfer transitions. The
latter corresponds to ligand (sulfur) to metal charge transfer
(LMCT) bands. High energy absorptions (e > 104 M−1 cm−1) in
the UV region are attributed to internal p–p* HOMO/LUMO
ligand transitions. A red shift of higher wavelength (lower
energy) bands is observed on going from dithiobenzoate con-
taining M(R-PhCS3)2(R-PhCS2) to dithiocarbamate contain-
ing M(R-PhCS3)2(Et2NCS2) complexes, as it appears from the
comparison of the electronic spectra of [Re(4-MeOPhCS3)2(4-
MeOPhCS2)] Re5 and [Re(4-MeOPhCS3)2(Et2NCS2)] Re14 re-
Fig.
2
Electronic spectra of Re(4-MePhCS3)2(4-MePhCS2) (Re2;
black line) and 99Tc(4MePhCS3)2(4-MePhCS2) (Tc2; gray line) (top
spectra); comparison of electronic spectra of Re(4-OMePhCS3)2-
(4-OMePhCS2) (Re5; black line) and Re(4-MePhCS3)2(Et2NCS2) (Re14;
gray line) (bottom spectra).
ported in Fig. 2, bottom spectra. This behaviour is in agreement
with the greater electron-donating character of dithiocarbamate
compared to dithiobenzoate ligands.
X-Ray crystal structure analysis
The ORTEP21 drawings of the complexes Re2 and M10·EtOH,
together with the numbering scheme used, are shown in Figs. 3
and 4 (ORTEP of Re10, isostructural with Tc10, is not shown);
relevant bond lengths and angles are reported in Table 3. The
‘inner core’ of the three complexes adopts a distorted trigonal
◦
˚
Table 3 Selected bond distances (A) and angles ( ) for Re2, Re10 and
Tc10·EtOH
Re2
Re10
Tc10·EtOH
M–S(1)
M–S(2)
M–S(4)
M–S(5)
M–S(7)
M–S(8)
S(2)–S(3)
S(5)–S(6)
2.352(3)
2.221(3)
2.354(3)
2.226(3)
2.495(4)
2.501(4)
2.100(4)
2.116(5)
2.385(5)
2.237(5)
2.365(5)
2.240(5)
2.527(5)
2.513(5)
2.140(7)
2.126(7)
2.344(1)
2.221(2)
2.346(1)
2.233(1)
2.508(2)
2.497(2)
2.096(2)
2.097(2)
S(1)–M–S(2)
S(4)–M–S(5)
S(7)–M–S(8)
M–S(1)–C(1)
M–S(2)–S(3)
M–S(4)–C(2)
M–S(5)–S(6)
M–S(7)–C(3)
M–S(8)–C(3)
S(2)–S(3)–C(1)
S(5)–S(6)–C(2)
S(1)–C(1)–S(3)
S(4)–C(2)–S(6)
S(7)–C(3)–S(8)
88.8(1)
89.4(1)
67.6(1)
112.7(4)
111.3(2)
110.9(4)
110.1(2)
90.5(5)
89.0(2)
89.9(2)
68.5(2)
111.4(7)
110.7(3)
112.6(8)
110.3(3)
90.5(8)
89.45(5)
89.69(5)
69.04(6)
111.8(2)
110.64(7)
111.9(2)
110.11(7)
89.3(2)
91.3(5)
89.8(7)
89.5(2)
105.3(4)
104.1(4)
121.8(7)
125.0(7)
110.5(9)
104.3(7)
104.7(7)
122.5(9)
122.3(9)
111(1)
104.9(2)
105.2(2)
122.8(3)
123.0(3)
112.2(3)
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
2 8 7 3

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and one four-membered ring around the metal centre. The
four-membered rings of the three complexes are planar and the
same can be said of the five-membered rings defined by the M,
S(4), S(5), S(6), C(2) atoms. The remaining five-membered
ring of Re10 and Tc10·EtOH assumes instead a somewhat
envelope conformation with the metal atom ‘at the flap’ (by
˚
0.39 and 0.13 A, respectively), while planarity is confirmed
for Re2.
Comparison of M–S bond lengths of isostructural mononu-
clear Re(III) and Tc(III) complexes collected in this work with the
structural data of M1 compounds reported previously8,9 reveals
that in all cases the coordination sphere comprises several types
of metal–sulfur interactions (Table 4). Shorter distances include
˚
covalent metal–thiolate bonds (2.20–2.24 A) and coordinative
˚
metal–sulfur bonds (2.32–2.38 A) of the trithioperoxybenzoate
moieties. Longer distances belong to the unique dithiobenzoate
(or dithiocarbamate) ligand (2.45–2.53 A).
Fig. 3 The ORTEP diagram of Re2 showing essential numbering.
Hydrogen atoms are omitted for clarity; ellipsoids are drawn at the
40% probability level.
˚
In unsubstituted phenyl complexes M(PhCS3)2(PhCS2) (M1),
˚
the Tc–S distances are roughly 0.03 A longer than the corre-
sponding Re–S distances, whereas the reverse situation is found
in dithiocarbamate containing complexes M(PhCS3)2(Et2NCS2)
(M10), which show slightly shorter Tc–S distances compared
to Re–S ones. In the series of three rhenium complexes, a
lengthening of the Re–S bonds is observed by increasing the
electron donating character of the ligand donor set on going
from Re1 to Re2 and to Re10. This behaviour indicates that the
metal, while accepting more negative charge from the ligand
set, needs to redistribute this excess electron density over a
larger volume, and to transfer electrons more readily in the
oxidation processes. In fact, Re10 undergoes oxidation to Re(IV)
at less positive values (+ 0.050 V) than Re2 (+ 0.225 V) and
Re1 (+ 0.580 V).
The peculiar stoichiometry of M(R-PhCS3)2(R-PhCS2)
and M(R-PhCS3)2(Et2NCS2) deserves an additional comment.
While oxidation of dithiobenzoate to trithioperoxybenzoate is
required to balance the reduction of rhenium,22 the use of a
further excess of dithiobenzoate in the reduction–substitution
reactions starting from [MO4]− does not modify the 2 : 1
trithioperoxybenzoate : dithiobenzoate ratio,11 although oxi-
dation of a third dithiobenzoate would be accessible from
a stoichiometric point of view. The stability of the [MIII(R-
PhCS3)2]+ moiety, which is further confirmed by the one-pot
Fig. 4 The ORTEP diagram of Tc10·EtOH showing essential num-
bering. Hydrogen atoms and EtOH molecule are omitted for clarity;
ellipsoids are drawn at the 40% probability level. (Compound Re10 is
isostructural with Tc10.)
prism environment realized by six sulfur atoms, with metal–S
distances encompassing a wide range, from 2.221(3) to 2.527(5)
˚
A. In the three complexes the two trithioperoxybenzoate and the
third chelating ligands define, respectively, two five-membered
◦
Table 4 Comparison of some bond lengths (A) and angles ( ) reported for five homologous [MIII(SS)3] neutral complexes (M = Tc, Re; SS =
˚
bidentate ligand with sulfur donor atom)
Tc1
Tc10·EtOH
Re1
Re2
Re10
Reference
M–S(1)
M–S(2)
M–S(4)
M–S(5)
M–S(7)
M–S(8)
S(2)–S(3)
S(5)–S(6)
9
This work
2.344(1)
2.221(2)
2.346(1)
2.233(1)
2.508(2)
2.497(2)
2.096(2)
2.097(2)
8
This work
2.352(3)
2.221(3)
2.354(3)
2.226(3)
2.495(4)
2.501(4)
2.100(4)
2.116(5)
This work
2.385(5)
2.237(5)
2.365(5)
2.240(5)
2.527(5)
2.513(5)
2.140(7)
2.126(7)
2.349(4)
2.231(4)
2.354(4)
2.227(4)
2.510(4)
2.478(5)
2.099(6)
2.075(6)
2.318(2)
2.197(2)
2.321(2)
2.200(2)
2.481(2)
2.449(2)
2.103(3)
2.068(3)
S(1)–M–S(2)
S(4)–M–S(5)
S(7)–M–S(8)
S(1)–M–S(4)
ea
89.6(1)
89.2(1)
68.1(1)
175.4(1)
17.1
89.45(5)
89.69(5)
69.04(6)
177.60(5)
9.8
89.1(1)
88.9(1)
67.7(1)
175.6(1)
8.9
88.8(1)
89.4(1)
67.6(1)
176.8(1)
11.8
89.0(2)
89.9(2)
68.5(2)
176.9(2)
8.4
a Twist angle between the upper S(1)S(5)S(7) and the lower S(2)S(4)S(8) triangular faces.
2 8 7 4
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5

View Article Online
formation of the mixed compounds containing a dithiocarba-
mate ligand, arises from the appropriate matching of M(III)
electronic requirements with p-donor (covalent thiolate S)
and p-acceptor (coordinative thiourea S) properties of the
trithioperoxybenzoate groups. The arrangement of this metal-
fragment partially mimics the trigonal bipyramidal (tbp) ge-
ometry typical of M(III) complexes. However, in the pres-
ence of dithiobenzoate or dithiocarbamate, able to delocal-
ize electron density via p-orbitals, [M(R-PhCS3)2]+ does not
evolve to a five-coordinate tbp, but to the less common
six-coordinate trigonal prismatic array. The expansion of
the coordination number is balanced by the lengthening of
the bonds of the ‘third’ bidentate ligand (dithiobenzoate or
dithiocarbamate).
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Conclusions
Two series of neutral, lipophilic Tc(III) and Re(III) mixed-ligand
complexes comprising trithioperoxybenzoate and dithioben-
zoate (or dithiocarbamate) have been prepared and fully
characterised. The coordination sphere of the metal is com-
pletely filled by six sulfur donor atoms arising from two
bidentate trithioperoxybenzoate and a bidentate dithiobenzoate
(or dithiocarbamate) ligand arranged in a distorted trigonal
prismatic geometry.
In mixed trithioperoxybenzoate/dithiobenzoate complexes
M2–9 the insertion of variable substituents on the phenyl
ring does not alter the stoichiometry, stereochemistry and
stability of the resulting compounds, but modifies their overall
lipophilicity and red-ox properties. These variations might be
profitably utilised to tune the biological properties of this class
of compounds when prepared at nanomolar level with 99mTc and
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acceptor properties provided by the different sulfur atoms
in the bis-bidentate chelator, the unique dithiobenzoate is
labile and can be efficiently exchanged with better nucleophiles
such as dithiocarbamates, producing a series of more sta-
ble mixed trithioperoxybenzoate/dithiocarbamate complexes
M10–18. If the M–dithiocarbamate bond proves to be kinetically
stable in biological media, the availability of this ligand-
exchange route offers the possibility of introducing bio-
logically active molecules appended to the dithiocarbamate
fragment.
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Anna Moresco is gratefully acknowledged for assistance with
the manuscript preparation.
D a l t o n T r a n s . , 2 0 0 5 , 2 8 6 6 – 2 8 7 5
2 8 7 5