New water-soluble rhenium complexes with 1,3,5-triaza-7-phosphaadamantane (PTA) - X-ray crystal structures of [ReNCl2(PTA)3], [ReO2Cl(PTA)3], [ReCl3(PTA) 2(PPh3)], and [Re2N2Cl 3(Et2dtc)(PTA)4]

Article abstract of DOI:10.1002/ejic.200800114

The new water-soluble nitrido complex [ReNCl₂(PTA)₃] (1) was obtained by treatment of [ReNCl₂(PPh₃) ₂] with four equivalents of PTA (1,3,5-triaza-7-phosphaadamantane). The reaction of [ReOCl₂X(PPh₃)₂] (X = Cl ^-, EtO^-) with six equivalents of PTA gave the neutral dioxido species [ReO₂Cl-(PTA)₃] (2). The formation of a rhenium(III) species of formula [ReCl₃(PTA)₂(PPh ₃)] (3) is also described. The reaction of 1 with Na[Et ₂dtc] (Et₂dtc = N,N-diethyldithiocarbamate) yielded the neutral compound [ReNCl(Et₂dtc)(PTA)₂] (4). Recrystallization of 4 afforded an unexpected dinuclear species [Re ₂N₂Cl₃(Et₂dtc)(PTA)₄] (5), containing an asymmetric Re≡N-Re group. The nitrido compound [ReN(Et₂dtc)₂(PTA)] (6), was obtained by adding two equivalents of Na[Et₂dtc] to complex 1 or one equivalent to complex 4. The X-ray crystal structures of the new PTA complexes 1, 2, 3, and 5 have been determined. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800114

FULL PAPER
DOI: 10.1002/ejic.200800114
New Water-Soluble Rhenium Complexes with 1,3,5-Triaza-7-
phosphaadamantane (PTA) – X-ray Crystal Structures of [ReNCl2(PTA)3],
[ReO2Cl(PTA)3], [ReCl3(PTA)2(PPh3)], and [Re2N2Cl3(Et2dtc)(PTA)4]
Andrea Marchi,*[a] Elena Marchesi,[a] Lorenza Marvelli,[a] Paola Bergamini,[a]
Valerio Bertolasi,[b] and Valeria Ferretti[b]
Keywords: Water-soluble complexes / Rhenium / 1,3,5-Triaza-7-phosphaadamantane complexes / Dithiocarbamate com-
plexes
The new water-soluble nitrido complex [ReNCl2(PTA)3] (1)
was obtained by treatment of [ReNCl2(PPh3)2] with four
equivalents of PTA (1,3,5-triaza-7-phosphaadamantane). The
reaction of [ReOCl2X(PPh3)2] (X = Cl–, EtO–) with six equiva-
lents of PTA gave the neutral dioxido species [ReO2Cl-
(PTA)3] (2). The formation of a rhenium(III) species of formula
[ReCl3(PTA)2(PPh3)] (3) is also described. The reaction of 1
Recrystallization of 4 afforded an unexpected dinuclear spe-
cies [Re2N2Cl3(Et2dtc)(PTA)4] (5), containing an asymmetric
ReϵN–Re group. The nitrido compound [ReN(Et2dtc)2(PTA)]
(6), was obtained by adding two equivalents of Na[Et2dtc] to
complex 1 or one equivalent to complex 4. The X-ray crystal
structures of the new PTA complexes 1, 2, 3, and 5 have been
determined.
with Na[Et2dtc] (Et2dtc
yielded the neutral compound [ReNCl(Et2dtc)(PTA)2] (4).
=
N,N-diethyldithiocarbamate)
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
ranging from –1 to +7; moreover they are able to coordi-
nate different ligands giving complexes with various coordi-
nation geometries. This versatility is stressed in particular
cores which have been studied for developing new radio-
Introduction
Rhenium coordination chemistry has attracted attention
in view of the development of therapeutic agents. In fact,
two isotopes of rhenium are β-emitters (186Re, Emax
=
pharmaceuticals. These are oxido-Tc/ReV [M=O]3+ [5]
,
ni-
1.1 MeV, t1/2 = 90.64 h; 188Re, Emax = 2.1 MeV, t1/2 = 17 h)
and therefore they are suitable candidates for therapeutic
applications by means of β-irradiation in radiotherapy. In
particular, the availability of a 188W/188Re generator[1]
makes rhenium-188 the more promising choice for the de-
velopment of radiopharmaceuticals for cancer therapy.[2]
Also, 186Re has a photon emission at approximately the
same energy as 99mTc (γ = 137 keV) allowing the radioiso-
tope to be imaged by γ-cameras utilized in 99mTc diagnostic
imaging. The periodic relationship between Tc and Re sug-
gests that 99mTc diagnostic agents may be used as a model
in the design of 186,188Re radiopharmaceuticals which may
possess similar biodistribution properties[3]; the reverse case
is also true. A rhenium radiopharmaceutical, 186Re-HEDP,
has been developed for the palliation of painful bone metas-
tases.[4]
trido-[MϵN]2+ [6]
,
hydrazino-metal(III) [MNNR]n+ [7], and
more recently, carbonyl-Tc/ReI fac-[M(CO)3]+ [8] cores.
Since the chemical species eluted from the radionuclide gen-
erator are [MO4]–, many studies have been focused on ox-
ido-metal(V) complexes containing the [M=O]3+ fragment,
which is readily obtained by facile reduction of Tc and Re
permetalates. In the +5 oxidation state, Tc and Re com-
plexes are five- or six-coordinate species showing square py-
ramidal, trigonal bipyramidal, and octahedral geometries.
The most-common starting materials for ReV chemistry are
represented by the oxido-ReV complex [ReOCl3(PPh3)2] and
the nitrido complex [ReNCl2(PPh3)2]. They are the syn-
thetic precursors of a wide variety of well-characterized ox-
ido and nitrido compounds, obtained by ligand-exchange
reactions. These precursors, as well as many of their deriva-
tives, include PPh3 in their coordination sphere. It is well
known that aryl- or alkylphosphanes are common ligands
which influence both steric and electronic properties of
metal complexes and stabilize low oxidation states. On the
other hand, the hydrophobicity, high molecular weight, and
low biocompatibility of arylphosphanes makes their com-
plexes unsuitable for medical purposes; for this reason the
replacement of PPh3 with more hydrophilic and biocompat-
ible phosphanes is a very important challenge.
Rhenium and technetium show a very rich coordination
chemistry due to their variety of stable oxidation states
[a] Laboratorio di Chimica Inorganica e Nucleare, Dipartimento
di Chimica, Università di Ferrara,
Via L. Borsari 46, 44100 Ferrara, Italy
Fax: +39-0532-240709
E-mail: mha@unife.it
[b] Centro di Strutturistica Diffrattometrica, Dipartimento di Chi-
mica, Università di Ferrara,
Via L. Borsari 46, 44100 Ferrara, Italy
2670
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2670–2679

Water-Soluble Rhenium Complexes
The solubility in water of phosphanes can be achieved
In an effort to develop new water-soluble precursors of
by introducing polar or ionic substituents such as sulfonate, rhenium for radiopharmaceutical applications, we at-
carboxylate groups. Examples of water-soluble arylphos- tempted to exchange PPh3 with PTA in [ReOCl3(PPh3)2]
phanes are represented by the sulfonated analogues of the and [ReNCl2(PPh3)2]. The syntheses of the nitrido
corresponding mono-, bi- or tridentate arylphosphanes.
[ReNCl2(PTA)3] and dioxido [ReO2Cl(PTA)3] complexes,
The water solubility of coordination compounds can be their characterization by spectroscopic techniques and their
also enhanced utilizing water-soluble cage-like phosphanes. reactivity with sodium N,N-diethyldithiocarbamate are de-
PTA (1,3,5-triaza-7-phosphaadamantane, IUPAC no- scribed herein.
menclature: 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane)
Finally, the X-ray crystal structures of four new PTA-Re
is a cage-like, adamantane-type phosphane. Synthesized by complexes are reported.
Daigle in 1974,[9] PTA and its derivatives received renewed
interest in the 1990s with the development of research of
water-soluble metallo-phosphane catalysts.[10] They are also
Results and Discussion
excellent hydrophilic components of transition-metal com-
pounds for applications in medicine and biology. The high
hydrophilicity and small size of PTA combined with its
chemical and thermal stability makes this phosphane
unique in comparison with other alkyl or arylphosphanes.
Synthesis and Characterization of Nitridorhenium(V)
[ReNCl2(PTA)3] (1) and trans-Dioxidorhenium(V)
[ReO2Cl(PTA)3] (2) Complexes
The nitridorhenium complex 1 was prepared by a ligand
exchange reaction using [ReNCl2(PPh3)2] as the precursor
in a 1:4 metal to PTA ratio (Scheme 1).
The trans-dioxidorhenium compound [ReO2Cl(PTA)3]
(2) was prepared in
a similar manner using [Re-
An exhaustive report of the chemistry of PTA towards OCl2X(PPh3)2] (X = Cl–, OMe–, OEt–) as the precursor but
transition metals, its applications in homogeneous catalysis in a 1:6 metal/PTA ratio (Scheme 2). An excess of PTA was
and in medicinal chemistry has been recently published by required to minimize the formation of by-products. Com-
Peruzzini et al.[11] To date ruthenium and platinum com- plexes 1 and 2 were isolated as crystalline products from
pounds[12] have been the focus of interest in relation to use CH2Cl2/Me2CO and CH2Cl2/EtOH respectively and fully
of PTA complexes as medicinal compounds although 99mTc characterized also by X-ray crystallography. Both com-
complexes such as 99mTc-fosfim® and 99mTc-furifosfim® are plexes are soluble in water (S20 °C ≈ 0.5 gmL–1 for 1 and
currently used in diagnostic nuclear medicine for myocar- S20 °C ≈ 0.36 gmL–1 for 2) and slightly soluble in polar or-
dial perfusion.[5a]
ganic solvents.
Scheme 1.
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A. Marchi et al.
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Table 1. Selected bond lengths and angles [Å, °] for compound 1.
Bond lengths
A
B
A
B
Re1–N1
Re1–Cl1
Re1–Cl2
1.708(4)
2.634(1)
2.444(1)
1.679(4)
2.624(1)
2.444(2)
Re1–P1
Re1–P2
Re1–P3
2.377(1)
2.441(1)
2.449(1)
2.386(1)
2.453(1)
2.439(1)
Angles
N1–Re1–Cl1 168.7(2)
N1–Re1–Cl2 104.1(2)
169.6(2)
103.3(2)
90.2(2)
94.7(2)
93.2(2)
86.78(5)
79.96(5)
83.73(4)
Cl1–Re1–P3 92.96(4)
Cl2–Re1–P1 163.19(5) 166.11(5)
Cl2–Re1–P2 85.11(6)
Cl2–Re1–P3 81.61(5)
P1–Re1–P2 96.48(4)
P1–Re1–P3 96.39(4)
91.10(4)
N1–Re1–P1
N1–Re1–P2
N1–Re1–P3
92.6(2)
90.5(2)
92.2(2)
83.10(5)
80.65(5)
99.40(4)
95.40(4)
Cl1–Re1–Cl2 86.61(5)
Cl1–Re1–P1
Cl1–Re1–P2
76.80(5)
86.75(5)
P2–Re1–P3 166.71(4) 163.20(4)
Scheme 2.
The infrared spectrum of 1 was dominated by the signals
of coordinated PTA in the range 940–1015 cm–1 and 750–
850 cm–1. The proton NMR spectrum displayed complex
multiplets at δ = 4.5–4.9 ppm caused by methylene protons
of PTA, while no signal was observed in the typical range
of aromatic protons of PPh3. The 31P NMR spectrum
showed a doublet and a triplet at δ –78.2 and δ –74.5 ppm,
respectively (2JPP = 14.0 Hz), suggesting the presence of two
equivalent and one different coordinated PTA ligands. On
the basis of spectroscopic measurements together with ana-
lytical data, complex 1 was formulated as the ReV neutral
complex [ReNCl2(PTA)3]. The 31P NMR spectrum is in
agreement with two possible structures in which three PTA
ligands are on the basal plane or two PTA are trans to each
other on the basal plane and the third PTA is located in an
apical position trans to the ReϵN multiple bond.
Nitrido complexes of rhenium with alkyl-/arylphos-
phanes such as [ReNCl2(PR3)3] (R = alkyl and/or aryl) were
reported by Chatt and co-workers.[13] X-ray studies for the
ReV complex [ReNCl2(PR3)3] (R = Me2PhP, Et2PhP)[14]
showed an octahedral geometry with PR3/Me2PhP groups
on the basal plane and two halogen atoms in a cis position.
The X-ray crystallographic analysis of complex
[ReNCl2(PTA)3], 1, unambiguously showed that the same
ligand disposition is present also in this case. An ORTEP
diagram is shown in Figure 1 and selected bond lengths and
angles are given in Table 1.
The asymmetric unit of 1 contains two molecular com-
plexes and exhibits an approximately octahedral overall ge-
ometry around both ReV atoms with the equatorial planes
containing the three P atoms of PTA ligands and a chlorine
atom, while the apical positions are occupied by a nitrido
group and another Cl atom. In both molecules of the asym-
metric unit the nitrido groups induce octahedral distor-
tions, where the Re atoms are displaced by 0.1750(2) and
0.1927(2) Å, respectively, from the mean basal plane toward
the N1 atoms. The Re1ϵN1 triple bond lengths of 1.708(4)
and 1.679(4) Å are in accordance with those of other sim-
ilar derivatives showing distances in the range 1.67–
1.71 Å.[14a,15] The Re1–Cl1 bond lengthening of 2.634(1)
and 2.624(1) Å can be ascribed to the well-known strong
trans influence exerted by the nitrido group. Similar dis-
tances, in the range 2.50–2.71 Å, can be observed in the
previously quoted structures.[14a,15] With respect to the
Re1–P1 distances of 2.377(1) and 2.386(1) Å, where P1 is
trans to Cl2, the Re1–P2 and Re1–P3 bonds show signifi-
cant lengthening, in the range 2.439(1)–2.453(1) Å, which
can be ascribed to the mutual trans influence of the P
atoms. Each molecule of the asymmetric unit is surrounded
by water molecules linked, by hydrogen bond, mostly to the
nitrogen atoms of PTA groups.
Dioxidorhenium(V) complexes [ReO2L2]+ [L = 1,2-
bis(diphenylarsane)ethane, 1,2-bis(diphenylphosphane)eth-
ane, diphosphane tetraphosphonates] are known and fully
characterized.[16] Infrared spectra of these compounds ex-
hibited strong absorption bands in the range 780–840 cm–1
and were assigned to νasym(Re=O) stretching typical of the
O=Re=O unit. A comparison between the IR spectra of 1
and 2 allowed the assignment of the ReϵN and Re=O
stretching at 1050 cm–1 and at 788 cm–1, respectively. Mul-
tiplets at δ = 4.4–5.0 ppm were observed in the proton
NMR spectrum of 2, while a doubled-triplet pattern at δ =
–85.5 and δ = –70.5 ppm (2JPP = 7.5 Hz) was displayed in
the 31P NMR spectrum. These data support the proposed
formulation for complex 2, confirmed by X-ray crystal
structure. Figure 2 shows the perspective drawing of the
[ReO2Cl(PTA)3] complex and a selected list of bond lengths
and angles are given in Table 2.
Figure 1. ORTEP view of molecule A of complex 1 displaying the
thermal ellipsoids at 30% probability.
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Eur. J. Inorg. Chem. 2008, 2670–2679

Water-Soluble Rhenium Complexes
Stability Tests of 1 and 2 in Water and Physiological
Solution by 31P NMR Spectroscopy
The stability of Re-PTA complexes in aqueous solutions
is crucial for radiopharmaceutical purposes. By studying
their aqueous solution behavior at the macroscopic level it
is possible to obtain useful information concerning the
188Re-labeled-PTA species. For phosphane-metal com-
plexes, 31P NMR spectroscopy is an important analytical
tool for detecting ligand replacements by the solvent or de-
composition processes.
In order to evaluate the stability of 1 and 2, we per-
formed some 31P NMR experiments both in water and
physiological solution (0.154 molL–1). When a freshly pre-
pared solution of 1 in water (0.036 molL–1) was observed
by 31P NMR, the spectrum showed the signal of uncoordi-
nated PTA at δ = –96.5 ppm and three broad bands at
–69.4, –71.3, and –74.7 ppm. 31P NMR spectra were then
monitored after 3 h and 24 h, but the relative intensities of
the signals were not time-dependent.
The weak singlet at δ = –69.4 ppm could be tentatively
assigned to species generated by loss of PTA or its replace-
ment by water. The two more intense signals at –71.3 and
–74.7 ppm look similar to the doublet–triplet pattern of 1 in
CDCl3 (–74.5 and –78.2 ppm). The signal broadening and
downfield shift could be ascribed to a network of hydrogen
bonds established between coordinated PTA and water.
The hypothesis of a partial PTA dissociation was con-
firmed by the following experiment, which showed that the
process is reversible. The aqueous solution of 1 was care-
fully dried in vacuo, the solid residue was then redissolved
in CDCl3 and the 31P NMR spectrum collected again. The
typical doublet–triplet pattern of 1 at δ = –78.2 (d) and δ =
–74.5 (t) reappeared, while the peak of free PTA was no
longer observed.
Figure 2. ORTEP view of complex 2 displaying the thermal ellip-
soids at 30% probability.
Table 2. Selected bond lengths and angles [Å, °] for compound 2.
Bond lengths
Re1–O1
Re1–O2
Re1–Cl1
1.781(3)
1.780(3)
2.510(1)
Re1–P1
Re1–P2
Re1–P3
2.401(1)
2.469(1)
2.475(1)
Angles
O1–Re1–O2
O1–Re1–Cl1
O1–Re1–P1
O1–Re1–P2
O1–Re1–P3
O2–Re1–Cl1
O2–Re1–P1
O2–Re1–P2
177.2(2)
91.4(1)
89.2(1)
92.7(1)
91.4(1)
91.0(1)
88.4(1)
89.1(1)
O2–Re1–P3
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–P3
P1–Re1–P2
P1–Re1–P3
P2–Re1–P3
87.4(1)
176.74(4)
81.56(4)
85.38(4)
95.22(4)
97.79(4)
166.41(4)
These experiments were repeated under the same condi-
tions replacing water with a physiological solution as a sol-
vent: the 31P NMR spectra do not show any difference with
respect to the behavior previously observed in pure water.
With the same purpose, complex 2 was also dissolved
both in water and in physiological solution (0.036 molL–1)
and 31P NMR spectroscopic data were collected as above.
A downfield-shifted doublet–triplet pattern, less resolved in
comparison with the spectrum of 2 in CDCl3, was observed
at δ = –83.6 and –68.3 ppm. A small signal at δ =
–81.25 ppm and the presence of uncoordinated PTA at δ =
–96.5 ppm seemed to indicate also in this case partial loss
or replacement of a PTA ligand, reversible by changing
water with chloroform.
The coordination polyhedron for compound 2 is a dis-
torted octahedron where the P atoms of PTA ligands and
Cl1 atoms define the equatorial plane and the two O atoms
are situated at the apical positions. The central ReV atom is
displaced by 0.0484(1) Å toward the O1 atom. The greatest
molecular distortions are determined by the repulsions be-
tween PTA ligands causing, for instance, a significant en-
largement of P1–Re1–P2 and P1–Re1–P3 angles to 95.22(4)
and 97.79(4)°, respectively. The Re-dioxido moiety exhibits
Re=O distances of 1.781(3) and 1.780(3) Å, in agreement
with a number of Re-dioxido phosphane derivatives where
these bond lengths are in the range of 1.75–1.81 Å.[17]
In accordance with the structure of 1, the Re1–P1 and
Re1–P3 bonds, in mutual trans positions, display longer dis-
tances of 2.470(1) and 2.475(1) Å, with respect to the Re1–
P1 bond trans to the Cl1 atom, showing a distance of
2.401(1) Å.
In conclusion, these NMR experiments seem to indicate
that 1 and 2 in water undergo a partial PTA dissociation,
which can be reverted by the elimination of water, followed
by re-dissolution in organic solvent.
The molecules of the complex in the crystals are linked,
in chains, by means of water molecules that act as bridges
between O1 and O2 oxygen atoms of two vicinal molecules
through hydrogen bonds: O3(w)···O1 2.836(6) Å and
O3(w)···O2(–x, y – 1/2, 172 – z) = 2.827(6) Å.
Synthesis and Characterization of Rhenium(III)
[ReCl3(PTA)2(PPh3)] (3)
Numerous investigations have been carried out on
rhenium(III) phosphane complexes of the type [ReX3-
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A. Marchi et al.
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(PR2PhP)3] (X = Cl, Br; R = alkyl) and several X-ray crys- Table 3. Selected bond lengths and angles [Å, °] for compound 3.
tal structures were determined.[18] Usually, these complexes
were prepared by exchange/reduction reactions of
Bond lengths
Re1–Cl1
Re1–Cl2
Re1–Cl3
2.351(1)
2.353(1)
2.464(1)
Re1–P1
Re1–P2
Re1–P3
2.439(1)
2.426(1)
2.428(1)
[ReCl4(PPh3)2] or by reduction reactions from the [ReO4]–
anion.[18b,19] Under similar reaction conditions, it was not
possible to isolate the analogous complex [ReCl3(PTA)3],
indicating the poor reducing properties of PTA in compari-
son with other alkyl- and arylphosphanes. The complex 3
reported herein, was prepared by ligand-exchange reaction
starting from the Re(III) precursor [ReCl3(NCMe)(PPh3)2].
In contrast to the above-reported reactions with [Re-
OCl3(PPh3)2] and [ReNCl2(PPh3)2], in this case only one
out of two triphenylphosphane ligands were substituted by
PTA. The product is an orange-yellow solid, soluble in
CH2Cl2, CHCl3, moderately soluble in water and ethanol,
insoluble in acetone and benzene. The presence of both
phosphanes was confirmed by the observation, in the infra-
red spectrum, of absorption bands at 1097 cm–1, typical of
PPh3, and in the range 950–1015 cm–1, characteristic of
PTA. As expected, the proton NMR spectrum of complex
3 showed a pattern characteristic of paramagnetic com-
pounds in agreement with a d4 octahedral configuration.
Both the signals of the protons of PPh3 and those of PTA
appeared as well-defined sharp bands. The aromatic pro-
tons of PPh3 resonated at δ = 14.95 and at δ = 7.92 ppm in
a 4:1 ratio due respectively to the protons in ortho and meta
(12) and to those in para positions (3) of the aromatic rings.
Angles
C1–Re1–Cl2
Cl1–Re1–Cl3
Cl1–Re1–P1
Cl1–Re1–P2
Cl1–Re1–P3
Cl2–Re1–Cl3
Cl2–Re1–P1
Cl2–Re1–P2
174.64(3)
93.18(4)
85.93(4)
83.87(4)
92.33(3)
86.17(3)
99.24(4)
90.76(4)
Cl2–Re1–P3
Cl3–Re1–P1
Cl3–Re1–P2
Cl3–Re1–P3
P1–Re1–P2
P1–Re1–P3
P2–Re1–P3
88.56(3)
82.63(4)
84.07(4)
174.06(3)
162.75(4)
95.55(4)
98.73(4)
ent compound and in other similar ReIII complexes no sys-
tematic trans influence exerted by P atoms can be ob-
served.[18b,21] Accordingly, no lengthening of P1–Re1–P2
distances in mutual trans positions can be observed in com-
plex 3, only a small lengthening of the Re1–Cl3 bond length
trans to a phosphane group is observed.
Reactivity of [ReNCl2(PTA)3] (1) and [ReO2Cl(PTA)3] (2)
Complexes with NaEt2dtc
The syntheses, structural characterizations, and reactions
The methylene protons of PTA occurred at δ = 12.80, 11.00, of rhenium and technetium nitrido complexes have been de-
9.05, and 7.11 ppm as multiplets of equal intensity. As re- scribed in a great number of papers. The N3– anion is one
ported by Randall,[20] no phosphorus–proton coupling was of the strongest π-donor ligands and the MϵN (M = Re,
observed, owing to rapid relaxation of the phosphorus nu- Tc) core is very stable. Ligand-exchange reactions of phos-
clei. These observations, however, are in good agreement phane complexes [MNCl2(PPh3)2] and [MNCl2(PR3)3] (R
with the elemental analysis results, corresponding to = alkyl, aryl) have been extensively exploited to study the
[ReCl3(PTA)2(PPh3)]. The X-ray structure analysis of 3 reactivity of several MϵN-containing complexes. Among
confirmed that the central metal atom is in an octahedral the substitution products, those containing dithiocarbamate
environment. An ORTEP view of complex 3 is shown in ligands have been widely studied and fully characterized. In
Figure 3 and selected bond lengths and angles are given in fact, the M–S2CNR2 fragment (M = Re, Tc) can include a
Table 3.
variety of organic substituents useful for the development
of new radiopharmaceuticals: e.g., nitrido complexes of
technetium of the type [TcN(S2CNR2)2] have been studied
as heart-imaging agents.[22] For these reasons, we have cho-
sen N,N-diethyldithiocarbamate as a relevant and useful li-
gand for starting the investigation of the reactivity of the
new Re-PTA complexes above described.
The reaction of 1 with one equivalent of Na[Et2dtc] at
room temperature gave the neutral complex [ReNCl-
(Et2dtc)(PTA)2] (4) in good yield (Scheme 1). The presence
of two PTA ligands makes 4 soluble in water. In the IR
spectrum it was not possible to assign the ReϵN vibration
in the typical range between 1000–1100 cm–1 because of the
overlap with the absorption bands of PTA, while those ob-
served at 1520 cm–1 and 1240 cm–1 could be assigned to
1
ν(C–N) and ν(C–S), respectively. The H NMR spectrum
displayed a series of resonances in the range δ = 4.0–
4.4 ppm caused by the methylene protons of PTA. The co-
Figure 3. ORTEP view of complex 3 displaying the thermal ellip-
soids at 30% probability.
Compound 3 is a ReIII complex with a mer arrangement ordinated Et2dtc resonated as a triplet at δ = 0.80 ppm
of three chlorine atoms, two PTA ligands in mutual trans (CH3), while two quartets at δ = 2.95 and at δ = 3.22 ppm
positions, and a PPh3 group trans to a Cl atom. In the pres- were attributed to the methylene protons. The integration
2674
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Eur. J. Inorg. Chem. 2008, 2670–2679

Water-Soluble Rhenium Complexes
of all these signals was in perfect agreement with the pres- Table 4. Selected bond lengths and angles [Å, °] for compound 5.
ence of coordinated PTA and Et2dtc in a 2:1 ratio. Finally,
Bond lengths
the 31P NMR showed a singlet at δ = –77.5 ppm indicating
Re1–N1
Re1–Cl1
Re1–P1
1.696(4)
2.568(2)
2.405(1)
2.423(1)
2.446(1)
2.424(1)
1.720(5)
1.711(7)
Re2–N1
Re2–N9
Re2–Cl2
Re2–Cl3
Re2–P3
Re2–P4
2.070(4)
1.621(11)
2.633(3)
2.444(2)
2.453(3)
2.385(2)
that the two phosphane ligands were equivalent. Nitrido
complexes of rhenium and technetium having this formula-
tion are known and were obtained from [MNCl2- Re1–P2
(PMe2Ph)3] (M = Re, Tc).[23] By analogy, complex 4 could
Re1–S1
Re1–S2
possess an octahedral geometry in which a Cl– anion lies in
C1–S1
a trans position to the ReϵN multiple bond, while biden-
C1–S2
tate Et2dtc and two PTA occupy the four basal posi-
Angles
tions.[23a] Recrystallization of 4 from a mixture of CH2Cl2
N1–Re1–Cl1
171.6(1)
93.0(1)
93.4(1)
N1–Re2–N9
N1–Re2–Cl2
N1–Re2–Cl3
N1–Re2–P3
N1–Re2–P4
N9–Re2–Cl2
N9–Re2–Cl3
N9–Re2–P3
N9–Re2–P4
Cl2–Re2–Cl3
Cl2–Re2–P3
Cl2–Re2–P4
Cl3–Re2–P3
Cl3–Re2–P4
P3–Re2–P4
99.5(6)
86.2(2)
86.0(1)
167.0(1)
89.7(1)
169.0(4)
100.6(6)
92.5(6)
90.5(6)
89.1(1)
82.9(1)
80.1(1)
86.71(6)
168.64(7)
95.33(6)
and MeOH induced its transformation into a new unexpec-
ted compound. In fact, the 31P NMR pattern changed from
a singlet at δ = –77.5 ppm to a series of four doublets at δ
N1–Re1–P1
N1–Re1–P2
N1–Re1–S1
103.0(1)
102.8(1)
82.39(5)
80.38(5)
83.24(5)
84.44(5)
98.74(5)
159.32(5)
91.88(5)
93.42(5)
160.10(5)
71.97(5)
= –89.5 and –84.8 (2JPP = 10 Hz), and at δ = –85.2 and N1–Re1–S2
–71.4 (2JPP = 14 Hz). A complex series of resonances in the
Cl1–Re1–P1
Cl1–Re1–P2
range δ = 4.4–4.8 ppm attributable to CH2 protons of PTA
Cl1–Re1–S1
were observed in the 1H NMR spectrum together with mul-
Cl1–Re1–S2
tiplets at δ = 1.42 and 3.68–4.10 ppm caused by methyl and
methylene protons of the dithiocarbamate ligand. On the
basis of these data and elemental analysis we tentatively
identified complex 5 as a dinuclear species having formula
[Re2N2Cl3(Et2dtc)(PTA)4].
P1–Re1–P2
P1–Re1–S1
P1–Re1–S2
P2–Re1–S1
P2–Re1–S2
S1–Re1–S2
The formation of multinuclear complexes with bridging
nitrido ligands between rhenium atoms ReϵN–Re has been
observed before, when the complex [ReN(Et2dtc)2-
(Me2PhP)] reacted with TlCl or Pr(O3SCF3)3.[24] cyclo-
[ReN]4 was formed when the nitrido starting material
[ReNCl2(PPh3)2] reacted with 1.5 equiv. of N,N-diethyldi-
Re1–N1–Re2
Re1–S1–C1
173.1(3)
87.0(2)
Re1–S2–C1
S1–C1–C2
87.9(2)
113.0(3)
Compound 5 is a dinuclear ReV complex where one
thiocarbamate ligand in methanol[25] or when the complex molecule of [ReNCl(Et2dtc)(PTA)2] coordinates with its ni-
[ReN(Et2dtc)2(Me2PhP)] reacted with SbCl3.[26] Detailed trido ligand to the fragment ReNCl2(PTA)2. The resulting
studies of these reactions have been described by Abram nitrido bridge is asymmetric with the distances Re1–N1
and co-workers and some of the complexes were structur- 1.696(4) Å, Re2–N1 2.070(4) Å, and almost linear with a
ally characterized.[27]
Re1–N1–Re2 bond angle of 173.1(3)°. These data are in
The X-ray crystal structure of complex 5 has been deter- perfect agreement with those of other similar bi or trinu-
mined, an ORTEP view is depicted in Figure 4 and selected clear Re complexes.[24,28] Both ReV atoms assume a dis-
bond lengths and angles are given in Table 4.
torted octahedral geometry where Re1 is displaced by
0.3175(2) Å from the equatorial plane defined by the P1,
P2, S1 and S2 atoms toward the nitrido N1 atom, while
Re2 is displaced by 0.229(2) Å from the plane defined by
P3, P4, Cl3, N1 atoms toward the N9 nitrido group. The
Re1–Cl1 and Re2–Cl2 bond lengths trans to the nitrido
groups display remarkable lengthening of 2.568(2) and
2.633(2) Å, respectively, as expected from the strong trans
influence exerted by nitrido groups. Re1–S1 and Re1–S2
bond lengths compare very well with those in a similar ReV
compound where both S atoms are trans to phosphane
groups.[24]
Neutral rhenium(V) and technetium(V) complexes of ge-
neral formula [MN(Et2dtc)2(Me2PhP)] are known and were
prepared by stepwise substitution reactions starting from
[MNCl2(Me2PhP)3] or [MNCl(Et2dtc)(Me2PhP)2].[23b,29]
The six-coordinate complex [ReNCl(Et2dtc)2(PTA)] (6) was
isolated in a similar way starting from [ReNCl2(PTA)3] (1),
or [ReNCl(Et2dtc)(PTA)2] (4), with 2 and 1 equiv. of N,N-
diethyldithiocarbamate, respectively (Scheme 1). In com-
plex 6, one PTA was retained as confirmed by the observa-
tion of a singlet at δ = –74.5 ppm in the 31P NMR spec-
Figure 4. ORTEP view of complex 5 displaying the thermal ellip-
soids at 30% probability.
Eur. J. Inorg. Chem. 2008, 2670–2679
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. Marchi et al.
FULL PAPER
1
trum. The H NMR spectrum displayed the resonances of
Experimental Section
the CH2 protons of PTA at δ = 4.6–4.0 ppm and those of
ethyl protons of dithiocarbamate ligands. In fact, methyl
protons resonated as four triplets at δ = 0.70 ppm (two
overlapped triplets), δ = 0.85 ppm and 0.97 ppm, while the
resonances due to the methylene protons appeared as four
overlapped multiplets between δ = 3.6 and 2.8 ppm. These
data support for 6 a six-coordinate disposition where one
sulfur donor of a coordinated Et2dtc is trans to the ReϵN
multiple bond, like in the structurally characterized analo-
General: Unless otherwise noted, all chemicals were of reagent-
grade quality and used without further purification. The starting
compounds [ReNCl2(PPh3)2],[32] [ReOXCl2(PPh3)2] (X
=
Cl–,
MeO–, OEt–),[33] [ReCl3(NCMe)(PPh3)2],[34] and 1,3,5-triaza-7-
phosphaadamantane (PTA),[35] were prepared according to litera-
ture procedures. Elemental analyses were performed using a Carlo–
Erba Instruments model EA 1110. FT-IR spectra were recorded in
a range 4000–200 cm–1 with a Nicolet 510 P FT-IR instrument in
KBr, using a Spectra-Tech collector diffuse reflectance accessory.
Proton spectra of CDCl3, CD3OD solutions of the compounds
were examined with a Bruker AM 200 spectrometer with SiMe4 as
internal standard, 31P NMR on the same instrument with an 85%
H3PO4 solution as external standard.
gous complexes [MN(Et2dtc)2(Me2PhP)] (M
=
Re,
Tc).[6b,23b,29] The most reactive site in the complexes
[MNCl2(Me2PhP)3] (M = Re, Tc) is the Cl– in a trans posi-
tion to the nitride group. In the reactions with monoanionic
bidentate ligands such as N,N-dialkyldithiocarbamates, one
phosphane and one Cl– anion are exchanged and the neu-
tral species [MNCl(R2dtc)(PMe2PhP)2] are formed. This
Synthesis and Characterization of Complexes 1–3
[ReNCl2(PTA)3] (1): A solution of PTA (110 mg, 0.70 mmol) in
CH2Cl2 (20 mL) was added to a suspension of [ReNCl2(PPh3)2]
substitution is followed by a rearrangement with migration (140 mg, 0.18 mmol, 30 mL of CH2Cl2). The reaction mixture was
of the remaining Cl– trans to the nitrido ion. Thus, a second
refluxed for 1 h. The color changed from pink to bright yellow, and
a solid precipitated upon evaporation of most of the solvent. The
molecule of dithiocarbamate substitutes one phosphane
and the trans-Cl–.[27] More recently Dilworth and co-
crude yellow-orange solid was collected and washed three times
with Et2O in order to eliminate PPh3. Crystallization from CH2Cl2/
workers have reported diazenide-rhenium complexes with
EtOH gave 1 as a yellow powder, which was separated and washed
dithiocarbamate ligands of the formula [ReNNC6H4-4-
with EtOH and Et2O. Recrystallization of 1 from CH2Cl2/Me2CO
OCH3(dtc)2(PPh3)][30] in which the position trans to the di-
azenide ligand is occupied by a sulfur atom of one of the
dithiocarbamate ligands. The treatment of 1, 4, or 6 with
an excess of Na[Et2dtc] gave rise to the displacement of all
(1:1, v/v) gave suitable crystals for X-ray diffraction analysis
(94 mg, 72% yield). C18H36Cl2N10P3Re (742): calcd. C 29.11, H
4.89, N 18.87; found C 29.20, H 4.75, N 18.90. IR (KBr): ν =
˜
1
1281, 1242 (νC–N), 1050 (νReϵN), 1015–940 (νPTA) cm–1. H NMR
the coordinated PTA giving the known disubstituted five- (200 MHz, CDCl3, 25 °C): δ = 4.5–4.9 (m, CH2, PTA) ppm. 31P
2
coordinate complex [ReN(Et2dtc)2], 7.[31]
NMR (81.15 MHz, CDCl3, 25 °C): δ = –78.2 (d, JPP = 14.0 Hz),
2
–74.5 (t, JPP = 14.0 Hz) ppm.
Analogously, the trans-dioxidorhenium(V) complex
[ReO2Cl(PTA)3] 2 reacted readily with an excess of Na-
[ReO2Cl(PTA)3] (2): PTA (1.45 mmol) was dissolved in the mini-
mum volume of CH2Cl2 and the solution was added to a suspen-
[Et2dtc] in aqueous solution at room temperature to yield
the known µ-oxo complex [Re2O3(Et2dtc)4] (8) (Scheme 2) sion of [ReOCl2X(PPh3)2] (X = Cl–, MeO–, EtO–) (0.18 mmol) in
CH2Cl2 (30 mL) at room temperature causing a color change to
yellow-orange. The reaction mixture was stirred for 1 h, the volume
of the solution was reduced in vacuo, and then EtOH (5 mL) was
added. Slow evaporation of the solvent at room temperature gave
product 2 as a red-orange solid, which was collected, washed with
EtOH, and dried with Et2O. Crystals of 2 suitable for X-ray crystal-
lography were obtained by recrystallization from CH2Cl2/EtOH;
yield 78.3 mg (60%). C18H36ClN9O2P3Re (725): calcd. C 29.80, H
which was characterized by elemental analysis and IR and
NMR techniques by comparison with a genuine sample.
Conclusions
We have described the syntheses of the new water-soluble
nitrido-[ReNCl2(PTA)3] (1) and dioxido-[ReO2Cl(PTA)3]
(2) complexes of rhenium(V). In water or physiological
solution they undergo partial reversible PTA dissociation.
5.00, N 17.38; found C 30.0, H 5.10, N 17.20. IR (KBr): ν = 940–
˜
1015 (νPTA), 788 (νO=Re=O) cm–1. 1H NMR (200 MHz, CD3OD,
The reactions of 1 with increasing quantities of sodium 25 °C): δ = 4.4–5.0 (m, 36 H, CH2) ppm. 31P NMR (81.15 MHz,
2
2
CD3OD, 25 °C): δ = –85.5 (d, JPP = 7.5 Hz), –70.5 (t, JPP
=
N,N-diethyldithiocarbamate gave the new complexes
[ReNCl(Et2dtc)(PTA)2] (4) and [ReN(Et2dtc)2(PTA)] (6)
and finally the known complex [ReN(Et2dtc)2], where the
coordinated PTA are progressively replaced. The recrystalli-
7.5 Hz) ppm.
[ReCl3(PTA)2(PPh3)] (3): PTA (73.2 mg, 0.48 mmol) dissolved in
CH2Cl2 was added to solution of [ReCl3(NCMe)(PPh3)2]
a
zation of [ReNCl(Et2dtc)(PTA)2] (4) afforded an unexpec- (100 mg, 0.12 mmol) in a 1:1 mixture of C6H6 and CH2Cl2. The
reaction mixture was refluxed for 30 min under nitrogen. The solu-
tion was filtered and concentrated to small volume causing the pre-
cipitation of a red-orange solid which was collected, washed with
EtOH, and dried with Et2O. Crystals of this compound were grown
from CHCl3/Me2CO (1:2, v/v); yield 55.3 mg (53%).
C30H39Cl3N6P3Re (869): calcd. C 41.43, H 4.52, N 9.66; found C
ted dinuclear species [Re2N2Cl3(Et2dtc)(PTA)4] (5).
The reaction of complex [ReO2Cl(PTA)3] (2) gave exclu-
sively the known µ-oxo complex [Re2O3(Et2dtc)4].
Although the chemical behavior of [ReNCl2(PTA)3] is
very similar to analogous nitrido complexes containing alk-
ylphosphanes [ReNCl2(PR3)3], it may be noted that this
new complex, as well as [ReO2Cl(PTA)3], is soluble in water
and could be used as a starting precursor to develop a new
chemistry of rhenium for applications of its radioisotopes
Re-188/186 in nuclear medicine.
41.52, H 4.61, N 9.60. IR (KBr): ν = 1281, 1242 (νC–N), 1015–947
˜
(νPTA), 1097 (νPPh3) cm–1. 1H NMR (200 MHz, CDCl3, 25 °C): δ =
14.95 (s, 12 H, PPh3), 12.80 (s, 6 H, CH2, PTA), 11.00 (d, 6 H,
CH2, PTA), 9.05 (m, 6 H, CH2, PTA), 7.92 (m, 3 H, PPh3), 7.11
(d, 6 H, CH2 PTA) ppm.
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Eur. J. Inorg. Chem. 2008, 2670–2679

Water-Soluble Rhenium Complexes
Tests of Stability of 1 and 2 in Water and Physiological Solution by
31P NMR Spectroscopy: Solutions of 1 or 2 in water or in physio-
logical solution (0.036 molL–1) with an internal capillary contain-
ing C6D6 for lock, were monitored by 31P NMR after 5 min, 3 h,
and 24 h at a constant T = 298.15 K.
[ReN(Et2dtc)2(PTA)] (6). Method A: One equivalent of Na[Et2dtc]
in acetone was added to a solution of [ReNCl(Et2dtc)(PTA)2] 4
(100 mg, 0.14 mmol) in CH2Cl2. The reaction mixture was refluxed
for 1 h, concentrated under vacuo and the bright yellow solid of 6
was washed with EtOH and Et2O; yield 77 mg (85%).
Method B: Complex 6 may also be prepared under the same condi-
tions as above adding 2 equiv. of Na[Et2dtc] to a solution of
[ReNCl2(PTA)3] (1) (100 mg, 0.13 mmol); yield 75 mg (88%).
C16H32N6PReS4 (654): calcd. C 29.36, H 4.93, N 12.84, S 19.57;
1: δ = –96.5 (s, PTA); –74.7, –71.3, –69.4 ppm (broad signals).
2: δ = –96.5 ppm (s, PTA); –83.6, –81.25, –68.3 ppm (broad sig-
nals).
found C 29.27, H 5.01, N 12.92, S 19.65. IR (KBr): ν = 1490, 1520
˜
Synthesis and Characterization of Complexes 4–6
(νC–N), 950–1015 (νPTA), 1240 (νC–S) cm–1. 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 4.6–4.0 (m, 12 H, CH2, PTA), 2.8–3.6 (m, 8,
CH2, Et2dtc), 0.97 (t, 3 H, CH3, Et2dtc), 0.85 (t, 3 H, CH3, Et2dtc),
0.70 (m, 6 H, CH3, Et2dtc) ppm. 31P NMR (81.15 MHz, CDCl3,
25 °C): δ = –74.5 (s, PTA) ppm.
[ReNCl(Et2dtc)(PTA)2] (4) and [Re2N2Cl3(Et2dtc)(PTA)4] (5): The
complex [ReNCl2(PTA)3] (100 mg, 0.13 mmol) dissolved in CH2Cl2
(40 mL) was treated with a solution containing 1 equiv. of Na-
[Et2dtc] dissolved in the minimum volume of acetone. The resulting
orange solution was stirred at room temperature for 1 h. Solid
NaCl was filtered off, the solvent was evaporated in vacuo and the
solid residue dissolved in a 1:1 mixture of CH2Cl2 and acetone.
Slow evaporation of the solvents at room temperature gave orange-
yellow crystals of 4; yield 75 mg (80%). C17H34ClN8P2ReS2 (698):
calcd. C 29.23, H 4.91, N 16.05, S 9.17; found C 29.12, H 4.99, N
Reaction of 1, 4, or 6 with an Excess of Na[Et2dtc]: Treatment of 1,
4, or 6 in CH2Cl2 with a ten-fold excess of Na[Et2dtc] resulted in
the formation of the known nitrido complex [ReN(Et2dtc)2] (7).
The identity of this product was based on comparison of its spec-
troscopic properties and elemental analysis with those of an au-
thentic sample;[31a] yield Ͼ70%.
15.94, S 9.2. IR (KBr): ν = 1520 (νC–N, Et2Dtc), 950–1015 (νPTA),
˜
1240 (νC–S) cm–1. 1H NMR (200 MHz, CDCl3, 25 °C): δ = 2.95,
3.22 (m, 4 H, CH2, Et2dtc), 0.80 (t, 6 H, CH3, Et2dtc), 4.4–4.0 (m,
24 H, PTA) ppm. 31P NMR (81.15 MHz, CDCl3, 25 °C): δ = –77.5
(s) ppm.
Reaction of 2 with an Excess of Na[Et2dtc]: Na[Et2dtc] (87 mg,
0.4 mmol) dissolved in water was added to an aqueous solution of
[ReO2Cl(PTA)3] (2) (70 mg, 0.1 mmol). The reaction mixture was
allowed to stir at room temperature for 30 min. A brown powder
precipitated, which was collected and washed with ethanol. The
product was then redissolved in CH2Cl2 and EtOH was added.
Slow evaporation of the solvents at room temperature afforded
brown-yellow crystals of [Re2O3(Et2dtc)4] (8). Analytical and spec-
troscopic data were coincident with those reported in the litera-
ture.[36]
Recrystallization of 4 (50 mg, 0.72 mmol) from CH2Cl2/MeOH
(1:1, v/v) gave crystals of complex [Re2N2Cl3(Et2dtc)(PTA)4] (5);
yield 37 mg (80%). C29H58Cl3N15P4Re2S2 (1283): calcd. C 27.12, H
1
4.55, N 16.37, S 4.98; found C 27.15, H 4.50, N 16.29, S 4.80. H
NMR (200 MHz, CDCl3, 25 °C): δ = 1.42 (m), 3.68–4.10 (m), 4.4–
4.8 (m) ppm. 31P NMR (81.15 MHz, CDCl3, 25 °C): δ = –89.5 (d,
2JPP = 10 Hz), –85.2 (d, JPP = 14 Hz), –84.8 (d, JPP = 10 Hz), Crystal Structure Determinations: Crystal data of compounds 1, 2,
2
2
2
–71.4 (d, JPP = 14 Hz) ppm.
3, and 5 were collected with a Nonius Kappa CCD diffractometer
Table 5. Crystallographic data.
Compound
1
2
3
5
Formula
M
Space group
Crystal system
a [Å]
b [Å]
c [Å]
α [°]
C
823.65
P21/c
monoclinic
14.8370(1)
21.2745(2)
20.7865(2)
90
18H36Cl2N10P3Re·4.5H2O C18H36ClN9O2P3Re·H2O
C30H39Cl3N6P3Re
869.13
R-3
trigonal
39.7586(8)
39.7586(8)
10.9037(2)
90
C29H58Cl3N15P4S2Re2·3H2O
1337.70
P21/n
monoclinic
12.1124(2)
23.3583(4)
17.9431(3)
90
743.13
P212121
orthorhombic
11.6936(2)
13.0066(3)
17.0937(3)
90
β [°]
93.0576(5)
90
6551.9(1)
8
1.670
3304
90
90
90
120
15008.9(5)
18
1.731
106.5142(9)
90
4867.1(1)
4
1.826
2640
γ [°]
V [Å3]
Z
2599.85(9)
4
1.899
1480
50.02
Dc [gcm–3
F(000)
]
7776
40.60
µ(Mo-Kα) [cm–1
]
40.62
54.00
Measured reflections
Unique reflections
Rint
59672
15793
0.057
25361
7456
0.055
37318
8037
0.046
35554
11107
0.054
Obsd. reflections] [I Ն 2σ(I)] 11796
6628
6175
8107
θmin–θmax [°]
hkl ranges
1.7–28.0
–19,19; –28,28; –27,27
0.0403
0.1084
691
3.3–30.0
–15,16; –17,18; –23,24
0.0323
0.0689
324
1.9–28.0
3.5–27.5
–39,52; –50,52; –13,14 –15,15; –30,30; –21,23
R(F2) (obsd. reflections)
wR(F2) (all reflections)
Number of variables
Goodness of fit
0.0317
0.0633
388
1.048
1.77; –1.48
0.0416
0.1081
552
1.019
1.40; –1.56
1.057
1.73; –1.77
1.032
1.33; –1.91
∆ρmax; ∆ρmin [eÅ–3
]
Eur. J. Inorg. Chem. 2008, 2670–2679
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A. Marchi et al.
FULL PAPER
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and absorption effects.[38] The crystal parameters and other experi-
mental details of the data collections are summarized in Table 5.
The structures were solved by direct methods (SIR97)[39] and re-
fined by full-matrix least square methods with all non-hydrogen
atoms anisotropic and hydrogen atoms included on calculated posi-
tions, riding on their carrier atoms. The asymmetric unit of com-
pound 1 contains two molecular complexes, differing slightly in the
rotation of PTA ligands, and nine water molecules, three of them
being disordered were refined over two positions with occupancy
of 0.5 each. All the hydrogen atoms of water molecules could not
be determined. In compound 5 the N9–Re2–Cl2 moiety, disordered
over two opposite orientations, was refined over two positions with
occupancies of 0.73 and 0.27, respectively. The asymmetric unit
contains also three water molecules, two of them being disordered
were refined over two positions with occupancies of 0.7 and 0.3.
All the hydrogen atoms of water molecules could not be deter-
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PARST[41] implemented in the WINGX system of programs.[42]
ORTEP[43] views are shown in Figures 1, 2, 3, and 4. Selected bond
lengths and angles are given in Tables 1, 2, 3, and 4.
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Acknowledgments
This work was supported by Ministero dell’Università e della
Ricerca Scientificia e Tecnologica (MURST) in the frame of the
project “Pharmacological and Diagnostic Properties of Metal
Complexes” (coordinator Prof. G. Natile). The authors thank Con-
sorzio Interuniversitario di Ricerca in Chimica dei Metalli nei Sis-
temi Biologici for a grant to E. M. We thank Mr. M. Fratta for
technical assistance and elemental analyses.
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Received: January 30, 2008
Published Online: April 29, 2008
Eur. J. Inorg. Chem. 2008, 2670–2679
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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