New Re(III) complexes with alkylthioureas as precursors to other Re(III) compounds. Crystal structures of [Re(N-ethylthiourea)6](PF6)3 and [Re(N,N′-dimethylthiourea)6](PF6)3

Article abstract of DOI:10.1016/S0277-5387(99)00096-0

New Re(III) complexes with thiourea derivatives have been synthesized by reduction of perrhenate with tin(II) chloride in 2N hydrochloric acid in the presence of excess alkylthiourea. The obtained compounds were [Re^III(alkylthiourea-S)₆]X₃.nH₂O, where X is Cl^- or PF₆^- and alkylthiourea is N-methylthiourea (Metu), N,N′-dimethylthiourea (Me₂tu) or N-ethylthiourea (Ettu). Complexes were characterized by elemental and thermal analyses and by electronic and FTIR spectroscopy. Their kinetic stabilities in aqueous and methanolic solutions were also studied. Results were compared with those previously reported for [Re^III(tu-S)₆]Cl₃.4H₂O, where tu=thiourea. Molecular structures of [Re^III(Ettu)₆](PF₆)₃ and [Re^III(Me₂tu)₆](PF₆)₃ were determined by single crystal X-ray diffraction methods. The coordination polyhedra around the Re(III) ion are distorted octahedra. The six alkylthiourea ligands are sulfur bonded to the central atom [d(Re-S) ranges from 2.402(4) to 2.441(4) A for the ethylthiourea complex and from 2.416(3) to 2.446(3) for the dimethylthiourea one]. Capability of working as starting materials via ligand substitution, in methanolic medium for these new Re(III) complexes and for previously reported [Re^III(tu)₆]Cl₃.4H₂O is stated. Selected incoming ligands, 1,2-bis(diphenylphosphino) ethane (dppe) and 1,3-bis(diphenylphosphino) propane (dppp), lead to the already known [Re^III(dppe)₂Cl₂]Cl.2MeOH and [Re^III(dppp)₂Cl₂]Cl with good yields. Re(III) complexes with thiourea and alkylthioureas can be ordered according to their substitution rate as follows: [Re(tu)₆]³⁺<[Re(Ettu)₆] ³⁺?[Re(Metu)₆]³⁺<[Re(Me ₂tu)₆]³⁺. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00096-0

Polyhedron 18 (1999) 2099–2107
New Re(III) complexes with alkylthioureas as precursors to other Re(III)
compounds. Crystal structures of [Re(N-ethylthiourea)6](PF6)3 and
[Re(N,N9-dimethylthiourea)6](PF6)3
a
a
a
b
Dinorah Gambinoa , , Julio Benıtez , Lucıa Otero , Eduardo Kremer , Enrique J. Baran ,
*
´
´
Oscar E. Piroc
a
´
´
´
´
Catedra de Quımica Inorganica, Facultad de Quımica, C.C.1157, Montevideo, Uruguay
bCEQUINOR, Facultad de Ciencias Exactas, UNLP, 1900-La Plata, Argentina
c
´
Departamento de Fısica, Facultad de Ciencias Exactas, UNLP and Programa PROFIMO (CONICET), C.C. 67, 1900- La Plata, Argentina
Received 1 September 1998; accepted 31 March 1999
Abstract
New Re(III) complexes with thiourea derivatives have been synthesized by reduction of perrhenate with tin(II) chloride in 2N
hydrochloric acid in the presence of excess alkylthiourea. The obtained compounds were [ReIII(alkylthiourea-S)6]X3.nH2O, where X is
Cl2 or PF26 and alkylthiourea is N-methylthiourea (Metu), N,N9-dimethylthiourea (Me2tu) or N-ethylthiourea (Ettu). Complexes were
characterized by elemental and thermal analyses and by electronic and FTIR spectroscopy. Their kinetic stabilities in aqueous and
methanolic solutions were also studied. Results were compared with those previously reported for [ReIII(tu-S)6]Cl3.4H2O, where
tu5thiourea. Molecular structures of [ReIII(Ettu)6](PF6)3 and [ReIII(Me2tu)6](PF6)3 were determined by single crystal X-ray diffraction
methods. The coordination polyhedra around the Re(III) ion are distorted octahedra. The six alkylthiourea ligands are sulfur bonded to the
˚
central atom [d(Re–S) ranges from 2.402(4) to 2.441(4) A for the ethylthiourea complex and from 2.416(3) to 2.446(3) for the
dimethylthiourea one]. Capability of working as starting materials via ligand substitution, in methanolic medium for these new Re(III)
complexes and for previously reported [ReIII(tu)6]Cl3.4H2O is stated. Selected incoming ligands, 1,2-bis(diphenylphosphino) ethane
(dppe) and 1,3-bis(diphenylphosphino) propane (dppp), lead to the already known [ReIII(dppe)2Cl2]Cl.2MeOH and [ReIII(dppp)2Cl2]Cl
with good yields. Re(III) complexes with thiourea and alkylthioureas can be ordered according to their substitution rate as follows:
[Re(tu)6]31,[Re(Ettu)6]31([Re(Metu)6]31,[Re(Me2tu)6]31
.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Rhenium(III); Alkylthioureas complexes; [Re(N-ethylthiourea)6](PF6)3 structure; [Re(N,N9-dimethylthiourea)6](PF6)3 structure; Ligand
substitution onto Re(III)-alkylthioureas; Synthesis of diphosphine rhenium(III) complexes by ligand substitution
1. Introduction
methylthiourea (Me2tu) are also able to stabilize Tc(III).
[TcIII(Metu-S)6]31and [TcIII(Me2tu-S)6]31 complexes
have been prepared and characterized [11,12]. These Tc
complexes have also been tested as precursors for further
Tc(III) compounds [13,14].
Ligand substitution onto suitable precursors is also an
important route of synthesis of Re complexes. This syn-
thetic route relies on labile Re species as preparative
intermediates [15–20]. Syntheses of Re(III) complexes
described in the literature are mainly based on substitution
onto the trans-[ReCl3(NCCH3)(PPh3)2] precursor, which
usually leads to mixed-ligand neutral species. Only scarce
examples of complete ligand substitution onto this pre-
cursor are reported [21]. Moreover, this precursor is not
suitable for ligand substitution in aqueous media. So,
substitution reactions are commonly performed in organic
Owing to the extensive use of the g-emitter 99mTc in
diagnostic nuclear medicine and the potential usefulness of
186Re and 188Re for radiotherapeutic purposes, the chemis-
try of Tc and Re compounds has become an active field of
research [1–4].
Ligand substitution onto suitable precursors is an im-
portant route of synthesis of Tc complexes. Being thiourea
(tu) a poor ligand, its easy substitution under mild con-
ditions turned [TcIII(tu-S)6]Cl3 into a useful precursor to
other Tc(III) compounds in aqueous and methanolic media
[5–10].
N-methylthiourea
(Metu)
and
N,N9-di-
*Corresponding author. Fax: 1598-2-9241-906.
E-mail address: dgambino@bilbo.edu.uy (D. Gambino)
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00096-0
1999 Elsevier Science Ltd. All rights reserved.

2100
D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
solvents such as dichloromethane, benzene or acetonitrile
[15,16,22–24].
are soluble in acetone, acetonitrile and methanol, slightly
soluble in ethanol and insoluble in water. Thermal analyses
TGA and DTA of [Re(Metu)6](PF6)3 agreed with one
water molecule of crystallization per complex ion (1.4%
weight loss centered at 1208C, 1.5% calc.). Absence of
water molecules of crystallization was demonstrated for
Me2tu and Ettu complexes.
On the other hand [ReIII(thiourea-S)6]Cl3.4H2O has
recently been synthesized and fully characterized [25].
Taking into account the chemical analogy between Re and
Tc compounds, this complex is obviously a potential
precursor to other Re(III) compounds, by ligand substitu-
tion. Alkylthioureas are also expected to stabilize Re(III)
2.1.1. [ReIII(N-methylthiourea-S)6 ](PF6 )3?H2O
by
sulfur
bonding
to
central
atom.
These
[ReIII(alkylthiourea-S)6]31 compounds could be also tested
as precursors. Differences in reactivity of these compounds
are expected, mainly due to the presence of bulkier groups
(compared to hydrogen) bonded to thioureas nitrogens
surrounding the central Re(III) atom. As in Tc(III) com-
pounds, substitution is expected to proceed via a dissocia-
tive intimate mechanism [26]. Therefore, changes in
leaving ligand nature can be a suitable way to modify
substitution kinetics, and provide a wider range of pre-
cursors which could find much use in the synthesis of other
Re(III) complexes in aqueous or alcoholic media.
Yield 60%. The complex was recrystallized from an
ethanolic solution by slow evaporation at room tempera-
ture. Anal (%): Found: C, 12.5; H, 3.1; N, 14.1; S, 16.4;
Re, 15.3. Calc. for C12H36N12S6Re P3F18?H2O: C, 12.2;
H, 3.2; N, 14.2; S, 16.3; Re, 15.8. Electronic spectrum
(ethanol): 358sh, 387 (8.13103
(4.83103 M21cm21), 241 nm.
M
21cm21), 410 sh, 454
2.1.2. [ReIII(N,N9-dimethylthiourea-S)6 ](PF6 )3
Yield 30%. The complex was recrystallized by slow
evaporation at room temperature of a 1:1 (v/v) mixture
acetone/2N HCl (0.04M Me2tu). Single deep red crystals,
suitable for X-ray analysis were obtained by this pro-
cedure. Anal. (%): Found: C, 17.4; H, 3.5; N, 13.2; S,
15.0; Re, 15.2. Calc. for C18H48N12S6Re P3F18: C, 17.3;
H, 3.9; N, 13.5; S, 15.4; Re, 14.9. Electronic spectrum
We report here results on synthesis and full characteriza-
tion of [ReIII(alkylthiourea)6]X3.nH2O complexes, where
X is Cl2 or PF26 and alkylthiourea is N-methylthiourea,
N,N9-dimethylthiourea or N-ethylthiourea (Ettu). Molecu-
lar
structures
of
[ReIII(Me2tu)6](PF6)3
and
[ReIII(Ettu)6](PF6)3 were determined by single crystal X-
ray diffraction methods and they are reported here.
(acetone): 370 sh, 391 (6.03103
M
21cm21), 425sh, 471
(3.53103 M21cm21) and 239 nm (ethanol).
A comparative stability study in aqueous and methanolic
media with the [ReIII(thiourea)6]Cl3 complex previously
reported, has also been performed for all new compounds.
Capability of working as starting materials via ligand
substitution in methanolic medium, is stated for
[ReIII(thiourea)6]Cl3 and alkylthioureas Re(III) complexes
with 1,2-bis(diphenylphosphino)ethane (dppe) and 1,3-bis-
(diphenylphosphino)propane (dppp) as incoming ligands.
2.1.3. [ReIII(N-ethylthiourea-S)6 ](PF6 )3
Yield 50%. Single deep red crystals, suitable for X-ray
analysis were obtained from a methanolic solution by slow
evaporation at room temperature. Anal (%): Found: C,
17.6; H, 3.6; N, 13.5; S, 15.0. Calc. for C18H48N12S6Re
P3F18: C, 17.3; H, 3.9; N, 13.5; S, 15.4. Electronic
spectrum (ethanol): 329sh, 389 (9.43103 M21cm21), 417
sh, 469 (6.43103 M21cm21), 241 nm.
2. Experimental
2.2. Preparation of hexakis(alkylthiourea-S) rhenium(III)
trichloride compounds
All common laboratory chemicals were purchased from
commercial sources and used without further purification.
These salts were obtained from the same solutions
previously detailed for the isolation of hexafluorophos-
phate salts. For all of them, thermal analyses showed no
water molecules of crystallization.
2.1. Preparation of hexakis(alkylthiourea-S) rhenium(III)
tri(hexafluorophosphate) compounds (alkylthiourea5N-
methylthiourea, N,N9-dimethylthiourea or N-
ethylthiourea)
2.2.1. [ReIII(N-methylthiourea-S)6 ]Cl3
This salt was obtained by adding a high volume of
acetone (50 cm3) to the reaction mixture. A bright yellow
solid was isolated and washed with acetone. Yield 64%.
The compound was recrystallized from a 2N HCl (0.2M
Metu)/acetone solution. Anal. (%): Found: C, 17.2; H, 4.2;
N,19.6; S, 22.8; Re, 21.3. Calc. for C12H36N12S6 ReCl3:
C, 17.3; H, 4.3; N, 20.1; S, 23.0; Re, 22.3. Electronic
spectrum (ethanol): 359sh, 385 (7.23103 M21cm21), 405
sh, 453 (4.33103 M21cm21), 241 nm. The compound is
SnCl2.2H2O (200 mg, 0.89 mmol) was dissolved in 2N
HCl (5.5 cm3). A mixture of alkylthiourea (15 mmol) and
NH4ReO4 (100 mg, 0.37 mmol) was added to the solution.
The solution was stirred overnight at room temperature and
filtered off, if necessary. After keeping the final solution at
258C for 1 h, 0.5ml of a 6M NaPF6 aqueous solution was
added. The yellowish solids obtained were washed with
small portions of cold water, and dried. The compounds

D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
2101
soluble in water, ethanol and methanol and insoluble in
acetone.
complex at each time was determined as the quotient
between measured absorbance and initial absorbance.
2.2.2. [ReIII(N,N9-dimethylthiourea-S)6 ]Cl3
2.4. Ligand substitution experiments onto [ReL6 ]X3 (L5
tu, Metu, Ettu or Me2tu; X5Cl2 or PF62 ) by dppe and
dppp
This salt was obtained using a reaction mixture volume
of 2.7 cm3. A yellow solid appeared after stirring over-
night. It was dissolved in acetone and a white solid,
probably excess ligand, was discarded. The acetone solu-
tion was evaporated to dryness and the sticky solid was
treated with n-butanol to give a yellow solid which was
then washed with several small portions of n-buthanol.
Yield: 20%. Anal (%): Found: C, 24.1; H, 5.3; N, 17.8; S,
20.5. Calc. for C18H48N12S6ReCl3: C, 23.6; H, 5.3; N,
18.3; S, 20.9. Electronic spectrum (aqueous 2N HCl): 363
sh, 391 (5.13103 M21 cm21), 409 sh, 454 (2.13103 M21
cm21), 240 nm. The compound is soluble in water,
acetonitrile and methanol and less soluble in acetone and
ethanol.
0.1 mmol of [ReL6]X3 were dissolved in a mixture of
15 ml of methanol and 0.2 ml of 12N HCl. To this yellow
solution 1,2-bis(diphenylphosphino)ethane (dppe) (200 mg,
0.5 mmol) or 1,3-bis(diphenylphosphino)propane (dppp)
(200 mg, 0.48 mmol) was added. The reaction mixture was
heated to reflux (6–7 h). Solvent was evaporated in vacuo
to about 5 ml. The diphosphine complex was isolated by
keeping the solution at 2–88C for at least 2 days. For dppe,
a red intermediate (lmax5474 nm) was detected during the
refluxing period which turned completely into the final
orange [Re(dppe)2Cl2]1 complex.
2.2.3. [ReIII(N-ethylthiourea-S)6 ]Cl3
2.4.1. [ReIII(dppp)2Cl2 ]Cl
This compound was also obtained using a lower reaction
volume (2.7 cm3). A dark orange solid was isolated by
keeping the solution for several days at –58C and dried
under vacuo. Yield: 50%. Anal (%): Found: C, 23.1; H,
5.3; N, 17.8; S, 20.5. Calc. for C18H48N12S6ReCl3: C,
23.6; H, 5.3; N, 18.3; S, 20.9. Electronic spectrum
(methanol): 328 sh, 387 (9.03103 M21 cm21), 417 sh,
468 (5.83103 M21 cm21), 240 nm. The compound is
soluble in water and methanol and less soluble in acetone
and ethanol.
The
yellow
solid
was
recrystallized
from
dichloromethane-methanol-2N HCl by slow evaporation at
room temperature. Electronic spectrum (methanol): 432
nm. Main IR bands: 3063 (CH stretching of the phenyl
groups), 2932 (CH2 stretching), 1484 (CH2 bending), 1434
(P–phenyl stretching), 1092 (C–C stretching), 745 and
697 (out of plane CH2 bending), 327 cm21 (Re–Cl
stretching) [28]. The compound is a 1:1 electrolyte in
acetonitrile. Anal (%): Found: C, 56,2; H, 5.9. Calc. for
C54H52Cl2P4ReCl?H2O.CH3OH: C, 56.6; H, 5.4. Yields
and times required to complete ligand substitution were
determined and reported in Table 1.
2.3. Characterization
C, H, N and S elemental analyses were carried out with
a Carlo Erba Model EA 1108 elemental analyzer. Rhenium
was determined spectrophotometrically by reaction with
a-furyldioxime, modifying a reported method [27].
2.4.2. [ReIII(dppe)2Cl2 ]Cl.2MeOH
The orange solid was washed with ether/ethanol (10:1
v/v) and dried in vacuo. Yields: 40–55%. Crystals suitable
for X-ray diffraction determinations were obtained by slow
evaporation of a methanol solution at room temperature.
Anal (%): Found: C, 56.3%; H, 4.4%. Calc. for
C52H48Cl2P4ReCl.2CH3OH: C, 56.2%; H, 4.9%. Crystal
data, together with electronic and IR spectra agreed with
those previously reported for [Re(dppe)2Cl2]Cl.2MeOH
[29,30].
Thermogravimetric and differential thermal analyses
(TGA and DTA) were performed up to 4008C on
Shimadzu analyzers TGA-50 and DTA-50 (calcined Al2O3
as reference) with a 50 cm3 min21 N2 flow and a heating
rate of 68C min21
.
FTIR spectra (4000–400 cm21) were measured as KBr
pellets on a Bruker IFS 66 instrument. Low frequencies
FTIR spectra (500–50 cm21) were performed as poly-
ethylene pellets on a Bruker 113v equipment.
Table 1
Electronic absorption spectra were performed on a
Spectronic 3000 spectrophotometer.
Yield and time required for the Re(III) precursors to complete ligand
substitution with dppp as incoming ligand
Yield (%)
Timea (h)
Kinetic stability studies were carried out as previously
described for [Re(tu)6]Cl3.4H2O [25]. Decomposition of
[Re(Metu)6]Cl3, [Re(Ettu)6]Cl3 and [Re(Me2tu)6]Cl3 in
the different conditions tested, i.e. aqueous or methanolic
solution 1023–1024 M, pH range 1–5 and temperature
25.08C60.1, was followed spectrophotometrically. For a
fixed set of conditions, the remaining percentage of the Re
[Re(tu)6]31
55
70
75
58
4.5
1.0
1.2
0.5
[Re(Metu)6]31
[Re(Ettu)6]31
[Re(Me2tu)6]31
a Time necessary to complete substitution of the alkylthiourea or
thiourea by dppp.

2102
D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
2.5. X-ray diffraction data and crystal structure
determination and refinement of [Re(Ettu)6 ](PF6 )3 and
[Re(Me2tu)6 ](PF6 )3
thermal parameters of the ethyl and dimethylthiourea
ligands toward their free ends suggests relatively large
librational vibrations and/or displacive disorder of these
groups. Several hydrogen atoms were located at approxi-
mate positions in a difference Fourier map suggesting that
amide hydrogens lay on S5CN2Cethyl planes for
Crystal data, data collection procedure, structure de-
termination methods and refinement results are summa-
rized in Table 2. The observed trend of an increase in the
[Re(Ettu)6](PF6)3 and on S5C(NCmethyl
)
planes for
2
Table 2
Crystal data and structure solution methods and refinement for [Re(SC(NHCH3)2)6](PF6)3 (I) and [Re(SC(NH2)NHCH2CH3)6](PF6)3 (II)
Structure I
Structure II
Empirical formula
Formula weight
Temperature (K)
Crystal system
C18H48N12S6ReF18P3
1246.15
293(2)
C18H48N12S6ReF18P3
1246.15
293(2)
Monoclinic
Orthorhombic
Space group
P21 /c
P21cnf
a
g
Unit cell dimensions
˚
a (A)
13.239(3)
20.905(6)
17.005(5)
102.240(2)
4599(2)
11.828(2)
15.484(2)
25.099(3)
˚
b (A)
˚
c (A)
b (8)
3
˚
Cell volume (A )
Formula units/unit cell
Dcalc (Mg/m3)
4597(1)
4
4
1.800
1.801
Absorption coefficient
F(000)
3.124 mm21
2472
3.126 mm21
2472
Crystal size
0.2030.1530.07 mm
Red/parallelepiped
0.1430.2030.32 mm
Red/parallelepiped
Crystal color/shape
Diffractometer/scan
Radiation,
graphite monochromator
Scan width
Enraf-Nonius CAD-4/v22u
˚
MoKa, l50.71073 A
0.810.35 tan u
Standard reflection
Decay of standard (%)
u range for data collection
Index ranges
Reflections collected
Independent reflections
Observed reflections
[I.2s(I)]
(22,8,7)
62%
1.57 to 24.998
215#h#15, 0#k#24, 0#l#20
8633
(1,2,214)
62%
1.55 to 27.968
0#h#15, 0#k#20, 21#l#33
6308
6477 [Rsymm50.034]
4906 [Rsymm50.049]
3668
3006
b
h
Data reduction and correction
and structure solutionc and
refinementd programs
Refinement method
Weights, w
SDP [39],SHELX-76 [40], SHELX-86 [41], SHELX-93 [42]
Full-matrix least-squares on F2
[s2(F2o)1(0.05P)211.19P]21
[s2(F2o)1(0.0522P)210.68P]21
P5[Max(F2o,0)12F2c]/3
Data/restraints/parameters
Goodness-of-fit on F2
Final R indicese [I.2s(I)]
R indices (all data)
6477/0/524
1.061
R150.058, wR250.111
R150.126, wR250.138
4906/1/524
1.048
R150.0481, wR250.0973
R150.1031, wR250.1202
20.006(12)
Absolute structure parameter
Largest diff. peak and hole
a
23
23
i
˚
˚
0.79 and 20.83 e.A
0.913 and 21.205 e.A
Least-squares refinement of [(sin u )/l]2 values for 22 reflections in the 17.54,2u,27.048 range.
b Corrections: Lorentz, polarization and absorption [38]. The maximum and minimum transmission factors were 0.814 and 0.598.
c Neutral scattering factors and anomalous dispersion corrections.
d Structure solved by Patterson and Fourier methods and the final molecular model obtained by anisotropic full-matrix least-squares refinement of
non-hydrogen atoms.
e R indices defined as: R15SuuFou2uFcuu/SuFou, wR25[Sw(Fo22Fc2)2 /Sw(F2o)2]1 / 2
.
f Related to the standard space group Pna21 by the interchange of a and c axes.
g Least-squares refinement of [(sinu )/l]2 values for 25 reflections in the 23.6,2u,34.98 range.
h Corrections: Lorentz, polarization and absorption [38]. After this later correction, the Rsym agreement factor among symmetry related reflections
dropped from 0.049 to 0.026; the corresponding maximum and minimum transmission factors were 0.706 and 0.523.
i Located close to the rhenium atom position.

D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
2103
[Re(Me2tu)6](PF6)3 and that methyl hydrogens are at
staggered positions. All hydrogens were positioned on
stereochemical basis and included in the refinement riding
on the atom to which they are bonded with a common
stretchings), 1636 s (NH2 bending), 1575 s (combination
mode of CN and CS stretchings and NCN bending), 1509 s
(CN asymmetric stretching), 1459 w (CH3 bending) and
776 m cm21 (CS stretching). The s, m, w and vw symbols
denote strong, medium, weak and very weak bands respec-
tively. Decrease in CS stretching frequencies and all the
other changes observed for the complexes compared to the
free ligands agree with S-bonding to the rhenium atom
[25,34,35]. New bands at 341 cm21 for [Re(Me2tu)6]-
(PF6)3, at 351 cm21 for [Re(Metu)6](PF6)3?H2O and at
337 cm21 for [Re(Ettu)6](PF6)3 can be tentatively as-
signed to Re–S stretching modes even though low-fre-
quency data were not reported for other Re thiourea
complexes.
Decomposition of [Re(Ettu)6]Cl3, [Re(Metu)6]Cl3 and
[Re(Me2tu)6]Cl3 in water proceeds with lowering of the
intense yellow color of their solutions. ReO2 is the
resulting product. Decomposition reaction has a first order
dependence on complex concentration, in all tested con-
ditions. Stability improves around pH 1.3–2.0 for
[Re(Metu)6]Cl3 and [Re(Me2tu)6]Cl3 and around pH 2.0–
3.0 for [Re(Ettu)6]Cl3. As pH increases, oxidation occurs
with increasing rate. At constant pH, decomposition takes
place according to the following rate order:
isotropic thermal parameter, which in the final run con-
2
˚
verged to U50.12(1) A for [Re(Ettu)6](PF6)3 and to
2
˚
U50.16(1) A for [Re(Me2tu)6](PF6)3.
3. Results and discussion
Reduction of perrhenate by stannous chloride in strongly
acidic aqueous solution in presence of excess N-
methylthiourea or N-ethylthiourea leads to the formation of
hexafluorophosphate and chloride salts of [Re(Metu)6]31
and [Re(Ettu)6]31 with good yields, though the
ethylthiourea complex is more difficult to isolate due to the
formation of sticky solids. Regarding N,N9-di-
methylthiourea, the yields are lower. The reaction proceeds
via a dark red intermediate, that does not disappear
completely. Probably a Re(V) oxo dimethylthiourea com-
plex is formed, as reported in the synthesis of [Re(tu)6]31
[25].
The electronic spectra of all the complexes show a band
shape similar to that reported previously for [Re(tu)6]Cl3.
The visible spectra show also a similar pattern to the Tc
analogs but shifted to higher frequencies [11,12,25].
The FTIR spectra (4000–400 cm21) of the six com-
pounds rule out the presence of ReO12 , ReO31 or m-oxo
species since the characteristic absorptions of these moi-
eties around 830 cm21 and in the 1000–900 cm21 region
are not detected [15,16]. Typical signals of the ligands are
found in the complexes [31,32]. Previous theoretical
assignment of the IR bands for the free N-ethylthiourea
ligand was not available. Tentative assignments are made
based on those for N-methylthiourea. The hexafluoro-
phosphate salts show in addition the nas(PF) and das(FPF)
of the PF26 moiety [33]. Main bands for
[Re(Metu)6](PF6)3?H2O: 3348 s, 3318 s and 3282 s (NH
and symmetric and asymmetric NH2 stretchings), 2970 vw
and 2850 vw (symmetric and asymmetric CH3 stretchings),
1635 s (NH2 bending), 1578 s (combination mode of CN
and CS stretchings and NCN bending), 1503 s (CN
asymmetric stretching), 1461w and 1422 m (symmetric
and asymmetric CH3 bendings), 1293 m (NH bending) and
[Re(Metu)6]Cl3,[Re(tu)6]Cl3<[Re(Me2tu)6]Cl3
as
showed in Fig. 1 and Table 3. [Re(Ettu)6]Cl3 decomposes
more slowly than the others at pH values higher than 2.0.
Therefore kinetics of decomposition in aqueous media
depends on pH and also on ligand nature.
Decomposition reactions in methanol show also a first
order dependence on complex concentration. Decomposi-
tion takes place more slowly in methanol than in aqueous
media (pH values above 2). The complexes decompose in
methanol according to the following rate order:
[Re(Ettu)6]Cl3,[Re(Metu)6]Cl3<[Re(Me2tu)6]Cl3.
So, decomposition by oxidation of the precursors would
compete with substitution of thiourea or alkylthioureas by
other ligands more or less efficiently depending on the
experimental conditions selected [26]. Owing to this
competition, substitution in aqueous solution should be
tried in acidic media despite the fact that the chelating
capability of incoming ligands usually increases with pH.
Therefore, syntheses of new Re compounds by substitution
onto these complexes should be tried in methanolic media
in order to minimize simultaneous oxidation of the starting
material. Such substitution experiments in methanolic
medium onto [ReIIIL6]31 complexes, with L5tu, Ettu,
Metu or Me2tu and dppe as incoming ligand, lead to the
already known [ReIII(dppe)2Cl2]Cl.2MeOH with good
yield. Substitution onto the same starting compounds with
dppp as incoming ligand leads to [ReIII(dppp)2Cl2]Cl in
high yield. This complex has been previously reported but
not fully characterized [36]. A comparison between the
four starting complexes was performed in terms of substi-
tution rate and yield of the substitution. Results with dppe
and dppp as incoming ligands show similar trends. As
755
m
cm21 (CS stretching). Main bands for
[Re(Me2tu)6](PF6)3: 3388 s and 3299 s (in and out of
plane NH stretchings), 2958 w and 2850 vw (symmetric
and asymmetric CH3 stretchings), 1606 s (combination
mode of CN stretching and trans NH bending), 1527 s
(combination mode of CN stretching and cis NH bending),
1482 w and 1450 w (symmetric and asymmetric CH3
bendings) and 715 m cm21 (mainly CS stretching). Main
bands for [Re(Ettu)6](PF6)3: 3371 s, 3310 s and 3271 s
(NH and symmetric and asymmetric NH2 stretchings),
2989 vw and 2850 vw (symmetric and asymmetric CH3

2104
D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
Fig. 1. Decomposition at 25.08C of [Re(tu)6]Cl3, [Re(Metu)6]Cl3 and [Re(Me2tu)6]Cl3 1024 M aqueous solutions at pH 1.6: , [Re(Metu)6]Cl3;
[Re(tu)6]Cl3; ; [Re(Me2tu)6]Cl3.
,
shown in Table 1, [Re(Me2tu)6]31 seems to be a good
precursor despite being the least stable of the series.
[Re(Metu)6]31 and [Re(Ettu)6]31 seem to be the best
precursors, leading faster to a complete substitution and
with the highest yield. So, having in mind measured times
to complete substitution, yields and decomposition rates of
the precursors, Re(III) complexes with thiourea and
alkylthioureas can be ordered according to their substitu-
interesting features. Precursors can be easily prepared in
high yields. Moreover, salts of these starting complexes
with different counterions can be isolated. Taking into
account solubilities, the selection of the appropriate salt of
the precursor offers the possibility of performing ligand
substitution reactions with a wide range of incoming
ligands by working in different media. [Re(Metu)6]31
seems to be the best precursor of the series since the
synthesis of the ethylthiourea complex does not lead to
easily isolable compounds and the synthesis of the Me2tu
analog leads to relatively low yields. In addition, the Metu
complex shows higher ligand substitution rates than
tion rate as follows: [Re(tu)6]31,[Re(Ettu)6]31
(
[Re(Metu)6]31,[Re(Me2tu)6]31. These results agree with
those reported on ligand substitution rate constants of
[Tc(alkylthiourea)6]Cl3 by pyrimidine-thione derivatives:
[Tc(tu)6]Cl3,[Tc(Metu)6]Cl3,[Tc(Me2tu)6]Cl3[9]. Then,
substitution kinetics for these Re complexes depend on
leaving ligand nature as stated for the Tc(III) analogues.
A new easy procedure has been developed to lead to low
valent Re complexes in high yield. This new route relies
upon the labile Re(III) thioureas complexes as preparative
intermediates. This new family of precursors shows some
[Re(tu)6]31
.
3.1. Molecular structure of hexakis (N-ethylthiourea)
rhenium (III) trihexafluorophosphate
Selected bond distances and angles are given in Tables 4
and 5. Fig. 2 is an ORTEP drawing of the compound
Table 3
Stability at 25.08C in aqueous media at different pH values, and in methanol for [Re(Ettu)6]Cl3, [Re(Metu)6]Cl3 and [Re(Me2tu)6]Cl3
[Re(Metu)6]Cl3
Solvent
[Re(Ettu)6]Cl3
Solvent
[Re(Me2tu)6]Cl3
Solvent
a
a
a
pH
t50%
pH
t50%
pH
t50%
Water
Water
Water
MeOH
1.3
2.0
2.7
–
360
74
13
Water
Water
Water
MeOH
2.2
2.7
3.0
–
287
190
Water
Water
Water
MeOH
1.5
2.0
2.2
–
64
41
26
35
43
560
260
a t50% is the time of 50% decomposition for each complex, in minutes.

D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
2105
Table 4
Table 5
˚
Selected interatomic bond distances (A) for [Re(Ettu)6](PF6)3 and
[Re(Me2tu)6](PF6)3 (e.s.d.’s in parentheses)
Selected bond angles (8) for [Re(Ettu)6](PF6)3 and [Re(Me2tu)6](PF6)3
(e.s.d.’s in parentheses)
[Re(Ettu)6](PF6)3
[Re(Me2tu)6](PF6)3
[Re(Ettu)6](PF6)3
[Re(Me2tu)6](PF6)3
Re–S(1)
Re–S(2)
Re–S(3)
Re–S(4)
Re–S(5)
Re–S(6)
2.432(4)
2.420(4)
2.419(4)
2.402(4)
2.422(3)
2.441(4)
1.72(2)
1.74(2)
1.75(2)
1.70(2)
1.76(2)
1.75(2)
1.33(2)
1.37(3)
1.30(2)
1.32(2)
1.36(2)
1.32(2)
1.32(2)
1.34(2)
1.30(2)
1.30(3)
1.28(3)
1.33(2)
2.423(3)
2.416(3)
2.446(3)
2.431(3)
2.429(3)
2.417(3)
1.732(13)
1.735(14)
1.75(2)
1.725(13)
1.744(11)
1.719(12)
1.286(14)
1.35(2)
1.33(2)
1.31(2)
1.31(2)
1.36(2)
1.31(2)
1.33(2)
1.31(2)
1.31(2)
S(1)–Re–S(2)
S(1)–Re–S(3)
S(1)–Re–S(4)
S(1)–Re–S(5)
S(1)–Re–S(6)
S(2)–Re–S(3)
S(2)–Re–S(4)
S(2)–Re–S(5)
S(2)–Re–S(6)
S(3)–Re–S(4)
S(3)–Re–S(5)
S(3)–Re–S(6)
S(4)–Re–S(5)
S(4)–Re–S(6)
S(5)–Re–S(6)
C(1)–S(1)–Re
179.8(2)
98.34(13)
81.16(14)
82.78(13)
97.93(13)
81.54(14)
98.95(13)
97.44(14)
81.85(14)
179.1(2)
99.17(13)
80.39(13)
81.49(14)
98.96(14)
179.20(12)
116.0(6)
115.2(6)
116.8(5)
114.9(6)
116.3(7)
115.8(7)
121(2)
118.7(13)
120.5(11)
122(2)
13.3(14)
124.9(13)
121(2)
122.1(12)
116.7(12)
118(2)
125.2(13)
117(2)
178.62(11)
84.07(12)
96.83(12)
98.82(11)
80.34(11)
96.08(12)
83.04(12)
82.52(11)
98.31(11)
178.72(11)
98.45(12)
81.16(12)
80.52(11)
99.88(10)
179.11(11)
116.4(4)
115.5(5)
113.8(7)
116.3(5)
114.5(5)
116.1(4)
119.4(12)
119.7(11)
120.9(9)
120.0(14)
119.6(13)
120.4(11)
120(2)
S(1)–C(1)
S(2)–C(2)
S(3)–C(3)
S(4)–C(4)
S(5)–C(5)
S(6)–C(6)
C(1)–N(11)
C(1)–N(12)
C(2)–N(21)
C(2)–N(22)
C(3)–N(31)
C(3)–N(32)
C(4)–N(42)
C(4)–N(41)
C(5)–N(52)
C(5)–N(51)
C(6)–N(62)
C(6)–N(61)
C(2)–S(2)–Re
C(3)–S(3)–Re
C(4)–S(4)–Re
C(5)–S(5)–Re
C(6)–S(6)–Re
N(11)–C(1)–N(12)
N(11)–C(1)–S(1)
N(12)–C(1)–S(1)
N(22)–C(2)–N(21)
N(22)–C(2)–S(2)
N(21)–C(2)–S(2)
N(31)–C(3)–N(32)
N(31)–C(3)–S(3)
N(32)–C(3)–S(3)
N(42)–C(4)–N(41)
N(42)–C(4)–S(4)
N(41)–C(4)–S(4)
N(52)–C(5)–N(51)
N(52)–C(5)–S(5)
N(51)–C(5)–S(5)
N(62)–C(6)–N(61)
N(62)–C(6)–S(6)
N(61)–C(6)–S(6)
1.319(14)
1.323(14)
showing the labeling of the non-hydrogen atoms and their
vibrational ellipsoids [37].
122(2)
118(2)
117.7(12)
122.6(11)
119.7(10)
120.5(11)
119.0(11)
120.4(10)
118.7(11)
118.5(10)
122.6(9)
3.2. Molecular structure of hexakis (N,N9-
dimethylthiourea) rhenium (III) trihexafluorophosphate
121(2)
115(2)
124.5(12)
124(2)
121.3(14)
115(2)
Selected bond distances and angles are given in Tables 4
and 5. Fig. 3 is an ORTEP drawing of the compound
showing the labeling of the non-hydrogen atoms and their
vibrational ellipsoids [37].
3.3. Discussion of structural results
errors. Re–S bond distances lay in the wide range of Re–S
lengths reported for other six-coordinate rhenium complex-
es and are quite similar to those reported for
[Re(tu)6]Cl3.4H2O. In contrast to [Re(tu)6]Cl3.4H2O both
complexes show a set of six different Re–S distances [25].
Similar departures from perfect octahedral coordination
have also been observed in [Tc(Me2tu)6](PF6)3,
[Tc(Metu)6](PF6)3?H2O and [Tc(tu)6]Cl3.4H2O. Possible
reasons for these distortions have been previously dis-
cussed, including Jahn-Teller effect and ligand–ligand
repulsion [6,25].
The Re–S–C bond angles are slightly greater than the
tetrahedral value, varying from 113.8(7) to 116.4(4)8 for
the dimethylthiourea complex and from 114.9(6) to
116.8(5)8 for the ethylthiourea complex. The S–C–N
angles are in the range from 118(2) to 123(1)8 for
[Re(Me2tu)6](PF6)3 as expected for a C(sp2) bonding. The
The X-ray diffraction results show that both new
complexes consist of discrete monomeric molecules. The
coordination polyhedra around the Re(III) ion are distorted
octahedra. The six alkylthiourea ligands are sulfur bonded
to the central atom. Though trans S–Re–S angles are close
to 1808 [varying from 178.6(1) to 179.1(1)8 for
[Re(Me2tu)6](PF6)3 and from 179.1(2) to 179.8(2)8 for
[Re(Ettu)6](PF6)3], there are appreciable departures from
ideal octahedral symmetry. The cis S–Re–S angles differ
significantly from 908 [vary from 80.3(1) to 99.9(1)8 for
[Re(Me2tu)6](PF6)3 and from 80.4(1) to 99.2(1)8 for
[Re(Ettu)6](PF6)3]. The Re–S bond distances vary from
˚
˚
2.416(3) to 2.446(3) A [average of 2.43(1) A] for
˚
[Re(Me2tu)6](PF6)3 and from 2.402(4) to 2.441(4) A
˚
[average of 2.42(1) A] for [Re(Ettu)6](PF6)3 within a
maximum of five standard deviations of bond length

2106
D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
sponding values for [Re(tu)6]Cl3?4H2O [mean S–C and
˚
C–N distances of 1.746(8) and 1.32(1) A respectively
[25]] and for [Tc(Me2tu)6](PF6)3 [mean d(S–C)51.73(1)
12
˚
˚
A and mean d(C–N)51.34(2) A ]. The N–CH3 bond
lengths in [Re(Me2tu)6](PF6)3 vary from 1.44(2) to
˚
˚
1.48(2) A [mean d(C–N)51.46(1) A] as observed in
[Tc(Me2tu)6](PF6)3. In [Re(Ettu)6](PF6)3 mean N–
C(ethyl) and ethyl C–C bond distances are 1.47(3) and
˚
1.47(5) A, respectively. In this structure the increasing
dispersion in bond lengths towards the ligand ethyl free
end is a consequence of librational disorder.
The C–N bonds of thiourea derivatives have an evident
double bond character. Therefore N-alkylthioureas can
exist in different configurations where the thioamide H
atom and the thiocarbonyl bonds are either cis or trans
[12]. For the described ethylthiourea compound the six
ethylthiourea ligands have the cis configuration. The ethyl
groups are oriented away from the Re atom. In
[Re(Me2tu)6](PF6)3 all the dimethylthiourea ligands have
the cis–trans configuration as in the free ligand.
Similarly to the other thiourea and alkylthioureas Re and
Tc compounds, the arrangement of the dimethylthiourea
and ethylthiourea ligands around rhenium atom results
from a compromise between steric hindrance and the
tendency of the ReSC(NCmethyl)2 or ReSCN2Cethyl groups
to be as planar as possible. In [Re(Me2tu)6](PF6)3 the
rhenium atom departs from the least-squares planes
through the S5C(NCmethyl)2 groups in distances that range
Fig. 2. ORTEP view of [Re(SC(NH2)NHCH2CH3)6]31 ion in
[Re(Ettu)6](PF6)3 showing the labeling of the non-hydrogen atoms and
their vibrational ellipsoids at 20% probability.
variation
[Re(Ettu)6](PF6)3, from 113(1) to 125(1)8.
The S5C(NCmethyl and S5CN2Cethyl groups are
in
S–C–N
angles
is
greater
for
)
2
planar to within experimental accuracy, while in
[Re(Ettu)6](PF6)3 the methyl carbons separations from the
˚
˚
from 0.050(1) A for ligand 6 to 1.157(1) A for ligand 3. In
[Re(Ettu)6](PF6)3 the rhenium atom departs from the least-
squares planes through the S5CN(NC) groups in distances
˚
corresponding least-squares planes vary from 0.04(2) A for
˚
ligand labeled 5 to 1.30(2) A for ligand 3. Average S–C
˚
and C–N bond lengths are 1.74(1) and 1.32(2) A for
˚
˚
that range from 0.045(4) A for ligand 5 to 0.640(4) A for
ligand 1.
˚
[Re(Me2tu)6](PF6)3 and 1.74(2) and 1.32(2) A for
[Re(Ettu)6](PF6)3, respectively, in agreement with corre-
As
reported
for
[Tc(Me2tu)6](PF6)3
and
[Tc(Metu)6](PF6)3.H2O, the PF26 ions in both structures
present appreciable rotational disorder as shown by the
relatively large displacement parameters of F atoms [12].
The corresponding observed bond distances and angles are
therefore strongly distorted, with P–F lengths varying for
example for [Re(Me2tu)6](PF6)3 from 1.45(1) to 1.62(1)
˚
˚
A (average d(P–F)51.53(4) A) and cis F–P–F angles
ranging from 85(1) to 96(1)8.
Supplementary data
Listings of atomic fractional coordinates and equivalent
isotropic temperature parameters, anisotropic thermal pa-
rameters, hydrogen atoms positions and calculated as well
as observed structure factor amplitudes of both reported
structures are available as supplementary data. Cambridge
Crystallographic Data Centre codes are: 102605 for hexa-
kis (N,N9-dimethylthiourea-S) rhenium(III) tri (hexa-
fluorophosphate) and 102606 for hexakis(N-ethylthiourea-
S) rhenium(III) tri(hexafluorophosphate).
Fig. 3. ORTEP drawing of [Re(SC(NHCH3)2)6]31 ion in
[Re(Me2tu)6](PF6)3 showing the labeling of the non-hydrogen atoms and
their vibrational ellipsoids at 20% probability.

D. Gambino et al. / Polyhedron 18 (1999) 2099–2107
2107
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Acknowledgements
This work was partially supported by the Consejo
Nacional de Investigaciones Cientıficas
(CONICYT) and PNUD-UNESCO (Programa de Desar-
rollo de las Ciencias Basicas) of Uruguay, The Third
World Academy of Sciences and the Consejo Nacional de
Investigaciones Cientıficas y Tecnicas (CONICET) of
Argentina. The X-ray diffraction experiments were carried
out at the National Diffraction Laboratory (LANADI), La
Plata, Argentina. We are grateful to the government of
Japan for the donation of the TGA and DTA Shimadzu
analyzers.
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