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Inorganica Chimica Acta 290 (1999) 247 – 250
Note
Five-coordinate rhenium(III)-thiolato complexes: the structure of
[Re(SCH
2
PhOCH
3
)
3
(PPh
3
)
2
]
M.S. Papadopoulos
a
, P. Bouziotis
a
, I.C. Pirmettis
a
, C.P. Raptopoulou
b
, A. Terzis
b
,
E. Chiotellis
a,
*
a
Institute of Radioisotopes -Radiodiagnostic Products, NCSR ‘Demokritos’, PO Box 60228, 15310, Aghia Paraskei, Athens, Greece
b
Institute of Materials Science, NCSR ‘Demokritos’, PO Box 60228, 15310, Aghia Paraskei, Athens, Greece
Received 10 December 1998; accepted 9 March 1999
Abstract
A novel five-coordinate rhenium(III)-thiolato complex, Re(SCH
2
C
6
H
4
OCH
3
-p )
3
(PPh
3
)
2
has been isolated during the reaction of
trans -ReOCl
3
(PPh
3
)
2
with p -methoxybenzyl mercaptan. In the unexpected structure that was acquired, the central metal has
undergone a reduction from Re(V) to Re(III). The five-coordinate Re(III) complex has been characterized by spectroscopic
methods, elemental analysis and X-ray crystallography. X-ray crystallographic studies showed the coordination geometry around
rhenium to be that of a trigonal bipyramid. The basal plane is defined by three sulfur atoms of the monodentate ligand, while the
two apical positions are occupied by two phosphines of the precursor. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Rhenium complexes; Thiolato complexes; Five-coordinate complexes
1. Introduction
The coordination chemistry of technetium and rhe-
nium has attracted much attention due to the wide-
spread use of
99m
Tc in diagnostic imaging and
186
Re
and
188
Re in radiotherapy [1]. Rhenium is technetium’s
third row congener, thus exhibiting similar chemical
properties to technetium. Minor chemical differences
between complexes of these two isotopes can result in
different biological behavior. The most pronounced of
these is the redox potential of the central metal. Com-
plexes of rhenium are more difficult to reduce than the
analogous technetium complexes [2].
As part of our investigations into thiolato complexes
of rhenium, we have looked into the side products of
different reaction systems involving a variety of thiols
as coligands [3–6]. In the course of a systematic study,
we reacted trans -ReOCl
3
(PPh
3
)
2
with an excess of p -
methoxybenzyl mercaptan, p -CH
3
OC
6
H
4
CH
2
SH. Sur-
prisingly, we obtained a complex with the unexpected
structure [Re(SCH
2
C
6
H
4
OCH
3
-p )
3
(PPh
3
)
2
], where the
central rhenium atom had undergone a reduction from
Re(V) to Re(III). So far, the acquisition of pentacoordi-
nate Re(III) complexes has been described in the litera-
ture only a few times [7,8]. The Re(III) products might
be thermodynamically more stable, thus more favorable
than the Re(V) products [9].
This report presents the complex [Re(SCH
2
C
6
H
4
-
OCH
3
-p )
3
(PPh
3
)
2
] as the major reaction product, while
among the minor products we can find the pentavalent
Re(V) anion [ReO(SCH
2
C
6
H
4
OCH
3
-p )
4
]
-
, where the
central metal is surrounded by four thiolato groups.
2. Experimental
2.1. Materials and methods
IR spectra were recorded as KBr pellets in the range
4000–500 cm
-1
on a Perkin-Elmer 1600 FT-IR spec-
* Corresponding author. Tel.: +30-1-651 3793; fax: +30-1-654
3526.
E-mail address: mainathe@cyclades.nrcps.ariadne-t.gr (E. Chiotel-
lis)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII:S0020-1693(99)00143-7