FULL PAPER
DOI: 10.1002/ejic.200900613
Polyoxothiomolybdenum Wheels as Anionic Receptors for Recognition of
Sulfate and Sulfonate Anions
Jean-François Lemonnier,
[a]
Sébastien Floquet,*
[a]
Jérôme Marrot,
[a]
and
Emmanuel Cadot*
[a]
Keywords: Molybdenum / Polyoxometalates / Sulfur / Molecular recognition / Self-assembly
The formation of supramolecular host–guest cyclic architec-
tures, built up through the self-condensation process of
[Mo
2
O
2
S
2
]
2+
oxothiocations driven by sulfate and sulfonate
anions is reported. The complexes [(SO
4
)
2
Mo
10
O
10
S
10
(OH)
10
-
(H
2
O)
5
]
4–
and [(EtSO
3
)
2
Mo
10
O
10
S
10
(OH)
10
(H
2
O)
5
]
2–
were
characterized in the solid state by X-ray diffraction, and par-
ticular attention was given to the analysis of the hydrogen-
Introduction
Polyoxometalates (POMs) represent a family of inorganic
compounds rich of thousands of compounds that are of
current interest for recognized applications in catalysis,
[1–5]
medicine
[6,7]
magnetism,
[8,9]
or in supramolecular chemis-
try.
[10–14]
In marked contrast with POMs, polyoxothiometal-
ates (POTMs) are far less common, but they can provide
original compounds and especially transition-metal-ring-
like clusters based on the self-condensation of [M
2
O
2
S
2
]
2+
oxothiocations (M = Mo
V
or W
V
).
[15]
In contrast to the
standard structures of polyoxometalates, these compounds
are characterized by a host–guest self-adaptability. The self-
assembly process can be controlled by templating agents,
mainly anionic groups such as phosphates
[16,17]
met-
alates,
[18]
or polycarboxylates,
[19–23]
which are encapsulated
covalently as guests in the adapted central cavity. In the
presence of halides, supramolecular assemblies based on hy-
drogen bonding with water molecules within the cavity of
the ring were evidenced in the solid state and in solution,
thus highlighting anionic recognition properties for this
class of compounds.
[24,25]
We notably established that sup-
ramolecular interactions between inner water molecules and
halides in solution increase in the following sequence I
–
Br
–
Cl
–
.
[16]
In this context, we were interested to extend
this study to the interactions of molybdenum rings with sul-
fates and sulfonates by keeping in mind the possible exten-
sion of this work for the preparation of polymeric materials
incorporating molybdenum rings. Herein, we report the
[a] Institut Lavoisier de Versailles, UMR 8180, University of Ver-
sailles,
45 avenue des Etats-Unis, 78035 Versailles, France
E-mail: sebastien.floquet@chimie.uvsq.fr
cadot@chimie.uvsq.fr
Eur. J. Inorg. Chem. 2009, 5233–5239 © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 5233
bonding interactions, which ensure the host–guest stability
of such architectures. Taking into account these properties,
we report preliminary results on the grafting of oxothiomo-
lybdenum cyclic materials onto sulfonated resin such as
Dowex 50–80.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
synthesis and the characterization of two new decamolyb-
denum rings self-assembled around sulfate or ethylsulfonate
anions. Such host–guest interactions open the way for im-
mobilization of these cyclic compounds by functionalized
surfaces, such as sulfonated resins.
Results
Syntheses
Some years ago, we demonstrated that the condensation
of [Mo
2
O
2
S
2
]
2+
oxothiocations in aqueous media in the
presence of halides led to [X
2
Mo
10
O
10
S
10
(OH)
10
(H
2
O)
5
]
2–
systems where a decamolybdenum ring is bicapped by two
halide ions through a convergent hydrogen-bonding net-
work. Furthermore, in nearly pure water, at pH 3, the ha-
lide-containing decamolybdenum rings evolve towards the
formation of the neutral dodecamolybdenum ring
[Mo
12
O
12
S
12
(OH)
12
(H
2
O)
6
].
[26]
At pH values above 5, the
inner water molecules of the Mo rings are deprotonated
successively to give anionic compounds such as
[Mo
10
O
10
S
10
(OH)
12
(H
2
O)
3
]
2–
or [Mo
8
O
8
S
8
(OH)
10
(H
2
O)]
2–
.
Such acid–base processes change the ionic character of the
inner cavity from cationic to anionic. Consequently, the
synthesis of sulfate or sulfonate-containing rings presented
in this study were carried out below pH 5 to keep the inner
cavity cationic.
[24–27]
Under these conditions, the self-as-
sembly of the [Mo
2
O
2
S
2
]
2+
oxothiocations in the presence
of an excess amount of sulfate or ethylsulfonate anions
gives the exclusive complexes [(SO
4
)
2
Mo
10
O
10
S
10
(OH)
10
-
(H
2
O)
5
]
4–
{1; [(SO
4
)
2
Mo
10
]
4–
} and [(EtSO
3
)
2
Mo
10
O
10
S
10
-
(OH)
10
(H
2
O)
5
]
2–
{2; [(EtSO
3
)
2
Mo
10
]
2–
}, which were isolated
in moderate yield.