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Accueil > Equipes de recherche > Chimie Bioinorganique Supramoleculaire > Thémes de recherche

Systèmes bimétalliques

complexation of ditopic calix[6]ligands

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Encapsulation of a (H3O2)- Unit in the Aromatic Core of a Calix[6]arene Closed by Two Zn(II) Ions at the Small and Large Rims

The coordination of a first Zn(II) ion to a calix[6]arene presenting three imidazolyl arms at the small rim and three aniline moieties at the large rim allows the binding of a second Zn(II) ion while hosting a (H3O2)- unit in the aromatic cavity.
Its stability is related to its encapsulation in the hydrophobic π-basic calixarene core that disfavors a second deprotonation event that is classically observed with the “simple” tripodal N3 ligand-based systems. Such an unusual coordination behavior is also attributable to the geometrical constrain set by the calixarene skeleton that presents distant binding sites too far away from each other to allow a -hydroxo complex to form. The XRD structure of the dinuclear complex emphasizes the remarkable preorganization for a second metal ion binding, since the water molecule coordinated to the first Zn site stabilizes, through hydrogen bonding, the hydroxide bound to the second Zn ion, in spite of the very weak donor set constituted by three ArNH2 moieties.
Interestingly, a [Zn(H3O2)Zn]3+ core has been proposed to be the active species of hydrolytic multinuclear Zn enzymes. Such model complexes are particularly rare and were obtained with anionic ligands that either are highly bulky12 or present a deprotonated pyrazol moiety spanning the Zn ions. The calix-complex actually represents the first example of such a unit stabilized by neutral ligands. This study thus shows the importance of the preorganization and second coordination sphere in the selective stabilization of such a species.
We are currently exploring the possible coordination of other metal ions, replacement of the (H3O2)- core by other bridging units, as well as the modification of the large rim donor set.

A Ditopic Calix[6]arene Ligand with N-Methyl-Imidazole and 1,2,3-Triazole Substituents: Synthesis and Coordination with Zn(II) Cations.

The first member of a new class of ditopic calix[6]arene has been synthesized, which is decorated with three N-methyl-imidazoles at the small rim and three 1,4-disubstituted-1,2,3-triazoles at the large rim.
The coordination of a first Zn(II) cation selectively takes place at the small rim. Addition of a second equivalent results in the complexation of the three triazoles, providing a rare example of 1,2,3-triazole ligands embedded within a supramolecular system.
The presence of the three triazole ligands enables the formation of a bimetallic Zn(II) complex that, despite the closure of the cavity, can accommodate an exchangeable nitrile guest. This complex differs from the above mentioned calix[6]arene-based bimetallic complex, where a H3O2- unit occupies the cavity and bridges the Zn(II) centers. In the present system, the second metal ion orients its labile site in the opposite direction, being easily accessible to exogenous binding, although protected by the microenvironment defined by the triazole substituents. Hence, whereas the mononuclear complex offers an extended and tunable cavity for host-guest recognition, the dinuclear complexes provide a novel platform for studying biomimetic catalysis.