Département de chimie moléculaire

We present the aggregation mechanism in a novel class of heat-set metallosupramol. Ni2BTC gels formed by complexation of a bis-terpyridine-cyclam (BTC), a tritopic ligand, with nickel ions (ii). Viscosimetry, rheol., small-angle X-ray scattering, dynamic light scattering and impedance spectroscopy measurements are used to investigate the aggregative properties. Gels are obtained by heating the homogeneous solns. (Ni2BTC in dimethylformamide) from room temp. to 50 °C for 24 h, which is a remarkable phenomenol. in the class of org. mol. gels. The hierarchical aggregation mechanism relies on a temp.-triggered cis-to-trans mol. conversion of the tritopic ligand at the central cyclam unit. At the nanoscale, the expansion of the coil-like species in the liq. phase to rodcoils allows, beyond a crit. concn., their percolation into transient gel networks. The use of such tritopic ligands gives access to homo- or hetero-metallogels that adapt their properties to the environmental conditions (temp., pH, mech. stress and applied elec. potential). Various mol. adjustment parameters (metal ions, metal sequence, metal-ligand stoichiometry, cyclam substituents) can be used to tune the aggregative properties of the system. [on SciFinder(R)]