Novel paramagnetic clays obtained through intercalation of Gd 3+ -complexes.

Novel paramagnetic lanthanide-exchanged saponite clays, bearing in the interlamellar region positively charged Gd3+-complexes, were synthesized using a hydrothermal approach followed by a classical ion exchange reaction. A detailed characterization was performed to assess the physico-chemical properties of the samples, which showed a hydrodynamic diameter between 50 and 90 nm and good thermal stability. 1H-NMR relaxometric studies in aqueous solution as a function of magnetic field and temperature were carried out to evaluate the local chemical environment of the intercalated paramagnetic centres and their interaction with water molecules. The data indicate a strong interaction of the confined complexes with the lamellae, resulting in a restriction of the local rotational dynamics and of the exchange process of water molecules between the inner coordination sphere of Gd3+ and the bulk. The stability over time in aqueous solutions of varying complexity was also studied by relaxometric techniques.