Topochemical silanization of the Aurivillius phase Bi2SrTa2O9 and post-synthesis complexation

Functionalization of layered oxides to convey a reactive function prone to coordinate metal cations in-between the inorganic layers is a challenge with respect the potential reactivity of the oxides with these groups. Here, silanization by amine-bearing alkoxysilanes was proposed as a convenient way to bring in free amine groups in the interlayer space. Yet, silanization in itself has seldom been explored for layered oxides.

This study presents a microwave-assisted multistep approach for functionalizing the Aurivillius Bi₂SrTa₂O₉ phase by organosilanes. Three different organosilanes were inserted in the interlayer space, triethoxyoctylsilane, 3-(aminopropyl)triethoxysilane and N-[3(trimethyoxysilyl)propyl]ethylenediamine. The synthetic pathway described here constitutes a fast and efficient approach to silanize the interlayer space of layered perovskites, while preserving the layered structure. The compounds were fully characterized, notably by X-Ray Diffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR), which demonstrated that the organosilanes were effectively grafted onto the oxide layers, forming stable Si-O-Ta bonds, and allowed to precise the grafting scheme, evidencing the very limited formation of siloxane network. Using this approach, free amino groups were introduced in-between the inorganic oxide layers due to the preferential reactivity of the oxide sheets with the alkoxysilane groups compared to amine. These amino groups are available for further coordination by transition metal ions using a post-synthesis complexation reaction. As a proof of concept their complexation ability towards Cu²⁺ ions was demonstrated by UltraViolet-Visible (UV–Vis) and Electron Paramagnetic Resonance (EPR) spectroscopies.

This soft chemistry strategy constitutes a new versatile, fast and efficient method to introduce transition metal cations into layered oxides and paves the way for the design and synthesis of complex architectures, specifically designed for application, in catalysis, sensors, metal cation remediation or luminescence for instance.