Study of cloverite molecular sieves modified by grafting organometallic complexes inside the pores: II. Adsorption properties of cloverite modified by grafting -SnR₃ fragments (R=Me, Et, nBu, Cy)

The adsorption properties of as-synthesized cloverite and of cloverite modified by grafting -SnR₃ (R=Me, Et, nBu, Cy) organometallic tin complexes were studied by a volumetric method. Three hydrocarbons, n-hexane, benzene and iso-octane, were investigated. The adsorption capacities of unmodified cloverite correspond to a filling of the 20 T channel system for benzene and iso-octane, and to a filling of the 8 T and 20 T channel systems for n-hexane. Grafting -SnCy₃ fragments onto the external surface of cloverite has no effect on the adsorption capacities of the three hydrocarbons but decreases significantly the diffusion rate of iso-octane. In contrast, the adsorption capacities of cloverite modified by -SnR₃ fragments grafted inside the crystal (R=Et, nBu: one fragment per window of the supercage; R=Me: 4 fragments per window) are completely modified: (i) iso-octane is completely excluded from the pore channels, due to steric constraints; (ii) n-hexane can only fill the 20 T pore channel system, and (iii) the decrease of the pore volume by grafting the organometallic fragment results in a reduction of the adsorption capacities of n-hexane and benzene.