FT-IR Analysis of Pillared Clay Pore Structure via Adsorbed Bipyridine Surface Probe Species

Abstract

Adsorption interactions of the bidentate molecules 2,2'-bipyridine and 4,4'-bipyridine with the surfaces of different alumina-pillar interlayered clays have been investigated by FT-IR spectroscopy. These interactions were examined in an attempt to establish a spectroscopic method for the determination of interpillar distances in the galleries of pillared clays. 2,2'-Bipyridine adsorbs in a bidentate C_2v, interaction to single Lewis acid sites on the surfaces of individual pillars and not to adjacent pillars, indicating that the distances between binding sites on adjacent pillars are too great to be successfully probed by this molecule. 4,4'-Bipyridine maintains the D_2h symmetry of the free molecule through interaction with Lewis acid sites on two adjacent pillars simultaneously via both ends of the molecule, thereby exhibiting possible utility as a probe of the interpillar distance. Surface-adsorbed monoprotonated 2,2'-bipyridinium cations are formed through interaction with Brönsted acid sites on the pillared clay surfaces. The IR spectrum of the surface-adsorbed protonated species suggests C_2/i transoid symmetry and is presented for the first time.