Stabilization of a distorted conformation of cyclohexane adsorbed in the voids of silicalite-1

Abstract

The dimensions and topology of the voids in porous zeolites can influence the conformational geometry of guest molecules confined within it. Here we report an infrared and Raman vibrational spectroscopic study of cyclohexane confined within the voids of a medium-pore zeolite, Silicalite-1. We find that on confinement two conformers of cyclohexane are in thermal equilibrium, one of which lacks a center of inversion and is the preferred conformation at lower temperatures. Molecular modeling supports this observation; in the intersection-voids of Silicalite-1 host-guest dispersive interactions favour a distorted-chair conformer of cyclohexane with symmetry lower than D_3d. The results are compared with those for cyclohexane confined in the comparatively larger voids of Zeolite-Y, where it is known to exist exclusively in the chair conformer.