Effects of tert-Butyl Halide Molecular Siting in Crystalline NaX Faujasite on The Infrared Vibrational Spectra

Abstract

Experimental, analytical, and modeling techniques employed in this study elucidate interactions between adsorbate molecules and the interior surfaces of the porous host faujasite. The vibrational spectroscopies of guest and host offer opportunities to locate the guest site in the host. We present Fourier transform (FT) infrared (IR) studies of sodium-X (NaX) faujasite supercage-included tert-butyl halides, (CH(3))(3)C-X (X=Cl, Br, I) in comparison with the adsorbate molecular gas-phase and host solid-state spectra at 295 K. Four observations of guest (nu(5,) nu(6), nu(7), and {nu(3), nu(16), nu(17)}) vibrational mode changes, three of them concomitant with host mode changes, together with modeling studies, point to a particular preferred siting of the guest molecules at host hexagonal prisms (D6R). The siting involved simultaneous interactions of the host with methyl group axial protons and the halide atom. All three methyl group axial protons interact preferentially with a single D6R O1 oxygen atom via C-H...O bonding. The halide atom also interacts with a site III' Na cation. The cation, in turn, is coordinated by three O atoms (two O1 and an O4). Two of these O atoms (O1) bridge the double six-rings that form the hexagonal prism part of the NaX substructure. O4 connects the two D6R units.