Theoretical study of the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and Brönsted acid sites of zeolites

Abstract

AbstractThe main interaction between thiophene and zeolites leads to the formation of a hydrogen bond between the S atom of thiophene and the OH group of zeolites, giving 1:1 stable molecular complexes. The present work reports a theoretical study about the structural, vibrational, and topologic properties of the charge distribution of the molecular complexes between thiophene and a series of Brönsted acid sites of zeolites, modeled as the H3SiOHAlH3(B1), (OH)3Si(OH)Al(OH)3(B1OH), and H3Si(OH)Al(OH)2OSiH3(B2) clusters. The studied properties were calculated at a Hartree–Fock level with the standard 6‐31+G(d,p) basis set. Additionally, electron correlation effects for geometric and vibrational properties were evaluated at second‐order Møller–Plesset (MP2) and BLYP for B1–thiophene complex, whereas the BLYP technique was employed for the complexes of thiophene with B1OH and B2 clusters. Symmetry restriction was considered for structure calculations, beingC2vfor thiophene,Csfor zeolite clusters, andCslinear conformation for the complexes. It was found that these linear thiophene–zeolite complexes reproduce the tendencies in the experimental frequency shifts of the OH vibration mode from the adsorption of thiophene in ZSM5 zeolites. The topologic properties of the complexes give a pattern for the interaction of thiophene–zeolite. The results are compared with previous ones from silanol–thiophene calculations. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001