Relative Stability of ᗒAl—O—Al ᗕ Linkages in Zeolites. A Nonempirical Molecular Orbital Study

Nonempirical quantum chemical STO-3G calculations were performed for cluster models of two oxygen-bridged TO4 tetrahedra (T = Si, Al). The models are based on [(HO)3TOT(OH)3]n− structures and, in case of Al-containing models (n = 1,2), their electric neutrality is ensured by adding positive point charges. The calculations suggest the occurrence of ᗒAl - O -Al ᗕpairings provided certain electric fields act at the corresponding sites.