Quantum-chemical calculation for fluorine ion influence on double four-membered ring of zeolite molecular sieves structure

On the full optimization of geometry, the eight model clusters(including F- held in the double four-membered ring and no F-) have been peformed by using semi-empirical quantum-chemical PM3 method to obtain their geometric, electronic structures and stability. The influence of fluorine ion on structures and properties of four-membered ring has been examined. The stabilities of full Si, P-Al and P-Ga forming four-membered rings were found to be gradually increased with F- encapsulation, However, the forming four-membered ring for the Si-Al cluster is unstable. The calculated results show that the distances between F- locating in the four-membered ring and framework elements are in agreement with the experimental values.