The Effects of the Structural Characteristics on Properties of Their Bridging OH Groups for AlPO4-5 Molecular Sieve : MNDO Calculations

摘要

Semiempirical MNDO calculations are employed to study relation properties on bridging OH group with Al-O(P-O) bond length and Al-O-P bond angle of structural characteristics using birdging (OH)3AlOP(OH)3 and (OH)3AlOHP(OH)3+ model culster. We know that the O-H bond dissociation energy of bridging OH group is increased with increasing Al-O(P-O) bond length and decreasing Al-O-P bond angle. The bridging OH group is formed into enlarged Al-O(P-O) bond length and shortened Al-O-P bond angle in bridging oxygen atom by a hydrogen migration. The negative net charge of bridging oxygen atom is increased with longer Al-O-P bond angle, while the positive net charge is decreased with longer Al-O-P bond angle.