Three-coordinate extraframework Nb2+ and Mo+ in zeolite A. Crystal structures of Nb,Cl,Tl-A containing Nb2+ and NbCl6- and of Mo,Cl,Tl-A containing Mo+ and MoCl6-

摘要

In zeolite Nb,Cl,Tl-A (cubic, a = 12.120(2) angstrom), a 3-coordinate Nb2+ ion lies opposite a 6-ring in 22% of the large cavities. In Mo,Cl,Tl-A (a = 12.110(2) angstrom), 32% of the large cavities contain a 3-coordinate Mo+ ion at that position. A continuum of formula NbCl6Tl32+ per unit cell, consisting of octahedral NbCl6- ions linked together in three dimensions by bridging Tl+ ions, fills the large cavities and 8-ring windows in 45% of the volume (that nearest the surface) of a single crystal of Nb,Cl,Tl-A. For Mo,Cl,Tl-A, the respective formulas and values are MoCl6-, MoCl6-, and 32%. Four additional octahedral Tl+ ions per unit cell bridge between each NbCl6-, or MoCl6-, and 32%. Four additional octahedral Tl+ ions per unit cell bridge between e, ion and the zeolite framework, supporting those ions at the very centers of the large cavities. Interactions with all of these Tl+ ions have lengthened all bonds in NbCV, and MoCV, by about 0.5 angstrom. To prepare Nb,Cl,Tl-A, a crystal of fully dehydrated Tl-A (vertical bar Tl-12 vertical bar[Si12Al12O45]-A) was treated with NbCl5(g). A second such crystal was treated with MoCl5(g). The structures of the products were determined crystallographically and their compositions were confirmed by energy dispersive X-ray analysis. They were refined in the space group Pm (3) over barm using all data to the final error indices R-1 = 0.047 for Nb,Cl,Tl-A and 0.051 for Mo,Cl,Tl-A. Both reactions failed to go to completion, presumably because the surface continua obstructed the passage of the reagent gases to the interiors of the crystals.