Synthesis and Crystal Structure of Zinc Iodide in the Sodalite Cavities of Zeolite A (LTA).

The crystal structure of Znl(2) molecule synthesized in zeolite A (LTA) has been studied by single-crystal X-ray diffraction techniques. A single crystal of vertical bar Zn-6 vertical bar[Si12Al12O48]-LTA, synthesized by the dynamic ion-exchange of vertical bar Na-12 vertical bar[Si12Al12O48]-LTA wit haqueous 0.05 M Zn(NO3)(2) and washed with deionized water, was placed in a stream of flowing 0.05 M Kl in CH3OH at 294 K for four days. The resulting crystal structure of the product (vertical bar K6Zn3(KI)(3)(zNi(2))(0.5)vertical bar[Si12Al12O48]-LTA alpha = 12.1690(10)angstrom) was determined at 284 K by single-crystal X-ray diffraction in the space group Pm (3) over bar m. It was was refined with all measured reflections to the final error index R-1 = 0.078 for 431 reflections which F-o > 4 sigma(F-o). At four crystallographically distinct positions, 3.5 Zn2+ and nine K+ ions per unit cell are found: three Zn2+ and five K+ ions lie on the 3-fold axes opposite 6-rings in the large cavity, two K+ ions are off the plane of the 8-rings, two K+ ions are recessed deeply off the plane of the 8-rings and the remaining a half Zn2+ ion lie on the 3-fold axes opposite 6 rings in the sodalite cavity. A half Zn2+ ion and and I- ion per unit cell are found in the sodalite units, indicating the formation of ZnI2 molecule in 50% of the sodalite cavties, Each ZnI2 (Zn-I = 3.35(5)angstrom) is held in place by the coordination of its one Zn2+ ion to the zeolite framework. Oxygens and by the coordination of its two I- ions to K+ ions through 6-rings (I-K = 3.33(8)angstrom). Three additional I- ions per unit cell are found opposite a 4-ring in the large cavity and form a K(3)l(2+) and two K2ZnI3+ ionic clusters, respectively.