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

Abstract

The positions of PbI 2 molecule synthesized into the molecular-dimensioned cavities of |K 6 (Pb 4 I 2 )(PbI 2 ) 0.67 -(H 2 O) 2 |[Si 12 Al 12 O 48 ]-LTA have been determined. A single crystal of |Pb 6 |[Si 12 Al 12 O 48 ]-LTA, prepared by the dynamic ion-exchange of |Na 12 |Si 12 Al 12 O 48 -LTA with aqueous 0.05 M Pb(NO 3 ) 2 and washed with deionized water, was placed in a stream of flowing aqueous 0.05 M KI at 294 K for three days. The resulting crystal structure of the product (|K 6 (Pb 4 I 2 )(PbI 2 ) 0.67 (H 2 O) 2 |[Si 12 Al 12 O 48 ]-LTA, a = 12.353(1) A) was determined at 294 K by single-crystal X-ray diffraction in the space group Pm 3m. It was refined with all measured reflections to the final error index R 1 = 0.062 for 623 reflections which F o > 4σ(F o ). 4.67 Pb 2+ and six K + ions per unit cell are found at three crystallographically distinct positions: 3.67 Pb 2+ and three K + ions on the 3-fold axes opposite six-rings in the large cavity, three K + ions off the plane of the eight-rings, and the remaining one Pb 2+ ion lies opposite four-ring in the large cavity. 0.67 Pb 2+ ions and 1.34 I - ions per unit cell are found in the sodalite units, indicating the formation of a PbI 2 molecule in 67% of the sodalite units. Each PbI 2 (Pb-I = 3.392(7) A) is held in place by the coordination of its one Pb 2+ ion to the zeolite framework (a Pb 2+ cation is 0.74 A from a six-ring oxygens) and by the coordination of its two I - ions to K + ions through six-rings (I-K = 3.63(4) A). Two additional I - ions per unit cell are found opposite a four-ring in the large cavity and form Pb 2 K 2 I 5+ and PbK 2 I 3+ moieties, respectively, and two water molecules per unit cell are also found on the 3-fold axes in the large cavity.