PREPARATION, CRYSTAL STRUCTURE, AND THERMAL STABILITY OF THE CADMIUM SULFIDE NANOCLUSTERS CD6S44+ AND CD2NA2S4+ IN THE SODALITE CAVITIES OF ZEOLITE A (LTA)

Abstract

The crystal structure and thermal stability of two cadmium sulfide nanoclusters prepared in zeolite A (LTA) have been studied by XPS, TGA, and single-crystal and powder XRD. The crystal structures of parallel to Cd2.4Na3.2(Cd6S4)(0.4)(Cd2Na2S)(0.6)(H2O)(>= 5.8)parallel to[Si12Al12O48]-LTA (a = 12.2919(7) A, crystal 1 (hydrated)) and parallel to Cd4Na2(Cd2O)(Na2O)parallel to[Si12Al12O48]-LTA (a = 12.2617(4) A, crystal 2 (dehydrated)) were determined by single-crystal methods in the cubic space group Pm(3)over bar>m at 294(1) K. Crystal 1 was prepared by ion exchange of Na-12-LTA in an aqueous stream 0.05 M in Cd2+, followed by washing in a stream of water, followed by reaction in an aqueous stream 0.05 M in Na2S. Crystal 2 was made by dehydrating crystal 1 at 623 K and 1 x 10(-6) Torr for 3 days. In crystal 1, Cd6S44+ nanoclusters were found in and extending out of about 40% of the sodalite cavities. Central to each Cd6S44+ cluster is a Cd4S4 unit (interpenetrating Cd2+ and S2- tetrahedra with near T-d symmetry, Cd-S = 2.997(24) A, Cd-S-Cd = 113.8(12)degrees, and S-Cd-S = 58.1(24)degrees). Each of the two remaining Cd2+ ions bonds radially through a 6-ring of the zeolite framework to a sulfide ion of this Cd4S4 unit (Cd-S = 2.90(8) A). In each of the remaining 60% of the sodalite cavities of crystal 1, a planar Cd2Na2S4+ cluster was found (Cd-S/Na-S = 2.35(5)/2.56(14) A and Cd-S-Cd/Na-S-Na = 122(5)/92(7)degrees). Cd6S44+ and Cd2Na2S4+ are stable within the zeolite up to about 700 K in air. Upon vacuum dehydration at 623 K, all sulfur was lost (crystal 2). Instead as anions, only two oxide ions remain per sodalite unit. One bridges between two Cd2+ ions (Cd2O2+, Cd-O = 2.28(3) A) and the other between two Na+ ions (Na2O, Na-O = 2.21(10) A).