Crystal Structure of a Cadmium Sorption Complex of Dehydrated Fully Cd²⁺-Exchanged Zeolite X Containing Cd²⁺, Cd⁺, and Cd⁰

Abstract

A single crystal of fully dehydrated fully Cd2+-exchanged zeolite X, Cd46Si100Al92O384 per unit cell, was exposed at 320 °C to 0.005 Torr of Cd vapor for 9 days. The resultant crystal, Cd68Si100Al92O384 per unit cell [a = 24.953(6) Å], was determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3̄m at 21(1) °C. The structure was refined to the final error indices R1 = 0.073 and R2 = 0.100 with 249 reflections for which I > 3σ(I). In this structure, Cd species (formally Cd2+, Cd+, and Cd0) are found at seven crystallographic sites. Twenty-eight Cd2+ ions per unit cell are found at three crystallographic sites: eight occupy site I‘ in the sodalite unit and associate with four Cd0 atoms near site II‘ to form four (Cd3)4+ clusters [Cd2+−Cd0−Cd2+ = 105.2(7)°, Cd2+−Cd0 = 2.76(5) Å, Cd2+−O = 2.176(25) Å, Cd0−O = 3.03(5) Å] in four of the eight sodalite cavities per unit cell. The remaining 20 Cd2+ ions are found at sites II‘ and II with occupancies of six and 14 [trigonal, Cd−O = ca. 2.19(2) Å for both]. Thirty-six Cd+ ions are found at three crystallographic sites: six Cd+ ions are at site I, at the centers of the double six-oxygen rings [octahedral, Cd−O = 2.559(14) Å]; 18 Cd+ ions lie at site I‘, in the sodalite cavity opposite double six-oxygen rings [trigonal, Cd−O = 2.393(25) Å]; and 12 Cd+ ions occupy site II in the supercage [trigonal, Cd−O = 2.418(23) Å]. Of the 46 Cd2+ cations initially present per unit cell, 18 have reacted to form 36 monatomic Cd+, and eight associate with four Cd0 atoms to give four (Cd3)4+ cations. Highly reducing cadmium species are highly dispersed within the zeolite.