Encapsulating Photoluminescent Materials in Zeolites. II. Crystal Structure of Fully Dehydrated Ce₂₁H₄₆O₁₈–Y (Si/Al = 1.69) Containing Ce₄O₄⁴⁺, CeOH²⁺, Ce³⁺, and H⁺

Encapsulating photoluminescent centers within zeolites may give them long-term stability and enhanced luminosity. A single crystal of zeolite Na–Y (FAU, Si/Al = 1.69) was fully exchanged with Tl⁺, then exchanged with Ce³⁺ and dehydrated at 623 K and 2 × 10^–4 Pa to give |Ce₄O₄⁴⁺_3.5CeOH²⁺_4.6Ce³⁺_2.1H⁺_41.7|[Si₁₂₁Al₇₁O₃₈₄]–FAU. Its structure was determined crystallographically (space group <i>Fd</i>3̅<i>m</i>, <i>a</i> = 24.909(1) Å) with synchrotron X-radiation and was refined using all 1236 unique data to <i>R</i>₁ = 0.067 (<i>F</i>_o > 4σ­(<i>F</i>_o)) and <i>R</i>₂ = 0.247. The 20.5 Ce³⁺ ions per unit cell occupy four crystallographically distinct cation sites: 0.5 are octahedral at site I, 1.6 trigonal at site I′, 13.8 octahedral at a second site I′, and 4.6 tetrahedral at site II. The 13.8 Ce³⁺ ions at the second site I′ are members of Ce₄O₄⁴⁺ clusters, tetrahedrally distorted cubes occupying 43% of the sodalite cavities. Each of these Ce³⁺ ions bonds octahedrally to three oxygen atoms of the zeolite framework (2.482(7) Å) and to three extraframework oxide ions (2.521(11) Å). Those at site II are 4-coordinate; each bonds to three oxide atoms of the zeolite framework (2.420(7) Å) and to one hydroxide ion (2.06(14) Å). The ultaviolet photoluminescence spectrum of this material has a broad emission band between 320 and 400 nm, peaking at 347 nm