Single crystal structure of fully dehydrated fully Tl +-exchanged zeolite Y, ∣Tl 71∣[Si 121Al 71O 384]- FAU

Abstract

The structure of fully dehydrated, fully Tl +-exchanged zeolite Y, ∣Tl 71∣[Si 121Al 71O 384]- FAU ( a = 24.948(2) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd 3 ¯ m at 21(1) °C. An aqueous exchange solution 0.05 M in Tl + with pH = 7.2 was allowed to flow past the crystal for 7 days. The resulting colorless crystal became black after being dehydrated at 400 °C and 2 × 10 −6 Torr for 2 days. Diffraction data were then gathered and were refined using all 702 unique reflections to the final error indices (based upon the 365 reflections for which F o > 4 σ( F o)) R 1 = 0.058 and wR 2 = 0.130. In this structure, Tl + ions occupy four crystallographic sites. About 30.4(6) Tl + ions fill or nearly fill site I′ in the sodalite cavities on 3-fold axes opposite double 6-rings; each is 1.37 Å from the plane of three oxygens (Tl–O = 2.568(17) Å, O–Tl–O = 93.9(5)°). Each is also 3.673(4) Å from three (perhaps sometimes only two) equivalent site-I′ Tl + ions. Thirty-two Tl + ions fill site II opposite single 6-rings in the supercage; each is 1.63 Å from the plane of three oxygens (Tl–O = 2.724(15) Å, O–Tl–O = 87.9(6)°). The remaining Tl + ions are located at two nonequivalent sites III′ with occupancies of 5.7(8) and 3.0(4) per unit cell; each coordinates to three framework oxygens. It appears that TlOH was imbibed during aqueous ion exchange at pH = 7.2, and that it decomposed upon vacuum dehydration at 400 °C to deposit as Tl 2O (black) on the surface of the zeolite crystal.