KCS

The single-crystal structure of |Ca_35.5|[Si₁₂₁Al₇₁O₃₈₄]-FAU, Ca_35.5Si₁₂₁Al₇₁O₃₈₄ per unit cell, a = 24.9020(10) Å, dehydrated at 673 K and 2 × 10^-6 Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3-m at 294 K. The large single crystals of zeolite Y (Si/Al = 1.70) were synthesized up to diameters of 200 µm and Ca²⁺-exchanged zeolite Y were prepared by ion exchange in a batch method of 0.05 M aqueous Ca(NO₃)₂ for 4 hrs at 294 K. The structure was refined using all intensities to the final error indices (using only the 971 reflections for which F_o > 4σ(F_o)) R₁ = 0.038 (based on F) and R₂ = 0.172 (based on F²). About 35.5 Ca²⁺ ions per unit cell are found at an unusually large number of crystallographically distinct positions, four. Nearly filling site I (at the centers of the double 6-rings), 14.5 octahedrally coordinated Ca²⁺ ions (Ca-O = 2.4194(24) Å and O-Ca-O = 87.00(8)^o) are found per unit cell. One Ca²⁺ ion per unit cell is located at site II' in the sodalite cavity and extends 0.50 Å into the sodalite cavity from its 3-oxygen plane (Ca-O = 2.324(13) Å and O-Ca-O = 115.5(10)^o). The remaining twenty Ca²⁺ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 10 and 10 ions, respectively. Each of these Ca²⁺ ions coordinates to three framework oxygens, either at 2.283(3) or 2.333(5) Å, respectively, and extends either 0.24 or 0.54 Å, respectively, into the supercage from the three oxygens to which it is bound. In this crystal, site I is the most populated; sites II' and II are only sparsely occupied. Ca²⁺ appears to fit the octahedral site I best. No cations are found at sites III or III', which are clearly less favorable for Ca²⁺ ions in dehydrated zeolite Y.