제올라이트 X 착물의 결정구조

Crystal Structure of a Carbon Monoxide Sorption Complex of Fully Ca^2+-Exchanged Zeolite X

The structure of a carbon monoxide sorption complex of dehydrated fully Ca^{2+}-exchanged zeolite X, |Ca_{46}(CO)_{27}|[Si_{100}Al_{92}O_{384}]-FAU, has been determined in the cubic space group Fd;{overline{3}} at 21^{circ}C (a = 24.970(4) ) by single-crystal X-ray diffraction techniques. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous {Ca(NO_3)_2} for three days, followed by dehydration at 400^{circ}C and 2{times}10^{-6} Torr for two days, and exposure to 100 Torr of zeolitically dry carbon monoxide gas at 21^{circ}C. The structure was determined in this atmosphere and was refined, using the 356 reflections for which F_o > 4{sigma}(F_o), to the final error indices R_1 = 0.059 and wR_2 = 0.087. In this structure, Ca^{2+} ions occupy three crystallographic sites. Sixteen Ca^{2+} ions fill the octahedral site I at the centers of hexagonal prisms (Ca-O = 2.415(7) {AA}). The remaining 30 Ca^{2+} ions are found at two nonequivalent sites II (in the supercages) with occupancies of 3 and 27 ions. Each of these Ca^{2+} ions coordinates to three framework oxygens, either at 2.276(10) or 2.298(8) {AA}, respectively. Twenty-seven carbon monoxide molecules have been sorbed per unit cell, three per supercage. Each coordinates to one of the latter 16 site-II Ca^{2+} ions: C-Ca = 2.72(8) {AA}. The imprecisely determined N-C bond length, 1.26(14) {AA}, differs insignificantly from that in carbon monoxide(g), 1.13 {AA}.