Crystal structure of a methylamine sorption complex of fully dehydrated fully Ca2+ -exchanged zeolite X, |Ca46(CH3NH2)16|[Si100Al92O384]-FAU.

Abstract

The structure of a methylamine sorption complex of fully dehydrated fully Ca2+-exchanged zeolite X, |Ca46(CH3NH2)16|[Si100Al92O384]-FAU, has been determined in the cubic space group Fd3 at 21(1) degrees C (a = 24.994(4) angstroms) by single-crystal X-ray diffraction techniques. The crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous Ca(NO3)2 for 3 days, followed by dehydration at 480 degrees C and 2 x 10(-6) Torr for 2 days, and exposure to 160 Torr of zeolitically dry methylamine gas at 21(1) degrees C. The structure was determined in this atmosphere and was refined, using the 739 reflections for which I > 0, to the final error indices R1 = 0.152 and R2 = 0.061. In this structure, Ca2+ ions occupy three crystallographic sites. Sixteen Ca2+ ions fill the octahedral site at the centers of hexagonal prisms (Ca-O = 2.429(7) angstroms). The remaining 30 Ca2+ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 14 and 16 ions. Each of these Ca2+ ions coordinates to three framework oxygens, either at 2.296(7) or 2.334(7) angstroms, respectively. Sixteen methylamine molecules have been sorbed per unit cell, two per supercage. Each coordinates to one of the latter 16 site-II Ca2+ ions: N-Ca = 2.30(9) angstroms. The imprecisely determined N-C bond length, 1.48(23) angstroms, differs insignificantly from that in methylamine(g), 1.474(5) angstroms. The positions of the hydrogen atoms were calculated. One of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and the other forms a bifurcated hydrogen bond to two other 6-ring oxygens. The methyl group does not hydrogen bond to anything.