Positions of cations and molecules in zeolites with the chabazite framework II Adsorption of carbon monoxide on dehydrated Ca-exchanged chabazite

Abstract

Adsorption of CO onto the single crystal of dehydrated Ca-chabazite described in Pt. I reduced slightly the perturbation of TO distances ( ∼ 0.01 A ̊ ) and perhaps the OTO angles (∼ 0.2°). The distances between Ca and framework oxygens increased about 0.02Å. The CO molecule is adsorbed onto the Ca(II) cation which is displaced into the large cavity from the 6-ring. Although the structure refinement is uncertain because of large “temperature” factors for C and O, it is certain that the CO molecule is canted off the triad axis. The oxygen is apparently at ∼ 3.7 A ̊ to framework oxygens, the Ca(II)C and CO distances are 2.74(5) and 1.31(8)Å, and the Ca(II)CO angle is 134(5)°, but the errors may be unrealistically low.