Positions of cations and molecules in zeolites with the mordenite-type framework II dehydrated hydrogen-ptilolite

Abstract

A single crystal of natural ptilolite was ion-exchanged with NH 4 +, heated to 320°C, sealed in a capillary at temperature, and the crystal structure was refined to R=0.048. Upon heating, NH 3 and H 2O were expelled and hydrogen condensed with framework oxygens. A strong correlation between T-O-T angle and the perturbation of T-O distances in adjacent tetrahedra is very similar to that in dehydrated-Ca-mordenite and is consistent with similar correlations in feldspar which were attributed to molecular-orbital effects. After adjustment for this correlation, mean T-O distances indicate slight Si, Al ordering. Remaining perturbations in T-O distances are small, and there is no convincing evidence for preferential attachment of protons to any particular framework oxygen. Some residual Na and K ions were located in site I at a twisted eight-ring. Two percent of the rings are not correctly stacked in Cmcm.