Structure of a 1,4-Diazabicyclo[2,2,2]Octane-Vermiculite Intercalate

Abstract 1-4-diazabicyclo[2,2,2]octane dihydrochloride (DABCO·2HC1) was reacted with two vermic-ulite samples to produce intercalates which, at room temperature, had relatively sharp, single crystal X-ray diffraction patterns. At higher temperatures (250°C) the stacking order decreased, and consequently the 0 kl reflections with k ≠ 3n became increasingly diffuse. The stacking order of previously heated samples returned when they were cooled. A superstructure was present in which DABCO cations occupied the corners and center of a cell 3 a × b , compared with the standard vermiculite cell. DABCO-intercalated Nyasaland vermiculite had the following monoclinic subcell (symmetry C 1) parameters under ambient conditions: a = 5.341(2), b = 9.249(3), c = 14.50(1) Å, and ß = 96.98(5)°. Differential Fourier analyses and least-squares refinement led to a final R value of 12.6% for 1814 reflections. The crystal structure analysis showed that individual DABCO ions were not symmetrically positioned between the silicate layers. A network of inorganic cations and water molecules was also present and governed the interlayer separation. At 250°C the d value was 13.7 Å, consistent with a dehydrated structure, in which each organic pillar has one amino group keyed into a ditrigonal cavity and the other amino group riding on the basal oxygens of an opposite tetrahedron.