The crystal structure of synthetic zeolite Na-P 1, an isotype of gismondine

Abstract

AuszugDie Kristallstruktur des synthetischen Zeoliths Na-P 1 ("kubisches" Ρ) basiert auf dem Gismondin-Gerüst mit der Maximalsvmmetrie Ii\¡amd. Die Strukturanalyse wurde mangels Einkristalldaten mittels genauer Intensitäts-werte eines mehrfach verzwillingten Kristalls durchgeführt. Für die Gitterkonstanten wurden a = c = 10,04 Â gefunden; die Intensitäten ließen jedoch eindeutig eine Abweichung von kubischer Symmetrie erkennen. Schwache 6-Reflexe, für welche h -k + l = 2η + 1, wurden ebenfalls festgestellt, sind jedoch in der vorliegenden Arbeit nicht berücksichtigt worden. Die Struktur konnte unter Annahme der Raumgruppe Ii auf einen R(I)-Wert von 0,077 verfeinert werden. Die wahre Symmetrie der Struktur muß niedriger sein, wobei ausgeprägte Pseudosymmetrie in Erscheinung tritt.Präparate von Na-P 1 dürften fast ausnahmslos submikroskopisch verzwillingt sein. Die Zwillingsbildung wird durch die Topologie und die außer-ordentliche Flexibilität des Gerüstes begünstigt. Die große Flexibilität des Zeolithgerüstes spiegelt sich in den auffallenden Unterschieden in den Gitterkonstanten der bekannten gismondinartigen Strukturen, und das Auftreten scheinbar verschiedener P-Phasen läßt sich damit erklären. AbstractThe crystal structure of synthetic zeolite Na-P 1 (or Bi) has been solved using x-ray data obtained from a multiply twinned crystal. The structure is shown to be based on a gismondine-type framework with maximum possible symmetry IAi/amd.The cell dimensions were found to be α = c = 10.04 Â but the intensity data clearly indicated noncubic symmetry. Weak b reflections with h + k + I = 2/1+1 have also been recorded but were not used in this investigation. Refinement assuming space group 14 proceeded to an intensity R value of 0.077. The true symmetry must be lower and the structure appears to be highly pseudosymmetrie.The typical sphorulitic aggregates (if most Xa-P 1 preparations are thought to be Kiibmicroscopically twinned. The formation of twins is favoured by the topology and the extraordinary flexibility of the framework. Its flexibility also explains the comparatively large variations in cell dimensions and apparent symmetry of known gismondine isotypes, and could account for the occurrence of various Ρ phases.

Synthesis and Characterization of Zeolites in the System Na2O-K2O-Al2O3-SiO2-H2O

“…The tetragnnal sodium-form (designated as Na-P~) was first synthesized by Barrer et al (1959a), and was recently discovered to occur naturally as the zeolite gobbinsite by Nawaz and Malone (1982). The crystal structure originally proposed for the P zeolites by Barrer et al (1959b) was later disproved by Baerlocher and Meier (1972), who showed the framework to be an isotype of gismondine.…”

Rietveld refinement of the crystal structure of the new zeolite mineral gobbinsite

“…A skeletal diagram is shown in Figure 1. The twinning in gobbinsite (Nawaz and Malone, 1982;Nawaz, 1983) is readily explained on the basis of this framework structure (Baerlocher and Meier, 1972). This structure can also be described as a stacking of two-dimensional arrays of double crankshaft chains parallel [100] and [010], This allows for a flexibility in the framework which is manifested in the different symmetries observed.…”

“…At the time, four zeolites with the gismondine-type framework structure ( Figure 1) had been reported: gismondine (Fischer, 1963, andFischer andSchramm, 1971), TMA-gismondine (Baerlocher and Meier, 1970), Na -PI (Baerlocher and Meier, 1972), and amicite (Alberti and Vezzalini, 1979). These had been refined in the space group P2 x \c, 14^/amd, 14, and 12, respectively.…”

Synthesis and characterization of Na-P1 (GIS) zeolite using a kaolinitic rock

“…Despite having variable Si/Al ratios, all P zeolites are characterised by the same framework topology, which is the GIS net, gismondine, according to Meier and Olson 10 . Three polymorphs are recognized for Na-P: the cubic phase called Na-P 1 , refined in I 4 11 and with a unit cell content of Na 6 Al 6 Si 10 O 32 . 12H 2 O; the orthorhombic one, the so-called Na-P 2 with formula Na 4 Al 4 Si 12 O 32 .…”