New family of silicate phases with the pollucite structure

Abstract

A new family of Silicate phases, Cs2MSisOi2: M = Be, Mg, Fe, Co, Ni, Zn, Cd; RbzMSijOiz: M = Mg, Fe, (Co, Zn) has been prepared with the cubic polludte structure, a in the ränge 13.3 to 13.8 A, Space group Idid, Z = 8. The structure of one, Rb2MgSisOi2, has been refined to R 10.8% using X-ray powder data. The structures are built of a 3D, [MSi50i2]^~ framework containing large, 12-coordinated cavities for the alkali cations. These structures are unusual in that a wide ränge of divalent cations have pardally replaced Si"^"^ in the Silicate anion framework. IntrodoctionPolludte, CsAlSi206, is a framework aluminosilicate containing large, 12-coordinated cavities suitable for occupation by Cs"^ ions (Strunz, 1936; Naray-Szabo, 1938;Newnham, 1967). The unit cell is cubic with space group läid, Z = 16. Similar alumino-silicate frameworks are present in analdte, NaAlSizOe • H2O and leudte, KAlSi206 (Taylor, 1938;Beattie, 1954;Knowles et al., 1965;Wyart, 1941;Deer et al., 1963; Wyckoff, 1968), although leudte is tetragonal below 605° (Wyart, 1941;Deer et al., 1963; Wyckoff, 1968).Structxu-al studies on these phases are complicated by the occurrence of twinning in tetragonal leudte ^azzi et al., 1976) and by Si, AI disorder in the aluminosilicate framework. Various analogues of polludte and leudte, containing other trivalent ions instead of Al^"^ have been reported: Fepolludte, CsFeSi206 (Kopp et al., 1963;Kume and Koizumi, 1965), FeBrought to you by |

Characterization of a New Microporous Lithozincosilicate with ANA Topology

“…The topology of the pollucite structure has the International Zeolite Association (IZA) structure type ANA originating from the name and topology of a mineral analcime (Na[AlSi 2 O 6 ]·H 2 O) . The mineral leucite (K[AlSi 2 ]O 6 ) and synthetic compounds such as members of the M 2 [TSi 5 O 12 ] family (M = Cs, Rb, K, Na; T = Be, Mg, Fe, Co, Ni, Zn, Cd, B, Ga, Ge) also crystallize in the ANA structure type. Typically, ANA-type materials are thermally stable and readily incorporate penta-, tetra-, tri-, and divalent cations in the framework T sites.…”

RbCuPO4 – a maximum copper tetrahedral framework adopting the zeotype ABW structure

“…5 We have found that the zeotype structures that permit high levels of transition metal substitution are generally denser, in terms of tetrahedral units per unit volume, and exist with low levels of hydration, for example the ABW, CAS, ANA and BIK zeolite families. 6 In terms of transition metal substitutions, the ANA structure type is the most versatile with transition metal substituted leucite 7 and pollucite 8,9 phases described in the literature. However the levels of substitution in this system are limited through compound stoichiometry at 16.6% of the framework sites, i.e.…”