Hypothetical Structures of Magadiite and Sodium Octosilicate and Structural Relationships Between the Layered Alkali Metal Silicates and the Mordenite- and Pentasil-Group Zeolites

Abstract

Abstract--Hypothetical model structures for magadiite and sodium octosilicate, based on the structure of the zeolite dachiardite, are proposed that consist of layers of 6-member tings of tetrahedra and blocks containing 5-member rings attached to both sides of the layers. The infrared (IR) and nuclear magnetic resonance spectra of magadiite and sodium octosilicate have features in common with spectra of zeolites in the ZSM-5 and mordenite groups. A peak at 1225 cm l in the IR spectra of magadiite and sodium octosilicate is characteristic of zeolites containing 5-member rings, such as ZSM-5-and mordenite-type zeolites. The defect structures of pentasil zeolites may therefore be akin to layered alkali metal silicates containing zeolite-like domains, in which part of the silanol groups from adjacent silicate layers are condensed (cross-linked) forming siloxane linkages.

Chemical Characterization, Structural Features, and Thermal Behavior of Sodium and Hydrogen Octosilicate

“…Garc6s et al (1988) presented an IR spectrum identical with that of the re-exchanged sample (spectrum b, Figure 4). The 29SiMAS-NMR spectra published by Schwieger et al (1985) and Garc6s et al (1988) of equal intensity. However, in their spectra the highfield signal is about twice as broad and only half as high as the low-field signal.…”

“…This results in 8-membered rings parallel to the a-b plane. Another hypothetical structure model for octosilicate, based on the structure of the zeolite, dachiardite, was proposed by Garc6s et al (1988). Neither of these hypothetical structures has been proven by exact structure analysis.…”

Chesnokovite, Na2[SiO2(OH)2] · 8H2O, the first natural sodium orthosilicate from the Lovozero alkaline pluton, Kola Peninsula: Description and crystal structure of a new mineral species

“…An extremely rare (Si-O) complex consisting of doubled chains combined are transformed into a ribbon similar to that of caysichite and composed of four-member rings, as was recently established for the structure of synthetic NaSi 2 O 4 (OH) (Sassi et al, 2003). Bilateral networks of natrosilite-type six-mem- ber rings occur in the structures of makatite (Annehed et al, 1982) and kanemite (Garvie et al, 1999), and two-dimensional (Si-O) complexes were established in the structures of magadiite (Garces et al, 1988) and Na 4 Si 6 O 14 (Jamieson, 1967 1 and a spiral pseudochain owing to the hydrogen bonds (Schmidt and Felscher, 1990). While the number of crystallohydrate water molecules increases to 2 per formula unit, this type of one-dimensional chain is retained; however, two orthorhombic Na 3 [SiO 3 (OH)] · 2H 2 O modifications arise.…”

Contamination of Magadiite by Fluorine in Commonly Used Synthetic Procedures

“…The synthesis of this mineral was reported for the first time in 1972 by Lagaly et al The appropriate amounts of NaOH, SiO2 and H20 were mixed and heated in sealed glass vessels or ampullae at 100 ~ for at least 4 weeks. With the interest generated by these lamellar minerals in the late eighties, other synthetic approaches have been proposed, using shorter times of reaction (Fletcher and Bibby 1987;Garces et al 1988;Sprung et al 1990;Dailey and Pinnavaia 1992b). Most of these syntheses were performed in a Teflon-lined autoclave at higher temperatures for shorter periods of time (Garces et al 1988;Sprung et al 1990;Dailey and Pinnavaia 1992b).…”

“…With the interest generated by these lamellar minerals in the late eighties, other synthetic approaches have been proposed, using shorter times of reaction (Fletcher and Bibby 1987;Garces et al 1988;Sprung et al 1990;Dailey and Pinnavaia 1992b). Most of these syntheses were performed in a Teflon-lined autoclave at higher temperatures for shorter periods of time (Garces et al 1988;Sprung et al 1990;Dailey and Pinnavaia 1992b). For example, reaction mixtures heated at autogenous pressure in a Teflon-lined autoclave to 175 ~ for 21.5 h produced magadiite (Sprung et al 1990).…”