Sodalite, structure

Fig. 1. A photograph of a model representing the sodalite structure. The spheres indicate chlorine ions, and the tetrahedra have an oxygen ion at each corner, and a silicon or aluminum ion at the center.

Cancrinites are one of the rarest members of the feldspathoid group, classified as such due to its low silicon content. However, cancrinite is also classified as a zeolite, due to its open pore structure, which confers molecular sieve properties [1], Likewise, variable sodium carbonate and NaOH concentrations in the hydrothermal synthesis of cancrinite could direct the synthesis of the intermediate phase or the disordered cancrinite formation [2], The intermediate phase is described as a phase between cancrinite and sodalite [3], The disordered cancrinite is an intermediate phase which is much closer to the cancrinite structure than sodalite structure [2],... 

FIGURE 14.2 The structure of zeolites derived from the sodalite structure shown in (a). 

Figure 12. The structure of zeolite-A formed by linking truncated octahedra through double four-membered rings (a), the sodalite structure formed by direct face-sharing of four-membered rings in the neighboring truncated octahedra (b), and the faujasite structure formed by linking the truncated octahedra through double six-membered rings (c).

In addition to the influence of neighbors on 29Si chemical shifts, the geometrical effects (such as Si-O-T angles) already described above are also evident of mixed frameworks with elements other than Si on tetrahedral positions. This is reflected by the broadness of the bars shown in Fig. 1. Multinuclear NMR investigations on a large set of sodalite structures with various framework compositions show that T-O-T bond angle (T = Si, Al, Ga) and dTT distance chemical shift dependences exist, and mutual correlations between chemical shift of these NMR nuclei can be observed [68],... 

Obviously, in solution, 83 is not stable against oxidation. It is stable in the mineral lapis lazuli, and the industrial ultramarine blue pigment [28]. In these materials, the radical 83 is encapsulated in the -cages of the sodalite structure, which protects it against oxidation. In ultramarine pigments, another radical anion polysulfide, 82 , has been observed. 

Ultramarine is essentially a three-dimensional aluminosilicate lattice with entrapped sodium ions and ionic sulfur groups (Fig. 32). The lattice has the sodalite structure, with a cubic unit cell dimension of ca. 0.9 nm. In synthetic ultramarine derived from china clay by calcination (see Section 3.5.3), the lattice distribution of silicon and aluminum ions is disordered. This contrasts with the ordered array in natural ultramarines. 

The ground mixture is heated to about 750 °C under reducing conditions, normally in a batch process. This can be done in directly fired kilns with the blend in lidded crucibles of controlled porosity, or muffle kilns. The heating medium can be solid fuel, oil, or gas. The sodium carbonate reacts with the sulfur and reducing agent at 300 °C to form sodium polysulfide. At higher temperatures the clay lattice reforms into a three-dimensional framework, which at 700 °C is transformed to the sodalite structure, with entrapped sodium and polysulfide ions. 

Fig. 62. High-resolution electron micrograph of erionite viewed along [ 100] direction (476). The stacking defect marked by arrows consists of a single sheet of the sodalite structure.

We further illustrate the approach by reference to studies (331) of two related zeolite structures zeolite ZK-4 (isostructural with Linde A) and the highly siliceous analogue of sodalite known as TMA-sodalite. As was shown earlier (Sections III,A and III,D), the structure of zeolite A consists of a cubic array of / -cages linked through double four-membered rings so as to form larger polyhedral a-cages. The sodalite structure (Fig. 7) consists of a dense,... 

Precursor heating method. The gel mixture was maintained at 100°C for 3 days for precursor formation. The precursor with the mother liquor was transferred to autoclaves, and the temperature was raised at a constant rate of 1.7°C,min 1 to 130, 160, 190, and 220°C. The temperature was maintained at each level for 0.5 h. The synthesized materials were also treated in the same manner as the standard preparation method. XRD patterns showed that the zeolites prepared at 190 and 220°C were ZSM-34 however, the zeolite prepared at 220°C contained some sodalite structure. The zeolites crystallized at 130 and 160°C had insufficient XRD intensity of ZSM-34 patterns and showed an activity of only DME formation. When the crystallization temperature was raised to 190°C, DME decreased to ca. 1/10, and C2-C, olefins increased dramatically. However, when the crystallization temperature was raised to 220°C, ethylene formation decreased markedly and DME increased. 

The nature of the sulfur groups responsible for the color and their incorporation into the sodalite structure is reviewed in Refs. [3.158-3.162]. There are two types of... 

For zeolites, the simulated annealing method has been used to solve the structures of some new materials [35], including the product that results from a framework reconstruction on dehydration of Na6(ZnAs04)6.8H20 with the sodalite structure at 190°C [43] and the novel aluminosilicate UiO-7 [44], Analogously to the impact of simiilated annealing in structure solution sind hypothetic framework structure development, simulation will also be an exciting medium for new approaches to structure completion and refinement. 

Examples of zeolites sitting close to or on one side of periodic minimal surfaces are shown in Figs. 2.9(a),(b) the zeolite known as Linde-A on the P-surface and faujasite on the D-surface. Other examples are zeolite N in which the D-surface partitions the ZK5 and sodalite structures, and also paulingite which is described by the P-surface. 

Fig. 1. Silica sodalites a) The topology of the sodalite fiamework (oxygen atoms omitted) b) position of a 1,3,5-trioxane molecule in the cage of the silica sodalite structure. This corresponds to a snapshot because the trioxane molecule is disordered in the sodalite cage c) disorder cluster of the trioxane molecule in the sodalite cage d) organic molecules known to direct the silica sodalite structure.

The relation between SDAs and the zeotype structures they direct is not simply bijective. Usually, the formation of a certain zeotype structure can be directed by more than one SDA [5]. For example, the sodalite structure shown in Fig. 1 can also be directed by molecules other than trioxane, namely, 1,3-dioxolane [15], 1,3-dioxane [16], ethylene glycol [17], ethanolamine [18], and ethylenediamine [18]. Also, depending upon the reaction conditions, an organic molecule may direct the formation of different frameworks [8, 9]. It has therefore been proposed that the term "template", formerly used instead of SDA, should now be reserved for cases of strong structure direction and strong host-guest relationships, in line with its usage in other areas of the natural sciences [5]. A strict condition for a true "template" is that it should not exhibit disorder in the voids of the silica host. 

A related sequence involves the sodalite structure. Here the structure was determined for sodalite (Al Si = 1 1). AlPO4-20 was then discovered, with the same structure. And more recently Bibby and Dale (13) have reported an all-silica form of sodalite. 

Figure 1.1 Microporous (zeolitic) crystal structures showing the sodalite cage (bottom), zeolite A structure (top), sodalite structure (left), and zeolite Y (right).

In the crystallization of gallosilicates at 90 °C, we observed that every reaction mixture with a final pH higher than about 12 yielded a sodalite structure, whereas a faujasite-type material crystallized below pH 12. 

Temperature. Temperature influences the polymerization-depolymerization equilibrium. Higher temperatures cause denser materials to crystallize. Selbin and Mason (23) reported that they had to use a lower temperature to obtain the gallosilicate analog of zeolite X. Temperatures above 70 °C caused a gallosilicate of sodalite structure to crystallize. Countless examples for the temperature effect are given in the literature (see, e.g., Ref. 2). 

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