Chemistry Reference
In-Depth Information
Fig. 10 The space-filling
packing of [4
6
6
8
] cubo-
octahedra in the SOD
framework
3.2.5 SOD-Type Clathrates
The aluminosilicate mineral sodalite |M
2
|[T
12
[4]
O
24
[2]
] usually has an Al:Si ratio
close to 1, but silica- and alumina-rich sodalites have also been synthesised. The
structure (Fig.
10
) is one of the simplest tetrahedral frameworks with a space-filling
packing of [4
6
6
8
] cubooctahedral cages in a bcc-like configuration. These regular
truncated octahedra are relatively large cavities with rather small windows, which
prevent the guest molecules from migration from one cavity to the next.
Cages per unit cell: 2
[4
6
6
8
].
Rings per unit cell: (6
4R)
รพ
(8
6R).
Examples of this type of clathrate are:
(a) Hydrates:
|(HPF
6
)
2
|[O
12
[4]
H
24
[2]
]
Clathrate-hydrate SOD
[
57
]
|(ClNa
4
)
2
|[Al
6
[4]
Si
6
[4]
O
24
[2]
]
(b) Oxides:
Sodalites
[
58
]
|(C
2
H
4
(OH)
2
)
2
|[Si
12
[4]
O
24
[2]
]
[
59
]
No SOD-type Zintl phases have been reported so far.
More examples of sodalite-type compounds can be found in an extensive review
3.2.6 AST-Type Clathrates
The framework of the AST-type clathrate, |M
4
M
0
4
|[(T
32
T
0
8
)
P
40
[4]
O
80
[2]
], consists of
a three-dimensional assemblage of [4
6
6
12
] octadecahedral cages that share all their
