Chemistry Reference
In-Depth Information
Fig. 15 (a) Tetrahedral
structure of the
aluminosilicate |Rb
4
|
compare with the
C
-Si
[AlO
4
] and [SiO
4
] are
depicted as
unshaded
and
shaded tetrahedra
,
respectively
[4
2
6
2
8
2
].
Cages per unit cell: 4
Rings per unit cell: (4
4R)
þ
(4
6R)
þ
(4
8R).
Examples of this type of zeolite are:
(a) Oxides:
|Li
4
(H
2
O)
4
|[Al
4
[4]
Si
4
[4]
O
16
[2]
]
ABW
[
69
]
|Rb
4
|[Al
4
[4]
Si
4
[4]
O
16
[2]
]
[
70
]
(b) Zintl phases:
|Sr
4
|[Al
8
]
Clathrate hydrates with ABW structure are unknown.
It is remarkable that this structure is identical to that adopted by the Al (
-Si)
atoms in the Zintl phase SrAl
2
. The structural similarity between the Zintl phase and
the tectosilicate is shown in Fig.
15
. This similarity is consistent with the EZKC: In
|Rb
4
|[Al
4
Si
4
O
16
], the Rb atoms would donate 4e
to the [Al
4
Si
4
] skeleton, which is
formally converted into a [Al
4
Si
4
]
4
polyanion, that is, a
C
-Si framework. The
oxygen atoms are then situated near the bonding electron pairs, thus giving rise to
C
