Chemistry Reference
In-Depth Information
Structural Relationships Between Intermetallic
Clathrates, Porous Tectosilicates and
Clathrate Hydrates
D. Santamar
´
a-P
´
rez and F. Liebau
Abstract Intermetallic clathrate-type compounds, such as |Eu
8
|[Ga
16
Ge
30
], are
Zintl phases in which a formal charge transfer from the more electropositive
guest atoms (Eu) to the more electronegative host atoms (Ga or Ge) allows the
latter to form skeletons with strong directed covalent bonds (polyanions
[Ga
16
Ge
30
]
16
). On the other hand, in clathrasils, porous silica polymorphs, such
as melanophlogite |(CH
4
,N
2
,CO
2
,
)
8
| [Si
46
[4]
O
92
[2]
] the Si atoms form skeletons
which are related to those of Zintl phases, if oxygen atoms are neglected. As in
other silicates, in clathrasils the oxygen atoms are located near to hypothetical
Si(Al)-Si(Al) bonds, thus producing the tetrahedral coordination around the Si(Al)
atoms. The similarities between the structures of intermetallic clathrates and cla-
thrasils can be understood in the light of both the extended Zintl-Klemm concept
and the Pearson's generalised octet rule. It is recalled that these principles were
successfully applied to describe the structures of other ternary and quaternary
aluminates and silicates. In this article, we report a comprehensive and comparative
study of both clathrate-like and zeolite-like porous tectosilicate structures to show
that their skeletons obey the same general principles. Clathrate hydrates, which also
adopt similar skeletons to clathrasils, are also discussed in detail.
...
Keywords Clathrates
Hydrates
Tectosilicates
Zintl-Klemm concept
