Chemistry Reference
In-Depth Information
Fig. 14 Structure of the intermetallic clathrate |K
32
|[Sn
100
][
67
]. The Sn atoms form a polyanion
with pseudo-stoichiometry
C
-Si
68
P
32
(
C
-Si
17
P
8
), where
C
-P atoms are only tri-connected.
A pentagonal dodecahedron cavity is also accentuated
per formula unit. These excess electrons were considered by the authors as conduc-
tion electrons. Electrical resistivity measurements above 230 K seem to confirm its
slight metallic character.
4 Similarities Between Zeolites and Intermetallic Clathrates
Compounds of the zeolite family are characterised by polyhedral cavities
interconnected in such a way that they form infinite channels in which the guest
atoms or molecules can migrate. In this section, we will see that the structures of
some of these zeolites are also similar to certain Zintl phases. These similarities
occur when the framework density FD of zeolites is higher than 18.5 T/1,000
˚
3
.
For lower FD values, the structure of the Zintl phases should be very open,
becoming unstable.
4.1 ABW-Type Zeolites
Compounds belonging to this group form 3D tetrahedral frameworks consisting of
four-, six- and eight-membered rings. The oxygen atoms are located near the
midpoints of all the T-T lines, producing the tetrahedral coordination of these
atoms. This structure is represented in Fig.
15
.
