Chemistry Reference
In-Depth Information
Oxygen atoms seek to complete their outer valence-electron shells with two
electrons. These would be provided by the bonding electron pairs. This is the
main reason why oxides tend to adopt structures similar to those of isoelectronic
Zintl polyanions.
Another interesting aspect is the existence of a correspondence between the
metal atom sites in some compounds and the location of the cage centres in
clathrates. Frank and Kasper were the first to recognise that type I and type II
clathrates were dual to the structures of Cr
3
Si and MgCu
2
alloys. In this work, we
have seen that there are more similarities of this kind, i.e.: DOH-type clathrates and
the structure of CaCu
5
or SGT-type clathrates and the high pressure modification of
SrSi
2
. One might assume that these similarities were just mere coincidences, but
nature does not usually act at random. The challenge of giving insight into these
resemblances remains open.
Acknowledgements Thanks are due to Dr. Olga Prieto and Dr. Raquel Chulia for valuable
suggestions. Financial support from Spanish MICCIN under project CTQ2009-14596-C02-01 as
well as from Comunidad de Madrid and European Social Fund: S2009/PPQ-1551 4161893
(QUIMAPRES) is gratefully acknowledged.
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