Structural Relationships Between Intermetallic Clathrates, Porous Tectosilicates and Clathrate Hydrates - Inorganic 3D Structures - page 3

To understand the structures of oxides, Vegas and coworkers have analysed
hundreds of structures within the last 20 years, focusing on their cation subarrays
[ 3 - 14 ] . They based their studies on the assumption that the global structure of the
oxide is determined by that of the parent metal or the corresponding alloy [ 5 , 8 ] .
Some striking structural coincidences between elements and alloys, on the one hand,
and the cation subarray in different oxides, on the other, have been reported by
Wondratschek (Mn 5 Si 3 alloy and apatite, Ca 5 (PO 4 ) 3 Cl) [ 15 ] , Addison (elemental
phosphorus and corresponding oxides) [ 16 ], Wells (

-Ge and SiO 2 keatite, see Fig. 1 )
[ 17 ] and O'Keeffe and Hyde (the reader is referred to their article to see the complete
list of structural similarities) [ 18 ]. These coincidences have motivated Vegas et al. to
study in a systematic way the cation subnets of binary, ternary and quaternary oxides.
According to the initial hypothesis, they confirmed the surprising fact that cations do
not arrange in an arbitrary way, but try to reproduce the structure of the corresponding
elements and alloys in spite of being embedded in an oxygen matrix. This led the
authors to establish the concept of “real stuffed alloy” for those oxides whose cation
arrays maintain the structure of the corresponding alloy [ 5 ].
Another step forward in understanding the structures of ternary and quaternary
aluminosilicates was taken by Santamar´a-P´rez et al. [ 3 , 6 , 19 ], who reinterpreted

g

Fig. 1 (a) Projection of the
keatite structure in which the
Si-Si “links” have been
drawn with thick lines to
show its similarity with (b)
the structure of g -Ge