Chemistry Reference
In-Depth Information
Na and Al atoms, behaving as an average
C
-Mg, form the pseudo-structure
C
-Mg
2
Si
6.35
˚
). The important
consequence here is that such antifluorite-type structure has ever been obtained by
heating the olivine-like Mg
2
[SiO
4
] at elevated temperatures, although it has been
obtained with NaAl[SiO
4
] which is its pseudo-compound
with the antifluorite structure, just like Mg
2
Si itself (
a
¼
-Mg
2
[SiO
4
].
The case of the related compound LiCs[SO
4
] is also very illustrative, also
supporting our interpretation. Thus, the [CsS] subarray forms a NaCl-type structure
which can be interpreted as the result of the one-electron transfer from Li to S,
converting it into
C
-CsCl. On the other hand, if the transfer would occur from Cs to
Li, then the subarray [LiS] would be converted into
C
C
-BeS forming so a zinkblende
structure in agreement with the structure of BeS itself. The structures of similar
compounds such as LiMgP and LiAlP also agree with this approach.
5 Conclusions
Resulting from the detailed analysis given above, a profound analysis of the cation
arrays of the inorganic structures provides many keys for the understanding of
crystal structures. In many aspects, our results coincide with many of the topological
similarities reported by Blatov and which are collected in this volume [
9
].
be formulated in the following way: “The Extended Zintl-Klemm Concept, applied
to any cation array, appears as the most useful tool for both, description and
understanding of the structures”. This statement leads to a second conclusion:
“When a crystal structure is analysed in this way, one discovers that several
structures co-exist simultaneously as if they would behave as resonance structures”.
Focusing our discussion on FeLi[PO
4
], we see that in triphylite, the FeLiP sub-
array forms a distorted Ni
2
In-like structure. The Ni
2
In array has implicit a distorted
graphite-like network formed by the FeP pair of atoms. The same FeP subarray
converted into
-FeS forms, at the same time, blocks of the PbO type (like in both,
Cu
2
Sb and NaAlSi), identical to one of the phases of FeS itself. Within this FeS
substructure, infinite 4
4
planar nets of metallic Fe persist in the structure. Considering
the [LiP] subarray, we discover a tetragonally distorted rocksalt structure, where
fragments of real LiCl are formed. In this rocksalt structure, one half of the cubes are
filled by Fe in alternate layers. If the Fe atoms were distributed in alternate cubes in
the whole structure, they would form a zinkblende structure instead of the occurring
PbO-type skeleton. In both cases, however, the rocksalt
C
C
-LiCl exists!
-FeLi[PO
4
], the dissection leads to similar conclusions. The [FeLiP] sub-
array also forms a distorted Ni
2
In-type structure. Within this subarray, if the Li
atoms act as donors, the FeP pair of atoms, converted into
In
b
C
-FeS, convert the
compound into a Li-stuffed
-Fe[SO
4
], forming an NiAs-type array, identical to
that of real Fe[SO
4
] and also identical to another phase of FeS!
Another important conclusion is that this compound represents a new and
significant example of what has previously been reported concerning the
C
