Crystal Structures of Inorganic Oxoacid Salts Perceived as Cation Arrays: A Periodic-Graph Approach - Inorganic 3D Structures - page 57

Fig. 18 Topological
resemblances between (a)
ZnS (sphalerite) net ( F 43 m )
and ZnSO 4 ;(b) PtS net ( P 4 2 /
mmc ) and PdSO 4

Na 2 SO 4 (thenardite), as well as the Ag 2 SO 4 cation array, adopts the 5,10-coordinated
TiSi 2 -like motif [ 16 ] . This means that the reported relations between thenardite and
the spinel structure type as well as between other Na 2 SO 4 modifications and the
olivine structure type [ 6 ] reflect geometrical similarities of the structure types, but
do not take into account all their topological features. As was mentioned in
Sect. 3.3.1 , the olivine structure type is not topologically equal to the Ni 2 In type,
also the TiSi 2 underlying net does not coincide with the spinel-like net. This
example demonstrates that visual analysis cannot detect some tiny topological
differences, although the general (not strict) similarities of the motifs under consid-
eration are unquestionable. The reader is referred to two chapters of this volume
[ 55 , 72 ] where the structures are analyzed visually, producing discrepancies with
the results exposed here.
g ¼ 2:3. Like orthophosphates (Table 10 ) , some sulfates and selenates of this

g ratio adopt two topological types of binary compounds: alw and cor. The corundum-
like cation array typical for this g ratio is realized for most sulfates of trivalent
d -elements (Fig. 7 ) ; however, for large M cations alw is more preferable.
g ¼

-Zr(SO 4 ) 2 , is related to cotun-
nite (PbCl 2 ) if one ignores two long (3.65 ˚ ) Pb-Cl contacts and considers the
cotunnite net as 3,4,7-coordinated, not 4,5,9-coordinated.

1:2. The only representative of this g ratio, a

3.3.4 Perchlorates, Perbromates, and Periodates

g ¼

1:1. There are clear dependences of the underlying net topology on the kind of
M + cation and XO 4 - anion (Table 12 ). For perchlorates, the increase in the M + cation
size in the row Li-Na-K, Rb, Cs gives rise to the sequence nia-pcu-b-FeB at
ambient conditions, while the cation arrays in the high-temperature modification of
MClO 4 (M K, Rb, Cs) decrease their topological density and transform to the pcu-

b type. The FeB-like NaClO 4 was obtained by chance in the presence of cucurbit[5]
uril ions in the mother solution [ 77 ] . Perbromates and periodates prefer to have denser

¼