Crystal Structures of Inorganic Oxoacid Salts Perceived as Cation Arrays: A Periodic-Graph Approach - Inorganic 3D Structures - page 51

Fig. 14 Topological
resemblance between the scu
(BaTe 2 ) net ( P 4/ mmm , Te-Te
contacts are ignored) and the
Ba(IO 3 ) 2 crystal structure

nia nets, thanks to existence of E-pairs (cf. Figs. 3 and 4 ). Further increase in the
size of the M + cation gives rise to 7-coordinated kwh and bcu-7- Pnnm underlying
nets that have not yet been found in binary inorganic compounds. In the high-
temperature phases of LiIO 3 , the coordination of the structure units decreases
yielding the 4- and 5-coordinated cation arrays with the crb (boron subnet in
CrB 4 or the silicon framework in the tectosilicates of the BCT family) and NiAs-
related nia-5,5- Pna 2 1 topologies, respectively. A NaIO 3 modification [ 60 ] contains
the 6-coordinated underlying net FEQWOO topologically close to nia (Table 1 )
that was found in [4,4 0 -bipyridinium]( m 6 -benzene-1,2,4,5-tetracarboxylato) 2 Pr(III) 2

hydrate (CSD Reference code FEQWOO) as well as in 13 other metal-organic
frameworks [ 57 ] .
g ¼

1:2. There are two main groups of M(LO 3 ) 2 compounds: small M 2+ cations
together with iodine cations form the 3,6-coordinated rutile array as in the
corresponding selenites (Table 7 ), while large alkaline-earth cations and Pb 2+
provide topologically denser 4,8-coordinated sqc 1964 or scu underlying nets. The
scu topological type is related to barium ditelluride (BaTe 2 )[ 61 ] if one ignores
Te-Te bonds in the Te 2 2- anions (Fig. 14 ) .
g ¼

1:3. A large group of M(IO 3 ) 3 iodates contains M 3+ cations bridged by
iodate anions; the resulting 6-coordinated WC (acs) underlying net does not include
the iodine atoms because they transform to edges at the second step of the
simplification procedure (Fig. 2 ) . Among binary compounds, AgF 3 and AuF 3 [ 62 ]
have the same topology as MI 3 array in M(IO 3 ) 3 . According to [ 63 ] , there is a close
relation between MIO 3 , M(IO 3 ) 2 , and M(IO 3 ) 3 crystal structures: the iodate anions
form a pseudo-hexagonal close packing, where M cations occupy all, one half or
one third of the octahedral holes, respectively. This reflects in more detail the
relations between nia, rtl, and acs nets.

3.3 Oxoacid Salts with Tetragonal Anions

Tetragonal coordination of a nonmetal cation provides its good shielding; hence,
the model of the oxygen-stuffed alloy seems even more valid in this case. The
coordination types of XO 4 anions are rather diverse (Fig. 15 ) and provide the topol-
ogies with quite different coordination of the nodes. Indeed, many examples of
correspondences between this class of oxoacid salts and binary compounds were
reported in [ 4 , 7 , 16 ]. Below these results are summarized and updated.