Crystal Structures of Inorganic Oxoacid Salts Perceived as Cation Arrays: A Periodic-Graph Approach - Inorganic 3D Structures - page 54

omitted. Note that this topology differs from other 5,10-coordinated nets (alb and
fit) revealed in cation arrays in carbonates (Table 2 ) . One more high-pressure phase,
Zn 2 SiO 4 -II, has a 4,8-coordinated sqc 1964 underlying net that we saw in chlorates
(Table 8 ) .
g ¼

4:3. Bi 4 (SiO 4 ) 3 (eulitite) and isostructural Bi 4 (GeO 4 ) 3 have a Th 3 P 4 -like
cation array [ 4 ] .

3.3.2 Orthophosphates and Orthoarsenates

g ¼ 1:1. In this group of oxoacid salts, the pcu-b and nia underlying nets are again

observed (Table 10 ). Orthophosphates and orthoarsenates with small trivalent
cations belonging to the CrVO 4 structure type [ 66 ] are based on the nia motif
(Fig. 4 ) , while pcu-b is realized only in a high-temperature modification of BiPO 4
[ 67 ]. The underlying nets lsz (scheelite type), bcu-7- P 2 1 / c (monazite type), and
msw (zircon/xenotime type) found in orthosilicates and orthogermanates (Fig. 15 ;
Table 9 ) are quite common for orthophosphates and orthoarsenates, which reflects
well-known relations between these groups of compounds [ 68 ].
Orthophosphates and orthoarsenates with tetrahedrally coordinated M 3+ cations
represent a large group of silica-like structures most of which are microporous

Table 10 Underlying nets in orthophosphates and orthoarsenates
Underlying net Orthophosphate/orthoarsenate Correspondence XO 4 coordination

type

K 42

pcu-b (NaCl) BiPO 4 -HT Normal

K 6

nia (NiAs) MPO 4 (M ¼ Al, In, Ti, V, Cr, Fe,

Tl); MAsO 4 (M

Normal

¼ Cr, Mn)

K 8

lsz MPO 4 (M ¼ Yb, Lu); MAsO 4 Normal

(M ¼ Bi, Sm)

K 61 ,K 52

bcu-7- P 2 1 / c (RhSi) MPO 4 (M Bi, La, Ce, Pr, Nd,

Sm, Eu, Gd); MAsO 4 (M

¼ Normal

¼ Bi,

La, Ce, Nd) (monazite type)

K 42

msw MPO 4 (M Sc, Y, Tb, Dy, Ho, Er,

Tm, Lu); MAsO 4 (M

¼

Sc, Y,
Sm, Eu, Tb, Dy, Ho, Yb, Lu)

¼

K 42

sma MPO 4 (M ¼ La, Ce, Nd)

K 5

nia-5,5- P 2 1 / c FeXO 4 (X ¼ P, As)

K 4

dia-b (ZnS, sphalerite) MPO 4 (M ¼ Al, Ga); AlAsO 4 Normal

K 4

qtz ( a -HgS) MPO 4 (M ¼ Al, Fe, Ga); MAsO 4 Normal

(M ¼ Al, Ga)

K 4

lon (ZnS, wurtzite) AlPO 4 Normal

K 4

alw (Rh 2 O 3 -HP) Sb 2 (PO 4 ) 3 Normal

K 4

cor ( a -Al 2 O 3 ) Nb 2 (PO 4 ) 3 Normal

K 61

XEBHOB M 3 (PO 4 ) 2 (M ¼ Mg, Co, Zn);

Zn 3 (AsO 4 ) 2

K (12) Cu 3 Sb Li 3 XO 4 (X ¼ P, As) Normal

K (12) ith (Cr 3 Si) Ag 3 XO 4 (X ¼ P, As) Normal

K 68 wzz K 3 AsO 4