Rationalization of the Substructures Derived from the Three Fluorite-Related [Li6(MVLi)N4] Polymorphs: An Analysis in Terms of the “Barnighausen Trees” and of the “Extended Zintl–Klemm Concept” - Inorganic 3D Structures - page 120

indicating that the four-connected network maintains in part the threefold connectivity
of the N. This longer contact (3.91 ˚ ) is drawn in the shaded square of Fig. 17f .
Because this is the unique long contact drawn, the reader can appreciate the
interweaving of the two N-like networks. What is really surprising is that

b -Li 7 VN 4

provides evidence of how two interconnected -N 2 nets, when compressed, lead to

the formation of the 3D nitrogen [ 45 ] . Expressed in other words, the characteristics of
both the molecular and the 3D structures of nitrogen can be recognized in the nitride!

a

4.1.2 Cu 3 WO 4

a 3. The

Further searching revealed the compound Cu 3 WO 4 [ 46 ] in space group P

data are as follows:
W in 8 c at 0.1170, 0.1170, 0.1170: Cu in 24 d at 0.4044, 0.2457, 0.1376:
O(1) in 24 d at 0.2193, 0.3016, 0.0891: O(2) in 24 d at 0.4446, 0.4636, 0.1953.
Comparing these figures with the corresponding data for -Li 7 VN 4 , it is clear that

the W-atom sites correspond with the Li(1) site, and the copper sites are in fair
agreement with those for Li(2) - a Cu site at 0.904, 0.254, 0.862 compares with a Li
(2) site at 0.885, 0.368, 0.870: there is some significant difference in the y -parameter,
but this is not major. The two drawings are shown in Fig. 18a, b , wherewe compare the
WO 6 octahedra of Cu 3 WO 4 with the Li(1)N 4 tetrahedra of

b

b -Li 7 VN 4 . The Li(1)-Li(1)

-Li 7 VN 4 is 4.47 ˚ , and the W-W distance in Cu 3 WO 4 is 3.97 ˚ . Looking
at Fig. 18, it is evident that the structure can also be described as a [WO 6 ] 2 body-
centred cube with an inscribed Cu 6 icosahedron.

distance in b

Fig. 18 (a) The structure of b -Li 7 VN 4 ( a ¼ 9.586 ˚ ), represented by Li(1)N 4 tetrahedra at three
mean levels: x

¼ 1- red ; x ¼ 0.5 - blue ; x ¼ 0- green . Li(2) atoms - yellow .(b) The structure

9.797 ˚ ) represented by WO 6 octahedra at three mean levels: x

of Cu 3 WO 4 ( a ¼ ¼ 1- red ;

x ¼ 0.5 - blue ; x ¼ 0- green . Cu atoms - yellow

Fig. 17 (a) The fcc-array of N 2 molecules in a -N 2 at 20 K ( a ¼ 5.661 ˚ ). N-N bonds (1.04 ˚ ).
(b) b -Li 7 VN 4 ( a ¼ 9.599 ˚ ). Pairs of VN 4 tetrahedra - blue , which, when linked, form the same
fcc array as the N 2 molecules: V atoms - red .(c) The same array formed by the Li(1)N 4 tetrahedra -
grey , but displaced by a/2: Li(1) atoms - green . Small yellow spheres are drawn at the centre of the
Li-Li contacts to help identify the fcc cell. (d) The four-connected network of the HP phase g -Si.
(e) The HT, HP phase of 3D nitrogen. (f) The [Li(1)V] network of b -Li 7 VN 4 showing its similarity
with -Si(Ge). It also shows the two interconnected nets as drawn in (e): the dark green diagonal

link drawn in the grey square is the V-Li contact. (g) Perspective view of the same array as that in
(f) to show the two N-subnets

g