Using the power product
f
recently developed for a M
2Q structure map, a partial substitution of Mo for Ti in Ti
5As
3 was predicted to lead to a change from the Yb
5Sb
3 type to the Y
5Bi
3 type. ...Our subsequent experiments resulted in the discovery of the isostructural arsenides Ti
4MoAs
3 and Ti
3.7Mo
1.3As
3, which actually do form the Y
5Bi
3 type, with the lattice dimensions:
a=666.9(5)–665.9(2),
b=783.9(6)–785.3(3) and
c=973.1(6)–970.4(3) pm,
Z=4 (space group
Pnma). The binaries Ti
5As
3 and Ti
5Sb
3 both occur in the Yb
5Sb
3 type, while Zr
5Sb
3 and Hf
5Sb
3 adopt the Y
5Bi
3 type. These very similar structures all contain extended three-dimensional metal atom substructures, incorporating the As/Sb atoms in bi- and tri-capped trigonal prismatic voids. According to our calculations based both on the extended Hückel and LMTO approaches, the Y
5Bi
3 type comprises in total stronger metal–metal bonding, as suggested by higher
f
values of its representatives. This explains why adding more valence-electrons and increasing the averaged principal quantum number of the metal atoms by substituting Ti with Mo atoms leads to the structural change from the Yb
5Sb
3 to the Y
5Bi
3 type.
