Using the power product f recently developed for a M2Q structure map, a partial substitution of Mo for Ti in Ti5As3 was predicted to lead to a change from the Yb5Sb3 type to the Y5Bi3 type. Our subsequent experiments resulted in the discovery of the isostructural arsenides Ti4MoAs3 and Ti3.7Mo1.3As3, which actually do form the Y5Bi3 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 Ti5As3 and Ti5Sb3 both occur in the Yb5Sb3 type, while Zr5Sb3 and Hf5Sb3 adopt the Y5Bi3 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 Y5Bi3 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 Yb5Sb3 to the Y5Bi3 type.