Synthesis, structure and bonding feature of new metallic Zintl phases RE3Cu3Sb4 (RE = Nd, Sm, Tb, Dy, Ho)

RE3Cu3Sb4(RE = Nd, Sm, TD, Dy, Ho) was synthesized by are-melting method and their crystal structures were characterized by powder X-ray method. The compounds crystallize in cubic system, Y3Au3Sb4 type, space group I (4) over bar 3d(No. 220), Pearson code cI40. The unit cell parameters are: Nd3Cu3Sb4: a = 0.96749(1) nm, V = 0.90561(3) nm(3); Sm3Cu3Sb4: a = 0.96145(1) nm, V = 0.88875(3) nm(3); Tb3Cu3Sb4: a = 0.95362(1) nm, V = 0.86721(3) nm(3); Dy3Cu3Sb4: a = 0.95088(1) nm, V = 0.85975(3) nm(3); Ho3Cu3Sb4: a = 0.9488(2) nm, V = 0.8541(5) nm(3); Z = 4. The structures are characterized by covalent bonded Cu-Sb tetrahedra which form three-dimensional networks by sharing corners. The rare earth atoms are distributed in the cages. The formula with the charge balance can be written as RE33+ Cu-3(1+) Sb-4(3-) which are metallic Zintl phases having the weak metallic conductivity. The bonds have typical transitional features. General atomic coordination environment rules are followed. The unit cell parameters show the lanthanide contraction.