MA(delta)Sb2-(delta) (M = Zr, Hf; A = Si, Ge): A New Series of Ternary Antimonides and Not "(beta)-ZrSb2"

The ternary antimonides ZrSi(delta)Sb2-(delta), HfGe(delta)Sb2-(delta), and ZrGe(delta)Sb2-(delta) were prepared by annealing of the elements in stoichiometric ratios below 800 °C. ZrSi(delta)Sb2- was earlier erroneously described as the binary "(beta)-ZrSb2", which does not exist as such, because the incorporation of tetrel atoms is necessary for the formation of this structure. ZrSi(delta)Sb2-(delta) has a small yet significant phase width with at least 0.066(7) =< (delta)=< 0.115(3), whereas the Ge analogues exist with larger tetrel concentration, i.e., ZrGe0.211(5)Sb1.789 and HfGe0.205(6)Sb1.795. The whole series of title compounds crystallizes in the Co2Si type (space group Pnma), with lattice dimensions of, e.g., for ZrGe0.211(5)Sb1.789, a = 730.4(1) pm, b = 395.13(6) pm, c = 957.6(2) pm, V = 0.27635(7) nm3, Z = 4. The anionic substructure comprises infinite ribbons formed by the atom sites Q1 and Sb2, with Q1 being mixed occupied by Si or Ge and Sb atoms. These ribbons exhibit Q1-Q1 single bonds and Q1-Sb2 "half" bonds. Assuming the validity of the 8 - N rule, one can assign seven valence-electrons to Sb2 but only five to Q1, which might explain the preference of the tetrel atoms for the latter site.