Synthesis, crystal and electronic structure of BaLi${}_2$Cd${}_2$Ge${}_2$

A new quaternary germanide has been synthesized and structurally characterized. BaLi${}_2$Cd${}_2$Ge${}_2$ adopts the rhombohedral CaCu${}_4$P${}_2$ structure type (Pearson code hR7; space group R$\overline{3}$m, Z = 3) with unit cell parameters a = 4.5929(6) and c = 26.119(5) Å. Structure refinements from single-crystal X-ray diffraction data demonstrate that the layered crystal structure can be regarded as an ordered quaternary variant of the ternary archetype; structural parallels to layered pnictides and binary germanides can also be drawn. The layered crystal structure is characterized by the absence of direct Ge–Ge and Cd–Cd homoatomic bonds, which suggests that BaLi${}_2$Cd${}_2$Ge${}_2$ should be classified as a Zintl phase, according to the formulation (Ba${}^{2+}$)(Li${}^{+}$)${}_2$(Cd${}^{2+}$)${}_2$(Ge${}^{4-}$)${}_2$. Electronic structure calculations show that the Fermi level crosses a distinct peak in the DOS, although the presence of an electronic band gap or a dip in the electronic density of states at the Fermi level is expected based on the electron partitioning.