[Ge2](4-) Dumbbells with Very Short Ge-Ge Distances in the Zintl Phase Li3NaGe2: A Solid-State Equivalent to Molecular O2.

ABSTRACT

The novel ternary Zintl phase Li3NaGe2 comprises alkali-metal cations and [Ge2](4-) dumbbells. The diatomic [Ge2](4-) unit is characterized by the shortest Ge-Ge distance (2.390(1) Å) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8-N) rule. Raman measurements support these findings. The multiple-bond character is confirmed by electronic-structure calculations, and an upfield (6)Li NMR shift of -10.0 ppm, which was assigned to the Li cations surrounded by the π systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand-free dumbbell in Li3NaGe2, the π- bonding py and pz orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled π-type bands of the neat solid Li3NaGe2 cross the Fermi level, resulting in metallic properties. Li3NaGe2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.