'Excess' electrons in LuGe

The monogermanide LuGe is obtained via high‐pressure high‐temperature synthesis (5–15 GPa, 1023–1423 K). The crystal structure is solved from single‐crystal X‐ray diffraction data (structure type FeB, space group Pnma, a=7.660(2) Å, b=3.875(1) Å, and c=5.715(2) Å, RF=0.036 for 206 symmetry independent reflections). The analysis of chemical bonding applying quantum‐chemical techniques in position space was performed. It revealed—beside the expected 2c‐Ge‐Ge bonds in the germanium polyanion—rather unexpected four‐atomic bonds between lutetium atoms indicating the formation of a polycation by the excess electrons in the system Lu3+(2b)Ge2−×1 e−. Despite the reduced VEC of 3.5, lutetium monogermanide is following the extended 8‐N rule with the trend to form lutetium‐lutetium bonds utilizing the electrons left after satisfying the bonding needs in the anionic Ge‐Ge zigzag chain.
The germanium monogermanide is prepared by high‐pressure, high‐temperature synthesis. Chemical bonding in LuGe is described as covalently bonded zigzag chains of Ge atoms with the counterpart Lu4 polycations formed using excess electrons in sense of the Zintl count Lu3+(2b)Ge2−×1 e−. The homonuclear bonding in polycation in Lu4Ge4, which makes use of the electrons not required in the polyanion, resembles the situation in Ga2Se2.