Ge32 Co9-x : Creating "Empty" Space by High Pressure

Abstract

The compound Ge₃₂ Co_9-x (x=0.54(6), a=10.9861(3) Å, space group Im $\bar{3}$ m) prepared under high pressure and at high temperature is metastable under ambient conditions. It crystallizes in a new structure type, Pearson symbol cI82-1.08. The crystal structure represents a slightly distorted cubic primitive arrangement of germanium atoms with part of the Ge cubes filled by cobalt. Analysis of the chemical bonding by real-space methods revealed three-core cluster units Ge₁₆ Co₃ and seemingly empty regions comprising either covalent inter-polyhedral Ge-Ge bonds or lone-pairs located at the germanium atoms. The electrical conductivity is metal-like.

Keywords: chemical bonding in position space; cobalt; electron localizability; germanium; high-pressure synthesis.