The cesium oxide mercuride Cs${}_{18}$Hg${}_8$O${}_6$

By reacting Cs with Cs${}_2$O and elemental mercury the new double salt Cs${}_{18}$Hg${}_8$O${}_6$ could be obtained. Its crystal structure (cubic, space group I23 with a=13.3920(10) Å, Z=2, R1=0.026/0.032 for I≥2σ(I)/all I, respectively) comprises isolated oxide anions in octahedral coordination by cesium cations next to the mercuride anion [Hg${}_8$]${}^{6-}$. This first isolated anion of mercury has cubic shape and is coordinated by cesium atoms capping the faces and the edges of the [Hg${}_8$]${}^{6-}$ cube. The ionic character of the double salt is shown in DFT calculations of the electronic structure. Raman spectra show distinct features in the low energy region arising from the vibrations of the mercuride anion. Cs${}_{18}$Hg${}_8$O${}_6$ has very close structural analogies to the thallide oxide Cs${}_{18}$Tl${}_8$O${}_6$. (© 2022 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH)