Alkali Halide Cubic Cluster Anions ([Cs₈X₂₇]^19-, X = Cl, Br) Isolated from Water

Herein we report the syntheses and the X-ray structure of [Cs₈X₂₇]^19- (X = Cl, Br) clusters, the first binary cluster anions isolated in bulk crystal structures. They were obtained by electrostatic capture and face-directed recognition of the prenucleation [Cs_mCl_n]^(n-m)- clusters from water solutions, using [M₄(OH)₈(OH₂)₁₆]⁸⁺ (M = Zr^IV or Hf^IV) as the counter cations. These compounds have been thoroughly characterized with a variety of techniques including vibrational spectroscopy and superionic conductivity analysis. This work not only provides structural models for a better understanding of the nucleation of binary materials but also shows that magic number binary clusters adopting a cubic lattice structure do form, in agreement with the time-honored theoretical and spectroscopic predictions.