| Summary: | Ab initio calculations are applied to the question as to whether a AeX<sub>5</sub><sup>−</sup> anion (Ae = Kr, Xe) can engage in a stable complex with another anion: F<sup>−</sup>, Cl<sup>−</sup>, or CN<sup>−</sup>. The latter approaches the central Ae atom from above the molecular plane, along its C<sub>5</sub> axis. While the electrostatic repulsion between the two anions prevents their association in the gas phase, immersion of the system in a polar medium allows dimerization to proceed. The aerogen bond is a weak one, with binding energies less than 2 kcal/mol, even in highly polar aqueous solvent. The complexes are metastable in the less polar solvents THF and DMF, with dissociation opposed by a small energy barrier.
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