Crystallographic and Theoretical Evidences of Anion⋅⋅⋅Anion Interaction

Planar (HgCl3)− anions are stacked fairly closely together in a slipped parallel arrangement within several crystal structures. Quantum chemical analysis shows evidence of strong noncovalent spodium bonds between the Hg π‐hole of one unit and the Cl atom of an adjacent unit. Anion⋅⋅⋅anion spodium bonds work in tandem with crystal packing forces. Combined experimental and theoretical analysis elaborates on a new idea in noncovalent bonding (namely, spodium bonding) linking two anionic subunits. This counterintuitive interaction involves Hg atoms as electron‐density acceptors.