Key-to-lock halogen bond-based tetragonal pyramidal association of iodonium cations with the lacune rims of beta-octamolybdate.

The structure-directing "key-to-lock" interaction of double σ-(I III )-hole donating iodonium cations with the O-flanked pseudo-lacune rims of [β-Mo 8 O 26 ] 4- gives halogen-bonded iodonium-beta-octamolybate supramolecular associates. In the occurrence of their tetragonal pyramidal motifs, deep and broad σ-(I III )-holes of a cation recognize the molybdate backbone, which provides an electronic pool localized around the two lacunae. The halogen-bonded I⋯O linkages in the structures were thoroughly studied computationally and classified as two-center, three-center bifurcated, and unconventional "orthogonal" I⋯O halogen bonds. In the latter, the O-atom approaches orthogonally the C-I III -C plane of an iodonium cation and this geometry diverge from the IUPAC criteria for the identification of the halogen bond.