The Interplay between Various σ- and π-Hole Interactions of Trigonal Boron and Trigonal Pyramidal Arsenic Triiodides

Boron and arsenic triiodides (BI3 and AsI3, respectively) are similar molecules that differ mainly in their geometries. BI3 is a planar trigonal molecule with D3h symmetry, while AsI3 exhibits a trigonal pyramidal shape with C3v symmetry. Consequently, the As atom of the AsI3 molecule has three σ-holes, whereas the B atom of the BI3 molecule has two symmetrical π-holes. Additionally, there are σ-holes on the iodine atoms in the molecules studied. In the first step, we have studied σ-hole and π-hole interactions in the known monocrystals of BI3 and AsI3. Quantum mechanical calculations have revealed that the crystal packing of BI3 is dominated by π-hole interactions. In the case of AsI3, the overall contribution of dihalogen bonding is comparable to that of pnictogen bonding. Additionally, we have prepared the [Na(THF)6][I(AsI3)6](AsI3)2 complex, which can be described as the inverse coordination compound where the iodine anion is the center of the aggregate surrounded by six AsI3 molecules in the close octahedral environment and adjacent two molecules in remote distances. This complex is, besides expected dihalogen and pnictogen bonds, also stabilized by systematically attractive dispersion interactions.