Combined - and -Hole Donor Properties of Perfluorinated Iodo(or bromo)benzenes: Halogen Bonding and -Hole Interactions in Cocrystals Including Cu₄I₄ Clusters

Cocrystallization of CuI with NCNMe2 in the presence of 1,4-diiodotetrafluorobenzene (1,4-FIB) and 1,4-dibromotetrafluorobenzene (1,4-FBrB) in MeCN gave cocrystals [Cu4I4(NCNMe2)(4)]center dot 1,4-FIB, [Cu4I4(NCNMe2)(2)(NCMe)(2)]center dot 1,4-FIB, and [Cu4I4(NCNMe2)(4)]center dot 1,4-FBrB, whose solid-state structures were studied by X-ray diffraction. In these three cases, the perfluorinated haloarenes function as combined sigma- and pi-hole donors, and their crystal structures exhibit intermolecular contacts, including halogen bonding (HaB) and pi-hole interactions with the iodine ligands of the copper clusters. Analysis of the theoretical calculation data indicated that the formation of (cubane)center dot(perfluorinated haloarene) pi-hole dimer is slightly energetically more favorable than (cubane)center dot(perfluorinated haloarene) HaB-based sigma-hole dimer. The pi-hole contacts and HaBs are accompanied by additional hydrogen bonding and also pi-hole(N-CN)center dot center dot center dot X (X = Br, I) contacts. Altogether, these interactions lead to the occurrence of moderately strong noncovalent binding between copper clusters and the aromatic HaB donors.