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

Abstract

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]·1,4-FIB, [Cu4I4(NCNMe2)2(NCMe)2]·1,4-FIB, and [Cu4I4(NCNMe2)4]·1,4-FBrB, whose solid-state structures were studied by X-ray diffraction. In these three cases, the perfluorinated haloarenes function as combined σ- and π-hole donors, and their crystal structures exhibit intermolecular contacts, including halogen bonding (HaB) and π-hole interactions with the iodine ligands of the copper clusters. Analysis of the theoretical calculation data indicated that the formation of (cubane)·(perfluorinated haloarene) π–hole dimer is slightly energetically more favorable than (cubane)·(perfluorinated haloarene) HaB-based σ-hole dimer. The π-hole contacts and HaBs are accompanied by additional hydrogen bonding and also π-hole(NCN)···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.