Supramolecular interactions between hexabromoethane and cyclopentadienyl ruthenium bromides: Halogen bonding or electrostatic organisation?

The interaction between hexabromoethane and [CpRu(CO)₂Br] (Cp = (η-C₅H₅), results in the deposition of two different isostoichiometric co-crystals, 2[CpRu(CO)₂Br]·C₂Br₆, one crystallising in space group P (Z = 1) and the other in P2₁/n (Z = 4). These were produced in the reaction of HCBr₃ and [(CpRu(CO)₂)₂] under indoor illumination, following a slight modification of the literature procedure. The origin of the hexabromoethane is as yet unknown but it appears to have been formed in the reaction rather than being an impurity in the bromoform. We have analysed the structures using the Hirshfeld surface approach and electrostatic potentials, supported by DFT theoretical calculations to better define the nature of intermolecular interactions in the solid state. The results indicate that the most significant interactions within both crystal forms arise not from the closest van der Waals contacts but, rather, from more distant interactions between the unsymmetrical electron distributions about the bromine atoms in the solvate and substrate molecules.