An accurate vibrational signature in halogen bonded molecular crystals.

The far infrared (FIR) and Raman fingerprints of the halogen bond in two representative 1D halogen bonded networks based on the recognition of TFIB, tetrafluorodiiodobenzene, with piperazine or azopyridine, have been accurately identified. It was demonstrated that the signature of the halogen bonding in the solid state, especially the N⋯I signal can be simply and directly evidenced in the far infrared region. The DFT theoretical calculations identified the N⋯I interaction in the molecular crystals and allowed estimation of the corresponding energies and distances of the involved halogen bonds, in accordance with the cristallographic data.