Halogen bonding in a series of Br(CF2)nBr-DABCO adducts (n = 4, 6, 8).

Halogen bonding (XB) is a highly-directional class of intermolecular interactions that has been used as a powerful tool to drive the design of crystals in the solid phase. To date, the majority of XB donors have been iodine-containing compounds, with many fewer involving brominated analogues. We report the formation of adducts in the vapour phase from a series of dibromoperfluoroalkyl compounds, BrCF2(CF2)nCF2Br (n = 2, 4, 6), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Single-crystal X-ray diffraction studies of the colourless crystals identified 1,4-diazabicyclo[2.2.2]octane-1,4-dibromoperfluorobutane (1/1), C4Br2F8·C6H12N2, (I), 1,4-diazabicyclo[2.2.2]octane-1,6-dibromoperfluorohexane (1/1), C6Br2F12·C6H12N2, (II), and 1,4-diazabicyclo[2.2.2]octane-1,8-dibromoperfluorooctane (1/1), C8Br2F16·C6H12N2, (III), each of which displays a one-dimensional halogen-bonded network. All three adducts exhibit N...Br distances less than the sum of the van der Waals radii, with butane analogue (I) showing the shortest N...Br halogen-bond distances yet reported between a bromoperfluorocarbon and a nitrogen base [2.809 (3) and 2.818 (3) Å], which are 0.58 and 0.59 Šshorter than the sum of the van der Waals radii.

Halogen-bonded adduct of 1,2-dibromo-1,1,2,2-tetrafluoroethane and 1,4-diazabicyclo[2.2.2]octane.

Halogen bonding is an intermolecular interaction capable of being used to direct extended structures. Typical halogen-bonding systems involve a noncovalent interaction between a Lewis base, such as an amine, as an acceptor and a halogen atom of a halofluorocarbon as a donor. Vapour-phase diffusion of 1,4-diazabicyclo[2.2.2]octane (DABCO) with 1,2-dibromotetrafluoroethane results in crystals of the 1:1 adduct, C2Br2F4·C6H12N2, which crystallizes as an infinite one-dimensional polymeric structure linked by intermolecular N...Br halogen bonds [2.829 (3) Å], which are 0.57 Šshorter than the sum of the van der Waals radii.