Halogen bond distance as a function of temperature

The halogen bond, that is, the attractive interaction between a halogen atom and an electron lone pair, was studied as a temperature function in the range 90-292 K. Three model structures containing the bonds Ar-(IN)-N-..., Ar-(IO)-O-..., and Ar-(BrN)-N-..., where Ar is a perfluorinated aromatic residue, were considered: (E)-1,2-bis(4-pyridyl)ethylene 1,4-diiodo-2,3,5,(3-tetrafluorobenzene (bpe(.)F(4)dIb), (E)-1,2-bis-(4-pyridyl)ethylene 1,4-dibromo2,3,5,6-tetrafluorobenzene (bpe(.)F(4)dBrb), and 4,4'-dipyridyl-N,N-dioxide 1,4-diiodo-2,3,5,6-tetrafluorobenzene (bpNOF(4)dlb). All three Ar-(XB)-B-... systems (B = lone pair donor) are nearly linear, and the change of (XB)-B-... bond lengths spans from 0.030 to 0.059 Angstrom in the studied temperature range; the least change is found in bpNO(...)F(4)dIb where the interaction between the two molecules is enforced by the presence of an (HO)-O-... hydrogen bond. Other weak packing features, present in all the three structures, such as (HF)-F-..., show larger variations in the same temperature range.