Hydrogen bonding and fluorous weak interactions in the non-isomorphous...

The polyfluorinated title compounds, [MBr₂(C₁₈H₁₆F₈N₂O₂)] or [4,4'-(HCF₂CF₂CH₂OCH₂)₂-2,2'-bpy]MBr₂, (1) (M = Pd and bpy is bipyridine) and (2) (M = Pt), have -CH_(α)2OCH_(β)2CF₂CF₂H side chains with methylene H-atom donors at the α and β sites, and methine H-atom donors at the terminal sites, in addition to aromatic H-atom donors. In contrast to the original expectation of isomorphous structures, (1) crystallizes in the space group C2/c and (2) in P2₁/n, with similar unit-cell volumes and Z = 4. The asymmetric unit of (1) is one half of the molecule, which resides on a crystallographic twofold axis. Both (1) and (2) display stacking of the molecules, indicating a planar (bpy)MBr₂ skeleton in each case. The structure of (1) exhibits columns with C-H_(β)...Br hydrogen bonds between consecutive layers which conforms to a static (β,β) linkage between layers. In the molecular plane, (1) shows double C-H_(α)...Br hydrogen bonds self-repeating along the b axis, the planar molecules being connected into infinite belts. Compound (2) has no crystallographic symmetry and forms π-dimer pairs as supermolecules, which then stack parallel to the a axis. The π-dimer-pair supermolecules exhibit (Pt-)Br...Br(-Pt) contacts [3.6937 (7) Å] to neighbouring π-dimer pairs crosslinking the columns. The structure of (2) reveals many C-H...F(-C) interactions between F atoms and aromatic C-H groups, in addition to those between F atoms and methylene C-H groups.