Hydrogen bonding and fluorous weak interactions in the non-isomorphous {4,4'-bis[(2,2,3,3-tetrafluoropropoxy)methyl]-2,2'-bipyridine-κ2N,N'}dibromidopalladium and -platinum complexes.

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(ß)2CF2CF2H side chains with methylene H-atom donors at the α and ß 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(ß)...Br hydrogen bonds between consecutive layers which conforms to a static (ß,ß) 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.