Side-chain conformations in the isomorphous polyfluorinated {4,4'-bis[(2,2-difluoroethoxy)methyl]-2,2'-bipyridine-κ²N,N'}dichloridopalladium and -platinum complexes

The polyfluorinated title compounds, [MCl₂(C₁₆H₁₆F₄N₂O₂)] or [4,4'-(HCF₂CH₂OCH₂)₂-2,2'-bpy]MCl₂ [M = Pd, (1), and M = Pt, (2)], have -C(H_α)₂OC(H_β)₂CF₂H side chains with H-atom donors at the α and β sites. The structures of (1) and (2) are isomorphous, with the nearly planar (bpy)MCl₂ molecules stacked in columns. Within one column, π-dimer pairs alternate between a π-dimer pair reinforced with C-H...Cl hydrogen bonds (α,α) and a π-dimer pair reinforced with C-H_β...F(-C) interactions (abbreviated as C-H_β...F-C,C-H_β...F-C). The compounds [4,4'-(CF₃CH₂OCH₂)₂-2,2'-bpy]MCl₂ [M = Pd, (3), and M = Pt, (4)] have been reported to be isomorphous [Lu et al. (2012). J. Fluorine Chem. 137, 54-56], yet with disorder in the fluorous regions. The molecules of (3) [or (4)] also form similar stacks, but with alternating π-dimer pairs between the (α,β; α,β) and (β,β) forms. Through (C-)H...Cl hydrogen-bond interactions, one molecule of (1) [or (2)] is expanded into an aggregate of two inversion-related π-dimer pairs, one pair in the (α,α) form and the other pair in the (C-H_β...F-C,C-H_β...F-C) form, with the plane normals making an interplanar angle of 58.24 (3)°. Due to the demands of maintaining a high coordination number around the metal-bound Cl atoms in molecule (1) [or (2)], the ponytails of molecule (1) [or (2)] bend outward; in contrast, the ponytails of molecule (3) [or (4)] bend inward.