Side-chain conformations in the isomorphous polyfluorinated {4,4′-bis[(2,2-difluoroethoxy)methyl]-2,2′-bipyridine-κ2 N,N′}dichloridopalladium and -platinum complexes

Abstract

The polyfluorinated title compounds, [MCl2(C16H16F4N2O2)] or [4,4′-(HCF2CH2OCH2)2-2,2′-bpy]MCl2 [M = Pd, (1), and M = Pt, (2)], have –C(Hα)2OC(Hβ)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—Hβ...F(—C) interactions (abbreviated as C—Hβ...F—C,C—Hβ...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—Hβ...F—C,C—Hβ...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.