Fluorine-hydrocarbon separation and microdomain formation in N-(2,3,5,6-Tetrafluoropyridin-4-yl)benzene-diamines

Abstract

Compounds with both aromatic and perfluoro aromatic moieties often assemble in the form of π-stacks with alternating arene perfluoroarene arrangements. The 1,4 and 1,3-diamines of N-(2,3,5,6-tetrafluoropyridin-4-yl)benzene (1) and (2), C₁₁H₇F₄N₃, however, show a behavior more commonly observed for diblock perfluoro alkyl derivatives: the fluorinated and the hydrocarbon moieties of the molecules segregate from each other and form fluoro and hydrocarbon microdomains with parallel layers of π-stacked tetrafluoropyridine rings and diamino-phenyl moieties. The structural features of the two derivatives are, despite the different substitution patterns and cell settings, strikingly similar. The main feature in the non-fluorinated domains of 1 and 2 is a set of N–H···H and N–H···π interactions that connect the amino groups of four molecules with each other, which are augmented by some weaker C–H···π and C–H···F interactions, but no π–π stacking is observed. The fluoro microdomains in both 1 and 2 are characterized by extremely short interplanar distances between the tetrafluoropyridine rings of only about 3 Å. The molecules in the layers are shifted sideways against each other by half a pyridyl ring thus bringing the fluorine atoms to atop of the aromatic carbon atoms and vice versa.