Weak hydrogen bonding and fluorous interactions in the chloride and bromide salts of 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium

Abstract

Neutralization of 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridine with hydrohalo acids HX(X= Cl and Br) yielded the pyridinium salts 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium chloride, C9H10F4NO+·Cl−, (1), and 4-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium bromide, C9H10F4NO+·Br−, (2), both carrying a fluorous side chain at theparaposition of the pyridinium ring. Single-crystal X-ray diffraction techniques revealed that (1) and (2) are isomorphous. The halide anions accept four hydrogen bonds from N—H,ortho-C—H and CF2—H groups. Two cations and two anions form a centrosymmetric dimeric building block, utilizing complimentary N—H...X...H—Csp3connections. These dimers are further crosslinked, utilizing another complimentary Csp2—H...X...H—Csp2connection. The pyridinium rings are π-stacked, forming columns running parallel to theaaxis that make angles ofca44–45° with the normal to the pyridinium plane. There are also supramolecular C—H...F—C interactions, namely bifurcated C—H...F and bifurcated C—F...H interactions; additionally, one type II C—F...F—C halogen bond has been observed.