Weak hydrogen and halogen bonding in 4-[(2,2-difluoroethoxy)methyl]pyridinium iodide and 4-[(3-chloro-2,2,3,3-tetrafluoropropoxy)methyl]pyridinium iodide.

To enable a comparison between a C-H...X hydrogen bond and a halogen bond, the structures of two fluorous-substituted pyridinium iodide salts have been determined. 4-[(2,2-Difluoroethoxy)methyl]pyridinium iodide, C8H10F2NO+·I-, (1), has a -CH2OCH2CF2H substituent at the para position of the pyridinium ring and 4-[(3-chloro-2,2,3,3-tetrafluoropropoxy)methyl]pyridinium iodide, C9H9ClF4NO+·I-, (2), has a -CH2OCH2CF2CF2Cl substituent at the para position of the pyridinium ring. In salt (1), the iodide anion is involved in one N-H...I and three C-H...I hydrogen bonds, which, together with C-H...F hydrogen bonds, link the cations and anions into a three-dimensional network. For salt (2), the iodide anion is involved in one N-H...I hydrogen bond, two C-H...I hydrogen bonds and one C-Cl...I halogen bond; additional C-H...F and C-F...F interactions link the cations and anions into a three-dimensional arrangement.

Molecular structures of 3-[(2,2,3,3-tetrafluoropropoxy)methyl]- and 3-[(2,2,3,3,3-pentafluoropropoxy)methyl]pyridinium saccharinates.

The salts 3-[(2,2,3,3-tetrafluoropropoxy)methyl]pyridinium saccharinate, C9H10F4NO+·C7H4NO3S-, (1), and 3-[(2,2,3,3,3-pentafluoropropoxy)methyl]pyridinium saccharinate, C9H9F5NO+·C7H4NO3S-, (2), i.e. saccharinate (or 1,1-dioxo-1λ6,2-benzothiazol-3-olate) salts of pyridinium with -CH2OCH2CF2CF2H and -CH2OCH2CF2CF3 meta substituents, respectively, were investigated crystallographically in order to compare their fluorine-related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven-membered ring reveals a double hydrogen-bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation-anion π-interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Šin (1), and 3.409 (3) and 3.458 (3) Šin (2).

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

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 the para position 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-Csp3 connections. These dimers are further crosslinked, utilizing another complimentary Csp2-H...X...H-Csp2 connection. The pyridinium rings are π-stacked, forming columns running parallel to the a axis that make angles of ca 44-45° 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.

New fluorous ponytailed 4-[(2,2,2-trifluoroethoxy)methyl]pyridinium halide salts.

It is possible that fluorous compounds could be utilized as directing forces in crystal engineering for applications in materials chemistry or catalysis. Although numerous fluorous compounds have been used for various applications, their structures in the solid state remains a lively matter for debate. The reaction of 4-[(2,2,2-trifluoroethoxy)methyl]pyridine with HX (X = I or Cl) yielded new fluorous ponytailed pyridinium halide salts, namely 4-[(2,2,2-trifluoroethoxy)methyl]pyridinium iodide, C8H9F3NO+·I-, (1), and 4-[(2,2,2-trifluoroethoxy)methyl]pyridinium chloride, C8H9F3NO+·Cl-, (2), which were characterized by IR spectroscopy, multinuclei (1H, 13C and 19F) NMR spectroscopy and single-crystal X-ray diffraction. Structure analysis showed that there are two types of hydrogen bonds, namely N-H...X and C-H...X. The iodide anion in salt (1) is hydrogen bonded to three 4-[(2,2,2-trifluoroethoxy)methyl]pyridinium cations in the crystal packing, while the chloride ion in salt (2) is involved in six hydrogen bonds to five 4-[(2,2,2-trifluoroethoxy)methyl]pyridinium cations, which is attributed to the smaller size and reduced polarizability of the chloride ion compared to the iodide ion. In the IR spectra, the pyridinium N-H stretching band for salt (1) exhibited a blue shift compared with that of salt (2).