Halogen Bonds of Halotetrafluoropyridines in Crystals and Co‐crystals with Benzene and Pyridine

Abstract

The structures of the three para‐substituted halotetrafluoropyridines with chlorine, bromine, and iodine have been determined in the solid state (X‐ray diffraction). The structures of these compounds and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivatives exhibit halogen bonding as a structure‐determining motif. On the way to an investigation of halogen bond formation of halotetrafluoropyridines in the solid state with the stronger Lewis base pyridine, co‐crystals of benzene adducts were investigated to gain an understanding of the influence of aryl–aryl interactions. These co‐crystals showed halogen bonding only for the two heavier halotetrafluoropyridines. In the pyridine co‐crystals halogen bonding was observed for all three para‐halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum‐chemical calculations of electron density topologies and natural bond orbitals.

Friedel–Crafts Type Methylation with Dimethylhalonium Salts

“…The normalized contact (observed distance divided by sum of van der Waals radii) [15] is with 0.92 quite large, indicating a weak interaction. For comparison, in the solid state structure of tetrafluoro‐ para ‐iodopyridine a rather strong I–N interaction with a normalized contact of 0.80 is found [16] . No cocrystals were obtained when 2I was crystallized from dichloromethane solution at −80 °C in the presence of pentafluoropyridine.…”

“…Teflic acid was prepared according to literature [20] as well as cyanuric fluoride [21] and tetrafluoro-para-iodopyridine. [16] The salts [ 4 ]w here synthesized as already described. [7] The salt [NEt 4 ][AlCl 4 ]w as synthesized according to the literature with MeCl as as olvent instead of thionyl chloride.…”

“…Triethylaluminium was purchased from abcr and handled in a glovebox under a dry argon atmosphere. Teflic acid was prepared according to literature [20] as well as cyanuric fluoride [21] and tetrafluoro‐ para ‐iodopyridine [16] . The salts [Me 2 Cl][Al(OTeF 5 ) 4 ], [Me 2 Br][Al(OTeF 5 ) 4 ] and [Me 2 I][Al(OTeF 5 ) 4 ] where synthesized as already described [7] .…”

“…For comparison, in the solid state structure of tetrafluoro-para-iodopyridinearather strong I-N interaction with an ormalized contact of 0.80 is found. [16] No cocrystals were obtained when 2I was crystallized from dichloromethane solutiona tÀ80 8Cint he presence of pentafluoropyridine.…”

Synthesis and Structural Diversity of Triaryl(phenylethyl)silanes

“…Recently, Schwabedissen et al investigated the structure of several 1:1 co-crystals containing p-halotetrafluoropyridines and benzene. 15 They showed that the columnar structures had high similarities to the co-crystal C 6 H 6 •C 6 F 6 . 1 As depicted in Scheme 4, we consequently synthesized the tetrafluoropyridyl substituted TAPS 16 by salt elimination starting from chlorosilane 2.…”