New. J. Chem. 31, 936-946 (2007)

Doi: 10.1039/b617988f

The structure of fluorinated indazoles: the effect of the replacement of a H by a F atom on the supramolecular structure of NH-indazoles

The structures of three NH-indazoles (3-methyl, 3-trifluoromethyl and 3-trifluoromethyl-4,5,6,7-tetrafluoroindazoles) have been determined by X-ray crystallography. These three compounds, together with 3-methyl-4,5,6,7-tetrafluoroindazole, whose X-ray structure could not be determined, have been studied using multinuclear magnetic resonance spectroscopy, including solid-state CPMAS. They all are 1H-tautomers. In the crystal, 3-methyl-1H-indazole forms hydrogen bonded dimers, whereas 3-trifluoromethyl-1H-indazole and 3-trifluoromethyl-4,5,6,7-tetrafluoro-1H-indazole crystallize as catemers. These catemers are chiral space groupP32. They are the first examples of indazoles crystallizing in the form of helices of three-fold screw axis. Attempts at rationalizing this behavior on the basis of supramolecular interactions (hydrogen bonds and aromatic interactions) and GIAO calculations are discussed.