Disordered crystal structures of three halogenated propionamides CF3CFXCONH2 (X=Cl, Br, I)

The disordered crystal structures of three halogenated propionamides of the general formula CF3CFXCONH2, X = Cl (I), Br (II), and I (III), were studied by X-ray diffraction (CAD-4 automatic diffractometer, lambdaMok(alpha)). All these structures are monoclinic with space group P2(l)/c. The structures were solved by direct methods and refined by the full-matrix least-squares procedure anisotropically for nonhydrogen atoms. It was established that structures H and III is isomorphic to each other, whereas structure I is not isomorphic to them, although it has a similar molecular packing. The same crystallographic position is statistically (with different probabilities) occupied by two identical molecules (I, II, or III) with different configurations, which may be regarded as one disordered molecule where two substituents at the C-2 atom (halogen X atom and CF3 group) are mutually statistically interchangeable in the space of the unit cell. The amide fragment (-CONH2) of these disordered molecules is practically ordered. The crystal structures of I, II, and III have a developed system of intermolecular H-bonds of N-H...O type and unusual intramolecular H-bonds of N-H...F-C type.