Acta Crystallographica Section B

Structural Science

Volume 55, Part 1 (February 1999)

Acta Cryst. (1999). B55, 70-77 [doi:10.1107/S0108768198006570]

Low-temperature crystallization and structure determination of N-(trifluoromethyl)formamide, N-(2,2,2-trifluoroethyl)formamide and 2,2,2-trifluoroethyl isocyanide

G. J. Perpétuo, J. Buschmann, P. Luger, D. Lentz and D. Dreissig

Abstract: Crystals of N-(trifluoromethyl)formamide, C₂H₂F₃NO, (I), N-(2,2,2-trifluoroethyl)formamide, C₃H₄F₃NO, (II), and 2,2,2-trifluoroethyl isocyanide, C₃H₂F₃N, (III), were grown in situ on an X-ray diffractometer and analysed by single-crystal X-ray diffraction methods at low temperatures. Crystal data: (I) orthorhombic, P2₁2₁2₁, a = 4.547 (2) Å, b = 5.947 (3) Å, c = 14.731 (9) Å, V = 398.3 (4) Å³, Z = 4, M_r = 113.05, T = 143 K, D_x = 1.885 Mg m^-3; (II) monoclinic, P2₁/n, a = 4.807 (1) Å, b = 16.707 (3) Å, c = 6.708 (1) Å, [beta] = 109.90 (1)°, V = 506.6 (2) Å³, Z = 4, M_r = 127.07, T = 141 K, D_x = 1.666 Mg m^-3; (III) orthorhombic, P2₁2₁2₁, a = 5.668 (2) Å, b = 9.266 (3) Å, c = 8.626 (2) Å, V = 453.0 (2) Å³, Z = 4, M_r = 109.06, T = 163 K, D_x = 1.599 Mg m^-3. The results showed that in the crystal both formamides (I) and (II) are exclusively present in the form of the Z isomer, although measurements of solutions of (I) have shown that the E isomer prevails [Lentz et al. (1987). Angew. Chem. 99, 951-953]. In addition ab initio calculations for (I) predicted the E isomer to be the more stable one. In compound (III) the isocyanide group is staggered with respect to the trifluoroethyl group. In the crystal packing of (I) and (II) intermolecular N-H $\cdots$ O hydrogen bonds generate infinite chains. In (I), these chains are linked to form sheets by C-H $\cdots$ O contacts. In the crystal structure of (III) each isocyanide dipole is surrounded by four electronegative F atoms with intermolecular C $\cdots$ F contacts between 3.4 and 3.5 Å.

Online 1 February 1999


	Structure factor file (CIF format) (57.6 kbytes) Contains datablock I

	Structure factor file (CIF format) (72.9 kbytes) Contains datablock lenz2

	Structure factor file (CIF format) (76.5 kbytes) Contains datablock lent1

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