Structural features of 4,4 '-diaminooctafluorobiphenyl

Molecules of C12H4F8N2 crystallize in the orthorhombic space group P2(1)2(1 )2(1) with cell constants a = 9.200(1), b = 10,896(1), c = 23.178(3) Angstr om and V = 2323.4(5) Angstrom(3). There are two molecules in the asymmetric unit which have D-2 symmetry. However these two molecules have C-2 symmetr y in central C-C bonds, separately. Intramolecular steric repulsions betwee n F atoms and N-H ... F hydrogen bonds have very much affected the molecula r conformation. The mean dihedral angle between intramolecular phenyl rings is 119.2(1)degrees. The N-C bonds have lengths 1.363(4)-1.407(4) Angstrom with a mean of 1.388 Angstrom. This is shorter than the conventional C-N (1 .47(1) Angstrom) bond length due to pi-electron delocalizations (F.H. Alien , O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R. Taylor, J. Chem. Sec. Perkin Trans. II(1987) S1-S19). The molecular structure of the title compound was also investigated by IR s pectroscopy. It was shown that the IR spectra are in agreement with the cry stal structure, On the other hand, theoretical and semi-emprical molecular mechanic calculations were carried out to obtain the most probable low-ener gy conformations by using MM3, PM3 and AM1 programs. (C) 2000 Elsevier Scie nce B.V. All rights reserved.