Structual Studies of Some 2,6(2′,6′)-Halogen-Substituted Biphenyl Derivatives

Abstract

Single-crystal X-ray structure determinations have been carried out at 295 K on a number of biphenyl derivatives substituted with chlorine or bromine in the 2- and 6-positions in order to ascertain the effect of substitution on the torsion angle about the central bond. 2,2′,6,6′- Tetrachlorobiphenyl, (1), is orthorhombic, P nca, a 12.35(1), b 10.521(7), c 9.390(8)Ǻ, Z 4; the structure was refined to a residual of R 0.040 for N_o 528 independent 'observed' reflections. The interplanar dihedral angle, θ, is 81.7°. 4′-Bromo-2,4,6-trichlorobiphenyl, (2), is monoclinic, C2/c, a 19.27(1), b 7.940(2), c 33.315(8)Ǻ, β 90.93(6)°, Z 16; R 0.036 for N_o 1795 with θ 84.3 and 80.6° for the two independent molecules. 2,2′,4,4′,6,6′-Hexabromobiphenyl, (3), is orthorhombic, P nca, a 14.48(1), b 12.71(1), c 8.534(7)Ǻ; R 0.044 for N_o 693 with θ 83.0°. 2,4,4′,6-Tetrabromobiphenyl, (4), is triclinic, Pī, with a 8.14(1), b 10.74(2), c 35.42(4)Ǻ, α 87.87(10), β 79.39(10), γ 63.55(10)°, Z 8; R 0.049 for N_o 3962, with θ 89.8, 80.7 86.9, 83.6°, for the four independent molecules. Steric interactions between the substituents ortho to the central inter-ring bond are not the sole determinant of the geometry of these compounds in the solid state. The pairs (1) and (3), and (2) and (4), are pseudo-isostructural in each case.