Etude Structurale d′un Compose Nematogene: Polymorphe Basse Temperature du 4,4′-di-n-Propoxyazoxybenzene

Abstract

M_r = 314,38, monoclinic, P2₁n,a = 21,507 (6) Å, b = 9,648 (3) Å, c = 7,942 (3) Å, β = 93,28[ddot], V = 1645 ų, Z = 4, D_m = 1,29 gcm⁻³, D _x = 1,270 g cm⁻³ Δ(CuKα) = 1,5418 Å, μ = 7,13 cm⁻¹, F(000) = 672, T = 298 K, Rw = 0,058 for 2590 observed reflections.

The molecules are packed in an imbricated structure in accordance with the nematogenic behaviour of this compound but statistical disorder involving displacement of the molecules parallel to their long axes was not observed. The lateral chains were found to be almost fully extended. A comparison with reported structures of some other members of the 4,4′-di-n-alkoxyazoxybenzene series leads us to conclude that in these compounds the benzene ring close to the nitroxide bond is nearly coplanar with the central NNO group (because of mesomeric effects) but the other ring is tilted by a variable angle (depending on the length of the lateral alkoxy groups) enabling the packing to be as compact as possible. Consequently, and with respect to the small distances between the nitroxide oxygen atom and the aromatic hydrogen atoms located in the ortho position we find all the compounds to have similar angular distortions of the CarNONCar group.

Key Words:

• Crystal structure
• nematogen
• low temperature form