The Crystal and Molecular Structure of Mesogenic Malonates

The crystal and molecular structures of diethylene-6-4-(4′-nitrophenylazo)phenoxy]dodecylmalonate (12 PhNO₂) and -propylmalonate (3 PhNO₂) were determined with CuK_α to a = 19.235(5) Å, b = 7.620(1) Å, c = 22.400(4) Å; α = 90°, β = 103.27(1)°, γ = 90°; space group P2₁/c for 12 PhNO₂ and a = 6.797 (6) Å, b = 7.756 (8) Å, c = 22.74(2) Å; α = 81.48(7)°, β = 88.29(7)°, γ = 68.10(9)°; space group P1 for 3 PhNO₂. Refinement with 1130 observed reflections (> 3σ) for 12 PhNO₂ and 1615 for 3 PhNO₂ leads to R (12 PhNO₂) = 5.8% and R(3 PhNO₂) = 4.4%. The molecular conformation in the crystalline state is the most extended trans conformation for both compounds. On rapidly cooling from the isotropic melt, 12 PhNO₂ shows a smectic A-phase. In agreement with prior investigations on polar mesogens, the molecules arrange in an antiparallel packing. The azo-mesogen is nearly coplanar with the alkoxy spacer up to the branching atom. The low molecular weight malonates investigated may serve as model compounds for side-group liquid crystalline polymers.