Structures of two crystal forms of chiral smectogenic 4′-hexyloxy-4-biphenylyl p-[(S)-2-methyIbuty 1] benzoate

Abstract

Three crystal forms were found for the title compound. The relationship of the polymorphs was elucidated by DSC and powder X-ray diffraction methods. Two crystal structures, stable at room temperature, have been determined by single crystal X-ray analysis. Crystal data: 4′-hexyloxy-4-biphenylyl p-[(S)-2-methylbutyljbenzoate

M_r = 444·6, C₃₀H₃₆O₃, 1, triclinia P1, T=298K, a= 11·550(2), b = 22·940 (3), c= 11–810(3) Å, α= 104–08(2), β= 112 87(2), γ = 99–49(2)°, V= 2676(1) ų, d _x =1·110gcm⁻³, μ = 4·74cm⁻¹, F(000) = 960; 2, monoclinic, P2₁, T=298K, a= 23·304(2), b = 5·6080(5), c = 20·451(4) Å, β = 98–39(1)°, V=2644·1(6) ų, Z=4, d _x =1.117gcm⁻³, μ=4·80cm⁻¹, F(000) = 960. Each crystal is composed of a smectic-like layer structure with a large molecular tilt angle (45° and 60°, respectively). The molecules in 1 have largely twisted paraffin chains and the twisted biphenyl moieties, while those in 2 have all-trans zigzag paraffin chains and coplanar biphenyl moieties. Packing modes of the core moieties are also largely different: some of the mutual arrangements of the phenyl rings are nearly parallel (∼20°) in 1, while the contact angle of the phenyl rings between the neighbouring molecules is 60° on average in 2.