Structural aspects of [2.2]heterophanes. Part II. Molecular structure of [2.2](2,5)thiophenophane and [2.2](2,5)furanophane

Abstract

The crystal and molecular structure of the title compounds has been determined from the three-dimensional X-ray data by conventional Patterson and Fourier methods for (I) and by direct methods for (II). Crystals of (I) are monoclinic, space group P2₁/c, with a= 6.052(6), b= 12.63(1), c= 7.111(7)Å, β= 101.34(9)°, Z= 2. Crystals of (II) are orthorhombic, space group Pbca, with a= 13.60(1), b= 7.507(7), c= 9.725(7)Å, Z= 4. The structures were refined by least squares techniques to R 0.030 (I) and 0.041 (II) on the basis of 1215 and 421 independent reflections. The molecules of both compounds are centrosymmetric and well approximate to C_2h symmetry. The heteroatoms are displaced (S 0.196, O 0.082 Å) from the planes of the aromatic rings which are parallel and separated by 2.63 (I) and 2.34 Å(II). The CH₂–CH₂ bond lengths are significantly stretched [1.592(2)(I), and 1.569(6)Å(II)]. The differently stepped structures are related to the different steric hindrance of oxygen and sulphur which determines the considerably different conformational mobility of such phanes.