Binding neutral guests to concave surfaces of molecular hosts. Rigid structural model for complexation between two lipophilic entities

The 1:2 compound formed between a new cavitand C₄₀H₄₈Si₄O₈ [chemical name: 5,10;12,17;19,24;26,3-tetrakis(dimethylsiladioxa)-1,8,15,22-tetramethyl[1₄]metacyclophane] and CS₂ (M_r=921.42) provided a suitable structural model for a rigid inclusion complex between uncharged lipophilic molecules. The detailed structure of this compound has been determined by single crystal X-ray diffraction at 128 K (Crystal data:a=11.233, b=20.018, c=10.069 Å, β=90.84^o, Z=2, space group P2₁/m). Anisotropic refinement converged at R=0.040 for 3768 reflections above the intensity threshold, leading to positional and thermal parameters of a relatively high precision. The cavitand has an enforced cavity appropriately sized to include only slim linear guests. The crystallographic analysis revealed a 1:1 molecular inclusion complex with CS₂, the guest species being almost entirely encapsulated within the 'basket'-shaped cavity of the host. The complex is stabilized by dispersion forces. All the guest atoms lie within van der Waals distances from the surrounding sections of the host and are well ordered. The second CS₂ molecule is located in the crystal lattice between molecules of the complex and is slightly disordered. Mirror plane symmetry characterizes the entire structure.