Crystalline inclusion compounds of 1-(9-anthryloxy)anthraquinone as a host compound: X-ray structural characterization and π–π interaction modes in the crystal enclathrating benzene as a guest

Abstract

Inclusion properties of the clathrate crystals, (1)(C₆H₆) and (1)₂(hydroquinone)(C₆H₆), derived from a conformationally flexible host compound 1-(9-anthryloxy)anthraquinone (1), have been investigated by means of X-ray crystallography, DSC analysis and ²H NMR spectroscopy. Complex (1)(C₆H₆) is a true clathrate: benzene is embedded in a host lattice constituted of the intermolecular face-to-face π–π overlap (π–π; 3.54 Å) of the anthraquinone rings of 1. Crystal data: P2₁/c, a= 16.882(2), b= 8.970(1), c= 16.405(2)Å, β= 91.53(2)°, Z= 4, D_c= 1.280 g cm^–3. The crystal structure of a three-component clathrate (1)₂(hydroquinone)(C₆H₆) shows the rigid two-component host lattice composed of 1 and hydroquinone. Crystal data: Pl, a= 11.779(3), b= 12.747(2), c= 8.818(1)Å, α= 107.14(1), β= 92.59(3), γ= 101.86(3)°, Z= l, D_c= 1.335 g cm^–3. The two host components are linked by the hydrogen bonds (O–O; 2.908, 2.912 Å) as well as the unique orthogonal C–H–π–H–C (C–π; 3.2 Å) and face-to-face π–π interactions (π–π; 3.43 Å). Benzene is retained within the host lattice up to 173 °C. The crystal structure of guest-free host 1 has also been determined. Crystal data: P1, a= 15.566(5), b= 15.625(5), c= 11.571(2)Å, α= 98.21(2), β= 94.20(2), γ= 132.74(2)°, Z= 4, D_c= 1.337 g cm ^–3. ²H NMR spectroscopy has been used to study the molecular motion of [²H₆]benzene in the clathrates. Quadrapole echo line shapes, measured as a function of temperature, could be accounted for in terms of an in-plane 60° jump about the major symmetry axis. The activation parameters for a 60° jump are 9.4 and 19 kJ mol^–1 for (1)(C₆D₆) and (1)₂(hydroquinone)(C₆D₆), respectively.