Versatility in Complexation of Six-Membered Heterocyclic Guests by Singly Bridged Triarylmethanol Hosts. X-Ray Crystal Structures and Thermal Stabilities of Inclusion Compounds with Piperidine, Thioxane/Dioxane, and Morpholine

Abstract

Abstract 9-Phenylfluoren-9-ol (1), 2,7-dibromo-9-phenylfluoren-9-ol (2), and 9-phenylethynylfluoren-9-ol (3) enclathrate different six-membered heterocyclic guests involving piperidine, thioxane, dioxane, and morpholine. X-Ray crystal structure determinations of corresponding inclusion compounds [1·piperidine (1 : 1), 1·thioxane·dioxane (2 : 2 : 1), 2·morpholine (1 : 2), and 3·morpholine (1 : 1)] are reported, showing remarkable variety in the packing relations. Host compound 1 forms H-bonded 1 : 1 host : guest units with both piperidine and thioxane, but in the latter case additional dioxane guests are incorporated in the crystal, thus yielding a ternary complex. Host compound 3 is capable of forming closed loops of hydrogen bonds with full hydrogen bond saturation in its inclusion compound with morpholine, whereas in the related morpholine complex of 2 H-bonded 1 : 2 associates are created without maximal saturation of the hydrogen bonds, and with different binding modes for the two guests of the stoichiometric unit. In the crystals, the various H-bonded host-guest units are linked together by Van der Waals’ forces, occasionally supported by weak electrostatic interactions. The stabilities of the four different inclusion compounds were studied by thermal analysis indicating complex decomposition modes.