Crystal Structures of β‐Cyclodextrin Inclusion Complexes with 7‐Hydroxycoumarin and 4‐Hydroxycoumarin and Substituent Effects on Inclusion Geometry

Two inclusion complexes of β‐cyclodextrin‐7‐hydroxycoumarin ( 1 ) and β‐cyclodextrin‐4‐hydroxycoumarin ( 2 ) were prepared and their crystal structures were investigated by single crystal X‐ray crystallography under cryogenic condition. Both structures consist of stacks of face‐to‐face cyclodextrin dimers arranged in brickwork‐like pattern along the crystallographic a‐axis. For complex 1 , each of the two dimeric β‐cyclodextrins includes one 7‐hydroxycoumarin molecule that penetrates deeply into the cyclodextrin dimer and locates its lactonering at the center of the dimer cavity. For complex 2 , each cyclodextrin dimer accommodates three 4‐hydroxycoumarin molecules. One of them is sandwiched between two units of the cyclodextrin dimer, the other two are shallowly included in the cavities of the dimeric cyclodextrins respectively and protrude their lactone rings from the primary end of the cyclodextrin. The substituent effects of guest molecules on inclusion geometry of various coumarin molecules in β‐cyclodextrin were examined.