Structures and complexing properties of crown ethers incorporating 1,8-dioxyxanthones

The X-ray crystal structures of three crown ethers containing the 1,8-dioxyxanthone residue are reported. 1,8-[3,6,9-Trioxaundecane-1,ll-diyl)dioxy]xanthone, 1(n = 3), and 1,8-[(3,6,9,12,15-pentaoxaheptadecane-1,17-diyl)dioxy]xanthone, 1 (n = 5), have been crystallized from acetonitrile and their crystals shown to incorporate acetonitrile, Crystals of the former also contain water which forms a tight hydrogen-bonded bridge between the xanthone carbonyl oxygen and the most remote oxygen of the 18-membered macrocycles, Crystals of 1,8-[(3,6,9, 12-tetraoxatetradecane-1,14-diyl)dioxy]xanthone, 1 (n = 4), from toluene do not incorporate solvent molecules. Earlier UV measurements for the basicity of the carbonyl oxygen for these crowns and for 1,8-diethoxyxanthone have been re-examined using the excess acidity method and revised values of pK(a) and m* are reported, The UV spectra of methanolic solutions of the ketones show shifts with added strontium or barium salts and these are associated with complex formation which places the metal ion in close proximity to the carbonyl oxygen, Binding constants for formation of complexes are reported.