Complexation and structural studies of a sulfonamide aza-15-crown-5 derivative

An aza-15-crown-5 derivative, N-[4-(phenyldiazo)benzenesulfonyl]-aza-15-crown-5, 1 was synthesised from commercially available starting materials in 55% yield. Compound 1, which contains a sulfonamide link between the crown ether macroring and the azobenzene, readily binds alkali metals in buffered ethanol–water (75:25 v/v, pH 6.66). Titration data for both sodium and potassium were readily fitted to a 1:1 metal ion/ligand binding model to obtain stability constants (log K) of 4.7 ± 0.4 and 4.8 ± 0.2 dm3 mol− 1, respectively. We also investigated the structures of 1 and the sodium perchlorate salt of 1, [Na(1)(H2O)]2(ClO4)2, which were determined by X-ray crystallography. [Na(1)(H2O)]2(ClO4)2 is a dimer in the solid state whereby a sulfonamide oxygen atom from one of the [Na(1)(H2O)] cations provides solvation of the adjacent macroring bound sodium cation. In the crystal structure, binding of a water molecule to the sodium cation is supported by hydrogen bonding to the sulfonamide oxygen, which represents a supramolecular lariat ether-like interaction.