Molecular design of crown ethers.: 19.: Synthesis of novel disulfide- and diselenide-bridged bis(benzo-12-crown-4)s and their Ag+-selective electrode properties

Two novel heteroatom-bridged bis(benzo-12-crown-4 ether)s, i.e., bis(2-nitro-4,5-(1,4,7,10-tetraoxadecamethylene)phenyl) disulfide (4) and diselenide (5), have been synthesized and characterized by elemental analysis and mass, IR, UV, and H-1 NMR spectroscopy. An X-ray crystallographic structure was obtained for 4. Ion-selective electrodes (ISE) for Ag+, containing 4 and 5 in PVC membrane as neutral carriers, were prepared, and their selectivity coefficients for Ag+ (K-Ag,M(pot)) were determined against other heavy metal ions, alkali and alkaline-earth metal ions, and ammonium ion using the matched potential method. These ISEs showed excellent Ag+ selectivities, log K-Ag.M(pot) less than or equal to -4.0, against most of the interfering cations examined. except for Hg+ (log K-Ag.M(pot) greater than or equal to -1.2). These K-Ag.M(pot) values are comparable to those reported for the representative Ag+-selective thioethers 6 and 7, revealing that both disulfide and diselenide functionalities in 4 and 5 are equally effective Ag+-selective binding sites as the 1,7-dithia-4-oxa functionality in 6 and 7, irrespective of the different atom type and relative position of the sulfur/selenium donors in the ligands. Also discussed are the steric and electronic effects of the nitro groups in 4 and 5 on the Nernstian slopes obtained with the 4- and 5-based ISEs.