TRANSITION-METAL COMPLEXES OF CROWN-ETHER BENZODITHIOLENES .2. THE EFFECTS OF ALKALI-METAL CATION-BINDING

The binding of Li+, Na+ and K+ cations to the crown ether rings of a series of transition-metal complexes with crown ether benzodithiolene ligands has been monitored. Fast atom bombardment mass spectrometry and UV/VIS spectroscopy have been used to demonstrate the binding of the cations to the complexes, and cyclic voltammetric studies provide a quantitative measure of the perturbations which result upon cation binding. The results support the view that the electronic transitions arise primarily from sulfur-to-metal charge-transfer transitions, provide information concerning the dithiolate(2-) or dithioketonic form of the dithiolene ligand, and indicate whether a particular redox process is primarily metal- or ligand-based. Some selectivity within the series Li+, Na+ and K+ is observed, with the benzo-15-crown-5 ring showing a preference for the first two and the benzo-18-crown-6 ring preferring K+. Tris(crown ether benzodithiolene) complexes of molybdenum and tungsten show the most promise as sensors for alkali-metal cations.