Spectrophotometric Studies on the Ion-pair Formation of Hexamminecobalt(III) and Tris(ethylenediamine)cobalt(III) Complexes with Halide and Sulfate Ions

Abstract

The optical density of charge transfer spectra of some tervalent substitution-inert complex cations in an ultraviolet region increases by the addition of halide and sulfate ions. From the change in optical density the association constants were determined at ionic strength 0.07 (NaClO4) and 25°C. The values are 2.2±0.5 for Co(NH3)63+Cl−, 2.2±0.6 for Co(NH3)63+Br−, 0.71±0.5 for Co(NH3)63+ I−, 114±3 for Co(NH3)63+SO42−, 2.9±0.5 for Co(en)33+ Cl− and 102±8 for Co(en)33+SO42− respectively. The difference of these values from the reported values are related to the method for the measurements. Absorption maxima of the third absorption bands are obtained at 196 mμ for Co(NH3)63+ and at 210 mμ for Co(en)33+.