Electronic absorption spectroscopy for the investigation of the solution binding of gold, palladium, mercury and silver salts to the lower rim substituted calix[4]arenes 25,26,27,28-(2-N,N-dimethyldithiocarbamoylethoxy)calix[4]arene and 25,26,27,28-(2-methylthioethoxy)calix[4]arene

The two uncharged compounds 25,26,27,28-(2-N,N-di methyldithiocarbamoylethoxy)calix4]arene (1) and 25,26,27,28- (2-methylthioethoxy)calix4]arene (2) are effective extractants for transferring Hg(II), Ag(I), Pd(II) and Au(III) from aqueous solution into chloroform. The electronic absorption spectra of 1 and 2 show additional bands at long wavelength upon complexation with AuCl₄^?, PdCl₄^2? and PdBr₄^2?, and analogous bands for Hg²⁺ and Ag⁺ with 1. For 1 these new bands are considered to be either of the charge transfer type or transitions within the C=S moiety. These new bands for the complexes with 2 are assigned to LMCT transitions of the S → M type. These spectral features are used to obtain information about the solution structures of the complexes that are formed between these metal ions and both 1 and 2.