Vibrational spectroscopic study of the ionic association and ion-pair structures in solutions of silver(I), copper(I) and thallium(I) thiocyanates in N,N-dimethylthioformamide

Solutions of silver(I), copper(I) and thallium(I) thiocyanate in N,N-dimethylthioformamide, over a range of concentrations 0.05-0.5 mel dm(-3), have been analysed by dispersive IR and FT-Raman spectroscopy. The thiocyanate anion v(CN) band was examined in detail using deconvolution and band-fitting procedures; the appearance of one [silver(I) and copper(I) thiocyanate solutions] or two [thallium(I) thiocyanate solutions] new components, reveals the presence of ionic pairs with the thiocyanate (S-bonded) structure in AgSCN solutions and the isothiocyanate (N-bonded) structure in the CuSCN solutions. Both types are simultaneously detected in Tl(SCN) solutions. The corresponding association constants, calculated in the limit of infinite dilution, were (in dm(3) mol(-1)): 2.1 +/- 0.1 [Cu(NCS)], 4.8 +/- 0.3 [Ag(SCN)], 1.4 +/- 0.2 [Tl(NCS)] and 0.3 +/- 0.1 [Tl(SCN)].