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

Abstract

Solutions of silver(I), copper(I) and thallium(I) thiocyanate in N,N-dimethylthioformamide, over a range of concentrations 0.05–0.5 mol dm^-3, have been analysed by dispersive IR and FT-Raman spectroscopy. The thiocyanate anion ν(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 d 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)].