Raman Study of Solvent-Solute Interactions in Solutions of Mercury(II)-Thiocyanate Complexes

Abstract

Raman spectra of the Hg(SCN)2, [Hg(SCN)3]- and [Hg(SCN)4]2- complex species in solution were investigated for 10 donor solvents in the v(CN) and v(CS) wavenumber regions. Attempts were made to relate the solvent donor strength to overall vibrational properties of the complexes. A good correlation of v(CN) with v(HgS) and consequently with solvent donor properties was found in solutions Of Hg(SCN)2 and [Hg (SCN)3]-. Wavenumber differences Δṽ(CN), calculated as the difference between wavenumbers of coordinated and free SCN- ligands, correlate well with the solvent donor strength scale, Ds. The Δv(CN) values for Hg(SCN)2 and [Hg(SCN)3]- can be used as an indicator of solvent donor capacity. Data derived from the Δv(CN) shifts show a better correlation with solvent donor ability than those obtained from the v(CS) wavenumber. The spectral properties of [Hg(SCN)4]2- complex depend only on the electrophilic properties of the solvent and not on its donor strength, because solvent molecules cannot penetrate into the first coordination sphere and donate an electron pair to Hg(II). Solvent electrophilic interaction with coordinated thiocyanate is proportional to its acceptor number.