Solvent — solute interactions in solutions of mercury(II) halides and halogeno‐complexes in aprotic donor solvents

Raman spectral data for the species HgX 2 , HgX 3 − and HgX 4 2− (X = Cl and Br) in solution in 24 class A donor solvents are presented. The complex ions were present in the solutions as lithium salts. The frequencies (ν 1 ) of the symmetric stretching vibrations of HgX 2 and Hg 3 − correlate well with solvent donicity (DN) and with other measures of solvent donor strength. A two‐parameter regression equation of the form ν 1 = a o + a 1 ( DN ) + a 2 ( E τ ), where E τ is the Dimroth‐Reichardt electrophilicity parameter, gives good correlations for the HgX 4 2− ions. Evidence based on (i) the frequency values of the symmetric and antisymmetric (ν 3 ) stretching vibrations of HgCl 2 and HgBr 2 , (ii) the Raman intensities of the ν 3 mode of HgBr 2 and (iii) the depolarization ratios of the ν 1 bands of HgCl s and HgBr 2 in various solvents, supports the view that these molecules in solution undergo a progressive departure from linearity as a result of increasing solvent coordination to the mercury atom. For solvents of high donor strength (e.g. pyridine), the XHgX interbond angle may approach 120°.