The preparation and vibrational spectra of compounds of the type M(CO)4(HgX)2

Abstract

Compounds of the type M(CO)₄(HgX)₂(M = Fe or Os; X = Cl, Br, or I) and Ru(CO)₄(HgX)₂(X = Cl or Br) have been prepared and characterised, those of ruthenium and osmium for the first time. Their i.r. and Raman spectra have been recorded over the regions 2200–1900 and 700–70 cm.^–1 both in the solid state, and where solubilities permitted, also in tetrahydrofuran solution. It is concluded that all the compounds are monomers, with cis-octahedral structures. The CO stretching frequencies, which are assigned, lie in the order Fe < Ru ⩽ Os for a given X and in the order HgCl > HgBr > Hgl for a given M. The data are discussed with reference to the spectra of other molecules of the type M(CO)₄L₂, and correlated with the electronegativities of the ligands L; the lower these are, the greater the reduction in the effective nuclear charge of the central metal atom and the lower the CO stretching frequencies. In addition, assignments for M–C, M–Hg–X stretching vibrations and MCO and CMC bending vibrations are made where possible. The compound cis-Os(CO)₄(HgCl)Cl has also been isolated and characterised, and its vibrational spectra studied.