Compounds of the type RuL4−nX2+n where L = dimethyl sulphoxide (DMSO), tetramethylene sulphoxide (TMSO) and X = Cl, Br or I for n = 0 and L = di-n-propyl sulphoxide (n-Pr2SO) and di-n-butyl sulphoxide (n-Bu2SO) X = Cl or Br for n = 1 and also Ru(DMSO)6Br3 have been prepared and studied. The important i.r. bands of all compounds together with their electronic spectra and the thermograms of some of them are discussed. In order to interpret the i.r. data, the corresponding deuteriated (DMSO-d6) analogues have also been prepared. In the majority of the compounds of the type RuL4X2 the sulphoxide ligands are bonded through the sulphur atom; in a few cases, bonding through both S- and O-donor sites has been found. A mixed type of bonding is also observed in Ru(DMSO)6Br3 and in RuL3X3.