Solute–solvent interaction and preferential solvation of VO(salen) complex in the binary mixtures of an ionic liquid (IL) + organic solvent were studied. For this purpose, density, viscosity, and electrical conductivity of ternary VO(salen) + 1-pentyl-3-methylimidazolium bromide ([PnMIm]Br) + DMSO mixtures were measured at T = (288.15 to 318.15) K. From density data, standard partial molar volumes (Vϕ 0), partial molar expansibilities (Eϕ 0), and Hepler constants were calculated. The obtained viscosity B-coefficients and their temperature dependency were used to interpret the structure-making or structure-breaking tendency of the complex. To verify the volumetric and viscometric results, limiting molar conductivities (Λ0) and ion association constants (KA) of the IL in VO(salen) + DMSO mixtures were computed. All the obtained parameters were used to discuss the solute-solvent interactions of the mixture. © 2015, Springer-Verlag Berlin Heidelberg.