Equilibrium phase diagrams of the toluene-hexafluorobenzene and thep-xylene-hexafluorobenzene binary systems are experimentally determined by differential scanning calorimetry and X-ray diffraction analyses. Both diagrams present a complex 1:1 with a rich polymorphism. The optimization of these systems shows the existence of high associated degree in the liquid phase. The comparison of these two systems with the benzene-hexafluorobenzene binary shows that the complex stability increases with number of H-atoms substituted by CH3-methyl groups in the benzenic ring.