The vapor-liquid equilibria of binary systems containing imidazolium-based ionic liquids (ILs) have been investigated using an equation of state (EOS) for the heteronuclear square-well chain fluids (hetero-SWCFs). ILs are represented by "diblock compounds", with the alkyl group as one block and the imidazolium ring-anion pair as the other block. Model parameters of the imidazolium ring-anion block are obtained by fitting the experimental pressure-volume-temperature (pVT) data of ILs, and they are combined with those of the alkyl block from our previous work to correlate and predict the molar volumes of homologous imidazolium ILs, with the average deviations of 0.62% and 3.24%, respectively. Vapor-liquid equilibria (VLE) of 22 binary systems that contain imidazolium ILs and solvents are correlated, with an average deviation of 5.38%. The results reveal that the imidazolium ILs can be regarded as diblock compounds fairly well and the hetero-SWCF-EOS is well-suited for calculation of their thermophysical properties.