This work reports on a theoretical and experimental study on selected non-halogenated ionic liquids based in the imidazolium cation. The halogen–free ionic liquids are stable solvents regarding hydrolysis whose availability, toxicologically favourable features and well documented biodegradability turns them into suitable candidates for different multiton-scale industrial applications. The pressure–volume–temperature behaviour of these fluids has been evaluated accurately over wide temperature and pressure ranges using a vibrating tube densimeter setup and correlated successfully with an empirical equation. From the measured data the relevant derived coefficients isothermal compressibility, isobaric expansibility and internal pressure have been calculated. The viscosity-pressure-temperature was also measured with an electromagnetic viscometer in the same pressure-temperature ranges than density. Other valuable properties such as isobaric heat capacity, speed of sound and refractive index were measured at several temperatures and atmospheric pressure. Microwave dielectric spectroscopy was applied to obtain a deeper insight into the fluids structure according to a detailed analysis of the relaxational behaviour. The selected ionic liquids were also studied at molecular level by quantum computations at the B3LYP/6-311++g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS–AA forcefield from which structural and dynamic information was inferred and the predictive ability of the simulations was inferred by the comparison among experimental and predicted thermophysical properties. Both macroscopic and microscopic studies concur in complex structures which involve microheterogenities in the fluids structure.