X-ray diffraction data for 1-alkyl-3-methylimidazolium his{(trifluoromethyl)sulfonyl}amides are reported as a function of the length of the alkyl chain on the imidazolium ring. The measured diffraction patterns have been compared with the theoretical patterns calculated (from the geometries obtained) with molecular dynamics simulations. This provides a detailed description (at the atomistic level) of the morphology in the liquid state of these salts, highlighting the role played by the alkyl chain length. An analysis of the behavior of the hydrogen bonds that are formed between the imidazolium acidic protons and the anion is presented.