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Temperature dependent crystal structure analyses and ion volume determinations of organic salts
The crystal structures of nine organic salts of which seven are ionic liquids (ILs), comprising imidazolium, ammonium, piperidinium, and sulfonium cations, were determined. The occurrence of short contacts in the compounds' crystal structures was quantified with Hirshfeld surface analyses. Temperature dependent crystal structure data for several organic salts were recorded systematically in the temperature range from 100 K to room temperature. The thermal behavior of the cell constants was linear and anisotropic for almost all compounds. The accuracy of the molecular volume (Vm) – the key quantity in volume based thermodynamics (VBT) – was investigated in terms of its temperature dependency and the statistical error of the constituent ion volumes (Vma+/–). The former effect turned out to be at most on the same order of magnitude as the errors of Vm+/–. The same analysis was applied to the recently proposed new internally consistent molecular ion volumes (Vm, new+/–). For this purpose, a set of overall 40 Vm, new+/– values of typical polyatomic ions constituting ILs was established. In general, it is recommended to use as many salts as possible and as many temperature dependent data as available for the derivation of new Vm+/– and Vm, new+/– values.