Is the liquid or the solid phase responsible for the low melting points of ionic liquids? Alkyl-chain-length dependence of thermodynamic properties of [Cnmim][Tf2N]

To establish the alkyl-chain-length dependences of thermodynamic properties of typical ionic liquids [C(n)mim][Tf2N], the heat capacities of compounds with n = 2 and 18 were measured by adiabatic calorimetry. The comparison with other ionic liquids and typical molecular substances reveals that the low melting point of [C(n)mim][Tf2N] with a short alkyl chain mainly originate in the large fusion entropy arising from the low entropy of the crystalline phase. (C) 2009 Elsevier B. V. All rights reserved.