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Heat capacities of the spin crossover complex 3 ]Cl 2 ‚MeOH (2-pic: 2-picolylamine or 2-aminomethylpyridine) were measured with an adiabatic calorimeter between 12 and 355 K. A broad heat capacity peak, starting from ∼80 K, culminating at ∼150 K, and terminating at ∼250 K, was observed. The temperature range of the heat capacity anomaly corresponds to that where the low-spin and high-spin states coexist in the 57 Fe Mössbauer spectra. The enthalpy and entropy changes arising from the heat capacity anomaly were 8.88 kJ mol -1 and 59.5 J K -1 mol -1 , respectively. The entropy gain was much larger than the contribution expected from the change in the spin-manifold R ln 5 (13.4 J K -1 mol -1 ) where R is the gas constant. The remaining entropy gain is attributed to the contribution from the change in the internal vibrations. On the basis of the domain model, the number of molecules per domain was found to be very close to unity, implying a very weak cooperativity in the spin crossover occurring in the solid state of this complex.

Air-and water-stable hydrophobic ionic liquids N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([C n py][NTf 2 ], n = 3, 6) were synthesized. The density, surface tension, dynamic viscosity, and electrical conductivity of [C 6 À ILs as a hydrophobic compound has attracted much more attention in some fields. 5À8Tokuda et al. 9 have studied the properties of a series of imidazolium-based ILs, for example, the melting temperature, glass transition temperature, dynamic viscosity, and electrical conductivity. The melting temperatures are lower than room temperature, so these ILs are liquid at room temperature; the decomposition temperatures are higher than 690 K, so these ILs exhibit excellent thermal stability. The electrical conductivities are also high enough to be applied in electrochemical devices. Oliveira et al.10 studied the properties of a series of pyridiniumbased ILs. The density and dynamic viscosity of the dried and saturated ILs were studied. The water content has a strong effect on the dynamic viscosity, but only a very small effect on density was observed. Jacquemin et al.11 have also studied the density and dynamic viscosity of several pure and watersaturated ILs. The same results were obtained for the effect of water content on the density and dynamic viscosity. The ILs with [NTf 2 ] À anion were studied widely because this type of ILs has a relatively low viscosity, a wide electrochemical window, and a high electrical conductivity to be applied in the electrochemical devices. 12À16In view of the above facts, the density, surface tension, dynamic viscosity, and electrical conductivity of the ILs [C n py][NTf 2 ] (n = 3, 6) were measured at different temperatures, except for the surface tension of [C 3 py][NTf 2 ]. The speed of sound was estimated by the Auerbach relation at the different temperatures. 17The standard molar entropy and lattice energy were estimated in terms of Glasser's theory. 18 Parachor was estimated by the equation reported in the ref 19. The molar enthalpy of vaporization was estimated in terms of Kabo's empirical equation. 20 The interstice volume, interstice fraction, and thermal expansion coefficient were estimated by the interstice model theory. 21,22 The VogelÀFulcherÀTammann (VFT) and Arrhenius equations were used to fit the temperature dependence on dynamic viscosity and electrical conductivity values.' EXPERIMENTAL SECTION Preparation of ILs [C n py][NTf 2 ] (n = 3, 6). N-Alkylpyridinium bromide ([C n py][Br], n = 3, 6) was synthesized according to the procedure described in earlier paper. 23 [C n py][NTf 2 ], n = 3, 6, were synthesized according to the ion exchange reaction. The 80 g of salt [C n py][Br], n = 3, 6 was placed in a 500 mL roundbottomed flask and dissolved in 30 mL of distilled water; the equivalent amount of bis(trifluoromethanesulfonyl)imide (HN-(SO 2 CF 3 ) (Rhodia Co., mass purity 99.9 %) was added dropwise

Density and surface tension of the air-and water-stable hydrophobic ionic liquids N-alkylpyridinium bis(trifluoromethylsulfonyl)imide ([C n py][NTf 2 ], n ) 2, 4, 5) were measured in the temperature range T ) (283.15 to 338.15) K. The melting temperatures of the samples were determined by differential scanning calorimetry (DSC). Decomposition temperatures are higher than 600 K as determined by thermogravimetric analysis (TG).