Molecular cages for cations and anions

The relationship between cavity size and van der Waals radii is reinforced when the complex is stabilized by additional factors, such as symmetry, that 

Tris(2-aminoethyl)amine (tren) [TOXIC] Conical flask (500 mL) 

Methanol [FLAMMABLE] Pressure equalized dropping funnel 

Note This reaction should be carried out in a fume hood 

Add isophthalaldehyde (1.01 g, 7.5 mmol) to methanol (200 mL) in a 500 mL conical flask equipped with a stirrer bar. Stir to dissolve the solids. Add a solution of tren (0.73 g, 0.75 mL, 5.0 mmol) in methanol (20 mL) dropwise (ca. 15 min) to the clear solution which turns pale yellow during the addition. Once all the tren has been added reflux for 45 min then allow the solution to cool to room temperature. Transfer to a round-bottomed flask and reduce the volume to ca. 75 mL on the rotovap. Place the flask in an ice bath for 30 min then isolate the product, tren-derived cryptand (37), by filtration. 

---

Dynamic information such as reorientational correlation functions and diffusion constants for the ions can readily be obtained. Collective properties such as viscosity can also be calculated in principle, but it is difficult to obtain accurate results in reasonable simulation times. Single-particle properties such as diffusion constants can be determined more easily from simulations. Figure 4.3-4 shows the mean square displacements of cations and anions in dimethylimidazolium chloride at 400 K. The rapid rise at short times is due to rattling of the ions in the cages of neighbors. The amplitude of this motion is about 0.5 A. After a few picoseconds the mean square displacement in all three directions is a linear function of time and the slope of this portion of the curve gives the diffusion constant. These diffusion constants are about a factor of 10 lower than those in normal molecular liquids at room temperature. 

---