Ionic Volumes in Nonaqueous Solvents

Ion solvent MeOH EtOH EG Me CO PC FA NMF DMF DMA MeCN MeNOj DMSO HMPT 

Values of y (I, S) for some other ions, for example, some divalent cations (in PC, FA, DMF, and DMSO) and in some other solvents, are available in the review by Marcus and Hefter [48]. 

Statistical correlations have been estabUshed by Marcus et al. [49] between y (I , S) and the properties of the ions and those of the solvents, but these cannot be deconvoluted to separate dependences on such properties. For the tetraalkylammo-nium ions (from Et N onwards), there is a linear dependence of F (I, S) on the intrinsic volumes of the ions, meaning that there is a constant volume increment for each -CHj- group, 16cm mol , irrespective of the solvent. For small ions, the dependence of F (1, S) is about equally shared by the intrinsic ionic volumes and their basicities (for anions) and acidities (for cations), the dominant solvent property being their tightness, measured by their solubility parameter. 

The standard molar volumes of transfer at 25°C of small ions are represented by the operative expression reported by Marcus [36]  

The solvent property included in Equation 4.29 that is not defined in the previous sections is g, the Kirkwood dipole orientation parameter (Section 3.3. l).The corresponding ion property is ABj, the ability of the ion to partake in Lewis acid-base interactions (Table 2.2 for anions). For large, hydrophobic ions the corresponding expression is  

---