Table 1.
Chaotropicity scale based on the ion hydration parameters proposed by Marcus (Refs. 68, 80): Water‐structural entropies of different anions (TΔS struct), their size (radius, r), and net effects on the number of surrounding hydrogen bonds (ΔHB).
| anion | r [pm][a] | TΔS struct [kcal mol−1][b] | ΔHB [c] |
|---|---|---|---|
| kosmotropes | |||
| SO4 2− | 230 | −6.7 | 0.78 |
| HPO4 2− | 238 | −4.4 | 0.46 |
| CO3 2− | 178 | −4.0 | 0.40 |
| F− | 133 | −2.1 | 0.12 |
| chaotropes | |||
| Br− | 196 | 5.8 | −1.01 |
| SCN− | 213 | 5.9 | −1.03 |
| BF4 − | 230 | 6.6 | −1.12 |
| ClO4 − | 240 | 7.6 | −1.27 |
| I− | 220 | 8.3 | −1.37 |
| PF6 − | 295[d] | 8.7 | −1.43 (1.93)[e] |
| superchaotropes | |||
| Fe(CN)6 3− | 373 | 12.8 | −2.01[e] |
| S2O8 2− | 300 | 13.0 | −2.04[e] |
| S4O6 2− | 310 | 13.2 | −2.06[e] |
| B10H10 2− | 393[f] | 11.5 | −1.83 |
| B12H12 2− | 400[f] | 14.8 | −2.31 |
| B12F12 2− | 430[f] | 12.6 | −1.98 |
| B12Cl12 2− | 525[f] | 15.3 | −2.37 |
| B12Br12 2− | 560[f] | 16.3 | −2.51 |
| B12I12 2− | 590[f] | 17.1 | −2.63 |
| PMo12O40 3− | 629[f] | 18.2 | −2.79 |
| PW12O40 3−[g] | 654[f] | 18.9 | −2.89 |
| P2W18O62 6−[h] | 701[f] | 20.3 | −3.08 |
[a] As tabulated in Refs. 80, 124. [b] Calculated according to Marcus, see Refs. 80, 124, values for ions for which no hydration enthalpies are known were interpolated (for PF6 −) or extrapolated (for borate clusters and POMs) from a correlation of ΔS struct versus r for chaotropic anions listed in this table as well as the data for SiF6 −, PdCl6 2−, PtCl6 2−, Co(CN)6 3−, and Fe(CN)6 4− (ΔS struct=4.48+0.399r, n=14, r=0.77). [c] From eq. 25 in Ref. 68, there abbreviated as ΔG HB. [d] From Ref. 125. [e] From Ref. 124, multiplied with the correction factor of 1.25 subsequently introduced in Ref. 68. [f] Calculated from the diameter (the distance between the outer atoms including the vdW radii) obtained from their geometry‐optimized structures (for borate clusters) or XRD structures (for POMs). [g] Keggin‐type POM. [h] Dawson‐type POM.