Table 2. Thermodynamic and Structural Properties of Dimeric Calcium Hydrogen Phosphate Clustersa.
| species | number of OW in Ca coordination shell | change in OW in coordination shell from 2[Ca(HPO4)n]−2n+2 | ΔG (kJ/mol) |
|---|---|---|---|
| [Ca2(HPO4)2] | 8 | –2 | –16.4 |
| [Ca2(HPO4)3]2– | 6 | –3 | –20.5 |
| [Ca2(HPO4)4]4– | 6 | –2 | –11.3 |
| [Ca2(HPO4)5]6– | 4 | –3 | +1.4 |
| [Ca2(HPO4)6]8– | 2 | –4 | +15.6 |
a
Column two gives a summary of the average number of water oxygens (OW) in the two hydration shells of the calcium cations to the nearest integer. The change in water coordination number is given relative to [Ca(HPO4)j,k]−2n+2 (where j+k = n is the number of phosphate species in the cluster; if there is an even number of phosphate species then j = k and if odd j = k – 1). The free energy (ΔG) relative to 2[Ca(HPO4)n]−2n+2 is given as the average over the different pathways for formation, as listed fully in Table S2.