Small Ionic Radius Limits Magnesium Water Interaction in Amorphous Calcium/Magnesium Carbonates
Anders C. S. Jensen, Silvia Imberti, Wouter J. E. M. Habraken, Luca Bertinetti
Abstract
The stabilizing effect of magnesium ions on amorphous calcium carbonate has been studied extensively due to its widespread occurrence in biogenic minerals. It has long been suggested that magnesium binds water more strongly compared to calcium given its relatively high dehydration energy. However, recent work has shown that mobility increases in the presence of a magnesium ion relative to the pure calcium phase. Using total scattering and EPSR modeling, we show here that in amorphous magnesium carbonate, because of the small size of the ion, the coordination number of magnesium is smaller and the interaction with water are therefore limited. As a result, ∼35% of water molecules are bound exclusively by hydrogen bonds mainly to the anions.