Divalent metal halide double salts in equilibrium with their aqueous solutions I. Factors determining their composition

Using a few simple assumptions based on the hard and soft acid and base model and the bond-valence model, we explain why the five most common double salt compositions xMeX2 · yMe′X2 · zH2O (Me, Me′ = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd; X = Cl, Br) found in equilibrium with the corresponding saturated solutions at room temperature will have x:y:z equal to 2:1:12, 1:1:8, 1:1:6, 1:2:6, and 1:4:10 and predict that these will belong to nine …