Therefore, the oxo-acidity of the hydroflux can be adjusted by the water content: the higher the water content (lower pH2O), the more acidic the medium. An acidic hydroflux has a pH2O value below half of the pKd value, on the contrary, if pH2O is higher it is basic. If pH2O = pKd/2, the hydroflux is neutral. Kd depends on the temperature and the alkali cation. For example, Kd is 5 orders of magnitude higher for NaOH-based hydrofluxes than for KOH-based ones at 230 ºC. Because the K:Mn ratio is maintained in all syntheses described in Figure , the speciation in KOH-based hydrofluxes is related to the oxo-acidity of the medium: increased acidity (decreased pH2O and increased q(H2O)K) favors Sr5(MnO4)3OH over KSrMnO4. No data are available on the solubility and speciation of Sr 2+ in hydrofluxes nor in molten hydroxides, but Zur Loye et al. discussed the solubility of other metals in hydrofluxes as a function of pH2O, where acidic conditions favor the solubilization of metal cations. One can then hypothesize that as acidity decreases (pH2O increase), the concentration of Sr 2+ concentration decreases, which triggers a switch of phase speciation from a Sr-rich Mn(V) phase (Sr5(MnO4)3OH) to a Sr-poor one (KSrMnO4). The liquid-phase speciation may also change, the mixture becoming more efficient as an alkali donor as p(H2O)K increases. We also note that increasing the oxo-basicity (pH2O increase and q(H2O)K decrease) promotes the precipitation of SrCO3 carbonate byproducts (Figures ), in a similar manner to aqueous solutions and Brönstedt basicity, which parallels the hypothesis of decreased Sr 2+ solubility as pH2O increases.