The reactions were performed for (q(H2O)K, q(Sr)) = (2.8, 4.0) and varying q(Cl). The corresponding XRD patterns are displayed in Figure . When q(Cl) increases, the preferential orientation is strongly reduced and totally vanishes at q(Cl) = 0.75, with relative intensities in agreement with the simulated pattern (Figure ). The loss of control over anisotropic growth for low hydroxide contents is confirmed by SEM images (Figures 3D) with a large polydispersity arising at high q(Cl). These data confirm that the OH -content of the hydroflux is a key factor influencing the anisotropic growth of Sr5(MnO4)3OH crystals. The Sr 2+ concentrations calculated near the crystallization onset with the same assumptions as mentioned above (see supplementary text 1) show that the concentration of solubilized Sr 2+ increases as q(Cl) increases, as for an increase of q(H2O)K, but anisotropy do not increase accordingly: it is favored for q(Cl) decreasing and q(H2O)K increasing. Therefore, we rule out a possible impact of the Sr 2+ concentration at the crystallization onset on anisotropic growth.