x value was determined by ICP-OES, finding that the average composition remained unaltered, (xEmpiric = 0.18 for both samples). Although the Mn 2+ incorporation under these synthetic conditions was insensitive to slight variations in the amount of surfactant, the sample with the smaller molar ratio between OA/metallic precursors ratio showed more irregular shapes (Figure in the S.I.). A plausible explanation is that when OA is scarce, a preferential growth of the initial seeds along certain crystal directions normal to the facets ({111} and {110}) which are poorly stabilized by the OA could be promoted, giving rise to more irregular shapes. In contrast, if the amount of OA is enough during the nanocrystal growth, it ensures well-capped and stabilized crystal planes, leading to MNPs with controlled faceted shapes .