Theory predicts blue emission of a lead bromide perovskite QD such as Cs112Pb64Br240 (Cs•QD4, Fig. , see Supplementary Note 1) . However, in practice, previous works showed it is unstable and has poor metrics because of dangling bonds and surface defects and the dynamic nature of the QD-ligand interaction . We report here the synthesis of QDs of lead bromide perovskite (MLA•M•QD4, M = Cs + or methylammonium ion, MA + ) at room temperature in air via self-organization of a lead malate chelate complex and PbBr3 -via a corner-edge-corner intermediate similar to the one we previously described (Fig. ) . As shown by in situ dynamic SMART-EM imaging and other analytical methods, the nanocluster is a structurally uniform cube made of 4 Pb atoms, where eight malate molecules form a stable Pb-O chelate on the eight corners (Fig. ), and oleylammonium cations (OAMH + ) lipophilize and stabilize the edges that otherwise suffer from a large penalty of surface energy (Fig. ). Thus, the cube is to be viewed as a molecule of near centrosymmetry rather than a nanocrystal devoid of translational symmetry. Both MLA•MA•QD4 (1) and MLA•Cs•QD4 (2) exhibit deep blue photo-and electroluminescence at »460 nm with quantitative PLQY andnarrow FWHM below 15 nm reflecting minimum structural defects. Thus, controlled self-assembly and SMART-EM imaging have opened a venue for synthesis and analysis of nm-sized nanoclusters at a level of precision so far considered possible only for organic and inorganic molecules.