Indeed, after a colloidally stable solution of Au•MUA + Au•TMA in saturated aqueous (NH4)2CO3 (Fig. , stage 2) was left undisturbed overnight, well-defined and highly faceted colloidal crystals (superlattices) were observed (Fig. , stage 3). Importantly, all the steps proceeded at room temperature, which allowed the NPs to retain their high charge. We adopted this procedure to ~200 combinations of positively and negatively charged NPs and identified two distinct phases of colloidal crystals, which are mapped onto the phase diagram in Fig. . We will begin the discussion with crystals obtained from equally or similarly sized Au•MUA and Au•TMA; the stoichiometry of these crystals is 1:1; we will refer to them as AB-type.