The cubic ZnS structure type and the size dependent properties of related nanoparticles are of both fundamental and technological importance. Yet, it remains a challenge to synthesize large atom-precise dusters of this structure type: Currently, only supertetrahedral clusters with 4, 10, 20, and 35 metal sites (denoted as T2, T3, T4, and TS, respectively) are known. Because the synthesis of. T5 in 2002, numerous synthetic efforts targeting larger clusters only resulted in T2-T5 clusters in various compositions and intercluster-connectivity, with T6 (56 metal and 84 anion sites) being elusive. Here, we report the so-far largest supertetrahedral cluster (T6, [Zn25In31S84](25-))New T6 clusters can serve as the host Matrix for optically active centers. Mn-doped variants of T4 and T6 have also been made, allowing the investigation of site-dependent Mn emission. The results lead to the elucidation of the mechanism regulating Mn emission via size-dependent crystal lattice strain and provide new insight into Mn-doping chemistry in cluster-based chalcogenides at the atomic level.