Atomically Precise PbSe Nanocrystal Protected by Carboxylates

Pb-based semiconductor nanocrystals (NCs) are versatile building blocks for energy and information nanotechnologies. However, atomic-level control of these NCs remains an important challenge. Here we report achieving atomic precision in a PbSe NC capped with labile carboxylate ligands: Pb₆₈Se₂₈O₈(O₂CR)₆₄ (R = 4-<i>tert</i>-butylbenzyl). The 1.8 nm rock-salt NC features precise excitonic absorption at 564 nm and emission at 746 nm. Its core adopts an expanded octahedral shape, exposing exclusively Pb-rich (111) facets. Unexpectedly, a "dangling" Pb atom is found on each facet, anchored by an oxo group (O^2-) to form a Pb-oxo motif with remarkable ambipolar binding affinity (Pb²⁺-O^2-), which stabilizes the surface Pb-carboxylate network. Six distinct carboxylate binding modes are identified, with mounting-type and bridging-type carboxylates passivating facet and edge sites, respectively. Importantly, the ligands' primary binding oxygens self-assemble into ordered O(111) adlayers. The atomically defined PbSe NC establishes a model system, paving the way for the precision engineering of Pb-based NCs.