Pb(II)-Carboxylate Structure and Reactivity: from Pb(II) Coordination Compounds to PbS Colloidal Nanocrystals

Lead(II)-carboxylates are important precursors for preparing Pb-based semiconductor nanocrystals (NCs). However, the atomic structure of common Pb-carboxylate precursors (e.g., Pb-oleate) remains elusive. Here, we use a rigid yet soluble 4-tert-butylbenzoate (TBBA) as a model ligand to probe the binding and reactivity of Pb-carboxylates. We found that a multinuclear Pb-oxo cluster, Pb₄O(TBBA)₆, was obtained when the coordination reaction was performed in chloroform, in contrast to a mononuclear Pb(TBBA)₂(CH₃OH)₂ complex obtained from methanol. Both compounds are assembled into coordination polymers via bridging carboxylates and can be distinguished by their characteristic carbonyl vibrations in infrared (IR) spectra. The two compounds can also interconvert in different solvents: noncoordinating toluene triggers the Pb(TBBA)₂ to Pb₄O(TBBA)₆ transformation, while coordinating methanol induces the reverse conversion. Importantly, when used as the precursor for PbS NC synthesis, the Pb₄O(TBBA)₆ cluster is less reactive than the Pb(TBBA)₂ complex. The preparation method, reactivity, and IR features of Pb₄O(TBBA)₆ are reminiscent of those of the Pb-oleate precursor, suggesting that the latter is likely a Pb-oxo species. The resolved carboxylate binding modes also shed light on the possible metal-ligand interactions on the PbS NC surface. Our results provide atomic-level insights into the Pb(II)-carboxylate precursor chemistry, which is important for the rational synthesis of Pb-based semiconductor NCs.