Polyoxometalate Ligation of PbS Nanocrystals

While metal-oxide cluster anions (polyoxometalates, or POMs) stabilize metal nanoparticles (NPs) and metal-oxide nanocrystals (NCs) via established interactions, little is known concerning how POMs might stabilize PbS NCs. Small (ca. 3 nm) Rh and Ir NPs are stabilized "electrosterically", i.e, via combined electrostatic and steric factors, while larger Au NPs, with less severe curvatures, are protected by electrostatically stabilized monolayers involving the intercalation of countercations between close-packed assemblies of the POM polyanions. By contrast, heteropolytungstates stabilize metal-oxide NCs electrostatically, as observed for charged colloids, but also through direct coordination, wherein monolacunary heteropolytungstate-coordinated metal cations form μ-oxo linkages to metal ions at the NC surface. This raises a general question as to how POMs might stabilize metal-chalcogenide NCs. We now report that room-temperature reaction of the Pb²⁺-substituted monolacunary Wells-Dawson anion, α₂-[P₂PbW₁₇O₆₁]^8-, with Na₂S in water provides 4 ± 1 nm PbS NCs. These, in turn, are stabilized by the lacunary ions α₂-[P₂W₁₇O₆₁]^10- (1) generated via the delivery of Pb²⁺ to sulfide. Unlike POMs on metal NPs, or coordinated via μ-oxo linkages to metal-oxide NCs, the four formally W-O^- atoms at the periphery of the defect site of 1 bind to Pb atoms at the (111) surface of the PbS NCs.