# Polyoxometalate Ligation of PbS Nanocrystals

## TL;DR

This paper explores how polyoxometalates (POMs) can stabilize lead sulfide nanocrystals (PbS NCs) through a unique coordination mechanism.

## Contribution

The study reveals a new stabilization mechanism for PbS NCs using monolacunary POMs via out-of-pocket coordination.

## Key findings

- 4 ± 1 nm PbS NCs are formed by reacting α2-[P2PbW17O61]8– with Na2S in water.
- The POM α2-[P2W17O61]10– stabilizes PbS NCs by coordinating to Pb atoms at their (111) surfaces.
- This mechanism differs from POM interactions with metal NPs or metal-oxide NCs.

## Abstract

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.

Polyoxometalate cluster anions (POMs) and their countercations
form electrostatically stabilized protecting layers on Au NPs, while
POM ligation to metal-oxide NCs via the formation of bridging-oxo
linkages gives macroanion-like nanostructures. These findings raise
a general question as to how POMs might stabilize metal-chalcogenide
NCs. We now show that the monolacunary Wells–Dawson cluster-anion,
α2-[P2W17O61]10−, stabilizes 4 nm PbS NCs in water by out-of-pocket
coordination to Pb atoms at their (111) surfaces.