The surface chemistry of a colloidal nanoparticle is intrinsic to both its structure and function. It is therefore necessary to characterize the surfaces of colloidal materials to rationally underpin any synthetic, catalytic, or transformative mechanisms they enable. Here we characterize the surface properties of colloidal InP clusters and quantum dots by examining the binding of traditional stabilizing ligands including carboxylates, phosphonates, and thiolates. By using the In37P20X51 (X = carboxylate) cluster species as an ideally monodisperse and well-defined starting scaffold, we quantify surface-exchange equilibria. Using quantitative 1H and 31P NMR spectroscopy, we show that 1:1 metathesis-type binding models are insufficient to fully describe the surface dynamics. In particular, for the case of the highly reversible carboxylate ligand exchange, a more detailed isotherm approach using a two-site, competitive model is necessary. This model is used to deconvolute L- and X-type binding modalities. We additionally quantify the reversible and irreversible ligand-exchange reactions observed in the thiolate and phosphonate  systems.

CONSPECTUS: Clusters are unique molecular species that can be viewed as a bridge between phases of matter and thus between disciplines of chemistry. The structural and compositional complexity observed in cluster chemistry serves as an inspiration to the material science community and motivates our search for new phases of matter. Moreover, the formation of kinetically persistent cluster molecules as intermediates in the nucleation of crystals makes these materials of great interest for determining and controlling mechanisms of crystal growth. Our lab developed a keen interest in clusters insofar as they relate to the nucleation of nanoscale semiconductors and the modeling of postsynthetic reaction chemistry of colloidal materials. In particular, our discovery of a structurally unique In 37 P 20 X 51 (X = carboxylate) cluster en route to InP quantum dots has catalyzed our interest in all aspects of cluster conversion, including the use of clusters as precursors to larger nanoscale colloids and as platforms for examining postsynthetic reaction chemistry. This Account is presented in four parts. First, we introduce cluster chemistry in a historical context with a focus on main group, metallic, and semiconductor clusters. We put forward the concept of rational, mechanism-driven design of colloidal semiconductor nanocrystals as the primary motivation for the studies we have undertaken. Second, we describe the role of clusters as intermediates both in the synthesis of well-known material phases and in the discovery of unprecedented nanomaterial structures. The primary distinction between these two approaches is one of kinetics; in the case of well-known phases, we are often operating under high-temperature thermolysis conditions, whereas for materials discovery, we are discovering strategies to template the growth of kinetic phases as dictated by the starting cluster structure. Third, we describe reactions of clusters as model systems for their larger nanomaterial progeny with a primary focus on cation exchange. In the case of InP, cation exchange in larger nanostructures has been challenging due to the covalent nature of the crystal lattice. However, in the higher energy, strained cluster intermediates, cation exchange can be accomplished even at room temperature. This opens opportunities for accessing doped and alloyed nanomaterials using postsynthetically modified clusters as single-source precursors. Finally, we present surface chemistry of clusters as the gateway to subsequent chemistry and reactivity, and as an integral component of cluster structure and stability. Taken as a whole, we hope to make a compelling case for using clusters as a platform for mechanistic investigation and materials discovery.

We have synthesized InP nanocrystals of an unprecedented crystal phase at low temperature (35-100 °C) by templated growth of InP magic-sized clusters. With the addition of stoichiometric equivalents of P(SiMe ) to the starting cluster, we demonstrate nanocrystal growth mediated through a partial dissolution and recrystallization pathway. This growth process was monitored using a combination of in situ UV/Vis and P NMR spectroscopy, revealing the intermediacy of smaller cluster species of higher symmetry. The nanocrystals that result from this templated growth exhibit a crystal structure that is neither zincblende nor wurtzite, and instead is derived from the original cluster. This structure is best described as a 3D polytwistane phase as deduced from a combination of X-ray diffraction, Raman, and solid-state NMR spectroscopy methods.

We have synthesized InP nanocrystals of an unprecedented crystal phase at low temperature (35-100 8 8C) by templated growth of InP magic-sizedc lusters.W itht he addition of stoichiometric equivalents of P(SiMe 3 ) 3 to the starting cluster,w ed emonstrate nanocrystal growth mediated through ap artial dissolution and recrystallization pathway. This growth process was monitored using ac ombination of in situ UV/Vis and 31 PNMR spectroscopy, revealing the intermediacy of smaller cluster species of higher symmetry. The nanocrystals that result from this templated growth exhibit ac rystal structure that is neither zincblende nor wurtzite,a nd instead is derived from the original cluster.This structure is best described as a3 Dp olytwistane phase as deduced from ac ombination of X-ray diffraction, Raman, and solid-state NMR spectroscopym ethods.

This text presents a method for the synthesis of In 37 P 20 (O 2 C 14 H 27) 51 clusters and their conversion to indium phosphide quantum dots. The In 37 P 20 (O 2 CR) 51 clusters have been observed as intermediates in the synthesis of InP quantum dots from molecular precursors (In(O 2 CR) 3 , HO 2 CR, and P(SiMe 3) 3) and may be isolated as a pure reagent for subsequent study and use as a single-source precursor. These clusters readily convert to crystalline and relatively monodisperse samples of quasi-spherical InP quantum dots when subjected to thermolysis conditions in the absence of additional precursors above 200 °C. The optical properties, morphology, and structure of both the clusters and quantum dots are confirmed using UV-Vis spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The molecular symmetry of the clusters is additionally confirmed by solution-phase 31 P NMR spectroscopy. This protocol demonstrates the preparation and isolation of atomically-precise InP clusters, and their reliable and scalable conversion to InP QDs.