Magic-sized clusters (MSCs) can provide valuable insight into the atomically precise progression of semiconductor nanocrystal transformations. We report the conversion of an InP MSC to a Cd3P2 MSC through a cation exchange mechanism and attempt to shed light on the evolution of the physical and electronic structure of the clusters during the transformation. Utilizing a combination of spectroscopic (NMR/UV–vis) and structural characterization (ICP-OES/MS/PXRD/XPS/PDF) tools, we demonstrate retention of the original InP MSC crystal lattice as Z-type ligand exchange initially occurs. Further cation exchange induces lattice relaxation and a significant structural rearrangement. These observations contrast with reports of cation exchange in InP quantum dots, indicating unique reactivity of the InP MSC.

In this work, we examine the direct influence of ligand coverage on a catalytically active surface for the hydrogen evolution reaction (HER). We tested the electrochemical and electrocatalytic properties of colloidally synthesized WSe2 with dodecylamine ligands before and after treatment with Meerwein’s reagent, which was shown to reduce the coverage of amine and lead to an improvement in the overpotential for HER by as much as 180 mV on the same electrode (reversible upon re-ligation with amine). The underlying mechanism of the improvement in HER catalysis following treatment with Meerwein’s reagent was investigated using a combination of Tafel slope analysis, electrochemically active surface area measurements, and impedance spectroscopy. These electrochemical measurements are rationalized with Fermi level and d-band center analysis from XPS. Together, these measurements suggest that, while the surface area of the WSe2 increases upon ligand stripping, the intrinsic catalytic capability of the WSe2 also changes. This is likely due to a decrease in ΔGH in the Meerwein’s treated WSe2, improving the HER kinetics.Keywords: HER; hydrogen evolution; ligand; TMDC; WSe2;

The reaction of primary amines with In37P20(O2CR)51 is found to remove In(O2CR)3 subunits from In37P20(O2CR)51. This loss of Z-type ligands coincides with structural rearrangement to alleviate core strain and passivate phosphorus atoms. This result consolidates conflicting claims that primary amines both promote and retard precursor conversion rates for InP nanocrystals.

The kinetic parameters governing cation exchange between molecular Cd2+ precursors and ZnTe nanorods is mapped out in detail to provide an all-inclusive rubric for tuning the rate and extent of cation exchange in this system—allowing for band gap tunability over a 1 eV range. Evaluation of cation exchange as a function of concentration, temperature, and time supports a mechanism involving initial, rapid Cd2+ adsorption followed by a rate determining cation exchange step with a measured activation energy of 24 kJ/mol. Provided there is sufficient cadmium to occupy the available surface sites, the solution concentration of cadmium has little influence on the rate of cation exchange, allowing the system to be modeled using pseudo-first-order kinetics, with observed rates ranging from 0.03 × 10–3 s–1 at 20 °C to 2.8 × 10–3 s–1 at 240 °C. It is also demonstrated that, due to the ease of cation exchange in these systems, previous claims of ZnTe/CdSe heterostructures are more accurately described as alloys.

Magic-sized nanoclusters have been implicated as mechanistically relevant intermediates in the synthesis of group III-V quantum dots. Herein we report the single-crystal X-ray diffraction structure of a carboxylate-ligated indium phosphide magic-sized nanocluster at 0.83 Å resolution. The structure of this cluster, In37P20(O2CR)51, deviates from that of known crystal phases and possesses a non-stoichiometric, charged core composed of a series of fused 6-membered rings. The cluster is completely passivated by bidentate carboxylate ligands exhibiting predominantly bridging binding modes. The absorption spectrum of the cluster shows an asymmetric line shape that is broader than what would be expected from a homogeneous sample. A combination of computational and experimental evidence suggests that the spectral line width is a result of multiple, discrete electronic transitions that couple to vibrations of the nanocrystal lattice. The product of reaction of this nanocluster with 1 equiv of water has also been structurally characterized, demonstrating site selectivity without a drastic alteration of electronic structure.

[EtZnP(SiMe3)2]3 has been identified as a competent intermediate for the growth of stoichiometric α-Zn3P2 nanocrystals from Zn-rich zinc phosphide seeds as determined by powder X-ray diffraction, solid-state nuclear magnetic resonance (NMR) spectroscopy, and transmission electron microscopy analysis. Solution-phase NMR data show that this trimer forms in situ upon reaction of P(SiMe3)3 and ZnEt2 in the presence of Zn(O2CR)2 under zinc carboxylate-limited conditions. [EtZnP(SiMe3)2]3 can also be used to nucleate zinc phosphide; however, in comparison to a previously examined nucleation pathway involving (Et2Zn)P(ZnO2CR)2(SiMe3), a decrease in relative reactivity leads to fewer nuclei and larger, more crystalline particles. These data, in combination with previous literature on the synthesis of zinc phosphide nanocrystals, were then aggregated to propose a set of design principles for the synthesis of zinc phosphide nanocrystals using P(SiMe3)3 as the phosphorus precursor.

InP quantum dots have emerged as an exciting class of phosphors for displays and energy-efficient solid state lighting. Unfortunately, the synthesis of these materials has lagged behind that of related II-VI and IV-VI materials. It is becoming increasingly apparent that this may be due, in many cases, to the inability to control quantum dot nucleation and crystallization using precursor conversion kinetics. In this perspective, recent work on understanding the nucleation and growth of InP from the perspective of nonclassical nucleation models is discussed. In particular, the recent discovery that kinetically persistent magic-size nanoclusters build up during the high temperature synthesis of this material will be highlighted. Isolation and complete structural characterization of one such InP nanocluster has offered unprecedented insight into the structure and surface chemistry of InP and its deviation from how we think about quantum dot structure and composition based on models built for II-VI materials. Moreover, this cluster offers an exciting playground to test hypotheses related to ligand and cation exchange as well as serving as a stepping stone to develop a more complete understanding of the properties that govern nanomaterial nucleation.

An electrocatalytically active cobalt diimine monoxime monoximate complex was deprotonated by 1-methylimidazole affording a doubly deprotonated complex that serves as a versatile precursor for synthesis of a variety of multimetallic complexes with Co–Zn, –Cd, –Mn and –Ru coordination. These complexes were studied using a combination of spectroscopic, analytical and electrochemical techniques, revealing the electronic and structural parameters unique to this new class of compounds. The ability of these complexes to catalyze proton reduction was also investigated. These complexes are homogeneous electrocatalysts for the hydrogen evolution reaction through reduction of [NEt3H][BPh4] in CH3CN, however decompose under extended electrolysis conditions.

We demonstrate the ability of M2+ Lewis acids (M = Cd, Zn) to dramatically enhance the photoluminescence quantum yield (PL QY) of InP quantum dots. The addition of cadmium and zinc is additionally found to red- and blue-shift, respectively, the lowest energy absorption and emission of InP quantum dots while maintaining particle size. This treatment results in a facile strategy to post-synthetically tune the luminescence color in these materials. Optical and structural characterization (XRD, TEM, XAS, ICP) have led us to identify the primary mechanism of PL turn-on as surface passivation of phosphorus dangling bonds, affording PL QYs up to 49% without the growth of a type I shell or the addition of HF. This route to PL enhancement and color tuning may prove useful as a standalone treatment or as a complement to shelling strategies.

A Ru(NH-NHC) complex with an open coordination site on the metal center adjacent to ligand N–H moieties has been synthesized and characterized. This complex exhibits unique reactivity upon reaction with either CO2 or NaHCO3, yielding a formate-bridged bimetallic complex via a spontaneous deoxygenation reaction and formal reduction at carbon. Dehydrogenation of the formate complex leads to a Ru–carbamate species following carbon–nitrogen bond formation between the CO2 moiety and the NHC ligand. This reactivity opens up new pathways for CO2 reduction and is relevant to H2 storage.

We report on the role of magic-sized clusters (MSCs) as key intermediates in the synthesis of indium phosphide quantum dots (InP QDs) from molecular precursors. Heterogeneous growth from the MSCs directly to InP QDs was observed without intermediate sized particles. These observations suggest that previous efforts to control nucleation and growth by tuning precursor reactivity have been undermined by formation of these kinetically persistent MSCs prior to QD formation. The thermal stability of InP MSCs is influenced by the presence of exogenous bases as well as choice of the anionic ligand set. Addition of a primary amine, a common additive in previous InP QD syntheses, to carboxylate-terminated MSCs was found to bypass the formation of MSCs, allowing for homogeneous growth of InP QDs through a continuum of isolable sizes. Substitution of the carboxylate ligand set for a phosphonate ligand set increased the thermal stability of one particular InP MSC to 400 °C. The structure and optical properties of the MSCs with both carboxylate and phosphonate ligand sets were studied by UV–vis absorption spectroscopy, powder XRD analysis, and solution 31P{1H} and 1H NMR spectroscopy. Finally, the carboxylate-terminated MSCs were identified as effective single-source precursors (SSPs) for the synthesis of high-quality InP QDs. Employing InP MSCs as SSPs for QDs effectively decouples the formation of MSCs from the subsequent second nucleation event and growth of InP QDs. The concentration dependence of this SSP reaction, as well as the shape uniformity of particles observed by TEM suggests that the stepwise growth from MSCs directly to QDs proceeds via a second nucleation event rather than an aggregative growth mechanism.

We report here a photocathode based on a high surface area conductive metal oxide scaffold sensitized by CdSe quantum dots attached via organic linkers. Photoreduction of methylviologen demonstrates efficient photoreactions occuring at electrode surfaces and verifies that the high surface area scaffold is promising for use as a photocathode material.

The synthesis and characterization of crystalline colloidal zinc phosphide quantum dots with observable excitonic transitions ranging between 424–535 nm (2.3–2.9 eV) are reported. A ternary combination of ZnEt2, Zn(O2CR)2, and P(SiMe3)3, forms a pentanuclear zinc cluster on mixing followed by conversion to (Et2Zn)P(ZnO2CR)2(SiMe3) in a rate-determining step prior to quantum dot formation.

We have developed a two-phosphine strategy to independently tune nucleation and growth kinetics based on the relative reactivity of each precursor in the synthesis of indium phosphide (InP) quantum dots (QDs). This approach was allowed by the exploration of the synthesis and reactivity of a series of sterically encumbered triarylsilylphosphines substituted at the para position of the aryl group, P(Si(C6H4-X)3)3 (X = H, Me, CF3, or Cl), as a contrast to P(SiMe3)3, the P3– source commonly employed in such syntheses. UV–vis absorption spectroscopy of aliquots taken during InP QD growth revealed a stark contrast between triarylsilylphosphines with electron-donating and electron-withdrawing groups in both the rate of InP formation and the final particle size. 31P{1H} nuclear magnetic resonance spectroscopy confirmed that precursor conversion remains rate-limiting throughout the nanocrystal synthesis when P(SiPh3)3 is incorporated as the sole phosphorus precursor; however, this is insufficient for effective separation of nucleation and growth in this system because of the slow nucleation rates that result. In all cases, syntheses that employ a single chemical species as the P3– source were found to suffer from a poor match in reactivity with In(O2C(CH2)12CH3)3 as they either fail to separate nucleation from growth because of slow precursor conversion rates [P(SiPh3)3 and P(Si(C6H4-Me)3)3] or preclude size selective growth from rapid precursor conversion [P(SiMe3)3, P(Si(C6H4-Cl)3)3, and P(Si(C6H4-CF3)3)3]. To balance these two extreme cases, we developed a novel approach in which two different P3– sources were introduced to segregate nucleation and growth based on the relative reactivity of each precursor.

A bisimidazole-phosphine ligand, PhP[(CH2)2ImArMe2]2, has been prepared and has been metalated using [Cp*Ru(μ3-Cl)]4, generating a bis(N-heterocyclic carbene)-phosphine Ru(II) species through ligand coordination followed by tautomerization. This is the first example of an NHC–donor–NHC complex with two unsubstituted N–H wingtips. Furthermore, a second metal center was installed by deprotonation of both N–H wingtips and subsequent salt metathesis to generate Ru(II)–Fe(II) and Ru(II)–Co(II) bimetallic complexes.

We survey the chemical reactions between common precursors used in the synthesis of metal chalcogenide nanocrystals and outline how they affect the mechanism and kinetics of nanocrystal growth. We emphasize syntheses of cadmium selenide and cadmium sulfide where a variety of metal and chalcogenide precursors have been explored, though this is supplemented by studies of zinc and lead chalcogenide formation where appropriate. This review is organized into three sections, highlighting kinetics, metal precursors, and chalcogenide precursors, respectively. Section I is dedicated to the role of precursor conversion as a source of monomers and the importance of the supply rate on nanocrystal nucleation and growth. Section II describes the structure and reactivity of cadmium carboxylates, phosphonates, and chalcogenolates. Section III describes the reaction chemistry of commonly employed chalcogenide precursors and the mechanisms by which they react with metal precursors.Keywords: cadmium chalcogenide; II−VI; mechanism; precursor conversion; quantum dot;

We have studied the speciation of P(SiMe3)3 during the synthesis of colloidal InP quantum dots in the presence of proton sources. Using 31P NMR spectroscopy, we show H3-nP(SiMe3)n formation on exposure of P(SiMe3)3 to a variety of protic reagents including water, methanol, and carboxylic acid, corroborating observations of P(SiMe3)3 speciation during the hot injection synthesis of InP QDs. Quantitative UV–vis comparisons between InP growth from P(SiMe3)3 and HP(SiMe3)2 show unambiguously that when total H+-content is accounted for, particle size, size dispersity, and concentration are indistinguishable for these two reagents. The dual role of myristic acid in P–Si bond cleavage and as a source of the myristate anion, an essential component of the quantum dot surface, is interrogated using tetrabutylammonium myristate, confirming that it is the protons that are responsible for increased quantum dot polydispersity. Together these data support the existence of a competing acid-catalyzed pathway in the conversion of P(SiMe3)3 to InP and demonstrate its impact. By preventing a constant solute supply and affecting the concentration of quantum dot surfactant over the course of the reaction, the existence of competing precursor conversion pathways is detrimental to formation of monodisperse colloids, explaining much of the irreproducibility in InP quantum dot syntheses to date.Keywords: III−V; mechanism; phosphide; precursor conversion; quantum dot;

We report here a photocathode based on a high surface area conductive metal oxide scaffold sensitized by CdSe quantum dots attached via organic linkers. Photoreduction of methylviologen demonstrates efficient photoreactions occuring at electrode surfaces and verifies that the high surface area scaffold is promising for use as a photocathode material.

An electrocatalytically active cobalt diimine monoxime monoximate complex was deprotonated by 1-methylimidazole affording a doubly deprotonated complex that serves as a versatile precursor for synthesis of a variety of multimetallic complexes with Co–Zn, –Cd, –Mn and –Ru coordination. These complexes were studied using a combination of spectroscopic, analytical and electrochemical techniques, revealing the electronic and structural parameters unique to this new class of compounds. The ability of these complexes to catalyze proton reduction was also investigated. These complexes are homogeneous electrocatalysts for the hydrogen evolution reaction through reduction of [NEt3H][BPh4] in CH3CN, however decompose under extended electrolysis conditions.

The synthesis and characterization of crystalline colloidal zinc phosphide quantum dots with observable excitonic transitions ranging between 424–535 nm (2.3–2.9 eV) are reported. A ternary combination of ZnEt2, Zn(O2CR)2, and P(SiMe3)3, forms a pentanuclear zinc cluster on mixing followed by conversion to (Et2Zn)P(ZnO2CR)2(SiMe3) in a rate-determining step prior to quantum dot formation.

The reaction of primary amines with In37P20(O2CR)51 is found to remove In(O2CR)3 subunits from In37P20(O2CR)51. This loss of Z-type ligands coincides with structural rearrangement to alleviate core strain and passivate phosphorus atoms. This result consolidates conflicting claims that primary amines both promote and retard precursor conversion rates for InP nanocrystals.