Facile synthesis of atomically precise metal-chalcogenide semiconductor nanoclusters via combining coordination and colloidal methods

Abstract

Facile synthesis of atomically precise semiconductor nanoclusters remains an important challenge, especially for systems containing heavier chalcogens. The present disclosure describes a synthetic approach that combines coordination chemistry and colloidal methods to produce atomically precise cadmium chalcogenide nanoclusters with defined compositions and structures. In representative embodiments, an atomically defined cadmium coordination complex is reacted with a phosphine-chalcogen precursor to yield cadmium telluride nanoclusters exhibiting distinct excitonic absorption features. The disclosed methods enable access to multiple size and structural regimes, including zinc blende-derived clusters, higher- nuclearity tetrapodal clusters formed through continued growth, and ultrasmall icosahedral clusters formed under mild conditions. Structural analysis reveals precise atomic frameworks and, in some embodiments, emergent chirality or photoluminescence. The disclosed approach provides an accessible platform for atomic-level control of semiconductor nanoclusters for optoelectronic applications.

Description

[0001] Docket No. 10457-627PC0

[0002] Facile Synthesis of Atomically Precise Metal-Chalcogenide Semiconductor Nanoclusters via Combining Coordination and Colloidal Methods

[0003] BACKGROUND

[0004] Metal chalcogenide semiconductors, such as cadmium telluride (CdTe), have broad applications in thin-film solar cells, infrared detectors, bioimaging, and photocatalysis because of their tunable bandgap and prominent optoelectronic properties.1 4For example, thin-film CdTe solar cells are among the most efficient solar cells (with > 23 % power conversion efficiency).1Colloidal CdTe nanocrystals are promising building blocks for solution-processible solar cells, but their efficiency still lags behind 10%).5 7Achieving atomic-level control of CdTe nanomaterials is important for understanding their precise compositions, surface structures, and sintering mechanisms, which could potentially improve thin-film quality and enhance power conversion efficiency.

[0005] Colloidal nanoclusters represent an intermediate state between smaller coordination molecules (typically < ~1 nm) and larger colloidal nanocrystals (typically > ~ 3 nm, Scheme I).8,9These clusters, sometimes referred to as ‘giant’ molecules or ‘ultrasmall’ nanocrystals, have been synthesized via both coordination and colloidal methods. Since 1980s, several structures of atomically precise CdS and CdSe clusters have been determined by single-crystal X-ray diffraction (sc-XRD), including [Cd10S4(SR)16]10Cd32Si4(SR)36,n’12[Cd54S32(SR)48]4C13’14and their CdSe analogues.15 19In comparison, the reports on atomically precise CdTe nanoclusters are rather rare.20-22This is likely due to the instability of most Te2−precursors, such as (Me3Si)2Te,23compared to the analogous (Me3Si)2Se used in cluster synthesis.15 18For example, a Cd10Te4(TePh)12(PPr3)4cluster with a broad absorption around 328 nm was synthesized by reacting CdCl2with (Me3Si)2Te and Me2Si(TePh) at -50 to 4 °C.21The inaccessibility of organometallic tellurium precursors hinders the further exploration of other possible atomically defined CdTe clusters using this method.

[0006] On the other hand, CdTe magic-sized clusters (MSCs), characterized by sharp and reproducible absorption peaks (such as -370 nm, -420 nm, and -450 nm), are frequently observed in the colloidal synthesis of CdTe nanocrystals.24 31These MSCs were typically obtained byDocket No. 10457-627PC0

[0007] reacting various Cd(II) precursors (such as Cd-oleate and Cd-oleylamine compounds) with a phosphine-tellurium source (TePRs).31The precise excitonic absorption indicates the uniform compositions of these CdTe MSCs. For example, CdTe MSCs with 370 and 450 nm absorption peaks are often assigned to (CdTe)i3 and (CdTe)34, respectively.30However, the exact structures of these MSCs remain largely elusive, as the labile surface ligands and dynamic cores make it challenging to isolate and characterize these clusters in their intact form.31It is unclear whether these MSCs share similar structures with those atomically precise CdE clusters resolved by X-ray crystallography.

[0008] BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1. Synthesis of an atomically precise Cd32Te14(SR)36(PR3)4nanocluster. (a) Reaction scheme, (b) Tetrahedral unit in [Cd4(TBBT)9]ncoordination polymer and resulted Cd32Te14cluster. (c) UV-vis spectra of the reaction mixture and crystals dissolved in toluene. Inset: corresponding crystal photo.

[0010] Figure 2. Structural anatomy of the Cd32Te14(SR)36(PPh3)4cluster. (a) Tetrahedral Cd4Te10kernel with a zincblende structure, (b) Four Cd6Te(SR)9flakes capping the facets, (c) Four Cd(PPh3) units capping the comers. Light green: core Cd; dark green: surface Cd; blue: tip Cd; orange: Te; yellow: S; pink: P. Carbon and hydrogen atoms are omitted for clarity.

[0011] Figure 3. Packing of cation and anion sublattices in Cd32Te14(SR)36(PR3)4cluster. (a) Construction of Cd32lattice from a six-layer Cd56tetrahedron (T6) with cubic-close packing (ABC), (b) Similar packing of anions (Te, S from thiolate, and P from phosphine) based on a seven-layer Te84tetrahedron (T7). (c) Zincblende CdTe cluster framework with four wurtzite twinning tips.

[0012] Figure 4. Ligand packing induces chirality on CdTe cluster surface, (a) Rotating stacking of six TBBT ligands into a hexagonal vertex on tetrahedron facet. Tertbutyl groups are omitted to show the stacking of phenyl rings on the top panel, (b) Rotating packing of three TBBT and one PPh3 ligand on tetrahedron tip. (c, d) Distribution of hexagonal and triangular ligand patches into a spherical shell. Left and right enantiomers are indicated by blue and red colors, respectively.Docket No. 10457-627PC0

[0013] Figure 5. Body-centered cubic (BCC) packing of CdTe clusters. (a,b) Atomically coherent superlattice viewed from (100) and (111) directions, respectively. (c) Body-centered cubic packing of left and right CdTe clusters. (d) Intercluster interaction between tip PPh3ligands of one cluster and facet TBBT ligands of another cluster. Blue, left isomer; Red: right isomer.

[0014] Figure 6. Synthesis and crystal structure of {[HNEt3][Cd4(TBBT)9]}n compound, (a) Reaction scheme, (b) Unit cell structure, (c) One dimensional chain of [Cd4(TBBT)9]ncoordination polymer. Hydrogen atoms are omitted for clarity.

[0015] Figure 7. Powder XRD pattern of a Cd32Te14(TBBT)36(PPh3)4cluster. Black line: experimental pattern from finely ground powders of CLUTCH crystals (after baseline subtraction). Red line: simulated pattern from solved Cd32Tei4(TBBT)36(PPh3)4 structure. Grey line: diffraction pattern of bulk zincblende CdTe phase (ICSD 52840).

[0016] Figure 8. Emission spectra at different excitation wavelengths at room temperature.

[0017] Left: Cd32Te14cluster in chloroform. Right: pure chloroform. The sharp peaks are from the Raman scattering of the solvent.

[0018] Figure 9. Synthesis of Cd75Te42(TBBT)66(PBu3)4cluster. (a) Reaction scheme, (b) UV-vis absorption spectra of reaction mixtures at different times, (c) Absorption spectra of the reaction mixture and the crystals dissolved in toluene. Inset: picture of the crystals.

[0019] Figure 10. Effect of reaction temperature, (a) Reaction scheme, (b-f) Reactions at different temperatures.

[0020] Figure 11. Effect of additional PPh3. (a) Reaction scheme, (b-f) Reactions at different temperatures.

[0021] Figure 12. Effect of mixing methods and Cd amount, (a) Reaction scheme, (b-e) Corresponding reactions.

[0022] Figure 13. Crystal structures of Cd75Te42(TBBT)66(PBu3)4cluster. (a) Representation of the overall tetrapodal shape of the cluster, (b) Zinc blende tetrahedral [Cd31Te20]22−core. (c) Tetrahedral [Cd11Te5.5(TBBT)16.5(PBu3)]5.5−arms. Disordered Te atoms are highlighted in red. (d) Complete structures. Cd7sTe42(TBBT)66(PBu3)4 structure.Docket No. 10457-627PC0

[0023] Figure 14. Synthesis of a Cd14Te13Cl2(tmeda)6cluster. (a) Reaction scheme, (b) Normalized UV-Vis absorbance spectrum of the reaction mixture and the saturated solution used for crystallization, (c) Crystal structure determined by SC-XRD.

[0024] Figure 15. Monitoring the synthesis of a Cd14Te13cluster. (a) Reaction scheme, (b) UV-vis spectra at different reaction times. Samples were prepared by diluting 10 pL of the reaction mixture with 1 mL of CHCh. (c) Photos of corresponding reaction mixtures.

[0025] Figure 16. Structure analysis of a Cd14Te13cluster. (a) Icosahedral Te13anion framework viewed from 2-fold, 3-fold, and 5-fold rotation axes, respectively, (b) Positions of core Cd (red), face Cd (green), and edge Cd (blue), respectively, (c) Tetrahedral coordination environment of each type of Cd. The average Cd-Te bond lengths and Te-Te distances are labelled in A.

[0026] Figure 17. Chirality in a Cd14Te13cluster. (a) Left and right enantiomers, (b) Unit cell structure.

[0027] DETAILED DESCRIPTION

[0028] Presented herein are embodiments related to atomically precise semiconductor nanoclusters and synthesis thereof involving atomically defined precursors, pathways and products via synergizing coordination and colloidal chemistry in the reaction. Atomically precise nanoclusters include precise absorption peaks, precise formulas and precise structures. In a specific embodiment, disclosed is the facile synthesis of an atomically precise Cd32Te14(SR)36(PR3)4cluster with a distinct absorption peak at 377 nm (see FIG. 1 for example).

[0029] This is achieved by bridging the gap between coordination and colloidal synthesis and combining the advantages of both methods (Scheme 1). Instead of common colloidal precursors such as cadmium(II)-oleate with labile and flexible ligands, we select a more stable and rigid cadmium(II)-thiolate coordination complex for providing cation and ligand.10On the other hand, we adopt a more accessible phosphine-tellurium compound (TePR3), frequently used in colloidal synthesis.32−34as the Te precursor. The reaction between the precise Cd-thiolate complex and theDocket No. 10457-627PC0

[0030] facile Te source at 150 °C yields an atomically precise CdTe cluster in high purity and stability. The cluster can be readily isolated and crystallized, unveiling the ‘magic’ of the CdTe nanocluster.

[0031]

[0032] Scheme 1. Facile synthesis of atomically precise CdTe nanoclusters by combining a precise Cd(II)-thiolate complex from coordination synthesis and an accessible phosphine-tellurium precursor from colloidal method (M, E, and L represent metal, chalcogen, and ligand, respectively). The above scheme can be extended to other II- VI semiconductor nanoclusters.

[0033] Metal (Ml Chalcogen ME Ligand

[0034] Zn • S • ZnS • ZnSe • ZnTe * Different thiolates ♦ Cd + • Se -> • CdS » CdSe * CdTe * Different phosphines

[0035]

[0036] P Hg • Te • HgS • HgSe • HgTe * Different amines * Different carboxylates * Different halides

[0037] Suitable phosphines useful in the synthesis methods may include, but are not limited to, PPh?, PEt3, PPi’3, PBU3, PEt2Ph, P(octyl)3, among others. Suitable thiolates useful in the synthesis methods may include, but are not limited to, SPh-fBu, SPh, SCH2PI1, SCFECFEPh, SCFEPh-fBu, SC6H4F, among others. Suitable amines may include, but are not limited to, tetramethylenediamine, NH2Bu, NH2Ph, NH2Ph-tBu, NH2CH2Ph, NH2CH2CH2PI1, NH2CH2Ph- / Bu. NH2C6H4F, among others. Suitable carboxylates may include, but are not limited to OOCPh. OOCPh-rBu, OOCCH2Ph, OOCCH2CH2Ph. OOCCH2Ph-rBu, OOCC6H4F, among others. Suitable halides may include F−, Cl−, Br−, and I−. Also, for the MxEyLzformula, x ranges from 10 to several hundreds, y is typically less than x, and z is equal to or more than (x-y)2. The relativeDocket No. 10457-627PC0

[0038] stoichiometry of the various nanoclusters with the MxEyLzformula can be tuned by temperature, reaction time, and the ratio of the three precursors.

[0039] Previous work has shown that Cd(II) salts often react with thiols to form tetrahedral-based [Cd4(SR)10]2−compound, where Cd and S atoms are arranged into adamantane-like cages similar to that shown in the zincblende lattice.35We selected 4-tert-butylbenzenethiol (TBBT-H) as the target ligand, considering its previous success in synthesizing various atomically precise metal nanoclusters,36though others can be implemented based on the teachings provided herein. Following the procedure by Dance et al,35Cd(acetate)2 was mixed with TBBT-H and EtsN in methanol. The resulting white precipitates were recrystallized in CH2CI2. Sc-XRD unveiled the product to be a coordination polymer, {[HNEt3][Cd4(TBBT)9] }n(Fig. 6). Each Cd4(TBBT)9 unit adopts the same tetrahedral structure described previously (Fig. lb),35but two of the corner thiolates are connected to the neighboring units, leading to the polymeric structure. The negative charge of each [Cd4(TBBT)9]−unit is balanced by a [HNEt3]+counterion.

[0040] Remarkably, when Cd4(TBBT)9 compound (1 mmol of Cd) was reacted with tributylphosphine tellurium (TePBu3, 0.75 mmol of Te) and triphenylphosphine (PPh3, 15 mmol) in octadecene at 150 °C for 10 minutes (Fig. la), a cluster species with a sharp absorption peak at 377 nm was observed in the reaction mixture (Fig. 1c, dashed line, see SI for details). The distinct peak indicates the formation of a magic-sized cluster. Colorless cubic crystals were obtained overnight by overlaying acetonitrile on top of the toluene solution of isolated clusters (Fig. 1c, insert). When the crystal was dissolved in toluene, the same peak at 377 nm was observed, suggesting the high purity of the generated cluster (Fig. 1c, solid line). Sc-XRD revealed the product as Cd32Te14(TBBT)36(PPh3)4. Its structure is homologous to the previously reported Cd32S14(SR)36L4clusters11−13and Cd32Se14(SeR)36L4clusters15−17. thus completing the missing link in the Cd32Ei4 cluster family (L = neutral ligand).

[0041] The Cd32Te14(TBBT)36(PPh3)4cluster has a cadmium-rich [Cd32Te14]36+core charge-balanced by 36 thiolates (RS ). The inorganic framework has a truncated tetrahedron shape, with a size of 1.9 nm (measured from two phosphorous tips, Fig. 2). The cluster can be dissected into three parts: (i) a Cd4Teio zincblende kernel (Fig. 2a); (ii) four facet-capping Cd6Te(SR)9flakes (Fig. 2b); and (iii) four Cd-P capping tips (Fig. 2c). The four flakes create open ‘clefts’ at tetrahedron edges (Fig. 2b).11 13In terms of bonding, all Cd atoms are tetrahedrally coordinated toDocket No. 10457-627PC0

[0042] Te atoms or surface ligands. The 10 kernel Te atoms also exhibit saturated tetrahedral bonding, but the remaining surface Te atoms are each coordinated to only three Cd atoms, leaving behind a dangling bond. All the thiolates form bridging bonds with Cd. The Cd-Te bonds, ranging from 2.75-2.77 A, are slightly shorter than the Cd-Te bond in the bulk lattice (2.80 A), while the Cd-S bonds of the surface thiolates (2.55-2.56 A) are slightly longer than the bulk Cd-S bond (2.52 A).

[0043] The Cd32Te14cluster can also be interpreted as a fragment of the zincblende lattice (Fig.

[0044] 3). All Cd atoms, except for the comer ones, follow the cubic-close packing (ABC) arrangement characteristic of the zincblende sublattice. The Cd28framework is derived from a six-layer Cd56tetrahedron (T6) by removing edge atoms (Fig. 3a). The tip AB layers are replaced with single Cd atoms with A-layer stacking symmetry (Fig.3a, blue), leading to a ‘wurtzite’ like twinning tip.13 15The anion lattice mirrors the cation lattice on a larger scale (Fig. 3b). Sulfur atoms from thiolate ligands also contribute to the packing. Together with Te atoms, the 50 anions form a truncated tetrahedron, which can be cropped from a seven-layer E84tetrahedron (T7, Fig. 3b). Additionally, the four P atoms from phosphine ligands occupy the wurtzite twinning positions (Fig. 3b, pink). The cation lattice is embedded within the anion lattice with an offset along the <111> direction (Fig. 3c). Interestingly, the Cd28framework is similar to the Au28kernel in an Au36(TBBT)24cluster.36This resemblance suggests that semiconductor cluster sublattices can adopt similar packing as metal clusters, despite their fundamentally different bonding structure.

[0045] While the Cd32Tei4 zincblende kernel is not chiral, the rotational stacking of ligands induces chirality on the cluster surface (Fig. 4). This is shown in the arrangement of six TBBT ligands, which form a hexagonal vortex on each tetrahedral (111) facet (Fig. 4a). We assign the cluster with counterclockwise ligand rotation as the left enantiomer (Fig. 4a, blue), while clockwise rotation corresponds to the right enantiomer (Fig.4a, red). A similar rotational packing is observed at each tetrahedron tip, involving one PPI13 and three TBBT ligands (Fig. 4b). The ligand packing reduces the cluster’s symmetry from the achiral Ta point group of the inorganic core to the chiral T point group of the entire cluster. Such ligand-packing-induced chirality is frequently observed in atomically precise clusters, such as the pentagonal vortex in the Au246(SPhCH3)80cluster37and square swirl in the Au133(TBBT)52cluster.38These ligand patterns are stabilized by numerous intermolecular C-H©©©7t interactions.37Note that this surface-induced chirality differs from the core-based chirality observed in the Cd26Se17I18(PPr3)10cluster,Docket No. 10457-627PC0

[0046] where chirality arises from twisted Cd-Se bonds.39These atomic structures demonstrate the diverse origins of chirality in semiconductor nanomaterials.40 42The left and right isomers are crystallized as a 1:1 racemic mixture. Unlike typical racemic crystals, where enantiomers are related by symmetry operations of the space group, the two Cd32Te14isomers are crystallographically independent, leading to a rare crystal structure coined as the ‘kryptoracemate’,43

[0047] Another unique feature of the Cd32Te14clusters is their assembled into a highly ordered, atomically coherent body-centered-cubic (BCC) superlattice (Fig. 5). This is manifested in the alignment of the atomic (100) planes of the cluster lattice with the (100) planes of the crystal superlattice (Fig. 5a). A similar alignment is observed for the atomic and superlattice (111) planes (Fig.5b). Although the inorganic core has a tetrahedral shape, the overall cluster is nearly spherical due to the symmetric distribution of hexagonal and triangular ligand patches (Fig. 4c, d). Each cluster connects to eight nearest neighbors of opposite chirality (Fig. 5c). This directional intercluster interaction is enabled by a single type of ‘bond’ between the tip PPI13 ligands of one cluster and the facet thiolate ligands of another cluster (Fig. 5d). In this way, the hexagonal vortex and the unsaturated Te atom beneath it are shielded by the PPh3ligand of a neighboring cluster. In turn, the PPh3ligand is compressed and flattened due to the intercluster interaction. Since each tetrahedron has four tips and four facets, each cluster can connect to eight clusters via tip-facet interactions. This leads to a BCC superlattice reminiscent of that formed by colloidal nanocrystals.44 46

[0048] Powder XRD pattern of the Cd32Te14cluster shows two broad peaks centered around 25° and 42° (Fig. 7). The experimental pattern matches well with the simulated pattern derived from the resolved cluster structure. Compared to bulk zincblende CdTe, all diffraction peaks are shifted to higher angles, due to the large portion of shorter Cd-S bonds on the cluster surface. The Cd32Te14cluster exhibits a sharp absorption peak at 377 nm with a line width of 20 nm (175 meV). This contrasts with the homologous Cd32Si4 and Cd32Sei4 clusters, which show broad peaks at 358 nm and 373 nm, respectively.11,17,47The absorption peak of Cd32Te14is close to the ~370 nm peak observed in a CdTe MSC assigned to (CdTe)i3.30This similarity in peak positions suggests comparable nuclearity between the clusters (Te14vs Te13). The extinction coefficient (e) of the Cd32Tei4 cluster at 377 nm is 1.0 x 105M1cm1in toluene, comparable to that of Cd32S14(SPh)36(DMF)4(8.5 x 104in THF) and Cd32Se14(SePh)36(PPh3)4(5.2 x 104inDocket No. 10457-627PC0

[0049] acetonitrile).11 19,47Like other members of this family, as well as most atomically precise IT- VI and III-V clusters,39’48’49the CdszTci 4 cluster exhibits no photoluminescence at room temperature (Fig.

[0050] 8). The absence of emission in these clusters is often attributed to the dark states from undercoordinated surface chalcogenides or to fast nonradiative relaxation caused by coupling between core exciton transitions and surface ligand vibrations.39,48’49Note that aggregation of the clusters to larger species can sometimes trigger emissions, as shown in our previous work on CdTe MSCs.31

[0051] In conclusion, our work bridges the gaps between conventional coordination and colloidal synthesis, enabling the facile synthesis of an atomically precise CdTe nanocluster. The obtained cluster fills the missing links in the CdE nanocluster family, precisely correlates the magic size with atomic structure, and unveils the highly ordered, hierarchical assemblies at atomic, molecular, and cluster levels. The method reported here is expected to provide a facile approach to access other atomically precise semiconductor nanoclusters for further atomic engineering, thus enhancing their existing applications or enabling emergent ones.

[0052] Exemplary Embodiments

[0053] In view of the teachings herein, one disclosed embodiment pertains to a method for producing an atomically precise nanocluster, wherein the atomically precise nanocluster is produced by reacting a metal-ligand coordination complex and a chalcogenide precursor used in colloidal synthesis, according to the following M-L + E-PR3 -> MxEyLzwherein M is selected from Cd, Zn or Hg; E is selected from Te, S, and / or Se; L is selected from a thiolate and / or phosphine, and R is selected from alkyl, alkenyl, and / or aryl group, and wherein x is 32, y is 14 and z is 36. In a specific embodiment, M-L is Cd4(TBBT)9. In another specific embodiment, E-PR3 is TePBus. According to one specific example, MxEyLzis Cd32Tei4(TBBT)36(PPh3)4.

[0054] According to further embodiments, provided is a nanocluster comprising the formula MxEyLz wherein M is selected from Cd, Zn or Hg; E is selected from Te, S, or S; L is selected from a thiolate, carboxylate, halide, amine, and / or phosphine, and R is selected from alkyl, alkenyl, or aryl group, and wherein x is 32, y is 14 and z is 36. In one example, MxEyLzmay be Cd32Tei4(TBBT)36(PPh3)4.Docket No. 10457-627PC0

[0055] A further method relates to a more specific synthesis protocol for synthesizing Cd32Tei4(TBBT)36(PPh3)4, that involves following reaction:

[0056] Cd4(TBBT)9+ TePBu3+ PPh3* Cd32Te14(TBBT)36(PPh3)4

[0057]

[0058] Other embodiments pertain to a solar cell comprising a plurality of nanoclusters as described herein. A further embodiment pertains to a light-emitting diode comprising a plurality of nanoclusters as described herein.

[0059] EXAMPLES

[0060] Chemicals

[0061] Cadmium acetate dihydrate (Cd(OAc)2- 2H2O, Alfa-Aesar, 99.99%), triethylamine (EtsN, Oakwood Chemicals, 99.99%), 4-tert-butylbenzene thiol (TBBT-H, Fisher Scientific, 97%), granular tellurium (Te, Sigma- Aldrich, 99.99%), triphenylphosphine (PPI13, Sigma- Aldrich, 99%), tri-n-butylphosphine (PBU3, Sigma-Aldrich, 97%), methanol (MeOH, Fisher Scientific, 99.8%), toluene (Sigma- Aldrich, >99.0%), acetonitrile (MeCN, Sigma-Aldrich, 99.8%), dichloromethane (CH2CI2, Fisher Scientific, 99.5%), and octadecene (ODE, Sigma-Aldrich, 90%) were used as received.

[0062] [HNEt3][Cd4(TBBT)9] compound. The synthesis was adapted from the procedure reported by Dance et al.29Cd(OAc)2·2H2O (1.4 g, 5.3 mmol) was mixed with 2 mL of MeOH under N2 using standard Schlenk technique. Et3N (1.681 mL, 12.06 mmol) and TBBT-H (2.087 mL, 12.3 mmol) were mixed in 8 mL of methanol and injected at room temperature. The clear colorless reaction mixture was stirred for 20 minutes, slowly turning turbid white over time. The white precipitate was washed with excess MeOH (~15 mL) and centrifuged at 6000 rpm for 5 min. The supernatant was decanted, and the precipitate was collected and sonicated in excess MeOH. The washing cycle was repeated twice. The final white solid was allowed to dry, with a typical yield of ~2.1 g (78% based on Cd, MW = 2039.17 g / mol). After dissolving the white solid in excess CH2CI2, colorless needle-like crystals formed overnight.Docket No. 10457-627PC0

[0063] TePBu3 stock solution (2.62 M of Te): TePBu3 was prepared in a N2-filled glovebox by stirring Te (0.5104 g, 4 mmol) in PBu3 (1.526 mL, 6 mmol) at 120 °C. Tellurium dissolved within an hour to form a yellow solution. The solution was cooled and stored at room temperature.

[0064] Cd32Te14(TBBT)36(PPh3)4cluster: In a typical synthesis, [HNEt3][Cd4(TBBT)9] complex (0.51 g, 1 mmol Cd) and PPI13 (3.9 g, 15 mmol) were mixed with 5.9 mL of ODE and stirred at 150 °C under N2 atmosphere to form a white cloudy suspension. TePBu3 stock solution (286.2 μL, containing 0.75 mmol Te and 1.125 mmol PBu3) mixed with 0.1 mL of dry ODE was removed from the glovebox and injected into the reaction flask. The cloudy yellow suspension became clear as the Cd-thiolate complex quickly dissolved during the reaction. The reaction mixture was stirred for 10 minutes, and then cooled to room temperature in a water bath. The clear yellow solution became opaque and yellowish white. The reaction mixture was combined with 15 mL of MeCN, transferred to the freezer, and stored overnight. The suspension was then centrifuged for 5 minutes at 6000 rpm. The clear light-yellow supernatant was decanted, and the yellowish- white precipitate was collected. The precipitate was dispersed in ~ 1 mL of toluene, and 6 mL of MeCN was added, followed by centrifugation at 6000 rpm for 5 min. The washing cycle was repeated twice. The final precipitate was dried under vacuum, yielding 265.8 mg of yellowish-white powder (-40% yield based on Te). To crystallize the product, a concentrated toluene solution of clusters was made by suspending the powder (-209 mg) in -6 mL of toluene, followed by centrifugation at 6000 rpm for 5 minutes (the solubility of the clusters in toluene is about 40 mg / mL). 6 mL of the yellow supernatant was filtered into a vial. 6 mL of MeCN was also filtered and carefully layered on top of the toluene solution. Clear colorless cubic crystals formed overnight at ambient temperature. The crystals were dried, producing an average weight of 182.5 mg (27.5% yield based on Te, MW = 12,382.58 g / mol).

[0065] Additional Embodiments: Larger Atomically Precise Cadmium Telluride Nanoclusters In additional embodiments, atomically precise cadmium telluride nanoclusters having a larger nuclearity and a distinct three-dimensional morphology are provided, In one exemplary embodiment, a charge-neutral cadmium telluride nanocluster having the formula Cd75Te42(TBBT)66(PBu3)4is obtained. The nanocluster is atomically precise, isolable, and crystallizable, and exhibits a well-defined inorganic framework.

[0066]

[0067] Docket No. 10457-627PC0

[0068] Some embodiments include larger nanoclusters that may be synthesized using a reaction platform similar to that employed for the formation of smaller, Cd32Te14-based clusters described above. Specifically, both classes of clusters are accessed from cadmium thiolate coordination complexes and phosphine- tellurium precursors, with the resulting cluster nuclearity and structure being governed by reaction conditions.

[0069] Under modified reaction conditions, smaller atomically precise cadmium telluride clusters may undergo continued growth and structural reorganization to form larger clusters. As described herein, increasing reaction temperature, extending reaction time, and reducing or removing growth-inhibiting ligands may shift the reaction pathway from formation of smaller clusters toward higher-nuclearity species. In this manner, the Cd75Te42nanocluster may be accessed within the same general synthetic framework as Cd32Te14clusters, while occupying a different region of the reaction parameter space.

[0070] Referring to Fig. 9a, a representative reaction scheme for synthesis of the Cd75Te42nanocluster is illustrated. In one embodiment, a cadmium thiolate coordination complex is combined with a phosphine-tellurium precursor in a high-boiling solvent and heated under an inert atmosphere. Relative to conditions favoring formation of Cd32Te14clusters, the reaction is conducted at a higher temperature and for a longer duration, and growth-inhibiting ligands such as triphenylphosphine are reduced or omitted. As illustrated in Fig.10, monitoring the reaction under these modified conditions reveals the gradual emergence of new optical absorption features associated with formation of a larger cadmium telluride species. Over time, absorption features characteristic of smaller clusters diminish as features corresponding to the Cd75Te42nanocluster increase in intensity.

[0071] In further embodiments, the reaction may be carried out using a heat-up method rather than hot injection, as illustrated in Fig. 12. In this approach, the reaction mixture is gradually heated to the target temperature, allowing more controlled growth of larger clusters. As further shown in this figure, the amount of cadmium precursor may be adjusted to promote formation of the Cd75Te42nanocluster while suppressing decomposition at elevated temperatures. The cadmium precursor may also serve to replace phosphine ligands and stabilize the growing cluster framework.

[0072] Removal or reduction of additional phosphine ligands may further promote formation of the larger Cd75Te42species in some embodiments. As shown by Fig. 11, reactions conducted withDocket No. 10457-627PC0

[0073] reduced phosphine content exhibit increased formation of the larger cluster and improved stability at elevated temperatures, relative to reactions carried out in the presence of excess phosphine.

[0074] Following completion of the reaction, the Cd75Te42nanocluster may be isolated and purified using solvent-induced precipitation and centrifugation techniques similar to those described above for smaller atomically precise cadmium telluride clusters. The purified nanocluster may be crystallized from suitable solvent systems to yield discrete crystals suitable for further characterization.

[0075] Structure

[0076] As shown in Fig. 13, the Cd75Te42nanocluster adopts a tetrapodal architecture comprising a central tetrahedral core and four tetrahedral arms extending from the faces of the core. The overall shape of the cluster resembles a tetrapod, with four protruding arms arranged symmetrically around the core, analogous in form to tetrapod-shaped cadmium telluride nanostructures observed in colloidal systems, while maintaining atomic precision.

[0077] Referring to Fig. 13a, the overall tetrapodal morphology of the Cd75Te42nanocluster is illustrated. The cluster may be described as having a core-arm architecture, in which a cadmium-rich tetrahedral core provides a structural scaffold for attachment of the four arms. As shown in Fig. 13b, the tetrahedral core comprises a zinc blende-derived cadmium telluride framework that defines the central region of the cluster. The size and geometry of the core are well-defined and provide symmetry for attachment of the arms. Further, and referring to Fig. 13c, each arm comprises a tetrahedral cadmium telluride subunit coordinated by thiolate and phosphine ligands. The arms are chalcogen-rich relative to the core and are attached to the faces of the core tetrahedron. When assembled, the four arms and core together form the complete Cd75Te42(TBBT)66(PBu3)4structure, as shown in Fig.13d (carbon and hydrogen atoms are omitted for clarity).Docket No. 10457-627PC0

[0078] Additional Embodiments: Icosahedral Cd14Te13Nanoclusters

[0079] In further embodiments, atomically precise cadmium telluride nanoclusters having a nonbulk-derived atomic framework may be synthesized through a reaction pathway distinct from the zincblende-derived clusters described above.

[0080] One representative synthesis route is illustrated in Fig. 14a, in which a cadmium halideamine coordination complex is reacted with a phosphine-tellurium precursor under mild conditions to produce a discrete Cd14Te13nanocluster. In one embodiment, cadmium chloride is first coordinated with a neutral bidentate amine ligand, such as tetramethylethylenediamine (tmeda), to form a soluble cadmium coordination complex. A phosphine tellurium compound (TePR3) is then introduced into the reaction mixture. In some embodiments, a secondary phosphine is additionally present to promote conversion of the tellurium precursor. The reaction may proceed at or near room temperature and does not require elevated temperatures, high-boiling solvents, or injection.

[0081] As shown in Fig. 14b, the resulting reaction mixture exhibits a sharp and well-defined optical absorption feature centered at approximately 370 nm. This precise and narrow absorption peak is indicative of the formation of a discrete single- sized cadmium telluride nanocluster rather than a distribution of growing nanocrystals. The reproducibility and sharpness of the absorption feature are consistent with the formation of a magic-sized atomically precise cluster. Further, as shown in Fig. 14c, single-crystal X-ray diffraction analysis reveals the product to be a Cd14Te13Cl2(tmeda)6nanocluster. The cluster comprises a discrete molecular entity with a defined cadmium-to-tellurium ratio and defined cadmium coordination environments, which is consistent with the observed optical absorption features.

[0082] Formation of the Cd14Te13nanocluster may be further corroborated by time-dependent monitoring of the reaction, as illustrated in Figs. 15a-15c. UV spectra collected at different reaction times (Fig. 15b) show rapid emergence of the absorption feature at approximately 370 nm without substantial peak shifting or broadening, which is consistent with formation of a singlesized cluster. The visual appearance of the reaction mixtures shown in Fig. 15c is further consistent with this behavior.

[0083] StructureDocket No. 10457-627PC0

[0084] Structural analysis of the Cd14Te13nanocluster reveals an inorganic framework distinct from bulk-derived cadmium telluride lattices. Fig. 16a shows a cluster comprising a Te13anion framework having an icosahedral geometry, including one tellurium atom positioned at the center of the framework and twelve tellurium atoms forming an outer shell arranged in an icosahedral configuration.

[0085] As shown in Fig. 16b, cadmium atoms occupy multiple distinct positions relative to the Te13framework. In one embodiment, four cadmium atoms are located within the icosahedral framework, each coordinated to the central tellurium atom and three shell tellurium atoms. Additional cadmium atoms are positioned at triangular faces of the icosahedron, with certain cadmium atoms forming bonds with the central tellurium atoms and others forming bonds with chloride ligands. Further cadmium atoms are located along edge positions of the Te13framework and bridge pairs of tellurium atoms while also coordinating to neutral amine ligands. Additionally, the coordination environments of the different cadmium sites are illustrated in Fig. 16c. Each cadmium atom exhibits a generally tetrahedral coordination environment involving combinations of tellurium, halide, and nitrogen atoms. The cluster thus forms a discrete molecular entity with multiple cadmium coordination motifs within a single, atomically precise inorganic framework.

[0086] Chirality of Cd14Te13Nanocluster

[0087] Fig. 17 illustrates the chirality of the Cd14Te13nanocluster. Unlike ligand-packing-induced chirality observed in other cadmium telluride nanoclusters, the chirality of the Cd14Te13cluster is associated with the inorganic core. A pair of left and right isomers is identified within the crystallographic unit cell, as shown in Fig. 17a.

[0088] The enantiomers may be distinguished by the relative arrangement of cadmium atoms within the cluster. Fig. 17b demonstrates when the cluster is oriented with its principal rotational axis positioned vertically and the chloride ligands located at the bottom, the left-handed isomer exhibits a left-leaning arrangement of three cadmium atoms, while the right-handed isomer exhibits a right-leaning arrangement. The chirality arises from the geometric arrangement of cadmium atoms within the icosahedral tellurium framework, as reflected in the tetrahedral cadmium-tellurium bonding observed within the clusterDocket No. 10457-627PC0

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Claims

Docket No. 10457-627PC0CLAIMSWhat is claimed is:

1. A method for producing anatomically precise nanocluster, wherein the atomically precise nanocluster is produced by reacting a coordination metal-ligand complex and a phosphine-chalcogenide colloid precursor, according to the following M-L + E-PR3 - MxEyLzwherein M is selected from Cd. Zn, Hg, Cu, or Ag; E is selected from Te, S, and / or Se; L is selected from a thiolate, carboxylate, halide, and / or phosphine, and R is selected from alkyl, alkenyl, and / or aryl group, and wherein x is 10 to several hundreds, y is less than of x and z is equal or more than (x-y)2.

2. The method of claim 1, wherein M-L is Cd4(TBBT)9.

3. The method of claim 1, wherein E-PR3 is TePBu3.

4. The method of claim 1, wherein MxEyLzis Cd32Tei4(TBBT)36(PPh3)4.

5. A nanocluster comprising the formula MxEyLzwherein M is selected from Cd, Zn or Hg; E is selected from Te. S, or S; L is selected from a thiolate, carboxylate, halide, and / or phosphine, and R is selected from alkyl, alkenyl, or aryl group, and wherein x is 10 to several hundreds, y is less than of x and z is equal or more than (x-y)2, optionally x is 32, y is 14 and z is 36 (thiolate) + 4 (phosphine).

6. The nanocluster of claim 5, wherein MxEyLzis Cd32Tei4(TBBT)36(PPh3)4.

7. A method for synthesizing Cd32Tei4(TBBT)36(PPh3)4, the method comprising the following reaction:Docket No. 10457-627PC0Cd4(TBBT)9+ TePBu3+ PPh3Cd32Te14(TBBT)36(PPh3)48. The method of claim 1, wherein x is greater than 32.

9. The method of claim 8. wherein the nanocluster is formed under conditions that promote continued growth of a smaller atomically precise nanocluster.

10. The method of claim 9, wherein the conditions comprise at least one of increased reaction temperature, extended reaction time, or reduced concentration of a growth-inhibiting phosphine ligand.

11. The nanocluster of claim 5, wherein x is between 50 and 100.

12. The nanocluster of claim 11, wherein the nanocluster comprises a central tetrahedral core and a plurality of cadmium telluride arms extending from faces of the core.

13. The nanocluster of claim 12, wherein the nanocluster has a tetrapodal morphology.

14. The nanocluster of claim 15, wherein the nanocluster comprises the formula Cd75Te42(TBBT)66(PBu3)4.

15. A method for producing an atomically precise nanocluster, comprising reacting a coordination complex and a phosphine-chalcogen precursor, according to the following M-L + E-PR3 MxEyLz wherein M is selected from Cd, Zn, or Hg; E is selected from Te, S, or Se; L is selected from a halide, an amine, or a combination thereof; R is selected from alkyl, alkenyl, or aryl; x is from 10-100; y is less than of x; and z is determined by charge balance.

16. The method of claim 15, wherein the nanocluster comprises the formula Cd Teu.

17. The method of claim 16, wherein the nanocluster comprises halide ligands and neutral amine ligands coordinated to cadmium atoms.

18. The method of claim 17, wherein the neutral amine ligand comprises a bidentate amine.

19. The method of claim 15, wherein the reaction reacting is performed at an ambient or a near-ambient temperature.Docket No. 10457-627PC020. The method of claim 15, wherein the resulting nanocluster is chiral due to the arrangement of cadmium atoms within the tellurium framework.

21. A solar cell comprising a plurality of nanoclusters according to any of claims 5-6, 13-16, or 18-22.

22. A light-emitting diode comprising a plurality of nanoclusters according to any of claims 5-6, 11-14, or 16-20.

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