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. 2026 Jan 15;148(4):4579–4587. doi: 10.1021/jacs.5c20164

A Golden Fullerene Encapsulating Schmid Gold

Peiyao Pan †, Sami Malola ‡, Rui Zhao §, Wentao Huang †, Emmi Pohjolainen ‡, María Francisca Matus ‡, Meng Zhou §,*, Xi Kang †,∥,*, Hannu Häkkinen ‡,*, Manzhou Zhu †,∥,*
PMCID: PMC12879730  PMID: 41538406

Abstract

Since its first synthesis in 1981, determining the structure of the “Schmid gold”initially determined as a Au55(PPh3)12Cl6 clusterhas remained a big challenge. In this study, fluorine chemistry is exploited to stabilize the largest structurally resolved gold nanocluster stabilized by phosphine ligands, Au75(P­(C6H4-4-CF3)3)20Cl12, with which the atomically precise structure of the Schmid gold was optimized. The Au75 nanocluster displays a Russian doll-like shell-by-shell configuration of Au13@Au42@Au20@Cl12@(PR)20. The first two shells resemble the metallic core of the Schmid gold, which is encapsulated by an Au20 shell showcasing a fullerene-like topology. Consequently, the structure of the Au75 nanocluster is referred to as the “golden fullerene encapsulating Schmid gold”. The geometric constraints of Au20@Au55 dominate over size effects in dictating photodynamics in the Au75 nanocluster. Density functional theory analysis revealed the superatomic character of the fluorinated Au75 nanocluster and molecular dynamics simulations up to three microsecond time scale confirmed the role of fluorine chemistry in stabilizing its structure. This study demonstrates the potential to stabilize large phosphine-protected gold nanoclusters by fluorine chemistry opening doors to understanding their functionality in catalysis and biological applications.

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Introduction

Gold nanoparticles have garnered significant attention due to their unique electronic, optical, and catalytic properties. − Since Faraday reported colloidal gold in 1857, the precise synthesis and atomic-level structural determination of these nanomaterials have remained at the forefront of nanoscience. A key challenge in their development lies in the stability control of ultrasmall-sized (2 nm or smaller) nanoparticles which, historically, has been achieved with either phosphine or thiol chemistry. In 1994, Brust, Schiffrin and collaborators published a recipe to stabilize small gold nanoparticles with thiols, which has led to numerous variants of the so-called “Brust-Schiffrin” synthesis yielding hundreds of various atomically precise thiolate-protected noble metal clusters. ,− In contrast, the roots of gold-phosphine chemistry go back to 1969 when McPartlin, Mason and Malatesta discovered the “undecagold” Au11 cluster stabilized with seven phosphine and three electronegative ligands. Although phosphine chemistry proved initially successful for achieving atom-precise structural characterization of very small gold clusters, the largest crystallographically resolved phosphine-stabilized cluster to date is still Au39(PPh3)14Cl6 from 1992 while thiol chemistry has yielded very large accurately resolved clusters up to size Au279.

Among the phosphine-stabilized gold clusters, the “Schmid gold” with an initial formula of Au55(PPh3)12Cl6 has received widespread attention since 1981 due to its unique electronic properties and promising applications in nanoelectronics, catalysis and biology, − leading even to commercial bioimaging products. Despite its widespread interest, the atomically precise structure of the “Schmid gold” remains elusive. Significant effortssuch as extended X-ray absorption fine structure, powder X-ray diffraction, high-resolution transmission electron microscopy, X-ray scattering, analytical ultracentrifugation, aberration-corrected scanning transmission electron microscopy, and theoretical calculationshave been made to determine the possible structure of the “Schmid gold”. As a result, various structural forms have been suggested, including cuboctahedron, icosahedron, hybrid icosahedron-cuboctahedron, and even amorphous structure. −

It has been acknowledged that the relatively weak phosphine-gold bond is the culprit for the failure to grow large enough, good quality crystals for definite structural determinations of the “Schmid gold”. Recently, fluorochemical modification has been exploited to address the crystallization challenges in several research fields. − The fluorine chemistry improves the crystallizability of nanomaterials from two key aspects: (i) enhancing structural rigidity through the replacement of hydrogen with fluorine at the molecule level; (ii) promoting long-range ordered arrangements of molecules through supramolecular fluorine–fluorine interactions. In this context, we perceived a promising opportunity to stabilize and crystallize metal nanoclusters with inaccessible structures.

Here, with fluorination of triphenylphosphine ligands, we report the largest structurally resolved phosphine-protected gold nanocluster to date, Au75(P­(C6H4-4-CF3)3)20Cl12. The Au75 nanocluster follows a Russian doll-like shell-by-shell configuration of Au13@Au42@Au20@Cl12@(PR)20, wherein the first and second shells enlighten the metallic kernel of the “Schmid gold” and the third shell showcases a fullerene-like topology, similar to the smallest fullerene C20. Strong F-initiated interactions are observed at both molecule and supramolecular levels, endowing the Au75 nanocluster with strong stability and good crystallinity. Transient absorption analyses indicate that Au75 exhibits unique excited-state dynamics that transcend conventional size classifications. Density functional theory calculations shed light onto the electronic structure of this novel cluster as well as onto the stabilizing role of the C20-symmetric [Au­(P­(C6H4-4-CF3)3)]20 mantle around the Au55 kernel, which is also demonstrated via extensive molecular dynamics simulations of the cluster in solvent using a dedicated classical force field developed in this work. While shedding light to the long-standing controversy of “Schmid gold”, our work opens doors for synthetic control and characterization of large phosphine-stabilized gold nanoclusters via fluorination chemistry (Figure ).

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Previous efforts (A) and this work (B) in determining the structure of “Schmid gold”.

Results and Discussion

The Au75(P­(C6H4-4-CF3)3)20Cl12 nanocluster, featuring fluorinated phosphine ligands, is synthesized using a one-pot method. The process involved the sequential addition of HAuCl4, P­(C6H4-4-CF3)3, and cyclohexyl mercaptan to a mixed solvent of methanol and dichloromethane. After stirring for 30 min, a freshly prepared aqueous solution of NaBH4 was added dropwise. The reaction continued for 10 h, after which centrifugation was employed to remove insoluble impurities. The resulting supernatant was evaporated to dryness, yielding a green solid that was then washed with n-hexane, resulting in the preparation of the Au75 nanocluster. High-quality crystals of the Au75 nanocluster were obtained by diffusing n-hexane into the dichloromethane solution containing the nanocluster over 1 week (Figure S1). The cyclohexyl mercaptan is crucial for the formation of the Au75 nanocluster; its absence results in the generation of an undesired product, Au11(P­(C6H4-4-CF3)3)7Cl3 (Figure S2). In addition, the presence of fluorinated phosphine ligands is essential for synthesizing Au75(P­(C6H4-4-CF3)3)20Cl12, as nonfluorinated PPh3 ligands lead to the formation of the smaller Au25(PPh3)10(SC6H11)5Cl2 nanocluster (Figure S2). In this context, the involvement of fluorine chemistry is beneficial for the successful synthesis of the Au75 nanocluster, which, to the best of our knowledge, is the largest structurally resolved gold nanocluster stabilized by phosphine ligands (Figure S3).

X-ray photoelectron spectroscopy identifies an Au 4f7/2 binding energy of 83.8 eV, indicating that the gold atoms in the Au75 nanocluster primarily exist in the Au0 oxidation state (Figure S4). Thermogravimetric analysis reveals an experimental weight loss of 21.63% (Figure S5), closely matching the theoretical value of 21.55% derived from chemical formula analysis. The UV–vis spectrum of Au75 in methanol reveals five prominent optical absorption bands at 320, 345, 385, 420, 475, 600, and 715 nm (Figure S6), and the unattenuated absorptions of the nanocluster demonstrate its structural robustness and high stability (Figure S7). In addition, we compared the 19F nuclear magnetic resonance (19F NMR) spectroscopy of the P­(C6H5-4-CF3)3 ligand and fluorine-containing nanoclusters (Au75 and Au11). As shown in Figure S8, 19F NMR spectra of the three samples are located very closely around −64 ppm, demonstrating that the −CF3 groups on the nanocluster surface maintain an almost unchanged chemical environment. Indeed, for the spherical Au75 cluster structure, all P­(C6H5-4-CF3)3 ligands follow the same Au–P interactions.

Single-crystal X-ray diffraction analysis reveals that the Au75 cluster molecules crystallize in the trigonal space group R-3 with an ABAB stacking arrangement (Figures S9 and S10; Table S1), together with Cl– counterions with a molar ratio of 1:2 (cluster:counterion) in the crystalline lattice. A detailed molecular-level analysis reveals that the cluster comprised 75 gold atoms, 20 P­(C6H4-4-CF3)3 ligands, and 12 Cl ligands, resulting in its overall formula of Au75(P­(C6H4-4-CF3)3)20Cl12 (Figure S11). As illustrated in Figure , the Au75 nanocluster adopts a Russian doll-like shell-by-shell configuration: Au13@Au42@Au20@Cl12@(PR)20. The innermost core of the Au75 nanocluster is an Au13 icosahedron, surrounded by an Au42 McKay icosahedral shell (Figure A,B). The first two shells of the Au75 nanocluster form an Au55 kernel (Figure C), aligning with the nuclei number of the well-known “Schmid gold”. The axial thickness of the Au55 kernel is 1.10 nm, while the equatorial diameter is 1.23 nm (Figure S12). Furthermore, the Au55 kernel is fully encapsulated by 20 peripheral Au atoms, which are arranged in a configuration resembling the smallest fullerene, C20; in this context, this Au20 shell is referred to as the “golden fullerene” (Figure D,E). Then, the fourth and fifth layers of the Au75 cluster consist of 12 chlorine ligands arranged in an icosahedral configuration and 20 phosphine ligands configured similarly to a C20 fullerene, respectively, providing an all-around protection for the Au75 metallic kernel (Figure F–H). The average Au–Au bond lengths in Au13 and Au42 shells are 2.791 and 2.916 Å, respectively (Table S4). The Au–Au distances between the Au55 core and the golden fullerene Au20 shell range from 2.718 to 2.769 Å (Table S5). In addition, the average bond lengths at the interface between the metallic kernel and the organic ligand layer are determined to be 2.306 Å for Au–Cl bonds and 2.311 Å for Au–P bonds.

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Structure anatomy of the Au75 nanocluster. (A) The first shell (labeled in blue): Au13 Mackay icosahedron. (B) The second shell (labeled in yellow): Au42 Mackay icosahedron. (C) The Au55 core. (D) The third shell (labeled in pink): Au20 shell with a C20 fullerene-like configuration. (E) Metallic structure of the Au75 nanocluster. (F) The fourth shell (labeled in green): Cl12 icosahedral shell. (G) The fifth shell (labeled in red): (PR)20 shell with a C20 fullerene-like configuration. (H) Russian doll-like shell-by-shell configuration of the Au75 nanocluster.

A detailed structural analysis is then conducted to elucidate how the golden fullerene Au20 shell stabilized the Au55 kernel. Considering that the Au55 kernel contains an inner Au13 icosahedral core and an outer Au42 Mackay icosahedron shell, we mainly focus on the interactions between the golden fullerene Au20 shell and the Au42 shell. The Au42 Mackay icosahedron comprises 12 vertexes, 30 edges, and 20 faces. As depicted in Figure A,B, the 42 shell atoms are classified into two groups: 12 Au atoms located at the vertices and 30 Au atoms along the edges of the Mackay icosahedron. First, each gold atom at vertex positions is positioned at the center of a five-membered Au5 face from the golden fullerene Au20 shell, corresponding to 12 faces of this fullerene-like shell (Figure C). The average bond angle of the Au1@Au5 ring is 60.98°. In this context, although the overall arrangement displays C 5 symmetry, the sum of angles (304.9°) indicates that the Au12 vertex of the Au55 kernel slightly protrudes above the golden fullerene Au20 shell (Figure D). In addition, every three adjacent Au atoms from the edges of the Mackay icosahedron form a tetrahedron together with an Au atom from the golden fullerene Au20 shell (Figure E). These 20 generated tetrahedra correspond perfectly to the 20 faces of the Mackay icosahedron, fully encapsulating and stabilizing the Au55 kernel (Figure F). The average Au–Au bond length within these tetrahedra is 2.739 Å, much shorter than the Au–Au distances within Au13 and Au42 shells, suggesting robust interactions between the golden fullerene Au20 shell and its stabilized Au55 kernel.

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Interactions between the Au20 golden fullerenes and the Au42 shell. (A) 12 Au atoms locating at vertexes of the icosahedral Au42 shell. (B) Each Au atom in Au12 situating in the central position of the pentagon from the fullerene-like Au20. (C) A typical golden pentagon. (D) 30 Au atoms locating on edges of the icosahedral Au42 shell. (E) Every three adjacent Au atoms in Au30 forming a tetrahedron with an Au atom from the fullerene-like Au20. (F) Space-filling form of the metallic kernel.

Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) in positive mode reveals two dominant signals at m/z of 12261.59 and 8331.80 Da, corresponding to the [Au75(P­(C6H4-4-CF3)3)20Cl12]2+ and its dissociated peak [Au55(P­(C6H4-4-CF3)3)12Cl6Na]2+, respectively (Figure S13). First, the +2-charge state of the Au75 nanocluster matches the presence of twice the molar quantity of Cl– of cluster molecules in the crystal lattice. In this context, the nominal electron count of the Au75 nanocluster is determined as 61, i.e., 75 (Au) – 12 (Cl) – 2 (positive charge) = 61e, suggesting the presence of an unpaired electron within the cluster framework. Electron paramagnetic resonance (EPR) further confirms an open-shell electronic configuration for the Au75 nanocluster, displaying a distinct signal with a single local maximum and minimum at S = 1/2 (g = 1.4078, 2.0314) (Figure S14). Second, the detected [Au55(P­(C6H4-4-CF3)3)12Cl6Na]2+ molecule is anchored by a Na+ in the mass detection environment, leading to the direct observation of the molecule-ion mass signal of the fluorinated “Schmid gold”, [Au55(P­(C6H4-4-CF3)3)12Cl6]+.

The structural analysis further indicates that the fluorinated ligands introduce rich F···F and H···F interactions at both the Au75 nanocluster surface and the intercluster interface (Figure S15). In comparison to the PPh3 ligands, the fluorinated ligands enhance the cluster stability by improving interactions between the gold kernel and the ligand shell, facilitating the detection of the Au75 nanocluster in mass spectrometry. Furthermore, the abundance of F-initiated interactions can be thought to contribute to greater structural rigidity at the molecular level and promote the long-range ordered arrangement of cluster molecules within the crystal lattice, endowing the Au75 nanocluster with good crystallinity. We performed the analysis for the solvent-accessible surface area SASA (see Supporting Information for technical details) for the Au75(P­(C6H4-4-CF3)3)20Cl12 cluster, its hypothetical counterpart Au75(PPh3)20Cl12, and a hypothetical icosahedral model for the fluorinated “Schmid cluster” Au55(P­(C6H4-4-CF3)3)12Cl6 (for visualization of their full atomic structures, see Figure S16). The larger the value of SASA is, the more accessible the gold core surface is for small molecules to penetrate from solvent, hence a zero SASA value means a fully sterically protected metal–ligand interface. By using a typical “small molecule size” of 1.4 Å, we found that both Au75(P­(C6H4-4-CF3)3)20Cl12 and Au75(PPh3)20Cl12 clusters are fully sterically protected but the hypothetical fluorinated “Schmid cluster” has a large SASA value of 23.3 Å2.

We performed density functional theory (DFT) calculations to analyze the electronic structure and evaluate the optical absorption of [Au75(P­(C6H4-4-CF3)3)20Cl12]2+ (Figure A; for technical details of DFT calculations, Supporting Information). Figure B shows that the computed UV–vis absorption spectrum compares rather well with the measured data in its overall shape, reproducing a major experimental feature at 600 nm. We also computed the spectrum using a few other charge states of the cluster, including charges of −1, +3, and +5, but found out that the computed spectra did not match the experimental data well (Figure S17). This gives indirect support for the experimentally determined cluster charge of +2.

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(A) Visualization of the atomic structure of Au75(P­(C6H4-4-CF3)3)20Cl12 2+. Color labels: orange = Au; green = Cl; brown = P; gray = C; purple = F; white = H. (B) Computed and measured UV–vis spectra of the Au75 nanocluster. The computed spectrum is scaled to the experimental intensity at 600 nm. (C) Superatom-projected density of electron states PDOS. PDOS for spin-alpha states are shown in top and spin-beta states in the bottom panel. The electron shell closures at 58 and 92 are shown as well. (D) PDOS of the hypothetical fluorinated “Schmid cluster” Au55(P­(C6H4-4-CF3)3)12Cl6 +. The Fermi energy is at zero in (C) and (D).

Figure C,D compare the electronic density of states of Au75(P­(C6H4-4-CF3)3)20Cl12 2+ and hypothetical fluorinated “Schmid cluster” [Au55(P­(C6H4-4-CF3)3)12Cl6]+. The electronic states are projected to spherical harmonics centered at the clusters’ center of mass. One can see that Au75(P­(C6H4-4-CF3)3)20Cl12 2+ has narrow “bands” of electronic states in the frontier region with energies ranging from one eV below to about 2 eV above the Fermi energy. All these states are mainly localized in the gold core and follow a nice succession of expected angular momentum symmetries between 58 and 92 electron shell closing in the sequence: 1S2 1P6 1D10 2S2 1F14 2P6 1G18 (58e) 1H22 2D10 3S2 (92e) 1I26 2F14. Thus, the “superatom” electronic structure is well established in [Au75(P­(C6H4-4-CF3)3)20Cl12]2+. On the contrary, the electron shells from 1F to 3S are much more split and mixed in the hypothetical fluorinated “Schmid cluster” [Au55(P­(C6H4-4-CF3)3)12Cl6]+. We attribute the more shell-like electronic structure of [Au75(P­(C6H4-4-CF3)3)20Cl12]2+ to its stabilizing Au20(P­(C6H4-4-CF3)3)20 fullerene-like overlayer discussed above.

We studied the stabilizing effect of the overlayer with the fluorinated phosphine by calculating the theoretical detachment energy of one phosphine from the corresponding cluster in (i) Au75(P­(C6H4-4-CF3)3)20Cl12 cluster, (ii) its hypothetical counterpart Au75(PPh3)20Cl12, and (iii) a hypothetical icosahedral model for the fluorinated “Schmid cluster” Au55(P­(C6H4-4-CF3)3)12Cl6 (Figure S15), by using an improved electron–electron exchange-correlation functional (see Supporting Information) taking into account the van der Waals interactions in the ligand layer. The detachment energies for the three clusters are (i) 4.74 eV, (ii) 3.02 eV, and (iii) 2.05 eV. This clearly shows that the hypothetical “Schmid cluster” is least stabilized by the fluorinated phosphine, and among the Au75 systems the fluorinated phosphine renders clear extra stability to the metal core as compared to the standard triphenylphosphine.

To investigate the impact of fluorination on ligand shell behavior, we performed molecular dynamics simulations (see technical details in the Supporting Information) to compare the stability and dynamics of the ligand layers in the Au75(P­(C6H4-4-CF3)3)20Cl12 and Au75(P­(Ph)3)20Cl12 clusters in a solvent environment. Gold–phosphorus interaction was parametrized using DFT procedure (described in Supporting Information and Figure S18). We analyzed several distance-based interactions (Figure A–H) and compiled average statistics from three independent 1 μs simulations, including the number of interactions, the fraction of simulation frames in which they occurred, and their lifetimes (Figure ).

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Representative visualizations from molecular dynamics snapshots illustrating intracluster interactions observed in the simulations: (A) Cl···H–C, (B) Cl···π, (C) π···π, (D) Au···π, (E) F···π, (F) F···F, (G) F···H–C, and (H) F···Cl. Cutoff distances and angular criteria used to define these interactions are summarized in the accompanying table. For each interaction type, the table also reports the average number of interactions per frame (±standard deviation), the percentage of frames in which the interaction occurs, and the maximum continuous lifetime of the interaction. These metrics are provided for two cluster systems: Au75(P­(C6H4-4-CF3)3)20Cl12 (abbreviated as C6H4-4-CF3) and Au75(P­(Ph)3)20Cl12 (abbreviated as Ph). In addition to intracluster interactions the final row of the table shows statistics of interactions with the solvent P···H–O.

Fluorination was found to influence the interactions and enhance stability through two distinct mechanisms: 1) Direct involvement of fluorine in interactionswhile clearly present these interactions tend to be more transient, appearing in fewer frames and exhibiting shorter lifetimes compared to interactions not involving fluorine. 2) Stabilization of nonfluorine-mediated interactionsin fluorinated systems, these interactions generally persist longer and are present in more frames than in the nonfluorinated counterpart. Regarding interaction types present in both clusters, Cl···π and Au···π contacts were more prevalent in the nonfluorinated system. This may indicate that the absence of fluorine leads to fewer interphosphine interactions, possibly due to increased ligand flexibility or reduced steric hindrance, allowing ligands to interact more with the cluster surface rather than with each other.

We also assessed interactions between the ligands’ phosphorus atoms and methanol solvent molecules. Although these interactions were infrequent and the differences between systems were minor, the nonfluorinated cluster exhibited slightly more frequent contacts with the solvent. This may suggest a less stable ligand shell in the absence of fluorination.

Finally, we examined the Tolman cone angles, which characterize the steric bulk of the ligands, for both systems. The cone angles were found to be very similar, 132.2 ± 7.2° and 132.7 ± 6.5° for fluorinated and nonfluorinated clusters, respectively, indicating that fluorination does not significantly influence ligand bulkiness. Instead, the majority of the steric contribution appears to originate from the phenyl rings. Moreover, the variation in cone angles throughout the simulations was relatively small in both cases, suggesting that the ligand bulk remains stable over time and does not undergo substantial dynamic changes.

Since the Au75 nanocluster possesses a large Au55 core, it would be insightful to probe its excited-state behaviors. The femtosecond transient absorption (fs-TA) spectrum of the Au75 nanocluster exhibits distinct features. Under 400 nm excitation (Figure A), the excited-state absorption signal decays completely to baseline within 100 ps (Figure B), in sharp contrast to the nanosecond-scale lifetimes observed in phosphine-stabilized clusters like Au11 (24 ns) and Au25 (1442 ns) (Figures B, S19, and S20). Global analysis reveals biphasic decay kinetics, comprising two components: 2.67 ps (τ1) and 7.33 ps (τ2) (Figure C). The picosecond lifetime significantly distinguishes Au75 from typical molecular nanoclusters (e.g., Au25), while it closely aligns with the electron relaxation behavior of large-sized nanoclusters (e.g., Au144, τ ∼ 3 ps). ,

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Femtosecond transient absorption dynamics of the Au75 nanocluster under 400 nm excitation. (A) fs-TA 2D pseudocolor map of Au75 excited at 200 μW (250 μJ/cm2). (B) Normalized ESA kinetic traces of Au75 (probe at 650 nm) and Au25 (probe at 490 nm), combining fs-TA and ns-TA data. (C) EAS obtained from global fitting of the Au75 fs-TA data. (D) Kinetic traces and corresponding global fits of Au75 at probe wavelengths of 550 and 650 nm. (E) Power-dependent experiment of Au75 under 400 nm excitation (54.9–250 μJ/cm2), probed at 650 nm. (F) Extracted fast component lifetime τ1 from biexponential fitting at 650 nm as a function of excitation power.

Differential pulse voltammetry measures the HOMO–LUMO gap of Au75 to be 1.58 eV (Figure S21), but its short lifetime suggests “metallic-like” electronic properties induced by the Au55 core (diameter 1.23 nm). The fast decay component (τ1 = 2.67 ps) exhibits a time scale similar to the electron–phonon (e-ph) coupling process in metallic nanoclusters. To understand its nature, we performed TA experiments under different pump fluences (54.9–250 μJ/cm2, 400 nm excitation; Figures S22 and S23). As shown in Figure E, the normalized TA kinetic traces probed at 650 nm remain unchanged at different power fluences. The fitted τ1 values stabilize at 2.46 ± 0.36 ps (Figure F), showing no significant power dependence, which indicates that its electron relaxation behavior retains molecular-like features. This finding is consistent with the absence of a surface plasmon resonance (SPR) peak in the UV–vis absorption spectrum of Au75 (Figure S6), which differs from the typical behavior observed in metallic nanoclusters like Au279 and aligns with the characteristics of nonmetallic clusters. Further validation through excitation at 500 and 600 nm reveals that τ1 decay component remains at all excitation wavelengths (Figure S24), with decay rates remaining unchanged, effectively excluding the contribution of intramolecular conversion (IC) processes. ,

Notably, the global fitting of the excited-state absorption spectra (EAS) shows similar spectral profiles for both τ1 and τ2 components (Figure C), indicating that the higher excited-state cooling and recombination processes show similar spectral features. The quality of the global fitting is further confirmed at representative probe wavelengths (550 and 650 nm), where the fitted curves closely match the experimental kinetic traces (Figure D). This “non-spectral evolution” characteristic is typical for large metallic nanoclusters, such as Au333, which can be attributed to the strong electronic coupling between the Au55 core and the Au20 fullerene shell (average Au–Au bond length of 2.739 Å). The strong core–shell coupling provides an efficient relaxation channel for hot electrons, thereby imparting a unique “size-dependent transitional” dynamic behavior to Au75.

As a medium-sized nanocluster, Au75 exhibits unique excited-state dynamics that transcend conventional size classifications. Its biphasic decay kinetics share similar features with larger metallic clusters: picosecond-scale lifetimes and temporally overlapping cooling/recombination processes manifest as “non-spectral evolution”, reminiscent of behaviors in systems like Au333. Yet simultaneously, Au75 retains molecular-like features including pump-fluence-independent relaxation and absence of SPR-traits characteristic of small quantum-confined clusters. This dual behavior is particularly striking when compared to similarly sized counterparts: the subnanosecond decay in Au75 contrasts sharply with nanosecond-scale lifetime in Au64. The rapid excited-state relaxation in Au75 can be attributed to the Russian doll architecture, where strong electronic coupling at the Au55 core/Au20 fullerene interface (evidenced by shortened 2.739 Å bonds) creates efficient relaxation pathways. However, the curved fullerene topology imposes geometric confinement that suppresses electron delocalization, preserving the 1.58 eV HOMO–LUMO gap and preventing metallic bond formation. This fundamentally contrasts with the hybrid electronic structure in Au156 where dense energy bands enable partial metallization. Collectively, these findings demonstrate that geometric constraints dominate over size effects in dictating electron relaxation pathways in Au75, establishing a new design principle for tailoring nanocluster photodynamics.

Conclusion

In summary, we reported the integration of the cluster chemistry with fluorine chemistry, which generated the largest structurally resolved nanocluster protected by phosphine ligands, Au75(P­(C6H4-4-CF3)3)20Cl12, whose geometric structure could be likened as an Au20 golden fullerene encapsulating the “Schmid gold”. The reported Au75 nanocluster followed a Russian doll-like shell-by-shell configuration of Au13@Au42@Au20@Cl12@PR20, wherein the first-second shell resembled the metallic kernel of the “Schmid gold”, and the third shell showcased a fullerene-like topology, similar to the smallest fullerene C20. DFT analysis shows the superatom character of the fluorinated Au75 cluster and the stabilizing effect of the fullerene-like overlayer on the electronic structure and chemical stability of the fluorinated Au75 nanocluster. Molecular dynamics simulations confirm that fluorination enhances ligand-shell stability in Au75 clusters by mediating transient fluorine-involved interactions, reducing solvent exposure and promoting longer-lived nonfluorine-mediated contacts. The femtosecond transient absorption analysis revealed that geometric constraintsspecifically, the golden fullerene encapsulating Schmid golddominate over size effects in dictating electron relaxation pathways in Au75, establishing a new design principle for tailoring the photodynamics of nanoclusters. Collectively, we demonstrate that the introduction of fluorine chemistry to the cluster study carries significant importance. The fluorination ushers in a new era for the fabrication of novel nanoclusters with strong stability and good crystallinity, thus heralding a significant step forward in their downstream applications.

Methods

Synthesis of Au75

A solution consisting of HAuCl4·3H2O and P­(C6H4-4-CF3)3 was prepared by dissolving these compounds in a mixed solvent of methanol and dichloromethane. After vigorous stirring for 15 min, cyclohexyl mercaptan was added. The solution was then stirred for 30 min, after which NaBH4 aqueous solution was added dropwise. The reaction was proceeded at room temperature for 10 h. After this, the solution was centrifuged to remove insoluble precipitates. The supernatant was evaporated to dryness, and the resulting product was washed with n-hexane, giving rise to the Au75 nanocluster. High-quality crystals of the Au75 nanocluster were obtained by diffusing n-hexane into the dichloromethane solution containing the nanocluster over 1 week.

Computational Details

The Density Functional Theory calculations were done by using the GPAW software. The molecular dynamics simulations were done by using the GROMACS software. See Supporting Information for computational details.

Supplementary Material

ja5c20164_si_001.pdf (2.3MB, pdf)

Acknowledgments

The experimental work was supported by financial support of the National Natural Science Foundation of China (U24A20480, 22371003, 22471001, and 22273095), the Ministry of Education, Natural Science Foundation of Anhui Province (2408085Y006), and the State Key Laboratory of Optoelectronic Information Acquisition and Protection Technology (OEIAPT20250201). The computational work at the University of Jyväskylä was supported by the Research Council of Finland (grant 355083) and by the European Commission (ERC Advanced Grant DYNANOINT). The computations were done at the Finnish supercomputing center CSC.

All data supporting the findings of this study are included within the article and its Supporting Information. Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Center, under deposition numbers CCDC 2429951 (Au75), 2442163 (Au25), and 2442020 (Au11). Copies of the data can be obtained free of charge via https://www.ccdc.cam. ac.uk/structures/. Source data are provided with this paper.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.5c20164.

  • Detailed discussion on experimental and computational methods (Figures S1–S23 and Tables S1–S5) (PDF)

#.

P.P., S.M., and R.Z. contributed equally.

The authors declare no competing financial interest.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ja5c20164_si_001.pdf (2.3MB, pdf)

Data Availability Statement

All data supporting the findings of this study are included within the article and its Supporting Information. Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Center, under deposition numbers CCDC 2429951 (Au75), 2442163 (Au25), and 2442020 (Au11). Copies of the data can be obtained free of charge via https://www.ccdc.cam. ac.uk/structures/. Source data are provided with this paper.

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