Ligand-protected Metal Clusters Research Articles

Chemical Flexibility of Atomically Precise Metal Clusters.

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

Metal-ligand bond in group-11 complexes and nanoclusters.

Density functional theory is used to study geometric, energetic, and electronic properties of metal-ligand bonds in a series of group-11 metal complexes and ligand-protected metal clusters. We study complexes as the forms of M-L (L = SCH3, SC8H9, PPh3, NHCMe, NHCEt, NHCiPr, NHCBn, CCMe, CCPh) and L1-M-L2 (L1 = NHCBn, PPh3, and L2 = CCPh). Furthermore, we study clusters denoted as [M13L6Br6]- (L = PPh3, NHCMe, NHCEt, NHCiPr, NHCBn). The systems were studied at the standard GGA level using the PBE functional and including vdW corrections via BEEF-vdW. Generally, Au has the highest binding energies, followed by Cu and Ag. PBE and BEEF-vdW functionals show the order Ag-L > Au-L > Cu-L for bond lengths in both M-L complexes and metal clusters. In clusters, the smallest side group (CH3) in NHCs leads to the largest binding energy whereas no significant variations are seen concerning different side groups of NHC in M-L complexes. By analyzing the projected density of states and molecular orbitals in complexes and clusters, the M-thiolate bonds were shown to have σ and π bond characteristics whereas phosphines and carbenes were creating σ bonds to the transition metals. Interestingly, this analysis revealed divergent behavior for M-alkynyl complexes: while the CCMe group displayed both σ and π bonding features, the CCPh ligand was found to possess only σ bond properties in direct head-to-head binding configuration. Moreover, synergetic effects increase the average binding strength to the metal atom significantly in complexes of two different ligands and underline the potential of adding Cu to synthesize structurally richer cluster systems. This study helps in understanding the effects of different ligands on the stability of M-L complexes and clusters and suggests that PPh3 and NHCs-protected Cu clusters are most stable after Au clusters.

Circular dichroism and circularly polarized luminescence of ligand-protected molecular metal clusters: insights into structure-chiroptical property relationships.

Molecular noble metal clusters are an emerging class of circularly polarized luminescent (CPL) nanomaterials. Many of the ligand-protected metal clusters exhibit discrete electronic absorption bands, which are assigned to their structural components such as metal core, ligands and metal-ligand interfaces. This implies the suitability of the chiroptical spectroscopic approach to unravel the structure-chiroptical property relationships in molecular metal clusters. Due to the tremendous developments in computational methods for investigating chiroptical properties, along with circular dichroism (CD) and CPL spectroscopy, understanding of the structure-chiroptical properties of these clusters is rapidly progressing. This review discusses various strategies such as the use of chiral ligands, metal atom substitution, ligand exchange, co-crystallization with chiral ligands, etc., for inducing and enhancing the CPL of such metal clusters. This review demonstrates the potential of combined CD-CPL spectroscopic investigations and theoretical calculations to unravel the origins of photoluminescence and CPL activity of chiral metal clusters.

What Determines If a Ligand Undergoes Coordination or Catalytic Activation on a Metal Cluster?

We report a joint experimental and theoretical study on the reactivity of Agn+ clusters with H2S, D2O, and NH3. Complete dehydrogenation products are observed for Agn+ reacting with H2S, but no dehydrogenation products are found for D2O or NH3 under the same reaction condition. Theoretical calculations elucidate why Agn+ clusters show different reactivities with these inorganic hydrides. NH3 shows strong coordination with Agn+, but the dehydrogenation reactions are unfavorable; in contrast, the fragile H-S bonds and stable AgnS+ products facilitate the hydrogen evolution of H2S on Agn+. We fully analyzed the metal-ligand interactions of Agn+ clusters with three molecules and illustrated the reaction dynamics and charge-transfer interactions and altered the superatomic states during the formation of cluster sulfides. We expect this study to benefit the design of stable environmentally friendly desulfurization catalysts and also the understanding of the mechanism on ligand-protected metal clusters in wet chemistry.

Enhanced Fluorescence with Tunable Color in Doped Diphosphine-Protected Gold Nanoclusters.

Rational control of the luminescent properties of ligand-protected coinage metal clusters has long been pursued but remains challenging. Here we explore the crucial structural and electronic factors governing the fluorescence of a diphosphine-protected [Au13(dppe)5Cl2]3+ cluster by time-dependent density functional theory calculations. By substituting the central Au atom with group 5 to group 11 transition metal atoms, the emission wavelength is adjustable from red to blue, accompanied by enhanced fluorescence intensity compared with the undoped cluster. The evolution of light-emitting behavior upon doping and the corresponding roles of the dopant, Au cage, ligands, and their interplay are interpreted at the electronic structure level. In particular, strong dopant-Au cage interaction associated with large electron-hole overlap on the dopant are is a key factor to endow large emission energy and intensity. These theoretical results provide vital guidance for designing atomically precise nanoclusters with visible fluorescence and high quantum yield for practical uses.

Optical Properties and Applications of Crystalline Materials

Optical Properties and Applications of Crystalline Materials

Chemical transformations of [MAu8(PPh3)8]2+ (M = Pt, Pd) and [Au9(PPh3)8]3+ in methanol induced by irradiation of atmospheric pressure plasma.

The reaction processes of ligand-protected metal clusters induced by irradiating atmospheric pressure plasma (APP) were investigated using optical spectroscopy, mass spectrometry, and density functional theory (DFT) calculations. The target clusters were phosphine-protected gold-based clusters [MAu8(PPh3)8]2+ (M = Pt, Pd) and [Au9(PPh3)8]3+, which have a crown-shaped M@Au8 (M = Pt, Pd, Au) core with an unligated M site at the central position. The APP irradiation of [MAu8(PPh3)8]2+ (M = Pt, Pd) in methanol resulted in the selective formation of [PtAu8(PPh3)8CO]2+ and [PdAu9(PPh3)8CN]2+ via the addition of a CO molecule and AuCN unit, respectively, generated in situ by the APP irradiation. In contrast, the APP irradiation of [Au9(PPh3)8]3+ in methanol yielded [Au9(PPh3)7(CN)1]2+ and [Au10(PPh3)7(CN)2]2+ as the main products, which were produced by sequential addition of AuCN to reactive [Au8(PPh3)7]2+ formed by dissociation equilibrium of [Au9(PPh3)8]3+. DFT calculations predicted that a unique chain-like {-(CNAu)n-PPh3} (n = 1, 2) ligand was formed via the sequential insertion of -CNAu- units into the Au-PPh3 bond of [PdAu8(PPh3)8]2+ and [Au8(PPh3)7]2+. These findings open up a new avenue for developing novel metal clusters via the chemical transformation of atomically defined metal clusters by APP irradiation.

Crucial Role of Conjugation in Monolayer-Protected Metal Clusters with Aromatic Ligands: Insights from the Archetypal Au144L60 Cluster Compounds.

Ligand-protected metal clusters are employed in a great many applications that include notably energy conversion and biomedical uses. The interaction between the ligands and the metallic cores, mediated by an often complex interface, profoundly influences the properties of small clusters, in particular. Nonetheless, the mechanisms of interaction remain far from fully understood. The Au144L60 class of cluster compounds has long played a central role in the study of monolayer-protected clusters, but total structure determination has been achieved only recently for a thiolated and an all-alkynyl cluster. Both ligands contain aromatic rings but differ in their ligation to the metal core: conjugation along a triple bond in the latter, saturation in the former. We demonstrate the paramount importance of the conjugation in the connection between aromatic ligand rings and metal cores for the electronic and optical properties and, by extension, the critical transport properties, providing a crucial element for the development of design-principle-based synthesis.

Diarsine- vs diphosphine-protected Au13 clusters: Effect of subtle geometric differences on optical property and electronic structure.

In the design of ligand-protected metal clusters, the choice of protecting ligands is a critical factor because they can profoundly affect the nuclearity, geometry, and electronic structures to afford a diverse range of cluster compounds. Here, we report the synthesis of two novel diarsine-protected Au13 clusters ([Au13L5Cl2]3+, L = diarsine) and compare these clusters with diphosphine analogs in terms of the core geometry and optical properties. In the crystal structure, the cluster bearing C3-bridged diarsines {[Au13(dpap)5Cl2]3+, 3} had an apparently identical icosahedral Au13 core to [Au13(dppe)5Cl2]3+ (1) with C2-bridged diphosphines, but slight structural differences associated with the bridging unit of the ligands were found. Despite similar icosahedral Au13 cores 1 and 3, their absorption and photoluminescence profiles were evidently different. Theoretical calculations revealed that the subtle deformation of the Au13 icosahedron, rather than the coordinating atoms (As or P), notably influences the electronic structure to cause the difference in the absorption profiles.

Thermal stability of crown-motif [Au9(PPh3)8]3+ and [MAu8(PPh3)8]2+ (M = Pd, Pt) clusters: Effects of gas composition, single-atom doping, and counter anions

The thermal behaviors of ligand-protected metal clusters, [Au9(PPh3)8]3+ and [MAu8(PPh3)8]2+ (M = Pd, Pt) with a crown-motif structure, were investigated to determine the effects of the gas composition, single-atom doping, and counter anions on the thermal stability of these clusters. We successfully synthesized crown-motif [PdAu8(PPh3)8][HPMo12O40] (PdAu8-PMo12) and [PtAu8(PPh3)8][HPMo12O40] (PtAu8-PMo12) salts with a cesium-chloride-type structure, which is the same as the [Au9(PPh3)8][PMo12O40] (Au9-PMo12) structure. Thermogravimetry-differential thermal analysis/mass spectrometry analysis revealed that the crown-motif structure of Au9-PMo12 was decomposed at ∼475K without weight loss to form Au nanoparticles. After structural decomposition, the ligands were desorbed from the sample. The ligand desorption temperature of Au9-PMo12 increased under 20% O2 conditions because of the formation of Au nanoparticles and stronger interaction of the formed O=PPh3 than PPh3. The Pd and Pt single-atom doping improved the thermal stability of the clusters. This improvement was due to the formation of a large bonding index of M-Au and a change in Au-PPh3 bonding energy by heteroatom doping. Moreover, we found that the ligand desorption temperatures were also affected by the type of counter anions, whose charge and size influence the localized Coulomb interaction and cluster packing between the cationic ligand-protected metal clusters and counter anions.

Symmetric Growth of Dual-Packed Kernel: Exploration of the Evolution of Au40(SR)24 to Au49(SR)27 and Au58(SR)30 Clusters via the 2e --Reduction Cluster Growth Mechanism.

The symmetric and periodic growth of metal core and ligand shell has been found in a number of ligand-protected metal clusters. So far, the principle of symmetric growth has been widely used to understand and predict the cluster structure evolution. In this work, based on the experimentally resolved crystal structure of Au40(o-MBT)24 and Au49(2,4-DMBT)27 clusters and a newly proposed two-electron (2e–) reduction cluster growth mechanism, the evolution pathway from the quasi-face-centered-cubic (fcc)-structured Au40(SR)24 cluster to the dual fcc- and nonfcc-packed Au49(SR)27 and Au58(SR)30 clusters was studied. The current research has clarified two important issues of cluster structure evolution. First, the formation of the dual-packed fcc and nonfcc kernel structure has been rationalized based on a 2e—reduction-based seed-mediated cluster growth pathway. Second, it is found that the symmetrical growth does not necessarily lead to the formation of stable cluster structures. It was found that the formation of dual-packed kernels in the Au49(SR)27 cluster is favorable because of the stability of the intermediate cluster structures and the relatively high thermodynamic stability of the cluster itself. However, although the structure of Au58(SR)30 cluster conforms to the principle of symmetric growth, the tension between the ligand shell and the gold atom of the metal nucleus increases significantly during the cluster size evolution, and the stability of the intermediate clusters is poor, so the formation of the Au58(SR)30 cluster is unfavorable. This study also shows that the 2e–-reduction cluster growth mechanism can be used to explore the structural evolution and stability of thiolate-protected gold clusters.

Secondary Phosphine Oxide Functionalized Gold Clusters and Their Application in Photoelectrocatalytic Hydrogenation Reactions.

Ligands in ligand-protected metal clusters play a crucial role, not only because of their interaction with the metal core, but also because of the functionality they provide to the cluster. Here, we report the utilization of secondary phosphine oxide (SPO), as a new family of functional ligands, for the preparation of an undecagold cluster Au11-SPO. Different from the commonly used phosphine ligand (i.e., triphenylphosphine, TPP), the SPOs in Au11-SPO work as electron-withdrawing anionic ligands. While coordinating to gold via the phosphorus atom, the SPO ligand keeps its O atom available to act as a nucleophile. Upon photoexcitation, the clusters are found to inject holes into p-type semiconductors (here, bismuth oxide is used as a model), sensitizing the p-type semiconductor in a different way compared to the photosensitization of a n-type semiconductor. Furthermore, the Au11-SPO/Bi2O3 photocathode exhibits a much higher activity toward the hydrogenation of benzaldehyde than a TPP-protected Au11-sensitized Bi2O3 photocathode. Control experiments and density functional theory studies point to the crucial role of the cooperation between gold and the SPO ligands on the selectivity toward the hydrogenation of the C═O group in benzaldehyde.

Chiroptical activity of Au13 clusters: experimental and theoretical understanding of the origin of helical charge movements.

Ligand-protected gold clusters with an asymmetric nature have emerged as a novel class of chiral compounds, but the origins of their chiroptical activities associated with helical charge movements in electronic transitions remain unexplored. Herein, we perform experimental and theoretical studies on the structures and chiroptical properties of Au13 clusters protected by mono- and di-phosphine ligands. Based on the experimental reevaluation of diphosphine-ligated Au13 clusters, we show that these surface ligands slightly twist the Au13 cores from a true icosahedron to generate intrinsic chirality in the gold frameworks. Theoretical investigation of a monophosphine-ligated cluster model reproduced the experimentally observed circular dichroism (CD) spectrum, indicating that such a torsional twist of the Au13 core, rather than the surrounding chiral environment by helically arranged diphosphine ligands, contributes to the appearance of the chiroptical response. We also show that the calculated CD signals are dependent on the degree of asymmetry (torsion angle between the two equatorial Au5 pentagons), and provide a visual understanding of the origin of helical charge movements with transition-moment and transition-density analyses. This work provides novel insights into the chiroptical activities of ligand-protected metal clusters with intrinsically chiral cores.

Chiral Functionalization of an Atomically Precise Noble Metal Cluster: Insights into the Origin of Chirality and Photoluminescence.

We probe the origin of photoluminescence of an atomically precise noble metal cluster, Ag24Au1(DMBT)18 (DMBT = 2,4-dimethylbenzenethiolate), and the origin of chirality in its chirally functionalized derivatives, Ag24Au1(R/S-BINAS)x(DMBT)18-2x, with x = 1-7 (R/S-BINAS = R/S-1,1'-[binaphthalene]-2,2'-dithiol), using chiroptical spectroscopic measurements and density functional theory (DFT) calculations. Combination of chiroptical and luminescence spectroscopies to understand the nature of electronic transitions has not been applied to such molecule-like metal clusters. In order to impart chirality to the achiral Ag24Au1(DMBT)18 cluster, the chiral ligand, R/S-BINAS, was incorporated into it. A series of clusters, Ag24Au1(R/S-BINAS)x(DMBT)18-2x, with x = 1-7, were synthesized. We demonstrate that the low-energy electronic transitions undergo an unexpected achiral to chiral and back to achiral transition from pure Ag24Au1(DMBT)18 to Ag24Au1(R/S-BINAS)x(DMBT)18-2x, by increasing the number of BINAS ligands. The UV/vis, luminescence, circular dichroism, and circularly polarized luminescence spectroscopic measurements, in conjunction with DFT calculations, suggest that the photoluminescence in Ag24Au1(DMBT)18 and its chirally functionalized derivatives originates from the transitions involving the whole Ag24Au1S18 framework and not merely from the icosahedral Ag12Au1 core. These results suggest that the chiroptical signatures and photoluminescence in these cluster systems cannot be solely attributed to any one of the structural components, that is, the metal core or the protecting metal-ligand oligomeric units, but rather to their interaction and that the ligand shell plays a crucial role. Our work demonstrates that chiroptical spectroscopic techniques such as circular dichroism and circularly polarized luminescence represent useful tools to understand the nature of electronic transitions in ligand-protected metal clusters and that this approach can be utilized for gaining deeper insights into the structure-property relationships of the electronic transitions of such molecule-like clusters.

An efficient hybrid scheme for time dependent density functional theory.

A hybrid approach able to perform Time Dependent Density Functional Theory (TDDFT) simulations with the same accuracy as that of hybrid exchange-correlation (xc-) functionals but at a fraction of the computational cost is developed, implemented, and validated. The scheme, which we name Hybrid Diagonal Approximation (HDA), consists in employing in the response function a hybrid xc-functional (containing a fraction of the non-local Hartree-Fock exchange) only for the diagonal elements of the omega matrix, while the adiabatic local density approximation is employed for the off-diagonal terms. HDA is especially (but not exclusively) advantageous when using Slater type orbital basis sets and allows one to employ them in a uniquely efficient way, as we demonstrate here by implementing HDA in a local version of the Amsterdam Density Functional code. The new protocol is tested on NH3, C6H6, and the [Au25(SCH3)18]- cluster as prototypical cases ranging from small molecules to ligand-protected metal clusters, finding excellent agreement with respect to both full kernel TDDFT simulations and experimental data. Additionally, a specific comparison test between full kernel and HDA is considered at the Casida level on seven other molecular species, which further confirm the accuracy of the approach for all investigated systems. For the [Au25(SCH3)18]- cluster, a speedup by a factor of seven is obtained with respect to the full kernel. The HDA, therefore, promises to provide a quantitative description of the optical properties of medium-sized systems (nanoclusters) at an affordable cost, thanks to its computational efficiency, especially in combination with a complex polarization algorithm version of TDDFT.

Photophysical and Thermodynamic Properties of Ag29(BDT)12(TPP)x (x = 0–4) Clusters in Secondary Ligand Binding–Dissociation Equilibria Unraveled by Photoluminescence Analysis

Despite the huge effort that has been devoted to the atomically precise synthesis and structural and physicochemical property characterization of ligand-protected noble metal clusters, quantitative...

Growth-Rule-Guided Structural Exploration of Thiolate-Protected Gold Nanoclusters.

Understanding the structure and structure-property relationship of atomic and ligated clusters is one of the central research tasks in the field of cluster research. In chemistry, empirical rules such as the polyhedral skeleton electron pair theory (PSEPT) approach had been outlined to account for skeleton structures of many main-group atomic and ligand-protected transition metal clusters. Nonetheless, because of the diversity of cluster structures and compositions, no uniform structural and electronic rule is available for various cluster compounds. Exploring new cluster structures and their evolution is a hot topic in the field of cluster research for both experiment and theory. In this Account, we introduce our recent progress in the theoretical exploration of structures and evolution patterns of a class of atomically precise thiolate-protected gold nanoclusters using density functional theory computations. Unlike the conventional ligand-protected transition metal compounds, the thiolate-protected gold clusters demonstrate novel metal core/ligand shell interfacial structures in which the Au m(SR) n clusters can be divided into an ordered Au(0) core and a group of oligomeric SR[Au(SR)] x ( x = 0, 1, 2, 3, ...) protection motifs. Guided by this "inherent structure rule", we have devised theoretical methods to rapidly explore cluster structures that do not necessarily require laborious global potential energy surface searches. The structural predictions of Au38(SR)24, Au24(SR)20, and Au44(SR)28 nanoclusters were completely or partially verified by the later X-ray crystallography studies. On the basis of the analysis of cluster structures determined by X-ray crystallography and theoretical prediction, a structural evolution diagram for the face-centered-cubic (fcc)-type Au m(SR) n clusters with m up to 92 has been preliminarily established. The structural evolution diagram indicates some basic structural and electronic evolution patterns of thiolate-protected gold nanoclusters. The fcc Au m(SR) n clusters show a genetic structural evolution pattern in which each step of cluster size increase results in the formation of another Au4 tetrahedron or Au3 triangle unit in the Au core, and every increase of a structural unit in the Au core leads to an increase of two electrons in the whole cluster. The unique one- or two-dimensional cluster size evolution, the isomerism of the Au-S framework, and the formation of a double-helical and cyclic tetrahedron network in the fcc Au m(SR) n clusters all can be addressed from this evolution pattern. The summarized cluster structural evolution diagrams enable us to further explore more stable cluster structures and understand their structure-electronic structure-property relationships.

X-ray Absorption Spectroscopy on Atomically Precise Metal Clusters

Abstract Metal clusters show novel and size-specific properties due to unique geometric and quantized electronic structures. State-of-the art synthetic methods allow us to control with atomic precision the size and compositions of clusters stabilized with polymers, protected by ligands, and immobilized on supports. The geometric structure is key information for understanding the origin of the specific and novel properties and for rationally designing their functions. Single-crystal X-ray diffraction analysis provides direct and atomic-level structural information on ligand-protected metal clusters that can be crystallized, but cannot be applied to polymer-stabilized and supported clusters even though their size and composition are precisely defined. X-ray absorption spectroscopy (XAS) is a versatile tool for determining the local structure and electronic state of a specific element within the clusters regardless of their environment. In addition to static structures, dynamic changes in electronic and geometric structures can be probed by a time-resolved measurement. Simultaneous measurement of XAS with other spectroscopies provides further insight into the reaction mechanism. This article summarizes our XAS studies on the size and atomic packing of metal clusters, location of dopant in the clusters, interfacial structures between the clusters and the surroundings, thermal properties of the clusters, and structural and electronic dynamics during the reactions.

Mechanical Vibrations of Atomically Defined Metal Clusters: From Nano- to Molecular-Size Oscillators.

Acoustic vibrations of small nanoparticles are still ruled by continuum mechanics laws down to diameters of a few nanometers. The elastic behavior at lower sizes (<1-2 nm), where nanoparticles become molecular clusters made by few tens to few atoms, is still little explored. The question remains to which extent the transition from small continuous-mass solids to discrete-atom molecular clusters affects their specific low-frequency vibrational modes, whose period is classically expected to linearly scale with diameter. Here, we investigate experimentally by ultrafast time-resolved optical spectroscopy the acoustic response of atomically defined ligand-protected metal clusters Au n(SR) m with a number n of atoms ranging from 10 to 102 (0.5-1.5 nm diameter range). Two periods, corresponding to fundamental breathing- and quadrupolar-like acoustic modes, are detected, with the latter scaling linearly with cluster diameters and the former taking a constant value. Theoretical calculations based on density functional theory (DFT) predict in the case of bare clusters vibrational periods scaling with size down to diatomic molecules. For ligand-protected clusters, they show a pronounced effect of the ligand molecules on the breathing-like mode vibrational period at the origin of its constant value. This deviation from classical elasticity predictions results from mechanical mass-loading effects due to the protecting layer. This study shows that clusters characteristic vibrational frequencies are compatible with extrapolation of continuum mechanics model down to few atoms, which is in agreement with DFT computations.

Interconversions of Structural Isomers of [PdAu8(PPh3)8]2+ and [Au9(PPh3)8]3+ Revealed by Ion Mobility Mass Spectrometry

Collision cross sections (CCSs) of ligand-protected metal clusters were evaluated using ion mobility mass spectrometry. The targets used in this study were phosphine-protected clusters [PdAu8(PPh3)8]2+ and [Au9(PPh3)8]3+, for which the total structures have been resolved by single-crystal X-ray analysis. The arrival time distributions of [PdAu8(PPh3)8]2+ as a function of the He flow rate in a cell located just in front of a traveling wave ion mobility cell filled with N2 buffer gas demonstrated that it got converted to another structural isomer having a smaller CCS, with the increase in the nominal collision energy. A similar phenomenon was observed for [Au9(PPh3)8]3+. These results were explained by the collisional excitation and cooling with the buffer gas inducing the conversion of the packing arrangement of the ligands rather than the atomic structure of the metallic core: the ligand layer was converted from disordered to the closely packed arrangement found in a single crystal during this process. Th...