Monolayer-protected Clusters Research Articles

Influence of Aliphatic versus Aromatic Ligand Passivation on Intersystem Crossing in Au25(SR)18.

The electronic relaxation dynamics of gold monolayer protected clusters (MPCs) are influenced by the hydrocarbon structure of thiolate protecting ligands. Here, we present ligand-dependent electronic relaxation for a series of Au25(SR)18- (SR = SC8H9, SC6H13, SC12H25) MPCs using femtosecond time-resolved transient absorption spectroscopy. Relaxation pathways included a ligand-independent femtosecond internal conversion and a competing ligand-dependent picosecond intersystem crossing process. Intersystem crossing was accelerated for the aliphatic (SC6H13, SC12H25) thiolate MPCs compared to the aromatic (SC8H9) thiolate MPCs. Additionally, a 1.2 THz quadrupolar acoustic mode and a 2.4 THz breathing acoustic mode was identified in each cluster, which indicated that differences in ligand structure did not result in significant structural changes to the metal core of the MPCs. Considering that the difference in relaxation rates did not result from ligand-induced core deformation, the accelerated intersystem crossing was attributed to greater electron-vibrational coupling to Au-S vibrational modes. The results suggested that the organometallic semiring was less rigid for the aliphatic thiolate MPCs due to reduced steric effects, and in turn, increases in nonradiative decay rates were observed. Overall, these results imply that the protecting ligand structure can be used to modify carrier relaxation in MPCs.

Functionalized Gold Nanoparticles and Halogen Bonding Interactions Involving Fentanyl and Fentanyl Derivatives.

Fentanyl (FTN) and synthetic analogs of FTN continue to ravage populations across the globe, including in the United States where opioids are increasingly being used and abused and are causing a staggering and growing number of overdose deaths each year. This growing pandemic is worsened by the ease with which FTN can be derivatized into numerous derivatives. Understanding the chemical properties/behaviors of the FTN class of compounds is critical for developing effective chemical detection schemes using nanoparticles (NPs) to optimize important chemical interactions. Halogen bonding (XB) is an intermolecular interaction between a polarized halogen atom on a molecule and e--rich sites on another molecule, the latter of which is present at two or more sites on most fentanyl-type structures. Density functional theory (DFT) is used to identify these XB acceptor sites on different FTN derivatives. The high toxicity of these compounds necessitated a "fragmentation" strategy where smaller, non-toxic molecules resembling parts of the opioids acted as mimics of XB acceptor sites present on intact FTN and its derivatives. DFT of the fragments' interactions informed solution measurements of XB using 19F NMR titrations as well as electrochemical measurements of XB at self-assembled monolayer (SAM)-modified electrodes featuring XB donor ligands. Gold NPs, known as monolayer-protected clusters (MPCs), were also functionalized with strong XB donor ligands and assembled into films, and their interactions with FTN "fragments" were studied using voltammetry. Ultimately, spectroscopy and TEM analysis were combined to study whole-molecule FTN interactions with the functionalized MPCs in solution. The results suggested that the strongest XB interaction site on FTN, while common to most of the drug's derivatives, is not strong enough to induce NP-aggregation detection but may be better exploited in sensing schemes involving films.

Cesium ion-guided detection of trichloroethylene in air

Whereas the close associations of cesium ion with organochlorine compounds have been previously documented, the present report is the first attempt to exploit these interactions to create a trichloroethylene (TCE)-selective sensor. Gold monolayer-protected clusters peripherally functionalized with Cs+ ions were used to prepare a chemiresistance film on MEMS-fabricated interdigitated electrodes. Vapor sensing properties of the cesium-rich chemiresistor were determined using a panel of chlorinated hydrocarbons including TCE as well as polar and non-polar VOCs for comparison. The sensor was selective and highly sensitive toward VOCs containing a 1,2-dichloro group at concentrations as low as 0.1 ppm. The results suggest the key interaction contributing to sensor response is a bidentate, metallocycle-like coordination of the 1,2-dichloro group to the cesium cations at the sensor surface.

Combined experimental and computational study of the photoabsorption of the monodoped and nondoped nanoclusters Au24Pt(SR)18, Ag24Pt(SR)18, and Ag25(SR)18.

Assessing the accuracy of first-principles computational approaches is instrumental to predict electronic excitations in metal nanoclusters with quantitative confidence. Here we describe a validation study on the optical response of a set of monolayer-protected clusters (MPC). The photoabsorption spectra of Ag25(DMBT)18-, Ag24Pt(DMBT)182- and Au24Pt(SC4H9)18, where DMBT is 2,4-dimethylbenzenethiolate and SC4H9 is n-butylthiolate, have been obtained at low temperature and compared with accurate TDDFT calculations. An excellent match between theory and experiment, with typical deviations of less than 0.1 eV, was obtained, thereby validating the accuracy and reliability of the proposed computational framework. Moreover, an analysis of the TDDFT simulations allowed us to ascribe all relevant spectral features to specific transitions between occupied/virtual orbital pairs. The doping effect of Pt on the optical response of these ultrasmall MPC systems was identified and discussed.

Elucidating the Structures of Intermediate Fragments during Stepwise Dissociation of Monolayer-Protected Silver Clusters.

Fragmentation dynamics of ligated coinage metal clusters reflects their structural and bonding properties. So far methodological challenges limited probing structures of the fragments. Herein, we resolve the geometric structures of the primary fragments of [Ag29 L12 ]3- , i.e. [Ag24 L9 ]2- , [Ag19 L6 ]- and [Ag5 L3 ]- (L is 1,3-benzene dithiolate). For this, we used trapped ion mobility mass spectrometry to determine collision cross sections of the fragments and compared them to structures calculated by density functional theory. We also report that following two sequential [Ag5 L3 ]- elimination steps, further dissociation of [Ag19 L6 ]- also involves a new channel of Ag2 loss and Ag-S and C-S bond cleavages. This reflects a competition between retaining the electronic stability of 8 e- superatom cluster cores and increasing steric strain of ligands and staples. These results are also of potential interest for future soft-landing deposition studies aimed at probing catalytic behavior of Ag clusters on supports.

Single-Electron Charging of Thioctic Acid Monolayer-Protected Gold Clusters.

There is great interest in the use of Monolayer-Protected Gold Clusters (AuMPCs) as nanoscale capacitors in aqueous media for nanobiotechnological applications, such as bioelectrocatalysts, biofuel cells, and biosensors. However, AuMPCs exhibiting subattofarad double-layer capacitance at room temperature, and the resolution of single-electron charging, has been mainly obtained in an organic medium with nonfunctional capping ligands. We report here the synthesis of Thioctic Acid Monolayer-Protected Au Clusters (TA-AuMPCs) showing electrochemical single electron quantized capacitance charging in organic and aqueous solutions and when immobilized onto different self-assembled monolayer-modified gold electrodes. The presence of functional carboxylic groups opens a simple strategy for interfacing a nanoparticle assembly to biomolecules for their use as electron donors or acceptors in biological electron transfer reactions.

Harnessing the cation-π interactions of metalated gold monolayer-protected clusters to detect aromatic volatile organic compounds

The strong, non-covalent interactions between π-systems and cations have been the focus of numerous studies on biomolecule structure and catalysis. These interactions, however, have yet to be explored as a sensing mechanism for detecting trace levels of volatile organic compounds (VOCs). In this article, we provide evidence that cation-π interactions can be used to elicit sensitive and selective chemiresistor responses to aromatic VOCs. The chemiresistors are fitted with carboxylate-linked alkali metals bound to the surface of gold monolayer-protected clusters formulated on microfabricated interdigitated electrodes. Sensor responses to aromatic and non-aromatic VOCs are consistent with a model for cation-π interactions arising from association of electron-rich aromatic π-systems to metal ions with the relative strength of attraction following the order K+ > Na+ > Li+. The results point toward cation-π interactions as a promising research avenue to explore for developing aromatic VOC-selective sensors.

(Digital Presentation) Fabrication of Monolayer-Protected Gold Cluster Thin Films: Electrochemical and Optical Properties

Quantum-sized monolayer-protected gold clusters have captivated the imagination of scientists over the last two decades and show exciting optical, electrochemical and catalytic properties when compared to larger-sized plasmonic gold nanoparticles, making them useful for myriad new applications in photonics, catalysis and sensors. One interesting property is the photoluminescence (PL) of gold clusters making them suitable as biological imaging labels. However, the low PL Quantum Yields (QY) are a concern for these clusters and research is focused on improving the PL QYs. One strategy, our research group has worked on is the shell-gold rigidification via the use of surfactants and proteins. Shell ligand rigidification was achieved by ion pairing with bulky tertiary alkyl ammonium groups and aromatic chromophores. Another strategy to reduce the non-radiative deactivation pathways is by making the gold cluster thin films. In a recent study, it was shown that solid state films of clusters not only have manifold increase in PL quantum yield but also their luminescent lifetimes and two photon absorption cross-sections are greatly enhanced in comparison to their solution analogues. Researchers have worked on various strategies to make gold cluster thin films for device applications. One problem with thin films of gold clusters is that the clusters lose their interesting optical and electrochemical properties that were observed in solution phase. For making the clusters useful by enhancing PL for photonic device applications, it is important for the clusters to retain their properties in solid state, which is the main objective of the study carried out here. One problem is that drying intrinsic gold clusters results in crystallization whose optical properties are difficult to characterize. In this study, we have used Nafion and polyvinylpyrrolidone (PVP) to make thin films of water-soluble glutathione-protected gold clusters. Water soluble cluster Au22(SG)18 with reported PLQY of 8% were synthesized and characterized by UV-VIS absorption and PL measurements and thin films of these clusters were made using water soluble PVP and Nafion polymers via drop casting. Enhanced PL and electrochemical properties were observed for clusters in solid state. Similarly, non-polar gold cluster films are fabricated with Polystyrene and optical absorption and PL properties were retained in the solid state.Although drop casting with polymers was found to retain the optical properties, the uniformity of films is a problem. The uniformity of the film is dependent on solvent’s surface tension thus diminishing the quality of the film. Therefore, there is a need of depositing films of gold clusters in a controlled manner which governs their thickness and uniformity. Electropolymerization technique is known to make films during the polymerization of monomers possessing functional groups whose oxidation or reduction via anti-bonding or non-boding electrons on a heteroatom. In this study, we have used electropolymerization strategy to fabricate thin films of gold clusters on conducting substrates. The film is deposited at the working electrode during cyclic voltammetric (CV) sweep when passed through the required reduction or oxidation potential of the monomer under suitable conditions. This technique makes a uniform film throughout the exposed area of the working electrode active surface and the thickness of the film is often proportional to the number of sweep cycles employed. Therefore, introduction of gold clusters in this process with monomers which are previously known to bond with each other will incorporate clusters in the film during the polymerization process and will ease their film formation with uniform thickness. Amongst various size gold clusters, the one which shows good stability as a result of following the magic number series is Au25(SR)18 - . The stability of clustersis one of the important parameter required for practical applications. Aniline and other amine based monomers are used as precursors to make thin films of Au25 on conducting substrate such as Indium tin oxide. By solubilizing the gold clusters with the monomers they are deposited along with the polymers.

Monolayer-Protected Gold Nanoparticles Functionalized with Halogen Bonding Capability─An Avenue for Molecular Detection Schemes.

The use of functionalized nanoparticles (NPs) and their aggregation in the presence of a targeted analyte is a well-established molecular detection strategy predicated on harnessing specific molecular interactions to the NP periphery. Molecules able to specifically interact with the functionalized NPs alter the unique optical and electrochemical properties of the NPs as a function of interparticle spacing. While many intermolecular interactions have been successfully exploited in this manner in conjunction with aqueous NP systems, the use of non-aqueous NPs in the same capacity is significantly less explored. A fundamental interaction that has not been previously investigated in NP schemes is halogen bonding (XB). XB is an orthogonal, electrostatic interaction between a region of positive electrostatic potential (δ+) on a halogen atom (i.e., XB donor) and a negative (δ-) Lewis base (XB acceptor) molecule. To couple XB with NP systems, ligands featuring a molecular structure that promotes XB interactions need to be identified, optimized, and synthesized for subsequent attachment to NPs. Herein, density functional theory (DFT) and NMR techniques are used to identify a strong XB-donor moiety (-C6F4I) and a synthetic scheme for a thiolate ligand featuring that functionality is devised and executed with high purity/yield (78%). Ligand-exchange reactions allow functionalization of non-aqueous alkanethiolate-protected gold NPs or monolayer-protected clusters (MPCs) with the XB-donor ligands. Functionalized MPCs (f-MPCs), within both assembled films and in solution, are shown to engage in XB interactions with target XB-acceptor molecules. Molecular recognition events, including induced aggregation of the f-MPCs, are characterized with UV-vis spectroscopy, cyclic voltammetry, TEM imaging, and diffusion-ordered spectroscopy NMR with limits of detection of 50-100 nM for strong XB acceptors. While fundamental exploration of XB interactions is ongoing, this study represents a step toward utilizing XB within molecular detection schemes, an application with implications for supramolecular chemistry, forensic, and environmental chemical sensing.

Harnessing the Cation-Π Interactions of Metalated Gold Monolayer-Protected Clusters to Detect Aromatic Volatile Organic Compounds

Harnessing the Cation-Π Interactions of Metalated Gold Monolayer-Protected Clusters to Detect Aromatic Volatile Organic Compounds

Crystal Structure and Optical Properties of a Chiral Mixed Thiolate/Stibine-Protected Au18 Cluster.

We report the first example of a chiral mixed thiolate/stibine-protected gold cluster, formulated as Au18(S-Adm)8(SbPh3)4Br2 (where S-Adm = 1-adamantanethiolate). Single crystal X-ray crystallography reveals the origin of chirality in the cluster to be the introduction of the rotating arrangement of Au2(S-Adm)3 and Au(S-Adm)2 staple motifs on an achiral Au13 core and the subsequent capping of the remaining gold atoms by SbPh3 and Br- ligands. Interestingly, the structure and properties of this new Au18 cluster are found to be different from other reported achiral Au18 clusters and the only other stibine-protected [Au13(SbPh3)8Cl4]+ cluster. Detailed analyses on the geometric and electronic structures of the new cluster are carried out to gain insights into its optical properties as well as reactivity and stability of such mixed monolayer-protected clusters.

The effect of magic number phosphine stabilised mono- and bimetallic Au, Cu and Au-Cu nanoparticles as catalysts in the reduction of 4-nitrophenol–A kinetic study

Phosphine stabilised mono- and bimetallic nanoparticles (NPs) of varying sizes were synthesised using a combined dendrimer encapsulated-monolayer protected cluster (DEN-MPC) method. According to this method, the NPs encapsulated within the dendrimer framework (DENs) are extracted using a ligand such as 1,3,5-triaza-7-phosphaadamantane (PTA), forming hydrophilic monolayer protected clusters (MPCs). The synthesis of MPCs with different average sizes (Aum, Cun, Aum–Cun and Au–Cu(m:n), where n = 55, 70, 95, 130 and 147 and m = 7, 13, 18, 31, 55) was achieved by varying the dendrimer to metal ratio. Various analytical techniques, including ultraviolet–visible (UV–Vis) spectroscopy, high-resolution transmission electron microscopy (HRTEM) and inductively coupled plasma optical electron spectroscopy (ICP-OES), were used to confirm the synthesis of the MPCs. The MPC were evaluated as catalysts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-Amp), using excess sodium borohydride (NaBH 4) as the reducing agent. The catalytic reaction was studied by monitoring the absorbance of the 4-nitrophenolate ions at 400 nm using UV–Vis spectroscopy. The average particle sizes of the MPCs ranged from 5–10 nm and were found to be active catalysts for the reduction of 4-NP. The Cun-PTA NPs exhibited a higher activity compared to the Aum-PTA NPs. However, they were not considered ideal catalysts due to their structural instability. The bimetallic Aum-Cun PTA NPs were more stable and displayed higher catalytic activity than the monometallic Aum NPs due to a synergistic effect between the Au NPs and Cu NPs; hence, the bimetallic NPs have proven to be the best catalysts for the reduction of 4-NP. The effect of various parameters, such as the concentration of NaBH4 and 4-NP, catalyst concentration, temperature and the average particle size, on the reaction rate was studied. In addition, the thermodynamic parameters relating to the reaction rate (Kapp) were also calculated and the kinetic data showed that the reduction of 4-NP to 4-Amp using PTA NPs follows the Langmuir–Hinshelwood model.

Development of monolayer-protected gold clusters-based hydrolytic nanozymes containing catalytic units

<p indent=0mm>Nanozymes can catalyze the biochemical reactions mediated by natural enzymes under physiological conditions, and show natural enzymes-like reaction kinetics and catalytic mechanism. Monolayer-protected gold clusters (Au MPCs) containing catalytic units can greatly improve the catalytic abilitys of nanozymes, so it has been developed rapidly in recent years. In this review, the progress of Au MPCs hydrolytic nanozymes containing catalytic units in recent years is summarized. The design of surface catalytic units, supramolecular assembly and application of Au MPCs hydrolytic nanozymes are discussed.

Ultrafast relaxation dynamics of Au38(SC6H13)24 monolayer-protected clusters resolved by two-dimensional electronic spectroscopy.

Electronic relaxation dynamics of neutral Au38(SC6H13)24 monolayer-protected clusters (MPCs), following excitation of the mixed 15875cm-1 charge transfer resonance, were studied using femtosecond transient absorption (fsTA) and two-dimensional electronic spectroscopy (2DES). The excited carriers relax by three different mechanisms, including an ∼100fs HOMO-12/-13 to HOMO-4/-6 hole transfer, picosecond HOMO-4/-6 to HOMO hole transfer, and subsequent electron-hole recombination that persisted beyond the hundreds of picoseconds measurement range. The fsTA data revealed two transient bleach components at 15820 and 15625cm-1, where the lower frequency component exhibited a delayed first-order buildup of 80 ± 25fs that matched the decay of the high-energy bleach component (110 ± 45fs). These results suggested that the excited charge carriers internally relax within the exited-state manifold in ≈100fs. 2DES resolved multiple electronic fine-structure transient peaks that spanned excitation frequencies ranging from 15500 to 16100cm-1. State-to-state dynamics were understood by the analysis of time-dependent 2DES transient signal amplitudes at numerous excitation-detection frequency combinations. An off-diagonal cross peak at 15825-15620cm-1 excitation-detection signified the HOMO-12/-13 to HOMO-4/-6 hole transfer process. The lowest-frequency (15620cm-1) 2DES diagonal fine-structure peak exhibited instantaneous amplitude but intensified following a 75 ± 10fs buildup when compared to diagonal peaks at higher frequencies. This observation indicated that the charge transfer resonance in Au38(SC6H13)24 MPCs is comprised of several electronic transitions of unique spectral weights, which may result from different orbital contributions associated with specific cluster domains. The use of 2DES in combination with structurally precise MPCs can provide a platform for understanding structure-dependent electronic dynamics in metal nanoclusters and technologically important metal-chalcogenide interfaces.

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.

Predictive optical photoabsorption of Ag24Au(DMBT)18 - via efficient TDDFT simulations.

We report a computational study via time-dependent density-functional theory (TDDFT) methods of the photo-absorption spectrum of an atomically precise monolayer-protected cluster (MPC), the Ag24Au(DMBT)18 single negative anion, where DMBT is the 2,4-dimethylbenzenethiolate ligand. The use of efficient simulation algorithms, i.e., the complex polarizability polTDDFT approach and the hybrid-diagonal approximation, allows us to employ a variety of exchange-correlation (xc-) functionals at an affordable computational cost. We are thus able to show, first, how the optical response of this prototypical compound, especially but not exclusively in the absorption threshold (low-energy) region, is sensitive to (1) the choice of the xc-functionals employed in the Kohn-Sham equations and the TDDFT kernel and (2) the choice of the MPC geometry. By comparing simulated spectra with precise experimental photoabsorption data obtained from room temperature down to low temperatures, we then demonstrate how a hybrid xc-functional in both the Kohn-Sham equations and the diagonal TDDFT kernel at the crystallographically determined experimental geometry is able to provide a consistent agreement between simulated and measured spectra across the entire optical region. Single-particle decomposition analysis tools finally allow us to understand the physical reason for the failure of non-hybrid approaches.

Size-Scalable Near-Infrared Photoluminescence in Gold Monolayer Protected Clusters.

Near-infrared photoluminescence of a series of three gold monolayer protected clusters (MPCs) with volumes spanning 50-200 Å3 was studied by using variable-temperature photoluminescence (VT-PL) spectroscopy. The three MPCs, which included Au20(SC8H9)15-diglyme, Au25(SC8H9)18, and Au38(SC12H25)24, all exhibited temperature-dependent intensities that reflected a few-millielectronvolt energy gap that separated bright emissive and dark nonradiative electronic states. All clusters showed increased PL intensities upon raising the sample temperature from 4.5 K to a cluster-specific value, upon which increased sample temperature resulted in emission quenching. The increased PL in the low-temperature range is attributed to thermally activated carrier transfer from dark to bright states. The quenching at elevated temperatures is attributed to nonradiative vibrational relaxation through Au-Au stretching of the MPCs metal core. Importantly, the results show evidence of a common and size scalable metal-centered intraband PL mechanism that is general for ultrasmall metal nanoclusters, which are expected to show nonscalable optical properties.

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Electron Transfer in Films of Atomically Precise Gold Nanoclusters

In applications of monolayer-protected gold clusters, assessing the dynamic behavior of the capping monolayer is crucial, as this determines the cluster’s effective size and electron-transfer (ET) properties. Here, we describe a systematic study on the effect of the monolayer thickness on the ET between molecular Au25(SR)180 nanoclusters in films. The length of the ligands protecting the Au core was varied by using a series of linear-chain thiolate (SCnH2n+1) protected Au25 clusters, where n = 3, 4, 5, 6, 7, 8, and 10. The effect of branching was assessed by using the 2-methyl-1-butanethiolate-protected Au25 cluster. Conductivity measurements were carried out on dry films obtained by drop-casting Au25(SR)180 solutions onto interdigitated gold electrodes. Changing the alkyl chain from C3 to C10 induces a smooth decrease in the film conductivity by 3.5 orders of magnitude. By using electrochemically determined Stokes radii, the conductivity results were transformed into the corresponding ET rate constants (kETs) between neighboring clusters. kET exponentially depends on the distance, and the data show that the average Au center-to-center distance in the film is not larger than the sum of two Stokes radii. This indicates that linear alkyl chains hold a detectable degree of fluidity in films, although not as much as in solution, as shown by the trend of the corresponding heterogeneous standard rate-constant values. For both physical states, these conclusions are precisely confirmed by the much slower ET rate determined for the Au25 cluster protected by the hindered thiolate. ET in films was also studied as a function of temperature, and the results were analyzed in the framework of the ET theory. We found that the outer and inner reorganization energies increase with n. For these ETs, the electronic coupling resonance between the reactant and product states, HRP, ranges from 12 (n = 3) to 0.7 cm–1 (n = 10) and therefore ETs are nonadiabatic. The data also show that 3/4 of the effect of distance on kET is related to HRP, while the rest is associated with the intrinsic barrier and thus the distance dependence of the outer and inner reorganization energies.

The Role of Oxidation during the Synthesis of Silver-Glutathione Monolayer-Protected Clusters.

The synthesis of metal monolayer-protected clusters (MPCs) is still not well understood. It was recently shown that the mechanism of MPC formation involves sequential growth, wherein small MPCs form first and then grow into progressively larger sizes. The sequential growth model does not entirely explain all experimental observations, however. For example, the evolution of MPC product sizes is found to be a non-monotonic function of reaction kinetics, whereas the sequential growth model predicts monotonic behavior. Size evolution of MPCs is studied during synthetic reactions for a wide range of kinetics and it is found that all syntheses began with the sequential growth of MPCs but also found that growth transitioned to degradation if reduction kinetics are fast enough to give way to ambient oxidation. It is identified that MPCs can degrade via oxidation during syntheses and in a manner that is opposite to sequential growth, namely by forming smaller known MPC species from larger MPC species. This sequential degradation process therefore played an important role in determining final MPC products for reactions with fast reduction kinetics. Together, complementary oxidative and reductive processes provide a more complete description of MPC synthesis as well as new tools for controlling metal MPC synthesis.