Observable but Not Isolable: The RhAu24 (PET)181+ Nanocluster

The synthesis and characterization of RhAu₂₄ (PET)₁₈ (PET = 2-phenylethanethiol) is described. The cluster is cosynthesized with Au₂₅ (PET)₁₈ and rhodium thiolates in a coreduction of RhCl₃ , HAuCl₄ , and PET. Rapid decomposition of RhAu₂₄ (PET)₁₈ occurs when purified from the other reaction products, precluding the study of isolated cluster. Mixtures containing RhAu₂₄ (PET)₁₈ , Au₂₅ (PET)₁₈ , and rhodium thiolates are therefore characterized. Mass spectrometry, X-ray photoelectron spectroscopy, and chromatography methods suggest a combination of charge-charge and metallophilic interactions among Au₂₅ (PET)₁₈^1- , rhodium thiolates and RhAu₂₄ (PET)₁₈ resulting in stabilization of RhAu₂₄ (PET)₁₈ . The charge of RhAu₂₄ (PET)₁₈ is assigned as 1+ on the basis of its stoichiometric 1:1 presence with anionic Au₂₅ (PET)₁₈ , and its stability is contextualized within the superatom electron counting rules. This analysis concludes that the Rh atom absorbs one superatomic electron to close its d-shell, giving RhAu₂₄ (PET)₁₈¹⁺ a superatomic electron configuration of 1S² 1P⁴ . Overall, an updated framework for rationalizing open d-shell heterometal dopant electronics in thiolated gold nanoclusters emerges.

Metal Nanoclusters: New Paradigm in Catalysis for Water Splitting, Solar and Chemical Energy Conversion

A sustainable future demands innovative breakthroughs in science and technology today, especially in the energy sector. Earth-abundant resources can be explored and used to develop renewable and sustainable resources of energy to meet the ever-increasing global energy demand. Efficient solar-powered conversion systems exploiting inexpensive and robust catalytic materials for the photo- and photo-electro-catalytic water splitting, photovoltaic cells, fuel cells, and usage of waste products (such as CO₂ ) as chemical fuels are appealing solutions. Many electrocatalysts and nanomaterials have been extensively studied in this regard. Low overpotentials, catalytic stability, and accessibility remain major challenges. Metal nanoclusters (NCs, ≤3 nm) with dimensions between molecule and nanoparticles (NPs) are innovative materials in catalysis. They behave like a "superatom" with exciting size- and facet-dependent properties and dynamic intrinsic characteristics. Being an emerging field in recent scientific endeavors, metal NCs are believed to replace the natural photosystem II for the generation of green electrons in a viable way to facilitate the challenging catalytic processes in energy-conversion schemes. This Review aims to discuss metal NCs in terms of their unique physicochemical properties, possible synthetic approaches by wet chemistry, and various applications (mostly recent advances in the electrochemical and photo-electrochemical water splitting cycle and the oxygen reduction reaction in fuel cells). Moreover, the significant role that MNCs play in dye-sensitized solar cells and nanoarrays as a light-harvesting antenna, the electrochemical reduction of CO₂ into fuels, and concluding remarks about the present and future perspectives of MNCs in the frontiers of surface science are also critically reviewed.

Fluorescent iridium nanoclusters for selective determination of chromium(VI)

Fluorescent iridium nanoclusters (IrNCs) consisting of up to 7 Ir atoms were prepared by heating IrCl₃ in N,N-dimethylformamide. No other reagents are required. High resolution transmission electron microscopy (HRTEM) shows the IrNCs to be monodispersed with an average size of 0.9 ± 0.2 nm. They are well soluble in polar solvents and stable in these solvents for at least 6 months. Under photoexcitation with 365 nm light, they emit strong bluish green fluorescence with peaks that depend on the excitation wavelength and range from 530 to 650 nm. The fluorescence lifetime typically is 2.2 ns and the quantum yield is 8.3%. Fluorescence is quenched by Cr(VI) ion (chromate), and the emission peak is gradually red-shifted. According to the absorbance spectra of IrNCs in the presence and absence of Cr(VI) and Stern-Volmer quenching behavior study, static quenching is involved. Based on these findings, a selective assay was developed for the determination of Cr(VI). It has a linear response in the 0.1 to 100 μM chromate concentration range and a 25 nM detection limit. Graphic abstract Fluorescent iridium nanoclusters (IrNCs), consisting of up to 7 Ir atoms, were prepared in N,N-dimethylformamide (DMF) solution without using any other reagents. Their fluorescence is statically quenched by Cr(VI).

Au22Ir3(PET)18: An Unusual Alloy Cluster through Intercluster Reaction

An intercluster reaction between Au₂₅(PET)₁₈ and Ir₉(PET)₆ producing the alloy cluster, Au₂₂Ir₃(PET)₁₈ exclusively, is demonstrated where the ligand PET is 2-phenylethanethiol. Typical reactions of this kind between Au₂₅(PET)₁₈ and Ag₂₅(SR)₁₈, and other clusters reported previously, produce mixed cluster products. The cluster composition was confirmed by detailed high-resolution electrospray ionization mass spectrometry (ESI MS) and other spectroscopic techniques. This is the first example of Ir metal incorporation in a monolayer-protected noble metal cluster. The formation of a single product was confirmed by thin layer chromatography (TLC). Density functional theory (DFT) calculations suggest that the most favorable geometry of the Au₂₂Ir₃(PET)₁₈ cluster is one wherein the three Ir atoms are arranged triangularly with one Ir atom at the icosahedral core and the other two on the icosahedral shell. Significant contraction of the metal core was observed due to strong Ir-Ir interactions.

[Ag59(2,5-DCBT)32]3-: a new cluster and a precursor for three well-known clusters

We report the synthesis of a new silver cluster, [Ag₅₉(2,5-DCBT)₃₂]^3- (I) (2,5-DCBT: 2,5-dichlorobenzenethiol), which acts as a precursor for the synthesis of three well-known silver clusters, [Ag₄₄(2,4-DCBT/4-FTP)₃₀]^4- (II) (4-FTP: 4-fluorothiophenol and 2,4-DCBT: 2,4-dichlorobenzenethiol), [Ag₂₅(2,4-DMBT)₁₈]^- (III) (2,4-DMBT: 2,4-dimethylbenzenethiol) and [Ag₂₉(1,3-BDT)₁₂(PPh₃)₄]^3- (IV) (1,3-BDT: 1,3-benzenedithiol and PPh₃: triphenylphosphine). This newly synthesized silver cluster, I, is characterized using UV-vis absorption studies, high resolution electrospray ionization mass spectrometry (ESI MS) and other analytical tools. The optical absorption spectrum shows distinct features which are completely different from the previously reported silver clusters. We perform the rapid transformations of I to other well-known clusters II, III and IV by reaction with different thiols. The time-dependent UV-vis and ESI MS measurements reveal that I dissociates into distinct thiolate entities in the presence of thiols and the thiolates recombine to produce different clusters. The conversion mechanism is found to be quite different from the previous reports where it occurs through the initial formation of ligand exchanged products. Here, we also show the synthesis of a different cluster core, [Ag₄₄(2,4-DCBT)₃₀]^4- (IIa) using 2,4-DCBT, a structural isomer of 2,5-DCBT under the same synthetic conditions used for I. This observation demonstrates the effect of isomeric thiols on controlling the size of silver clusters. The conversion of one cluster to several other clusters under ambient conditions and the effect of ligand structure in silver cluster synthesis give new insights into the cluster chemistry.