On the Remarkable Role of the Nitrogen Ligand in the Gas-Phase Redox Reaction of the N2 O/CO Couple Catalyzed by [NbN]+

Ligand effect on Ru-centered species toward methane activation

Ligands have been known to profoundly affect the chemical transformations of methane, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we demonstrate that the conversion of methane can be regulated by Ru centered cations with a series of ligands (C, CH, CNH, CHCNH). Gas-phase experiments complemented by theoretical dynamic analysis were performed to explore the essences and principles governing the ligand effect. In contrast to the inert Ru+, [RuC]+, and [RuCNH]+ toward CH4, the dehydrogenation dominates the reaction of ligand-regulated systems [RuCH]+/CH4 and [RuCHCNH]+/CH4. In active cases, CH acts as active sites, and regulates the activation of CH4 assisted by the "seemingly inert" CNH ligand.

Nitrogen adsorption on Nb2C6H4+ cations: the important role of benzyne (ortho-C6H4)

N2 adsorption is a prerequisite for activation and transformation. Time-of-flight mass spectrometry experiments show that the Nb2C6H4+ cation, resulting from the gas-phase reaction of Nb2+ with C6H6, is more favorable for N2 adsorption than Nb+ and Nb2+ cations. Density functional theory calculations reveal the effect of the ortho-C6H4 ligand on N2 adsorption. In Nb2C6H4+, interactions between the Nb-4d and C-2p orbitals enable the Nb2+ cation to form coordination bonds with the ortho-C6H4 ligand. Although the ortho-C6H4 ligand in Nb2C6H4+ is not directly involved in the reaction, its presence increases the polarity of the cluster and brings the highest occupied molecular orbital (HOMO) closer to the lowest occupied molecular orbital (LUMO) of N2, thereby increasing the N2 adsorption energy, which effectively facilitates N2 adsorption and activation. This study provides fundamental insights into the mechanisms of N2 adsorption in "transition metal-organic ligand" systems.

Benchmark Models for Elucidating Ligand Effects: Thiols Ligated Isostructural Cu6 Nanoclusters

Atomically precise copper nanoclusters (Cu NCs) have attracted tremendous attention for their huge potential in many applications. However, the uncertainty of the growth mechanism and complexity of the crystallization process hinder the in-depth understanding of their properties. In particular, the ligand effect has been rarely explored at the atomic/molecular level due to the lack of feasible models. Herein, three isostructural Cu6 NCs ligated with diverse mono-thiol ligands (2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole, respectively) are successfully synthesized, which provide an ideal platform to unambiguously address the intrinsic role of ligands. The overall atom-by-atom structural evolution process of Cu6 NCs is mapped out with delicate mass spectrometry (MS) for the first time. It is intriguingly found that the ligands, albeit only atomic difference (NH, O, and S), can profoundly affect the building-up processes, chemical properties, atomic structures, as well as catalytic activities of Cu NCs. Furthermore, ion-molecule reactions combined with density functional theory (DFT) calculations demonstrate that the defective sites formed on ligand can significantly contribute to the activation of molecular oxygen. This study provides fundamental insights into the ligand effect, which is vital for the delicate design of high-efficient Cu NCs-based catalysts.

Dinitrogen Activation by Heteronuclear Bimetallic Cluster Anion FeV- in the Gas Phase

Nitrogen activation is a significant but difficult project in the chemical area. Photoelectron spectroscopy (PES) and calculated results are used to investigate the reaction mechanism of the heteronuclear bimetallic cluster FeV^- toward N₂ activation. The results clearly show that N₂ can be fully activated by FeV^- at room temperature, forming the FeV(μ₂-N)₂^- complex with the totally ruptured N≡N bond. Electronic structure analysis reveals that the activation of N₂ by FeV^- is achieved by the electron transfer of bimetallic atoms and electron back-donation to the metal core, which demonstrates that heteronuclear bimetallic anionic clusters are very important to nitrogen activation. This study provides important information for the rational design of synthetic ammonia catalysts.

Spectroscopic Identification of the Dinitrogen Fixation and Activation by Metal Carbide Cluster Anions PtCn- (n = 4-6)

Nitrogen fixation is confronted with great challenges in the field of chemistry. Herein, we report that single metal carbides PtC_n^- and PtC_nN₂^- (n = 4-6) are indispensable intermediates in the process of nitrogen fixation by mass spectrometry coupled with anionic photoelectron spectroscopy, quantum chemical calculations, and simulated density-of-state spectra. The most stable isomers of these cluster anions are characterized to have linear chain structures. The fixation and activation of dinitrogen are facilitated by the charge transfer from Pt and C_n to N₂. The significance of π back-donation of the 5d orbital of the Pt atom to the antibonding π orbits of N₂ for dinitrogen fixation and activation is discussed in detail. This study not only provides a theoretical basis at the molecular level for the activation of dinitrogen by mononuclear metal carbide clusters but also provides a new paradigm for dinitrogen fixation.

On the Catalytic Performance of (ZrO)n (n=1-4) Clusters for CO Oxidation: A DFT Study

The unique characteristic of superatoms to show chemical properties like those of individual atoms opens a new avenue towards replacing noble metals as catalysts. Given the similar electronic structures of the ZrO superatom and the Pd atom, the CO oxidation mechanisms catalysed by (ZrO)_n (n=1-4) clusters were investigated in detail to evaluate their catalytic performance. Our results reveal that a single ZrO superatom exhibits superior catalytic ability in CO oxidation than both larger (ZrO)_n (n=2-4) clusters and a Pd atom, indicating the promising potential of ZrO as a "single-superatom catalyst". Moreover, the mechanism of CO oxidation catalysed by ZrO^+/- suggests that depositing a ZrO superatom onto the electron-rich substrates is a better choice for practical catalysis application. Accordingly, a graphene nanosheet (coronene) was chosen as a representative substrate for ZrO and Pd to assess their catalytic performances in CO oxidation. Acting as an "electron sponge", this carbon substrate can both donate and accept charges in different reaction steps, enabling the supported ZrO to achieve enhanced catalytic performance in this process with a low energy barrier of 19.63 kcal/mol. This paper presents a new realization on the catalytic performance of Pd-like superatom in CO oxidation, which could increase the interests in exploring noble metal-like superatoms as efficient catalysts for various reactions.

Formation of Carbon Dioxide Attached Fragment Ions in the Fragmentation of Deprotonated Tolfenpyrad and Tebufenpyrad

The in-source collision-induced dissociation (CID) and MS/MS mass spectra of deprotonated tolfenpyrad and tebufenpyrad both showed an unusual fragment ion at m/z 187, but its fragmentation pattern and structure could not be explained by logical neutral losses. Accurate mass measurement indicated that the mass difference between this fragment ion and the dominant fragment ion at m/z 143 equaled to a carbon dioxide (CO₂) molecule. The isolation of the fragment ion m/z 143 in the mass analyzer could spontaneously give rise to the ion m/z 187. The Gibbs free energy of carbon dioxide addition to deprotonated pyrazole ion was significantly negative from the computational results. According to these results, we derived a proposal for the formation and structure of the ion m/z 187, which was an attachment of molecular carbon dioxide to the fragment ion m/z 143 to produce a carboxylate anion. The trace carbon dioxide was speculated to be derived from the residual atmosphere or collision gas in the instrument. This study is valuable for the qualitative and quantitative mass spectrometry analysis of pesticides containing the pyrazole functional group.

The mechanism and structure–activity relationship of amide bond formation by silane derivatives: a computational study

The detailed reaction mechanism and structure–activity relationship of substrates in silane reagent-mediated amide bond formation reactions are clarified.