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Icosahedral gold clusters with high-symmetry geometry and magic electronic shells are potential candidates for cluster-assembling, while their assembling rules are still awaiting further investigation. In this work, we use the all-metal icosahedral M@Au12as a building block to assemble a series of bi-, tri-, tetra-, and penta-superatomic molecules with diverse superatomic bonding patterns via face-fusion, aiming to systemically explore the bonding rule of superatoms. Chemical bonding analyses indicate that these bi-, tri-, tetra-, and penta-superatomic molecules [M@Au12]n+/0(M = Re, W, Ta, Ti, Hf, Ir, and Pt) can be considered electronic analogues to Cl2, O2, N2, CO, O3, CO2, NCl3, and CF4molecules with single, double, triple, and multicenter bonds, respectively. In multi-superatomic molecules, the central superatom undergoes super S–P orbital hybridizations to form super σ bonds with each peripheral superatom, mimicking the bonding rules of molecules. Due to the large size of superatoms, superatomic molecules also present some distinct bonding characters in structure and relative energy compared to their analogues. This paper systemically investigated the superatomic bonding rules, giving references to further design and synthesis of superatom-assembled materials.

Searching for a useful way to build stable hypercoordinate carbon species is a great way to enrich carbon-based chemical rules. Here, we extend the super valence bond model into superatom–atom superbonding to theoretically predict a two-dimensional (B3CB3)N2monolayer, which is the first design of a stable nonplanar hexacoordinate carbon containing material, featuring a sandwich B3CB3configuration. Chemical bonding analyses indicate that its stability originates from the unique super CO2structures, where each tricoordinate B3unit has six delocalized electrons acting as a super oxygen (S2P4), and the B3CB3unit mimics the bonding pattern of the CO2molecule via the superatom–atom super double bond. Thus, the (B3CB3)N2monolayer can be visualized as an assembly of super CO2units linked by N atoms. The calculated moderate direct band gap (∼1.71 eV) and high light absorption coefficient of the (B3CB3)N2monolayer make it a promising candidate for further applications in electronics and optoelectronics. This work provides a possible pathway to design hypercoordinate carbon materials via superatom–atom cluster assembly, which is expected to be applied across diverse fields.

Three-center two-electron bridging bonding plays a vital role in rationalizing structures and stabilities of certain molecules. Herein, the π electron rule of pyrene (C16H10) was unraveled based on a newly proposed two-dimensional (2D) superatomic-molecule theory, where the superatomic sextet rule was regarded as a π electron counting target. C16H10can be taken as a ◊N2◊F2superatomic molecule, where ◊N and ◊F denote 2D superatoms bearing 3π and 5π electrons, respectively. Interestingly, it represents the first 2D superatomic halogen-bridge molecule, which realizes π electronic shell-closure via two three-supercenter two-electron bridging bonds. Additionally, a N-doped nanoporous graphene with a wide band gap (1.22 eV) was designed based on C16H10, which can be considered as a periodic aggregate of 2D superatomic wires composed of 2π-◊C and bridging ◊F superatoms. This work enriches the 2D superatomic-molecule chemistry and provides a practicable bottom-up assemble approach to obtain 2D functional materials with tunable band gaps.

Anthraquinone hydrogenation to produce H2O2is an economically interesting reaction with great industrial importance. Here, we report a series of Pd/xAl catalysts with different AlCl3contents by a conventional stepwise impregnation method. The optimal Pd/1.0Al catalyst exhibits a higher performance toward anthraquinone hydrogenation with 8.3 g·L−1hydrogenation efficiency, 99.5% selectivity and good stability, obviously superior to that of Pd/Al2O3catalyst (5.2 g·L−1and 97.2%). Detailed characterization demonstrates that AlCl3can be grafted on the γ-Al2O3support to obtain a modified support with abundant surface weak acid and Lewis acid, which can adsorb and activate anthraquinone. Meanwhile, its steric hindrance could isolate and disperse active metals to form more active sites. The synergies between metal sites and acid sites promotes the anthraquinone hydrogenation. Furthermore, the good stability after grafting AlCl3could attribute to the enhanced metal-support interaction inhibiting metal particles agglomeration and leaching.

The aromaticity of π-conjugated compounds has long been a confusing issue. Based on a recently emerged two-dimensional (2D) superatomic-molecule theory, a unified rule was built to decipher the aromaticity of cyclic superatomic molecules of π-conjugated compounds from the chemical bonding perspective. Herein, a series of planar [n]helicenes and [n]circulenes, composed of benzene, thiophene, or furfuran, are systemically studied and seen as superatomic molecules ◊On-2◊F2or ◊On, where superatoms ◊F and ◊O denote π-conjugated units with 5 and 4 π electrons, respectively. The ascertained superatomic Lewis structures intuitively display aromaticity with each basic unit meeting the superatomic sextet rule of benzene, similar to classical valence bond theory, which is favored by the synthesized complex π-conjugated compounds comprising different numbers and kinds of subrings. The evolutionary trend of ring currents and chemical bonding suggests a local ribbon-like aromaticity in these π-conjugated compounds. Moreover, nonplanar helical π-conjugated compounds have the potential to evolve into spring-like periodic materials with excellent physical properties.

Reaction of Li2C2with elemental selenium in a molar ratio of 1:2 in liquid ammonia led to the formation of the ammoniate Li2[SeC2Se]·2NH3. Its crystal structure was solved and refined from high-resolution synchrotron powder diffraction data (P21/c, Z= 4). It contains the –Se–C≡C–Se–anion, unprecedented in a crystalline material, whose existence was corroborated by IR/Raman spectra and electronic-structure theory, showing an almost perfect agreement with calculated spectra. Elaborated magnetic-bottle and velocity-map imaging photoelectron spectroscopic investigations show that the –Se–C≡C–Se•radical anion can be transferred to the gas phase, where it was analyzed by NIPE (Negative Ion Photoelectron) and VMI (Velocity-Map Imaging) spectra, which correlate nicely with simulated spectra based on 2Πu→ 3Σg–and 2Πu→ 1Σg+transitions including spin–orbit couplings.

Six monosolvated cyanate analogue clusters ECX–·Sol (ECX–= NCSe–, AsCSe–, and AsCS–; Sol = H2O and CH3CN) were investigated using negative ion photoelectron spectroscopy (NIPES). NIPES experiments show that these clusters possess similar spectra overall compared to their respective isolated ECX–anions but shift to higher electron binding energy with CH3CN solvent, stabilizing the excess electrons slightly more than H2O. For the ECX–·H2O series, vertical detachment energies and their increments relative to the bare species are measured to be 3.700/0.370, 3.085/0.415, and 3.085/0.430 eV for NCSe–, AsCSe–and AsCS–, respectively, while the corresponding values in the ECX–·CH3CN series are 3.835/0.505, 3.145/0.475, and 3.135/0.480 eV. Ab initio electronic structure calculations indicate that the excess charges were located at the terminal N and Se atoms in NCSe–and migrated to the central C atom in AsCSe–and AsCS–. For NCSe–, the solvation is driven by the interactions with the two negatively charged terminal ends, while for AsCSe–and AsCS–, the solvation revolves around the interactions with the central C atom, where all the excess negative charge is concentrated. Two nearly degenerate isomers for NCSe–·H2O are identified, one forming a single strong N···H–O hydrogen bond (HB) and the other featuring a bidentate HB with two hydroxyl H atoms pointing to N and Se ends. In contrast, the negative central C atom in AsCSe–/AsCS–allows the formation of a bifurcated HB with H2O. Similar effects are observed for the acetonitrile case, in which the three H atoms of the methyl group interact with the two negatively charged terminal ends in NCSe–, while preferring to bind to the central negative carbon atom in AsCSe–/AsCS–. The different binding motifs derived in this work may suggest different solvation properties in NCSe–versus AsCSe–/AsCS–with the former anion leading to asymmetric solvation at the N end of the solute, while the latter species creates more “isotropic” solvation around the central C equatorial plane.

A great deal of effort has been focused on developing a metal-free catalytic system for epoxidation of unreactive alkenes. Fluoroketones are thought as remarkably promising catalysts for epoxidation reactions. The combination of fluorinated alcohols and catalytic amounts of hexafluoroacetone (HFA) gives a versatile and effective medium for epoxidation of various olefins with hydrogen peroxide. However, the fundamental physicochemical properties of HFA remained largely unclear, although they were very important to understand the related interactions. Here, we performed a joint study on the electron affinity and electronic structure of HFA employing negative ion photoelectron (NIPE) spectroscopy and quantum chemistry calculations. Two distinct bands with complicated vibrational progressions were observed in the 193 nm NIPE spectrum. The adiabatic/vertical detachment energies (ADE/VDE) were derived to be 1.42/2.06 and 4.43/4.86 eV for the ground singlet state and excited triplet state, respectively. Using the optimized geometries and vibrational frequencies of the anion and the neutral, the Franck–Condon factors were calculated for electron detachments to produce HFA in its lowest singlet and triplet states. Good agreements are obtained hereby for both bands between the experimental and calculated NIPE spectra, when taking into account combination vibrational excitations, unequivocally revealing that HFA possesses a singlet ground state with a giant singlet–triplet energy difference (ΔEST). The electron affinity (EA) and ΔESTof HFA were therefore determined to be EA = 1.42 ± 0.02 eV and ΔEST= −3.01 eV.

The recently synthesized acetylide compound KSeCCH containing the main group element selenium within the novel and in crystalline form unprecedented [SeCCH]−anion was successfully investigated in the gas phase by high-resolution velocity-map imaging (VMI) and magnetic-bottle (MB) photoelectron spectroscopy coupled with an electrospray ionization source. Both VMI and MB spectra exhibited identical electron affinities (EA, 2.517 ± 0.002 eV), spin–orbit coupling (SOC) splittings (1492 ± 20 cm–1), and Se–C stretching frequencies (573 ± 20 cm–1) of the corresponding neutral tetra-atomic radical [SeCCH]•with the VMI spectrum possessing six times higher spectral resolution compared with the MB spectrum. These experimental values were well reproduced by calculations at the CCSD(T) level, in which both the isolated [SeCCH]−anion and the [SeCCH]•radical adopted linear geometries. The simulated spectra based on the calculated Franck–Condon factors, the SOC splitting, and the experimental line width matched well with the measured spectra. Furthermore, comparisons of the EA and SOC splitting values with the previously reported isolobal species [SeCN]•are also made and discussed. The decrease in the EA and SOC splitting of [SeCCH]•is ascribed to the differences in the electronegativities between C and N atoms as well as the electron density on the Se atom in its singly occupied molecular orbital (SOMO).

A series of heteronuclear group 5 metal–nickel carbonyls MNi(CO)7–(M = V, Nb, Ta) have been generated via a laser ablation ion source and studied by photoelectron velocity-map imaging spectroscopy. Quantum chemical calculations have been performed to probe the electronic and geometric structures and help to assign the spectra. The adiabatic detachment energies (ADEs) and vertical detachment energies (VDEs) are deduced from spectra to be 3.40/3.58, 3.34/3.55, 3.30/3.50 eV, which are consistent with quantum chemical computational results. The MNi(CO)7–(M = V, Nb, Ta) consists of three bridging carbonyls, one carbonyl terminally bonded to the Ni atom and three carbonyls terminally bonded to the M (M = V, Nb, Ta) atom. These geometries are different from homobinuclear Cr2(CO)7+, Ni2(CO)7+, Pd2(CO)7+, and Fe2(CO)7–and heterobinuclear CuFe(CO)7–, CoZn(CO)7+, and CO is largely activated by a bridging coordination mode. The experimental and theoretical results would provide important information to understand the chemisorbed CO molecules on alloy surfaces or interfaces, which is of great significance to elucidate CO molecule activation processes.

The interactions between hexafluoroisopropanol (HFIP) and halogen anions X–(F–, Cl–, Br–, and I–) have been investigated using negative ion photoelectron (NIPE) spectroscopy and ab initio calculations. The measured NIPE spectrum of each [HFIP·X]−(X = Cl, Br, and I) complex shows a pattern identical to the corresponding X–by shifting to the high electron binding energy side, indicative of the formation of the [HFIP···X–] structure in which X–interacts with HFIP via charge–dipole interactions. However, the spectrum of [HFIP·F]−appears completely different from that of F–and is more similar to the spectrum of the deprotonated HFIP anion (HFIP–H–). The geometry and electron density calculations indicate that a neutral HF molecule is formed upon HFIP interacting with F–via proton transfer, rendering a stable structure of [HFIP–H···HF]−. Two conformers of [HFIP–H·HF]−with HFIP being in synperiplanar and antiperiplanar configurations, respectively, are observed, providing direct experimental evidences to show the distinctly different and orientation-specific interactions between HFIP and halide anions.

Negative ion photoelectron spectroscopy (NIPES) coupled with electrospray ionisation (ESI) has been proven to be a powerful gas-phase spectroscopic tool for characterising electronic structures, chemical bonding of a variety of cluster anions, and corresponding neutral radicals involved in the condensed phase reactions and transformations. Since the acquisition of cryogenic and temperature-controlling capabilities, a broader range of research has been covered. This review summarises our recent investigations on metal complexes employing cryogenic ESI-NIPES that provides essential information towards understanding complicated condensed phase reactions, including hydrocarbon activations and electron transfer reactions, and affords spectroscopic perspective of highly reactive transient species and intimate redox pairs. Special attention has been drawn to connect gas phase photodetachment processes with solution phase redox reactions. Photodetachment of transition metal-EDTA complexes has been systematically investigated to model the sequential oxidation reactions of these species in solutions. For each series of homologous metal complexes, the obtained gas phase electron affinity (EA) is compared with the solution redox potential (E1/2) and the metal ionisation potential (IP) to emphasise their intrinsic correlations, with deviations being largely modulated by different degrees of ligand participations.

Functionalization of electrodes with clusters of hydrophobic molecules may improve the energy efficiency and selectivity of electrochemical separations by modulating the desolvation process occurring at the interface. Ionic liquids (ILs), which have a broad range of compositions and properties, are potential candidates for controlling the transport, desolvation, and adsorption of target ions at electrochemical interfaces. Herein, we report a joint experimental and theoretical investigation of the structure, stability, and selective adsorption properties of IL clusters 1-ethyl-3-methylimidazolium chloride [EMIM]x[Cl]x+1–(x= 1–10) and demonstrate their ability to adsorb and separate ions from solution. The structure and stability of the IL clusters are determined experimentally using high-mass-resolution electrospray ionization mass spectrometry, collision-induced dissociation, and negative-ion photoelectron spectroscopy. Global optimization theory and ab initiomolecular dynamics simulations provide molecular-level insights into the bonding and structural fluxionality of these species. Ion soft landing is used to selectively functionalize the surface of highly oriented pyrolytic graphite (HOPG) working electrodes with [EMIM]1[Cl]2–, [EMIM]3[Cl]4–, and [EMIM]5[Cl]6–clusters. Kelvin probe microscopy provides insights into the relative stability of the clusters on HOPG and their effect on the work function of IL-functionalized electrodes. Cyclic voltammetry measurements reveal the irreversible adsorption of Fe(CN)64–/3–anions during redox cycling, while electrochemical impedance spectroscopy indicates a substantial decrease in the electron transfer resistance of the IL-functionalized electrodes due to adsorption of Fe(CN)64–/3–. Overall, our findings demonstrate that IL clusters with different sizes and stoichiometry may be used to increase the efficiency of electrochemical separations, opening new horizons in selective electrode functionalization.