Cationic Clusters Research Articles

Enhancing the Photovoltaic Performance of Cu2ZnSn(S,Se)4 Solar Cells with Ba Trace Doping: Large Chemical Mismatch Cation Incorporation

Being absent from larger mismatch of ionic radius and chemical coordination between the cations in Cu2ZnSn(S,Se)4 (CZTSSe) can aggravate the formation of detrimental cation antisite defects and clusters with low formation energy, which results in a serious open‐circuit voltage deficit and a challenge for higher power conversion efficiency of CZTSSe solar cells. External cation doping or alloying is a more effective strategy to solve this issue. Herein, samples of trace Ba doping into CZTSSe are fabricated by the sol–gel method and the mechanism of such trace Ba doping are studied combined by X‐ray diffraction (XRD), Raman, and photoluminescence (PL) measurements. The performance of CZTSSe solar cells is increased by 25.7% as 1% Ba is doped into CZTSSe to substitute Zn. The results highlight the roles of the trace Ba doping on the performance of CZTSSe solar cells, which is beneficial to the reduced formation of the detrimental defects and associated clusters. As a consequence, the bandgap fluctuations are reduced, which results in the improvement of V OC and thus the performance of the solar cell. The cation substitution engineering with larger chemical mismatched alkaline‐earth metal cations provides insights for further improvement of CZTSSe solar cells based on earth abundant elements.

Gas-phase laboratory study on PAH/amino-acid cluster cations

ABSTRACT As an important class of carbon reservoirs in the interstellar medium (ISM), polycyclic aromatic hydrocarbon (PAH) molecules play an important role in the evolutionary network of prebiotic molecules. Here, the experimental evidence of astronomically relevant amino-acid derivatives – PAH/amino-acid clusters – is provided, and we study their ion–molecular collision reactions in the gas phase. With the initial molecular precursors dicoronylene (DC, C48H20)/alanine (Ala, C3H7NO2) and DC/isoleucine (Ile, C6H13NO2), the experiments indicate that PAH–amino-acid cluster cations (e.g. (Ala)C48H$_{(0-19)}\, ^+$ and (Ile)C48H$_{(0-19)}\, ^+$) and graphene–amino-acid cluster cations (e.g. (Ala)nC$_{48}\, ^+$ and (Ile)nC$_{48}\, ^+$, n = 1, 2, 3, 4) are efficiently formed in a strong interstellar radiation field. In addition, the structure of clusters and the binding energy of their formation pathways are studied by a quantum chemistry calculation method: gas-phase reactions (ion–molecule reactions) between PAH cations with amino acids readily occur (exothermic energy around 2.0–4.7 eV), and these newly formed clusters have a complex molecular configuration (C–O and C–N bond type). These laboratory studies provide a cluster growth pathway (through an ion–molecule reaction) towards the formation of amino-acid derivatives in a bottom-up process and insight into their chemical-evolution behaviour, opening up aromatic-based chemistry that is available to the species (dehydrogenated PAHs or graphene molecules) that formed from the photofragmentation process of PAHs in interstellar environments. When conditions are suitable (e.g. have similar molecular abundance spatial distributions in the ISM), amino-acid derivatives can form efficiently, and newly built large PAH/amino-acid clusters may be widespread in space.

Modular Design of Supramolecular Ionic Peptides with Cell-Selective Membrane Activity.

The rational design of materials with cell-selective membrane activity is an effective strategy for the development of targeted molecular imaging and therapy. Here we report a new class of cationic multidomain peptides (MDPs) that can undergo enzyme-mediated molecular transformation followed by supramolecular assembly to form nanofibers in which cationic clusters are presented on a rigid β-sheet backbone. This structural transformation, which is induced by cells overexpressing the specific enzymes, led to a shift in the membrane perturbation potential of the MDPs, and consequently enhanced cell uptake and drug delivery efficacy. We envision the directed self-assembly based on modularly designed MDPs as a highly promising approach to generate dynamic supramolecular nanomaterials with emerging membrane activity for a range of disease targeted molecular imaging and therapy applications.

Modeling of photoabsorption spectra of small helium cluster cations through ab initio and semi-empirical approaches. A comparative study

A comparative study has been performed to assess the reliability of a diatomics-in-molecules (DIM) representation of the potential energy surfaces in calculations of the photoabsorption spectra of selected charged helium clusters, He N + ( N = 3 , 4 , 10 ). Results of the computationally cheap DIM approach have been compared to data resulting from accurate ab initio methods (MRCI, EOM-CCSD) and extended basis sets (up to d-aug-cc-pVQZ). Both single-point calculations and averaged photoabsorption spectra calculations have been performed to observe the effect of approximations employed within the DIM approach. DIM predictions of photoabsorption spectra are in a fairly good agreement with the ab initio ones, which seems to indicate that the semi-empirical DIM approach is suitable for simulating larger ionic helium clusters for which more elaborate ab initio models are not practicable.

Gas-phase Formation of Cationic Fullerene/Amino Acid Clusters: Evidence for the “Magic Number” Chemical Reactivity of Fullerene Cations

Abstract An experimental and theoretical investigation on the chemical reactivity of fullerene cations (C n +, n = [36, 60]) with amino acid molecules (e.g., isoleucine, C6H13NO2) is performed. The results show that, in the gas phase, fullerene cations can react with amino acid molecules to form fullerene/amino acid cluster cations with high efficiency. The formation rate constants for the ion–molecule collision reactions between fullerene cations and isoleucine are estimated under the pseudo-first-order reaction condition. We find the formation rate constants increase gradually with a declining C-atom number of fullerene cations (C n +, n = [46, 60]), and depict a plateau in the reactivity for smaller fullerene cations (C n +, n = [36, 44]). More importantly, by comparing to its neighbor fullerenes, the magic number of C-atom counts (54, 58) that process with enhanced chemical reactivity are determined. We also obtained the molecular structures and binding energies for the fullerene-monoisoleucine adducts by quantum chemical calculations, which give a good explanation for the magic number chemical reactivity and the enhanced chemical reactivity of smaller fullerene cations. We infer that our results demonstrate the importance of ion–molecule reactions to the formation of large and complex fullerene-amino acid derivatives in the ISM. The high reactivity of fullerene species may indicate that amino acid molecules or other related prebiotic compounds can accrete on small interstellar carbon dust grains.

Gold Clusters: From the Dispute on a Gold Chair to the Golden Future of Nanostructures.

The present work opens with an acknowledgement to the research activity performed by Luciana Naldini while affiliated at the Università degli Studi di Sassari (Italy), in particular towards gold complexes and clusters, as a tribute to her outstanding figure in a time and a society where being a woman in science was rather difficult, hoping her achievements could be of inspiration to young female chemists in pursuing their careers against the many hurdles they may encounter. Naldini’s findings will be a key to introduce the most recent results in this field, showing how the chemistry of gold compounds has changed throughout the years, to reach levels of complexity and elegance that were once unimagined. The study of gold complexes and clusters with various phosphine ligands was Naldini’s main field of research because of the potential application of these species in diverse research areas including electronics, catalysis, and medicine. As the conclusion of a vital period of study, here we report Naldini’s last results on a hexanuclear cationic gold cluster, [(PPh3)6Au6(OH)2]2+, having a chair conformation, and on the assumption, supported by experimental data, that it comprises two hydroxyl groups. This contribution, within the fascinating field of inorganic chemistry, provides the intuition of how a simple electron counting may lead to predictable species of yet unknown molecular architectures and formulation, nowadays suggesting interesting opportunities to tune the electronic structures of similar and higher nuclearity species thanks to new spectroscopic and analytical approaches and software facilities. After several decades since Naldini’s exceptional work, the chemistry of the gold cluster has reached a considerable degree of complexity, dealing with new, single-atom precise, materials possessing interesting physico-chemical properties, such as luminescence, chirality, or paramagnetic behavior. Here we will describe some of the most significant contributions.

Infrared Spectroscopy and Anharmonic Vibrational Analysis of (H2O-Krn)+ (n = 1-3): Hemibond Formation of the Water Radical Cation.

The hemibond is a nonclassical covalent bond formed between a radical (cation) and a closed shell molecule. The hemibond formation ability of water has attracted great interest, concerning its role in ionization of water. While many computational studies on the water hemibond have been performed, clear experimental evidence has been hardly reported because the hydrogen bond formation overwhelms the hemibond formation. In the present study, infrared photodissociation spectroscopy is applied to (H2O-Krn)+ (n = 1-3) radical cation clusters. The observed spectra of (H2O-Krn)+ are well reproduced by the anharmonic vibrational simulations based on the hemibonded isomer structures. The firm evidence of the hemibond formation ability of water is revealed.

Pseudo-zwitterions self-assembled from polycation and anion clusters showing exceptional water-cleanable anti-crude-oil-adhesion property

SummaryIt is of great importance and practical value to develop a facile and operable surface treatment method of materials with excellent antipollution and antiadhesion property, but still a huge challenge. In this work, a series of pseudo-zwitterions are prepared from electrostatic assembly of cationic polyethyleneimine and anionic phosphonic clusters. These pseudo-zwitterionic assemblies provide a strong hydration through electrostatic interaction with water and in turn create a barrier against oil foulants, leading to a nearly zero crude oil adhesion force. The pseudo-zwitterions-decorated surfaces exhibit exceptional water-cleanable oil-repellent property, even when they are completely dried and without prehydration before fouled by crude oil. While using these pseudo-zwitterions-modified polymeric membranes for separating surfactant stabilized oil-in-water emulsion, less than 10% decline of permeating flux is observed throughout a 2-h continuous separation experiment, showing excellent emulsion separation ability and antipollution performance for high viscous oil.

The ground state structures and spectra of Ag20 clusters and the adsorption to carbon monoxide

The most stable structures and spectra of neutral, anionic and cationic Ag20 clusters have been studied by using density functional theory in conjunction with an unbiased CALYPSO structure searching method. Structural searches indicate that the regular tetrahedron which was widely regarded as the ground-state of neutral Ag20 cluster is a low-lying isomer. Several new isomers with lower energy than the regular tetrahedron were found in geometry optimizations. The ground state structures of neutral and anionic Ag20 cluster are confirmed by the optical absorption and photoelectron spectra. On the other hand, the investigation of CO adsorption on Ag20 clusters shows that CO adsorption on anionic Ag20 cluster is stronger than that on neutral and cationic Ag20 clusters. The lowest energy structure of anionic Ag20 cluster can bind CO molecular number up to 19. The adsorption of CO on Ag20 clusters significantly changes the Infrared spectra of neutral and cationic Ag20 clusters and the Raman spectrum of anionic Ag20 cluster. Raman scattering intensity of CO adsorbed on Ag20 cluster was enormously enhanced.

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.

Search for Global Minimum Structures of (n = 1-15) Using xTB-Based Basin-Hopping Algorithm.

A new program for searching global minimum structures of atomic clusters using basin-hopping algorithm based on the xTB method was developed here. The program can be performed with a much higher speed than its replacement directly based on DFT methods. Considering the structural varieties and complexities in finding their global minimum structures, phosphorus cluster cations were studied by the program. The global minimum structures of cationic (n = 1–15) clusters are determined through the unbiased structure searching method. In the last step, further DFT optimization was performed for the selected isomers. For (n = 1–4, 7), the found global minimum structures are in consistent with the ones previously reported; while for (n = 5, 6, 8–12), newly found isomers are more energy-favorable than those previously reported. And those for (n = 13–15) are reported here for the first time. Among them, the most stable isomers of (n = 4–6, 9) are characterized by their C3v, Cs, C2v and Cs symmetry, in turn. But those of (n = 7, 8, 10–12), no symmetry has been identified. The most stable isomers of and are characterized by single P-P bonds bridging units inside the clusters. Further analysis shows that the pnicogen bonds play an important role in the stabilization of these clusters. These results show that the new developed program is effective and robust in searching global minimum structures for atom clusters, and it also provides new insights into the role of pnicogen bonds in phosphorus clusters.

An ultrahigh-energy-density lithium metal capacitor

Lithium-ion capacitors (LICs), shrewdly integrating a battery-type negative electrode and a capacitive-type carbon positive electrode, are expected to inherit simultaneously both the high specific energy of lithium-ion batteries (LIBs) and high specific power of electrochemical capacitors (ECs). However, state-of-the-art LICs are approaching their specific energy limits yet are still far away from that dictated by LIBs. Herein, we report an aprotic Li-metal capacitor (LMC) strategy to solve this problem through coupling a Li-metal negative electrode with a three-dimensional scaffold activated carbon (3D-SAC) positive electrode. The employment of metal Li negative electrode leads to an ultrahigh specific capacitance up to 280 F gpositive electrode−1 within high potential range from 1.5 to 4.3 V vs Li/Li+, giving a remarkable specific energy of 633 Wh kgpositive electrode−1. Combing with theoretical simulation and advanced characterizations, it is revealed that such a high capacitance is the contribution resulting from multiple electrical double-layer mechanisms on carbon positive electrode that involves the desorption of PF6− anions, the exchange between adsorbed PF6− anions and solvated cation clusters, and the adsorption of solvated cation clusters. The unique desolvation behavior and the electrochemical adsorption of desolvated Li+-related cations boost the specific capacitance and specific energy at low current rates. This is completely different from the reported LICs. This findings provide a new strategy for developing high-energy-and-power capacitors and batteries.

Hexa-aquadodeca-μ2-chlorido-octa-hedro-hexa-niobium diiodide.

The title compound, [Nb6Cl12(H2O)6]I2, consists of the niobium cluster cation [Nb6Cl12(H2O)6]2+ and two non-coordinating, charge-balancing iodide ions. The edges of the Nb6 octa-hedron are bridged by chlorido ligands. Each Nb atom is further coordinated by a water ligand. The cluster cation has a charge of +2, which is balanced by that of two iodide anions.

First-principles characterisation of spectroscopic and bonding properties of cationic bismuth carbide clusters

Vibrational and electronic absorption spectra calculated at the (time-dependent) density functional theory level for the bismuth carbide clusters BinC2n+ (3⩽n⩽9) indicate significant differences in types of bonding that depend on cluster geometry. Analysis of the electronic charge densities of these clusters highlighted bonding trends in these complex open-shell systems consistent with the spectroscopic information. The data indicate that larger clusters (n>5) have significant non-covalent bonding character and are likely to be kinetically unstable, in agreement with the cluster mass distribution obtained in gas-aggregation source experiments. The spectral fingerprints of the different clusters obtained from our calculations also suggest that identification of specific BinC2n+ structural isomers should be possible based on infra-red and optical absorption spectroscopy.

Cryokinetics and spin quenching in the N2 adsorption onto rhodium cluster cations

ABSTRACT The kinetics of N2 adsorption onto gas phase Rh i + clusters (i = 5–15) within 26 K He buffer gas have been investigated by Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry, with particular focus to clusters i = 5,6,7,9. The adsorption limits m = mmax of [Rh i (N2) m ]+ clusters strongly depend on the size of the clusters. Some Rh i + clusters reveal an intermittent adsorption limit mx , which implies a rough cluster surface. Most of the clusters reveal smooth surfaces, which consist of Rh atoms with similar next neighbour coordination. The kinetic fits and relative rate constants reveal the sequential adsorption of N2 as the only significant reaction channel. In some cases, we find N2 desorption steps at high N2 loads indicating adsorption–desorption equilibria. For these steps, we determined Gibbs energies from the relative rate constants. We observed a significant reluctance towards N2 adsorption for the Rh5 + cluster, indicated by significant desorption at low N2 coverage. Our DFT calculations model the energetics of the N2 adsorption onto Rh5 + in terms of coverage dependent ‘spin valley’ curves, and we conclude that an adsorption induced spin quenching takes place upon considerable N2 coverage, m > 4.

Electronic Structure of Superoxidized Radical Cationic Dodecaborate-Based Clusters.

The expanding field of boron clusters has attracted continuous theoretical efforts to understand their diverse structures and unique bonding. We recently discovered a new reversible redox event of B12(O-3-methylbutyl)12 in which the superoxidized radical cationic form [B12(O-3-methylbutyl)12]•+ was identified and isolated for the first time. Herein, comprehensive (TD-)DFT studies in tandem with electrochemical experiments were employed to demonstrate the generality of the reported behavior across perfunctionalized B12(OR)12 clusters (R = aryl or alkyl). While the spin density of radical cationic clusters is delocalized in the core region, the oxidation brings about notable gains of positive partial charges on the supporting groups whose electronics can readily tune the redox potential of the 0/•+ couple. The underlying changes of frontier orbitals were elucidated, and the resulting [B12(OR)12]•+ species manifest a general diagnostic absorption as a consequence of mixed local/charge-transfer excitations.

Argon Adsorption on Cationic Gold Clusters Aun+ (n ≤ 20).

The interaction of Aun+ (n ≤ 20) clusters with Ar is investigated by combining mass spectrometric experiments and density functional theory calculations. We show that the inert Ar atom forms relatively strong bonds with Aun+. The strength of the bond strongly varies with the cluster size and is governed by a fine interplay between geometry and electronic structure. The chemical bond between Aun+ and Ar involves electron transfer from Ar to Au, and a stronger interaction is found when the Au adsorption site has a higher positive partial charge, which depends on the cluster geometry. Au15+ is a peculiar cluster size, which stands out for its much stronger interaction with Ar than its neighbors, signaled by a higher abundance in mass spectra and a larger Ar adsorption energy. This is shown to be a consequence of a low-coordinated Au adsorption site in Au15+, which possesses a large positive partial charge.

A rechargeable 6-electron Al–Se battery with high energy density

Rechargeable aluminum ion batteries (AIBs) have attracted substantial interest due to their high theoretical energy density, low cost, and high security. However, the low-energy density and high-cost of the reported cathode materials hinder their further development. Herein, a Se-based 6-electron Al-Se battery was generated by activating the highly reversible Se(−II)/Se(0) couple into Se(0)/Se(IV) couple in AlCl3-based ionic liquid electrolyte, which exhibited an ultra-high theoretical specific capacity (2036 mAh g−1). For further activating the Se cathode and addressing the shuttle effect of the soluble products, the Se/graphene aerogel (Se/GA) and carbon-based modified separator with oxygen-containing functional groups (O-CNT) were collectively employed to promote stable high-energy density for Al-Se battery. Consequently, GA improved the utilization of Se cathode and reduced its overpotential, delivering super-high specific capacity with a sufficient voltage discharge plateau at au. 1.9 V. However, the O-CNT separator effectively blocked these Se-based cationic clusters, such as Sen2+ and SeCl3+, by a dual defense mechanism that integrated the physical barrier of porous structure and powerful chemical adsorption ability of the carboxyl (–COOH) group. Then, a high energy density of 1957 Wh kg−1 (1599 mAh g−1) was delivered at 100 mA g−1 and 624 Wh kg−1 (580 mAh g−1) at 1000 mA g−1. Furthermore, the Al-Se battery exhibited outstanding cycling performance of 421 Wh kg−1 (395 mAh g−1) at 1000 mA g−1 after 200 cycles with the record-setting cyclic performance achieved in the documented AIBs. These results provide useful insight into and a versatile strategy for boosting the performance of Al-Se battery.

Assembly of a Titanium-Oxo Cluster and a Bismuth Iodide Cluster, a Single-Source Precursor of a p-n-Type Photocatalyst.

Titanium oxides and bismuth halides or oxyhalides have been known to be excellent semiconductors with both excellent photocatalytic and photoelectric properties. The design of supersalts assembled by titanium-oxo clusters (TOCs) and bismuth iodide clusters is a hopeful strategy for exploring the chemistry and application of new titanium-oxo clusters. We report herein a series of unusual ionic TOCs with Ti12 oxo cluster cations and bismuth iodide anions, [Ti12O15(OiPr)17]3[Bi3I12] (Bi3), [Ti12O14(OiPr)18][Bi4I14(THF)2] (Bi4), and [Ti12O14(OiPr)18][Ti11BiO14(OiPr)17][Bi6I22] (Bi6). Single-crystal X-ray analysis revealed that the type and charge of the Ti12 clusters varied with the charges of different bismuth iodide clusters. Taking advantage of the easy hydrolysis of the TOCs and BiI clusters in water, we used these supersalt crystals as single-source precursors to prepare a p-n-type BiOI-TiO photocatalyst. The heterojunction materials were carefully characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, etc. The synergistic effect of the two components of BiOI and TiO on the photocatalytic degradation of RhB in water is demonstrated. This is a very convenient method for obtaining a p-n-type BiOI-TiO heterojuction photocatalyst by just placing the ground TOC crystals into water.

Room-Temperature Methane Activation Mediated by Free Tantalum Cluster Cations: Size-by-Size Reactivity.

The energetics of small cationic tantalum clusters and their gas-phase adsorption and dehydrogenation reaction pathways with methane are investigated with ion-trap experiments and spin-density-functional-theory calculations. Tan+ clusters are exposed to methane under multicollision conditions in a cryogenic ring electrode ion-trap. The cluster size affects the reaction efficiency and the number of consecutively dehydrogenated methane molecules. Small clusters (n = 1-4) dehydrogenate CH4 and concurrently eliminate H2, while larger clusters (n > 4) demonstrate only molecular adsorption of methane. Unique behavior is found for the Ta+ cation, which dehydrogenates consecutively up to four CH4 molecules and is predicted theoretically to promote formation of a [Ta(CH2-CH2-CH2)(CH2)]+ product, exhibiting C-C coupled groups. Underlying mechanisms, including reaction-enhancing couplings between potential energy surfaces of different spin-multiplicities, are uncovered.