Cluster Anions Research Articles

Structures and growth pathways of AunCln+3- (n ≤ 7) cluster anions.

Gold chloride clusters play an important role in catalysis and materials chemistry. Due to the diversity of their species and isomers, there is still a dearth of structural studies at the molecular level. In this work, anions of AunCln+3 - and AunCln+5 - (n = 2-4) clusters were obtained by laser desorption/ionization mass spectrometry (LDI MS), and the most stable isomers of AunCln+3 - were determined after a thorough search and optimization at the TPSSh/aug-cc-pVTZ/ECP60MDF level. The results indicate that all isomers with the lowest energy have a planar zigzag skeleton. In each species, there is one Au(III) atom at the edge connected with four Cl atoms, which sets it from the other Au(I) atoms. Four growth pathways for AunCln+3 - (n = 2-7) clusters are proposed (labelled R1, R2, R3 and R4). They are all associated with an aurophilic contact and are exothermic. The binding energies tend to stabilize at ∼ -41kcal/mol when the size of the cluster increases in all pathways. The pathway R1, which connects all the most stable isomers of the respective clusters, is characterized by cluster growth due to aurophilic interactions at the terminal atom of Au(I) in the zigzag chains. In the pathway of R4 involving Au-Au bonding in its initial structures (n ≤ 3), the distance between intermediate gold atoms grows with cluster size, ultimately resulting in the transfer of the intermediate Au-Au bonding into aurophilic interaction. The size effect on the structure and aurophilic interactions of these clusters will be better understood based on these discoveries, potentially providing new insights into the active but elusive chemical species involved in the corresponding catalytic reactions or nanoparticle synthesis processes.

Synthesis of novel supramolecular selenomolybdate as anticancer agents: An experimental and DFT computational analysis

A novel organic–inorganic material based on three-dimensional (3D) Strandberg-type polyoxoselenomolybdate, (C6H14N2)2[Se2Mo5O21]·2·6H2O (I, where C6H14N2 = DABCO cation) was successfully synthesized by solution process and characterized by scanning electron microscopy (SEM), infrared (FT-IR) and ultraviolet (UV–vis) spectroscopies, thermogravimetric analysis (TGA), cyclic voltammetry (CV) measurement. The electronic and electrochemical behavior of the compound was further evaluated as a function of pH and time via UV–vis spectroscopy and CV. Single crystal X-Ray diffraction (XRD) technique was used for complete structure elucidation. The title compound crystallizes in the non-centrosymmetric orthorhombic space group P212121, thus resulting in non-linear optical properties. The supramolecular framework exhibits a periodic arrangement of Strandberg clusters anions [Se2Mo5O21]4– connected to each other with water molecules and dabconium cations, through a network of hydrogen bonds and van der Waals interactions. The occurrence of intermolecular interactions, ensuring the cohesion between different entities, was assessed by density functional theory (DFT) calculations and Hirshfeld surface analysis. DFT calculations with different functionals have been used to better understand several properties like as RDG, QTAIMs, ELF, MEP and NLO.A good agreement was indeed found between the experimental and computational results. Furthermore, the (C6H14N2)2[Se2Mo5O21]·2·6H2O compound was tested for its biological activity. This selenomolybdate displayed a significant inhibitory effect on the growth of human ovarian cancer cells A2780, with an IC50 value of 4.05 ± 0.55 μM, being thus the first Strandberg-type polyoxometalate to show a significant anticancer activity.

Molecular Interactions Required for Activation of Complement Component C2 Include Exosites Located on the Serine Protease Domain of C1s and Mannose-Binding Lectin Associated Protease-2.

The activation of the CP/LP C3 proconvertase complex is a key event in complement activation and involves cleavage of C4 and C2 by the C1s protease (classical pathway) or the mannose-binding lectin-associated serine protease (MASP)-2 (lectin pathway). Efficient cleavage of C4 by C1s and MASP-2 involves exosites on the complement control protein and serine protease (SP) domains of the proteases. The complement control protein domain exosite is not involved in cleavage of C2 by the proteases, but the role of an anion-binding exosite (ABE) on the SP domains of the proteases has (to our knowledge) never been investigated. In this study, we have shown that the ABE on the SP of both C1s and MASP-2 is crucial for efficient cleavage of C2, with mutant forms of the proteases greatly impaired in their rate of cleavage of C2. We have additionally shown that the site of binding for the ABE of the proteases is very likely to be located on the von Willebrand factor domain of C2, with the precise area differing between the enzymes: whereas C1s requires two anionic clusters on the von Willebrand factor domain to enact efficient cleavage of C2, MASP-2 apparently only requires one. These data provide (to our knowledge) new information about the molecular determinants for efficient activation of C2 by C1s and MASP-2. The enhanced view of the molecular events underlying the early stages of complement activation provides further possible intervention points for control of this activation that is involved in a number of inflammatory diseases.

Luminescent Supramolecular Ionic Frameworks based on Organic Fluorescent Polycations and Polyanionic Phosphorescent Metal Clusters.

Emissive ionic supramolecular frameworks are designed by associating tetraphenylethylene-based tetra-cationic units and di-anionic molybdenum or tetra-anionic rhenium octahedral clusters. Obtained structures were characterized by single-crystal X-ray diffraction. The emission properties of the hybrids were investigated as dry powders or in various solvents by one photon and two photon absorption leading to a O2 concentration dependent luminescence color for the Mo based hybrid.

Unveiling geometric and electronic structures of NbSi4−/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation

AbstractThis article presents computational insights into the geometric and electronic structures of NbSi4−/0 clusters using density functional theory and the CASSCF/CASPT2 method. The anionic and neutral ground states are identified as the 1A′ and 2A′ states, respectively, within a trigonal bipyramidal isomer where the Nb atom occupies the equatorial position. The adiabatic detachment energy for the transition from the anionic ground state 1A′ to the neutral ground state 2A′ is estimated to be 2.30 eV. Additionally, an evaluation of the vertical detachment energies for transitions to the neutral states 12A′, 12A″, 22A′, 22A″, 32A′, 32A″, and 42A′ yields respective values of 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, and 4.28 eV. These computed electron detachment energies successfully account for all five bands observed in the photoelectron spectrum of the anionic cluster. Furthermore, the Franck–Condon factor simulations reveal extensive vibrational progressions associated with the transition to the neutral ground state 12A′, manifesting as an unresolved broad band at 2.41 eV in the spectrum.

Time-resolved photoelectron spectroscopy of iodide-4-thiouracil cluster: The ππ* state as a doorway for electron attachment.

The photophysics of thiobases-nucleobases in which one or more oxygen atoms are replaced with sulfur atoms- vary greatly depending on the location of sulfonation. Not only are direct dynamics of a neutral thiobase impacted, but also the dynamics of excess electron accommodation. In this work, time-resolved photoelectron spectroscopy is used to measure binary anionic clusters of iodide and 4-thiouracil, I- · 4TU. We investigate charge transfer dynamics driven by excitation at 3.88eV, corresponding to the lowest ππ* transition of the thiouracil, and at 4.16eV, near the cluster vertical detachment energy. The photoexcited state dynamics are probed by photodetachment with 1.55 and 3.14eV pulses. Excitation at 3.88eV leads to a signal from a valence-bound ion only, indicating a charge accommodation mechanism that does not involve a dipole-bound anion as an intermediate. Excitation at 4.16eV rapidly gives rise to dipole-bound and valence-bound ion signals, with a second rise in the valence-bound signal corresponding to the decay of the dipole-bound signal. The dynamics associated with the low energy ππ* excitation of 4-thiouracil provide a clear experimental proof for the importance of localized excitation and electron backfilling in halide-nucleobase clusters.

Vanadium-substituted Keggin structured polyoxometalate combined with fluconazole in α-SiW11V-FKZ for efficient bacterial inhibition

Pollution of the environment is becoming more and more serious due to the misuse of antibiotics. To protect the environment, polyoxometalates (POMs) emerged as potential green materials. These POMs contain anionic clusters of metal oxides, which exhibit favorable structural and physicochemical properties. They have demonstrated promising antiviral, antibacterial and antitumor activities in biomedicine. In the present study, fluconazole (FKZ)-modified POMs of Keggin structure were synthesized as an efficient bacteriostatic agent by the hydrothermal method. Furthermore, the bacteriostatic properties of the agent against various bacteria are analyzed. The bacteriostatic effect and bacterial inhibition rate are evaluated using three different methods: the filter paper slice method, determination of MIC value and the colony counting method. In addition, the leakage of morphologically repressive DNA of bacteria after being treated by the samples was investigated by TEM and UV, which resulted in speculation of repressive mechanisms. The experimental results demonstrated that the bacteriostat exhibited superior bacteriostatic properties compared to the classical polyoxometalate. Additionally, bacteriostatic agents are particularly effective in combating gram-negative bacteria.

Photoelectron velocity map imaging spectroscopy of group 14 elements and iron tetracarbonyl anionic clusters MFe(CO)4- (M = Si, Ge, Sn).

The heteronuclear group 14 M-iron tetracarbonyl clusters MFe(CO)4- (M = Si, Ge, Sn) anions have been generated in the gas phase by laser ablation of M-Fe alloys and detected by mass and photoelectron spectroscopy. With the support of quantum chemical calculations, the geometric and electronic structures of MFe(CO)4- (M = Si, Ge, Sn) are elucidated, which shows that all the MFe(CO)4- clusters have the M-Fe bonded, iron-centered, and carbonyl-terminal M-Fe(CO)4 structure with the C2v symmetry and a 2B2 ground state. The M-Fe bond can be considered a double bond, which includes one σ electron sharing bond and one π dative bond. The C-O bonds in those anionic clusters are calculated to be elongated to different extents, and in particular, the C-O bonds in SiFe(CO)4- are elongated more. The Si-Fe alloy thus turns out to be a better collocation to activate the C-O bonds in the gas phase among group 14. The present findings have important implications for the rational development of high-performance catalysts with isolated metal atoms/clusters dispersed on supports.

Aromatic and magnetic properties in a series of heavy rare earth-doped Ge6 cluster anions.

A series of pentagonal bipyramidal anionic germanium clusters doped with heavy rare earth elements, (RE = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), have been identified at the PBE0/def2-TZVP level using density functional theory (DFT). Our findings reveal that the centrally doped pentagonal ring structure demonstrates enhanced stability and heightened aromaticity due to its uniform bonding characteristics and a larger charge transfer region. Through natural population analysis and spin density diagrams, we observed a monotonic decrease in the magnetic moment from Gd to Yb. This is attributed to the decreasing number of unpaired electrons in the 4f orbitals of the heavy rare earth atoms. Interestingly, the system doped with Er atoms showed lower stability and anti-aromaticity, likely due to the involvement of the 4f orbitals in bonding. Conversely, the systems doped with Gd and Tb atoms stood out for their high magnetism and stability, making them potential building blocks for rare earth-doped semiconductor materials.

CO Oxidation Promoted by NO Adsorption on RhMn2O3- Cluster Anions.

CO oxidation represents an important model reaction in the gas phase to provide a clear structure-reactivity relationship in related heterogeneous catalysis. Herein, in combination with mass spectrometry experiments and quantum-chemical calculations, we identified that the RhMn2O3- cluster cannot oxidize CO into gas-phase CO2 at room temperature, while the NO preadsorbed products RhMn2O3-[(NO)1,2] are highly reactive in CO oxidation. This discovery is helpful to get a fundamental understanding on the reaction behavior in real-world three-way catalytic conditions where different kinds of reactants coexist. Theoretical calculations were performed to rationalize the crucial roles of preadsorbed NO where the strongly attached NO on the Rh atom can greatly stabilize the products RhMn2O2-[(NO)1,2] during CO oxidation and at the same time works together with the Rh atom to store electrons that stay originally in the attached CO2- unit. The leading result is that the desorption of CO2, which is the rate-determining step of CO oxidation by RhMn2O3-, can be greatly facilitated on the reactions of RhMn2O3-[(NO)1,2] with CO.

Dinitrogen Activation by Heteronuclear Metal Carbide Cluster Anions Y1‐3CoC1,2−: An Experimental and DFT Study

AbstractMass spectrometry was used to observe the reactions between Y−Co heteronuclear metal carbide cluster anions Y1‐3CoC1,2− and N2 at room temperature. Y2CoC1,2− can produce Co ejection products, in which Y2CoC− also has N2 association products; YCoC2− and Y3CoC− only generate N2 association products, while YCoC− and Y3CoC2− are inert to N2. Detailed reaction pathways were obtained through density functional theory calculations, which reasonably explain the experimental phenomena. Co is superior to Y as the electrophilic reaction site in the clusters and is the preferential initial adsorption site for N2. Some crucial steps were identified, including N−N dissociation, CC−N formation, C−CN dissociation, and C−N formation. The energy barriers of these steps are closely related to the coordination mode of N/N2 and C/C2 in clusters. Two indicators, the N−N bond length and the Mayer bond order, were utilized to describe the activation degree of the N−N bond. Analyses on the density of states and the frontier molecular orbitals reveal the electronic structures of key intermediates for N−N dissociation. The reaction mechanisms of N2 activation on Y−Co carbide clusters obtained may lay a preliminary foundation for the further development of catalysts for nitrogen reduction reaction (NRR).

Supramolecular Self-Assembly of Proteins Promoted by Hybrid Polyoxometalates.

Controlling the formation of supramolecular protein assemblies and endowing them with new properties that can lead to novel functional materials is an important but challenging task. In this work, a new hybrid polyoxometalate is designed to induce controlled intermolecular bridging between biotin-binding proteins. Such bridging interactions lead to the formation of supramolecular protein assemblies incorporating metal-oxo clusters that go from several nanometers in diameter up to the micron range. Insights into the self-assembly process and the nature of the resulting biohybrid materials are obtained by a combination of Small Angle X-ray Scattering (SAXS), Transmission Electron Microscopy (TEM), and Dynamic Light Scattering (DLS), along with fluorescence, UV-vis, and Circular Dichroism (CD) spectroscopy. The formation of hybrid supramolecular assemblies is determined to be driven by biotin binding to the protein and electrostatic interactions between the anionic metal-oxo cluster and the protein, both of which also influence the stability of the resulting assemblies. As a result, the rate of formation, size, and stability of the supramolecular assemblies can be tuned by controlling the electrostatic interactions between the cluster and the protein (e.g., through varying the ionic strength of the solution), thereby paving the way toward biomaterials with tunable assembly and disassembly properties.

Specificity of hexarhenium cluster anions for synthesis of Mn2+-based nanoparticles with lamellar shape and pH-induced leaching for specific organ selectivity in MRI contrasting

The present work demonstrates the structure variation of hexarhenium anionic cluster units [{Re6S8}(CN)(6–n)(OH)n]4– (n = 0, 2, 4) as the strategy to develop Mn2+-containing nanoparticles (NPs) exhibiting pH-dependent leaching. The dicyanotetrahydroxo complex [{Re6S8}(CN)2(OH)4]4– is the optimal for the synthesis of the Mn2+-based NPs with a lamellar shape exhibiting the pH-dependent aggregation and magnetic relaxation behavior. The pH-dependent behavior of the NPs derives from the easy protonation of the apical hydroxo ligands of [{Re6S8}(CN)2(OH)4]4– cluster, which triggers partial leaching of Mn2+ ions and aggregation of the NPs driven by the surface neutralization. The in vivo MRI scanning of the mice intravenously injected with the NPs indicates the preferable accumulation of the lamellar NPs within mouse intestine over liver and kidneys. This differs from the spherical NPs constructed from [{Re6Se8}(CN)6]4– units, which provide the preferable brightening of mouse liver over kidneys and intestine.

Cn, CnH and their anions: Quest for linearity with n≤8 even versus odd, and beyond

AbstractUsing the concept of quasi‐molecule (“tile”) and the database of quasi‐molecules embedded on a parent molecule, it is discussed whether the latter can attain linear form or otherwise. Besides anew accurate optimization of all tiles (quasi‐triatomics) at various levels of ab initio theory and basis‐sets, the nature of the predicted stationary points for the title parent molecules is probed through a priori calculations here too reported. Also discussed is the common rule that even‐ anions are linear while odd‐numbered ones tend to have nonlinear isomers. The reported quasi‐molecule approach is general, and allow the prediction of linearity or otherwise of the parent systems prior to calculations on them. When based on an extension of the bisection method (Varandas, Int. J. Quantum Chem. 2023, 123, e27036.), it is easy to use even for large parent molecules, as illustrated for neutral and anionic carbon clusters with .

Tuning the dimensionality of H bonded networks using different chalcogen atoms in [Re6Q8(CN)6]4– (Q = S, Se) clusters

Two novel compounds based on [Re6Q8(CN)6]4– (Q = S, Se) and small H bond donor bis-amidinium dication of 2,2’-methylenediimidazolium (Cat) (Cat)2[Re6S8(CN)6]∙2H2O (1) and (Cat)2[Re6Se8(CN)6]∙2H2O (2) were synthesized and structurally characterized. Depending of the chalcogen atom (S or Se) in the cluster anion, the dimensionality of the obtained (2D and 3D) network and the nature of the H bond pattern change.

Electronic properties and collision cross sections of AgOkHm± (k, m = 1-4) aerosol ionic clusters.

Experimental evidence shows that hydroxylated metal ions are often produced during cluster synthesis by atmospheric pressure spark ablation. In this work, we predict the ground state equilibrium structures of AgOkHm± clusters (k and m = 1-4), which are readily produced when spark ablating Ag, using the coupled cluster with singles and doubles (CCSD) method. The stabilization energy of these clusters is calculated with respect to the dissociation channel having the lowest energy, by accounting perturbative triples corrections to the CCSD method. The interatomic interactions in each of the systems have been investigated using the frontier molecular orbital (FMO), natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) methods. Many of the ground states of these ionic clusters are found to be stable, corroborating experimental observations. We find that clusters having singlet spin states are more stable in terms of dissociation than the clusters that have doublet or triplet spin states. Our calculations also indicate a strong affinity of the ionic and neutral Ag atom towards water and hydroxyl radicals or ions. Many 3-center, 4-electron (3c/4e) hyperbonds giving rise to more than one resonance structure are identified primarily for the anionic clusters. The QTAIM analysis shows that the O-H and O-Ag bonds in the clusters of both polarities are respectively covalent and ionic. The FMO analysis indicates that the anionic clusters are more reactive than the cationic ones. Using the cluster structures predicted by the CCSD method, we calculate the collision cross sections of the AgOkHm± family, with k and m ranging from 1 to 4, by the trajectory method. In turn, we predict the electrical mobilities of these clusters when suspended in helium at atmospheric pressure and compare them with experimental measurements.

The valence electron affinity of uracil determined by anion cluster photoelectron spectroscopy.

The unoccupied π* orbitals of the nucleobases are considered to play important roles in low-energy electron attachment to DNA, inducing damage. While the lowest anionic valence state is vertically unbound in all neutral nucleobases, it remains unclear even for the simplest nucleobase, uracil (U), whether its valence anion (U-) is adiabatically bound, which has important implications on the efficacy of damage processes. Using anion photoelectron spectroscopy, we demonstrate that the valence electron affinity (EAV) of U can be accurately measured within weakly solvating clusters, U-(Ar)n and U-(N2)n. Through extrapolation to the isolated U limit, we show that EAV = -2 ± 18 meV. We discuss these findings in the context of electron attachment to U and its reorganization energy, and more generally establish guidance for the determination of molecular electron affinities from the photoelectron spectroscopy of anion clusters.

Mixed-valence compounds based on heterometallic-oxo-clusters containing Sb(III,V): crystal structures and proton conduction.

Two isostructural Co(Cd)-antimony-oxo tartrate cluster-based compounds with a one-dimensional (1-D) belt-like structure, namely H9.2[Co(H2O)6]{M0.5(H2O)3.5{M'(H2O)4[SbVO6[Co4.2(H2O)5SbIII6(μ3-O)2(tta)6]]}}2·nH2O (M = Co, M' = Co, n = 9 (1); M = Cd0.39/Co0.61, M' = Cd0.24/Co0.76, n = 7 (2); H4tta = tartaric acid), have been synthesized by solvothermal methods. It is noteworthy that the relatively rare mixed-valence Sb(III,V) exists in the structures. The anionic clusters in both compounds appear to be in a sandwich configuration; the top and bottom layers are based on {Sb3(μ3-O)(tta)3} brackets, and the intermediate layer is occupied by {SbVO6[Co4.2(H2O)5]}. The title compounds have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, thermogravimetric analyses, and UV-Vis spectroscopy. We chose compound 2 as a representative to test its proton conductivity, and the results show that the conductivity can reach 1.42 × 10-3 S cm-1 at 85 °C under 98% relative humidity.

Magic cluster sizes of cationic and anionic sodium chloride clusters explained by statistical modeling of the complete phase space.

As one of the main components of sea salt aerosols, sodium chloride is involved in numerous atmospheric processes. Gas-phase clusters are ideal models to study fundamental physical and chemical properties of sodium chloride, which are significantly affected by the cluster size. Of particular interest are magic cluster sizes, which exhibit high intensities in mass spectra. In order to understand the origin of these magic cluster sizes, quantum chemical calculations at the CCSD(T)//DFT level are performed, yielding structures and binding energies of neutral (NaCl)x, anionic (NaCl)xCl- and cationic (NaCl)xNa+ clusters up to x = 8. Our calculations show that the clusters can easily isomerize, enabling dissociation into the lowest-energy isomers of the fragments. Energetics can explain the special stability of (NaCl)4Cl-, but (NaCl)4Na+ actually offers low-lying dissociation channels, despite being a magic cluster size. Collision-induced dissociation experiments reveal that the loss of neutral clusters (NaCl)x, x = 2, 4, is in most cases more favorable than the loss of NaCl or the atomic ion, i.e. sodium chloride clusters actually fragment via the cleavage of the entire cluster, not by evaporating small cluster building blocks. This is rationalized by the calculated high stability of even-numbered neutral clusters (NaCl)x, especially x = 2, 4. Analysis of the density of states and rate constants calculated with a modified Rice-Ramsperger-Kassel-Marcus (RRKM) equation called AWATAR - considering all energetically accessible isomers of reactants and fragments - shows that entropic effects are responsible for the magic cluster character of (NaCl)4Na+. In particular, low-lying vibrational modes provide a high density of states of the near-planar cluster. Together with the small contribution of an atomic ion to the sum of states in a loose transition state for dissociation, this leads to a very small unimolecular rate constant for dissociation into (NaCl)4 and Na+, which is the lowest energy fragmentation pathway. Thus, entropic effects may override energetics for certain magic cluster sizes.

A novel hydrophobic carborane-hybrid microporous material for reversed C2H6 adsorption and efficient C2H4/C2H6 separation under humid conditions.

Since ethylene (C2H4) is important feedstock in the chemical industry, developing economical and energy-efficient adsorption separation techniques based on ethane (C2H6)-selective adsorbents to replace the energy-intensive cryogenic distillation is highly demanded, which however remains a daunting challenge. While previous anionic boron cluster hybrid microporous materials display C2H4-selective features, we herein reported that the incorporation of a neutral para-carborane backbone and aliphatic 1,4-diazabicyclo[2.2.2]octane (DABCO) enables the reversed adsorption of C2H6 over C2H4. The generated carborane-hybrid microporous material ZNU-10 (ZNU = Zhejiang Normal University) is highly stable in humid air and maintains good C2H6/C2H4 separation performance under high humidity. Gas loaded single crystal structure and density-functional theory (DFT) calculations revealed that the weakly polarized carborane and DABCO within ZNU-10 induce more specific C-Hδ+⋯Hδ--B dihydrogen bonds and other van der Waals interactions with C2H6, while the suitable pore space allows the high C2H6 uptake. Approximately 14.5 L kg-1 of polymer grade C2H4 can be produced from simulated C2H6/C2H4 (v/v 10/90) mixtures under ambient conditions in a single step, comparable to those of many popular materials.