Neutral Clusters Research Articles

Near-threshold electron transfer in anion-nucleobase clusters: does the identity of the anion matter?

ABSTRACTLaser dissociation spectroscopy of I−·adenine (I−·A) and ·adenine (·A) has been utilised for the first time to explore how the anion identity impacts on the excited states. Despite strong photodepletion, ionic photofragmentation is weak for both clusters, revealing that they decay predominantly by electron detachment. The spectra of I−·A display a prominent dipole-bound excited state in the region of the detachment energy which relaxes to produce deprotonated adenine. In contrast, near-threshold photoexcitation of ·A does not access a dipole-bound state, but instead displays photofragmentation properties associated with ultrafast decay of an adenine-localised π→π* transition. Notably, the experimental electron detachment onset of ·A is around 4.7 eV, which is substantially lower than the expected detachment energy of an ion-dipole complex. The low value for ·A can be traced to initial ionisation of the adenine followed by significant geometric rearrangement on the neutral surface. We conclude that these dynamics quench access to a dipole-bound excited state for ·A and subsequent electron transfer. ·A represents an important new example of an ionic cluster where ionisation occurs from the neutral cluster component and where photodetachment initiates intra-molecular hydrogen atom transfer.

Silver cluster-amino acid interactions: a quantum-chemical study.

Binding of silver ion (Ag+) and two atomic neutral silver cluster (Ag2) with a set of amino acids has been studied using Density Functional Theory (DFT) and ab initio MP2 method. We show that binding energy with Ag2 is higher for deprotonated anionic amino acids. Cysteine, aspartic acid, and tyrosine with deprotonated side chain exhibit the highest binding energy (Gbind) values among all the amino acids: -30.1kcalmol-1, -30.7kcalmol-1, and -30.9kcalmol-1, respectively. Binding energies of deprotonated cysteine, glutamic acid, tyrosine, and aspartic acid with silver ion Ag+ are reported here for the first time. Natural bond orbital (NBO) analysis has also been performed to calculate charge transfer, natural populations, occupancies, and Wiberg bond indices of the amino acid-Ag2 complexes. Atoms-in-molecules (AIM) theory was used to establish the nature of interactions. It was shown that, in most cases, the bonds between amino acid and Ag2 cluster are partially electrostatic and partially covalent.

Possible low-energy isomers of OHn(H2O)4 (n = 0, ±1) clusters via the particle swarm optimization algorithm: An ab initio study

The possible low-energy structures of the anionic, neutral, and cationic water clusters OHn(H2O)4 (n = 0, ±1) were investigated using the particle swarm optimization algorithm together with ab initio calculations. Geometry optimization and vibrational analysis for possible low-lying water clusters were conducted at the MP2/aug-cc-pVDZ level and further verified at the CCSD(T)/aug-cc-pVTZ level. The results revealed obvious structural differences between the OH+(H2O)4, OH(H2O)4, and OH−(H2O)4 clusters. We found that correcting for the zero-point vibrational energies and basis set superposition error exerted a substantial influence on the order of relative energies for the OH−(H2O)4 and OH+(H2O)4 clusters. Topological analysis revealed that both the number and strength of hydrogen bonds were greater for the OH−(H2O)4 cluster compared with the OH+(H2O)4 and OH(H2O)4 clusters. The highest occupied molecular orbitals (HOMOs) of the anionic OH−(H2O)4 cluster were mainly located on the OH− ion and the HOMO-1s and HOMO-2s levels were mainly located on the H2O molecules, whereas in the neutral OH(H2O)4 and cationic OH+(H2O)4 clusters, the singly occupied molecular orbitals mainly originated from the water molecules.

Hadronization from color interactions * * Supported in part by National Natural Science Foundation of China (11435004, 11375069), the Ministry of Science and Technology of China (2015CB56901), and the Programme of Introducing Talents of Discipline to Universities (B08033)

A quark coalescence model, based on semi-relativistic molecular dynamics with color interactions among quarks, is presented and applied to pp collisions. A phenomenological potential with two tunable parameters is introduced to describe the color interactions between quarks and antiquarks. The interactions drive the process of hadronization that finally results in different color neutral clusters, which can be identified as hadrons based on some criteria. A Monte Carlo generator PYTHIA is used to generate quarks in the initial state of hadronization, and different values of tunable parameters are used to study the final state distributions and correlations. Baryon-to-meson ratio, transverse momentum spectra, pseudorapidity distributions and forward-backward multiplicity correlations of hadrons produced in the hadronization process, obtained from this model with different parameters, are compared with those from PYTHIA.

Octahedral chalcogenide rhenium cluster complexes with imidazole

Reactions of [{Re6Q8}Br6]4−/3− (Q = S, Se) with molten imidazole lead to the formation of two new neutral cluster complexes [{Re6Q8}(imzH)4(imz)2] (imzH = imidazole). The interaction of [{Re6Q8}(imzH)4(imz)2] with hydrohalic acids resulted in cationic complexes [{Re6Q8}(imzH)6]X2 (X = Cl, Br). All compounds were characterised by X-ray single-crystal and powder diffraction analyses, elemental analysis, energy dispersive X-ray and IR spectroscopies. The luminescence of the neutral compounds [{Re6Q8}(imzH)4(imz)2] was also studied.

On the Possibility of Using the Jellium Model as a Guide To Design Bimetallic Superalkali Cations.

The potential application of the jellium model as guidance in the rational design of bimetallic superalkali cations is examined under gradient-corrected density functional theory for the first time. By using Li, Mg, and Al as atomic building blocks, a series of bimetallic cationic clusters with 2, 8, 20, and 40 valence electrons are obtained and investigated. As the corresponding neutral clusters tend to lose one valence electron to achieve closed-shell states in the jellium model, these studied cations exhibit much lower vertical electron affinities (EAvert , 3.42-4.95 eV) than the ionization energies (IEs) of alkali metal atoms, indicating their superalkali identities. The high stability of these cationic clusters is guaranteed by their considerable HOMO-LUMO gaps and binding energies per atom. Moreover, the feasibility of using the designed superalkalis as efficient reductants to activate CO2 and N2 molecules and as stable building blocks to assemble ionic superatom compounds is explored. Therefore, this study may provide an effective method for obtaining various metallic superatoms with extensive applications on the basis of the simple jellium rule.

The ground and excited low-lying states of VSi20/−/+ clusters from CASSCF/CASPT2 calculations

The geometric and electronic structures of the ground and excited low-lying states of VSi20/−/+ clusters were investigated by the CASSCF/CASPT2 method. The structural parameters, harmonic vibrational frequencies, relative energies, and atomic charges of the low-lying electronic states were presented and discussed. The ground states of VSi20/−/+ clusters were 4B1, 5A1, and 3B1, respectively. At the CASPT2 level, the electron affinity and ionization energy of the neutral clusters were evaluated to be 1.08 and 7.07 eV, respectively. The vertical detachment energies of the detachments of one electron from several orbitals of the anionic cluster were computed.

Molecular dynamics simulation of formation of accelerated neutral atom and cluster beams

A molecular dynamics simulation of accelerated argon cluster ion collisions with residual gas atoms was carried out. Cluster ions having an icosahedral structure were considered. The dependence of the impact fragmentation results of cluster ions on their initial sizes and on the value of the accelerating potential was studied. The simulation demonstrated that in the case of impact breaking of cluster ions along with the forming of a “cloud” of individual atoms, the formation of heated fragments and their complete or partial melting are observed. Further intensive evaporative cooling of these fragments occurred, which caused the appearance and/or growth of an ordered (icosahedral or crystal) structure in them. The probability of charge loss of the fragments was estimated. It was demonstrated that certain of the fragments can to be a part of a mixed accelerated neutral atom and cluster beams.

Molecular dynamics simulation of argon clusters impacting on a poly(ether ether ketone) surface

Presented is the molecular dynamics simulation of electrically neutral small argon clusters impact on the surface of Poly(Ether Ether Ketone) (PEEK), a promising orthopedic implant material. The results of the simulation are compared with the data obtained in the experiments on the treatment of the PEEK surface by Accelerated Neutral Atom Beams (ANAB). The comparison results allow the conclusion that the clusters are a part of ANAB. This conclusion is in complete agreement with the results of previous molecular dynamics analysis of the ANAB generation process.

Possible lower energy isomer of carbon clusters Cn (n = 11, 12) via particle swarm optimization algorithm: Ab initio investigation

The low energy structures of neutral carbon clusters Cn (n = 11, 12) are predicted by means of particle swarm optimization and quantum chemistry calculation. The energy and geometrical structure of these isomers are further optimized by DFT, MP2 and CCSD computation methods. The relative Gibbs free energy below 5000 K was calculated, which indicates that C11 clusters are more sensitive to temperature. We also illustrate the computational simulated IR spectra obtained at B3LYP/cc-pVTZ level, which shown the vibrational modes and vibrational regions of different structural isomers. Combining nuclear independent chemical shift (NICS) and harmonic oscillator measure of aromaticity (HOMA), we have analyzed the aromaticity of the three single-ring structures and found that C11 cluster is not aromatic, while the ground stated structure of C12 is anti-aromaticity. Chemical bond analysis of the ground state is performed by Adaptive Natural Density Partition (AdNDP) injunction with electron localization function (ELF), it is found that the 2c-2e bonds of C11 and C12 planar ring structures presented strong and weak alternations, respectively, and their multi-central bonds were strongly dependent on the symmetry of molecular configuration. Finally, topological and natural bond orbital (NBO) analysis indicate that there is no electrostatic interaction in the Cn (n = 11, 12) clusters, and the high angular momentum orbital has a primary contribution to negative natural valance electron configuration. From the electronic configuration, we can see that the natural hybridized orbit of C11 and C12 clusters is mainly composed of sp hybrids.

The identification of Вi atoms and clusters in Mg[sbnd]Al silicate glasses

Bi-activated glasses from the MgO-Al2O3-SiO2 system with IR luminescence in the region of 1050–1600 nm have been studied by the high-angle annular dark-field scanning transmission electron microscopy. It was found that individual bismuth ions are present in all samples. Presumably, these ions are Bi3+ with low coordination number in the glass network or the subvalent bismuth cations, namely Bi+ and Bi2+. An increase in the bismuth content, the synthesis temperature together with the change of the synthesis atmosphere from oxidizing (air) to the reducing (nitrogen) leads to the growth of the number of cluster with dimensions in the range of ~3 Å to ~6 Å. The bismuth dimers are very probable in the samples with a bismuth content close to 0.2 at.%. The clusters with bigger size (~12 Å) are most likely to be neutral clusters (Bin)0, which are nuclei for the nano-sized inclusions of the phase of metallic bismuth. In another type of agglomerate with Bi - Bi atoms distances close to 2–4 Å and more correspond the nano-regions enriched in Bi atoms where Bi atoms are embedded in the glass network.

Infrared spectra of neutral dimethylamine clusters: An infrared-vacuum ultraviolet spectroscopic and anharmonic vibrational calculation study.

Infrared-vacuum ultraviolet (IR-VUV) spectra of neutral dimethylamine clusters, (DMA)n (n = 2-5), were measured in the spectral range of 2600-3700 cm-1. The experimental IR-VUV spectra show NH stretch modes gradually redshift to 3200-3250 cm-1 with the increase in the cluster size and complex Fermi Resonance (FR) pattern of the CH3 group in the 2800-3000 cm-1 region. Ab initio anharmonic vibrational calculations were performed on low-energy conformers of (DMA)2 and (DMA)3 to examine vibrational coupling among CH/NH and to understand the Fermi resonance pattern in the observed spectra features. We found that the redshift of NH stretching mode with the size of DMA cluster is moderate, and the overtone of NH bending modes is expected to overlap in frequency with the CH stretching fundamental modes. The FR in CH3 groups is originated from the strong coupling between CH stretching fundamental and bending overtone within a CH3 group. Well-resolved experimental spectra also enable us to compare the performance of ab initio anharmonic algorithms at different levels.

Spectroscopic, vibrational and structural properties analysis of CaXen (n = 1–4) clusters

A systematic ab initio calculations based on a complete Configuration Interaction (CI) including the pseudo-potential model where the core valence correlation was presented by the Core Polarization Potential (CPP), were employed to determine the geometric structures of CaXen (n = 1–4) neutral clusters. For the diatomic (CaXe) and tri-atomic (CaXe2) systems, the potential energy curves for the ground and several excited states are determined and the different spectroscopic constants are illustrated. Interested structures were seen in the PECs which their effects in the vibrational levels' spacing and the electric dipole moments variations were shown. The agreement with the experimental and the theoretical constants for n = 1 was excellent. Accordingly, for the higher clusters the predicted geometries should be reliable. The bent geometry of CaXe2 ground state with (C2v) symmetry was performed and hence was concluded to be the most adaptable with a bond angle of 54.84° and bond distance dXe-Xe of 8.08 a0. As well as, the bent isomer for the excited states was also studied to illustrate the most compact geometry for each state. For the ground state of CaXe3, the most stable geometry was trigonal-pyramidal with (C3v) symmetry with dXe-Xe = 8.13 a0. And concerned n = 4, four configurations were treated; the tetrahedral structure, the square pyramid structure, the trigonal bipyramid structure with (C3v) symmetry and the trigonal bipyramid structure with (C2v) symmetry. The comparison between their minimal energies showed that the most compact geometry for CaXe4 is the trigonal bipyramid with (C3v) symmetry with dXe-Xe = 8.17 a0. Consequently, this work illustrates that the mechanism of cluster forming is consistent with the calcium location on the xenon clusters' surface model.

N-Doping at the Sub-Nanoscale: Dielectric and Magnetic Response of Neutral Phosphorus-Doped Tin Clusters.

Doped semiconductors play a prevalent role in all aspects of modern technology. Because of the trend for smaller and smaller devices, we have investigated N-doping at the sub-nanoscale. For that purpose, we present molecular beam electric and magnetic deflection experiments on Sn NP ( N = 6-12) and Sn NP2 ( N = 7-12) clusters combined with quantum chemical calculations and classical beam deflection simulations. The theoretically identified and experimentally confirmed global minima structures resemble the valence-isoelectronic pure tin anions/dianions very closely, while each phosphorus dopant occupies the site of a tin atom. In Stern-Gerlach experiments, the single-doped clusters show a partial atom-like deflection behavior with total electronicangular momentum J = 1/2 whereas the results for the double-doped species suggest singlet states. This is in full agreement with quantum chemical results. The effect of vibrational excitation on magnetic and electric deflection experiments is examined. Our results provide insight into how the electric, magnetic, and structure properties are affected by n-doping at the sub-nanoscale.

Electrocatalytic property of water oxidation reaction depends on charging state of intermediates on Ag-M (M = Fe, co, Ni, Cu) in alkaline media

DFT calculations are performed to investigate the water oxidation reaction intermediates on Ag2M (M = Fe, Co, Ni, Cu), and Pt3 clusters in alkaline media both in the gas and solution (water) phases in the neutral and charged states. The calculated results revealed that the neutral and anionic clusters were found to be more suitable catalysts than cationic clusters because of weakly bonded water oxidation reaction intermediates. In addition, the calculated structural parameters of the water oxidation intermediates with Ag2M (M = Fe, Co, Ni, Cu) clusters revealed that M-OH bond strengths are found to be in the order of Cu < Ni < Co < Fe. Conclusively, Ag2Cu cluster was determined to be the best electrocatalyst regarding oxygen evolution reaction via 4e transfer, which is consistent with results on larger Ag2M clusters (13 atoms) and periodic Ag-M nanoalloys due to weaker binding energies of the water oxidation intermediates.

Structures and bonding of B4O5 and B4O5− clusters: Emergence of boroxol ring and competition between rhombic B2O2 and hexagonal B3O3 cores

AbstractBoron oxide clusters are electron‐deficient species with novel structures and bonding, in which the emergence of rhombic and boroxol rings is of interest. We report on computational prediction of the global‐minimum structures for two boron oxide clusters: B4O5 and B4O5−. These structures differ distinctly, as established through global machine searches and electronic structure calculations at B3LYP and single‐point CCSD(T) levels. While B4O5 neutral cluster has a rhombic B2O2 core, the B4O5− anion features a boroxol B3O3 ring. One electron completely changes the potential landscapes. Bonding analyses show that the 4π electron‐counting is crucial for a rhombic BO cluster, in contrast to π sextet for a boroxol ring, which underlies the competition between rhombic and boroxol rings in B4O5/B4O5− clusters. A possible pathway for rhombic‐to‐hexagonal transformation is proposed based on intrinsic reaction coordinate calculations. Anion B4O5− cluster, a new member of the inorganic benzene family, is among the smallest BO species with a free‐standing boroxol ring, governed collectively by composition and electron‐counting.

Structural, electronic and magnetic properties of stoichiometric cobalt oxide clusters (CoO)nq (n=3−10,q=0,+1): A modified basin-hopping Monte Carlo algorithm with spin-polarized DFT

The structural, electronic and magnetic properties of the neutral and cationic cobalt oxide clusters (CoO)[Formula: see text] ([Formula: see text], [Formula: see text]) have been studied using a modified basin-hopping Monte Carlo (BHMC) algorithm refined by spin-polarized DFT. A systematic search of global minimum structures predicts new global minima of (CoO)[Formula: see text] and reproduced other minima that are in excellent agreement with previous works. For most low-spin and high-spin states, the structural transition from planar-like to compact structure occurs at (CoO)[Formula: see text], which is in contrast with the general notion that the structural changes at (CoO)[Formula: see text]. Supported by the results of the binding energy, second-order total energy difference, chemical hardness, chemical potential and HOMO-LUMO gap confirms the stability of (CoO)4. Results of the spin magnetic moments for the global minima show that (CoO)4 and (CoO)8 spin configurations exhibit a fully antiferromagnetic (AFM) ordering, while (CoO)9 spin displays the highest ferromagnetic (FM) ordering. Interestingly, elongation of Co–Co bond in (CoO)4 causes O being polarized by the neighboring Co atoms that accordingly follows the Goodenough-Kanamori-Anderson rule of FM super-exchange coupling for the Co-O-Co structural rearrangement to 90∘ ([Formula: see text] structure) in order to accommodate the spin magnetic ordering changes. This rearrangement is a result of the valence band being shifted away from the Fermi level to lower energy causing high population of the spin-up density of state and leading to the asymmetrical polarization of the whole (CoO)4 structure. As far as the dissociation energy surfaces are concerned, the first ever such surfaces are constructed corresponding to [Formula: see text], which identify a complete dissociation pathway linking the cationic and neutral clusters and finally confirm (CoO)[Formula: see text] as the most stable cluster compared to the rest.

First-principles studies on the doping effect of Nin−1TM (n = 13, 19, 55)

The structural and electronic properties of different transition-metal atoms (TM = Cr, Mn, Fe, Co, Cu, Zn, Pd, Ag, Pt, Au) doped into Nin neutral and ionic clusters (n = 13, 19, 55) were investigated using density functional theory calculations with the PBE exchange-correlation energy functional. The properties of the Nin−1TM clusters differed substantially from those of Nin, implying that the substitution of a transition-metal atom (TMA) strongly affected the stability and electronic properties of the resultant clusters. The cluster size effect and element type influence are discussed. The stability and the total magnetic moments of Nin−1TM neutral and ionic clusters were found to increase as a function of cluster size. The size of the clusters had little effect on the amount of charge transferred. The AIP decreased with increasing cluster size, while the AEA is exhibited the opposite trend. All of the aforementioned electronic properties exhibited different degrees of variation due to doping of different TMAs.

Salts of Anionic Metal Carbonyl Clusters with Cryptand[2.2.2](Na+), DB‐18‐crown‐6(Na+), and Paramagnetic Cp*2Cr+ Cations Obtained by Reduction

Reduction of neutral metal clusters (Co4(CO)12, Ru3(CO)12, Fe3(CO)12, Ir4(CO)12, Rh6(CO)16, {CpMo(CO)3}2, {Mn(CO)5}2) by decamethylchromocene (Cp*2Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*2Cr+, cryptand[2.2.2](Na+), and DB‐18‐crown‐6(Na+) cations and [Co6(CO)15]2– (1, 2), [Ru6(CO)18]2– (3–4) dianions, [Rh11(CO)23]3– (6) trianions, and new [Ir8(CO)18]2– (5) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe3(CO)12 preserves the Fe3 core under reduction forming the [Fe3(CO)11]2– dianions in 7. The [CpMo(CO)3]2 and [Mn(CO)5]2 dimers dissociate under reduction forming mononuclear [CpMo(CO)3]– (8) and [Mn(CO)5]– (9) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1–9. In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*2Cr+ is defined by high spin Cp*2Cr+ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*2Cr+ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na+)}2[Co6(CO)15]2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co6 clusters to the Na+ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na+) cations.

Half- and mixed-sandwich metallacarboranes for potential applications in medicine

Abstract Today, medicinal chemistry is still clearly dominated by organic chemistry, and commercially available boron-based drugs are rare. In contrast to hydrocarbons, boranes prefer the formation of polyhedral clusters via delocalized 3c2e bonds, such as polyhedral dicarba-closo-dodecaborane(12) (closo-C2B10H12). These clusters have remarkable biological stability, and the three isomers, 1,2- (ortho), 1,7- (meta), and 1,12-dicarba-closo-dodecaborane(12) (para), have attracted much interest due to their unique structural features. Furthermore, anionic nido clusters ([7,8-C2B9H11]2−), derived from the neutral icosahedral closo cluster 1,2-dicarba-closo-dodecaborane(12) by deboronation followed by deprotonation are suitable ligands for transition metals and offer the possibility to form metallacarboranes, for example via coordination through the upper pentagonal face of the cluster. The isolobal analogy between the cyclopentadienyl(–1) ligand (Cp−) and [C2B9H11]2− clusters (dicarbollide anion, Cb2−) is the motivation in using Cb2− as ligand for coordination to a metal center to design compounds for various applications. This review focuses on potential applications of half- and mixed-sandwich-type transition metal complexes in medicine.