Cationic Clusters Research Articles

Structural assignments of yttrium oxide cluster cations studied by ion mobility mass spectrometry.

The geometric structures of yttrium oxide cluster ions, YnOm+ (n = 3-11), were experimentally assigned for stable compositions by ion mobility mass spectrometry combined with theoretical calculations. The stable compositions were firstly determined by collision induced dissociation experiments in mass spectrometry as YO(Y2O3)x+ and YO2(Y2O3)x+ for odd numbers of Y atoms (n = 2x + 1) and (Y2O3)x+ and O(Y2O3)x+ for even numbers of Y atoms (n = 2x). The structures of the ions with the above compositions were assigned by comparing the collision cross sections obtained in the ion mobility measurement with those obtained by theoretical calculations. The assigned structures have the following two characteristic features. Firstly, metal-metal or oxygen-oxygen bonds were rarely observed, and most of the oxygen atoms bridge two Y atoms, which is due to the ionic bonding nature between Y3+ and O2- ions. Secondly, common Y-atom frameworks were obtained for the ions with the same number of Y atoms n. For example, for the clusters with even numbers of Y atoms, one atomic oxygen radical anion (O-) in the most stable structures of (Y2O3)x+ was replaced with a superoxide ion (O2-) to form the most stable structures of O(Y2O3)x+ ions, keeping the Y-atom framework geometries.

Exploration of metal sulfide syntheses and the dissolution process of antimony sulfide in phosphonium-based ionic liquids.

Ionic liquids (ILs), especially task-specific ILs, are capable of dissolving various solids at moderate temperatures without the need for special reaction vessels. Direct synthesis of binary sulfides of B, Bi, Ge, Mo, Cu, Au, Sn, In, Ti, V, Fe, Co, Ga, Ni, Al, Zn, and Sb in [P66614]Cl was tested at 100 °C, i.e. below the melting point of sulfur. Under these conditions, substantial sulfide formation occurred only for nickel (Ni3S4, Ni3S2, NiS) and copper (Cu2S, CuS). Sb showed no formation of crystalline sulfide, but after addition of EtOH, an orange material precipitated which was identified as amorphous metastibnite. Subsequently, the dissolution of antimony sulfide (Sb2S3), the main source of antimony production, in the phosphonium-based ILs [P66614][OAc] and [P66614]Cl at 100 °C was studied in detail. The dissolution proceeds without H2S evolution, and amorphous Sb2S3 can be precipitated from these solutions. Heating Sb2S3 in the Lewis-acidic IL [BMIm]Cl·4.7AlCl3 led to the crystallization of [Sb13S16Cl2][AlCl4]5, which contains a new quadruple heterocubane cation.

CO2-Activation by size-selected tantalum cluster cations (Ta1-16+): thermalization governing reaction selectivity.

The reactions of tantalum cluster cations of different sizes toward carbon dioxide are studied in an ion trap under multi-collisional conditions. For all sizes studied, consecutive reactions with several CO2 molecules are observed. This reveals two different pathways, namely oxide formation and the pickup of an entire molecule. Supported by calculations of the thermochemistry of TanO+ formation upon reaction with CO2, changes in the branching ratios at a particular cluster size are related to heat effects due to the vibrational heat capacity of the clusters and the exothermicity of the reaction.

Importance of two-dimensional cation clusters induced by protein folding in intrinsic intracellular membrane permeability.

We investigated the cell penetration of Sp1 zinc finger proteins (Sp1 ZF) and the mechanism via which the total cationic charge and distribution of cationic residues on the protein surface affect intracellular trafficking. Sp1 ZFs showed intrinsic cell membrane permeability. The intracellular transfer of Sp1 ZFs other than 1F3 was dependent on the total cationic charge. Investigation of the effect of cationic residue distribution on intracellular membrane permeability revealed that the cellular uptake of unfolded Zn2+-non-coordinating Ala mutants was lower than that of the wild type. Therefore, the total cationic charge and distribution of cationic residues on the protein played crucial roles in intracellular translocation. Mutational studies revealed that the two-dimensional cation cluster on the protein surface significantly improved their cellular uptake. This study will contribute to the design of artificial cargoes that can efficiently transport target substances into cells.

Electron diffraction as a structure tool for charged and neutral nanoclusters formed in superfluid helium droplets.

This perspective presents the current status and future directions in using electron diffraction to determine the structures of clusters formed in superfluid helium droplets. The details of the experimental setup and data treatment procedures are explained, and several examples are illustrated. The ease of forming atomic and molecular clusters has been recognized since the invention of superfluid helium droplet beams. To resolve atomic structures from clusters formed in droplets, substantial efforts have been devoted to minimizing the contribution of helium to diffraction signals. With active background subtraction, we have obtained structures from clusters containing a few to more than 10 monomers, with and without heavy atoms to assist with the diffraction intensity, for both neutral and ionic species. From fittings of the diffraction profiles using model structures, we have observed that some small clusters adopt the structures of the corresponding solid sample, even for dimers such as iodine and pyrene, while others require trimers or tetramers to reach the structural motif of bulk solids, and smaller clusters such as CS2 dimers adopt gas phase structures. Cationic clusters of argon clusters contain an Ar3+ core, while pyrene dimers demonstrate a change in the intermolecular distance, from 3.5 Å for neutral dimers to 3.0 Å for cations. Future improvements in reducing the background of helium, and in expanding the information content of electron diffraction such as detection of charge distributions, are also discussed.

Modeling and Designing Particle-Regulated Amyloid-like Assembly of Synthetic Polypeptides in Aqueous Solution.

In cells, actin and tubulin polymerization is regulated by nucleation factors, which promote the nucleation and subsequent growth of protein filaments in a controlled manner. Mimicking this natural mechanism to control the supramolecular polymerization of macromolecular monomers by artificially created nucleation factors remains a largely unmet challenge. Biological nucleation factors act as molecular scaffolds to boost the local concentrations of protein monomers and facilitate the required conformational changes to accelerate the nucleation and subsequent polymerization. An accelerated assembly of synthetic poly(l-glutamic acid) into amyloid fibrils catalyzed by cationic silica nanoparticle clusters (NPCs) as artificial nucleation factors is demonstrated here and modeled as supramolecular polymerization with a surface-induced heterogeneous nucleation pathway. Kinetic studies of fibril growth coupled with mechanistic analysis demonstrate that the artificial nucleators predictably accelerate the supramolecular polymerization process by orders of magnitude (e.g., shortening the assembly time by more than 10 times) when compared to the uncatalyzed reaction, under otherwise identical conditions. Amyloid-like fibrillation was supported by a variety of standard characterization methods. Nucleation followed a Michaelis-Menten-like scheme for the cationic silica NPCs, while the corresponding anionic or neutral nanoparticles had no effect on fibrillation. This approach shows the effectiveness of charge-charge interactions and surface functionalities in facilitating the conformational change of macromolecular monomers and controlling the rates of nucleation for fibril growth. Molecular design approaches like these inspire the development of novel materials via biomimetic supramolecular polymerizations.

Cryo spectroscopy of N2 on cationic iron clusters.

Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fen(N2)m]+ for n = 8-20 reveal slightly redshifted IR active bands in the region of 2200-2340 cm-1. These bands mostly relate to stretching vibrations of end-on coordinated N2 chromophores, a μ1,end end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe13 + core structure. The first adsorbate shell closure at (n,m) = (13,12)-as recognized by the accompanying paper on the kinetics of N2 uptake by cationic iron clusters-comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N2 adsorbates. DFT modeling predicts spin quenching by N2 adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N2 adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N2 binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N2 adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120-2200 cm-1 region, which we associate with a μ1,side side-on motif. Some additional features in the (18,m) spectra at high N2 loads indicate a μ1,tilt tilted end-on adsorption motif.

Kinetics of stepwise nitrogen adsorption by size-selected iron cluster cations: Evidence for size-dependent nitrogen phobia.

We present a study of stepwise cryogenic N2 adsorption on size-selected Fen + (n = 8-20) clusters within a hexapole collision cell held at T = 21-28K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N2 uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe13 + with a peculiar metastable adsorption limit, Fe17 + with unprecedented nitrogen phobia (inefficient N2 adsorption), and Fe18 + with an isomeric mixture that undergoes relaxation upon considerable N2 uptake.

Facile quantization of semiconductor compounds in the zeolite: characterization of quantum dots of Zn4S6+ and Zn2S2+ in zeolite Y

The extra-framework zinc sulfide cationic clusters, Zn4S6+ and Zn2S2+, have been introduced into zeolite Y (FAU, Si/Al = 1.56). The |Zn24.5Na12(Zn4S6+)0.5(Zn2S2+)5.5|[Si117Al75O384]-FAU was prepared by allowing aqueous 0.1 M Na2S solution to flow past a |Zn37.5|[Si117Al75O384]-FAU at 294 K for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques. The crystallographic study showed that one sulfide ion at the center of the sodalite cavity coordinates to four Zn2+ ions at site I’ to give a centered-tetrahedral cationic cluster, Zn4S6+, and the other sulfide ion opposite 6-ring in the sodalite cavity bridges between two Zn2+ ions at site I’ to give a cationic cluster with bent arrangement, Zn2S2+, in 6.3% and 68.8% of the sodalite cavity of zeolite Y, respectively. Through high-resolution transmission electron microscope image, zinc sulfide quantum dots (QDs) group with the size of one unit cell (ca. 3 nm) in which hundreds were distributed was identified. By using UV–vis diffuse reflectance spectroscopy, it was confirmed that the zinc sulfide QDs occupied in the structure of zeolite Y exhibited enhanced optical activity because of the quantum size effect compared with that of bulk zinc sulfide. In this study, a method for quantizing semiconducting compounds in the cavity of zeolite Y was presented more easily, and its properties were investigated in more depth. The results proved that zeolite could be applied and used as a quantum container for the quantization of semiconductor compounds.

Solvothermal Synthesis of [Cr7 S8 (en)8 Cl2 ]Cl3 ⋅ 2H2 O with Magnetically Frustrated [Cr7 S8 ]5+ Double-Cubes.

A novel transition metal chalcohalide [Cr7S8(en)8Cl2]Cl3 ⋅ 2H2O, with [Cr7S8]5+ dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine (en) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant, θ=−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions between S=3/2 Cr(III) centers. Due to the complexity of the system with (2S+1)7=16384 microstates from seven Cr3+ centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to be J 1=−21.4 cm−1 and J 2=−30.2 cm−1, confirming competing AFM coupling between the shared Cr3+ center and the peripheral Cr3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J 1=−20.0 cm−1 and J 2=−21.0 cm−1, in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr3+ ions as compared to the AFM exchange between the central and peripheral Cr3+ ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks.

Cluster activation studies with a diffusive condensation particle counter: Effect of chemical composition

We use KanomaxFMT's Fast Condensation Particle Counter (CPC) to study the growth (activation) of purified singly charged cluster ions of several salts by condensation of n-butanol vapor. Salts investigated include 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (EMI-FAP), and four tetra-alkylammonium bromides (CpH2p+1)4N+-Br-, with p = 4, 6, 7, 12. The clusters studied contained up to 20 salt molecules, which were formed via a bipolar electrospray source, and were size-selected with a differential mobility analyzer. The CPC is operated at variable condenser and fixed saturator temperatures, Tc, Ts. It uses 75% sheath gas, such that most aerosol-containing fluid streamlines are near the channel center, and experience very similar maximal saturation ratios. This results in a steep initial dependence of the activation probability on Ts for selected particles. Therefore, a well-defined activation onset temperature Ts∗ is determined as a function of cluster composition, polarity (±), and mobility diameter (dp). Notwithstanding a modest material dependence found for the inferred Tc∗(dp) curves (±0.25 nm), the steepness of the activation curves measured permits determining particle size distributions for aerosols of known composition. There is some ambiguity in the precise temperature profile in the CPC channel. Nevertheless, using our best estimate, the onset condition for all but one of the seed particles studied agrees well with predictions from classical heterogeneous nucleation theory (Fletcher, 1962) when the pre-exponential term K in the nucleation rate is chosen appropriately. This enables the incorporation of materials properties into the sizing process in terms of only this single parameter K. This finding also provides a method to determine K experimentally, suggesting that the material dependence of the activation probability is due to the different interaction potentials between the clusters and the vapor. Tetraheptylammonium bromide is peculiar in that its cluster anions fit classical theory very much as all other materials studied, but its cluster cations do not.

Electronic spectra of positively charged carbon clusters-C2n + (n = 6-14).

Electronic spectra are measured for mass-selected C2n +(n = 6-14) clusters over the visible and near-infrared spectral range through resonance enhanced photodissociation of clusters tagged with N2 molecules in a cryogenic ion trap. The carbon cluster cations are generated through laser ablation of a graphite disk and can be selected according to their collision cross section with He buffer gas and their mass prior to being trapped and spectroscopically probed. The data suggest that the C2n +(n = 6-14) clusters have monocyclic structures with bicyclic structures becoming more prevalent for C22 + and larger clusters. The C2n + electronic spectra are dominated by an origin transition that shifts linearly to a longer wavelength with the number of carbon atoms and associated progressions involving excitation of ring deformation vibrational modes. Bands for C12 +, C16 +, C20 +, C24 +, and C28 + are relatively broad, possibly due to rapid non-radiative decay from the excited state, whereas bands for C14 +, C18 +, C22 +, and C26 + are narrower, consistent with slower non-radiative deactivation.

A systematic investigation of structural growth patterns and electronic properties of [LuGen]+/0 and [Gen+1]+/0 (n = 1–17) nanoalloy clusters

The geometries, stabilities, evolutions, and electronic properties of lutetium-doped germanium nanoalloy clusters LuGen (n = 1–17) in the neutral and cationic state are studied and compared with Gen+1 clusters by using unbiased global search method combined with a hybrid density functional approach. The results reveal that neutral and cationic structural growth patterns prefer Lu-substituted Gen+1 for n = 1–8, Lu-linked configuration for n = 9–14 (for cation n = 9–15) in which Lu atom links two Ge subclusters, and Lu-encapsulated Ge cage-like motif for n = 15–17 (for cation n = 16–17). A binding energy analysis reveals that Lu-encapsulated motifs enhance the nanocluster stability. Lu-doped neutral and cationic germanium clusters can decrease their ionization potential. Natural population analysis shows that Lu in Lu-substituted and Lu-linked configurations acts as electron donor, but acts as electron acceptor in Lu-encapsulated structures. HOMO-LUMO energy gap analysis discloses that Lu-doped Ge clusters can lessen their chemical stability excluding LuGe12 and LuGe17. Thorough analysis of stability, chemical bonding, density of states, iso-chemical shielding surface and UV-Vis spectra revealed that [LuGe17]+ is magic nanoalloy cluster, and has an ideal chemical and thermal stability, making it the most preferable building block for optoelectronic materials. Additionally, Infrared and Raman spectra of [LuGe17]+ are also reported. The accordance between theoretical and experimental values for binding energies of Ge2–8 and ionization potentials of Ge2–16,18 clusters suggest that the calculations and analysis of results in this study are successful.

Frontiers and applications of polyoxometalates-based porous ionic crystals

<p indent="0mm">Polyoxometalates (denoted as POMs) are discrete metal-oxide anions of V, Mo, W, etc., with variable structures and sub-nanometer sizes. Plenty of POMs and their derivatives have been reported due to their oxygen-enriched surface and abundant substitutional chemistry. However, few studies have focused on the modulation of the counter cations so far. Different from common cations, such as Na⁺, NH₄⁺ and other organic ammonium ions (tetramethylammonium, tetrabutylammonium, etc.), cation clusters with larger size can also be used as counter ions of POMs. They are arranged alternately through ionic bonds or hydrogen bonds to form the solid ionic crystal materials with special properties, which are named POM-based porous ionic crystals (PPICs). The use of cation clusters with different compositions greatly enriches the structure and type of PPICs, which further boosts the development of polyoxometalates chemistry. The POMs anions and large metal complex cations in PPICs are regularly arranged into a porous honeycomb or layered structure. Some PPICs also contain monovalent cations such as H⁺ and alkali metal ions to balance their extra negative charges. The use of ion clusters facilitates the formation of pore structures in the PPICs lattice because they can reduce the electrostatic interaction between cations and anions. Thus, the pore structure of PPICs is much larger than that of POMs. Note that the pore size in PPICs can be easily adjusted by changing the shape, size and charges of cation and anions. Apart from the electrostatic interaction, anisotropic π-π stacking and hydrogen bonding network among the components of PPICs also contribute to their assembly. All these interaction modes will affect the arrangement of anions and cations in the PPICs lattice, resulting in the formation of different hole sizes and various channels characteristics in the crystal lattice, such as hydrophilic, hydrophobic and amphiphilic pores. In addition, the long-range Coulomb interaction works isotropically, leading to the easy transformation of the flexible PPICs structure. Hence, the adjustment of the channel provides a useful strategy for constructing PPICs with unique structures. Most importantly, PPICs show better performance than individual components because they inherit the advantages from both anions and cations. Briefly, PPICs not only retain good redox reversibility, rich multi-electron transfer characteristics and strong Brønsted acidity of POMs, but also reserve the magnetic properties of large cation clusters. Therefore, the physical and chemical properties of PPICs can be modulated by the rational design of each component. The future research on PPICs should not be limited to expanding the categories of cations, and the innovative structural type of POMs is also an important aspect. In addition to the Keggin POMs, other POMs structures, such as Dawson, Anderson, and Preyssler, can also be used in PPICs, resulting in some unique properties. Besides, various POM-based materials (modified POMs or POM-based composites, etc.) can also be adopted to fabricate PPICs, which may bring unexpected performance. Thus, changing anions and cations makes PPICs have great potential in many interdisciplinary fields such as chemistry, materials science, and biomedicine. This review systematically summarizes the structural characteristics and composition of PPICs, which is essential for understanding the characteristics of PPICs, such as adjustable pore structure, unique redox behavior, strong acidity and magnetic properties. In general, PPICs with different properties can be constructed by using diverse POMs and distinct cation clusters, which will be widely applied in many fields such as guest adsorption, ion exchange, photoelectric catalysis, bioimaging and medical materials.

Bismuth-rich bimetallic clusters (CuBi8)3+ and [MBi10]4+ (M = Pd, Pt) from ionothermal synthesis

Abstract The reaction of Bi, BiBr3, and CuBr in the Lewis-acidic ionic liquid [BMIm]Br·4AlBr3 (BMIm = 1-n-butyl-3-limidazolium) at 180 °C yielded air-sensitive, shiny black crystals of (CuBi8)[AlBr4]2[Al2Br7]. Crystals of [MBi10][AlCl4]4 (M = Pd, Pt) were obtained by reacting Bi, BiCl3, and MCl2 under similar conditions. The structures have been determined by X-ray diffraction on single-crystals and were found to be very similar to that of the known analogues with other halogens, although not isostructural. In crystals of the complex salts, polyhedral bimetallic clusters (CuBi8)3+ or [MBi10]4+ are embedded in matrices of halogenidoaluminate anions. The heteroatomic nido-cluster (CuBi8)3+ consists of a (Bi8)2+ square antiprism η4-coordinating a copper(I) cation. In the cluster cation [MBi10]4+, the metal atoms M center a pentagonal antiprism of bismuth atoms.

Synergistic ionic interactions in EMAA ionomer blends: A rheological and mechanical property investigation

The rheological and mechanical (tensile) properties of ethylene methacrylic acid (EMAA) ionomers neutralized by Na, Li, and Zn are investigated in binary combinations of two pure ionomers with different counterions. Molecular weight, methacrylic acid content, degree of neutralization, and ion type are tested as experimental parameters to investigate the composition that leads to the largest enhancement in rheological and mechanical properties. Binary cation blend components with low molecular weight and high neutralization reveal enhancement in rheological and mechanical properties beyond a linear mixing combination of material properties such as zero-shear viscosity, relaxation time, and Young’s modulus. The sticky reptation model is applied to EMAA ionomer blends of binary counterions to calculate the timescales of chain dynamics delayed by ionic associations. The ionic clusters of binary cations have longer-lasting ionic associations forming a reinforced reversible crosslink network. The experimental analysis consists of linear and nonlinear viscoelastic experiments, uniaxial extension, and dynamic mechanical analysis, which reveal the conditions and extent of synergism seen in binary EMAA ionomer blends.

Computational probe for the geometrical structure and spectroscopic properties of Ga2Mgn+ (n = 1–11) clusters

Double gallium atoms doped cationic magnesium clusters, Ga2Mgn+ (n = 1–11), were systematically investigated through CALYPSO software with density functional theory (DFT). The structural growth of the ground state of Ga2Mgn+ (n = 1–11) clusters is two-dimensional structures (n = 1), tetrahedral-based (n = 2, 3), tent-like (n = 6, 7) and finally cake-like (n = 8, 9, 10, 11). It is found that Ga2Mg7+ cluster is the most stable one, and can therefore be identified as a “magic” cluster. Charge transfer studies showed that the charges are always transferred from magnesium atoms to gallium atoms. The geometric and electronic structure changes of the most stable Ga2Mg7+ ground state isomer in an external electric field were researched. In addition, the relationship between the bond nature of Ga2Mg7+ and its high stability had been studied through MOs and AdNDP. Finally, we obtained theoretical IR and Raman spectra of the average weights for each cluster at room temperature.

Growth mechanism, electronic properties and spectra of aluminum clusters

Density functional theory (DFT) and particle swarm optimization (PSO) have been applied to study the growth behavior, electronic properties and spectra of neutral, anionic and cationic aluminum clusters with 3–20 atoms. Many isomers have been obtained through a comprehensive structural search. The results indicate that the ground state structures of neutral and anionic aluminum clusters follow an identical periodic growth law. When the number of atoms is 6–11 and 13–18, Al atoms in these clusters grow around an octahedral cluster nucleus and an icosahedral cluster nucleus, respectively. For Aln+ (n ≤ 14 and n ≠ 7) clusters, the most stable structure is different from that of Aln or Aln−clusters. When n > 14, the ground state structure of Aln+ clusters is similar to that of Aln or Aln−clusters. The electronic properties of aluminum clusters have been analyzed by the averaged binding energy, second-order difference of energy, energy gap and dissociation energy. It is found that the Al7+ and Al13− clusters have very high stability and a large energy gap and can be regarded as two superatoms. The aluminum cluster with 18 or 40 valence electrons are the least likely to lose an electron. The dissociation behavior of Aln+ clusters caused by collision is reasonably explained by means of the dissociation energy. The optical absorption spectra of neutral aluminum clusters have been simulated by using the time-dependent density functional theory. The ground states of anionic aluminum clusters have been determined by comparing theoretical photoelectron spectra (PES) with experimental findings. Infrared and Raman spectra of cationic aluminum clusters have been forecasted and can assist in identifying the most stable structure in future experiments.

Gas-phase formation of cationic fullerene/9-aminoanthracene clusters: an indicator for interstellar dust growth

ABSTRACT Growth of clusters by adduction of monomers – as the first step in dust particle growth – is an area of much interest in astronomy. We focus on the fullerene/9-aminoanthracene cluster species, to illustrate the competition between the van der Waals bonding growth and the covalent bonding growth model versus the charge transfer model in the large cluster formation process. The experimental results show that fullerene-fragment (C56 and C58)/9-aminoanthracene cluster cations, e.g. [(C14H11N)nC56]+ and [(C14H11N)nC58]+, n = [1,7], are efficiently formed, while C$_{60}^+$ is insensitive to the cluster’s formation. With laser irradiation, all the fullerene/9-aminoanthracene clusters dissociate into 9-aminoanthracene and fullerene cations. The mechanisms for the reactions of fullerene cations and 9-aminoanthracene were investigated by theoretical calculations, under the assumption that the molecular geometries found for the formed complexes correspond to the global energy minima: the absence of C$_{60}^+$ clusters is mainly due to the charge transfer channel’s competition; [(C14H11N)C58]+ has three types of isomers, with van der Waals or covalent bonds, mainly depending on the reaction sites of fullerene cations. Importantly, in the size grown process, for the fullerene/9-aminoanthracene cluster there exists a geometry configuration conversion between the van der Waals and covalent bonding modes. The largest fullerene/9-aminoanthracene clusters, e.g. [(C14H11N)7C58]+ (240 atoms, ∼4 nm in size), are likely in a multishelled geometry, i.e. seven 9-aminoanthracene molecules surrounding fullerene cations in two layers, which can directly build the relationship between molecular clusters and carbonaceous grains. Nitrogen matters! The specific side chains (e.g. –NH2) play an important role in the growth of interstellar dust.

Structure analysis of aqueous Mg(NO3)2 solutions

An increasing amount of research has investigated whether direct contact ion pairs (CIP) exist in magnesium nitrate solutions. In this work, the relationship between the concentration and microstructure, as well as the details of the ion pair structure in magnesium nitrate solutions were studied by Raman spectroscopy, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. Component analysis showed that solvent-shared ion pairs (SIPs) and free hydrated ions were the dominant species in dilute solution. SIPs gradually transformed into contact ion pairs as the concentration increased. Complex structures and CIPs were the main species when WSR < 10, and as the concentration further increased, the CIP content gradually decreased, while the number of complex structures gradually increased. MD simulations and DFT calculations provide a new understanding of the structural units of ion pairs in magnesium nitrate solutions. The SIPs and CIPs were mainly composed of cationic triple ion clusters with two magnesium ions and one nitrate ion. The nitrate ion mainly existed as monodentate ligand to form a CIP with the magnesium ion. As the solution concentration increased, triple ion clusters gradually transformed into more complex chain structures. The structural complexity of magnesium nitrate solutions deserves further attention.