Study of Cluster Anions Generated by Laser Ablation of Titanium Oxides: A High Resolution Approach Based on Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Laser ablation of titanium oxides at 355 nm and ion–molecule reactions between [(TiO₂)_x]^–• cluster anions and H₂O or O₂ were investigated by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) with an external ion source. The detected anions correspond to [(TiO₂)_x(H₂O)_yOH]^– and [(TiO₂)_x(H₂O)_yO₂]^–• oxy-hydroxide species with x = 1 to 25 and y = 1, 2, or 3 and were formed by a two step process: (1) laser ablation, which leads to the formation of [(TiO₂)_x]^–• cluster anions as was previously reported, and (2) ion–molecule reactions during ion storage. Reactions of some [(TiO₂)_x]^–• cluster anions with water and dioxygen conducted in the FTICR cell confirm this assessment. Tandem mass spectrometry experiments were also performed in sustained off-resonance irradiation collision-induced dissociation (SORI-CID) mode. Three fragmentation pathways were observed: (1) elimination of water molecules, (2) O₂ loss for radical anions, and (3) fission of the cluster. Density functional theory (DFT) calculations were performed to explain the experimental data.     

Large Carbon Cluster Anions Generated by Laser Ablation of Graphene

The formation of large even-numbered carbon cluster anions, \textC_\textn ^- {\text{C}}_{\text{n}}^{ - } , with n up to 500 were observed in the mass spectra generated by laser ablation of graphene and graphene oxide, and the signal intensity of the latter is much weaker than that of the former. The cluster distributions generated from graphene can be readily altered by changing the laser energy and the accumulation period in the FT - ICR cell. By choosing suitable experimental conditions, weak signals of odd-numbered anions from \textC₁₂₅ ^- {\text{C}}_{{125}}^{ - } to \textC₂₁₁ ^- {\text{C}}_{{211}}^{ - } , doubly charged anions from \textC₇₀^{2 -} {\text{C}}_{{70}}^{{2 - }} to \textC₂₃₀^{2 -} {\text{C}}_{{230}}^{{2 - }} and triply charged cluster anions from \textC₈₀^{3 -} {\text{C}}_{{80}}^{{3 - }} to \textC₂₂₄^{3 -} {\text{C}}_{{224}}^{{3 - }} can be observed. Tandem MS was applied to some selected cluster anions. Though no fragment anions larger than \textC₂₀ ^- {\text{C}}_{{20}}^{ - } can be observed by the process of collisional activation with N₂ gas for most cluster ions, several cluster anions can lose units of C₂, C₄, C₆ or C₈ in their collision process. The differences in their dissociation kinetics and structures require further calculations and experimental studies.     

Negative ion photoelectron spectroscopy of solvated electron cluster anions, (H2O) n − and (NH3) n −

The photodetachment spectra of (H₂O) _n ^=2?69/? and (NH₃) _n ^=41?1100/? have been recorded, and vertical detachment energies (VDEs) were obtained from the spectra. For both systems, the cluster anion VDEs increase smoothly with increasing sizes and most species plot linearly withn ^?1/3, extrapolating to a VDE (n=∞) value which is very close to the photoelectric threshold energy for the corresponding condensed phase solvated electron system. The linear extrapolation of this data to the analogous condensed phase property suggests that these cluster anions are gas phase counterparts to solvated electrons, i.e. they are embryonic forms of hydrated and ammoniated electrons which mature with increasing cluster size toward condensed phase solvated electrons.     

Coordination compounds of electron-deficient boron cluster anions BnH n2? (n = 6, 10, 12)

This survey concerns the coordination ability of B _n H _n ²⁻ (n = 6, 10, 12) boron cluster anions and their derivatives in complex formation. Boron cluster anions form four types of compounds: salts of organic cations and alkali-metal cations, including Cat₂B _n H _n , where specific interactions can be observed between a cation Cat and a boron cluster anion; salts of protonated anions CatB₆H₇ and CatB₁₀H₁₁, analogues of Cat[MB _n H _n ] complexes, where an extra hydrogen atom appears bound with the BBB face of a boron polyhedron and performs as a hard acceptor; metal complexes with outer-sphere boron cluster anions where specific ligand-ligand interactions may be observed between a boron cluster anion and an inner-sphere ligand; and true metal complexes with boron cluster anions that enter the inner coordination sphere. The last case characterizes closo-hydroborate anions as polydentate ligands whose denticity can vary widely under the effect of substituents or other ligands in the complex.     

Photoemission from tin and lead cluster anions

Photoelectrons from mass-identified jet-cooled tin and lead cluster anions (Sn _n ^? , Pb _n ^? ) are detached by ultraviolet laser light (hν=3.68 eV). The photoelectron energy spectra give the detachment energies of ground state cluster anions (electron affinities) as well as excitation energies of neutral clusters in the geometry of the anions. The energy spectra for Sn _n ^? are dominated by flat thresholds with ann-dependence similar to that of other group IV clusters. In contrast, for Pb _n ^? we find pronounced narrow lines close to threshold, generally followed by a 0.3–1.4 eV gap which indicates closed-shell behaviour of Pb _n ^? for nearly alln.     

Activation of Methane Promoted by Adsorption of CO on Mo2C2− Cluster Anions

Atomic clusters are being actively studied for activation of methane, the most stable alkane molecule. While many cluster cations are very reactive with methane, the cluster anions are usually not very reactive, particularly for noble metal free anions. This study reports that the reactivity of molybdenum carbide cluster anions with methane can be much enhanced by adsorption of CO. The Mo₂C₂^? is inert with CH₄ while the CO addition product Mo₂C₃O^? brings about dehydrogenation of CH₄ under thermal collision conditions. The cluster structures and reactions are characterized by mass spectrometry, photoelectron spectroscopy, and quantum chemistry calculations, which demonstrate that the Mo₂C₃O^? isomer with dissociated CO is reactive but the one with non‐dissociated CO is unreactive. The enhancement of cluster reactivity promoted by CO adsorption in this study is compared with those of reported systems of a few carbonyl complexes.     

Studies of cluster anions C n X− (X=N,P, As,Sb, Bi) produced by laser ablation

A series of cluster anions C _n X^? are produced from laser ablation of appropriate samples, where X is selected as a group-VB element. The recorded mass spectra of these cluster anions display a drastic even/odd alternation on ion intensities: For C _n N^?, only anions with oddn can be observed; For C _n P^? and C _n As^?, cluster anions with evenn are produced but with lower signal intensities; For C _n Sb^?, the signal intensity of clusters does not show even/odd alternation; Finally, for C _n Bi^?, the intensities of cluster anions with evenn are higher than those with oddn. This parity effect can be attributed to the linear structure of the cluster anions, and the parity reversal of C _n X^? from C _n N^? to C _n Bi^? can be explained from the electronegativity decreasing of the heteroatom X as it descends in the group. The Hückel model was applied to account the structural feature of these clusters.     

Hexanuclear Niobium Cluster Compounds with Protonated N-Base Cations

Octahedral clusters of the [M₆X₁₂] type offer numerous possibilities to form structural arrangements through different choices of bonding situations. In this paper a series of new cluster compounds of the transition metal niobium is described, which consist of the [Nb₆Cl₁₈]^2–, and in one case [Nb₆Cl₁₈]^3–, anion and protonated N-base cations ([MIm-H]⁺, [nPr₃N-H]⁺, [TMGu-H]⁺, and [Tzn-H]⁺). They all are prepared using water scavenger compounds [SOCl₂ or (Ac)₂O] under oxidising conditions, resulting in two-electron (or one-electron, respectively) oxidized cluster units with respect to the starting material [Nb₆Cl₁₄(H₂O)₄] · 4H₂O. Of five members of this group single-crystal X-ray structures were determined. The cluster anions exist in all structures as discrete units. The acidic H atoms of all N-bases are hydrogen bonded to H acceptors, in 4 cases to outer, exo bonded Cl atoms of the cluster unit and in one case to the O atom of a co-crystallized THF molecule. In [TMGu-H]₂[Nb₆Cl₁₈] chains of cluster anions exist hydrogen-bonded through bridging [TMGu-H]⁺ cations. ESI mass spectra of [MIm-H]₂[Nb₆Cl₁₈] · 2SOCl₂ and [TMGu-H]₂[Nb₆Cl₁₈] show the expected isotopic distribution patterns for the anions together with other peaks associated to chloride mass losses and/or reduction processes.     

Cyanide Complexes Based on {Mo6I8}4+ and {W6I8}4+ Cluster Cores

Compounds based on new cyanide cluster anions [{Mo₆I₈}(CN)₆]^2–, trans-[{Mo₆I₈}(CN)₄(MeO)₂]^2– and trans-[{W₆I₈}(CN)₂(MeO)₄]²⁻ were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo₆I₈}⁴⁺ and {W₆I₈}⁴⁺ cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo₆I₈} and {W₆I₈} cluster cores can be achieved by coordination of cyanide ligands.     

Structural peculiarities and the possibility of the existence of small water cluster anions (H2O) n − withn≤4

Structures of (H₂O) _n ⁻ anions withn≤4 were optimized at the UHF/4-31++G^** level and their stability was estimated at the MP2/4-31++G^** level. The trimer anion has a chain-like structure while the tetramer anion can exist either in a chain-like or a cyclic configuration. In the dimer anion and in the chain-like anions, the excess electron density is localized on the terminal water molecule, an acceptor of the H-bond proton. In the cyclic anion, it is uniformly distributed over the free hydrogen atoms. All considered anions have energy values higher than those of the corresponding neutral oligomers. The detachment of an electron from the anions should proceed with the liberation of energy. However, trimer and larger anions are stable against dissociation into individual water molecules and a free electron. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–46, January, 1997.     

Can Fluorinated Molecular Cages Be Utilized as Building Blocks of Hyperhalogens?

Based on the density functional theory for exchange‐correlation potential, fluorocarbon molecular cages are investigated as building blocks of hyperhalogens. By utilizing C₈F₇ as a ligand, a series of hyperhalogen anions, that is, M(C₈F₇)₂^? (M=Li, Na, and K) and M(C₈F₇)₃^? (M=Be, Mg, and Ca), are modeled. Calculations show that all the C₈F₇ moieties preserve their geometric and electronic integrity in these anions. These anionic molecules possess larger vertical electron detachment energies (5.11–6.45 eV) than that of C₈F₇^?, verifying their hyperhalogen nature. Moreover, it is also revealed that using larger fluorinated cage C₁₀F₉ as ligands can bring about hyperhalogen anions with larger vertical electron detachment energies. The stability of these studied anions is determined by their large HOMO–LUMO gaps and positive dissociation energies of predetermined possible fragmentation pathways. It is hoped this study will provide an approach for the construction of new types of hyperhalogens and stimulate more research in superatom chemistry.     

Systematic DFT Studies on Binary Pseudo-tetrahedral Zintl Anions: Relative Stabilities and Reactivities towards Protons,Trimethylsilyl Groups,and Iron Complex Fragments

Binary pseudo-tetrahedral Zintl anions composed of (semi)metal atoms of the p-block elements have proven to be excellent starting materials for the synthesis of a variety of heterometallic and intermetalloid transition metal–main group metal cluster anions. However, only ten of the theoretically possible 48 anions have been experimentally accessed to date as isolable salts. This brings up the question whether the other species are generally not achievable, or whether synthetic chemists just have not succeeded in their preparation so far. To contribute to a possible answer to this question, global minimum structures were calculated for all anions of the type (TrTt₃)⁵⁻, (TrPn₃)²⁻, and (Tt₂Pn₂)²⁻, comprising elements of periods 3 to 6 (Tr: triel, Al⋅⋅⋅Tl; Tt: tetrel, Si⋅⋅⋅Pb; Pn: pnictogen, P⋅⋅⋅Bi). By analyzing the computational results, a concept was developed to predict which of the yet missing anions should be synthesizable and why. Additionally, the results of an electrophilic attack by protons or trimethylsilyl groups or a nucleophilic attack by transition metal complex fragments are described. The latter yields butterfly-like structures that can be viewed as a new form of adaptable tridentate chelating ligands.     

Following the Reaction of Heteroanions inside a {W18O56} Polyoxometalate Nanocage by NMR Spectroscopy and Mass Spectrometry

By incorporating phosphorus(III)‐based anions into a polyoxometalate cage, a new type of tungsten‐based unconventional Dawson‐like cluster, [W₁₈O₅₆(HP^IIIO₃)₂(H₂O)₂]^8?, was isolated, in which the reaction of the two phosphite anions [HPO₃]^2? within the {W₁₈O₅₆} cage could be followed spectroscopically. As well as full X‐ray crystallographic analysis, we studied the reactivity of the cluster using both solution‐state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO₃} moieties dimerize to form a weakly interacting (O₃PH???HPO₃) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P^III template moieties to form P^V centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells–Dawson {W₁₈O₅₄} cluster.     

Specific interactions in metal salts and complexes with cluster boron anions BnH n2? (n = 6, 10, 12)

Specific interactions that appear in metal salts and complexes with cluster boron anions B _n H _n ²⁻ (n = 6, 10, 12) have been discussed. These interactions, as well as chemical bonds, involve vertices, edges, or faces of boron polyhedra. Specific interactions have a considerable effect on the structure of compounds, making a significant contribution to the formation of the unit cell and forming supramolecular assemblies. Compounds containing B _n H _n ²⁻ cluster anions shed new light onto the nature of specific interactions owing to their many-center character and great variety.     

Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including V_xO_y ^n– and V_xO_yCl^n– ions (x = 1–14, y = 2–36, n = 1–3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V₁₄O₃₆Cl(L)₅ (L = Et₄N⁺, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged V_xO_yCl^n– and V_xO_yCl(L)^(n–1)– clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller V_xO_yCl^(1–2)– and V_xO_y ^(1–2)– anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged V_xO_yCl and V_xO_y species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of V_xO_yCl and V_xO_y anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a wide range of singly and multiply charged gas-phase metal oxide cluster anions for subsequent investigations of structure and reactivity using mass spectrometry and ion spectroscopy techniques.      

Synthesis,Crystal Structure and Characterization of 3d–4d–4f Heterometallic Clusters Based on Super Tetrahedron Anions

Five heterometallic complexes were prepared in aqueous solution at 3–5 °C and characterized by elemental analyses, inductively coupled plasma analysis, IR spectra, UV–Vis spectra, powder X-ray diffraction and X-ray single-crystal diffraction. Complex 1–5 all contain 4d–4f super tetrahedron cluster anions, which are constructed by Ln^III ions (Ln = Nd^III, Pr^III), [MoO₄]^2? and [Mo₇O₂₄]^6? anions. Differences among 1–5 lie on the assembly of super tetrahedron anions by excess Ln^III and TM^II (TM = Co^II, Ni^II, Cu^II or Zn^II), which generates bigger cluster anions (complex 1–4) or anions with 1D infinite structure (complex 5). The assemble styles for synthons mentioned above show with capped style, head-to-head linking style or side-by-side linking style.     

Geometrical structures and dissociation channels of MP<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><Superscript>+</Superscript> (M = Fe,Co or Ni; <Emphasis Type="Italic">n</Emphasis> = 2, 4, 6 or 8) binary cluster ions

A density functional theory study on the geometrical structures and dissociation channels of MP _n ⁺ (M = Fe, Co or Ni; n = 2, 4, 6 or 8) binary cluster ions has been performed. The tetrahedral P₄ structure and linear P₂ structure are found to be two relatively stable units in these ions. The lowest energy structures of MP _n ⁺ cluster ions are constructed by bonding a twofold or fourfold M atom with a P₄ or P₂ unit. The M–P bond is clearly weaker than the P–P bond. The most likely dissociation channel of the MP _n ⁺ cluster ions is the detachment of a P₄ or P₂ fragment. This conclusion is well consistent with the published experimental data and consistent with our previously reported theoretical study on the CrP _m ⁺ (m = 2, 4, 6 or 8) cluster ions.     

Nonempirical Description of the Atmospherically Important Anionic Species. I. Water Cluster Anions

Water cluster anions, comprising up to 20 molecules, are simulated at the second-order unrestricted Møller–Plesset perturbation theory level with 6-31++G** basis set augmented with a floating center of 8 s diffuse functions. Interface structures composed of two to four chainlike or cyclic subclusters found to be most stable among anions of the same molecular size are shown to serve as a reliable restricted model of the hydrated electron. The calculated values of the adiabatic electron affinity of neutral clusters and the vertical energies of electron detachment from anions fit in with n ^–1/3 dependences that provide the corresponding estimates of the bulk water or ice specimens. The radius of a circumsphere containing about 85% of the excess electron density is treated as an effective radius of the excess electron and found to approach 2.5 Å as the size of cluster increases to infinity.     

Heteroselenometallic cluster compounds with tetraselenometalates

The coordination cluster compounds of tetraselenomolybdate and tetraselenotungstate anions with metal ions are reviewed. New heteroselenometallic cluster compounds are primarily of interest regarding their structures and reactivities, and their potential as non-linear optical (NLO) materials. This article focuses from a synthetic and structural point of view on coordination cluster compounds with tetraseleno-molybdate and -tungstate anions as polydentate ligands. A comprehensive survey is presented of the heteroselenometallic clusters known to date according to the number of center [MSe₄]²⁻ (M=Mo, W) anions. Representative spectroscopic and NLO properties of these clusters are also discussed.     

Manipulating Coulombic Efficiency of Cathodes in Aqueous Zinc Batteries by Anion Chemistry

Electrolyte environments, including cations, anions, and solvents are critical for the performance delivery of cathodes of batteries. Most works focused on interactions between cations and cathode materials, in contrast, there is a lack of in-depth research on the correlation between anions and cathodes. Here, we systematically investigated how anions manipulate the coulombic efficiency (CE) of cathodes of zinc batteries. We take intercalation-type V₂O₅ and conversion-type I₂ cathodes as typical cases for profound studies. It was found that electronic properties of anions, including charge density and its distribution, can tune conversion or intercalation reactions, leading to significant CE differences. Using operando visual Raman microscopy and theoretical simulations, we confirm that competitive coordination between anions and I⁻ can regulate CEs by modulating polyiodide diffusion rates in Zn−I₂ cells. In Zn−V₂O₅ cells, anion-tuned solvation structures vastly affect CEs through varying Zn²⁺ intercalation kinetics. Conversion I₂ cathode achieves a 99 % CE with highly electron-donating anions, while anions with preferable charge structures that interact strongly with Zn²⁺ afford an intercalation V₂O₅ a nearly 100 % CE. Understanding the mechanism of anion-governed CEs will help us evaluate compatibility of electrolytes with electrodes, thus providing a guideline for anion selection and electrolyte design for high-energy, long-cycling zinc batteries.