The Geometric Structure of Silver‐Doped Silicon Clusters

Cationic silver‐doped silicon clusters, Si_nAg⁺ (n=6–15), are studied using infrared multiple photon dissociation in combination with density functional theory computations. Candidate structures are identified using a basin‐hopping global optimizations method. Based on the comparison of experimental and calculated IR spectra for the identified low‐energy isomers, structures are assigned. It is found that all investigated clusters have exohedral structures, that is, the Ag atom is located at the surface. This is a surprising result because many transition‐metal dopant atoms have been shown to induce the formation of endohedral silicon clusters. The silicon framework of Si_nAg⁺ (n=7–9) has a pentagonal bipyramidal building block, whereas the larger Si_nAg⁺ (n=10–12, 14, 15) clusters have trigonal prism‐based structures. On comparing the structures of Si_nAg⁺ with those of Si_nCu⁺ (for n=6–11) it is found that both Cu and Ag adsorb on a surface site of bare Si_n⁺ clusters. However, the Ag dopant atom takes a lower coordinated site and is more weakly bound to the Si_n⁺ framework than the Cu dopant atom.     

TiS2 and ZrS2 single‐ and double‐wall nanotubes: First‐principles study

Hybrid density functional theory has been applied for investigations of the electronic and atomic structure of bulk phases, nanolayers, and nanotubes based on titanium and zirconium disulfides. Calculations have been performed on the basis of the localized atomic functions by means of the CRYSTAL‐2009 computer code. The full optimization of all atomic positions in the regarded systems has been made to study the atomic relaxation and to determine the most favorable structures. The different layered and isotropic bulk phases have been considered as the possible precursors of the nanotubes. Calculations on single‐walled TiS₂ and ZrS₂ nanotubes confirmed that the nanotubes obtained by rolling up the hexagonal crystalline layers with octahedral 1T morphology are the most stable. The strain energy of TiS₂ and ZrS₂ nanotubes is small, does not depend on the tube chirality, and approximately obeys to D^–2 law (D is nanotube diameter) of the classical elasticity theory. It is greater than the strain energy of the similar TiO₂ and ZrO₂ nanotubes; however, the formation energy of the disulfide nanotubes is considerably less than the formation energy of the dioxide nanotubes. The distance and interaction energy between the single‐wall components of the double‐wall nanotubes is proved to be close to the distance and interaction energy between layers in the layered crystals. Analysis of the relaxed nanotube shape using radial coordinate of the metal atoms demonstrates a small but noticeable deviation from completely cylindrical cross‐section of the external walls in the armchair‐like double‐wall nanotubes. © 2013 Wiley Periodicals, Inc.     

Clustering of sulfamic acid: ESI MS and theoretical study

Sulfamic acid has wide application in industry and has been suggested to act as an effective nucleation agent for the formation of aerosols and cloud particles. From the point of view of the role that sulfamic acid may play in aerosol formation, the study of its homoaggregation is important. Gas phase clustering study was performed for sulfamic acid H₃N·SO₃, (ASA), from water and methanol–water solutions, by help of a TOF‐Q spectrometer equipped with electrospray ionization source, in the negative‐ion mode. The structure and stability of the (H₃N·SO₃)_n and [(H₃N·SO₃)_n‐H]^? (n = 1–6) were studied using DFT/B3LYP/aug‐cc‐pVDZ method. The ESI MS study evidenced that both singly and doubly charged clusters are formed when the acids are electrosprayed from water solutions; they may be described as [(H₃N·SO₃)_n‐zH]^z? where z = 1 or 2. The largest identified clusters are built of 20 monomers. The theoretical studies showed that formation of higher order (ASA)_n aggregates in the gas phase is energetically profitable. In contrast with the gas phase, aqueous solution does not favor the formation of (ASA)_n aggregates. The study led to the conclusion that the ASA clusters are formed in the gas phase under the experimental conditions of the mass spectrometer. A hypothetical mechanism concerning the formation of the doubly negatively charged anionic aggregates is discussed. The obtained data suggest that small (NH₃·SO₃)_n aggregates may also contribute to formation of aerosols in heavily polluted atmospheres with relatively large NH₃ concentration. Copyright © 2015 John Wiley & Sons, Ltd.     

Probing the Chemical Functionalization of Single‐Walled Carbon Nanotubes with Multiple Carbon Ad‐Dimer Defects

Drying‐tube‐shaped single‐walled carbon nanotubes (SWCNTs) with multiple carbon ad‐dimer (CD) defects are obtained from armchair (n,n,m) SWCNTs (n=4, 5, 6, 7, 8; m=7, 13). According to the isolated‐pentagon rule (IPR) the drying‐tube‐shaped SWCNTs are unstable non‐IPR species, and their hydrogenated, fluorinated, and chlorinated derivatives are investigated. Interestingly, chemisorptions of hydrogen, fluorine, and chlorine atoms on the drying tube‐shaped SWCNTs are exothermic processes. Compared to the reaction energies for binding of H, F, and Cl atoms to perfect and Stone–Wales‐defective armchair (5,5) nanotubes, binding of F with the multiply CD defective SWCNTs is stronger than with perfect and Stone–Wales‐defective nanotubes. The reaction energy for per F₂ addition is between 85 and 88 kcal mol^?1 more negative than that per H₂ addition. Electronic structure analysis of their energy gaps shows that the CD defects have a tendency to decrease the energy gap from 1.98–2.52 to 0.80–1.17 eV. After hydrogenation, fluorination, and chlorination, the energy gaps of the drying‐tube‐shaped SWCNTs with multiple CD defects are substantially increased to 1.65–3.85 eV. Furthermore, analyses of thermodynamic stability and nucleus‐independent chemical shifts (NICS) are performed to analyze the stability of these molecules.     

Inception of Acetic Acid/Water Cluster Growth in Molecular Beams

The influence of carboxylic acids on water nucleation in the gas phase has been explored in the supersonic expansion of water vapour mixed with acetic acid (AcA) at various concentrations. The sodium‐doping method has been used to detect clusters produced in supersonic expansions by using UV photoionisation. The mass spectra obtained at lower acid concentrations show well‐detected Na⁺?AcA(H₂O)_n and Na⁺?AcA₂(H₂O)_n clusters up to 200 Da and, in the best cooling expansions, emerging Na⁺?AcA_m(H₂O)_n signals at higher masses and unresolved signals that extend beyond m/e values >1000 Da. These signals, which increase with increasing acid content in water vapour, are an indication that the cluster growth taking place arises from mixed water–acid clusters. Theoretical calculations show that small acid–water clusters are stable and their formation is even thermodynamically favoured with respect to pure water clusters, especially at lower temperatures. These findings suggest that acetic acid may play a significant role as a pre‐nucleation embryo in the formation of aerosols in wet environments.     

Magnesium-Based Clusters as Building Blocks of Electrolytes in Lithium-Ion Batteries

Superhalogens, owing to their large electron affinity (EA, exceeding those of any halogen atom), play an essential role in physical chemistry as well as new material design. They have applications in hydrogen storage and lithium-ion batteries. Owing to the unique geometries and electronic features of magnesium-based clusters, their potential to form a new class of lithium salts has been investigated here theoretically. The idea is assessed by conducting ab initio computations on Li⁺/Mg_nF_2n+1-2mO_m⁻ compounds (n=2, 3; m=0-3) and analyzing their performance as potential Li-ion battery electrolytes. The Mg₃F₇⁻ cluster, with large electron binding energy (EA of 7.93 eV), has been proven to serve as a building block for lithium salts. It is shown that, apart from high electronic stability, the new superhalogen-based electrolytes exhibit a set of desirable properties, including a large band gap, high electrolyte stability window, easy mobility of the Li⁺, and favorable insensitivity to water.     

From an Icosahedron to a Plane: Flattening Dodecaiodo‐dodecaborate by Successive Stripping of Iodine

It has been shown by electrospray ionization–ion‐trap mass spectrometry that B₁₂I₁₂^2? converts to an intact B₁₂ cluster as a result of successive stripping of single iodine radicals or ions. Herein, the structure and stability of all intermediate B₁₂I_n^? species (n=11 to 1) determined by means of first‐principles calculations are reported. The initial predominant loss of an iodine radical occurs most probably via the triplet state of B₁₂I₁₂^2?, and the reaction path for loss of an iodide ion from the singlet state crosses that from the triplet state. Experimentally, the boron clusters resulting from B₁₂I₁₂^2? through loss of either iodide or iodine occur at the same excitation energy in the ion trap. It is shown that the icosahedral B₁₂ unit commonly observed in dodecaborate compounds is destabilized while losing iodine. The boron framework opens to nonicosahedral structures with five to seven iodine atoms left. The temperature of the ions has a considerable influence on the relative stability near the opening of the clusters. The most stable structures with five to seven iodine atoms are neither planar nor icosahedral.     

Structural Preferences of Single‐Walled Silica Nanostructures: Nanospheres and Chemically Stable Nanotubes

Structural preferences of single‐walled and coordinatively saturated spherical and tubular nanostructures of silica have been determined by ab initio calculations. Two families of spherical (SiO₂)_n clusters derived from Platonic solids and Archimedean polyhedra are depicted, with n ranging from 4–120. The analogue of a truncated icosidodecahedron, I_h‐symmetric Si₁₂₀O₂₄₀, is favored in energy, closely followed by the I_h‐symmetric Si₆₀O₁₂₀‐truncated icosahedron. The silica nanotubes derived from spherical clusters are capped by Si₂O₂ rings, whereas the tubular section consists of single oxygen bridges. Periodic studies performed with open‐ended silica nanotubes and the α‐quartz polymorph of silica, along with a comparisons to fullerenes and carbon nanotubes, suggest that tubes with diameters of approximately 1 nm should be chemically stable.     

The electronic structure of small sodium clusters

Ab initio molecular orbital calculations using the STO3-21G basis set has been carried out for the cluster series Na _n ⁺ , Na _n , and Na _n ^– (wheren=2–7). The basis set is shown to be reliable compared with more extensive basis sets at the Hartree-Fock level. Thirty-one optimized structures are reported and discussed, many of which (especially for the anions) have not been considered. The STO3-21G//STO3-21G calculations suggest that for most of the species the optimum geometries are planar. In particular, the optimized structures for the anionic species should provide a starting point for more sophisticated configuration interaction calculations.     

Structure and photoelectron spectral properties of I(-)·nCO2 clusters: an ab initio study

Structures and photoelectron spectral properties of I^??nCO₂ (n=1–7) clusters are presented at the level of second‐order Møller–Plesset perturbation theory with relativistic corrections. Triple split‐valence 6‐311++G(d,p) basis set functions are employed herein. It is observed that the CO₂ molecules approach the I^? anion from one side in all the clusters and that I^??nCO₂ clusters prefer the surface structure. The calculated vertical detachment energy of these clusters is in excellent agreement with the reported experimentally measured values (within 4 %). Efforts are also made to extract vertical detachment energy of large size of clusters, including the bulk. The extracted vertical detachment energy values for larger clusters (n=8–13) by employing the microscopic theory‐based expression are also close (within 4 %) to that of the experimentally measured values.     

Theoretical studies on the structure and protonation of Cu(II) complexes of a series of tripodal aliphatic tetraamines: Good correlations with the experimental data

DFT(B3LYP) studies on first protonation step of a series of Cu(II) complexes of some tripodal tetraamines with general formula N[(CH₂)_nNH₂][(CH₂)_mNH₂][(CH₂)_pNH₂] (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4; ppb) are reported. First, the gas‐phase proton macroaffinity of all latter complexes was calculated with considering following simple reaction: [Cu(L)]²⁺(g) + H⁺(g) → [Cu(HL)]³⁺(g). The results showed that there is a good correlation between the calculated proton macroaffinities of all complexes with their stability constants in solution. Then, we tried to determine the possible reliable structures for microspecies involved in protonation process of above complexes. The results showed that, similar to the solid state, the [Cu(L)(H₂O)]²⁺ and [Cu(HL)(H₂O)₂]³⁺ are most stable species for latter complexes and their protonated form, respectively, at gas phase. We found that there are acceptable correlations between the formation constants of above complexes with both the ? and ? of following reaction: [Cu(L)(H₂O)]²⁺(g) + H⁺(g) + H₂O(g) → [Cu(HL)(H₂O)₂]³⁺(g). The ? of the latter reaction can be defined as a theoretically solvent–proton macroaffinity of reactant complexes because they have gained one proton and one molecule of the solvent. The unknown formation constant of [Cu(epb)]²⁺ complex was also predicted from the observed correlations. In addition, the first proton affinity of all complexes was studied in solution using DPCM and CPCM methods. It was shown that there is an acceptable correlation between the solvent–proton affinities of [Cu(L)(H₂O)]²⁺ complexes with formation constants of [Cu(HL)(H₂O)₂]³⁺ complexes in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Structure of Modified Polytetrafluoroethylene According to DFT Calculations and 19F NMR Spectroscopy

The molecular structure of n-C₇F₁₆ and the ¹⁹F nuclear magnetic screening tensors are calculated by density functional theory (DFT) methods. The results of calculations are compared with ¹⁹F NMR data, and it is shown that fine polytetrafluoroethylene (PTFE) contains the terminal CF₃ groups in its structure.     

Stability,Infrared Spectra and Electronic Structures of (ZrO2)n(n=3-6)Clusters:DFT Study

The stability, infrared spectra and electronic structures of (ZrO₂)_n (n=3–6) clusters have been investigated by using density‐functional theory (DFT) at B3LYP/6‐31G* level. The lowest‐energy structures have been recognized by considering a number of structural isomers for each cluster size. It is found that the lowest‐energy (ZrO₂)₅ cluster is the most stable among the (ZrO₂)_n (n=3–6) clusters. The vibration spectra of Zr? O stretching motion from terminal oxygen atom locate between 900 and 1000 cm^?1, and the vibrational band of Zr? O? Zr? O four member ring is obtained at 600–700 cm^?1, which are in good agreement with the experimental results. Mulliken populations and NBO charges of (ZrO₂)_n clusters indicate that the charge transfers occur between 4d orbital of Zr atoms and 2p orbital of O atoms. HOMO‐LUMO gaps illustrate that chemical stabilities of the lowest‐energy (ZrO₂)_n (n=3–6) clusters display an even‐odd alternating pattern with increasing cluster size.     

Sandwich Double‐Decker Lanthanide(III) “Intracavity” Complexes Based on Clamshell‐Type Phthalocyanine Ligands: Synthesis,Spectral, Electrochemical,and Spectroelectrochemical Investigations

Phthalocyanine compounds of novel type based on a bridged bis‐ligand, denoted “intracavity” complexes, have been prepared. Complexation of clamshell ligand 1,1′‐[benzene‐1,2‐diylbis(methanediyloxy)]bis[9(10),16(17),23(24)‐tri‐tert‐butylphthalocyanine] (^clam,tBuPc₂H₄, 1 ) with lanthanide(III) salts [Ln(acac)₃] ? n H₂O (Ln=Eu, Dy, Lu; acetylacetonate) led to formation of double‐deckers ^clam,tBuPc₂Ln ( 2 a – c ). Formation of high molecular weight oligophthalocyanine complexes was demonstrated as well. The presence of an intramolecular covalent bridge affecting the relative arrangement of macrocycles was shown to result in specific physicochemical properties. A combination of UV/Vis/NIR and NMR spectroscopy, MALDI‐TOF mass‐spectrometry, cyclic voltammetry, and spectroelectrochemistry provided unambiguous characterization of the freshly prepared bis‐phthalocyanines, and also revealed intrinsic peculiarities in the structure–property relationship, which were supported by theoretical calculations. Unexpected NMR activity of the paramagnetic dysprosium complex 2 b in the neutral π‐radical form was observed and examined as well.     

First Hyperpolarizability Evolutions of Some Extended Sesquifulvalene Compounds

Molecular orbital calculations of some extended sesquifulvalene compounds as O_n with olefins bridge and T_n with thiophenes bridge as well as their corresponding cyclopentadienyl‐iron(II) coordination compounds as IO_n and IT_n at the hybrid density functional theory level demonstrate that the dipole moment depends linearly on the molecular size (n), and the linear polarizability depends linearly on n² as well as the first hyperpolarizability also has a linear dependence on n³.     

Linear Multiselenium Interactions in Dicationic Oligomers of 1,5-(Diselena)canes: Behavior of Semc σ(mcc-nee) (6≤mc≤16) Elucidated with QTAIM Dual Functional Analysis

The intrinsic dynamic and static nature m_c center-n_e electron interactions of the σ-type σ(m_cc-n_ee) were elucidated for the Se-Se interactions in dicationic oligomers of Se(CH₂CH₂CH₂)₂Se ( 1 (Se, Se)) [ n ²⁺ (Se, Se): n=1–8], especially for m_c≥6, where n ²⁺ (Se, Se: n=1–8) are abbreviated by n ²⁺ (n=1–8), respectively. QTAIM dual functional analysis (QTAIM-DFA) was applied to the interactions. Perturbed structures generated using coordinates derived from the compliance constants (C_ii) were employed for QTAIM-DFA. Each Se-*-Se in 1 ²⁺ and 2 ²⁺ has the nature of CT-TBP (trigonal bipyramidal adduct formation through CT) and Cov-w (weak covalent), respectively, which supply the starting points of the investigations. The asterisk emphasizes the existence of a bond critical point on the interaction. All Se-*-Se in 3 ²⁺ are classified by the regular closed shell (r-CS) interactions and characterized as CT-MC (molecular complex formation through CT), which are denoted as r-CS/CT-MC, except for the central interaction, of which nature is r-CS/CT-TBP. Most interactions in 4 ²⁺– 8 ²⁺ are r-CS/t-HB_wc (typical-HB with covalency) but some are pure-CS/t-HB_nc (t-HB with no covalency). The linear Se_2n²⁺ interactions in 2 ²⁺– 8 ²⁺ seem close to those without any limitations, since the nature of Se-*-Se inside and outside of (CH₂CH₂CH₂)₂ are very similar with each other. The linear Se_2n²⁺ interactions in 3 ²⁺– 8 ²⁺ are shown to be analyzed as σ(m_cc-n_ee: 6≤m_c≤16), not by the accumulated σ(3c–4e).     

Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Co^II salts in the presence of HCO₃⁻/CO₃²⁻ in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E_pa≈0.71 V (vs. Ag/AgCl) owing to the Co^III/II redox couple. (ii) A second wave is observed at E_pa≈1.10 V with a considerably larger current. In which the Co^III undergoes oxidation to form a Co^IV species. The large current is attributed to catalytic oxidation of HCO₃⁻/CO₃²⁻ to HCO₄⁻. (iii) A process with very large currents at >1.2 V owing to the formation of Co^V(CO₃)₃⁻, which oxidizes both water and HCO₃⁻/CO₃²⁻. These processes depend on [Co^II], [NaHCO₃], and pH. Chronoamperometry at 1.3 V gives a green deposit. It acts as a heterogeneous catalyst for water oxidation. DFT calculations point out that Coⁿ(CO₃)₃ⁿ⁻⁶, n=4, 5 are attainable at potentials similar to those experimentally observed.     

Reactions of the dications C7H6, C7H7, and C7H8 with methane: Predominance of doubly charged intermediates

The reactions of methane with the dications C₇H₆²⁺, C₇H₇²⁺, and C₇H₈²⁺ generated by electron ionization of toluene are studied using mass-spectrometry tools. It is shown that the reactivity is dominated by the formation of doubly charged intermediates, which can either eliminate molecular hydrogen to yield doubly charged products or undergo charge-separation reactions leading to the formation of a methyl cation and the corresponding C₇H_n+1⁺ monocation. Typical processes observed for dications, like electron transfer or proton transfer, are largely suppressed. The theoretically derived mechanism of the reaction between C₇H₆²⁺ and CH₄ indicates that the formation of the doubly charged intermediate is kinetically preferred at low internal energies of the reactants. In agreement, the experimental results show a pronounced hydrogen scrambling and dominant formation of the doubly charged products at low collision energies, whereas direct hydride transfer prevails at larger collision energies.     

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations,Al+(H2O)n,n=1–10

Hydrated aluminium cations have been investigated as a photochemical model system with up to ten water molecules by UV action spectroscopy in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Intense photodissociation was observed starting at 4.5 eV for two to eight water molecules with loss of atomic hydrogen, molecular hydrogen and water molecules. Quantum chemical calculations for n=2 reveal that solvation shifts the intense 3s–3p excitations of Al⁺ into the investigated photon energy range below 5.5 eV. During the photochemical relaxation, internal conversion from S₁ to T₂ takes place, and photochemical hydrogen formation starts on the T₂ surface, which passes through a conical intersection, changing to T₁. On this triplet surface, the electron that was excited to the Al 3p orbital is transferred to a coordinated water molecule, which dissociates into a hydroxide ion and a hydrogen atom. If the system remains in the triplet state, this hydrogen radical is lost directly. If the system returns to singlet multiplicity, the reaction may be reversed, with recombination with the hydroxide moiety and electron transfer back to aluminium, resulting in water evaporation. Alternatively, the hydrogen radical can attack the intact water molecule, forming molecular hydrogen and aluminium dihydroxide. Photodissociation is observed for up to n=8. Clusters with n=9 or 10 occur exclusively as HAlOH⁺(H₂O)_n-1 and are transparent in the investigated energy range. For n=4–8, a mixture of Al⁺(H₂O)_n and HAlOH⁺(H₂O)_n-1 is present in the experiment.     

The Silicon Carbonyls Revisited: On the Existence of a Planar Si(CO)4

Recently, some works have focused attention on the reactivity of silicon atom with closed-shell molecules. Silicon may form a few relatively stable compounds with CO, i.e. Si(CO), Si(CO)₂, Si[C₂O₂], while the existence of polycarbonyl (n>2) silicon complexes has been rejected by current literature. In this paper, the reaction of silicon with carbonyl has been reinvestigated by density functional calculations. It has been found that the tetracoordinated planar Si(CO)₄ complex is thermodynamically stable. In Si(CO), silicon carbonyl, and Si(CO)₂, silicon dicarbonyl, the CO are datively bonded to Si; Si(CO)₄, silicon tetracarbonyl, may be viewed as a resonance between the extreme configurations (CO)₂Si + 2CO and 2CO + Si(CO)₂; while Si[C₂O₂], c-silicodiketone, is similar to the compounds formed by silicon and ethylene. A detailed orbital analysis has shown that the Si bonding with two CO is consistent with the use of sp ²-hybridized orbitals on silicon, while the Si bonding with four CO is consistent with the use of sp ² d-hybridized orbitals on silicon, giving rise to a planar structure about Si.