A noble interaction: An assessment of noble gas binding ability of metal oxides (metal = Cu,Ag, Au)

An in silico study is performed on the structure and the stability of noble gas (Ng) bound MO complexes (M = Cu, Ag, Au). To understand the stability of these Ng bound complexes, dissociation energies, dissociation enthalpy, and dissociation free energy change are computed. The stability of NgMO is also compared with that of the experimentally detected NgMX (X= F, Cl, Br). It is found that MO has lower Ng binding ability than that of MX. All the dissociation processes producing Ng and MO are endothermic in nature and for the Kr‐Rn bound MO (M = Cu, Au), and Xe and Rn bound AgO cases, the corresponding dissociation processes are turned out to be endergonic in nature at standard state. The Wiberg bond indices of Ng? M bonds and Ng→M electron transfer gradually increase from Ar to Rn and for the same Ng they follow the order of NgAuO > NgCuO > NgAgO. Energy decomposition analysis shows that the Ng? M bonds in NgMO are partly covalent and partly electrostatic in nature. Electron density analysis further highlights the partial covalent character in Ng? M bonds. © 2016 Wiley Periodicals, Inc.     

Theoretical investigation on the structure and stability of some neutral noble gas compounds containing Xe-Xe bond

DFT calculations are performed to investigate the structure, stability, and nature of chemical bonding of some neutral noble gas insertion compounds containing a Xe-Xe bond; including HXeXeR, FXeXeR as well as RXeXeR (R = CN, NC, CCH, and BS). Geometry optimization of the considered molecules anticipate the existence of just four stable compounds (HXeXeCN, HXeXeNC, FXeXeCN, and FXeXeCCH); and rest of the molecules dissociate during the structural optimization. The results of NBO and AIM calculations show that a H(F)XeXeR molecule has a covalent H(F)-Xe bond in the H(F)XeXe⁺ fragment, which is bonded to R⁻ mainly through columbic interaction. Thermodynamic study indicates that all of the considered unimolecular dissociation channels for decomposition of H(F)XeXeR molecules to neutral fragments are both exothermic and exorergic; but dissociation to ionic species (H(F)XeXe⁺ and R⁻) is endothermic. Also kinetic study of the most probable dissociation reaction shows that FXeXeR molecules are metastable with respect to the global minimum F-R + 2Xe. Therefore, FXeXeCN molecule is more kinetically protected against the decomposition reaction than the other molecules and its experimental detection is more likely.     

Electron density properties and metallophilic interactions of gold halides AuX2 and Au2X (X = F–I): Ab Initio calculations

We present ab initio calculations of the electron density properties and metallophilic interactions of the gold halide series, AuX₂ and Au₂X (X = F–I) as well as their anions performed at MP2 theoretical level with extended basis sets. The gold halide's structure, stability, and interactions with alkali metal atoms were investigated. The mechanisms of metallophilic interactions were explored by natural bond orbital analyses, electron localization function, electron density deformation, atoms in molecules, and reduced density gradient analyses. © 2016 Wiley Periodicals, Inc.     

Three‐dimensional networks containing rectangular Sr4 and Ba4 units: Synthesis,structure, bonding,and potential application for Ne gas separation

New porous three‐dimensional metal‐organic frameworks are synthesized that contain infinite chains of Sr_n and Ba_n rectangles. Their structures are elucidated by means of spectroscopic techniques such as nuclear magnetic resonance and Fourier transform infrared, and the respective crystal structures are determined. The electronic structure of basic units of the crystals are computed using density functional theory at the B3LYP/6‐31G(d,p)/def2‐TZVP level, and the bonding and reactivity are analyzed using natural bond orbital analysis, the quantum theory of atoms in molecules, and conceptual density functional theory. The possibilities of noble gas (Ng) storage inside the crystal structures are explored through modeling a Ng atom inside the frozen geometry of the crystal. It was found that a neon atom can fit into a cavity in the Sr and Ba crystal structures whereas other Ngs (He, Ar, Kr) exhibit repulsive interactions with the crystal structure. Ab initio molecular dynamics simulations for up to 500 fs at 77 and 298 K suggest that the structures incorporating a neon atom are kinetically stable. © 2015 Wiley Periodicals, Inc.     

Ab initio investigations on the stabilities of AuOnq− (q = 0 to 3; n = 1 to 4) species: Superhalogen behavior of AuOn (n ≥ 2) and their interactions with an alkali metal

Theoretical density functional calculations are performed on AuO_n^q? species for q = 0–3 and n = 1–4 in various spin states. AuO_n species are found to be relatively more stable in their mono‐anionic forms and behave as superhalogens for n ≥ 2. The maximum oxidation state of Au is found to be +7 in these species, but limited to +5. This fact is explained by considering interactions of AuO_n superhalogens with K atom and which leads to the formation of more stable KAuO_n complex up to n = 3, only. Thus, the present study is expected not only to motivate the synthesis of a new class of salts but also to assign the maximum oxidation state of gold. © 2013 Wiley Periodicals, Inc.     

Quantum Study on the Hydrogen Bonding Interaction of Luteolin-（CH_3OH）_n

The optimized geometries and vibration frequencies of luteolin,methanol and luteolin-(CH3OH)n complexes have been investigated by density functional theory using B3LYP method.Four stable luteolin-CH3OH complexes,six stable luteolin-(CH3OH)2 complexes and four stable luteolin-(CH3OH)3 complexes have been obtained.The theories of atoms in molecules(AIM) and natural bond orbital(NBO) have been used to analyze the hydrogen bonds of these compounds,and their interaction energies corrected by basis set superposition error are between-8.046 and-76.124 kJ/mol.The calculation results indicate strong hydrogen bonding interactions in the luteolin-(CH3OH)n complexes.Then the nuclear magnetic resonance(NMR) and electronic absorption spectrum of luteolin have been calculated,and the results are in agreement with the experimental data.     

The highest oxidation state of Au revealed by interactions with successive cl ligands and superhalogen properties of AuCln (n = 1–6) species

This study deals with a reinvestigation on the maximum oxidation state of gold. Density functional calculations are performed on geometries and stabilities of AuCl_n species for n = 1–6 in their neutral and anionic states. The calculations clearly reveal that the maximum oxidation state of Au is limited to +5. The high adiabatic electron affinities of AuCl_n (n ≥ 2), as compared to Cl, suggest their superhalogen behavior. The interaction of AuCl_n superhalogens with an alkali metal, K is found to be similar to but stronger than that between K and Cl, leading to the formation of KAuCl_n complexes. The stabilities of these complexes explore the possibility of synthesis of new class of salts by interaction of with appropriate metal cations. © 2014 Wiley Periodicals, Inc.     

A density functional theory study on lewis acid‐catalyzed transesterification of β‐oxodithioesters

The detailed mechanisms of the Lewis acid‐catalyzed transesterification of β‐oxodithioesters at a solvent‐free condition were studied using density functional theory. Five possible reaction pathways, including one noncatalyzed (channel 1) and four Lewis acid‐catalyzed channels (SnCl₂‐catalyzed channels 2 and 3 and SnCl₂·2H₂O‐catalyzed channels 4 and 5), were investigated. Our calculated results indicate that the energy barriers of the catalyzed channels are significantly lower than that of channel 1. Channel 5, which has an energy barrier of 33.70 kcal/mol as calculated at the B3LYP/[6‐31G(d, p)+LANL2DZ] level, is the most energy‐favorable channel. Moreover, one water molecule of SnCl₂·2H₂O participated in the transesterification in channel 5. Thus, we report a novel function of the SnCl₂·2H₂O catalyst, which is quite different from the function of the conventional nonhydrated Lewis acid SnCl₂. To understand the function of these two Lewis acid catalysts better, the global reactivity indexes and natural bond orbital charge were analyzed. This work helps in understanding the function of the Lewis acid in transesterification, and it can provide valuable insight for the rational design of new Lewis acid catalysts. © 2014 Wiley Periodicals, Inc.     

Stability of Noble‐Gas‐Bound SiH3+ Clusters

The stability of noble gas (Ng)‐bound SiH₃⁺ clusters is explored by ab initio computations. Owing to a high positive charge (+1.53 e^?), the Si center of SiH₃⁺ can bind two Ng atoms. However, the Si?Ng dissociation energy for the first Ng atom is considerably larger than that for the second one. As we go down group 18, the dissociation energy gradually increases, and the largest value is observed for the case of Rn. For NgSiH₃⁺ clusters, the Ar–Rn dissociation processes are endergonic at room temperature. For He and Ne, a much lower temperature is required for it to be viable. The formation of Ng₂SiH₃⁺ clusters is also feasible, particularly for the heavier members and at low temperature. To shed light on the nature of Si?Ng bonding, natural population analysis, Wiberg bond indices computations, electron‐density analysis, and energy‐decomposition analysis were performed. Electron transfer from the Ng centers to the electropositive Si center occurs only to a small extent for the lighter Ng atoms and to a somewhat greater extent for the heavier analogues. The Si?Xe/Rn bonds can be termed covalent bonds, whereas the Si?He/Ne bonds are noncovalent. The Si?Ar/Kr bonds possess some degree of covalent character, as they are borderline cases. Contributions from polarization and charge transfer and exchange are key terms in forming Si?Ng bonds. We also studied the effect of substituting the H atoms of SiH₃⁺ by halide groups (?X) on the Ng binding ability. SiF₃⁺ showed enhanced Ng binding ability, whereas SiCl₃⁺ and SiBr₃⁺ showed a lower ability to bind Ng than SiH₃⁺. A compromise originates from the dual play of the inductive effect of the ?X groups and X→Si π backbonding (p_z–p_z interaction).     

Theoretical investigations on the superhalogen properties and interaction of PdOn (n = 1–5) species

Density functional calculations on the ground state geometries and stabilities of PdO_n species (n = 1–5) are performed in neutral as well as anionic forms. Calculations reveal that Pd can bind stably with four O atoms indicating the maximum oxidation state of Pd as high as +8. The electron affinities of PdO_n suggest that these species behave as superhalogens for n ≥ 2. The large electron affinities of PdO_n species along with stability of their anions point toward the synthesis of new class of compounds having unusual oxidizing capabilities. This possibility is explored by considering the interaction of PdO₂ superhalogen with Ca atom which forms a stable CaPdO₂ complex. In this complex, PdO₂ unit closely mimics the behavior of O atom when compared with CaO molecule. © 2013 Wiley Periodicals, Inc.     

Lanthanide metals in the boron cages: Computational prediction of M@Bn (M = Eu,Gd; n = 38, 40)

Endohedral metalloborofullerenes (EMBFs) are novel boron analogues of the famous endohedral metallofullerenes (EMFs). Many EMBFs have been proposed by theoretical calculations thus far. However, in sharp contrast to EMFs, which trap most of the lanthanides with f electrons inside the cages, the corresponding lanthanide‐based EMBFs have never been reported. In this work, the encapsulation of Eu and Gd in the B₃₈ and B₄₀ fullerenes was studied by means of density functional theory calculations. Our results revealed that Gd@B₃₈(⁹A), Eu@B₄₀(⁸B₂), and Gd@B₄₀(⁷A″) all favor the endohedral configuration, and the electronic structures can be described as Gd³⁺@ , Eu²⁺@ , and Gd³⁺@ with jailed f electron spins. The large binding energies and sizable HOMO–LUMO gaps suggest that they may be achieved experimentally. They feature σ and π double aromaticity, and their excellent stabilities were confirmed by the Born–Oppenheimer molecular dynamics simulations. Finally, the infrared and UV/vis spectra were simulated to assist experimental characterization.     

Electronic,bonding, and optical properties of 1d [CuCN]n (n = 1–10) chains, 2d [CuCN]n (n = 2–10) nanorings,and 3d [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes studied by DFT/TD‐DFT methods

The electronic, bonding, and photophysical properties of one‐dimensional [CuCN]_n (n = 1–10) chains, 2‐D [CuCN]_n (n = 2–10) nanorings, and 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes are investigated by means of a multitude of computational methodologies using density functional theory (DFT) and time‐dependent‐density‐functional theory (TD‐DFT) methods. The calculations revealed that the 2‐D [CuCN]_n (n = 2–10) nanorings are more stable than the respective 1‐D [CuCN]_n (n = 2–10) linear chains. The 2‐D [CuCN]_n (n = 2–10) nanorings are predicted to form 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes supported by weak stacking interactions, which are clearly visualized as broad regions in real space by the 3D plots of the reduced density gradient. The bonding mechanism in the 1‐D [CuCN]_n (n = 1–10) chains, 2‐D [CuCN]_n (n = 2–10) nanorings, and 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes are easily recognized by a multitude of electronic structure calculation approaches. Particular emphasis was given on the photophysical properties (absorption and emission spectra) of the [CuCN]_n chains, nanorings, and tubes which were simulated by TD‐DFT calculations. The absorption and emission bands in the simulated TD‐DFT absorption and emission spectra have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2015 Wiley Periodicals, Inc.     

Theoretical investigation of LaC3n+ (n = 0, 1, 2) clusters by density functional theory

LaC₃ⁿ⁺ (n=0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter–Lee-Yang-Parr) density functional method. The basis set is Dunning/Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C_2v symmetry, the other two are linear chains with C_∞v symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC₃⁺, doublet and quartet for LaC₃ and LaC₃²⁺, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C_2v symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 301–307, 1998     

Nature of Bonding in Bowl‐Like B36 Cluster Revisited: Concentric (6π+18π) Double Aromaticity and Reason for the Preference of a Hexagonal Hole in a Central Location

The bowl‐shaped C_6v B₃₆ cluster with a central hexagon hole is considered an ideal molecular model for low‐dimensional boron‐based nanosystems. Owing to the electron deficiency of boron, chemical bonding in the B₃₆ cluster is intriguing, complicated, and has remained elusive despite a couple of papers in the literature. Herein, a bonding analysis is given through canonical molecular orbitals (CMOs) and adaptive natural density partitioning (AdNDP), further aided by natural bond orbital (NBO) analysis and orbital composition calculations. The concerted computational data establish the idea of concentric double π aromaticity for the B₃₆ cluster, with inner 6π and outer 18π electron counting, which both conform to the (4n+2) Hückel rule. The updated bonding picture differs from existing knowledge of the system. A refined bonding model is also proposed for coronene, of which the B₃₆ cluster is an inorganic analogue. It is further shown that concentric double π aromaticity in the B₃₆ cluster is retained and spatially fixed, irrespective of the migration of the hexagonal hole; the latter process changes the system energetically. The hexagonal hole is a destabilizing factor for σ/π CMOs. The central hexagon hole affects substantially fewer CMOs, thus making the bowl‐shaped C_6v B₃₆ cluster the global minimum.     

DFT study on the intermolecular interactions between Aun (n = 2–4) and thymine

Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H₂O)_n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H₂O, nine steady luteolin–(H₂O)₂ and ten steady luteolin–(H₂O)₃, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H₂O)_n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.     

Mechanistic study on gold(I)‐catalyzed crosscoupling of diazo compounds: A DFT study

The reaction mechanisms of the gold(I)‐catalyzed cross‐coupling reaction of aryldiazoacetate R1 with vinyldiazoacetate R2 leading to N‐substituted pyrazoles have been theoretically investigated using density functional theory calculations. Two possible reaction mechanisms were examined and discussed. The preferred reaction mechanism (mechanism A) can be characterized by five steps: the formation of the gold carbenoid A2 via the attack of catalyst to R1 (step I), nucleophilic addition of another reactant R2 to generate intermediate A3 (step II), intramolecular cyclization of A3 to form intermediate A4 (step III), hydrogen migration to give intermediate A5 (step IV), and catalyst elimination affording the final product P1 (step V). Step IV is found to be the rate‐determining step with an overall free energy barrier of 28.3 kcal/mol. Our calculated results are in good agreement with the experimental observations. The present study may provide a useful guide for understanding these kinds of gold(I)‐catalyzed cross‐coupling reactions of diazo compounds.     

(Rg = He ∼ Rn,n = 1–4): In quest of the potential trapping ability of the aromatic ring

A new series of divalent boron‐rare gas cations (Rg = He ∼ Rn, n = 1–4) have been predicted theoretically at the B3LYP, MP2, and CCSD(T) levels to present the structures, stability, charge distributions, bond natures, and aromaticity. The Rg B bond energies are quite large for heavy rare gases and increase with the size of the Rg atom. Because of steric hindrance new Rg atoms introduced to the B₄ ring will weaken the Rg B bond. Thus in the Rg B bond has the largest binding energy 90–100 kcal/mol. p‐ has a slightly shorter Rg B bond length and a larger bond energy than o‐ . NBO and AIM analyses indicate that for the heavy Rg atoms Ar ∼ Rn the B Rg bonds have character of typical covalent bonds. The energy decomposition analysis shows that the σ‐donation from rare gases to the boron ring is the major contribution to the Rg B bonding. Adaptive natural density partitioning and nuclear‐independent chemical shift analyses suggest that both and have obvious aromaticity.