Yi-hong Ding

Planar tetracoordinate carbon versus planar tetracoordinate boron: the case of CB4 and its cation.

In this study, we analyzed CB(4) and its cation, CB(4)(+). Using CCSD(T)/aug-cc-pVQZ//CCSD(T)/aug-cc-pVTZ quantum-chemical calculations, we found that the neutral molecule is in accord with the results of Boldyrev and Wang, having a C(s) global minimum with a planar tricoordinate carbon structure, contradicting previous studies. In contrast, CB(4)(+), which was reported by an early mass spectroscopic study, has a planar tetracoordinate carbon (ptC) atom, demonstrating that a modification of the charge can promote the stabilization of a ptC structure.

Unexpectedly strong anion–π interactions on the graphene flakes

Interactions of anions with simple aromatic compounds have received growing attention due to their relevancy in various fields. Yet, the anion–π interactions are generally very weak, for example, there is no favorable anion–π interaction for the halide anion F− on the simplest benzene surface unless the H‐atoms are substituted by the highly negatively charged F. In this article, we report a type of particularly strong anion–π interactions by investigating the adsorptions of three halide anions, that is, F−, Cl−, and Br−, on the hydrogenated‐graphene flake using the density functional theory. The anion–π interactions on the graphene flake are shown to be unexpectedly strong compared to those on simple aromatic compounds, for example, the F−‐adsorption energy is as large as 17.5 kcal/mol on a graphene flake (C84H24) and 23.5 kcal/mol in the periodic boundary condition model calculations on a graphene flake C113 (the supercell containing a F− ion and 113 carbon atoms). The unexpectedly large adsorption energies of the halide anions on the graphene flake are ascribed to the effective donor–acceptor interactions between the halide anions and the graphene flake. These findings on the presence of very strong anion–π interactions between halide ions and the graphene flake, which are disclosed for the first time, are hoped to strengthen scientific understanding of the chemical and physical characteristics of the graphene in an electrolyte solution. These favorable interactions of anions with electron‐deficient graphene flakes may be applicable to the design of a new family of neutral anion receptors and detectors.

Time-dependent density functional theory study on the absorption spectrum of Coumarin 102 and its hydrogen-bonded complexes

The effect of both solvent polarity and hydrogen bonding (HB) on the electronic transition energy of Coumarin 102 (C102) has been examined using the time‐dependent density functional theory (TDDFT). Solvent effect on both geometry and electronic transition energy is evaluated using the polarizable continuum model (PCM). A linear relation of the absorption maximum of C102 with the solvent polarity function Δf is found using the TDDFT‐PCM method for all solvents except dimethyl sulfoxide. The solvent polarity and the type B HB between the carbonyl oxygen and solvent hydrogen atom make the absorption wavelength redshift, whereas the type A HB between the amino nitrogen atom and solvent hydrogen atom has an opposite effect on the absorption wavelength. The calculated absorption wavelengths of C102 with two type B HB between the carbonyl oxygen and solvent hydrogen atom are in excellent agreement with experimental measurements. The solvatochromism of C102 is analyzed in terms of the Kamlet–Taft equation and the parameters s and a are discussed.

Catalytically healing the Stone–Wales defects in graphene by carbon adatoms

Graphene with a perfect hexagonal network structure is desirable for various reasons, e.g., mechanical, thermal conductivity and transport properties. Yet, the embedded defects generated either in synthesis or usage stages have posed obstacles for graphene applications. Therefore, removal of the structural defects in graphene has remained an important task. Stone–Wales (SW) defects are one typical topological structure in the carbon nanomaterials. Unfortunately, the SW defects in graphene have to overcome a very high restoration barrier (ca. 6 eV). Very recent theoretical work has shown the promise to reduce the restoration barrier by the adsorbed transition metal atoms down to 2.86 eV (for W) (yet this is still too high). In the present density functional theory (DFT) study, we find that through a mechanically different process, the adsorption of carbon atoms can dramatically reduce the restoration barrier to hitherto the lowest value, i.e., 20.0 kcal mol−1 (0.87 eV), which could make the SW-healing experimentally accessible. Subsequently, the C-adatom can migrate very easily on the graphene surface. As a result, one carbon adatom could principally catalyze the healing of all the SW defects in a cascade mode if no termination steps exist. During the graphene growth, the presently proposed carbon-adatom catalytic mechanism could have played a role in healing the SW defect. Moreover, we propose that in the post-treatment of graphene, adsorption of the carbon adatom could be used as an effective catalyst for the SW-healing. The catalytic role of carbon atoms on the SW defect should be included in the modeling of graphene growth.

Structures and Energetics of AlnHn2― (5 ≤ n ≤ 12) and AlnHn+2 (4 ≤ n ≤ 12): Are Alanes the Borane Analogues?

In this work, we report the first comparative study directly between Al(n)H(n)(2-) and B(n)H(n)(2-) (5 < or = n < or = 12), Al(n)H(n+2) and B(n)H(n+2) (4 < or = n < or = 12) covering diverse structural forms. It was shown that Al(n)H(n)(2-) each have a closo ground structure as B(n)H(n)(2-), nicely consistent with the Wade-Mingos rule. However, Al(n)H(n+2) adopt the closo-nido ground structures following the even-odd alternation in the number of Al atoms, showing distinct violation of the Wade-Mingos rule for the odd-numbered Al-atoms. Interestingly, the corresponding B(n)H(n+2) also have similar closo (even)-nido (odd) alternation. Therefore, our direct comparison showed that Al(n)H(n)(2-) (5 < or = n < or = 12) and Al(n)H(n+2) (4 < or = n < or = 12) can be viewed as the borane analogues, though not all Al(n)H(n+2) have the ability of being explained by Wade-Mingos rule. So, the analogy between alanes and boranes in form of X(n)H(n+2) should not be simply judged by the Wade-Mingos rule because of the significant influence of the additional two hydrogen atoms on the closo-structure.

Theoretical investigation of the divacancies in boron nitride nanotubes: Properties and surface reactivity toward various adsorbates

The recent study has shown that the point defects formed under electron irradiation in the boron nitride nanotubes (BNNTs) are primarily BN divacancies. In the present work, we explore the properties of BNNTs with divacancies and estimate their surface reactivity toward various adsorbates through density functional theory calculations. Divacancies in BNNTs can self-heal by spontaneously reconstructing stable structures that have two pentagons side by side with an octagon (585). The formation energies, which strongly depend on the divacancy orientation with respect to the tube axis, increase with increasing tube diameters. Compared to the reactivity of the perfect BNNT, those sites near the divacancies have a higher reactivity due to the formation of frustrated B-B and N-N bonds and the local strain induced by pentagonal and octagonal rings. The present results might be useful for deeply understanding the nature of defects in BNNTs and rendering BNNTs promising for many applications, especially in nanoelectronics.

Unusually Short Be-Be Distances with and without a Bond in Be2 F2 and in the Molecular Discuses Be2 B8 and Be2 B7 (.).

Quantum-chemical calculations at the CCSD(T)/cc-pVTZ level of theory show that beryllium subfluoride, Be2 F2 , has a bond dissociation energy of De =76.9 kcal mol(-1) , which sets a record for the strongest Be-Be bond. The synthesis of this molecule should thus be possible in a low-temperature matrix. The discus-shaped species Be2 B8 and Be2 B7 (-) possess the shortest Be-Be distance for a molecule in the electronic ground state, but there is no Be-Be bond. The cyclic species Be2 B8 and Be2 B7 (-) exhibit double aromaticity with 6σ and 6π electrons, which strongly bind the Be2 fragment to the boron atoms. The very short interatomic distance between the beryllium atoms is due to the Be-B σ and π bonds, which operate like spokes in a wheel pressing the beryllium atoms together. The formation of the Be-B bonds has effectively removed the electronic charge of the valence space between the beryllium atoms. Along the Be-Be axis, there are two cage critical points adjacent to a ring critical point at the midpoint, but there is no bond critical point and no bond path.

Theoretical Investigation of the Interaction between Carbon Monoxide and Carbon Nanotubes with Single-Vacancy Defects

Density functional theory calculations are used to study the healing process of a defective CNT (i.e. (8,0) CNT) by CO molecules. The healing undergoes three evolutionary steps: 1) the chemisorption of the first CO molecule, 2) the incorporation of the C atom of CO into the CNT, accompanied by the adsorption of the leaving O atom on the CNT surface, 3) the removal of the adsorbed O atom from the CNT surface by a second CO molecule to form CO(2) and the perfect CNT. Overall, adsorption of the first CO reveals a barrier of 2.99 kcal mol(-1) and is strongly exothermal by 109.11 kcal mol(-1), while adsorption of a second CO has an intrinsic barrier of 32.37 kcal mol(-1)and is exothermal by 62.34 kcal mol(-1). In light of the unique conditions of CNT synthesis, that is, high temperatures in a closed container, the healing of the defective CNT could be effective in the presence of CO molecules. Therefore, we propose that among the available CNT synthesis procedures, the good performance of chemical vapor decomposition of CO on metal nanoparticles might be ascribed to the dual role of CO, that is, CO acts both as a carbon source and a defect healer. The present results are expected to help a deeper understanding of CNT growth.

Role of Hydrocarbon Radicals CHx (x=1, 2, 3) in Graphene Growth: A Theoretical Perspective

Many outstanding properties of graphene are blocked by the existence of structural defects. Herein, we propose an important healing mechanism for the growth of graphene, which is produced via plasma-enhanced chemical vapor decomposition (PECVD), that is, the healing of graphene with single vacancies by decomposed CH(4) (hydrocarbon radical CH(x), x=1, 2, 3). The healing processes undergo three evolutionary steps: 1) the chemisorption of the hydrocarbon radicals, 2) the incorporation of the C atom of the hydrocarbon radicals into the defective graphene, accompanied by the adsorption of the leaving H atom on the graphene surface, 3) the removal of the adsorbed H atom and H(2) molecule to generate the perfect graphene. The overall healing processes are barrierless, with a huge released heat of 530.79, 290.67, and 159.04 kcal mol(-1), respectively, indicative of the easy healing of graphene with single vacancies by hydrocarbon radicals. Therefore, the good performance of the PECVD method for the generation of graphene might be ascribed to the dual role of the CH(x) (x=1, 2, 3) species, acting both as carbon source and as defect healer.

CSi2Ga2: a neutral planar tetracoordinate carbon (ptC) building block

Ever being a large curiosity, the “anti-van’t Hoff/Le Bel” realm that is associated with tetracoordinate or hypercoordinate planar centers has made rapid progress. In particular, it has been disclosed that silicon and gallium can be embedded in various planar species. However, to our best knowledge, assembly of silicon— and gallium-embedded planar units has never been reported, though such assembled species might be used as potential nanoscale devices. Here we report the first attempt on how to design assembled molecular compounds featuring silicon— and gallium-embedded planar tetracoordinate carbon (ptC) units. Taking the special silicon- and gallium-embedded ptC unit CSi2Ga2 as an example, we performed density functional calculations on a series of model compounds [DM(CSi2Ga2)]q+ as well as the saturated compounds (Cl−)q[CpM(CSi2Ga2)]q+ (D = CSi2Ga2, Cp−(C5H5−); M = Li, Na, K, Be, Mg, Ca) and the more extended sandwich-like species. For the six metals, CSi2Ga2 can only be assembled in the “hetero-decked sandwich” scheme (e.g., [CpM(CSi2Ga2)]q+) so as to avoid cluster fusion. Interestingly, among all the designed sandwich species, CSi2Ga2 generally prefers to interact with the partner deck at the corner (Ga atoms) or face (CSi2Ga2 planes) sites. Such interaction types serve as an interesting growth pattern that might be applicable to the assembly of Si- and Ga-embedded ptC unit CSi2Ga2 into highly extended sandwich-like complexes. Our results for the first time showed that the Si- and Ga-embedded ptC unit CSi2Ga can act as a new type of building block. The present results are expected to enrich planar tetracoordinate carbon chemistry and metallocenes.