Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

The Bond Order of C2 from a Strictly N‐Representable Natural Orbital Energy Functional Perspective

The bond order of the ground electronic state of the carbon dimer has been analyzed in the light of natural orbital functional theory calculations carried out with an approximate, albeit strictly N‐representable, energy functional. Three distinct solutions have been found from the Euler equations of the minimization of the energy functional with respect to the natural orbitals and their occupation numbers, which expand upon increasing values of the internuclear coordinate. In the close vicinity of the minimum energy region, two of the solutions compete around a discontinuity point. The former, corresponding to the absolute minimum energy, features two valence natural orbitals of each of the following symmetries, σ, σ*, π and π*, and has three bonding interactions and one antibonding interaction, which is very suggestive of a bond order large than two but smaller than three. The latter, features one σ–σ* linked pair of natural orbitals and three degenerate pseudo‐bonding like orbitals, paired each with one triply degenerate pseudo‐antibonding orbital, which points to a bond order larger than three. When correlation effects, other than Hartree–Fock for example, between the paired natural orbitals are accounted for, this second solution vanishes yielding a smooth continuous dissociation curve. Comparison of the vibrational energies and electron ionization energies, calculated on this curve, with their corresponding experimental marks, lend further support to a bond order for C ₂ intermediate between acetylene and ethylene.     

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.     

Manganese,Iron, Cobalt,and Nickel Oxo‐, Peroxo‐, and Superoxoclusters: A Density Functional Theory Study

The 3d‐transition‐metal dioxo‐, peroxo‐, and superoxoclusters with the general composition MO₂, M(O₂), and MOO (M=Mn, Fe, Co, and Ni) were studied by DFT by the B1LYP functional. The dioxides in their ground states represent the global minima for the M+O₂ system. Both ground‐state dioxides and the lowest‐energy peroxides are in their (d‐only) highest spin states. The ⁶A₁ state of Co(O₂) exceeds the d‐only spin‐multiplicity value (quartet), being nearly isoenergetic with the ⁴A₁ state of Co(O₂). The energy gain on transforming the peroxides to the corresponding dioxides decreases in the order Mn(O₂)>Fe(O₂)>Co(O₂)>Ni(O₂) and varies in the range 0.27–1.8 eV. The dissociation energy to M+O₂ for all studied peroxides is less than 1 eV being the lowest (0.47 eV) for Mn(O₂). The Mn and Fe peroxides need less than 0.3 eV to rupture one of the MO bonds to form the corresponding superoxide. Mn and Fe superoxides are less stable than the corresponding peroxides; the superoxide of Co is more stable than its peroxide, while Ni superoxide is unstable—its energy is above the limit of dissociation to Ni+O₂. According to the electrostatic potential maps, the oxygen atoms in the peroxides are more nucleophilic than those in the dioxides and superoxides, in which the terminal oxygen atom is more nucleophilic than the M‐bonded oxygen atom. This result differs from the expectations based on charge‐distribution analysis.     

Gold Behaves as Hydrogen in the Intermolecular Self‐Interaction of Metal Aurides MAu4 (M=Ti,Zr, and Hf)

We performed density functional calculations to examine the intermolecular self‐interaction of metal tetraauride MAu₄ (M=Ti, Zr, and Hf) clusters. We found that the metal auride clusters have strong dimeric interactions (2.8–3.1 eV) and are similar to the metal hydride analogues with respect to structure and bonding nature. Similarly to (MH₄)₂, the (μ‐Au)₃ C_s structures with three three‐center two‐electron (3c–2e) bonds were found to be the most stable. Natural orbital analysis showed that greater than 96 % of the Au 6s orbital contributes to the 3c–2e bonds, and this predominant s orbital is responsible for the similarity between metal aurides and metal hydrides (>99 % H 1s). The favorable orbital interaction between occupied Au 6s and unoccupied metal d orbitals leads to a stronger dimeric interaction for MAu₄‐MAu₄ than the interaction for MH₄‐MH₄. There is a strong relationship between the dimeric interaction energy and the chemical hardness of its monomer for (MAu₄)₂ and (MH₄)₂.     

A New Approach to the Design of Neutral 10‐C‐5 Trigonal‐Bipyramidal Carbon Compounds: A “π‐Electron Cap” Effect

DFT (B3LYP, M06‐2X) and MP2 methods are applied to the design of a wide series of the potentially 10‐C‐5 neutral compounds based on 6‐azabicyclotetradecanes: XC¹(YCH₂CH₂CH₂)₃N 1 – 3 , XC¹(YC₆H₄CH₂)₃N 4 – 6 , XC¹[Y(tBuC₆H₃)CH₂]₃N 7 – 9 and carbatranophanes 10 – 25 (X=Me, F, Cl; Y=O, NH, CH₂, SiH₂; Z=O, CH₂, (CH₂)₂, (CH₂)₃). Carbatranophanes 10 – 25 are characterized by a sterical compression of their axial 3c–4e XC¹←N fragment with respect to that in the parent molecules 4 – 6 . A magnitude of the revealed effect depends on a valence surrounding of the central carbon atom C¹, the size and the nature of the side chains (Z) that link the “π‐electron cap” with a tetradecane backbone. This circumstance allowed us to obtain 10‐C‐5 structures with the configuration of the bonds around the C¹ atom, which corresponds to practically an ideal trigonal bipyramid. In these compounds, the values of the covalence ratio χ of approximately 0.6 for the coordination C¹←N contacts with a covalent contribution (atoms in molecules (AIM) and natural bond orbital (NBO)) are record in magnitude. These values lie close to a low limit of the interval of the χ_Si←D change (0.6–0.9) being characteristic of the dative and ionic‐covalent (by nature) Si←D bond (D=N, O) in the known 10‐Si‐5 silicon compounds.     

Germa‐closo‐dodecaborate: A New Ligand in Transition‐Metal Chemistry with a Strong trans Influence

The strong nucleophilic character of germa‐closo‐dodecaborate towards late transition metal centres is described. The synthesis and characterisation of the first germa‐closo‐dodecaborate complexes are presented, and the solid state structures of the germaborate transition metal complexes were determined by X‐ray crystal structure analyses. The strong trans influence of the new germaborate ligand was determined by IR spectroscopy and NMR coupling constants.     

Mechanism of the Transition‐Metal‐Catalyzed Hydroarylation of Bromo‐Alkynes Revisited: Hydrogen versus Bromine Migration

A comprehensive mechanistic study of the InCl₃‐, AuCl‐, and PtCl₂‐catalyzed cycloisomerization of the 2‐(haloethynyl)biphenyl derivatives of Fürstner et al. was carried out by DFT/M06 calculations to uncover the catalyst‐dependent selectivity of the reactions. The results revealed that the 6‐endo‐dig cyclization is the most favorable pathway in both InCl₃‐ and AuCl‐catalyzed reactions. When AuCl is used, the 9‐bromophenanthrene product could be formed by consecutive 1,2‐H/1,2‐Br migrations from the Wheland‐type intermediate of the 6‐endo‐dig cyclization. However, in the InCl₃‐catalyzed reactions, the chloride‐assisted intermolecular H‐migrations between two Wheland‐type intermediates are more favorable. These Cl‐assisted H‐migrations would eventually lead to 10‐bromophenanthrene through proto‐demetalation of the aryl indium intermediate with HCl. The cause of the poor selectivity of the PtCl₂ catalyst in the experiments by the Fürstner group was predicted. It was found that both the PtCl₂‐catalyzed alkyne–vinylidene rearrangement and the 5‐exo‐dig cyclization pathways have very close activation energies. Further calculations found the former pathway would lead eventually to both 9‐ and 10‐bromophenanthrene products, as a result of the Cl‐assisted H‐migrations after the cyclization of the Pt–vinylidene intermediate. Alternatively, the intermediate from the 5‐exo‐dig cyclization would be transformed into a relatively stable Pt–carbene intermediate irreversibly, which could give rise to the 9‐alkylidene fluorene product through a 1,2‐H shift with a 28.1 kcal mol^?1 activation barrier. These findings shed new light on the complex product mixtures of the PtCl₂‐catalyzed reaction.     

HNgBeF3 (Ng = Ar‐Rn): Superhalogen‐supported noble gas insertion compounds

Ab initio and density functional theory‐based calculations are performed to study the structure, stability, and nature of bonding of superhalogen‐supported noble gas (Ng) compounds of the type HNgY where (Ng = Ar‐Rn; Y = BeF₃). Here, BeF₃ acts as the superhalogen. Calculations show that the HNgBeF₃ spontaneously dissociates into product following the dissociation channels: HNgBeF₃ → HBeF₃ + Ng and HNgBeF₃ → Ng + HF + BeF₂. The transition states are optimized and the energy barriers are computed to show the metastable behavior of HNgBeF₃. HNgBeF₃ molecules are kinetically stable with respect to the first dissociation process having energy barriers of 1.0, 5.0, 10.6, and 13.9 kcal/mol for Ar, Kr, Xe, and Rn analogues, respectively, at CCSD(T)/Aug‐cc‐pVTZ level. These calculations suggest that the HXeBeF₃ and HRnBeF₃ can be shown to be stable up to ∼100 K temperature with a half‐life of ∼10² seconds. The nature of H Ng and two different types of Ng F bonds in HNgBeF₃ molecules is explored through the natural bond orbital and electron density analyses. The large Wiberg bond index (WBI) values for the H Ng bond indicate the formation of almost a single bond in between H‐atoms and Ng‐atoms, whereas small WBI values for the two Ng F bonds indicate a noncovalent interaction in between them. The electron density analysis further supports the covalency of the H Ng bond and noncovalent interaction in the two Ng F bonds in HNgBeF₃.     

Structural Changes in 2‐Diarylthiophene‐Substituted Starburst Compounds upon Charging: A Theoretical and Spectroelectrochemical Study

The role of charging in structural changes of 2‐diarylaminothiophene‐substituted starburst compounds is clarified by combining theoretical and spectroelectrochemical studies. A systematic and comparative theoretical calculation based on density functional theory and semiempirical Austin Model 1 (AM1) calculations is performed on the neutral and charged states of four model tris(5‐diarylamino‐5‐thienyl)‐terminated starburst compounds with a central triphenylamine and 1,3,5‐triphenylbenzene moiety. Our results indicate that the charging of molecules leads to structural changes by quinoid‐type components mostly on the dendrimers terminated by phenothiazinyl fragments. Based on the optimal geometries, the spectroscopic properties were calculated using the semiempirical Zerner’s intermediate neglect overlap method. The presented theoretical results and the spin electron distributions of charged states and their spectra are supported by the spectroelectrochemical observations caused by the different electron localization within the studied molecules after charging. The satisfactory agreement between theoretical electronic transitions and experimental values indicates that a rational design of tunable molecular layers in organic devices based on the starburst compounds described is possible.     

Differences and Commonalities in the Gas‐Phase Reactions of Closed‐Shell Metal Dioxide Clusters [MO2]+ (M=V,Nb, and Ta) with Methane

High‐level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric studies, permit the mechanism by which closed‐shell, “naked” [TaO₂]⁺ brings about C?H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO₂]⁺ (M=V, Nb) are unreactive under ambient conditions.     

Density Functional Theory Calculations of 95Mo NMR Parameters in Solid‐State Compounds

The application of periodic density functional theory‐based methods to the calculation of ⁹⁵Mo electric field gradient (EFG) and chemical shift (CS) tensors in solid‐state molybdenum compounds is presented. Calculations of EFG tensors are performed using the projector augmented‐wave (PAW) method. Comparison of the results with those obtained using the augmented plane wave + local orbitals (APW+lo) method and with available experimental values shows the reliability of the approach for ⁹⁵Mo EFG tensor calculation. CS tensors are calculated using the recently developed gauge‐including projector augmented‐wave (GIPAW) method. This work is the first application of the GIPAW method to a 4d transition‐metal nucleus. The effects of ultra‐soft pseudo‐potential parameters, exchange‐correlation functionals and structural parameters are precisely examined. Comparison with experimental results allows the validation of this computational formalism.     

Turn‐On Colorimetric Platform for Dual Activity Detection of Acid and Alkaline Phosphatase in Human Whole Blood

The activity detection of acid phosphatase (ACP) and alkaline phosphatase (ALP) is of great importance to the diagnosis and prognosis of related diseases. In this work, we report for the first time a turn‐on colorimetric platform for the activity detection of ACP and ALP, by exploiting Cu(BCDS)₂^2? (BCDS=bathocuproinedisulfonate) as the probe. The presence of ACP or ALP dephosphorylates the substrate ascorbic acid 2‐phosphate to produce ascorbic acid, which then reduces Cu(BCDS)₂^2? into Cu(BCDS)₂^3?, leading to a turn‐on spectral absorption at 484 nm and a dramatic color change of the solution from colorless to orange‐red. The underlying metal‐to‐ligand charge‐transfer mechanism has been demonstrated by quantum mechanical computations. This platform allows a rapid, sensitive readout of ACP and ALP activities within the dynamic range from 0 to 220 mU ml^?1. In addition, it is highly immune to false‐positive results and also highly selective. More importantly, it is applicable in the presence of human serum and even whole blood samples. These results demonstrate that our platform holds great potential in clinical practices and in the point‐of‐care analysis.     

Structural and Magnetic Properties of 3d Transition‐Metal‐Atom Adsorption on Perfect and Defective Graphene: A Density Functional Theory Study

We systematically investigate the interactions and magnetic properties of a series of 3d transition‐metal (TM; Sc–Ni) atoms adsorbed on perfect graphene (G₆), and on defective graphene with a single pentagon (G₅), a single heptagon (G₇), or a pentagon–heptagon pair (G₅₇) by means of spin‐polarized density functional calculations. The TM atoms tend to adsorb at hollow sites of the perfect and defective graphene, except for G₆Cr, G₅Cr, and G₅Ni. The binding energies of TMs on defective graphene are remarkably enhanced and show a V‐shape, with G_NCr and G_NMn having the lowest binding energies. Furthermore, complicated element‐ and defect‐dependent magnetic behavior is observed in G_NTM. Particularly, the magnetic moments of G_NTM linearly increase by about 1 μ_B and follow a hierarchy of G₇TM<G₅₇TM<G₅TM as the TM varies from Sc to Mn, and the magnetic moments begin to decrease afterward; by choosing different types of defects, the magnetic moments can be tuned over a broad range, for example, from 3 to 6 μ_B for G_NCr. The intriguing element‐ and defect‐dependent magnetic behavior is further understood from electron‐ and back‐donation mechanisms.     

A Germacalicene: Synthesis,Structure, and Reactivity

The synthesis of the germacalicene 7 from the reaction of the dipotassium germole dianion K₂[ 6 ] with 1,2-bis-diisopropylamino-3-chlorocyclopropenyl perchlorate is reported. Based on the crystal structure analysis and the results of DFT calculations, the germacalicene 7 can be viewed as a cyclopropenium germacyclopentadienide ylide that is isoelectronic to α-cationic phosphanes. First reactivity studies revealed its nucleophilic character and resulted in the isolation of the air- and moisture-stable carbonyl iron complex 15 and the cationic silver complex 20 . One-electron oxidation of the germacalicene 7 was achieved by its reaction with [Ph₃C][B(C₆F₅)₄] and the bis-cationic Ge−Ge-bonded dimer 22 was isolated.