Accurate Computation of Cohesive Energies for Small to Medium-Sized Gold Clusters

High-level CCSD­(T)-F12-type procedures have been used to assess the performance of a variety of computationally less demanding methods for the calculation of cohesive energies for small to medium-sized gold clusters. For geometry optimization for small gold clusters, the PBE-PBE/cc-pVDZ-PP procedure gives structures that are in close agreement with the benchmark geometries. We have devised a CCSD­(T)-F12b-based composite protocol for the accurate calculation of cohesive energies for medium-sized gold clusters. Using these benchmark (nonspin–orbit vibrationless) cohesive energies, we find that fairly good agreement is achieved by the PBE-PBE-D3/cc-pVTZ-PP method. In conjunction with PBE-PBE/cc-pVDZ-PP zero-point vibrational energies and spin-obit corrections obtained with the PBE-PBE-2c/dhf-TZVP-2c method, we have calculated 0 K cohesive energies for Au₂–Au₂₀. Extrapolation of these cohesive energies to bulk yields an estimated value of 383.2 kJ mol^–1, which compares reasonably well with the experimental value of 368 kJ mol^–1

Accurate Computation of Cohesive Energies for Small to Medium-Sized Gold Clusters

High-level CCSD­(T)-F12-type procedures have been used to assess the performance of a variety of computationally less demanding methods for the calculation of cohesive energies for small to medium-sized gold clusters. For geometry optimization for small gold clusters, the PBE-PBE/cc-pVDZ-PP procedure gives structures that are in close agreement with the benchmark geometries. We have devised a CCSD­(T)-F12b-based composite protocol for the accurate calculation of cohesive energies for medium-sized gold clusters. Using these benchmark (nonspin–orbit vibrationless) cohesive energies, we find that fairly good agreement is achieved by the PBE-PBE-D3/cc-pVTZ-PP method. In conjunction with PBE-PBE/cc-pVDZ-PP zero-point vibrational energies and spin-obit corrections obtained with the PBE-PBE-2c/dhf-TZVP-2c method, we have calculated 0 K cohesive energies for Au₂–Au₂₀. Extrapolation of these cohesive energies to bulk yields an estimated value of 383.2 kJ mol^–1, which compares reasonably well with the experimental value of 368 kJ mol^–1

Computational Study on the Intramolecular Charge Separation of D‑A-π‑A Organic Sensitizers with Different Linker Groups

A series of D-A-π-A dyes based on the structure of 2-cyano-3-{6-{4-[<i>N</i>,<i>N</i>-bis­(4-hexyloxyphenyl)­amino]­phenyl}-4,4-dihexyl-4<i>H</i>-cyclopenta­[2,1-<i>b</i>:3,4-<i>b</i>′]­dithiophene-2-yl} acrylic acid (D1) were comprehensively investigated by computational methods, in order to understand the roles of CC (D2) and benzothiadiazole moiety (D3) as the linker groups in dye-sensitized solar cells (DSCs). Despite that both dyes exhibit similar energetics and bathochromic shifts in the absorption spectra, it was found that the different linker groups result in distinct solar cell performance. While DFT calculations reveal favorable energetics of these dyes for ultrafast electron injection into the conduction band of TiO₂, charge density difference analysis suggests that the CC group adversely hinders, while the benzothiadiazole group promotes the intramolecular electron transfer of the dyes upon photoinduced excitation, which leads to a great disparity of device performance. And the good agreement of theoretical calculations with the experimental findings provides interesting insights into the understanding of the influence of linker groups on cell performance, as well as rational designs of D-π-A dyes for high efficiency DSCs

Synthesis of an N‑Heterocyclic-Carbene-Stabilized Siladiimide

The reaction of the N-heterocyclic-carbene-stabilized disilicon(0) complex [IPr→SiSi←IPr] (<b>1</b>; IPr = :C­{N­(Ar)­CH}₂ and Ar = 2,6-<i>i</i>Pr₂C₆H₃) with ArN₃ afforded the N-heterocyclic-carbene-stabilized siladiimide [ArNSi­(IPr)­NAr] (<b>2</b>). X-ray crystallography and theoretical studies show that the N–Si–N skeleton in compound <b>2</b> possesses considerable double-bond character and the Si atom is stabilized by the N-heterocyclic carbene

Synthesis of an N‑Heterocyclic-Carbene-Stabilized Siladiimide

The reaction of the N-heterocyclic-carbene-stabilized disilicon(0) complex [IPr→SiSi←IPr] (<b>1</b>; IPr = :C­{N­(Ar)­CH}₂ and Ar = 2,6-<i>i</i>Pr₂C₆H₃) with ArN₃ afforded the N-heterocyclic-carbene-stabilized siladiimide [ArNSi­(IPr)­NAr] (<b>2</b>). X-ray crystallography and theoretical studies show that the N–Si–N skeleton in compound <b>2</b> possesses considerable double-bond character and the Si atom is stabilized by the N-heterocyclic carbene

Electrocatalytic Oxygen Evolution at Surface-Oxidized Multiwall Carbon Nanotubes

Large-scale storage of renewable energy in the form of hydrogen (H₂) fuel via electrolytic water splitting requires the development of water oxidation catalysts that are efficient and abundant. Carbon-based nanomaterials such as carbon nanotubes have attracted significant applications for use as substrates for anchoring metal-based nanoparticles. We show that, upon mild surface oxidation, hydrothermal annealing and electrochemical activation, multiwall carbon nanotubes (MWCNTs) themselves are effective water oxidation catalysts, which can initiate the oxygen evolution reaction (OER) at overpotentials of 0.3 V in alkaline media. Oxygen-containing functional groups such as ketonic CO generated on the outer wall of MWCNTs are found to play crucial roles in catalyzing OER by altering the electronic structures of the adjacent carbon atoms and facilitates the adsorption of OER intermediates. The well-preserved microscopic structures and highly conductive inner walls of MWCNTs enable efficient transport of the electrons generated during OER

ESI-MS Studies and Calculations on Second-Generation Grubbs and Hoveyda–Grubbs Ruthenium Olefin Metathesis Catalysts

Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS methods were used to study second-generation Grubbs catalysts <b>2</b> and <b>3</b> and first- and second-generation Hoveyda–Grubbs catalysts <b>4</b> and <b>5</b>, respectively, as well as the pyridine-tethered Ru carbene catalyst <b>6</b>. Direct ESI-MS analyses of Ru catalysts <b>2</b>–<b>6</b> showed the corresponding radical cations <b>2</b>^•+–<b>6</b>^•+ and the protonated ligand PCy₃ and H₂IMes, respectively. Alkali metal adduct ions <b>2</b>·M⁺ and <b>3</b>·M⁺ (M = Li, Na, K, Cs) and <b>4</b>·M⁺–<b>6</b>·M⁺ (M = Li, K) could be easily obtained by mixing the CH₂Cl₂ solution of catalysts <b>2</b>–<b>6</b> with the CH₃OH solution of alkali-metal chloride using an online microreactor coupled directly to the electrospray ion source of a quadrupole time-of-flight (Q-TOF) mass spectrometer and were studied by collision-induced dissociation (CID). Remarkably, the alkali metal cationized 14-electron Ru complexes <b>2a</b>·M⁺ and <b>3a</b>·M⁺ formed by dissociation of phosphine from <b>2</b> and <b>3</b>, respectively, were detected directly from solution. The ratio [<b>2a</b>·M⁺]/[<b>2</b>·M⁺] increased with decreasing Lewis acidity of M⁺ from Li⁺ to Cs⁺. Moreover, theoretical computations were performed on Ru complexes <b>2, 5</b>, and <b>6</b>, showing good agreement with experimental X-ray diffraction data and providing more structural information about the alkali metal adduct ions <b>2</b>·M⁺, <b>5</b>·M⁺, and <b>6</b>·M⁺ (M = Li, K) as well as about the 14-electron species <b>2a</b>, <b>5a</b>, and <b>6a</b> and the respective alkali metal adduct ions

Reactivity of a Base-Stabilized Germanium(I) Dimer toward Group 9 Metal(I) Chloride and Dimanganese Decacarbonyl

The reactivity of the 2-imino-5,6-methylenedioxylphenylgermanium­(I) dimer toward group 9 metal­(I) chloride and dimanganese decacarbonyl is described. [LGe:]₂ (<b>1</b>, L = 2-imino-5,6-methylenedioxylphenyl) underwent a disproportionation reaction with 1.5 equiv of group 9 metal­(I) chloride [MCl­(cod)]₂ (M = Rh, Ir) in toluene to afford a mixture of the group 9 metallogermylene-chlorometal­(I) complexes [LGeμ-{M­(cod)}₂Cl] (M = Rh (<b>2</b>), Ir (<b>4</b>)) and chlorogermylene-chlorometal­(I) complexes [L­(Cl)­GeM­(cod)­Cl] (M = Rh (<b>3</b>), Ir (<b>5</b>)), respectively. The disproportionation property of <b>1</b> is further evidenced by its reaction with 0.5 equiv of Mn₂(CO)₁₀ in refluxing toluene to form a mixture of the manganogermylene dimer [(LGe)­μ-{Mn­(CO)₄}]₂ (<b>7</b>) and free ligand [LH] (<b>8</b>). Compounds <b>2</b>–<b>5</b>, <b>7</b>, and <b>8</b> were elucidated by NMR spectroscopy, X-ray crystallography, and DFT calculations, respectively

High-Pressure Phase Transitions and Structures of Topological Insulator BiTeI

Being a giant bulk Rashba semiconductor, the ambient-pressure phase of BiTeI was predicted to transform into a topological insulator under pressure at 1.7–4.1 GPa [Nat. Commun. 2012, 3, 679]. Because the structure governs the new quantum state of matter, it is essential to establish the high-pressure phase transitions and structures of BiTeI for better understanding its topological nature. Here, we report a joint theoretical and experimental study up to 30 GPa to uncover two orthorhombic high-pressure phases of <i>Pnma</i> and <i>P</i>4/<i>nmm</i> structures named phases II and III, respectively. Phases II (stable at 8.8–18.9 GPa) and III (stable at >18.9 GPa) were first predicted by our first-principles structure prediction calculations based on the calypso method and subsequently confirmed by our high-pressure powder X-ray diffraction experiment. Phase II can be regarded as a partially ionic structure, consisting of positively charged (BiTe)⁺ ladders and negatively charged I^– ions. Phase III is a typical ionic structure characterized by interconnected cubic building blocks of Te–Bi–I stacking. Application of pressures up to 30 GPa tuned effectively the electronic properties of BiTeI from a topological insulator to a normal semiconductor and eventually a metal having a potential of superconductivity