Density functional study of platinum polyyne monomer,oligomer, and polymer: Ground state geometrical and electronic structures

Geometries of monomers and oligomers of a platinum polyyne and its free ligands were optimized using density functional theory with B3LYP hybrid functional. The LANL2DZ basis set was used for Pt and the 6‐31G* for other atoms in geometry optimizations. The electronic structures of these compounds were analyzed using Stuttgart/Dresden ECPs (SDD) basis set for metal atoms and 6‐311G* for others. The polymerization has very little effect on the bond lengths and by introducing the metal, the acetylide bond length increases slightly. The strong overlap between metal sp_x orbitals and σp_x orbitals of acetylides results in localized σ bonding. The hybridization between the ligand pπ orbitals and the platinum dπ orbital resulted in the π‐conjugation enhancement. This conjugation enhancement causes some effects such as the highest‐occupied molecular orbital–lowest‐unoccupied molecular orbital gap reduction and charge transfer characteristic of low‐energy vertical transitions. © 2013 Wiley Periodicals, Inc.     

Directly probing the hybrid bonding of styrene on Cu111

The interfacial electronic structure of chemisorbed styrene on Cu(111) was successfully investigated with two-photon photoemission spectroscopy. We observed unoccupied states 3.5 eV above the Fermi level and occupied states 2.0 eV below the Fermi level. Polarization results reveal that the occupied and unoccupied states arise from bonding and antibonding orbitals formed by hybridization of copper (surface state and d-band orbitals) and styrene (pi1* and pi2* orbitals).     

三配位[CuCl_3]~-的电子结构、化学键和配位化学性质

用INDO法从正则分子轨道和定域分子轨道讨论了[CuCl_3]~-的电子结构和化学键,铜的4p轨道对成键贡献最大,3d轨道不参与成键。根据[CuCl_3]~-的HOMO和LUMO的原子轨道成份,讨论了它的配位化学性质。     

Ligand-derived oxidase activity. Catalytic aerial oxidation of alcohols (including methanol) by Cu(II)-diradical complexes

Seven new bis(o-iminosemiquinonato)copper(II) complexes, 1- 5, 1a, 1b, derived from differently substituted N-phenyl-2-aminophenol-based ligands, are described. Their crystal structures were determined by X-ray diffraction, and their electronic structures were established by various physical methods including electron paramagnetic resonance and variable-temperature (2-290 K) susceptibility measurements. Like complex 6, which was reported recently by us, all complexes exhibit an S t = (1)/ 2 ground state, based on the "isolated" copper(II)-spin character resulting from the dominating antiferromagnetic spin coupling between the two radicals; the ground-state electronic configuration can thus be designated as (increasing, increasing, decreasing)[R-Cu-R]. In addition, broken spin symmetry density functional solutions have been obtained. From the set of unrestricted canonical Kohn-Sham orbitals, the magnetic orbitals have been identified. The identification procedure is based on the nonvanishing overlap integrals between the space parts of orbitals occupied by electrons of opposite spin. The theoretically determined magnetic orbitals support the spin configurations suggested by the experiments. Electrochemical measurements (cyclic voltammetry and square-wave voltammetry) indicate ligand-centered redox processes. Complex 1 is found to be the best catalyst among the Cu(II) complexes for oxidation of primary alcohols with aerial oxygen as the sole oxidant to afford aldehydes under mild conditions. Thus, the function of the copper-containing enzyme Galactose Oxidase has been mimicked. Kinetic measurements in conjunction with electron paramagnetic resonance and electronic spectral studies have been used to decipher the catalytic oxidation process. A ligand-derived redox activity has been proposed as a mechanism for the aerial oxidation of primary alcohols.     

An X-ray absorption spectroscopy study of the electronic structure of copper phthalocyanine and its fluorosubstituted analog

An X-ray absorption spectroscopy study of the electronic structure of unsubstituted and hexadecafluoro-substituted copper phthalocyanines is performed. L absorption spectra of the copper atom and K absorption spectra of carbon, nitrogen, and fluorine atoms of unsubstituted and hexadecafluorosubstituted copper phthalocyanine are examined. A comparison of the absorption spectra in one binding energy scale enabled the estimation of contributions of AOs of all atoms of the considered compounds to lower unoccupied molecular orbitals and to determine the sequence of levels, their energies, and the occurrence of the interaction between certain atoms.     

Transition‐Metal–Boron Intermetallics with Strong Interatomic d–sp Orbital Hybridization for High‐Performance Electrocatalysis

A theoretical and experimental study gives insights into the nature of the metal–boron electronic interaction in boron‐bearing intermetallics and its effects on surface hydrogen adsorption and hydrogen‐evolving catalytic activity. Strong hybridization between the d orbitals of transition metal (T_M) and the sp orbitals of boron exists in a family of fifteen T_M–boron intermatallics (T_M:B=1:1), and hydrogen atoms adsorb more weakly to the metal‐terminated intermetallic surfaces than to the corresponding pure metal surfaces. This modulation of electronic structure makes several intermetallics (e.g., PdB, RuB, ReB) prospective, efficient hydrogen‐evolving materials with catalytic activity close to Pt. A general reaction pathway towards the synthesis of such T_MB intermetallics is provided; a class of seven phase‐pure T_MB intermetallics, containing V, Nb, Ta, Cr, Mo, W, and Ru, are thus synthesized. RuB is a high‐performing, non‐platinum electrocatalyst for the hydrogen evolution reaction.     

Synthesis,Characterization, and Properties of [4]Cyclo‐2,7‐pyrenylene: Effects of Cyclic Structure on the Electronic Properties of Pyrene Oligomers

A cyclic tetramer of pyrene, [4]cyclo‐2,7‐pyrenylene ([4]CPY), was synthesized from pyrene in six steps and 18 % overall yield by the platinum‐mediated assembly of pyrene units and subsequent reductive elimination of platinum. The structures of the two key intermediates were unambiguously determined by X‐ray crystallographic analysis. DFT calculations showed that the topology of the frontier orbitals in [4]CPY was essentially the same as those in [8]cycloparaphenylene ([8]CPP), and that all the pyrene units were fully conjugated. The electrochemical analyses proved the electronic properties of [4]CPY to be similar to those of [8]CPP. The results are in sharp contrast to those obtained for the corresponding linear oligomers of pyrene in which each pyrene unit was electronically isolated. The results clearly show a novel effect of the cyclic structure on cyclic π‐conjugated molecules.     

Synthesis,Characterization, and Properties of [4]Cyclo‐2,7‐pyrenylene: Effects of Cyclic Structure on the Electronic Properties of Pyrene Oligomers

A cyclic tetramer of pyrene, [4]cyclo‐2,7‐pyrenylene ([4]CPY), was synthesized from pyrene in six steps and 18 % overall yield by the platinum‐mediated assembly of pyrene units and subsequent reductive elimination of platinum. The structures of the two key intermediates were unambiguously determined by X‐ray crystallographic analysis. DFT calculations showed that the topology of the frontier orbitals in [4]CPY was essentially the same as those in [8]cycloparaphenylene ([8]CPP), and that all the pyrene units were fully conjugated. The electrochemical analyses proved the electronic properties of [4]CPY to be similar to those of [8]CPP. The results are in sharp contrast to those obtained for the corresponding linear oligomers of pyrene in which each pyrene unit was electronically isolated. The results clearly show a novel effect of the cyclic structure on cyclic π‐conjugated molecules.     

Ligand to ligand charge transfer in (hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I)

Emission and UV-vis absorption spectra of (hydrotris(pyrazolyl)borato)(triphenylarsine)copper(I), (CuTpAsPh3), (hydrotris(pyrazolyl)borato)(triethylamine)copper(I), (CuTpNEt3), and (hydrotris(pyrazolyl)borato)(triphenylphosphine)copper(I), (CuTpPPh3), are reported. The spectra of the arsine complex contain low-energy bands (with a band maximum at 16,500 cm(-1) in emission and a weak shoulder centered at about 25,000 cm(-1) in absorption) that are not present in the corresponding spectra of the amine or phosphine complexes. The lowest energy electronic transition is assigned to ligand to ligand charge transfer (LLCT) with some contribution from the metal. This assignment is consistent with PM3(tm) molecular orbital calculations that show the HOMO to consist primarily of pi orbitals on the Tp ligand (with some metal orbital character) and the LUMO to be primarily antibonding orbitals on the AsPh3 ligand (also with some metal orbital character). The absorption shoulder shows a strong negative solvatochromism, indicative of a reversal or rotation of electric dipole upon excitation, and consistent with a LLCT. The trends in the energies of the electronic transitions and the role of the metal on the LLCT are discussed.     

Delocalization in platinum-alkynyl systems: a metal-bridged organic mixed-valence compound

A complex featuring two triarylamine redox centers bridged by Pt, trans-bis(triethylphosphine)-bis{4-[bis(4-methoxyphenyl)amino]phenylethynyl} platinum(II), has been synthesized as a model system for pi-conjugated Pt-containing polymers. Analysis of the intervalence charge-transfer band displayed by its mixed-valence monocation affords a quantitative assessment of electronic delocalization through the Pt bridge; this is found to be only slightly smaller than that determined for a benzene-bridged analogue. These results are supported by density functional theory calculations, which show that the active orbitals involved in the electron-transfer process in both cases have similar delocalization through the bridging unit.     

Adsorption of anions on ultra-thin metal deposits on single-crystal electrodes: II: Voltammetric and radiochemical study of bisulfate adsorption on Pt(111) and Pt(poly) electrodes containing copper adatoms

The formation of ultra-thin metal deposits of copper on Pt(111) and polycrystalline platinum electrodes, as well as the adsorption of bisulfate on the copper-covered platinum surfaces, were studied by cyclic voltammetry and radioactive labeling. The highest charge obtained by voltammetry in the underpotential stripping range nearly corresponds to a close-packed monolayer of copper. The radioactive labeling data indicate that there are inactive and active copper adlayers toward bisulfate adsorption. The transition from inactive to active behavior is interpreted in terms of an increase in surface—bisulfate interactions at the expense of surface—perchlorate interactions. Based on recent X-ray absorption near-edge spectroscopy (XANES) analysis of copper deposition onto platinum, the site for bisulfate adsorption is most probably a Cu⁺ surface species. Combining this spectroscopic information with coulometry shows that an additional electron is confined to surface platinum atom(s) covered by the copper species. The copper film attains bulk copper properties when approximately 2.5 monolayers of copper are deposited.     

Substoichiometric isotope dilution analysis of copper traces in zinc by adsorptive sampling

The spontaneous deposition of Cu²⁺ from aqueous solutions on a hydrogen-saturated platinum surface as a possibility for the substoichiometric sampling of copper is shown. A sensitive isotope dilution method has been developed for the determination of traces of copper in high purity zinc making use of the spontaneous deposition of microquantities of Cu²⁺ from aqueous solutions of zinc salts on a cathodically polarized platinum surface. If the same platinum surface is used in each run, the saturation values of the deposited copper are practically independent of the concentrations and contents of copper and zinc in the solution. The copper traces were labelled with the product of the⁶⁴Zn(n,p)⁶⁴Cu nuclear reaction. A copper content of 0.18±0.03 ppm in zinc was determined by this method.     

A theoretical study of the electronic effect of the ligand bite angle on the hydrosilylation reaction of ketones by Cu(I) diphosphine complexes

Diphosphine ligands are commonly used for the catalytic hydrosilylation of ketones using Cu(I) complexes. The electronic effect of the P-Cu-P bite angle has been investigated by a theoretical DFT study. An increase of the P-Cu-P bite angle induces a stronger phosphorus lone pair/Cu-H σ∗ orbital interaction due to a better overlap between these orbitals. This increase in overlap affects structural and electronic properties of the copper hydride catalyst. Increasing the bite angle leads to a decrease of the Cu-P distances and an increases of the Cu-H distances. From an electronic point of view, the effect of an increasing bite angle leads to a weakening of the σ Cu-H orbital, and an increase of the hydride population. The increased polarization of the hydride leads to an easier electron transfer from the σ Cu-H bond to the carbon of the ketone.     

Magnetic studies of a syn-anti triatomic carboxylate-bridging chainlike copper(II) complex exhibiting ferromagnetic exchange

The magnetic properties of triatomic syn-anti carboxylate bridging copper(II) complex, {[Cu(2,2'-bipydine)(maleate)].2H2O}infinity (complex 1), were investigated experimentally and theoretically, suggesting weak ferromagnetic intrachain interaction. The magnetic data were analyzed and interpreted in terms of Heisenberg chain model corrected by a mean molecular field. Fitting parameters obtained for J, g, and zJ' are 3.14 cm(-1), 2.08, and -0.13, respectively. Density functional theory with generalized gradient approximation was applied to calculate the electronic structure and spin distribution of the present complex. The structural and electronic factors controlling the magnetic interactions were also determined. Ferromagnetic intrachain interactions through triatomic syn-anti carboxylate bridge result from nonplanarity of the bridging network, the exchange pathway involving both the sigma and pi orbitals of the carboxylate bridge and the spin delocalization of each magnetic orbital on the atoms of the carboxylate bridge from the copper(II) centers.     

High Compression‐Induced Conductivity in a Layered Cu–Br Perovskite

We show that the onset pressure for appreciable conductivity in layered copper‐halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu–Cl perovskites require pressures >50 GPa to show a conductivity of 10^?4 S cm^?1, whereas here a Cu–Br congener, (EA)₂CuBr₄ (EA=ethylammonium), exhibits conductivity as high as 2×10^?3 S cm^?1 at only 2.6 GPa, and 0.17 S cm^?1 at 59 GPa. Substitution of higher‐energy Br 4p for Cl 3p orbitals lowers the charge‐transfer band gap of the perovskite by 0.9 eV. This 1.7 eV band gap decreases to 0.3 eV at 65 GPa. High‐pressure X‐ray diffraction, optical absorption, and transport measurements, and density functional theory calculations allow us to track compression‐induced structural and electronic changes. The notable enhancement of the Br perovskite's electronic response to pressure may be attributed to more diffuse Br valence orbitals relative to Cl orbitals. This work brings the compression‐induced conductivity of Cu‐halide perovskites to more technologically accessible pressures.     

Photoelectron spectroscopic studies of the adsorption of CO and CO2 on nickel,platinum and copper

The adsorption of CO and CO₂ on platinum, nickel and copper was studied by X-ray and UV photoelectron spectroscopy. The results indicate that CO₂ is physisorbed on platinum and copper and that the bonding of CO on all three metals involves the metal d-electrons and particularly the 5σ level of CO. It is suggested that the energy required to promote a copper d-electron to an unfilled level above the Fermi energy is responsible for the small heat of adsorption of CO on copper.     

The effect of phenyl group on the electronic and phosphorescent properties of cyclometalated analogues of platinum(II) terpyridine complexes: a theoretical study

In this work, we theoretically investigate the effect of phenyl group on the electronic and phosphorescent properties of cyclometalated platinum(II) complexes, thereby designing an efficient blue emitting material. Three platinum(II) complexes Pt(N^N^N)Cl (N^N^N = terpyridine), Pt(N^C^N)Cl (N^C^N = 1,3-di(2-pyridyl)-benzene) and Pt(N^N^C)Cl (N^N^C = 6-phenyl-2,2′-bipyridines) are chosen as the models. Their electronic and phosphorescent properties are investigated utilizing quantum theoretical calculations. The results reveal that the phenyl group significantly affects the molecular and electronic structures, charge distribution and phosphorescent properties. The coordination bond length trans to phenyl group is the longest among the same type of bonds owing to the trans influence of phenyl group. Moreover, the phenyl group largely restricts the geometry relaxation of cyclometalated ligand. The strong σ-donor ability of Pt–C bond makes more electrons center at Pt atom and the fragments trans to phenyl group. In comparison with Pt(N^N^N)Cl and Pt(N^N^C)Cl, the complex Pt(N^C^N)Cl has the smallest excited-state geometry relaxation and the biggest emission energy and spatial overlap between the transition orbitals in the emission process. As a result, Pt(N^C^N)Cl has the largest emission efficiency, which well agrees with the experimental observation. Based on these calculation results, a potentially efficient blue-emitting material is designed via replacing pyridine groups in Pt(N^C^N)Cl by 3-methylimidazolin-2-ylidene.     

草酰胺桥联双核铜配合物结构单元的从头算

运用Gaussian 94W量子化学程序包 ,采用LanL2DZ基组 ,对草酰胺桥联双核铜配 (聚 )合物结构单元Cu2 (oxen) (OH) 2 [H2 oxen =N ,N' 二 ( 2 胺乙基 )草酰胺 ](包括顺、反构型及其单、三重态电子组态 )进行从头算研究 ,探讨该配合物结构单元的稳定性 ,并从电荷布居及分子轨道组成等电子结构特征分析这种配合物反式三重态比较稳定的原因 .计算结果与实验规律相符合 .     

The symmetry-broken formalism applied to the electronic structure of an iminosemiquinone copper(II) catalyst: a key to the qualitative understanding of its reactivity

A concise outline of the known derivation of the singlet-triplet energy-gap equations within the symmetry-broken wavefunction framework is given. They allow a computation of the singlet-triplet energy gap for molecules that exhibit a weak antiferromagnetic coupling of electrons. The accuracy of the equations is assessed by computation of the singlet-triplet gaps in model Na2 molecules. Various antiferromagnetic coupling strengths are simulated by the use of different Na-Na bond lengths in the computations. The singlet-triplet energy gaps obtained with the different equations are compared with the gaps computed with the more accurate coupled-cluster methods. Subsequently, the equations are applied to an iminosemiquinone copper(II) complex found previously to have remarkable catalytic properties. The application is performed by employing wave-function equations but with quantities computed within the density functional framework. The electronic ground state of this complex is computed to be a singlet state, which is also the experimental finding. Moreover, the experimental geometry and the singlet-triplet gap are reasonably reproduced by the computation. A straightforward method to determine the magnetic orbitals is suggested and applied. We illustrate that the form of the magnetic orbitals indicates in a qualitative manner that hydrogen-atom abstraction should be a major reaction pathway of the iminosemiquinone copper(II) complex. Hydrogen-atom abstraction has been suggested previously to be the rate-determining step in a catalytic process initiated by the iminosemiquinone copper(II) complex. The results support the notion that the form of the magnetic orbitals might be a qualitative indicator for the reactivity of molecules that exhibit weak antiferromagnetic coupling.