Nonbonding Electrons Research Articles

Synthesis and characterization of core–shell gold nanoparticles with poly(vinyl pyrrolidone) from a new precursor salt

In this article, we report a facile one-step chemical synthesis of gold (Au) nanoparticles (GNPs) from a new precursor salt i.e., gold hydroxide in the presence of poly(vinyl pyrrolidone) (PVP) polymer. The non-aqueous dispersion of GNPs was comprehensively characterized by UV–Visible, FTIR, zeta potential, and transmission electron microscope (TEM). A strong surface plasmon resonance band at 529 nm in the UV–Visible spectrum confirms the formation of GNPs in the Au colloid. The FTIR spectroscopic results showed that PVP molecules get chemisorbed onto the surface of GNP via O-atom of carbonyl group. A negative zeta potential of (−)16 mV reveals accumulation of nonbonding electrons of O-atom of carbonyl group of PVP molecules on the nanosurface of GNP. TEM images demonstrate a core–shell nanostructure with an Au-crystalline core covered by a thin amorphous PVP-shell. PVP-capped GNPs could be a potential candidate for bio-sensing, catalysis, and other applications.

The role of surface defects in multi-exciton generation of lead selenide and silicon semiconductor quantum dots

Multi-exciton generation (MEG), the creation of more than one electron-hole pair per photon absorbed, occurs for excitation energies greater than twice the bandgap (E(g)). Imperfections on the surface of quantum dots, in the form of atomic vacancies or incomplete surface passivation, lead to less than ideal efficiencies for MEG in semiconductor quantum dots. The energetic onset for MEG is computed with and without surface defects for nanocrystals, Pb(4)Se(4), Si(7), and Si(7)H(2). Modeling the correlated motion of two electrons across the bandgap requires a theoretical approach that incorporates many-body effects, such as post-Hartree-Fock quantum chemical methods. We use symmetry-adapted cluster with configuration interaction to study the excited states of nanocrystals and to determine the energetic threshold of MEG. Under laboratory conditions, lead selenide nanocrystals produce multi-excitons at excitation energies of 3 E(g), which is attributed to the large dielectric constant, small Coulomb interaction, and surface defects. In the absence of surface defects the MEG threshold is computed to be 2.6 E(g). For lead selenide nanocrystals with non-bonding selenium valence electrons, Pb(3)Se(4), the MEG threshold increases to 2.9 E(g). Experimental evidence of MEG in passivated silicon quantum dots places the onset of MEG at 2.4 E(g). Our calculations show that the lowest multi-exciton state has an excitation energy of 2.5 E(g), and surface passivation enhances the optical activity of MEG. However, incomplete surface passivation resulting in a neutral radical on the surface drives the MEG threshold to 4.4 E(g). Investigating the mechanism of MEG at the atomistic level provides explanations for experimental discrepancies and suggests ideal materials for photovoltaic conversion.

Effects of Electron Beam Irradiation on Adhesive Force of Laminated Sheet of High Strength Polytetrafluoroethylene (PTFE) and Bio-Adaptable Polydimethylsiloxane (PDMS)

The effects of homogeneous low voltage electron beam irradiation (HLEBI) on the adhesive force of peeling ( o Fp) and peeling resistance energy ( o Ep) at each peeling probability (Pp) of laminated sheets of bio-adaptable polydimethylsiloxane (PDMS) with transparency and high strength polytetrafluoroethylene (PTFE) with sterilization were investigated without glue. Although both o Fp and o Ep of peeling at low Pp of 0.06 were 0.2N·m ¹1 and 4.0 © 10 ¹2 J·m ¹1 before treatment, HLEBI enhanced the o Fp and o Ep up to the largest values of 11N·m ¹1 and 2.2J·m ¹1 of the laminated sheets irradiated at 0.13MGy, respectively. They were more than 55 times larger that those before treatment. On the other hand, additional HLEBI reduced the o Fp and o Ep of laminated sheets irradiated at more than 0.22 to 0.86MGy, although they were apparently larger than those before treatment. In order to investigate the influence of EB irradiation on o Fp and o Ep, electron spin resonance (ESR) signals related to dangling bonds were observed. When HLEBI cut the chemical bonds and generated dangling bonds with nonbonding electrons in PTFE and PDMS, the electrons induced the chemical bonding and intermolecular attractive force. HLEBI induced strong adhesive force of laminated sheets was explained by the discussion. Therefore, it was concluded that HLEBI was a useful tool for quick lamination of bio-adaptable PDMS and high strength PTFE. [doi:10.2320/matertrans.M2012124]

J044116 医療用異種高分子材料とPTFEの接着

The effects of hot-press after homogeneous low voltage electron beam irradiation (HLEB1) on the adhesive force (^oF_p) of peeling resistance of laminated sheets of polytetrafluoroethylene (PTFE) and different polymers of polypropylene (PP) and polyethylene (PE) were investigated without glue. The adhesion with large ^oF_p between PTFE and different polymers of PE and PP treated by HLEBI was observed, although ^oF_p of the sample without HLEBI was negligible small within the experimental error. In order to discuss the influence of DST on °FP, electron spin resonance (ESR) signals related to dangling bonds were observed. When HLEBI cut the chemical bonds and generated dangling bonds with nonbonding electrons at terminated atoms in monomers of PTFE, PP and PE, the nonbonding electrons induced not only the intermolecular attractive force but also chemical bonding. Therefore, the hot- pressing after HLEBI was a useful tool for quick lamination of PTFE and different polymers of PP and PE without glue.

The electronic structure and chemical bonding in gold dihydride: AuH2− and AuH2

We report an investigation of the electronic structure and chemical bonding of AuH2− using photoelectron spectroscopy and ab initio calculations. We obtained vibrationally resolved photoelectron spectra of AuH2− at several photon energies. Six electronic states of AuH2 were observed and assigned according to the theoretical calculations. The ground state of AuH2− is known to be linear, while that of neutral AuH2 is bent with a ∠H–Au–H equilibrium bond angle of 129°. This large geometry change results in a very broad bending vibrational progression in the photoelectron spectra for the ground-state transition. The electron affinity of AuH2 is measured to be 3.030 ± 0.020 eV. A short bending vibrational progression is also observed in the second photodetachment band, suggesting a slightly bent structure for the first excited state of AuH2. The linear geometry is a saddle point for the ground and first excited states of AuH2, resulting in double-well potentials for these states along the bending coordinate. Spectroscopic evidence is observed for the detachment transitions to the double-well potentials of the ground and first excited states of AuH2. Higher excited states of AuH2 due to detachment from the nonbonding Au 5d electrons are all linear, similar to the anion ground state. Kohn–Sham molecular orbital analyses reveal surprising participation of H 2p orbitals in the Au–H chemical bonding and an unprecedented weak Au 5dπ to H 2pπ back donation. The simplicity of the linear AuH2− anion and its novel spectroscopic features make it a textbook example for understanding the covalent bonding properties and relativistic effects of Au.

High-TC superconductivity: a solid state chemistry model

We develop here a tentative explanation of the high-TC superconductivity mechanism, on the basis of solid state chemistry principles as well as some ancient ideas of Mott and Little. This is a real-space, non-retarded strong coupling model for the underdoped cuprate system. It develops the idea of a stabilized exciton phase formed during a Mott–Hubbard transition. Interactions between electric dipoles, as well as between doping charge and dipoles, bring the stability to achieve oxygen to copper charge transfer and hole pairing. We assume that, in order to minimize hole–hole Coulomb repulsion which increases strongly with doping, a hole ordering of 2D Wigner crystallisation-type favours the Bose–Einstein condensation and the superconducting state. We also discuss the specific role of copper and that of non-bonding electrons towards phonons when hole doping increases: instantaneous electric bond polarization, as for London's atomic forces, and soliton-type excitations allow the charge pairing which could be described thus in the scope of the BCS theory. This model is consistent with the main experimental and recent results characterizing the high-TC cuprates (phase diagram, oxygen holes, Fermi surface and superconducting gap symmetry, isotope effect, heterogeneity…).

Synthesis, Structure, and Reactivity of Carbene-Stabilized Phosphorus(III)-Centered Trications [L3P]3+

Carbene-stabilized [L(3)P](+3) cations have been synthesized for the first time by a reaction between 1-chloro-2,3-bis(dialkylamino)cyclopropenium salts and P(SiMe(3))(3). In addition, the first structural characterization of such an entity is reported. Consistent with the X-ray data, density functional calculations indicate that these P-centered cations, despite their high positive charge, still feature a nonbonding electron pair on the P-atom (HOMO) and a very low-lying LUMO depicting them as poor σ-donors and excellent π-acceptors.

First-principles study of the F-terminated Boron Nitride nanoribbons

Using first-principles calculations we study the electromagnetic properties of the F-terminated Boron Nitride nanoribbons (BNNRs) with both zigzag and armchair edges (ZBNNRs and ABNNRs). The results show that, compared with the indirect the H-terminated ZBNNRs, the F-terminated ZBNNRs are direct semiconductors and also the band gaps decrease monotonically with the increasing ribbon width, while the ABNNRs maintain the direct character. The band gap of the F-terminated BNNR is lower than that of the H-terminated one with the same ribbon width because of the mixing effects from the non-bonding 2p electrons of F and N atoms. Both the ZBNNRs and ABNNRs maintain the non-magnetic characters. Compared with the scarce contribution from H atom, the charge density of the highest valence band and the lowest conduction band analyses show that the contribution from F atom cannot be neglected. The N–B, B–F and B–H are ionic bonds with different bonding strength, while the N–F and N–H are all covalent bonds with different charge density accumulation.

An EPR Study on Nanographites

We present the results of an electron paramagnetic resonance study (EPR) in the range of 4–290 K on samples of nanographites obtained by ball milling graphite for different times. With a careful simulation of the spectral line shapes, we disentangled the EPR bands, providing the spectral profiles and intensities of the components on varying the temperature, their g tensors, and the homogeneous line widths of the contributing spin packets. We have been able to follow the effect of decreasing progressively the size of the flakes on the EPR bands due to mobile electrons and on Lorentzian lines due to nonbonding electrons on the zigzag edges of the crystallites. The temperature dependence of the EPR intensities shows a common trend for the signals attributed to edge electrons and to mobile electrons, showing that they belong to the same bath.

The crystal structure of franckeite, Pb21.7Sn9.3Fe4.0Sb8.1S56.9

The layer-like crystal structure of franckeite from the mine of San José, Bolivia, exhibits a pronounced one-dimensional transversal wave-like modulation and a non-commensurate layer match in two dimensions. It consists of alternating pseudohexagonal (H) layers and pseudotetragonal (Q) slabs and forms a homologous pair with cylindrite, which has thinner Q slabs. The Q slabs in franckeite are four atomic layers thick. The two components have their own lattices and a common modulation. The Q slab of the refined franckeite structure, Pb21.74Sn9.34Fe3.95Sb8.08S56.87, is an MS layer (M = Pb2+, Sn2+, Sb3+) four atomic planes thick, with a = 5.805(8), b = 5.856(16) Å, and the layer-stacking vector c = 17.338(5) Å. The lattice angles are α = 94.97(2)°, β = 88.45(2)°, γ = 89.94(2)°; the modulation vector q = -0.00129(8) a* + 0.128436(10) b* - 0.0299(3) c*. The H layer is a single-octahedron MS2 layer (M = Sn4+, Fe2+) with a = 3.665(8), b = 6.2575(16), c = 17.419(5) Å, α = 95.25(2)°, β = 95.45(2)°, γ = 89.97(2)°; the modulation vector is q = -0.00087(8) a* + 0.13725(16) b* - 0.0314(4) c*. The a and b vectors of both subsystems are parallel; the c vectors diverge. (3+2)D superspace refinement was performed in the superspace group C1, using 7397 observed reflections. It resulted in the overall R(obs) value equal to 0.094. The Q slabs are composed of two tightly bonded double-layers, separated by an interspace hosting non-bonding electron pairs. Average composition of cations on the outer surface was refined as Pb0.74(Sn,Sb)0.26, whereas that of cations, which are adjacent to the interspace with lone electron pairs, with a configuration analogous to that observed in orthorhombic SnS, corresponds to (Sn,Sb)0.73Pb0.27. Iron is dispersed over the octahedral Sn4+ sites in the H layer. Transversal modulation of the Q slab is achieved by local variations in the Pb:(Sn,Sb) ratios at its surface and interior. Its purpose is to re-establish a one-dimensional commensurate contact along [010] between the curved Q and H surfaces to the greatest extent possible. Layer-stacking disorder and divergence of the Q and H stacking directions, and the divergence between modulation wave-front and these stacking directions are typical for the composite structures of franckeite and cylindrite. Because of the increased rigidity of the Q component, franckeite usually forms masses of curved crystals rather than cylindrical aggregates. The existence of this family depends critically on the radius ratios of the cations involved, especially those involving (Pb2+, Sn2+) and Sn4+. Their replacement by a Pb2+:Bi3+ combination leads to misfit layer structures of a very different type, typified by cannizzarite.

Theoretical study of the V(4F) + NO(2Πr) → VO(4Σ−) + N(4S°) reaction compared with the Sc(2D) and Ti(3F) cases

To understand the title reaction, the MRCI, CCSD, CCSD(T), and DFT calculations have been done. A large domain of the ground-state potential energy surface has been explored including the activation energy barrier to form the triatomic complex, two stable intermediate complexes, V[NO] and NVO, the transition state connecting these two conformers, and the detachment of the nitrogen atom. We compared this reaction with the similar ones involving the Sc and Ti atoms. The activation barrier to form the VNO complex made from the ionic-covalent coupling decreases to approach the experimental data when the electron correlation effect is better included as in the Sc and Ti systems. The transition state connecting the two conformers was calculated to be higher than in the Sc and Ti cases probably due to larger number of nonbonding valence electrons and is probably too high with respect to the reactant energy level to allow the interconversion between the two conformers in the VNO. The direct concerted substitution (abstraction) reaction is improbable because this process will have to overcome a too high potential barrier. We have also found the transition state connecting two conformers of ScNO.

Preparation and characterization of quasi-solid-state electrolytes using a brominated poly(2,6-dimethyl-1,4-phenylene oxide) electrospun nanofiber mat for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are prepared with quasi-solid-state electrolytes by employing electrospun nanofiber mats. Here, we investigated the effects of a brominated poly(phenylene oxide) (BPPO) electrospun nanofiber mat used as a non-fluorinated polymer backbone in DSSCs. It was found that BPPO, which contains ether and bromine functional groups of non-bonding electrons, acts as a Lewis base. This Lewis basicity not only negatively shifted the flat band, but also coordinated Li ions in the electrolyte. As a result, by introducing a quasi-solid-state electrolyte, the open circuit voltage increased by 50 mV and the photon-to-current efficiency was comparable to a conventional liquid electrolyte. Furthermore, the quasi-solid-state DSSCs exhibited enhanced long-term stability, maintaining 97% of initial efficiency after 7 d under a mild acceleration condition at 50 °C.

A Stable Dialkylphosphinyl Radical

Dialkylphosphinyl radical 1 was synthesized as thermally stable yellow crystals and found to be monomeric both in solution and in the solid state. EPR spectrum showed that the spin density of 1 is mainly localized on the 3p orbital of the dicoordinated phosphorus atom. A distinct absorption band due to the electronic transition from nonbonding electron pair orbital to singly occupied 3p orbital on the phosphorus atom of 1 was observed at 445 nm in solution. Phosphinyl radical 1 underwent facile reaction with carbon tetrachloride, hydrogen abstraction, and a unique reaction with a persistent radical, galvinoxyl, giving a cyclic phosphaalkene and a silylether.

Ab initiostructure prediction for lead sulfide at standard and elevated pressures

As lead sulfide is an important semiconductor, it is of great interest to identify possible (meta)stable modifications, both at standard and elevated pressures. To predict such structures, global optimizations on the energy landscape of PbS were performed for several pressures, using simulated annealing followed by local optimization of the candidates found. In order to be able to take the effect of the nonbonding valence electrons of Pb into account, ab initio energies were employed for both the global and local optimization. Besides the experimentally known modifications (NaCl structure type at standard pressure and the CsCl structure type at high pressure), several additional promising structures, which might be accessible synthetically, were found; exhibiting, e.g., the TlI type (Cmcm), the FeB type (Pnma), and the \ensuremath{\alpha}-GeTe type ($R$3$m$).

Tuning HOMO–LUMO levels: trends leading to the design of 9‐fluorenone scaffolds with predictable electronic and optoelectronic properties

Highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) tuning is an important consideration in the development of organic‐based semiconducting materials. A study of the specific effects and overall trends for the HOMO–LUMO tuning of a diverse series of 9‐fluorenones by means of extended conjugation and substituent effects is described. Trends were explored in a range of compounds, beginning with structures having highly electron‐withdrawing substituents and progressing to structures having highly electron‐donating substituents. Compounds with an incremental increase in conjugation were also examined. Electrochemical and optical measurements were used to calculate the HOMO–LUMO levels and HOMO–LUMO bandgap (HLG) for each structure. Results from both methods were compared and correlated with the differences in molecular structure. Increasing the electron‐donating character of the substituents was observed to decrease the HLG and increase the energy levels of the HOMO and the LUMO, whereas an increase in the electron‐withdrawing character produced the opposite results. Increasing conjugation decreased the HLG, increased the HOMO energy level, but decreased the LUMO energy level. Spectroscopic evidence of substituent influence on the carbonyl suggests that substituents directly impact the HLG by influencing the availability of nonbonding electrons within the carbonyl, which impacts the probability of an nπ* transition. The data presented not only elaborate on the HOMO–LUMO tuning of 9‐fluorenone systems but also enable the consideration of 9‐fluorenones as analogous models for HOMO–LUMO tuning in other more complex polyaromatic systems such as bifluorenylidenes. These trends may provide insight into developing materials with specifically tuned HLGs and HOMO–LUMO levels for a variety of applications. Copyright © 2011 John Wiley & Sons, Ltd.

Local vibration assisted molecular configurations in poly(vinylidene fluoride) of ordered ferroelectric phase in N,N-dimethylformamide

Amide-based polymer liquids are important for developing biological and optical colloids or nanofluids. Functionalized properties arise from specific molecular structures. In this investigation, we report model molecular configurations of a polymer liquid, 0.3 g/L poly(vinylidene fluoride) (PVF 2) dissolved in liquid N,N-dimethylformamide (DMF), based on the characteristic IR vibration bands. Peculiarly, a ferroelectric β-PVF 2 phase reorders on a linear configuration in support with the DMF molecules, showing a characteristic band 840 cm − 1 (CH 2 rocking and CF 2 asymmetric stretching) with the trans band at 1275 cm − 1 . Four C O stretching bands ν 1 0, ν 1 1, ν 1 2, and ν 1 3 of 1650, 1675, 1725, and 1760 cm − 1 (bandwidth Δν ½ = 180 cm − 1 in the four bands) arise in four major configurations of DMF–PVF 2 pairs (or derivatives). Only one prominent ν 1 0 band 1660 cm − 1 (Δν ½ = 75 cm − 1 ) incurs with a shoulder ν 1 1 of 1725 cm − 1 (Δν ½ = 25 cm − 1 ) in two DMF configurations. A ferroelectric field cased in presence of β-PVF 2 leads to enhance IR absorption by as much as an order of magnitude. It leads to converging non-bonding electron density on the amide moiety.

2-(2-Methyl-6-phenyl-1-propyl-1,4-dihydropyridin-4-ylidene)propanedinitrile

In the title compound, C18H17N3, the dihedral angle between the dihydropyridine and phenyl rings is 72.57 (5)° and that between the dihydropyridine ring and malononitrile plane is 5.19 (20)°. The C—C bond lengths in the pyridine ring are considerably shorter than those of normal single bonds, indicating that electrons on the dihydropyridine ring, including the non-bonding electrons of the N atom, are delocalized on the ring.

Low-n Rydberg Transitions of Liquid Ketones Studied by Attenuated Total Reflection Far-Ultraviolet Spectroscopy

Far-ultraviolet (FUV) spectra in the 8.55-6.20 eV (145-200 nm) region were measured for several kinds of ketones in the liquid phase to investigate low-n Rydberg transitions using a uniquely developed technique of attenuated total reflection (ATR) FUV spectrometry. Assignments of the transitions are attempted for absorptions in this region by comparing the spectra for the liquid phase with those for the gas phase and ab initio calculations at the equation-of-motion coupled cluster theory with single and double substitutions at the aug-cc-pVDZ level. The transition from a nonbonding electron (n) to the 3s Rydberg orbital was found at around 6.7 eV for all investigated liquid ketones. Another intense band also appeared in the higher-energy region (ca. 8.5 eV) for all the ketones. A significant shoulder was found at around 7.4 eV for branched ketones. This shoulder band near 7.4 eV was assigned to the n-3p Rydberg transition. Band broadening and higher energy shifts were observed in the spectra of the liquid phase ketones in comparison with those of the gas phase ketones.

Interfacial water with special electron donor properties: Effect of water–surfactant interaction in confined reversed micellar environments and its influence on the coordination chemistry of a copper complex

In this work, we have investigated the behavior of the square-planar mixed-ligand transition-metal complex N, N, N′, N′-tetramethylethylenediamine copper (II) acetylacetonate tetraphenylborate, [Cu(acac)(tmen)][B(C 6H 5) 4], in anionic benzene/sodium 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs) as well as in cationic benzene/benzyl- n-hexadecyl dimethylammonium chloride (BHDC) RMs with and without water, using absorption spectroscopy. In the absence of water, W 0 = [H 2O]/[surfactant] = 0, our results show that the Cu complex structures are not the same in both reversed micellar media. In the BHDC RMs, due to the Cl − counterion present in the system, the Cu complex structure that exists at the interface is the neutral [Cu(acac)(tmen)(Cl)]. In contrast, in AOT RMs the surfactant sulfonate anion cannot act as a ligand and therefore the complex structure is square planar [Cu(acac)(tmen)] +. When water is added to both reversed micellar systems, different situations are observed. At low water content, the water sequestrated by BHDC RMs is unable to act as electron donor because the oxygen nonbonding electron pairs are completely involved in the cationic BHDC polar head group solvation through an ion–dipole interaction. On the contrary, in AOT RMs the results suggest that since the water molecules solvate the sulfonate group through hydrogen bonding interactions, the bulk hydrogen bond network is destroyed at the interface and therefore, the nonbonding electron pairs are more available to interact with the Cu complex. Thus, the electron donor ability of water in AOT RMs is enhanced in comparison with the BHDC RMs and bulk water, giving a remarkable electron donor character to the AOT reversed micellar interfacial water.

On the Directed Gas Phase Synthesis of the Imidoborane Molecule (HNBH) — An Isoelectronic Molecule of Acetylene (HCCH)

The elementary reaction of ground state boron atoms, (B((2)P(j))), with ammonia (NH(3)(X(1)A(1))) was conducted under single collision conditions at a collision energy of 20.5 ± 0.4 kJ mol(-1) in a crossed molecular beams machine. Combined with electronic structure calculations, our experimental results suggested that the reaction was initiated by a barrier-less addition of the boron atom to the nonbonding electron pair of the nitrogen atom forming a weakly bound BNH(3) collision complex. This intermediate underwent a hydrogen shift to a doublet HBNH(2) radical that decomposed via atomic hydrogen loss to at least the imidoborane (HBNH(X(1)Σ(+)) molecule, an isoelectronic species of acetylene (HCCH(X(1)Σ(g)(+))). Our studies are also discussed in light of the isoelectronic C(2)H(3) potential energy surface accessed via the isoelectronic carbon-methyl system.