Distortion Of Geometry Research Articles

A Comparative Study of Stabilities and Coordination Modes of β-Alaninephosphonic Acid in Copper(II) Heteroligand Complexes with Ethylenediamine, Diethylenetriamine or N,N,N′,N′,N″-Pentamethyldiethylene Triamine in Aqueous Solution

Solution equilibrium studies on Cu2+–L1–L2 ternary systems have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods {where L1 corresponds to a polyamine such as ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N′,N″-pentamethyldiethylenetriamine (Me5dien)} and L2 denotes 2-aminoethylphosphonic acid (β-alaninephosphonic acid)}. The results suggest the formation of heteroligand complexes with [Cu(L1)(β-Ala(P))] stoichiometry in all of the studied systems. Additionally, in the system with en, [Cu(en)(β-Ala(P))H−1]− is formed in basic solutions. Our spectroscopic results indicate tetragonal geometry for the [Cu(en)(β-Ala(P))] species, a geometry slightly deviated from square pyramidal for the [Cu(dien)(β-Ala(P))] complex, and somewhat stronger geometry distortion was present for the [Cu(Me5dien)(β-Ala(P))] complex. The coordination modes in these heteroligand complexes are discussed.

Investigating the Structural Origin of Trpzip2 Temperature Dependent Unfolding Fluorescence Line Shape Based on a Markov State Model Simulation

Vibrationally resolved fluorescence spectra of the β-hairpin trpzip2 peptide at two temperatures as well as during a T-jump unfolding process are simulated on the basis of a combination of Markov state models and quantum chemistry schemes. The broad asymmetric spectral line shape feature is reproduced by considering the exciton-phonon couplings. The temperature dependent red shift observed in the experiment has been attributed to the state population changes of specific chromophores. Through further theoretical study, it is found that both the environment's electric field and the chromophores' geometry distortions are responsible for tryptophan fluorescence shift.

High-temperature treatment of carbon-carbon composite materials. Communication 2. Thermal stabilization of two-dimensionally reinforced carbon-carbon composite material object geometry

The temperature field of industrial furnaces for high-temperature treatment of carbon composite blanks is studied. An error is established for temperature field reproduction within a furnace space. Mechanical, physical, and thermophysical properties of carbon blanks are studied. A safe temperature range is established for completing the production process. The required material properties are produced with observation of production regimes, and there is no distortion of component geometry.

Crystal Structure of a Mixed-Ligand Cu(II) Complex Forming Supramolecular Assembly via an Extensive H-Bonding and Ring–Ring π–π Interactions

The title ternary complex has been prepared and its structure determined using X-ray crystallography. The complex crystallizes in triclinic space group P-1 with a = 6.745(5), b = 10.551(5), c = 11.414(5) A, α = 95.770(5), β = 91.396(5), γ = 92.518(5)°, V = 807.1 A3 and Z = 2. The structural data are consistent with the presence of Jahn–Teller distortion in the overall hexacoordinate octahedral geometry of the molecule. The crystal packing is through an extensive hydrogen bonding and ring–ring π–π interactions resulting in a supramolecular framework. The supramolecular assembly results in via an extensive H-bonding and ring–ring π–π interactions in the present mixed-ligand Cu(II) complex indicated from X-ray crystallographic analyses.

Dihedral Angle Mesh Error: a fast perception correlated distortion measure for fixed connectivity triangle meshes

AbstractIn computer graphics, triangle meshes are ubiquitous as a representation of surface models. Processing of this kind of data, such as compression or watermarking, often involves an unwanted distortion of the surface geometry. Advanced processing algorithms are continuously being proposed, aiming at improving performance (compression ratio, watermark robustness and capacity), while minimizing the introduced distortion.In most cases, the final resulting mesh is intended to be viewed by a human observer, and it is therefore necessary to minimise the amount of distortion perceived by the human visual system. However, only recently there have been studies published on subjective experiments in this field, showing that previously used objective error measures exhibit rather poor correlation with the results of subjective experiments.In this paper, we present results of our own large subjective testing aimed at human perception of triangle mesh distortion. We provide an independent confirmation of the previous result by Lavoué et al. that most current metrics perform poorly, with the exception of the MSDM/MSDM2 metrics. We propose a novel metric based on measuring the distortion of dihedral angles, which provides even higher correlation with the results of our experiments and experiments performed by other researchers. Our metric is about two orders of magnitude faster than MSDM/MSDM2, which makes it much more suitable for usage in iterative optimisation algorithms.

Modulating the Strength of Hydrogen Bonds through Beryllium Bonds.

The mutual influence between beryllium bonds and inter- or intramolecular hydrogen bonds (HBs) has been investigated at the B3LYP/6-311++G(3df,2p) level of theory, using the complexes between imidazole dimer and malonaldehyde with BeH2 and BeF2 as suitable model systems. Imidazole and its dimer form very strong beryllium bonds with both BeH2 and BeF2, accompanied by a significant geometry distortion of the Lewis acid. More importantly, we have found a clear cooperativity between these two noncovalent interactions, since the intermolecular HB between the two imidazole molecules in the dimer-BeX2 complex becomes much stronger than in the isolated dimer, whereas the beryllium bond becomes also stronger in the dimer-BeX2 complex, with respect to that found in the imidazole-BeX2 complex. The effects of beryllium bonds are also dramatic on the strength of intramolecular HBs. Depending on to which center the BeX2 is attached, the intramolecular HB becomes much stronger or much weaker. The first situation is found when the beryllium derivative is attached to the HB donor, whereas the second occurs if it is attached to the HB acceptor. The first effect can be so strong as to produce a spontaneous proton transfer, as it is actually the case of the malonaldehyde-BeF2 complex.

Synthesis of Alkyl-Substituted Tribenzopentaphenes as Versatile Polycondensed Aromatic Hydrocarbon π-π Stacking Building Blocks

We show the versatile synthesis of four tribenzopentaphene derivatives bearing alkyl side chains at three different positions. Substitutions on two of these positions led to subtle intensity changes at the lines of the blue emission, whereas alkylation in the bay region led to dimerization of the pentaphene derivative, resulting in a distortion of the chromophore geometry and an emission shift to green.

A nine-node displacement-based finite element for Reissner–Mindlin plates based on an improved formulation of the NIPE approach

The nodally integrated plate element formulation is an assumed strain finite element technique for shear deformable plates that enforce weakly the balance and the kinematic equations. The strain–displacement operators are derived via nodal integration satisfying a priori the kinematic weighted residual statement. The present work analyzes the NIPE technique, including the new element, by testing thoughtfully the sensitivity of the elements to severe geometry distortions. We propose an improvement that confers robustness to all element shapes developed by the NIPE formulation.We present also a new nine-node NIP element configuration. The new nine-node element uses bi-quadratic interpolations of the transverse displacement and rotations and is computed by means of a nine-node quadrature rule.A brief review of the improved triangular and quadrangular NIPEs is reported for elastic plate analyses. A few challenging benchmarks carried out on extreme distorted meshes illustrate the performance of the introduced NIP-Q9 element. We detail that the new NIPE formulation confers insensitivity to extreme distortions for the quadratic quadrilateral element and allows to solve for severe distortion with the NIPE family.

Structure–Activity Correlations in a Nickel–Borate Oxygen Evolution Catalyst

An oxygen evolution catalyst that forms as a thin film from Ni(aq)(2+) solutions containing borate electrolyte (Ni-B(i)) has been studied by in situ X-ray absorption spectroscopy. A dramatic increase in catalytic rate, induced by anodic activation of the electrodeposited films, is accompanied by structure and oxidation state changes. Coulometric measurements correlated with X-ray absorption near-edge structure spectra of the active catalyst show that the nickel centers in activated films possess an average oxidation state of +3.6, indicating that a substantial proportion of nickel centers exist in a formal oxidation state of Ni(IV). In contrast, nickel centers in nonactivated films exist predominantly as Ni(III). Extended X-ray absorption fine structure reveals that activated catalyst films comprise bis-oxo/hydroxo-bridged nickel centers organized into sheets of edge-sharing NiO(6) octahedra. Diminished long-range ordering in catalyst films is due to their ostensibly amorphous nature. Nonactivated films display a similar oxidic nature but exhibit a distortion in the local coordination geometry about nickel centers, characteristic of Jahn-Teller distorted Ni(III) centers. Our findings indicate that the increase in catalytic activity of films is accompanied by changes in oxidation state and structure that are reminiscent of those observed for conversion of β-NiOOH to γ-NiOOH and consequently challenge the long-held notion that the β-NiOOH phase is a more efficient oxygen-evolving catalyst.

Implementation of edge detection algorithms to characterize magnetic micropillars patterned by X-ray lithography

The array of SU-8 photoresist pillars (10 ´ 10 ´ 50 µm) on a copper substrate was patterned by X-ray lithography using a synchrotron source. Flat cobalt films can then be sputter-deposited on the chemically stable and mechanically hardened SU-8 pillars in spite of geometry distortion and pattern collapse in some regions. Since any deviations from the pattern affect magnetic properties of the structure, images of these micropillars obtained from an optical microscope and a scanning electron microscope (SEM) were inspected using five different edge detection algorithms. The Canny and Laplacian of Gaussian (LoG) operators can detect all cross sections of micropillars, but noise points and lines were also included. The outputs from image processing by the Prewitt and Sobel operators yielded lower noise, but suffered from discontinuity, especially in the case of tilt angled SEM images. The Roberts cross edge detector had a weakest response to edges of the pattern under test. The 3D nature of the micropillars is an origin of low-contrast edge and background noise in the images. Key words: X-ray lithography, SU-8 photoresist, high-aspect-ratio microstructure, image processing, edge detection.

Oscillator Strength of Symmetry-Forbidden d-d Absorption of Octahedral Transition Metal Complex: Theoretical Evaluation

The theoretical evaluation of the oscillator strength of a symmetry-forbidden d-d transition is not easy even nowadays. A new approximate method is proposed here and applied to octahedral complexes [Co(NH(3))(6)](3+) and [Rh(NH(3))(6)](3+) as an example. Our method incorporates the effects of geometry distortion induced by molecular vibration and the thermal distribution of such distorted geometries but does not need the Herzberg-Teller approximation. The calculated oscillator strengths of [Co(NH(3))(6)](3+) agree well with the experimental values in both (1)A(1g) → (1)T(1g) and (1)A(1g) → (1)T(2g) transitions. In the Rh analogue, though the calculated oscillator strengths are somewhat smaller than the experimental values, computational results reproduce well the experimental trends that the oscillator strengths of [Rh(NH(3))(6)](3+) are much larger than those of the Co analogue and the oscillator strength of the (1)A(1g) → (1)T(1g) transition is larger than that of the (1)A(1g) → (1)T(2g) transition. It is clearly shown that the oscillator strength is not negligibly small even at 0 K because the distorted geometry (or the uncertainty in geometry) by zero-point vibration contributes to the oscillator strength at 0 K. These results are discussed in terms of frequency of molecular vibration, extent of distortion induced by molecular vibration, and charge-transfer character involved in the d-d transition. The computational results clearly show that our method is useful in evaluating and discussing the oscillator strength of symmetry-forbidden d-d absorption of transition metal complex.

Quantum molecular mechanics—a noniterative procedure for the fast Ab Initio calculation of closed shell systems

In this article, we advance the foundations of a strategy to develop a molecular mechanics method based not on classical mechanics and force fields but entirely on quantum mechanics and localized electron-pair orbitals, which we call quantum molecular mechanics (QMM). Accordingly, we introduce a new manner of calculating Hartree-Fock ab initio wavefunctions of closed shell systems based on variationally preoptimized nonorthogonal electron pair orbitals constructed by linear combinations of basis functions centered on the atoms. QMM is noniterative and requires only one extremely fast inversion of a single sparse matrix to arrive to the one-particle density matrix, to the electron density, and consequently, to the ab initio electrostatic potential around the molecular system, or cluster of molecules. Although QMM neglects the smaller polarization effects due to intermolecular interactions, it fully takes into consideration polarization effects due to the much stronger intramolecular geometry distortions. For the case of methane, we show that QMM was able to reproduce satisfactorily the energetics and polarization effects of all distortions of the molecule along the nine normal modes of vibration, well beyond the harmonic region. We present the first practical applications of the QMM method by examining, in detail, the cases of clusters of helium atoms, hydrogen molecules, methane molecules, as well as one molecule of HeH(+) surrounded by several methane molecules. We finally advance and discuss the potentialities of an exact formula to compute the QMM total energy, in which only two center integrals are involved, provided that the fully optimized electron-pair orbitals are known.

Adsorption of oxygen-containing functional groups on free and supported graphene using point contact

First-principles electronic structure calculations based on spin-polarized density functional theory were carried out to study the adsorption of oxygen-containing functional groups -OH, -CHO, and -COOH on a two-dimensional (2D) infinite graphene sheet without edge states and defects. We find that the energy gain of adsorption can be significantly improved when the graphene sheet is supported via a point contact, a prototype for graphene sheet supported by catalysts, nanoparticles or nanopillars, or a surface with steps, edges, adatoms, or defects. This was modeled by placing a single atom of Fe, Co, and Ni under the graphene surface. Thus supported graphene not only becomes magnetic, but the carbon atoms in contact with the metal atoms become chemically more active as well. The use of point contact support to improve adsorption has advantages over that of introducing defects: (1) It does not destroy the intrinsic 2D geometry of the graphene sheet. (2) Patterned structures can be created by tailoring the position of the metal atoms supporting the graphene sheet. (3) The geometry distortion created by point contact can be made more uniform and lead to better adsorption energies. (4) Reduction of the work function of supported graphene makes the manipulation of electrons more flexible and controllable in tuning their electronic structure and magnetic properties.

Resonance Raman Spectroscopic and Theoretical Study of Geometry Distortion of Thiourea in 21A State

The A-band resonance Raman spectra of thiourea were obtained in water and acetonitrile solution. B3LYP/6-311++G(3df,3pd) and RCIS/6-311++G(3df,3pd) calculations were done to elucidate the ultraviolet electronic transitions, the distorted geometry structure and the saddle point of thiourea in 21A excited state, respectively. The resonance Raman spectra were assigned. The absorption spectrum and resonance Raman intensities were modeled using Heller's time-dependent wavepacket approach to resonance Raman scattering. The results indicate that largest change in the displacement takes place with the C=S stretch mode ν6 (|Δ|=0.95) and noticeable changes appear in the H5N3H6+H8N4H7 wag ν5 (|Δ|=0.19), NCN symmetric stretch+C=S stretch+N3H6+H8N4 wag ν4 (|Δ|=0.18), while the moderate intensities of 2ν15 and 4ν15 are mostly due to the large excited state frequency changes of ν15, but not due to its significant change in the normal mode displacement. The mechanism of the appearance of even overtones of the S=CN2 out of plane deformation is explored. The results indicate that a Franck-Condon region saddle point is the driving force for the quadric phonon mechanism within the standard A-term of resonance Raman scattering, which leads to the pyramidalization of the carbon center and the geometry distortion of thiourea molecule in 21A excited state.

Multiple-decker phthalocyaninato dinuclear lanthanoid(iii) single-molecule magnets with dual-magnetic relaxation processes

The SMM behaviour of dinuclear Ln(III)-Pc multiple-decker complexes (Ln = Tb(3+) and Dy(3+)) with energy barriers and slow-relaxation behaviour were explained by using X-ray crystallography and static and dynamic susceptibility measurements. In particular, interactions among the 4f electrons of several dinuclear Ln(III)-Pc type SMMs have never been discussed on the basis of the crystal structure. For dinuclear Tb(III)-Pc complexes, a dual magnetic relaxation process was observed. The relaxation processes are due to the anisotropic centres. Our results clearly show that the two Tb(3+) ion sites are equivalent and are consistent with the crystal structure. On the other hand, the mononuclear Tb(III)-Pc complex exhibited only a single magnetic relaxation process. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole-dipole (f-f) interactions between the Tb(3+) ions in the dinuclear systems. Furthermore, the SMM behaviour of dinuclear Dy(III)-Pc type SMMs with smaller energy barriers compared with that of Tb(III)-Pc and slow-relaxation behaviour was explained. Dinuclear Dy(III)-Pc SMMs exhibited single-component magnetic relaxation behaviour. The results indicate that the magnetic relaxation properties of dinuclear Ln(III)-Pc multiple-decker complexes are affected by the local molecular symmetry and are extremely sensitive to tiny distortions in the coordination geometry. In other words, the spatial arrangement of the Ln(3+) ions (f-f interactions) in the crystal is important. Our work shows that the SMM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in a controlled SMM spatial arrangement.

New iso-propoxides, tert-butoxides and neo-pentoxides of niobium(v): Synthesis, structure, characterization and stabilization by trifluoroheteroarylalkenolates and pyridine ligands

The synthesis and characterization of nine new heteroleptic alkoxides of niobium is described. Metathesis reactions of Nb(2)Cl(10) with (t)BuCH(2)OH and pyridine (py) or 4-dimethylaminopyridine (DMAP) affords monomeric octahedral complexes Nb(OCH(2)(t)Bu)(5)py (1) and Nb(OCH(2)(t)Bu)(5)DMAP (2), respectively, in high yields (>60%). The same reaction with (t)BuOH resulted in a chloro functionalized alkoxide Nb(O(t)Bu)(4)pyCl (3) and could not be pushed to complete removal of remaining Cl(-) ligand. The introduction of a chelating bidental ligand 3,3,3-trifluoro-1-(pyridine-2-yl)propen-2-ol (2-PyCHCOHCF(3)) (4'') in the dimeric framework of Nb(2)(O(i)Pr)(10) (4') produced a heteroleptic, monomeric niobium complex Nb(O(i)Pr)(4)(2-PyCHCOCF(3)) (4) with significantly enhanced stability and volatility. As a comparison to (4), five different heteroaryl systems (5-9) with the same side chain have been synthesized and examined in order to understand the influence upon physio-chemical properties. All the new compounds (1-9) have been characterized by microanalysis, variable temperature multinuclear NMR spectroscopy, mass spectrometry, thermal analysis and single crystal X-ray diffraction studies ((3), (4) and (9)). The molecular structure of (3) revealed mononuclear species with Nb atoms present in the distorted octahedral environment of four (t)BuO, one chloride and one pyridine ligand. Compounds (4) and (9) consisting of four (i)PrO and a trifluoroheteroarylenolate exhibited a stronger distortion in the molecular geometry due to the rigidity of chelating β-alkenolate moiety.

Effect of Unsteadiness and Nozzle Asymmetry on Thrust of a Microthruster

Due to the small size and short propulsion pulses of solid propellant microthrusters, unsteady characteristics and/or fabrication errors may cause appreciable effects on the total thrust. The present work simulates a 2D planar and conical nozzle of 200 μm throat diameter using the traditional momentum equations and turbulence closure model. Unsteady characteristics were found to be insensitive to the inlet mass flux but sensitive to the chamber size. The characteristic time of transient momentum variations in the nozzle was found to be on the order of 0.1 ms, and that for decay was smaller than that for development by about 25%. This work confirmed that the magnitude of thrust was not sensitive to distortions in the nozzle geometry. A mismatch of the nozzle throat changed the position of sonic plane, but its effect on thrust was almost negligible.

Space-Variant Filtering for Wavefront Curvature Correction in Polar Formatted Bistatic SAR Image

An analytical expression of the phase error from wavefront curvature in bistatic spotlight-mode synthetic aperture radar (SAR) image reconstructed via polar format algorithm (PFA) is derived in this paper. The wavefront curvature effect, which arises from the unrealistic planar wavefront assumption in bistatic PFA, induces phase error terms resulting in space-variant geometry distortion and defocusing. Based on the analytical expression of the wavefront curvature error, a space-variant filtering approach is applied to compensate for it in the polar formatted bistatic SAR image. Analysis on the scene size limit after using the correction method indicates that the derived space-variant filter is capable of extending the focused scene size of bistatic PFA considerably. Point target (PT) simulation validates the approach.

CoxCu1−x(DDOP)(OH2)(NO3)](NO3): hydrogen bond-driven distortion of cobalt(ii) by solid solution ‘network mismatch’

Late-first row transition metal nitrate complexes of the tetradentate N-donor ligand cis-3,5-bis[(2-pyridinyleneamino]-trans-hydroxycyclohexane (DDOP) adopt a mono-cationic [M(DDOP)(H(2)O)(NO(3))](+) structure (M = Co, 1; Cu, 2; Zn, 3) in which the DDOP ligand occupies the equatorial plane. The complexes are essentially isostructural and isomorphous, allowing the Co(II) and Cu(II) complexes to co-crystallize in mixed-metal solid solutions with the formula [Co(x)Cu(1-x)(DDOP)(NO(3))(H(2)O)](NO(3)), where x = 0.4 (4), 0.1 (5), and 0.7 (6). For 4, structural and magnetochemical analysis indicate that the geometry of the octahedral Co(II) complex distorts to match that of the dominant Jahn-Teller distorted Cu(II) center. Magnetic susceptibility data of octahedral Co(II) are sensitive to ligand geometry distortions and have been analyzed accordingly, comparing 4 to the reference systems 1 and 2. Bond valence calculations have been used to estimate the relative stabilities of the six hydrogen bonded networks, suggesting that the stretching of the Co(II) coordination sphere 4 in is assisted by adoption of the most stable hydrogen bonded network; but that in 6 this is overcome by a higher loading of Co. This family of complexes therefore represent predictable metal-based tectons which can help probe the influence of secondary non-covalent interactions over metal coordination geometries and properties.

Methane-selective nanoporous graphene membranes for gas purification

The capability of functionalized graphene nanopores to efficiently separate methane from air is analyzed using density functional theory. We study the interaction between selected gas molecules and two finite model pores. Saddle point energies of the activated complexes are used to estimate transmission probabilities and selectivities as a function of temperature. We account for geometry distortions caused by the transient gas molecules and discuss the applicability and limitations of descriptions based on "molecular size" for the judgement of quasi-two-dimensional membranes.