Bond Axis Research Articles

Symmetry-correct bonding in density functional theory calculations for delta phase Pu

The long-held conclusion that magnetic order in delta phase Pu makes the structure mechanically unstable in density functional theory calculations is incorrect if the magnetic order is allowed to be non-collinear. The non-collinear 3Q spin structure is intrinsically cubic and makes all structurally equivalent bonds equivalent in their bonding character. Applied to density functional theory calculations on delta phase Pu, the 3Q spin structure results in elastic constants and phonons with the correct symmetry. The calculated phonon dispersion agrees better with experiment than previous calculations, and the calculated thermal expansion shows the unique behavior seen experimentally: it is negative.

Probing Copper and Copper-Gold Alloy Surfaces with Space-Quantized Oxygen Molecular Beam.

The orientation and motion of reactants play important roles in reactions. The small rotational excitations involved render the reactants susceptible to dynamical steering, making direct comparison between experiments and theory rather challenging. Using space-quantized molecular beams, we directly probed the (polar and azimuthal) orientation dependence of O2 chemisorption on Cu(110) and Cu3Au(110). We observed polar and azimuthal anisotropies on both surfaces. Chemisorption proceeded rather favorably with the O–O bond axis oriented parallel (vs perpendicular) to the surface and rather favorably with the O–O bond axis oriented along [001] (vs along [1̅10]). The presence of Au hindered the surface from further oxidation, introducing a higher activation barrier to chemisorption and rendering an almost negligible azimuthal anisotropy. The presence of Au also prevented the cartwheel-like rotations of O2.

Mixed chiral and achiral character in substituted ethane: A next generation QTAIM perspective

We use the newly introduced spanning stress tensor trajectory Uσ-space construction within next generation quantum theory of atoms in molecules (NG-QTAIM) for a chirality investigation of singly and doubly substituted ethane with halogen substituents: F, Cl, Br. Singly substituted ethane was overall achiral comprising cancelling chiral components in Uσ-space. The resultant axial bond critical point (BCP) sliding responded more strongly to the increase in atomic number of the substituted halogen than the chirality. The presence of the very light F atom was found responsible for a very high degree of achiral character of the doubly substituted ethane.

Atomistic insight into the ferroelastic post-stishovite transition by high-pressure single-crystal X-ray diffraction

Abstract The post-stishovite transition is a classic pseudo-proper typed ferroelastic transition with a symmetry-breaking spontaneous strain. This transition has been studied using high-pressure spontaneous strains, optic modes, and elastic moduli (Cij) based on the Landau modeling, but its atomistic information and structural distortion remain poorly understood. Here we have conducted synchrotron single-crystal X-ray diffraction measurements on stishovite crystals up to 75.3 GPa in a diamond-anvil cell. Analysis of the data reveals atomic positions, bond lengths, bond angles, and variations of SiO6 octahedra across the transition at high pressure. Our results show that the O coordinates split at ~51.4 GPa, where the apical and equatorial Si-O bond lengths cross over, the SiO6 octahedral distortion vanishes, and the SiO6 octahedra start to rotate about the c axis. Moreover, distortion mode analysis shows that an in-plane stretching distortion (GM1+ mode) occurs in the stishovite structure at high pressure while a rotational distortion (GM2+ mode) becomes dominant in the post-stishovite structure. These results are used to correlate with elastic moduli and Landau parameters (symmetry-breaking strain e1–e2 and order parameter Q) to provide atomistic insight into the ferroelastic transition. When the bond lengths of two Si-O bonds are equal due to the contribution from the GM1+ stretching mode, C11 converges with C12, and the shear wave VS1[110] polarizing along [110] and propagating along [110] vanishes. Values of e1–e2 and Q are proportional to the SiO6 rotation angle from the occurrence of the GM1+ rotational mode in the post-stishovite structure. Our results on the pseudo-proper type transition are also compared with that for the proper type in albite and improper type in CaSiO3 perovskite. The symmetry-breaking strain, in all these types of transitions, arises as the primary effect from the structural angle (such as SiO6 rotation or lattice constant angle) and its relevant distortion mode in the low-symmetry ferroelastic phase.

Bifurcated Chalcogen Bonds Based on One σ-Hole

Chalcogen bonds are noncovalent interactions and are increasingly coming into focus for the design of complex structures in research areas such as crystal engineering, molecular recognition and catalysis. Conceptionally, chalcogen bonds can be considered as interaction between one σ-hole and one Lewis base center. Herein, we analyze the interaction between bidentate chelating ligands having two nucleophilic centers with one single σ-hole of a chalcogenazole (two-lone-pair/one-σ-hole interactions). Referring to this, we show by quantum chemical calculations and X-ray studies that three bond types are possible: in the first case, a chalcogen bond is formed between the σ-hole and only one of the Lewis base centers. In the second case, a strong bond is formed by one nucleophilic center; the second center provides only a small amount of additional stabilization. In the third case, two equivalent bonds to the σ-hole are formed by both Lewis base centers. According to the calculations, the bifurcated bonds are stronger than simple chalcogen bonds and lead to a more rigid molecular arrangement in the complex.

Importance of an Axial LnIII-F Bond across the Lanthanide Series and Single-Molecule Magnet Behavior in the Ce and Nd Analogues.

The recently reported compound [DyIIILF](CF3SO3)2·H2O (L = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane) displays a strong axial magnetic anisotropy, due to the short axial Dy–F bond, and single-molecule magnet (SMM) behavior. Following our earlier [DyIIILF]2+ work, herein we report the systematic structural and magnetic study of a family of [LnIIILF](CF3SO3)2·H2O compounds (Ln(III) = 1-Ce, 2-Pr, 3-Nd, 4-Eu, 5-Tb, 6-Ho, 7-Er, 8-Tm, and 9-Yb). From this series, the Ce(III) and Nd(III) analogues show slow relaxation of the magnetization under an applied direct current magnetic field, which is modeled using a Raman process. Complete active space self-consistent field theoretical calculations are employed to understand the relaxation pathways in 1-Ce and 3-Nd and also reveal a large tunnel splitting for 5-Tb. Additional computational studies on model compounds where we remove the axial F– ligand, or replace F– with I–, highlight the importance of the F– ligand in creating a strong axial crystal field for 1-Ce and 3-Nd and for promoting the SMM behavior. Importantly, this systematic study provides insight into the magnetic properties of these lighter lanthanide ions.

Synthesis, covalency parameters, energy calculations and crystal features of acylpyrazolone derived pentavalent Uranyl complex along with DFT and Hirshfeld analysis

A σ-donating acylpyrazolone DMBPMP (4-(3,5-dimethyl benzoyl) 1-phenyl 3-methyl 5-pyrazolone) ligand and its Uranyl acylpyrazolone complex [UO2(DMBPMP)2(EtOH)] were synthesized to analyze the nature of covalency, reactivity, and redox properties. The structure, pentavalent bipyramidal geometry, and complex composition are mainly scrutinized through their single-crystal x-ray crystal data, molar conductivity, gravimetric estimation, FTIR significant vibrations, δ-values of 1H NMR, 13C NMR and TG-DTA plots. The covalency of the Uranyl complex mainly depends on average bond length values on the pentagonal equatorial plane, Uranyl axial bond lengths, stretching frequency values, coordinated solvent on the fifth coordination site, and different aryl group substitution on the first position of the pyrazolone ring; and it can be confirmed through FTIR, single-crystal, and electronic UV–Vis spectral characterization methods. The UV–Vis data was also valuable for identifying n → π*, π → π*, and LMCT transitions and calculating Sinha’s covalency parameters, which shows that the complex can show maximum covalent character in DMSO solvent and covalency decreases in DMSO > DMF > Ethyl acetate > Ethanol > CHCl3 order. DFT calculations were performed to get an excellent correlation and comparison with all experimental values. This correlation and comparision is helpful to identify global index parameters to get an idea of the physical as well as chemical properties of such systems and to confirm the characteristics theoretically by HOMO-LUMO energy gap, theoretical vibrations, natural electronic configuration, and NBO charges. The Hirshfeld surface analysis was also carried out to identify the crystal strength through interaction energies and energy frameworks in the ligand and intermolecular non-covalent surface interactions with fingerprint plot details in both ligand and complex. Electro-chemical analysis in CV-DPV plots provides information on the redox properties of uranyl moiety.

Cu-Catalyzed Asymmetric 1,3-Dipolar Cycloaddition of N-2,2,2-Trifluoroethylisatin Ketimines Enables the Desymmetrization of N-Arylmaleimides: Access to Enantioenriched F3C-Containing Octahydropyrrolo[3,4-c]pyrroles.

With a Cu(OTf)2/chiral ferrocenyl P,N-ligand complex as a catalyst, the enantioselective desymmetrization of N-arylmaleimides was successfully realized by taking advantage of the asymmetric 1,3-dipolar cycloaddition reaction of N-2,2,2-trifluoroethylisatin ketimines. A series of structurally diverse F3C-containing octahydropyrrolo[3,4-c]pyrroles, bearing four contiguous carbon stereocenters and one stereogenic chiral C-N axial bond, were obtained with excellent results (≤99% yield, >20:1 dr, and 99% ee).

Dynamics of rotation in two‐coordinate thiazolyl copper(I) carbazolyl complexes

Two‐coordinate carbene Cu(Ι) amide complexes with sterically bulky groups such as the diisopropyl phenyl (dipp) on the carbenes have been shown to have comparable performance to the phosphorescent emitters bearing heavy atoms such as iridium and platinum. These bulky groups enforce a coplanar molecular structure and suppress the nonradiative decay rates. Here, three different two‐coordinate Cu(Ι) complexes were investigated that bear a common thiazole carbene, 3‐(2,6‐diisopropylphenyl)‐4,5‐dimethylthiazol‐2‐ylidene, with only a single dipp group, and carbazolyl ligands with substituents of varying steric bulk ortho to N. These substituents have a negligible impact on luminescence energies of the complexes but serve to modulate the rotation barriers along the metal–ligand coordinate bond. The geometric arrangement of ligands (syn‐ or anti‐conformer) in complexes with alkyl substituents were found to differ, being syn in the solid state versus anti in solution as revealed by crystallographic analysis and nuclear magnetic resonance spectroscopy. In addition, calculations were performed to determine potential energy surfaces for different conformations of the three complexes to provide a theoretical evaluation of rotation barriers around the metal–ligand bond axis. The relationship between rotation barriers and photophysical properties demonstrate that rates for nonradiative decay decrease with increasing bulk of the substituents on the carbazolyl ligand.

Axial compression and bond behaviour of recycled aggregate concrete-filled stainless steel tubular stub columns

This paper presents a series of axial compression and push-out tests on recycled aggregate concrete-filled stainless steel tube (RAC-FSST) stub columns. A total of 36 specimens were tested, including 18 circular columns and 18 square ones, to determine the effect of the confinement factor and the recycled aggregate replacement ratio on the axial compressive behaviour of these columns. The axial compression load versus longitudinal strain curves of tested columns demonstrated three trends as the confinement factor increased: post-peak softening, plasticity, and strengthening. Correspondingly, push-out slip tests of RAC-FSST members were conducted and formulas for bond strength were proposed. Generally, the bond strength of RAC-FSST was lower than that of CFST due to the smoother surface of the stainless steel tube and the larger shrinkage deformation of the core RAC. A finite element model was developed and verified for further analysis. Based on the experimental and numerical study, the structural behaviour of RAC-FSST was compared with that of normal CFST. The feasibility of existing formulas for axial compression strength calculation of RAC-FSST was evaluated. Based on the collected experimental results of RAC-FSST stub columns and the statistical parameters of the strength for stainless steel tube, reliability analysis was carried out. The partial factors of axial compressive strength of RAC-FSST in building structures, highway bridges, and port engineering structures were proposed.

Synthesis and crystal structure of di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II) bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato)(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II).

In the asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II) trans-bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato-κO)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II), [Zn(C10H24N4)(H2O)2][Zn(C13H9O5P)2(C10H24N4)], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra-gonally elongated ZnN4O2 octa-hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol-ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans-III conformation. The average Zn-N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn-O bond lengths [2.189 (4) Å for phospho-nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles, the O-H groups of coordinated water mol-ecules and the P-O-H groups of the acids as proton donors, and the O atoms of the phospho-nate and carboxyl-ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.

Experimental investigation of bond-slip stress of cold-formed CFSTs stub-columns in a post fire based on four cycles push out tests

Concrete-filled steel tube (CFST) columns display a fine fire resistance. In the following research the performance of shear studs and their connection configuration in square concrete-filled steel tube stub-columns were investigated. The dimensions of the hollow square sections were 100x100 mm2 with a wall thickness of 4 mm. Shear studs including inward-bent studs welded from the back, inward-bent studs welded from inside and bolts which are stiffening elements were put in place and the tubes were filled with concrete and then placed in the furnace for 60 min under 20 °C, 250 °C, 500 °C and 750 °C. The columns were then loaded after cooling down to the room temperature. Moreover one tube without shear studs was tested as control specimen. In this research the effect of increasing temperature and cooling or post-fire behavior on bond stress and slip between concrete core and inner steel tube were investigated. A total of 16 specimens were tested for achieving this goal. According to the results the use of strip shear studs have a significant effect on increasing the lateral stiffness, axial compressive strength and bond stress of the column. Furthermore until 500 °C the bond between concrete and steel was weakened. But in the temperatures of 500 °C and 750 °C due to Poisson effect in concrete and increased volume regarding micro-cracks, the friction between steel and concrete is increased and the loading capacity of the cross section is enhanced consequently.

Anisotropic dynamics of resonant scattering between a pair of cold aligned diatoms

The collision dynamics between a pair of aligned molecules in the presence of a partial-wave resonance provide the most sensitive probe of the long-range anisotropic forces important to chemical reactions. Here we control the collision temperature and geometry to probe the dynamics of cold (1-3 K) rotationally inelastic scattering of a pair of optically state-prepared D2 molecules. The collision temperature is manipulated by combining the gating action of laser state preparation and detection with the velocity dispersion of the molecular beam. When the bond axes of both molecules are aligned parallel to the collision velocity, the scattering rate drops by a factor of 3.5 as collision energies >2.1 K are removed, suggesting a geometry-dependent resonance. Partial-wave analysis of the measured angular distribution supports a shape resonance within the centrifugal barrier of the l = 2 incoming orbital. Our experiment illustrates the strong anisotropy of the quadrupole-quadrupole interaction that controls the dynamics of resonant scattering.

Framing Victims: A Comparative Framing Analysis of Yemen and Syrian Conflict Victims in Pakistani Media

The current research scrutinizes how political proximity plays a vital role in the portrayal of conflict victims, happening in Yemen and Syria. Through the content analysis research demonstrate the victims of the Yemen conflict are more tinted than the victims of the Syrian conflict. In both the conflict, all the actors are having equivalent religious bonds with the reporting media of Pakistan. This study demonstrates the political proximity between the media of reporting country and actors of the conflict, direct strong effect on the framing of the conflict victims. The result demonstrates that Saudis is having a strong political relationship with Pakistan therefore in the Yemen conflict Yemen government (backed by Saudi Arabia) is demonstrated as more positive and Houthis rebels as negative. On the other side, Syria does not have a strong relationship with Pakistan so the Syrian war is demonstrated as the confusing war between different groups where no one is positively portrayed. The result demonstrates closer the political proximity between reporting country and conflict actor, the greater the chance that the actor will have highly empathized and opposite side framing will be highly brutalized.

Synthesis and characterization of negative thermal expansion of the Zr2(WO4)(PO4)2 system

In this study, Ti- and Mo-substituted Zr2(WO[Formula: see text](PO[Formula: see text] were synthesized using a conventional solid-state reaction technique. Coefficients of thermal expansions for samples were calculated by the results from the in situ high-temperature X-ray diffraction method. Doping with Ti[Formula: see text] reduces the voids occupied by the thermal vibration ellipsoid perpendicular to the bond axis. On the other hand, by doping Mo[Formula: see text], which has a smaller binding energy with oxygen atoms, thermal vibration in the direction of the bond axis is promoted. It is considered that the average linear thermal expansion coefficient became zero because the elliptical thermal vibration perpendicular to the coupling axis was suppressed by the synergistic effect of the co-doping of Ti and Mo.

A semi-empirical model for bond strength between FRP composites and concrete

An accurate estimate of fibre-reinforced polymer (FRP)–concrete bond is essential for a successful FRP repair. The present work aims at developing a semi-empirical model employing a large database (about 500 data points) collected from various literature works. In the beginning, an iterative regression process was followed to establish the trend in behaviour (of each key parameter against bond strength) and decide on insignificant ones. Then, the different equations were merged and manipulated into a simplified model with three regression constants. These were determined based on two-thirds of the database points using the statistical software SPSS. The key parameters involved in the final simplified model included concrete properties (compressive strength and maximum aggregate size) and mechanical and geometric characteristics of the FRP composites (axial stiffness and bond width and length). The proposed model showed a high fit of the regression database at 0.88 coefficient of determination (R2) with a very limited number of outliers. Moreover, the accuracy of prediction by the present model of the validation database far exceeds that of all well-known semi-empirical and empirical models. The sensitivity of the present model to the changes in the key parameters confirms the trend in behaviours reported in the various experimental works and models.

John-Teller Distortion in Octahedral hexaaquacopper (II) Transition for S=1/2, d9 Metal Complex

Jahn–Teller effect (JTE) describe how specific electrons distributions induce geometric deformation in molecules or ions. The distortion of Jahn–Teller (JT) takes place because of the uneven occupation of orbitals with the identical energies is disapproving. To prevent such inappropriate electronic arrangements, molecules distort (lose regularity), causing these orbitals to become non-degenerate. This distortion is most frequently seen in octahedral compounds, at which two axial bonds could be squeezed (compressed) or extend (elongated), leading to bond lengths that the different from equator bonds. The degeneracy of electronic states really isn’t accurately measured, but it would be measured precisely by the disparity in a concentration of electron among metal and the ligands upon on axil direction. The density functional theory has been used to calculate bond length in both cases geometry for , octahedral metal-complexes, the majority ordinary mechanism of distortion is elongation (z-out). In perfectly octahedral complexes deformation, the orbitals energy is changed more than the orbitals energy, causing elongation z-out distortion. The d-levels energy would be splitting in a ligand field throughout transition metal centers can frequently result in degenerate electron configurations that are subject to Jahn–Teller effects. In six-coordinate complexes of copper II ions. It is also significant in fewer regular oxidation levels of other transition ions with that count.

Slow-Relaxation Behavior of a Mononuclear Co(II) Complex Featuring Long Axial Co-O Bond.

Co(II) mononuclear complex with different coordination geometry would display various of field-induced single-ion magnet (SIM) behaviors. Here, we identify a field-induced single-ion magnet in a mononuclear complex Co(H2DPA)2·H2O (H2DPA = 2,6-pyridine-dicarboxylic acid) by the hydrothermal method. The long axial Co-O coordination bond (Co1‧‧‧O3) can be formed by Co1 and O3. Therefore, Co(II) ion is six-coordinated in a distorted elongated octahedron. AC magnetization susceptibilities show that the effective energy barrier is up to 43.28 K. This is much larger than most mononuclear Co(II). The distorted elongated octahedron caused by the axial Co-O coordination bond is responsible for the high effective energy barrier. The distribution of electron density in Co1 and O3 atoms in the long axial bond would influence the magnetic relaxation process in turn. Our work deepens the relationship between the effective energy barrier and the weak change of ligand field by long axial bonds, which would facilitate constructing SIM with high energy temperature.

Fibre optic measurements and model uncertainty quantification for Fe-SMA strengthened concrete structures

This investigation aimed at studying a novel strengthening method using ribbed memory-steel bars by means of quasi-static load experiments and computational modelling of large-scale concrete members in flexure. The first part of the study focussed on the strain in activated and non-activated memory-steel bars measured with a distributed fibre optic measurement system during external loading of strengthened slabs. In the second part, a computational cross-section analysis model was developed and enhanced with two uncertainty quantification methods: sensitivity analysis and Bayesian model calibration.The distributed fibre optic strain measurements enabled detailed monitoring of the peak strains owing to concrete cracking. The strain data was post-processed to obtain axial stress and bond shear stress in proximity to the largest bending crack. The sensitivity analysis provided the relative importance of the calibrated input parameters and their interdependencies. Model calibration quantified the uncertain parameters such as prestress, concrete parameters, and memory-steel constitutive laws, resulting in good accordance between the model and the experiments. The models were validated by independent strain measurements. Parametric studies enabled prediction of the effects of the investigated strengthening method on similar concrete members with different prestress, materials and geometries.

On the use of stereodynamical effects to control cold chemical reactions: The H + D2 ⟷ D + HD case study.

Quantum calculations are reported for the stereodynamic control of the H + D2 ↔ D + HD chemical reaction in the energy range of 1-50K. Stereodynamic control is achieved by a formalism similar to that reported by Perreault et al. [Nat. Chem. 10, 561 (2018)] in recent experimental works in which the alignment of the molecular bond axis relative to the incident relative velocity is controlled by selective preparations of the molecule in a specific or superposition of magnetic projection quantum numbers of the initial molecular rotational level. The approach presented here generalizes the experimental scheme of Perreault et al. and offers additional degree of control through various experimental preparations of the molecular alignment angle. Illustrative results presented for the H + D2 and D + HD reactions show significant control with the possibility of turning the reaction completely on or off with the appropriate stereodynamic preparation of the molecular state. Various scenarios for maximizing and minimizing the reaction outcomes are identified with the selective preparation of molecular rotational states.