Longer Bond Research Articles

Vibron Softening of Solid Hydrogen under Nanoconfinement.

The vibron behavior of hydrogen bears significant importance for understanding the phases of solid hydrogen under high pressure. In this work, we reveal an unusual high-pressure behavior of hydrogen confined within nanopores through a combination of experimental measurements and theoretical calculations. The nanoconfined hydrogen molecules retain an hcp lattice up to 170 GPa, yet significant deviations from the vibrational characteristics of bulk hydrogen are observed in the primary vibrons of both Raman and infrared spectra. This lowered vibron peak is linked to the disorder of the hydrogen molecules with longer bonds and enhanced intermolecular interactions at the interface. Further investigation reveals that this nanoscale confinement leads to a considerable decrease in the band gap of solid hydrogen, potentially facilitating band gap closure at considerably lower pressures. Our findings provide crucial insights into the behavior of solid hydrogen under spatial nanoconfinement, paving the way for novel explorations into hydrogen metallization.

Hydrogen Bonds Stabilize Chloroselenite Anions: Crystal Structure of a New Salt and Donor-Acceptor Bonding to SeO2.

The single-crystal X-ray diffraction structure characterizing a new 4-methylbenzamidinium salt of chloroselenite [C8H11N2][ClSeO2] is reported. This is only the second crystal structure report on a ClSeO2- salt. The structure contains an extended planar hydrogen bond net, including a double interaction with both O atoms of the anion (an R228 ring in Etter notation). The anion has the shortest Se-Cl distances on record for any chloroselenite ion, 2.3202(9) Å. However, the two Se-O distances are distinct at 1.629(2) and 1.645(2) Å, attributed to weak anion-anion bridging involving the oxygen with the longer bond. DFT computations at the RB3PW91-D3/aug-CC-pVTZ level of theory reproduce the short Se-Cl distance in a gas-phase optimized ion pair, but free optimization of ClSeO2- leads to an elongation of this bond. A good match to a known value for [Me4N][ClSeO2] is found, which fits to the Raman spectroscopic evidence for this long-known salt and to data measured on solutions of the anion in CH3CN. The assignment of the experimental Raman spectrum was corrected by means of the DFT-computed vibrational spectrum, confirming the strong mixing of the symmetry coordinate of the Se-Cl stretch with both ν2 and ν4 modes.

Component Distribution Regulation in Sn-Pb Perovskite Solar Cells through Selective Molecular Interaction.

Tin-lead (Sn-Pb) perovskite solar cells (PSCs) with near-ideal bandgap still lag behind the pure lead PSCs. Disordered heterojunctions caused by inhomogeneous Sn/Pb ratio in the binary perovskite film induce large recombination loss. Here, an Sn-Pb perovskite film is reported with homogeneous component and energy distribution by introducing hydrazine sulfate (HS) in Sn perovskite precursor. HS can form hydrogen bond network and coordinate with FASnI3 thus no longer bond with Pb2+ , which reduces the crystallization rate of tin perovskite to the level of lead analog. The strong bonding between SO4 2- and Sn2+ can also suppress its oxidation. As a result, the Sn-Pb PSCs with HS exhibit a significantly improved VOC of 0.91 V along with a high efficiency of 23.17%. Meanwhile, the hydrogen bond interaction network, strong bonding between Sn2+ and sulfate ion also improve the thermal, storage, and air stability of resulting devices.

Beyond the ionic radii: A multifaceted approach to understand differences between the structures of LnNbO4 and LnTaO4 fergusonites

Synchrotron X-ray powder diffraction methods have been used to obtain accurate structures of the lanthanoid tantalates, LnTaO4, at room temperature. Three different structures are observed, depending on the size of the Ln cation: P21/c (Ln = La, Pr), I2/a (Ln = Nd-Ho), and P2/c (Ln = Tb-Lu). BVS analysis indicated that TaV is six-coordinate in these structures, with four short bonds and two longer bonds. Synchrotron X-ray powder diffraction methods were also used to observe the impact of Ta doping on the orthoniobates, Ln(Nb1-xTax)O4 (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Yb, and Lu). Where both the niobate and tantalate oxide were isostructural (fergusonite structure, space group I2/a), complete solid solutions were prepared. In these solid solutions, the unit cell volume decreases as the Ta content increases. The subtle interaction evident between the LnO8 and BO6 sublattices in the fergusonite-type oxides was not observed in the related pyrochlore oxides. A combined synchrotron X-ray and neutron powder diffraction study of the series Ho(Nb1-xTax)O4 was used to determine accurate atomic positions of the anions, and hence, bond lengths. This revealed a change in the (Nb/Ta)-O bond lengths, reflective of the difference in the valence orbitals of Nb(4d) and Ta(5d). Examination of the partial density of states demonstrates differences in the electronics between Nb and Ta, leading to a difference in the bandgap. This study highlights the importance of the long B-O contacts in the fergusonite structures, and its potential impact on the I2/a to I41/a phase transition.

Unveiling structural, electronic properties and chemical bonding of (VH2)n (n=10–30) nanoclusters: DFT investigation

The geometries, electronic properties, and chemical bonding of (VH2)n (n=10–30) nanoclusters are systematically investigated by a combination of artificial bee colony optimization with density functional theory calculations. Structure analysis indicates that the structures of (VH2)n nanoclusters tend to be a disorder, where the hydrogen atoms prefer to occupy the hollow sites among different V atoms, binding three V atoms to form the HV3 moieties. The bond length suggests that the average V–V bond lengths are about 2.60 Å, and the average V–H bond lengths are near 1.86 Å, which close to the experimental values of 2.77 Å and 1.79 Å for the V–V and V–H of bulk vanadium hydride, respectively. Interestingly, the coordination numbers of V–H fluctuate around 5.50 in the nanoclusters, and the corresponding value of H–V is estimated at 3.00. Moreover, the electronic properties and chemical bonding analyses indicate that d orbitals of V atoms and s orbitals of H atoms have a relatively large overlap to form sigma bonds. Specifically, the σ molecular orbital of H2 can donate electronic density to the d orbital of V atom, exhibiting the Kubas interaction in V24H48 and V29H58 nanoclusters. Kubas interaction results in a longer bond between the hydrogen molecule and the V atom.

Exceptionally Long Covalent CC Bonds-A Local Vibrational Mode Study.

For decades one has strived to synthesize a compound with the longest covalent C−C bond applying predominantly steric hindrance and/or strain to achieve this goal. On the other hand electronic effects have been added to the repertoire, such as realized in the electron deficient ethane radical cation in its D form. Recently, negative hyperconjugation effects occurring in diamino-o-carborane analogs such as di-N,N-dimethylamino-o-carborane have been held responsible for their long C−C bonds. In this work we systematically analyzed CC bonding in a diverse set of 53 molecules including clamped bonds, highly sterically strained complexes such as diamondoid dimers, electron deficient species, and di-N,N-dimethylamino-o-carborane to cover the whole spectrum of possibilities for elongating a covalent C−C bond to the limit. As a quantitative intrinsic bond strength measure, we utilized local vibrational CC stretching force constants (CC) and related bond strength orders BSO n(CC), computed at the B97X-D/aug-cc-pVTZ level of theory. Our systematic study quantifies for the first time that whereas steric hindrance and/or strain definitely elongate a C−C bond, electronic effects can lead to even longer and weaker C−C bonds. Within our set of molecules the electron deficient ethane radical cation, in D symmetry, acquires the longest C−C bond with a length of 1.935 Å followed by di-N,N-dimethylamino-o-carborane with a bond length of 1.930 Å. However, the C−C bond in di-N,N-dimethylamino-o-carborane is the weakest with a BSO n value of 0.209 compared to 0.286 for the ethane radical cation; another example that the longer bond is not always the weaker bond. Based on our findings we provide new guidelines for the general characterization of CC bonds based on local vibrational CC stretching force constants and for future design of compounds with long C−C bonds.

Synthesis of a Series of Dual-Functional Chelated Titanate Bonding Agents and Their Application Performances in Composite Solid Propellants.

Titanate-based bonding agents are a class of efficient bonding agents for improving the mechanical properties of composite solid propellants, a kind of special composite material. However, high solid contents often deteriorate the rheological properties of propellant slurry, which limits the application of bonding agents. To solve this problem, a series of long-chain alkyl chelated titanate binders, N-n-octyl-N, N-dihydroxyethyl-lactic acid-titanate (DLT-8), N-n-dodecyl-N, N-dihydroxyethyl-lactic acid-titanate (DLT-12), N-n-hexadecyl-N, N-Dihydroxyethyl-lactic acid-titanate (DLT-16), were designed and synthesized in the present work. The infrared absorption spectral changes of solid propellants caused by binder coating and adhesion degrees of the bonding agents on the oxidant surface were determined by micro-infrared microscopy (MIR) and X-ray photoelectron spectroscopy (XPS), respectively, to characterize the interaction properties of the bonding agents with oxidants, ammonium perchlorate (AP) and hexogen (RDX), in solid propellants. The further application tests suggest that the bonding agents can effectively interact with the oxidants and effectively improve the mechanical and rheological properties of the four-component hydroxyl-terminated polybutadiene (HTPB) composite solid propellants containing AP and RDX. The agent with longer bond chain length can improve the rheological properties of the propellant slurry more significantly, and the propellant of the best mechanical properties was obtained with DLT-12, consistent with the conclusion obtained in the interfacial interaction study. Our work has provided a new method for simultaneously improving the processing performance and rheological properties of propellants and offered an important guidance for the bonding agent design.

No longer bond’s girl: Historical displacements of the top female spy in 1960s taiyupian

When the 1960s Bond craze reached Taiwan, the taiyupian produced a hugely popular new archetype: the female 007. Although the films in this sub-genre evoked Bond’s code name of 007, Bond gadgets, and high-stakes espionage, they reversed the gender of the top spy. This was dramatized in the narrative through the hidden identity of 007, who is often a glamorous female figure embedded in enemy ranks and swoops in in masked attire to save her team of agents. Meanwhile, the top male spy remains in the dark and believes it is his role to take responsibility for the team. Often 007’s lover, he is ultimately proved incompetent and dependent upon her prowess as top spy; his role, too, is a reversal of gender and agency. This paper explores the cinematic history and context for this gender irony. With close readings of 1964’s Female Agent No.7 and The Best Secret Agent, I argue that the female action lead had a radically different meaning in taiyupian as compared to British and American cinemas, or even other Sinophone and East Asian cinemas, due to its resonance with a specifically Taiwanese narrative of historical redemption. Furthermore, the reversal of 007’s gender points to the taiyupian’s sense of irony regarding its marginal status among other cinemas, and its embrace of the element of surprise inherent in the outsider’s role.

Realizing negative Poisson's ratio in spring networks with close-packed lattice geometries

When randomly displacing the nodes of a crystalline and unstressed spring network, we find that the Possion's ratio decreases with the increase of structural disorder and even becomes negative. Employing our finding that longer springs tend to contribute more to the shear modulus but less to the bulk modulus, we are able to achieve negative Poisson's ratio with lower structural disorder by attributing each spring a length dependent stiffness. Even with perfect crystalline structure, the network can have negative Possion's ratio, if the stiffness of each spring is set by its virtual length after a virtual network distortion. We also reveal that the nonaffine contribution arising from the structural or spring constant disorder produced in some cooperative way by network distortion is essential to the emergence of negative Poisson's ratio.

Iridium-Promoted B–B Bond Activation: Preparation and X-ray Diffraction Analysis of a mer-Tris(boryl) Complex

The tris(boryl) complex Ir(Bcat)3{κ3-P,O,P-[xant(PiPr2)2]} [Bcat = catecholboryl; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene] has been prepared and characterized by X-ray diffraction analysis. The boryl ligands are disposed in a mer arrangement. The Ir-B bonds situated mutually trans are ∼0.1 Å longer than that disposed cis to the other two. An energy decomposition analysis method coupled to natural orbitals for chemical valence has revealed that the level of π-back-donation from the metal to the p z atomic orbital of the boron atom decreases ∼43% in the longer bonds with respect to the shorter one, while the level of σ-bonding interaction diminishes by only ∼8%.

Probing Amyloid β and the Antibody Interaction Using Atomic Force Microscopy.

Amyloid β (Aβ) peptide is considered to be the critical causative factor in the pathogenesis of Alzheimer's disease (AD) because the hydrophilic molecules accumulated outside of the neural cells and results in the formation of highly toxicity amyloid plaque. In this study, we probed the interaction between Aβ and the antibody using atomic force microscopy (AFM). We compared two kinds of antibodies which are the antibody for Aβ 1-42 (antibody42) and the antibody for Aβ 1-16 (antibody16). To detect the interaction between Aβ and the antibodies, the single molecular force spectroscopy was carried out using Aβ modified glass substrate and the antibodies modified AFM probes. In the results, the single Aβ-antibody42 dissociation constant was estimated to be 5.2 × 10-3 s-1 and the single Aβ-antibody16 dissociation constant was 2.8×10-2 s-1. The Aβ-antibody42 showed 5.3 times longer bond life time compare with Aβ-antibody16. It suggested that antibody42 is better choice for the Aβ sensor development.

Influence of ligand-receptor interactions on force-extension behavior within the freely jointed chain model.

We study the influence of receptor-ligand interactions on the force response of single polymer chains theoretically. The extension of the chain is modeled in terms of freely jointed chain or elastic freely jointed chain (EFJC) models. The situation involving noninteracting bonds is solved exactly, while effects of interactions are treated within a mean-field approximation. The form with shorter bonds governs the low force situation, while the form with longer bonds is relevant in the high force regime. We further discuss the accuracy of approximate relations, which were used to describe the response of the EFJC model.

Anomalous local lattice disorder and distortion in A2Mo2O7 pyrochlores

We present an extended X-ray absorption fine structure study of the pyrochlores A2Mo2O7 (A = Gd, Dy, Ho, Er), as a function of temperature. While in the three spin-glass compositions Dy2Mo2O7, Ho2Mo2O7 and Er2Mo2O7 the Debye temperatures are in accordance with other pyrochlores and the static disorder contributions are compatible with a lattice frustration, in the low-temperature-ferromagnetic Gd2Mo2O7 system we point out an anomalous enhancement of the local structure disorder below about 225 K down to low temperatures. Moreover, considering the general pyrochlore predisposition towards structural disorder, we prove the presence on a local scale of at least a bimodal distribution of the Mo-O(1) octahedral interatomic distances for all the studied compounds, consisting of two shorter and four longer bond lengths.Our results suggest that the local structure order parameter plays an important role in the ferromagnetic or spin-glass phase stabilization.

A three-pronged approach to strong halogen bonds – crystallographic, solution and computational study of N-halosuccinimide-pyridine complexes

Over the past couple of decades halogen bonds (XB) have transformed from an obscure intermolecular interactions known only to a handful of experts into an indispensable tool of crystal engineering rivalling even to hydrogen bond (HB). However, detailed studies of XB energetics are still quite scarcer than those for HB. In our study we have used commercially available N-iodo, N-bromo- and N-chlorosuccinimide (NIS, NBS, NCS) as halogen bond donors, succinimide (S) as an equivalent HB donor, and 7 p-substituted pyridines as halogen (or hydrogen) bond acceptors. The pyridins have been selected to cover as wide as possible range of Hammet coefficients (-0.88 to 0.66), while avoiding functionalities which could act as hydrogen bond donors. This has ensured a relatively large variability of XB acceptor qualities, while ensuring that the observed XB is the only strong intermolecular interaction. In order to provide a detailed description of the halogen bonding in these systems, N-halosuccinimides were crystallised with the pyridines in order to study the formed complexes in the solid state. Simultaneously, microcalorimetric measurements were made to study the formation of halogen bonded complexes in acetonitrile solution, and, extensive computations in order to study the deformation of electron density upon XB formation, as well as the effect of various geometric parameters on the energy of XB. Solid state studies have shown that NIS and NBS form strong halogen bonds with all 7 pyridine derivatives. NIS is expectedly a better XB donor (N…X distances 29-32% shorter than the sum of van der Waals radii for NIS and 23-29% shorter for NBS). In both cases the more nucleophilic pyridine nitrogen atoms were better XB acceptors forming shorter bonds. The scattering of the datapoints was larger in the case of NBS indicating wider and more shallow potential well for XB with NBS, as confirmed computationally. The differences in the measured bond lengths were mirrored in the stability of the NIS-pyridine complexes in the solution - the stability constants were found to vary by over three orders of magnitude from logK = 4.003(9) for the complex exhibiting the shortest XB to logK = 0.825(3) for the one with the longest bond. In comparisson, S was found to produce hydrogen-bonded cocrystals only with the two strongest nucleophiles used, and the corresponding stability constants were nearly four orders of magnitude lower than those for halogen bonded complexes with NIS.

Alkoxide bridged Copper(II) Hinokitiolato and Tropolonato Complexes: Polymorphism, Reconstructive Phase Transition, and Magnetic Properties

AbstractPolymorphism and an unexpected reconstructive phase transition in [Cu(trop)(μ‐OMe)]2 (trop = tropolonate) were studied by single crystal and powder X‐ray diffraction; the phase transition is associated with a huge hysteresis of ca. 200 °C. In the readily reproducible crystal form, the methoxide‐bridged dinuclear subunits aggregate to infinite chains by longer bonds in the Jahn‐Teller distorted coordination sphere. Analogous alkoxide‐bridged derivatives with the substituted ligand hinokitiol (hino), [Cu(hino)(μ‐OR)]2 (R = Me, Et, iPr) form pairs of dinuclear complexes and aggregate to discrete tetranuclear molecules. The inter‐cation distance patterns are reflected in the magnetic properties of these two structure types: Strong antiferromagnetic coupling within the dinuclear subunits is observed in either case, but susceptibility measurements confirm differences in exchange coupling between neighboring central CuII atoms.

Investigations of the Fe sulfosalts berthierite, garavellite, arsenopyrite and gudmundite by Raman spectroscopy

AbstractArsenopyrite (FeAsS), gudmundite (FeSbS) and the rarer Fe sulfosalts berthierite (FeSb2S4) and garavellite (FeSbBiS4), were investigated by Raman spectroscopy. Whereas (Sb,Bi)S3 pyramids are responsible for the Raman spectra of berthierite and garavellite, the spectra of gudmundite and arsenopyrite arise from the stretching and bending modes of (Sb,As)S units. Internal vibrations for berthierite and garavellite occur between 400 and 50 cm–1, and those of the gudmundite and arsenopyrite between 500 and 100 cm–1. The longer bond distances of the SbS3 groups readily explain the lower frequencies for berthierite in comparison with garavellite. Similarly, the greater mass and the longer bond distances of the Sb–S units also explain the lower frequencies observed for gudmundite relative to arsenopyrite.

X-Ray Absorption Spectroscopy Analysis of the Effect of MnO2 Doping on Local Structure of ((K0.5Na0.5)0.935Li0.065)NbO3 Ceramics

In this work, the extend x-ray absorption fine structure (EXAFS) analysis was performed in combination with the density functional theory (DFT) calculation to investigate local structure of Mn-doped ((K0.5Na0.5)0.935Li0.065)NbO3. From the structural relaxation, Mn3+ is substituted on Nb5+ to produce oxygen vacancy in the longest bond length in c-axis. Further, from the EXAFS Fourier transform comparison in R-space, the bond lengths between Mn3+ and O2− are almost equal in both ab- and c-axis with increasing Mn-doping contents. This is strong evidence that Mn-doping played an important role in producing the polarization domains in opposite direction, which diminish remnant polarization, pinning the domains wall movement and increase coercive field.

Synthesis, characterisation and X-ray studies of mixed-ligand triruthenium cluster complexes, Ru3(CO)9(arphos)(L), where L = PCy3, PPh3, P(C6H4F-m)3, P(C6H4F-p)3, P(C6H4Cl-p)3 and PPh(C6H4OMe-p)2

Six trinuclear substituted complexes of the type Ru3(CO)9(arphos)(L) were synthesized by a substitution reaction involving Ru3(CO)10(arphos) (1) with L, where L=PCy3, PPh3, P(C6H4F-m)3, P(C6H4F-p)3, P(C6H4Cl-p)3 and PPh(C6H4OMe-p)2, using a thermal method. The structures of the resulting clusters were elucidated by single crystal X-ray diffraction, complemented by means of elemental analysis and spectroscopic methods, including infrared spectroscopy and 1H, 13C{1H} and 31P{1H} NMR spectroscopy. The longest Ru–Ru bond in Ru3(CO)9(arphos)(L) [L=PCy3 (2), P(C6H4F-m)3 (4), P(C6H4F-p)3 (5), P(C6H4Cl-p)3 (6) and PPh(C6H4OMe-p)2 (7)] is the bond that is cis to the monodentate phosphine ligands, while in Ru3(CO)9(arphos)PPh3 (3), the longest bond is the bond that is bridged by the arphos ligand.

Natural Bond Orbital (NBO) Population Study of Some Para-Substituted N-Methyl-N-nitrosobenzenesulfonamide Biological Molecules in MeCN Solution

A theoretical study of several para-substituted N-methyl-N-nitrosobenzenesulfonamide biological molecules in MeCN solution has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with the 6-311++G(d,p) basis set. Geometries obtained from DFT calculations were used to perform natural bond orbital analysis. The results show that an intramolecular hydrogen bond exists in the selected molecules, which is confirmed by the NBO analysis. The p characters of the two nitrogen natural hybrid orbitals \( \sigma_{{{\text{N}}3 - {\text{N}}2}} \) increase with increasing \( \sigma_{p} \) values of the para-substituent group on the benzene ring, which results in a lengthening of the N3–N2 bond. It is noted that the weakness of the N–N bond is due to \( n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} \) delocalization and is responsible for the longer N3–N2 bond. In addition, there is a direct correlation between hyperconjugation \( n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} \) and the bond dissociation energy in the system, which is confirmed by comparison with isoelectronic isomers.

The Relation Between the Bandgap and the Anisotropic Nature of Hydrogenated Amorphous Silicon

The bandgap of hydrogenated amorphous silicon (a-Si:H) is studied using a unique set of a-Si:H films deposited by means of three different processing techniques. Using this large collection of a-Si:H films with a wide variety of nanostructures, it is demonstrated that the bandgap has a clear scaling with the density of both hydrogenated divacancies (DVs) and nanosized voids (NVs). The presence of DVs in a dense a-Si:H network results in an anisotropy in the silicon bond-length distribution of the disordered silicon matrix. This anisotropy induces zones of volumetric compressed disordered silicon (larger fraction of shorter than longer bonds in reference to the crystalline lattice) with typical sizes of ~0.8 up to ~2 nm. The extent of the volumetric compression in these anisotropic disordered silicon zones determines the bandgap of the a-Si:H network. As a consequence, the bandgap is determined by the density of DVs and NVs in the a-Si:H network.