Bond Lengths Research Articles

X-ray Structure of Eleven New N,N′-Substituted Guanidines: Effect of Substituents on Tautomer Structure in the Solid State

Guanidine-containing molecules are an interesting class of compounds within both medicinal and material sciences. Having knowledge of their tautomerism is key in designing guanidines that interact with biological and chemical receptors. However, there are limited data on the solid-phase structure of N,N′-substituted guanidines. Thus, eleven guanidines bearing a 4,6-dimethylpyrimidyl at one end and substituents of varying sizes and electronic properties at the other side, were synthesised, crystallised, and analysed by X-ray crystallography. Calculations of isolated molecules of tautomer energies and bond lengths were performed for comparison. One class of guanidines crystallised as a cis–trans tautomer with the shorter bond directed towards the pyrimidyl unit. When more electron-deficient aniline substituents were inserted, the crystallised tautomer changed to a cis–cis form where the shorter bond was directed towards the aniline. The switch in the tautomer structure is concluded to be due to both the electronic properties of the substituents and the intermolecular hydrogen bonding in the crystal lattice.

Static disorder in perovskite-type proton-conducting oxides BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La): a novel approach based on statistical analysis of numerous DFT simulated structures.

Perovskite-type proton-conducting oxides inherently include defects such as substitutional aliovalent cations, oxide ion vacancies, and interstitial protons. These defects introduce static disorder into their crystal structures. To investigate such disorder in BaSn1-xMxO3-x/2-(y/2)H2O (M = Ga, Sc, In, Y, La), we employ a novel approach based on density functional theory (DFT) simulations. This approach involves the structural optimization of a large number of relatively small, randomly constructed supercells, followed by statistical analysis of their geometric, energetic, and vibrational properties. Our key findings are as follows. The structural disorder becomes more pronounced as the dopant concentration increases, and as the dopant ionic radius increases from Sc to La. The O-H covalent bond lengths, as well as the number densities, of hydrogen atoms display clearly different distributions depending on whether the hydrogen atoms are trapped by aliovalent cations or not. The hydrogen-trapping energies appear to decrease as the geometric similarity of O-H covalent bonds between trapped and untrapped hydrogen atoms increases. Hydrogen atoms simultaneously trapped by more than one dopant atom exhibit considerable stability, potentially hindering proton diffusion at high dopant concentrations. The O-H stretching wavenumber decreases as the O-H covalent bond length increases, showing a very strong and nearly linear correlation between the two. The simulated IR absorption spectra show semi-quantitative agreement with the measured spectra. These new findings demonstrate the effectiveness of the present 'statistical' approach for investigating static disorder.

Utilization of Schiff base ligands to chelate Ag+ for highly specific and sensitive Hg2+/Ag+ immunoassay

In this study, a planar benzothiazole Schiff base derivative ZX1 was designed and synthesized to selectively precipitate silver ions, in conjunction with the immunoassay detection of Hg2+ ions. The silver chelation process was highly effective in the pH range of 7–10, with a silver ion precipitation ratio of 99.9 %. The coordination behavior of ZX1 with Ag+ was studied using a series of spectroscopic measurements, topography analysis and DFT calculation. The shortest bond distances were 2.251 and 2.254 Å between nitrogen atom of thiazole and Ag+. Weak interactions were analyzed using the interaction region indicator (IRI) method and VMD. The immunoassay was developed through an anti-Hg2+/Ag+ monoclonal antibody, which showed similar sensitivities for Ag+ and Hg2+. The selectivity and anti-interference ability of the Schiff base ligands were tested for some hard metal ions and several anions. With co-existence of interference ion Ag+, Hg2+ was detected in rice matrix solution with 77 %∼123.5 % recovery by addition of ZX1 as the masking reagent and 90.3 %∼115 % for wheat matrix. This research provides a promising immunoassay strategy for simultaneous detection of silver ions and mercury ions in food matrix by utilization of Schiff base ligands. This novel Schiff base ligand was then used as the pre-treatment reagent to remove silver ions within 5 min for detection of Hg2+ or detection of both Ag+ and Hg2+ based on a novel bi-specific heavy metal antibody.

Symmetry Breaking in a Triferrous Extended Metal Atom Chain.

Semilocal and random phase approximation (RPA) density functional theory (DFT) and complete active space (CASSCF + NEVPT2) methodologies were applied to investigate a new class of extended metal atom chain (EMAC) complexes. A novel triferrous complex has been synthesized recently that does not utilize the usual 2,2'-dipyridylamine (dpa) ligand framework, which essentially always results in a tetragonal coordination environment and general formula M3(dpa)4X2, where X is an anion. Instead, the triferrous complex utilizes a dianionic, 2,6-bis(trimethylsilylamido)pyridine ligand (L2-) resulting in the formation of trigonal complexes with general formula Fe3L3. To better understand the electronic structure of this complex, calculations were utilized to explore the experimentally isolated Fe3L3, and a smaller theoretical complex, in order to compare and contrast with the traditional dpa-based EMACs. Due to the absence of anionic, axial ligands, the sigma nonbonding orbitals formed from the metal d orbitals are lower in energy than in the dpa complexes, and compete with the pi bonding orbitals for occupation in the Fe3L3 complex. While the idealized geometry of these complexes is D3h, a helical distortion of the ligands and subsequent electronic symmetry breaking due to Jahn-Teller distortions are predicted utilizing both semilocal and RPA DFT methods, ending in a C2 structure that closely matches the reported crystal structure. Predicted Mössbauer isomer shifts and ultraviolet/visible (UV/vis) spectra also agree with the experimental data available in the literature. Magnetic coupling constants also indicate ferromagnetic coupling between nearest neighbor irons. Two-dimensional (2D) potential energy surfaces were calculated for a range of fixed Fe-Fe bond lengths, revealing a flat potential energy surface over a wide range of Fe-Fe bond lengths and verifying the ability of RPA to act as a higher-level check on semilocal DFT results. In order to verify the predicted high-spin ground state, CASSCF + NEVPT2 was applied to selected molecular configurations and confirmed the predictions made by DFT. These calculations shed light on the physical ground state electron configuration of Fe3L3 and correlate this electronic configuration with the available experimental data.

Atomistic insights into scratch-induced structural evolution of silica glass

Understanding the mechanism of scratch damage is vital to developing better scratch-resistant glasses. To this extent, employing molecular dynamics simulations and experiments, we investigate the scratch damage of silica glass against a rigid diamond indenter. The glass surface is pre-indented to a constant depth and then dragged to simulate a linear scratch, and the structural impact in the indent-to-scratch transitioning phase is examined. We observe that despite the differences in length and timescales, the simulated values of indentation hardness and coefficient of friction exhibit excellent agreement with experimental values from nanoindentation and atomic force microscopy experiments. Interestingly, analysis of the subsurface deformation in the scratched region reveals densification and shear flow, in contrast to pure densification, as in the case of indentation. Furthermore, similar percentages of recovery from experiments and simulation reveal that the reversible component of plastic deformation owing to densification is comparable in both cases. Finally, in contrast to the common hypothesis, we demonstrate that while the bond angles and lengths recover significantly, the ring structure does not recover upon annealing, although they exhibit some relaxation. Thus, the present study sheds new light on the crucial role of the medium-range structure of glasses subjected to scratch deformation.

High-Resolution Spectroscopy and Structure of Heavy Carbon Subchalcogenides: Tricarbon Selenide, C3Se.

Linear tricarbon selenide, C3Se, has been studied spectroscopically for the first time using a combination of high-resolution infrared and microwave techniques. Probing laser ablation products from carbon-selenium targets in a free jet expansion with He, initial spectroscopic detection was accomplished in the infrared at a wavelength of 5 μm in search of the ν1 vibrational fundamental. Along with the band of the most abundant isotopic species C380Se found centered at about 2039 cm-1, the corresponding bands of the C382Se, C378Se, C376Se, and C377Se isotopologues were also detected. Pure rotational spectra of the five C3Se isotopologues in the 8-18 GHz frequency range were observed in a supersonic jet expansion using chirped-pulse microwave spectroscopy of the discharge products of selenophene, c-C4H4Se. Spectroscopic analyses were guided by results from high-level quantum-chemical calculations carried out at the coupled-cluster level of theory using large correlation-consistent basis sets. Using the experimentally derived ground-state rotational constants of five isotopologues and calculated zero-point vibrational corrections, an accurate semiexperimental equilibrium carbon-selenium bond length is derived.

Unveiling the adsorption mechanism of propanehydrazine derivatives on magnesium oxide surface: Insights from computational approach

The use of green and effective inhibitors for preventing metal oxide (MgO) corrosion in industrial applications is highly significant in promoting environmental protection and sustainable development. This study delves into the adsorption behavior and interfacial mechanism of environmentally friendly inhibitor derived from propane hydrazine (PH) on MgO surface. Specifically, PH1, PH2, PH3, and PH4 were explored for their effectiveness in preventing corrosion by using advanced theoretical simulations-based density functional theory (DFT) for assessing the reactivity and adsorption characteristics. The study considered a detailed exploration of local and global reactivity descriptors, providing insights into the inhibitors’ reactivity and adsorption abilities in both isolated and adsorbed states. These findings focus more in the mechanisms underlying organic-inorganic interactions and present promising prospects for further development and application. Using first-principles DFT calculations alongside quantitative molecular surface analyses, we examined the adsorption patterns of PHs on the MgO(100) surface. These investigations are boosted by the application of independent gradient model (IGM) framework, providing robust verification of PHs' adsorption behavior on MgO(100) surface. Our calculations reveal a substantial decrease in the energy gap following complex formation, suggesting that charge density changes occur upon interaction with MgO surfaces, thereby facilitating direct electron transfer in all the studied systems. Noreover, the results highlight the crucial role of intermolecular interactions in boosting the interaction between PHs and the [Mg(H2O)6]2+ cation. First-principles DFT calculations show that all PH molecules consistently display parallel adsorption on the MgO surface, where the oxygen atoms form bonds with adjacent magnesium atoms. The bond lengths vary from 2.18 to 2.35 Å when PHs bind to the Mg atoms in parallel orientations through the oxygen atom, suggesting a stable parallel arrangement for PH molecules on the MgO surface. The calculated adsorption energy (Eads) varies in the following order: MgO-PH3 (−815.14 Kcal mol−1) > MgO-PH2 (−803.85 Kcal mol−1)) > MgO-PH4 (−695.38 Kcal mol−1) > MgO-PH1 (−125.77 Kcal mol−1). This trend indicates that parallel interactions enhance the adsorption behavior and binding of PH compounds through inter- and intra-molecular interactions, resulting in the PHs being centered at specific sites on the MgO surface. The potential enhancement in electrochemical properties is believed to stem from the synergistic interaction between the PHs and the MgO surface, which theoretically allows for a precise adjustment of their adsorption and interaction within the composite structure. This understanding provides a fundamental framework for examining the complex interfacial dynamics between inhibitor structures and elucidating how these molecular interactions influence the selection of corrosion inhibitors and their adsorption behaviors on the corrosion layer's surface, rather than on metallic Mg.

Theoretical investigations of optoelectronic properties, photocatalytic performance as a water splitting photocatalyst and band gap engineering with transition metals (TM = Fe and Co) of K3VO4, Na3VO4 and Zn3V2O8: a first-principles study.

First-principles density functional investigations of the structural, electronic, optical and thermodynamic properties of K3VO4, Na3VO4 and Zn3V2O8 were performed using generalized gradient approximation (GGA) via ultrasoft pseudopotential and density functional theory (DFT). Their electronic structure was analyzed with a focus on the nature of electronic states near band edges. The electronic band structure revealed that between 6% Fe and 6% Co, 6% Co significantly tuned the band gap with the emergence of new states at the gamma point. Notable variations were highlighted in the electronic properties of Na3V(1-x)Fe x O4, Na3V(1-x)Co x O4, K3V(1-x)Fe x O4, K3V(1-x)Co x O4, Zn3(1-x)V2(1-x)Co x O8 and Zn3(1-x)V2(1-x)Fe x O8 (where x = 0.06) due to the different natures of the unoccupied 3d states of Fe and Co. Density of states analysis as well as α (spin up) and β (spin down) magnetic moments showed that cobalt can reduce the band gap by positioning the valence band higher than O 2p orbitals and the conduction band lower than V 3d orbitals. Mulliken charge distribution revealed the presence of the 6s2 lone pair on Zn, greater population and short bond length in V-O bonds. Hence, the hardness and covalent character develops owing to the V-O bond. Elastic properties, including bulk modulus, shear modulus, Pugh ratio and Poisson ratio, were computed and showed Zn3V2O8 to be mechanically more stable than Na3VO4 and K3VO4. Optimal values of optical properties, such as absorption, reflectivity, dielectric function, refractive index and loss functions, demonstrated Zn3V2O8 as an efficient photocatalytic compound. The optimum trend within finite temperature ranges utilizing quasi-harmonic technique is illustrated by calculating thermodynamic parameters. Theoretical investigations presented here will open up a new line of exploration of the photocatalytic characteristics of orthovanadates.

A homochiral Nickel(II) complex [Ni(P'N)2]Cl2: Synthesis, characterization, crystal structure, luminescence, DFT and Hirshfeld surface studies

A new complex ([Ni(P'N)2]Cl2) is synthesized from an anhydrous NiCl2 and a bidentate P'N (S,S)-NH2CHPhCHPhPPh2) ligand with an enantiopure ethylene backbone. The solubility of the complex in methanol aids its crystallization by slow evaporation. A single crystal X-ray diffraction study of the complex reveals a distorted square planar geometry with the phosphinyl groups coordinated in a cis(P,P) configuration. This imposes steric effects that influence the crystal packing of the complex in an orthorhombic unit cell. The complex possesses characteristic metal to ligand charge transfer (MLCT) transition in the UV region with a peak absorption at 294 nm corresponding to 4.22 eV, which correlates with 4.24 eV derived from the DFT calculation of the energy band gap between the highest molecular orbital (HOMO:7.39 eV) and lowest unoccupied molecular orbital (LUMO:3.15 eV) of the complex. With an excitation wavelength of 415 nm (3.00 eV), the complex emits photons with wavelength 488 nm (2.54 eV) in the blue region of the visible spectrum. The circular dichroism spectrum has multiple peaks in the UV region mainly associated with transitions within the chiral array of phenyl groups. The bond lengths, bond angles, and vibrational bands obtained by simulation of the optimized structure of the complex provide analytical details that strongly correlate with the experimental data with adjusted R2 of 0.9826 (bond lengths), 0.9911 (bond angles) and 0.9983 (vibrational bands). The Hirshfeld surface analysis shows that H…H and C…H interactions between phenyl rings of the cations contribute significantly to the crystal packing of the complex.

4-Bromo-N,N′-diphenylbenzimidamide N′-oxide

The title compound, C19H15BrN2O, crystallizes with two similar molecules in the asymmetric unit. The extended structure features dimers linked by pairs of N—H...O and C—H...O hydrogen bonds. The HNCNO moiety of the title compound shows delocalization over the N—C—N part, as evidenced by the similar C—N bond distances.

Substrate topography regulating membrane adhesion mediated by receptor–ligand bonds

Cell adhesion can be significantly influenced by the topography of the substrate surface. However, how the adhesion molecules essentially respond to this topographical stimulus is not fully understood yet. Here, we employ an effective Monte Carlo simulation to systematically investigate a fluctuating membrane interacting with a curved substrate via adhesive proteins. Interestingly, results show that, compared with the flat substrate, curved substrates regulate the membrane adhesion in a bond length dependent manner. The effects of the substrate surface amplitude and wavelength on the number of molecular bonds and adhesion pattern are also extracted from the scaling relationship between the characteristic lateral length of the membrane and the local substrate curvature radius. Furthermore, the local substrate curvature is found to select the bond distribution in terms of the bond length and stiffness. The results suggest that the bond stiffness enhances the clustering of molecular bonds, mainly due to synergistic interactions among these molecular bonds.

Accurate Geometries of Large Molecules at DFT Cost by Semiexperimental and Coupled Cluster Templating Fragments.

Accurate geometries of small semirigid molecules in the gas phase are available thanks to high-resolution spectroscopy and accurate quantum chemical approaches. These results can be employed for validating cheaper low-level quantum chemical models or correcting the corresponding structures of large molecules. On these grounds, in this work, a large panel of semiexperimental equilibrium structures already available in the literature is used to confirm the average error (1 mÅ for bond lengths and 2 mrad for valence angles) of a version of the Pisa composite schemes (PCS2), which is applicable to molecules containing up to about 20 atoms. Then, the geometries of 30 additional medium-sized systems were optimized at the PCS2 level to cover a more balanced chemical space containing moieties poorly represented in SE compilations. The final database is available on a public domain Web site (https://www.skies-village.it/databases/) and can be employed for correcting structures of larger molecules obtained by hybrid or double-hybrid density functionals in the framework of the templating molecule approach. Several examples show that corrections based on the structures of building blocks taken from this database reduce the error of the B3LYP geometrical parameters of large molecules by nearly an order of magnitude without increasing the computational cost. Furthermore, the results of different density functional theory (DFT) or wave function (e.g., MP2) models can be improved in the same way by simply computing both the whole molecule and suitable building blocks at the chosen level. Then, whenever reference structures of some building blocks containing up to about 20 atoms are not available, they can be purposely optimized at the PCS2 level by employing reasonable computer resources. Therefore, a new DFT-cost tool is now available for the accurate characterization of large molecules by experiment-oriented scientists.

Integrating Pt single atoms and Mo into PtNi/C through Mo doping-displacement synchronisation strategy for enhanced HER at all pH values

This paper proposes a Mo doping-displacement synchronization strategy to integrate Pt SAs and Mo atoms into PtNi/C, synthesizing Pt SAs/Mo-doped PtNi octahedra/carbon support catalyst (Pt SAs/Mo-PtNi/C). In this approach, Mo atoms are doped into PtNi alloy octahedra and displace some Pt atoms, forming Mo-PtNi octahedra. Importantly, the substituted Pt atoms can adhere to carbon substrate, creating Pt SAs. Pt SAs/Mo-PtNi/C exhibits lower overpotentials (38, 59, and 110 mV at 10 mA cm−2) and smaller Tafel slopes (44, 51, and 139 mV dec-1) in acidic, alkaline, and neutral environments. Additionally, the electron pathway of Mo-PtNi → Pt SAs/C has been confirmed, and Pt SAs/Mo-PtNi/C exhibits an optimized hydrogen adsorption energy (ΔGH*=-0.29 eV). Furthermore, catalyzed by Pt SAs/Mo-PtNi/C, the H-O bond length of H2O extends to 1.11 Å and the bond angle reduces to 102.741°, directly confirming that the Pt SAs and doped Mo could facilitate H-O bond breaking. The proposed Mo doping-displacement synchronization strategy not only simplifies the fabrication process of Pt SAs catalyst, but also improves its durability and activity across a wide pH range, thereby potentially advancing hydrogen production technologies.

Investigating fracture mechanisms in glassy polymers using coupled particle-continuum simulations

We study the fracture behavior of glassy polymers using a multiscale simulation method that integrates a molecular dynamics (MD) system within a continuum domain. By employing a nonlinear viscoelastic constitutive model in the continuum domain, the MD system undergoes non-uniform deformation with flexible boundaries through interaction with the surrounding continuum. Systems with pre-defined double cracks are subjected to tensile stretch under various geometric constraints and bond breakage criteria. The simulation results show that geometric constraints primarily affect deformation behavior at small strains, but their influence diminishes at larger strains. In the stage of fracture, increased deformation correlates with a narrowing distribution of microscopic structures at molecular scales, such as bond length. This distribution converges across different systems just before fracture, irrespective of ultimate stress, fracture strain, bond breakage criteria, and geometric constraints. This convergence suggests that the distribution of microscopic structures is a fundamental property linked to the fracture behavior of glassy polymers.

Structural and Dynamical Effects of the CaO/SrO Substitution in Bioactive Glasses.

Silicate glasses containing silicon, sodium, phosphorous, and calcium have the ability to promote bone regeneration and biodegrade as new tissue is generated. Recently, it has been suggested that adding SrO can benefit tissue growth and silicate glass dissolution. Motivated by these recent developments, the effect of SrO/CaO-CaO/SrO substitution on the local structure and dynamics of Si-Na-P-Ca-O oxide glasses has been studied in this work. Differential thermal analysis has been performed to determine the thermal stability of the glasses after the addition of strontium. The local structure has been studied by neutron diffraction augmented by Reverse Monte Carlo simulation, and the local dynamics by neutron Compton scattering and Raman spectroscopy. Differential thermal analysis has shown that SrO-containing glasses have lower glass transition, melting, and crystallisation temperatures. Moreover, the addition of the Sr2+ ions decreased the thermal stability of the glass structure. The total neutron diffraction augmented by the RMC simulation revealed that Sr played a similar role as Ca in the glass structure when substituted on a molar basis. The bond length and the coordination number distributions of the network modifiers and network formers did not change when SrO (x = 0.125, 0.25) was substituted for CaO (25-x). However, the network connectivity increased in glass with 12.5 mol% CaO due to the increased length of the Si-O-Si interconnected chain. The analysis of Raman spectra revealed that substituting CaO with SrO in the glass structure dramatically enhances the intensity of the high-frequency band of 1110-2000 cm-1. For all glasses under investigation, the changes in the relative intensities of Raman bands and the distributions of the bond lengths and coordination numbers upon the SrO substitution were correlated with the values of the widths of nuclear momentum distributions of Si, Na, P, Ca, O, and Sr. The widths of nuclear momentum distributions were observed to soften compared to the values observed and simulated in their parent metal-oxide crystals. The widths of nuclear momentum distributions, obtained from fitting the experimental data to neutron Compton spectra, were related to the amount of disorder of effective force constants acting on individual atomic species in the glasses.

Design, synthesis, and biological evaluation of novel imidazole derivatives as analgesic and anti-inflammatory agents: experimental and molecular docking insights

Imidazole moieties exhibit a broad range of biological activities, including analgesic, anti-depressant, anticancer, anti-fungal, anti-tubercular, anti-inflammatory, antimicrobial, antiviral, and antifungal properties. In this study, we explored the use of Schiff base for the synthesis of new imidazole derivatives as anti-inflammatory and pain-relieving agents. A series of eight novel imidazole analogues (2a–h) were prepared in three steps with excellent yields. All compounds were characterized using IR, NMR, and mass spectral data. Their analgesic and anti-inflammatory activities were evaluated using hot plate and paw oedema methods. Compound 2 g (1-(2,3-dichlorophenyl)-2-(3-nitrophenyl)-4,5-diphenyl-1H-imidazole) showed significant analgesic activity (89% at 100 mg/kg b.w.), while compounds 2a (2-(2,6-dichlorophenyl)-1-(4-ethoxyphenyl)-4,5-diphenyl-1H-imidazole) and 2b (2-(2,3-dichlorophenyl)-1-(2-chlorophenyl)-4,5-diphenyl-1H-imidazole) exhibited good anti-inflammatory activity (100% at 100 mg/kg b.w.), comparable to diclofenac salt (100% at 50 mg/kg b.w.). Molecular docking studies were conducted using Schrödinger software version 2021-2, employing the OPLS4 force field for both receptor and ligand preparation. The results were visualized using molecular visualization software such as PyMOL. These studies revealed that compound 2g exhibited the highest binding affinity with the COX-2 receptor (−5.516 kcal/mol). Compound 2g formed three conventional hydrogen bonds with residues GLN-242 (bond length: 2.3 Å) and ARG-343 (bond lengths: 2.2 Å & 2.4 Å). This binding affinity was comparable to that of Diclofenac salt, which showed the highest binding affinity of −5.627 kcal/mol with the COX-2 receptor. Diclofenac salt formed two conventional hydrogen bonds with the residues ARG-344 (bond length: 2.0 Å) and TRP-140 (bond length: 1.7 Å). Later, molecular dynamic simulations confirmed the stable binding affinity of compound 2g with the protein. Furthermore, other compounds also demonstrated potential binding to the receptor-binding pocket region. The anti-inflammatory potential of the synthesized compounds was evaluated using the carrageenan-induced rat hind paw oedema model, while the analgesic potential was assessed using the hot plate method. These evaluations were conducted in comparison with Diclofenac sodium, serving as the standard compound. However, compound 2g stood out for its superior analgesic activity, as confirmed by in-vivo examination. These findings suggest that these novel imidazole derivatives have potential as anti-inflammatory and analgesic agents.

Functionalization of single-walled aluminum nitride nanotube with amino acids using the first principle's study

In this study, we investigate the functionalization of aluminum nitride nanotube (AlNNT) with amino acids (Phenylalanine, Arginine, and Glutamine) using first-principle density functional theory (DFT) calculations. DFT methods were applied to model the interactions between amino acids and AlNNT, exploring the structural and electronic features of the functionalized systems, and examining various aspects of the structures, including their geometry and electronic properties, such as bond lengths, bond angles, total energy, formation energy, band structure, chemical potential, density of states (DOS), projected density of states (PDOS), charge transfer, and electron difference density. The (5, 5) AlNNT exhibits an energy bandgap value of 3.31 eV, implying its semiconducting nature. Furthermore, the pure system's chemical potential was -4.12 eV. The DOS examination shows that the pristine system's band structure profile and energy states match well. Notably, the valence band displays a more pronounced level of energy hybridization compared to the conduction band, which is reflected in the band structure. Functionalization of AlNNT with amino acids enhances the p character and polar covalency, thereby increasing the percentage ionic character and Gibb's free energy of solvation which are essential parameters to determine the aqueous solubility.

Semiconducting Mixed Valence Sulfido (Selenido) Ferrates: Optical, Dielectric, and Electrochemical Impedance Properties

The ternary potassium sulfido and selenido ferrates K9[Fe2S(e)7] were synthesized as pure phases through a facile and straightforward solid‐state method. The compounds crystalize isotypic as has been reported previously. UV‐visible measurements indicate semiconductivity, showing direct optical band gaps with energies of 1.91 eV for the sulfido and 1.72 eV for the selenido ferrate. Investigations of dielectric and impedance properties provide their dielectric constants in the range of 60 to 74 at room temperature at a frequency of 1 kHz, as well as ionic conductivity values in the range of 2.08∙10–5 and 2.61∙10–5 mS·cm–1. Both, the dielectric constants and the calculated ionic conductivity of the selenido ferrate are higher compared to the sulfido ferrate, corresponding to the larger unit cell volume and increased bond lengths in the selenido ferrates. The dielectric constants are comparably higher than the reference material of SiO2, which might introduce them for dielectric applications.

Improving Predictions of Spin-Crossover Complex Properties through DFT Calculations with a Local Hybrid Functional.

We conducted a study on the performance of the local hybrid exchange-correlation functional PBE0r for a set of 95 experimentally characterized iron spin-crossover (SCO) complexes [Vennelakanti, V.; J. Chem. Phys. 2023, 159, 024120]. The PBE0r functional is a variant of PBE0 where the exchange correction is restricted to on-site terms formulated on the basis of local orbitals. We determine the free parameters of the PBE0r functional against the experimental data and other hybrid functionals. With a Hartree-Fock (HF) exchange factor of 4%, the PBE0r functional accurately reproduces the electronic and free-energy trends predicted in prior DFT studies for these 95 complexes by using the B3LYP functional. Larger values of HF exchange stabilize high-spin states. The PBE0r-predicted bond lengths tend to exceed the experimental bond lengths, although bond lengths are less sensitive to HF exchange than in global hybrids. The predicted SCO transition temperatures T1/2 from PBE0r correlate moderately with the experimental transition temperatures, showing a slight improvement compared to the previous modB3LYP-predicted T1/2. This study suggests that the PBE0r functional is computationally cost-effective and offers the possibility of simulating larger complexes with accuracy comparable to global hybrid functionals, provided the HF-exchange parameter is carefully optimized.

Cooperativity and halonium transfer in the ternary NCI···CH3I···-CN halogen-bonded complex: An ab initio gas phase study.

The strength and nature of the two halogen bonds in the NCI···CH3I···-CN halogen-bonded ternary complex are studied in the gas phase via ab initio calculations. Different indicators of halogen bond strength were employed to examine the interactions including geometries, complexation energies, Natural Bond Order (NBO) Wiberg bond indices, and Atoms in Molecules (AIM)-based charge density topological properties. The results show that the halogen bond is strong and partly covalent in nature when CH3I donates the halogen bond, but weak and noncovalent in nature when CH3I accepts the halogen bond. Significant halogen bond cooperativity emerges in the ternary complex relative to the corresponding heterodimer complexes, NCI···CH3I and CH3I···-CN, respectively. For example, the CCSD(T) complexation energy of the ternary complex (-18.27kcal/mol) is about twice the sum of the complexation energies of the component dimers (-9.54kcal/mol). The halonium transfer reaction that converts the ternary complex into an equivalent one was also investigated. The electronic barrier for the halonium transfer was calculated to be 6.70kcal/mol at the CCSD(T) level. Although the MP2 level underestimates and the MP3 overestimates the barrier, their calculated MP2.5 average barrier (6.44kcal/mol) is close to that of the more robust CCSD(T) level. Insights on the halonium ion transfer reaction was obtained by examining the reaction energy and force profiles along the intrinsic reaction coordinate, IRC. The corresponding evolution of other properties such as bond lengths, Wiberg bond indices, and Mulliken charges provides specific insight on the extent of structural rearrangements and electronic redistribution throughout the entire IRC space. The MP2 method was used for geometry optimizations. Energy calculations were performed using the CCSD(T) method. The aug-cc-pVTZ basis set was employed for all atoms other than iodine for which the aug-cc-pVTZ-PP basis set was used instead.