Composition Of Molecular Orbitals Research Articles

Exploring the structure and hydrogen storage capacity of CeHn0/+ clusters.

The unique 4f orbitals and abundant electronic energy levels of rare earth elements enable effective doping and modification to enhance hydrogen storage performance, making it an increasingly prominent focus of research. The structures of neutral and cationic CeHn0/+ (n = 2-20) clusters have been determined using the Crystal Structure AnaLYsis by Particle Swarm Optimization (CALYPSO) method in conjunction with density functional theory (DFT). Interestingly, the CeH13 and CeH14+ exhibit remarkable stability in the doublet state with Cs and C2v symmetry, respectively. The adsorption energy of CeHn0/+ (n = 2-20) suggests a preference for H atoms to chemically adsorb on Ce atoms. The analysis of molecular orbital composition reveals that the stability of both CeH13 and CeH14+ is attributed to the significant hybridization between the H 1s and Ce 4f orbitals. Both CeH13 and CeH14+ demonstrate significant hydrogen storage capacities, with values reaching 8.5 wt% and 9.1 wt%, respectively.

Theoretical research on the geometric structure and electronic properties of medium-sized LaHnq (n=2–20, q=0, 1) clusters

In cluster scientific research, determining the ground state structure is a fundamental aspect of investigating the properties and applications of clusters. However, the determination of the lowest-energy structure of clusters is not only a complex global optimization problem but also a crucial challenge in current cluster research. In the work the geometric structure and electronic properties of LaHn0/+ (n = 2–20) nanoclusters with potential for hydrogen storage are investigated using Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) method and Density Functional Theory (DFT). By calculating the average adsorption energy and hydrogen storage mass fraction, it is predicted that neutral LaH13 and cationic LaH14+ clusters exhibit high hydrogen storage densities of 8.6 wt% and 9.2 wt%, respectively. Furthermore, the molecular orbital composition and internal chemical bond binding mode were analyzed using adaptive natural density partition (AdNDP) and natural bond orbital (NBO). The results indicate that the strong hybridization between La 5d orbitals and H 1s orbitals is the primary factor contributing to the high stability of both neutral LaH13 and cationic LaH14+ clusters.

Crystal Structure, Hirshfeld Surface, Optical, Thermal, NLO, and DFT Analyses of 5‐Methyl‐1H‐Imidazole‐3‐Ium‐4‐ Carboxybutanoate crystal

AbstractAn organic 5‐methyl‐1H‐imidazole‐3‐ium‐4‐carboxybutanoate (5MIC) co‐crystal is grown by slow evaporation solution growth technique (SEST) at room temperature. The 5MIC is synthesized using 4‐methylimidazole and glutaric acid in a 1:1 ratio using methanol as a solvent. The 5MIC crystal lattice parameters are identified using single‐crystal X‐ray diffraction analysis. The experimental X‐ray diffraction (XRD) and DFT structural parameter values have good correlations. The intermolecular interactions of the 5MIC crystal are found using Hirshfeld surface and 2D fingerprint plots. The computed C–N stretching vibration of the imidazole ring is observed at 1498, 1233, and 1064 cm−1. The HOMO is located on 4‐methylimidazole moiety of 5MIC molecule. Densities of state are used to find out the molecular orbital compositions of the 5MIC molecule. Mulliken analysis shows that the C13 (−0.86) atom has the lowest negative charge. The MEP surface color coded of 5MIC lies between 7.950 e−3 and −7.950 e−3. The 5MIC molecule has four types of intermolecular transitions. The first‐order hyperpolarizability (β) value of 5MIC molecule is 5.48×10−30 esu. The 5MIC crystal is thermaly stable up to 146 °C. The photoluminescence emission is observed from 400 to 600 nm. The 5MIC crystal shows SHG characteristics.

Theoretical Explorations of Structural, Electronic, and Spectroscopic Properties of a Series of Ruthenium Schiff-Base Complexes

The present work concentrates on theoretical investigations of the substituent effects on the reactivity, electronic properties, and UV-vis spectra of a series of ruthenium-Schiff base complexes using density functional theory (DFT). Four complexes are studied herein, where N-(2¢-hydroxyphenyl)benzaldimine is the Schiff base differing in the para-substituent (R) on the benzaldehyde fragment (R = CH3, H, Cl, CF3). B3LYP/SDD-6-31G(d,p) level of theory has been used for computational studies (Gaussian 16). All the structures have been optimized, and the compositions of the frontier molecular orbitals have been analyzed. The energies of HOMO and LUMO and the global indices parameters have been calculated, which reveals that [Ru(PPh3)2(CO)(L-CF3)] is the most reactive complex and [Ru(PPh3)2(CO)(L-Cl)] the least. Time-dependent density functional theory (TDDFT) has been performed to study the electronic absorption parameters. The effect of solvent polarity upon absorption spectra has also been observed. It is found that the lowest energy absorptions in all the complexes show a blue shift with the increase in polarity of the solvent. Natural bond orbital (NBO) analysis of the complexes has been conducted to examine the charge distribution on the donor and the acceptor atoms along with their variation with change in the para-substituent.

Understanding the Coordination Chemistry of AmIII/CmIII in the DOTA Cavity: Insights from Energetics and Electronic Structure Theory.

The minor actinides Am/Cm show multiple possibilities for coordination, providing great opportunities for their extraction and adsorption separation. Herein, we report complexation in an aqueous medium of AmIII/CmIII in the DOTA (H4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) cavity with axial ligands (OH-, F-, and H2O), based on the energetics and electronic structure properties using density functional theory (DFT). The formation and substitution reactions of OH--capped complexes are more likely to occur due to their enhanced hydration Gibbs free energies, followed by F-, and then H2O. Both the longer An-ODOTA bond lengths and the larger bite angle (∠O-An-O) in the OH--capped complexes reflect the enhanced coordination provided by the axial ligand, slightly less so for F-. Energy decomposition analysis based on the electronic structure supports the preference for OH--capped complexes with a near-perfect balance between attractive and repulsive contributions toward the interaction. Furthermore, molecular orbital analysis revealed that the frontier molecular orbitals of Am and Cm complexes are substantially different; that is, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) compositions of the Am complexes are all contributed by 5f, while the HOMO and LUMO compositions of the Cm complexes are derived from 5f and 6d, respectively. Finally, the metal-exchange reactions demonstrate competitive complexation of DOTA toward AmIII over CmIII for the OH--capped system. These results imply the importance of coordination chemistry in actinide chemistry in general and specifically in AmIII/CmIII solution chemistry.

Theoretical prediction for growth behavior and electronic properties of monoanionic Ru2Gen− (n = 3–20) clusters

We present a detailed theoretical study on the structural and electronic properties of monoanionic Ru2Gen− (n = 3–20) clusters using comprehensive genetic algorithm combined with density functional theory (CGA-DFT). It is shown that the geometrical growth patterns of the ground state Ru2Gen− clusters are polyhedral pyramidal structures with n ≤ 9 and gradually to form pentagonal prism-based structures with two endohedral Ru atoms from 10 ≤ n ≤ 15, then the structures evolve into a oblate cage-like configuration with two Ru atoms in center from cluster sizes n ≥ 16. In general, one extra electron will influence the geometric structures of Ru2Gen clusters to compare with their neutral ones we have studied. Based on the obtained ground state structures, we find that the clusters of Ru2Ge10−, Ru2Ge12− and Ru2Ge14− have relatively higher structural and chemical stability in which Ru2Ge14− is more prominent through the analysis of binding energy, second order of energy difference and highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap. Furthermore, we analyzed natural charge, natural electronic configuration, the frontier molecular orbitals and orbital composition to verify the clusters of Ru2Gen− with n = 10, 12, 14 and 16 have relatively higher chemical stability owning to the less contribution of Ru-d orbitals. In addition, the clusters of Ru2Ge3−, Ru2Ge4−, Ru2Ge6−, Ru2Ge10− and Ru2Ge16− have magnetic moment of 3 μB, while others are 1 μB. And also the vertical detachment energy (VDE) and adiabatic detachment energy (ADE) for all ground state clusters are computed to support future experiment.

6p valence relativistic effects in 5d photoemission spectrum of Pb atom and bonding properties of Pb-dimer using Dirac–Hartree–Fock formalism including many-body effects

There has been strong recent interest related to the large spin–orbit coupling in Pb monolayers on various properties of graphene and other 2D-materials. The underlying physical/chemical origin of the spin–orbit splitting has been discussed in terms of the valence 6p atomic level of the lead atom. Indeed, the photoelectron spectra of the Pb atom were the subject of investigations about 50 years ago in Dave Shirley’s laboratory at UC Berkeley. In a paper published in 1975, using He-I UV photoelectron spectroscopy, we reported an unexpected relative intensity ratio for the observed atomic Pb peaks (2P1/2 and 2P3/2) after removal of a 6p valence electron and attributed it to the large spin–orbit interaction in that level. In this contribution, we use the Dirac–Hartree–Fock formalism to reanalyze the complex spectral features reported five years later, for the 5d He-II UV photoelectron spectrum of atomic lead, to extract the 6p valence contribution, which turns out to be significant. Furthermore, we calculate the energy levels of the Pb-dimer at the experimental equilibrium geometry of the molecule to also find the significant contribution of the spin–orbit splitting of the atomic 6p levels in the composition of the valence molecular orbitals of the dimer. Such an approach can be extended to larger systems like monolayers containing lead or other heavy atoms, thus helping in designing 2D-materials with controlled and better targeted properties.

Synthesis, characterization and SOD activity of bisbenzimidazole-based copper(II) complexes

Three bisbenzimidazole-copper(II) coordination complexes, [Cu(MIDB)(NO3)(CH3OH)](NO3) (1), [Cu(MIDB)(H2O)2](NO3)2 (2), and [Cu(ODB)2](ClO4)2 (3) (MIDB =N-methyl bis(benzimidazol-2-ylmethyl) amine; ODB = bis(2-benzimidazolylmethyl) ether), were synthesized and characterized. The component ions in their crystals are linked by N-H...O, O-H...O, C-H...π and π...π interactions into three-dimensional networks which are quantitatively manifested by the Hirshfeld surface analysis. Their frontier molecular orbital compositions and natural charge population were conducted theoretically at the DFT/(UB3LYP)/6-31G+(d, p) level for the copper coordination units, indicating that the HOMO and LUMO orbitals are mainly contributed by the benzimidazole groups and the coordination bonds are stabilized by the delocalized stabilization energy between the lone-pair bonding orbitals from N and/or O atoms and the lone-pair anti bond orbitals of the copper center. The cyclic voltammetry showed irreversible one-electron redox reactions for the three complexes in DMF solutions. SOD activity of 1 (IC50=1.34 µM) was slightly better than that of 3 (IC50=1.36 µM) by using the NBT method.

Electronic, Vibrational, and Structural Study of Polysaccharide Agar-Agar Biopolymer

Polysaccharide biopolymer Agar-Agar extracted from red algae is a natural and biodegradable polymer. It is a combination of agarose (a neutral and linear polymer, with repeated units of agarobiose) and a heterogeneous mixture of agaropectin (a charged sulfated polymer). In this study, a comparative study of structural vibrational and electrochemical properties of agar-agar biopolymer with two different methods HF (Hartree-Fock) and DFT (Density Functional Theory) using a basis set 631+G (d, p) is performed. The comparative structural study of agar-agar biopolymer by HF and DFT method has been carried out to calculate the stability of the molecule. The thermionic properties and Mulliken charge distribution are analysed to deliver a quantitative study of partial atomic charge distribution. The overall vibrational analysis of primal modes of the biopolymer has been studied using FTIR analysis. Based on highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) composition and energies, various chemical parameters of the biopolymer have been evaluated. The Physico-chemical properties of this polysaccharide show a strong correlation with its optimized structure. Agar-agar has its application in the electrochemical, biotechnological, and pharmaceutical fields, as a stabilizer and gelling material.

Fluoride ion‐induced gas sensor based on the dipyrromethene boron difluoride derivative: A theoretical investigation

AbstractIn this study, density functional theory (DFT) studies were performed to evaluate the response of the BODIPY derivative (BNDP−) as a gas sensor toward CO2, COS, SO2, SO3, H2S, and NH3. The sensing ability of the BNDP− interacting with the gases was described in terms of geometric, electronic, and optical properties. Results showed that the strong interactions between BNDP− and the gases were ascribed to the short linkage distance and the large variation of geometries. The AIM analysis was used to shed light on the sensor mechanisms of the BNDP− toward the gases. The spectroscopic properties, UV‐vis absorption and fluorescence emission spectra, revealed the behavior of the interaction of BNDP− with these gases. These parameters, including the compositions of the frontier molecular orbitals and the values of orbital energy gaps, indicated that the BNDP− had good sensitivity toward CO2, COS, SO2, and SO3.

Theory of Long-Lived Room-Temperature Phosphorescence in Organic Aggregates.

ConspectusRoom-temperature phosphorescence (RTP) with a long afterglow from purely organic molecular aggregates has recently attracted many investigations because traditionally only inorganic and transition-metal complexes can emit phosphorescence at room temperature. Purely organic molecules can exhibit phosphorescence only at cryogenic temperatures and under inert conditions in solution. However, recently, a number of organic compounds have been found to demonstrate bright RTP upon aggregation, sometimes with a remarkable morphology dependence. We intended to rationalize such aggregation-induced organic RTP through theoretical investigation and quantum chemistry calculations by invoking intermolecular interaction effects. And we have identified the molecular descriptors for the molecular design of RTP materials.In this Account, we started with the proposition of the mechanism of intermolecular electrostatic-interaction-induced RTP at the molecular level by using molecular dynamics simulations, hybrid quantum mechanics, and molecular mechanics (QM/MM) coupled with the thermal vibration correlation function (TVCF) formalism we developed earlier. The effective intermolecular electrostatic interactions could stem from a variety of interactions in different organic RTP crystals, such as hydrogen bonding, π-halogen bonding, anion-π+ interaction, and d-pπ bonds and so forth. We find that these interactions can change the molecular orbital compositions involved in the lowest-lying singlet and triplet excited states that are responsible for phosphorescence, either through facilitating intersystem crossing from the excited-state singlet to the triplet and/or suppressing the nonradiative decay process from the lowest triplet to the ground state. This underlying RTP mechanism is believed to be very helpful in systematically and comprehensively understanding the aggregation/crystal-induced persistent organic RTP, which has been applied to explain a number of experiments.We then propose the molecular descriptors to characterize the phosphorescence efficiency and lifetime, respectively, derived from fundamental photophysical processes and requirements to obey the El-Sayed rule and generate phosphorescence. For a prototypical RTP system consisting of a carbonyl group and π-conjugated segments, the excited states can be regarded as an admixture of n → π* (with portion α) and π → π* (with portion β). The intersystem crossing (ISC) rate of S1 → Tn is mostly governed by the modification of the product of α and β, and the nonradiative rate of T1 → S0 is determined by the β value of T1. Thus, we employ γ = α × β and β to describe the phosphorescence efficiency and lifetime, respectively, which have been successfully applied in the molecular design of efficient and long-lived RTP systems in experiments. The molecular descriptors outlined in this Account, which are easily obtained from simple quantum chemistry calculations, are expected to play important roles in the machine-learning-based molecular screening in the future.

A rare hetero-bimetallic Zn(II)/Ca(II) Schiff base complex: Synthesis, crystal structure, DFT, molecular docking and unveiling antimicrobial activity

A new hetero-bimetallic Zn(II)/Ca(II) complex, [Zn2(LOMe-pn)2(ƞ1-NCS)2Ca] (1) has been synthesized using a potentially hexadentate N2O4 proligand, H2LOMe-pn = N,N-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3 diamine and structurally well characterized by different physicochemical techniques. Single crystal X-ray diffraction study of the complex revealed that, de-protonic form of the ligand utilizes two pockets, one is occupied by Zn(II) ion and other is housed by a Ca(II) ion. The Zn centres are fitted into the N2O2 compartment with distorted square pyramidal geometry while a large open O2O2′ compartment is occupied by a Ca(II) ion in a octacoordinated environment. DFT studies were successfully carried out using DFT/M06 functional level and 6–31 G * basis set (over all the atoms) to delineate the complex optimized structure, composition of the frontier molecular orbitals, global reactivity, total energy frameworks, MEP, total dipole moment, average polarizability and first hyperpolarizability. First hyperpolarizability value (59.62 × 10−31 esu) suggests that complex is a good NLO material. Hirshfeld surface revealed the presence of many short intermolecular contacts like C⋯H/S⋯H/N⋯H/O⋯H/H⋯H/C⋯C and S⋯S in the crystal structure. The experimental absorption spectra are comparable with the electronic transitions assigned from TD-DFT studies. CHEF based (π→π*) luminescence property has been measured in DMSO solvent at room temperature. Concentration dependant antibacterial efficacy was investigated against gram-negative bacterial strains viz. E. coli (ATCC 25,922) & Pseudomonas aeruginosa (ATCC 27,853) and gram-positive bacterial strains viz. Staphylococcus aureus (ATCC 25,923) & Bacillus subtilis (ATCC 6633). The bacterial killing efficiency and solvent effect of the complex was compared with that of ligand. Finally, a docking study with the active site of DNA Gyrase and DNA Polymerase III proteins has been carried out to corroborate the experimental findings.

Actinide 2-metallabiphenylenes that satisfy Hückel's rule.

Aromaticity and antiaromaticity, as defined by Hückel's rule, are key ideas in organic chemistry, and are both exemplified in biphenylene1-3-a molecule that consists of two benzene rings joined by a four-membered ring at its core. Biphenylene analogues in which one of the benzene rings has been replaced by a different (4n+2) π-electron system have so far been associated only with organic compounds4,5. In addition, efforts to prepare a zirconabiphenylene compound resulted in the isolation of a bis(alkyne) zirconocene complex instead6. Here we report the synthesis and characterization of, to our knowledge, the first 2-metallabiphenylene compounds. Single-crystal X-ray diffraction studies reveal that these complexes have nearly planar, 11-membered metallatricycles with metrical parameters that compare well with those reported for biphenylene. Nuclear magnetic resonance spectroscopy, in addition to nucleus-independent chemical shift calculations, provides evidence that these complexes contain an antiaromatic cyclobutadiene ring and an aromatic benzene ring. Furthermore, spectroscopic evidence, Kohn-Sham molecular orbital compositions and natural bond orbital calculations suggest covalency and delocalization of the uranium f2 electrons with the carbon-containing ligand.

Synthesis, spectroscopic and DFT studies of Schiff based (E)-N′-(Benzo[d][1, 3]Dioxol-5-ylmethylene)nicotinohydrazide monohydrate single crystal: a promising organic nonlinear optical material

(E)-N′-(benzo[d][1, 3]dioxol-5-ylmethylene)nicotinohydrazide monohydrate (BDMNH) material was synthesized by Schiff based method. The BDMNH material crystalizes in monoclinic crystal system with a space group of P21/n. The molecular structure was confirmed by 1H-NMR and 13C-NMR spectrum. The BDMNH compound has two rings namely piperonal and pyridine. The carbon-carbon stretching vibrations of piperonal ring have been observed at 1567 cm−1 in FT-IR and 1590 cm−1 in FT-Raman. The H…H (34.6%) interaction occupies the highest portion in the total area of Hirshfeld surface. The peak is observed at 376 nm in the electronic spectrum of the title compound reveals that the transition is π-π*. The EHOMO and ELUMO values are found to be −5.27 eV and −1.57 eV, respectively. The oxygen atom O3 possess high negative charge (−0.3573) comparing with the other oxygen atoms like O5, O9 and O32. From the partial density of states (PDOS) spectrum, fragment orbitals (H, C, N, and O) are contributing to the molecular orbitals composition. The molecular orbital interactions σ (N8–C14) → σ*(C7–C15) and σ (C10–H22) → σ*(C14–C18) have the stabilization energy values of 22.87 and 26.48 kJ mol−1, respectively. The third order nonlinear absorption coefficient value β = 6.246 × 10−5 cm/W.

Molecular orbital composition and its effect on electron-impact ionization cross sections of molecules: A comparative study

The composition of molecular orbitals (MO) is the key parameter in the calculation of electron-impact ionization cross sections (Qion) of a molecule using the Deutsch-Märk method. There are a few theoretical approaches for determining the MO composition, such as Mulliken-like methods [including Mulliken analysis, Stout-Politzer (SP) analysis, and c-squared population analysis] and natural atomic orbital (NAO) method. However, almost all the previous works chose the Mulliken analysis without explanation, which is arbitrary and can lead to meaningless results in some cases. In order to give a guide on how to select an appropriate method for the MO composition and reveal the effect of the MO composition on Qion, a comparative study is presented in this work based on the results of quantum chemical computation. It is found that the Mulliken-like and NAO methods output similar MO compositions for occupied orbitals and much different MO compositions for virtual orbitals. The results by the Mulliken and SP methods are not always in the range of 0%–100% for virtual orbitals. Moreover, the Mulliken-like methods are more dependent on basis sets than the NAO method. This basis-set dependence exists not only in the MO composition but also in ionization cross sections of molecular shells. As a result, we conclude that the NAO method is the best choice for the MO composition in calculating the Qion of a molecule.

Calculation of electron-impact ionization cross sections of perfluoroketone (PFK) molecules CxF2xO (x = 1–5) based on Binary-Encounter-Bethe (BEB) and Deutsch-Märk (DM) methods

Perfluoroketone (PFK) gases are widely used in industry, e.g. as an insulating medium in high-voltage apparatus and as a cleaning agent in chemical vapor deposition (CVD) chambers. A great deal of attention has been paid to them recently because of their low global warming potential (GWP). In order to describe the ionization processes in various plasmas resulting from PFK gases, the electron-impact ionization cross sections (Qion) of PFK molecules CxF2xO (x = 1–5) were calculated by the Binary-Encounter Bethe (BEB) and the Deutsch-Märk (DM) methods. The chemical structures of PFK molecules were optimized by the hybrid Density Functional Theory (DFT) method with the Austin-Petersson-Frisch functional including dispersion (APF-D). The binding and kinetic energies of electrons in molecular orbitals were also determined with the APF-D hybrid DFT method. The binding energies of valence electrons were then improved by the electron propagator theory (EPT) method. The ionization potentials of PFK molecules were calculated as the difference between the energy of a molecule and its cation using the complete basis set (CBS) method. The molecular orbital compositions were obtained by the natural atomic orbital (NAO) analysis. The results show that Qion determined by the BEB method are always larger than those by the DM method. The difference is reduced with the EPT corrections considered. The comparison between the theoretical and experimental Qion demonstrates that the EPT correction improves Qion considerably.

Choice of a spin singlet or triplet: electronic properties of Bis-Co(II), Bis-Ni(II), Bis-Cu(II) and Bis-Zn(II) oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1).

Fused hexaphyrins have many physical and chemical properties and can coordinate transition metal ions. In this study, we investigated the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-states of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a closed shell as previously reported. Moreover, based on analyses of the spin density and spin population of the spin triplet ONCP-d-Co and ONCP-d-Cu complexes, the charge transfer in ONCP-d-Cu is greater than that in ONCP-d-Co because the spin density in ONCP-d-Cu is concentrated not only on the Cu ion but also on the ONCP ligand. Thus, the CDA value for ONCP-d-Cu is larger. Finally, through comparative analysis of the FMO compositions and absorption spectra, the complexes and ligand are shown to have very similar absorption spectra with characteristics that arise mainly from π → π* transitions both in the B-band and the Q-band, which is due to the FMO compositions being dominated by the highly delocalized conjugated system, rather than by the metal ions. The absorption maxima of the Q-band are ONCP-d-Co (1020nm) > ONCP-d-Zn (1012nm) > ONCP-d-Ni (997nm) > ONCP-d-Cu (988nm), which is inversely proportional to the energy gap in their FMOs. Graphical Abstract The present work investigates the geometric structure, charge decomposition analysis (CDA), spin density, frontier molecular orbital (FMO) compositions and absorption spectra of four oxygen doubly N-confused hexaphyrin (1.1.1.1.1.1) (ONCP) complexes with the metal ions Co(II), Ni(II), Cu(II) and Zn(II) (designated ONCP-d-Co, ONCP-d-Ni, ONCP-d-Cu and ONCP-d-Zn). Based on their energies, geometric structures, FMO characteristics and comparison to experiments, ONCP-d-Co and ONCP-d-Cu have the mix-state of the triplet state and broken-symmetry state (antiferromagnetic state) rather than the spin singlet of a close shell as were previously reported. Meanwhile, ONCP-d-Ni and ONCP-d-Zn show spin singlet structure. The calculated CDA shows the following order: ONCP-d-Cu (1.487) > ONCP-d-Ni (1.255) > ONCP-d-Co (1.211) > ONCP-d-Zn (1.201). Through comparisons of spin density and spin populations of ONCP-d-Co and ONCP-d-Cu, charge transfer between Cu and ligand ONCP is greater than that of Co and ONCP, which makes the CDA value of ONCP-d-Cu obviously larger than that of the other complexes.

Photo-induced reduction of Cr6+ by the hybrid systems “CuII complex with Schiff base and TiO2”: dependence on irradiation wavelength

The synthesis of novel CuII complexes with a Schiff base obtained by condensation of salicylaldehyde and an l-aspartic acid ester are described. The physicochemical properties of the complexes were compared with those of related CuII complexes obtained earlier. All the complexes studied were characterized by elemental analysis as well as by IR, UV-Vis, and EPR spectroscopies. The activity of the complexes and their hybrid systems (HS) with TiO2 in visible-light-driven photocatalysis in organic solvents was investigated. After irradiation with visible light, the complexes and corresponding HS reduce Cr6+ to Cr3+ more efficiently than bare TiO2. To determine the molecular orbital compositions and energies and to explain the electronic spectra and redox properties of the systems studied, density functional calculations of the optimized structures of representative model complexes were performed.

Synthesis and properties of furan/thiophene substituted difluoroboron β-diketonate derivatives bearing a triphenylamine moiety

Two novel triphenylamine-modified difluoroboron β-diketonate derivatives containing either a furan or thiophene unit (2c and 2d) have been designed, synthesized and fully characterized. The effects of the triphenylamine substituent and different electron-rich heterocycle units (2-furyl and 2-thienyl) on the photoluminescence and electrochemical properties of these new BF2 complexes were investigated systematically. The two complexes bearing an electron-donating triphenylamine moiety showed broad absorption and intense emission bands in toluene with high fluorescence quantum yields. Significantly larger Stokes shifts were observed for these complexes in comparison to those of the corresponding reference complexes (2a and 2b). Cyclic voltammetry measurements revealed the amphoteric redox properties of the two new BF2 complexes. The results indicated that the introduction of a triphenylamine substituent into BF2 complex could result in large differences in their properties. However, making a contrast between 2c and 2d, it is found that replacing furan with thiophene in the BF2 complex showed slight effects on optical and electrochemical properties. The results of DFT calculations supported the structural and spectroscopic data and confirmed the compositions of frontier molecular orbitals in the BF2 complexes.

Investigating nanoscale mineral compositions: IronL3-edge spectroscopic evaluation of iron oxide and oxy-hydroxide coordination

The iron (Fe) L 2,3 -edge X-ray absorption near-edge structure (XANES) spectrum is sensitive to the local coordination environment around the Fe metal center, making it a useful probe for understanding Fe mineral speciation. The two dominant spectral peaks in the Fe L 3 -edge are parameterized according to the difference in the energy position (ΔeV), and the quotient (intensity ratio) of the two peaks’ maxima. Variations in the ΔeV value are strongly linked to factors that impact on the strength of the ligand field (e.g., Fe valence state, coordination number, and the nature of ligand bonding). The intensity ratio is affected by the strength of the ligand field and by the composition of the resultant molecular orbitals. The Fe valence state also strongly affects the intensity ratio, and an intensity ratio equal to one can be used to distinguish between Fe 2+ and Fe 3+ minerals. The effects of polyhedral distortion on the magnitudes of ΔeV and intensity ratio values were tested by considering the Fe oxide and -oxy-hydroxide mineral system, in which ligand effects are limited to the differences between the oxygen and hydroxyl ligands. In this system, the distribution of Fe oxide and -oxy-hydroxide minerals on a ΔeV vs. intensity ratio two-parameter plot could be explained by considering the Fe valence state, the ligand chemistry and the site symmetry of the Fe polyhedra. Furthermore, the ΔeV and intensity ratio values were found to be anti-correlated with respect to the various distortion measures considered in this study (e.g., polyhedral volume distortion percentage). This two-parameter plot is thus presented as a standard-less phase-specific identification tool for use in Fe speciation studies, applicable to both natural systems (e.g., aerosols, aquatic colloids) as well as to engineered systems (e.g., nanoparticle synthesis). A major advantage of this technique is that it is applicable to both crystalline and poorly crystalline phases, thus enhancing our ability to study amorphous and nano-crystalline phases that are typically difficult to characterize using X-ray diffraction techniques.