Lithium–silicon Si n Li (n = 2–10) clusters and their anions: structures, thermochemistry, and electron affinities

The molecular structures, electron affinities, and dissociation energies of neutral Si _n Li (n = 2–10) species and their anions have been studied by the B3LYP and the BPW91 methods in conjunction with a DZP++ basis set. The geometries have been fully optimized with each of the proposed methods. The ground state structure of neutral Si _n Li keeps the corresponding Si _n framework unchanged. For anion, the corresponding Si _n (or ${{\rm Si}_{n}^{-}}$ ) framework changes largely when n ≥ 7. To evaluate the stability of the resulting anions we have calculated the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The dissociating energies of Li from the lowest energy structures of neutral Si _n Li and their anions are calculated to examine relative stabilities.     

Exploration of superhalogen nature of Pt(CN)n complexes (n = 1–6) and their abilities to form supersalts and superacids: a DFT–D3 study

Structural Chemistry - Unique superhalogen properties of Pt(CN)n complexes (n = 1–6) have been investigated under the quantum chemical formalism. The study involves theoretical calculations...     

Entrap and release of Phe–Phe nanotubes in sol–gel derived silicate matrix: study through nanosilver interaction

After the discovery of the ability of dipeptide self-assembly, numerous research activities have been reported on Phe–Phe dipeptide based nano-materials. However, entrapping peptide nanotubes in a silicate matrix has not been carefully studied. This paper reports on self-assembled Phe–Phe nanotubes entrapped in a silicate matrix derived by a simple, and modified acid mediated sol–gel approach. Here, interaction of silver nanoparticles with regained nanotubes from the silicate matrix is reported. Mass spectrometry data showed the self-assembly of peptide monomers. Scanning electron microscopy and transmission electron microscopy studies have been used to examine the shapes and sizes of the nano-structures, and the results provide a promising method for trapping peptide based nanotubes. UV–Visible spectra suggest that there are some effects of silicate environment around Phe–Phe NTs on its absorbance. Density functional calculations showed the probable type of interaction between peptide and Ag atoms. This study can be useful for future applications, which are based on immobilization strategy for drug carrying and sensing.     

Cu(II)-alkyl chlorocomplexes: stable compounds or transients? DFT prediction of their structure and EPR parameters

DFT calculations were used for studying the structure and reactivity of organocuprates(II) usually considered as intermediates with very weak Cu-C bond. It was found that calculated principal g-tensor values of model compounds RCu(II)Cl(2(-)) are similar to the experimentally found values for organocopper product of photolysis of quaternary ammonium tetrachlorocuprates. The calculations confirm that the most of organocuprates(II) could be stable at ambient conditions, and short lifetimes of organocuprates(II) in solutions or soft matrices are caused by their high reactivity in various bimolecular processes; the rate of those may be close to the rate of diffusion controlled reactions. The charges, spin densities, and d-orbital populations of the Cu atom in them are typical for bivalent copper complexes. Natural bond orbital analysis of organochlorocuprates(II) confirms the formation of polar σ-bond between copper and carbon atoms.     

Specific heat of ternary Ag–Si–Ge alloys from 123 K to high temperatures: experiment and prediction

Journal of Thermal Analysis and Calorimetry - The knowledge of specific heat for Ag–Si–Ge alloys in a broad temperature range would facilitate their practical applications in various...     

A DFT study on the structure–property relationship of amino-, nitro- and nitrosotetrazoles, and their N-oxides: new high energy density molecules

We explore herein the structure, stability, heat of explosion, density, and the performance properties of amino, nitro, and nitroso substituted tetrazoles and their N-oxides using the density functional theory calculations at the B3LYP/aug-cc-pVDZ level. N-Nitro compounds have lower densities compared with those of C-nitrotetrazoles. Kamlet-Jacob semi-empirical equations were used to calculate the performance properties of designed compounds. The higher performance of tetrazole-N-oxides is due to their higher densities (2.110–2.287 g/cm³). Heat of explosion, stability, density and performance properties are related to the number and relative positions of NO₂, NH₂, and NO groups of the tetrazole ring. The designed molecules satisfy the criteria of high energy materials.     

Solid Solutions of Grimm–Sommerfeld Analogous Nitride Semiconductors II-IV-N2 (II=Mg,Mn, Zn; IV=Si,Ge): Ammonothermal Synthesis and DFT Calculations

Grimm–Sommerfeld analogous II-IV-N₂ nitrides such as ZnSiN₂, ZnGeN₂, and MgGeN₂ are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II-IV-N₂ compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (II^a_1−xII^b_x)-IV-N₂ with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom-built, high-temperature, high-pressure autoclaves by using the corresponding elements as starting materials. NaNH₂ and KNH₂ act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite-type superstructures with space group Pna2₁ (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy-dispersive X-ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed-occupancy structures by using the KKR+CPA approach.     

Unprecedented π···π interaction between an aromatic ring and a pseudo-aromatic ring formed through intramolecular H-bonding in a bidentate Schiff base ligand: crystal structure and DFT calculations

A combination of a single crystal X-ray diffraction study and density functional theory calculations has been applied to a bidentate Schiff base compound to elucidate different cooperative non-covalent interactions involved in the stabilization of the keto form over the enol one in the solid state. The single crystal X-ray structure reveals a remarkable supramolecular assembly of the keto form through a cyclic hydrogen bonded dimeric motif. The most interesting feature in the supramolecular assembly is the formation of a 'dimer of dimer' motif by π···π, CH···π and N···O/O···O interactions in which the π···π interaction involving the aromatic phenyl ring and the intramolecularly hydrogen bonded pseudo-aromatic ring of the keto form lying just above or below the phenyl ring of the other dimer seems to be unprecedented. The optimized geometry of the hydrogen bonded dimeric motif of the keto form of the organic molecule has been obtained by DFT calculations and agrees very well with that found within the crystalline state. The X-ray crystallographic geometry of the 'dimer of dimer' has also been computed, which shows that in the HOMO, the π electrons are localized in the phenyl rings away from each other, while in the LUMO, there is a strong π-π interaction between the phenyl ring of one dimer with the pseudo-aromatic ring of another dimer with an energy estimated to be 7.95 kJ mol(-1). Therefore, on HOMO → LUMO excitation there is localization of π electrons in the central part of the complex moiety which plays a stabilizing role of the dimer of dimer motif in the solid state.     

Studying (n, 0) and (m,m) GaP nanotubes (n = 3–10 and m = 2–6) through DFT calculations of Ga-69 quadrupole coupling constants

We investigated properties of representative zigzag and armchair gallium phosphide (GaP) nanotubes by performing density functional theory (DFT) calculations. To achieve our purpose, eight models of (n,0) zigzag GaP nanotubes with n = 3–10 and five models of (m,m) armchair GaP nanotubes m = 2–6 were considered. Each model was firstly optimized and quadrupole coupling constants (C_Q) were subsequently calculated for gallium-69 atoms of the optimized structures. The results indicated that the optimized properties including dipole moments, energy gaps, binding energies, and bond lengths could be mainly dependent on the diameters of GaP nanotubes, which are directly determined by n or m indices. Moreover, comparing the values of C_Q parameters indicated that the narrower GaP nanotubes could be considered as more reactive materials than the wider nanotubes, in which the reactivities are very important in determining the applications of nanotubes. And finally, the atoms at the sidewalls of nanotubes could be divided into atomic layers based on the similarities of properties for atoms of each layer, in which the properties of Ga atoms at the edges of nanotubes are significantly different from other layers only for wider nanotubes.     

Comparison of Nitrogen Activation on Trinuclear Niobium and Tungsten Sulfide Clusters Nb3Sn and W3Sn (n=0–3): A DFT Study

The reaction of N₂ with trinuclear niobium and tungsten sulfide clusters Nb₃S_n and W₃S_n (n=0–3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N−N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb₃S_n is generally higher than that of W₃S_n. In the favorite reaction pathways, the adsorbed N₂ changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N−N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb₃S_n decreases because of the hindering effect of S atoms, while W₃S and W₃S₂ have the highest reactivity among four W₃S_n clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N₂ are analyzed along the reaction pathways to show the activation process of the N−N bond in reactions. The charge transfer from the clusters to the N₂ antibonding orbitals plays an essential role in N−N bond activation, which is more significant in Nb₃S_n than in W₃S_n, leading to the higher reactivity of Nb₃S_n. The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR).     

Reactions that generate aromatic molecules: is aromatic stabilization less or more advanced than bond changes at the transition state? Kinetic and thermodynamic acidities of rhenium carbene complexes

A kinetic study of the reversible deprotonation of the rhenium carbene complexes 1H(+)(O), 1H(+)(S) and 2H(+)(O) by carboxylate ions, primary aliphatic and secondary alicyclic amines, water and OH(-) in 50% MeCN-50% water (v/v) at 25 degrees C is reported. These carbene complexes are of special interest because in their deprotonated form they represent derivatives of the aromatic heterocycles furan, thiophene and benzofuran. Intrinsic rate constants (k(o) for Delta G degrees = 0) determined from appropriate Br?nsted plots for these rhenium carbene complexes and for the corresponding selenophene (1H(+)(Se)) and benzothiophene (2H(+)(S)) derivatives investigated earlier follow the orders furan < selenophene < thiophene and benzofuran less, similar benzothiophene. These orders indicate that an increase in aromaticity leads to an increase in the intrinsic rate constant or a decrease in the intrinsic barrier. This is an unexpected result; it implies that, in contrast to common resonance effects, the development of aromaticity at the transition state is ahead of proton transfer, i.e., the percentage development of the aromatic stabilization energy at the transition state is higher than the percentage of proton transfer.     

Photodisintegration of light and medium-weight nuclei at intermediate energies—V: Mass-yield dependence of true direct (γ,n) and (γ,p) reactions

The mass-yield dependence of (γ,n) and (γ,p) reactions in the photon energy range (0.2–1) GeV has been investigated. A Monte Carlo calculation for these reactions has been carried out to compare values of the measured cross sections with those arising from different models of interaction. Very good agreement was found between experiment and estimates based on a fast-step, direct character for the reaction mechanism. As a result of the analysis, N- and Z-dependences of mean cross sections are given for the (γ,n) and (γ,p) reactions. Agreement with a more sophisticated theory is also quite reasonable.     

Liquid–Liquid Equilibrium of Water + 1-Propanol or 1-Butanol + Dibutyl Ether Ternary Systems: Measurements and Correlation at Three Temperatures

Liquid–liquid equilibrium (LLE) date for the ternary systems of {water?+?1-propanol?+?dibutyl ether (DBE)} and (water?+?1-butanol?+?DBE) were determined at T?=?(293.15, 303.15, 308.15) K under atmospheric pressure. Distribution coefficients and separation factors of 1-propanol in the mixtures were calculated and are discussed. The influence of temperature on the liquid phase regions was analyzed. In addition, the experimental values were correlated well with the modified and extended UNIQUAC models; the modified UNIQUAC model represents the data better than the extended UNIQUAC model.     

Infrared and Raman spectroscopic investigations of methylammonium haloantimonates(III), [N(CH3)4−nHn]3 Sb2X9 (n = 0–3, X = Cl or Br), through their phase transitions

Infrared and Raman spectra of methylammonium chloroantimonates(III) of the general formula [N(CH₃)_4−nH_n]₃Sb₂Cl₉ with n = 0, 1, 2 and 3 and of the methylammonium bromoantimonate(III), (CH₃NH₃)₃Sb₂Br₉, have been investigated in detail across their phase transitions. Vibration modes due to CH₃ deformation and those involving the NH_n (n = 1, 2 and 3) groups show significant changes across the phase transitions of the chloroantimonates, besides those due to the Sb₂Cl₉ anion. The anion modes differ with the number of CH₃ groups since the nature of the anion itself changes, the free anion being present only in the quarternary compound. The high-temperature phases of the chloroantimonates seem to involve random orientations of the methylamino groups; a plastic-type state clearly manifests itself in the trimethyl and the tetramethylamino derivatives. A phase transition is predicted in all the chloroantimonates below 150 K, based on the changes in the anion bands at low temperatures. Changes in the IR and Raman spectra accompanying the phase transitions of (CH₃NH₃)₃Sb₂Br₉ and (CH₃NH₃)₃Bi₂Br₉ are similar and in the high-temperature phase of these compounds the (CH₃NH₃)⁺ cations ard oriented randomly.     

In situ formation of p–n junction: A novel principle for photoelectrochemical sensor and its application for mercury(II) ion detection

The discovery and development of photoelectrochemical sensors with novel principles are of great significance to realize sensitive and low-cost detection. In this paper, a new photoelectrochemial sensor based on the in situ formation of p–n junction was designed and used for the accurate determination of mercury(II) ions. Cysteine-capped ZnS quantum dots (QDs) was assembled on the surface of indium tin oxide (ITO) electrode based on the electrostatic interaction between Poly(diallyldimethylammonium chloride) (PDDA) and Cys-capped ZnS QDs. The in situ formation of HgS, a p-type semiconductor, on the surface of ZnS facilitated the charge carrier transport and promoted electron-hole separation, triggered an obviously enhanced anodic photocurrent of Cys-capped ZnS QDs. The formation of p–n junction was confirmed by P–N conductive type discriminator measurements and current–voltage (I–V) curves. The photoelectrochemical method was used for the sensing of trace mercuric (II) ions with a linear concentration of 0.01 to 10.0 µM and a detection limit of 4.6 × 10⁻⁹ mol/L. It is expected that the present study can serve as a foundation to the application of p–n heterojunction to photoelectrochemical sensors and it might be easily extended to more exciting sensing systems by photoelectrochemistry.     

Liquid–Liquid Equilibria of Oxygenate Fuel Additives with Water at 25°C: Ternary and Quaternary Aqueous Systems of Methyl tert-Butyl Ether and tert-Amyl Methyl Ether with Methanol or Ethanol

Experimental tie-line data have been determined for the ternary system water + methyl tert-butyl ether + tert-amyl methyl ether and the quaternary systems water + methanol + methyl tert-butyl ether + tert-amyl methyl ether, and water + ethanol + methyl tert-butyl ether + tert-amyl methyl ether at 25°C and ambient pressure. The experimental results have been satisfactorily correlated using the modified UNIQUAC and extended UNIQUAC models with ternary and quaternary, in addition to binary parameters.     

Vapor–liquid equilibrium of octane-enhancing additives in gasolines: 4. Total pressure data and GE for ternary mixtures containing isopropyl ether or benzene and n-heptane + 1-hexene at 313.15 K

The experimental isothermal P–x data at T=313.15 K for the two ternary systems (isopropyl ether+n-heptane+1-hexene) and (1-hexene+n-heptane+benzene) are reported. Data reduction by Barker’s method provides correlation for G^E. The Wohl expansion, also Wilson, NRTL and UNIQUAC models have been applied successfully to the ternary systems. The experimental data, in this work are not available in the literature.     

Enantiopure (P)- and (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5]helicenediols and their helicene analogues: Synthesis,amplified circularly polarized luminescence and catalytic activity in asymmetric hetero-Diels–Alder reactions

Three pairs of enantiopure (P)- and (M)-3,14-bis(o-hydroxyaryl)tetrahydrobenzo[5]helicenediols (ArOH-H[5]HOLs), and enantiomers (P)- and (M)-3,14-bis(o-hydroxyphenyl)benzo[5]helicene-diols (PhOH-[5]HOLs) were designed and synthesized. It was found that compared with ArOH-H[5]HOLs, PhOH-[5]HOLs not only showed obvious red-shifts in both absorption and emission spectra, but also exhibited more intense CPL with amplified g_lum, which might be attributed to the more rigid structure of PhOH-[5]HOLs. However, rigid PhOH-[5]HOLs was less effective in the catalytic asymmetric hetero-Diels–Alder (HAD) reactions than those of ArOH-H[5]HOLs with the flexible tetrahydro[5]helicene backbone that could adjust conformation to suit the substrates. Therefore, the helical chirality amplification and chirality transfer could be efficiently achieved by adjusting the rigid and flexible structures of helical molecules, which might provide a useful strategy to optimize the structure of helicence derivatives for their applications in chiroptical materials and asymmetric catalysis.     

Liquid–Liquid Equilibrium of the Quaternary Systems <Emphasis Type="Italic">n</Emphasis>-Octane or Decane + Toluene + Dimethyl Sulfoxide + Methanol or Ethanol at 298.15 K: Experimental Data and Correlation

In this work, the effect of addition of methanol or ethanol to dimethyl sulfoxide to extract toluene from alkanes was studied. Liquid–liquid equilibria data of the four quaternary systems: {methanol (1)?+?DMSO (2)?+?octane (3)?+?toluene (4)}, {ethanol (1)?+?DMSO (2)?+?octane (3)?+?toluene (4)}, {methanol (1)?+?DMSO (2)?+?decane (3)?+?toluene (4)} and {ethanol (1)?+?DMSO (2)?+?decane (3)?+?toluene (4)} were obtained at 298.15 K and 101.3 kPa. The thermodynamic consistency of the experimental data was verified using the Othmer–Tobias and Hand tests. Selectivities and distribution ratios of the four quaternary systems were calculated from experimental data to evaluate the capacity of these two mixed solvents to extract toluene from octane and decane. A comparison of the results obtained was carried out. The NRTL model was used to correlate experimental data and the correlated results are in good agreement with experimental data.