Statistical properties of the energies and electric dipole moments of the bound vibrational states of the system HCO/COH

From the ab initio calculated three-dimensional adiabatic double-minimum potential energy surface of the HCO⁺/COH⁺ system and the corresponding dipole moment surface the energies of all bound vibrational states and their effective dipole moments are determined applying the Suttcliffe–Tennyson Hamiltonian for triatomic molecules. The energy and dipole data are analysed in terms of statistical methods such as the density of states approach and the nearest-neighbor level spacing distribution (NNSD). Special effort is put into investigating the effect of the tunnelling motion across the isomerization barrier on the NNSD representations.     

Do intramolecular halogen bonds exist? Ab initio calculations and crystal structures’ evidences

Cl···O intramolecular contacts are analyzed here. Hence, the Cambridge Structural Database search was performed to find five-membered Cl–C=C–C=O pseudo-rings closed through Cl···O intramolecular contacts. Such rings were analyzed and it was found that some of Cl···O distances are smaller than the corresponding sum of van der Waals radii. Additionally ab initio MP2/6-311++G(d,p) calculations and AIM analyses were carried out here on 3-chloropropenal and its fluoro derivatives to deepen the nature of intramolecular Cl···O interactions, some of findings may indicate that they are attractive and stabilizing ones. This article is dedicated to Prof. T. M. Krygowski on the occasion of his 70th birthday.     

Fermi surface and metallic properties of graphite at high pressures

A potential of superconductivity of pure graphite has been theoretically examined. At normal pressure, the carrier concentration is too low to exhibit superconductivity. On applying pressure, the band dispersion along the c-axis is significantly enhanced, resulting in an increase in the carrier concentration; 10²⁰ cm^-3 at p=30 GPa. This is favorable to observe superconductivity. Accurate Fermi surfaces are illustrated: a new Fermi surface appears around K point at p=25 GPa.     

High-temperature crystal structure and electronic properties of cesium niobate Cs2Nb4O11

The antiferroelectric material Cs₂Nb₄O₁₁ transforms at 165 °C from a low-temperature, antiferroelectric phase in space group Pnna to a high-temperature, paraelectric phase in space group Imma; the latter structure has been determined by single-crystal X-ray diffraction. The high-temperature lattice is comprised of niobium-centered tetrahedra and octahedra connected through shared vertices and edges; cesium atoms occupy channels afforded by the three-dimensional polyhedral network. Calculated band structures for both phases predict a bandgap of 3.1-3.2 eV, which is similar to that found experimentally through photoluminescence. The calculated band structure is also conducive to its observed photocatalytic properties.     

Studies on the complexing behavior of a potentially tetradentate Schiff-base ligand with some transition metal ions

The Schiff base furfural-histidine with Co(II), Ni(II), Cu(II), and Zn(II) in solution gives M(AB), M(AB)B, or M(AB)₂. The Schiff base is tetradentate in M(AB)₂ and M(AB)B and tridentate in M(AB)₂; [M(AB)₂] · 2H₂O (M = Co, Ni and Zn) and [Cu(AB)]NO₃ were synthesized and characterized by elemental analysis, molecular weight determination, conductance, IR, UV–Vis, and CV. The electronic spectral measurements indicate that M(AB)₂ (M = Co(II) and Ni(II)) are octahedral and Cu(AB) is square planar geometry. The donor groups in the complexes have been identified by IR. The complexes undergo irreversible one step, two-electron reduction. Antibacterial activity of the complexes was screened for Escherichia coli and Staphylococcus aureus. Cu(II) complex was found to be more active than the Co(II), Ni(II), and Zn(II) complexes.     

2‐(Dinitromethylene)‐1‐nitro‐1, 3‐diazacyclopentane‐Based Energetic Salts

Energetic salts that contain nitrogen‐rich cations and the 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐1‐ene anion were synthesized in high yield by direct neutralization reactions. The resulting salts were fully characterized by multinuclear NMR spectroscopy (¹H and ¹³C), vibrational spectroscopy (IR), elemental analysis, density and differential scanning calorimetry (DSC), and elemental analysis. Additionally, the structures of the ammonium ( 1 ) and isopropylideneaminoguanidinium ( 9 ) 2‐(dinitromethyl)‐3‐nitro‐1, 3‐diazacyclopent‐l‐ene salts were confirmed by single‐crystal X‐ray diffraction. Solid‐state ¹⁵N NMR spectroscopy was used as an effective technique to further determine the structure of some of the products. The densities of the energetic salts paired with organic cations fell between 1.50 and 1.79 g · cm^–3 as measured by a gas pycnometer. Based on the measured densities and calculated heats of formation, detonation pressures and velocities were calculated using Explo 5.05 and found to to be 25.2–35.5 GPa and 7949–9004 m · s^–1, respectively, which make them competitive energetic materials.     

Ab initio investigation of the synthesis of (3-(2,3,4,5-tetramethylcyclopentadienyl)propoxy)titanium dichloride

The two-step synthesis of [η⁵:η¹-C₅Me₄(CH₂)₃O]TiCl₂ from [C₅Me₄(CH₂)₃OMe]TiCl₃ is investigated through molecular orbital calculations. Results of ab initio, restricted Hartree–Fock calculations at the 6-311G(d) basis set level are reported for the reactants, products, and an intermediate, [C₅Me₄(CH₂)₃OMe]TiCl₂(CHPPh₃). These results provide insight into the mechanism of the second reaction, which is found to be a charge-controlled intermolecular nucleophilic attack. The nature of the titanium–ylid bond in the intermediate complex is also reported.