Study of the reaction of chalcone analogs of dehydroacetic acid and o-aminothiophenol: synthesis and structure of 1,5-benzothiazepines and 1,4-benzothiazines

Treatment of α,β-unsaturated carbonyl compounds, obtained by the reaction of DHA and aromatic (or heteroaromatic) aldehydes, with o-aminothiophenol results in the formation of 1,5-benzothiazepines and/or 1,4-benzothiazines depending upon the reaction conditions and structure of the aldehydes. The products were characterized by the combined use of multinuclear 1D and 2D NMR and GIAO/DFT calculations of ¹H, ¹³C and ¹⁵N chemical shifts. The tautomerism of these compounds in solution was determined, they have an exocyclic CC double bond.     

Metallic behavior of the Zintl phase EuGe2: combined structural studies, property measurements, and electronic structure calculations

The Zintl compound EuGe₂ crystallizes in the trigonal space group (No. 164) with the CeCd₂-structure type. Its structure can be formally derived from the hexagonal AlB₂-structure type by a strong puckering of the hexagonal layers. The chemical bonding in EuGe₂ can be rationalized according to the Zintl concept as (Eu²⁺)(Ge¹⁻)₂, since the europium atoms are divalent and each germanium atom receives one additional valence electron. In that sense, EuGe₂ is expected to be a closed-shell compound with semiconducting behavior. However, temperature dependent resistivity measurements show EuGe₂ to be metallic. Subsequently, detailed crystallographic studies revealed the structure and the composition of EuGe₂ to be free of defects and impurities, which, along with the confirmed divalent oxidation state of the europium atoms by means of magnetic measurements, make EuGe₂ another example of a metallic Zintl phase. These results are in good agreement with the results of electronic structure calculations such as TB-LMTO-ASA (LDA) and FLAPW (GGA), which reveal non-zero DOS at the Fermi level.     

Functionalized Crystalline N-Trimethyltriindoles: Counterintuitive Influence of Peripheral Substituents on Their Semiconducting Properties

Three crystalline N-trimethyltriindoles endowed with different functionalities at 3, 8 and 13 positions (either unsubstituted or with three methoxy or three acetyl groups attached) are investigated, and clear correlations between the electronic nature of the substituents and their solid-state organization, electronic properties and semiconductor behavior are established. The three compounds give rise to similar columnar hexagonal crystalline structures; however, the insertion of electron-donor methoxy groups results in slightly shorter stacking distances when compared with the unsubstituted derivative, whereas the insertion of electron-withdrawing acetyl groups lowers the crystallinity of the system. Functionalization significantly affects hole mobilities with the triacetyl derivative showing the lowest mobility within the series in agreement with the lower degree of order. However, attaching three methoxy groups also results in lower hole mobility values in the OFETs (0.022 vs. 0.0014 cm² V⁻¹ s⁻¹) in spite of the shorter stacking distances. This counterintuitive behavior has been explained with the help of DFT calculations performed to rationalize the interplay between the intramolecular and intermolecular properties, which point to lower transfer integrals in the trimethoxy derivative due to the HOMO wave function extension over the peripheral methoxy groups. The results of this study provide useful insights into how peripheral substituents influence the fundamental charge transport parameters of chemically modified triindole platforms of fundamental importance to design new derivatives with improved semiconducting performance.     

Electronic Structure of a Bi-Doped Σ = 13 Tilt Grain Boundary in ZnO

We have investigated Bi doping in the bulk and in a = 13 tilt grain boundary in ZnO using ab-initio DFT-calculations. We obtain a negative segregation energy suggesting that bismuth accumulates in the grain boundary. The Bi-atom causes considerable atomic displacements in the grain boundary increasing the local Bi–O bond length and attracting an O-atom on the opposite side of the structural unit in the grain boundary. The results suggest the formation of a Bi–rich phase in the grain boundary. The Bi-atoms act as donors and the conduction electrons are quasi-localised in the grain boundary region.     

Theoretical investigation of von Braun and von Braun-like reactions

The von Braun reaction, discovered at the dawn of the past century, consists of the reaction between a tertiary amine and cyanogen bromide. It leads to the cleavage of a C─N bond with the formation of an N-dialkylcyanamide and an alkyl bromide and has been extensively used in organic synthesis. A detailed in silico study (PCM/density functional theory [DFT]/B3LYP/6-31++G(d,p) calculations) of this venerable reaction has shown that in the first stage a zwitterionic adduct with a multibonded bromine atom is formed. The widely accepted mechanism involving an S_N2 reaction occurs in the second step, thus accounting for its selectivity. Quantum chemical calculations were performed for the von Braun-like reactions in systems formed by cyclic tertiary amines (N-alkyl azetidines). In these cases, the first stage is almost the same as in the classical von Braun processes, and selective S_N2 mechanisms can occur in the second step.     

Spectroscopic studies,Density Functional Theory calculations,and non-linear optical properties of binuclear Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) complexes of OONN Schiff base ligand

The binuclear complexes of Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) with 2-[3-(benzylideneamino)-2-(benzylidenehydrazono)-4-oxothiazolidin-5-yl] acetic acid ligand (HL) were prepared and their stoichiometry was determined by elemental analysis. The stereochemistry of the studied binuclear metal complexes was confirmed by analyzing their infrared spectra, ¹H NMR, and magnetic moment. Thermal decomposition studies of the binuclear complexes have been performed to demonstrate the status of water molecules present in these binuclear complexes and their general decomposition pattern. The equilibrium geometry of the ligand and its studied complexes were calculated using density function theory (DFT) calculations at the B3LYP/GENECP level of the theory. The results show that the ligand and its complexes are nonplanar structures as indicated from the values of the dihedral angles. Extent of distortion from regular geometry has been performed and discussed in terms of the values of the angles between the central metals and the coordinated sites. The E_HOMO and E_LUMO energies of the studied ligand and its complexes are used to calculate the global properties. The nonlinear optical parameters (NLO), anisotropy of the polarizibility (Δα), and the mean first-order hyperpolarizability (<β>) were calculated. The (<β>) values were compared with Urea as a reference molecule and the results of (<β>) values showed that the ligand and the studied complexes have good NLO behaviors.     

On the tautomerism of pyrazolones: the geminal J[pyrazole C-4,H-3(5)] spin coupling constant as a diagnostic tool

The tautomerism of pyrazolones unsubstituted at position 3(5) has been investigated by ¹³C- and ¹H NMR spectroscopic methods. Apart from chemical shift considerations and NOE effects the magnitude of the geminal ²J[pyrazole C-4,H3(5)] spin coupling constant permits the unambiguous differentiation between 1H-pyrazol-5-ol (OH) and 1,2-dihydro-3H-pyrazol-3-one (NH) forms. Whereas 1H-pyrazol-5-ols and 2,4-dihydro-3H-pyrazol-3-ones (CH-form) exhibit ²J values of approximately 9-11 Hz, in 1,2-dihydro-3H-pyrazol-3-ones this coupling constant is considerably reduced to 4-5 Hz. This can be mainly attributed to the removal of the lone-pair at pyrazole N−1 in the latter due to protonation or alkylation. According to the data obtained, 2-substituted 4-acyl-1,2-dihydro-3H-pyrazol-3-ones exist predominantly as pyrazol-5-ols in CDCl₃ or benzene-d₆ solution, whereas in DMSO-d₆ also minor amounts of NH tautomer may contribute to the tautomeric composition. 2,4-Dihydro-2-phenyl-3H-pyrazol-3-one (1-phenyl-2-pyrazolin-5-one) exists in benzene-d₆ solely in the CH-form, in CDCl₃ as a mixture of CH and OH-form, whereas in DMSO-d₆ a fast equilibrium between OH and NH isomer (with the former far predominating) is probable. For 11 compounds, including neutral and protonated molecules, we have calculated at the B3LYP/6-311++G** level, the ²J(¹H,¹³C) coupling constants which are in good agreement with those measured experimentally.     

Synthesis, structure and properties of the new rare-earth Zintl phase Yb11GaSb9

A new rare-earth rich Zintl phase Yb₁₁GaSb₉ was synthesized by direct fusion of the corresponding elements, and large single crystals of the compound were obtained from high temperature flux synthesis. Its crystal structure was determined by single-crystal X-ray diffraction to be orthorhombic in the non-centrosymmetric space group Iba2 (No. 45), Z=4 (R₁=3.24%, wR₂=6.40%) with , , measured at 90(3) K. The structure belongs to the Ca₁₁InSb₉-type and can be viewed as built of isolated Sb₄-tetrahedra centered by Ga, Sb-dimers and isolated Sb anions, which are separated by Yb²⁺ cations. Electron count according to the Zintl formalism suggests that the phase is electron-precise and charge-balanced, which is supported by the virtually temperature-independent magnetization for Yb₁₁GaSb₉. Electrical resistivity data from 2 to 400 K confirm that Yb₁₁GaSb₉ is a small band-gap semiconductor with room temperature resistivity , and low-temperature resistivity at 2 K . As such, Yb₁₁GaSb₉ and related compounds might be promising materials for thermoelectric applications, and currently, efforts to synthesize new members of this family and test their thermoelectric performance are under way.     

Synthesis,Characterization, DFT and Photocatalytic Studies of a New Pyrazine Cadmium(II) Tetrakis(4-methoxy-phenyl)-porphyrin Compound

This study describes the synthesis, theoretical investigations, and photocatalytic degradational properties of a new (pyrazine)(meso-tetrakis(4-tert-methoxyphenyl)-porphyrinato)-cadmium (II) ([Cd(TMPP)-Pyz]) complex (1). The new penta-coordinated Cd^II porphyrin complex (1) was characterized by various spectroscopic techniques, including FT-IR, NMR, UV-visible absorption, fluorescence emission, and singlet oxygen, while its molecular structure was studied using single crystal X-ray diffraction. The UV–Vis spectroscopic study highlighted the redshift of the absorption bands after the insertion of the Cd(II) metal ion into the TMPP ring. The co-coordination of the pyrazine axial ligand enhanced this effect. A fluorescence emission spectroscopic study showed a significant blueshift in the Q bands, accompanied by a decrease in the fluorescence emission intensity and quantum yields of Φ_f = 0.084, Φ_f = 0.06 and Φ_f = 0.03 for H₂-TMPP free-base porphyrin, [Cd(TMPP)] and [Cd(TMPP)(Pyz)] (1) respectively. Singlet oxygen revealed that the H₂-TMPP porphyrin produced the most efficient singlet oxygen quantum yield of (Φ_Δ = 0.73) compared to [CdTMPP] (Φ_Δ = 0.57) and [Cd(TMPP)(Pyz)] (1) (Φ_Δ = 0.13). In the crystal lattice, the [Cd(TMPP)Pyz] was stabilized through non-covalent intermolecular interactions (NCI), such as the hydrogen bonds C-H···N and C-H···Cg. Additionally, crystal explorer software was then utilized to measure the quantitative analysis of the intermolecular interactions in the unit cell of the crystal structure and established that the C-H···π interaction dominated. The Natural bond orbital (NBO) analysis revealed that each molecule is stabilized by hyperconjugation and charge delocalization. As a photocatalyst, the coordination complex 1 showed excellent photocatalytic activity toward the degradation of Levafix Blue CA reactive dye (i.e., dye photo-degradation of 80%).