A GGA plus U approach to effective electronic correlations in thiolate-ligated iron-oxo (IV) porphyrin

High-valent oxo-metal complexes exhibit correlated electronic behavior on dense, low-lying electronic state manifolds, presenting challenging systems for electronic structure methods. Among these species, the iron-oxo (IV) porphyrin denoted Compound I occupies a privileged position, serving a broad spectrum of catalytic roles. The most reactive members of this family bear a thiolate axial ligand, exhibiting high activity toward molecular oxygen activation and substrate oxidation. The default approach to such systems has entailed the use of hybrid density functionals or multi-configurational/multireference methods to treat electronic correlation. An alternative approach is presented based on the GGA+U approximation to density functional theory, in which a generalized gradient approximation (GGA) functional is supplemented with a localization correction to treat on-site correlation as inspired by the Hubbard model. The electronic structure of thiolate-ligated iron-oxo (IV) porphyrin and corresponding Coulomb repulsion U are determined both empirically and self-consistently, yielding spin-distributions, state level splittings, and electronic densities of states consistent with prior hybrid functional calculations. Comparison of this detailed electronic structure with model Hamiltonian calculations suggests that the localized 3d iron moments induce correlation in the surrounding electron gas, strengthening local moment formation. This behavior is analogous to strongly correlated electronic systems such as Mott insulators, in which the GGA+U scheme serves as an effective single-particle representation for the full, correlated many-body problem

Synthesis, characterization and crystal structures of two new phenolic mannich bases

Two new Mannich bases, 5-methyl-2-((4-(pyridin-2-yl)piperazin-1-yl)methyl)phenol (1) and 5-methyl-2-((4-(4-nitrophenyl)piperazin-1-yl)methyl)phenol (2), were prepared and characterized structurally with elemental analysis, IR, UV and NMR spectroscopic techniques as well as single crystal X-ray diffraction. Compound I crystallizes in the monoclinic space group P21/c with unit cell dimensions a = 6.6726(2) Å, b =   17.0542(6)   Å, c = 13.3222(4) Å, β = 100.832(1)°, V = 1489.00 (8) Å3, Z = 4, R1 = 0.0408, wR2 = 0.1143. Compound II crystallizes in the monoclinic space P21 with unit cell dimensions a = 5.9519(2) Å, b = 17.3315(8) Å, c = 15.7237(7) Å, β = 90.348(2)°, V = 1621.95(12) Å3, Z = 4, R1 = 0.0353, wR2 = 0.0965. Both compounds have their structures stabilized by hydrogen bonding and π∙∙∙π interactions.               KEY WORDS: Mannich base, Piperazine, X-ray diffraction, Hydrogen bonds Bull. Chem. Soc. Ethiop. 2019, 33(2), 341-348.DOI: https://dx.doi.org/10.4314/bcse.v33i2.1

3-Methyl-1-phenyl-4-[(phen­yl)(2-phenyl­hydrazin-1-yl)meth­ylidene]-1H-pyrazol-5(4H)-one

The title compound, C23H20N4O, is a heterocyclic phenyl­hydrazone Schiff base with a pyrazole moiety. In the crystal, a variety of inter­actions occur, including N—H⋯π and π–π stacking between the phenyl ring of the phenyl­hydrazinyl group and its symmetry-generated equivalent [centroid–centroid distance = 3.6512 (7) Å]

4-[(4-Meth­oxy­benzyl­idene)amino]­benzene­sulfonamide

The title Schiff base compound, C14H14N2O3S, is non-planar, with a dihedral angle of 24.16 (7)° between the benzene rings. In the crystal, N—H⋯O and N—H⋯N hydrogen bonds link the mol­ecules into a layer parallel to (011). Intra- and inter­layer C—H⋯O inter­actions and π–π inter­actions [centroid–centroid distances = 3.8900 (9) and 3.9355 (8) Å] are also present

Novel palladium(II) complex derived from mixed ligands of dithizone and triphenylphosphine synthesis, characterization, crystal structure, and DFT study

ABSTRACT. A novel distorted square-planar palladium(II) complex of the type [Pd(Hdz)(PPh3)Cl], where (Hdz = dithizone mono deprotonate and PPh3 = triphenylphosphine), was synthesized in dichloromethane reactions between PdCl2 and a mixture of Hdz and PPh3. The new Pd(II) complex has been identified by FT-IR, electronic spectra, DFT calculations, molar conductivity, and single-crystal X-ray diffraction. An X-ray diffraction study revealed the structure of this complex, indicating distorted square planar coordination geometry around the Pd(II) ion by N, S, P, and Cl donor atoms. XRD analysis has also shown that the Pd(II) complex contains one five-membered ring formed by the coordination of the Hdz ligand through the nitrogen and sulfur atoms to the palladium metal center. To comprehend the strength of nucleophilic and electrophilic attack between the ligands and metal ions, the natural bond orbital (NBO) was used. Finally, density functional theory (DFT) was used to show the molecular reactivity and stability of the ligands and palladium complex.   KEY WORDS: Palladium(II), Dithizone mono deprotonated, Distorted square planar geometry, NBO analysis, DFT calculations Bull. Chem. Soc. Ethiop. 2022, 36(3), 617-626.                                                               \ DOI: https://dx.doi.org/10.4314/bcse.v36i3.11                                                     &nbsp

Synthesis, characterization and DPPH scavenging activity of some benzimidazole derivatives

A base-catalyzed conversion of aldehydes to benzimidazoles has been achieved. The compounds have been characterized by IR, NMR, micoranalysis, and GC-MS. The reaction for the formation of benzimidazoles has been monitored with 1H NMR and IR. The crystal structures of two derivatives, 2-(2-chlorophenyl)-1H-benzimidazole and 2-(1H-benzimidazol-2-yl)-4-nitrophenol, are presented. A study of the DPPH scavenging activity of these compounds showed that 2-(1H-benzimidazol-2-yl)phenol (2), 2-p-tolyl-1H-benzimidazole (3) and 2-(4-methoxyphenyl)-1H-benzimidazole (7) gave IC50 values 1974, 773 and 800 µM.               KEY WORDS: Benzimidazole, o-Phenylenediamine, Aldehydes, Base catalysis, DPPH scavenging activity Bull. Chem. Soc. Ethiop. 2018, 32(2), 271-284.DOI: https://dx.doi.org/10.4314/bcse.v32i2.

1,5-Bis(2-methyl­phen­yl)-3-nitro­formazan

In the title compound, C15H15N5O2, the nitro O atoms are disordered over two sets of sites with an occupancy ratio of 0.75 (4):0.25 (4). Amine–imine tautomerism is observed in the formazan group. This was evident from the similar C—N bond distances in the formazan [1.319 (2) and 1.332 (3) Å], as well as the distribution of the imine proton in the Fourier difference map which refined to a 0.53 (3):0.47 (3) ratio. C—H⋯O and π–π inter­actions [centroid–centroid distances = 3.4813 (1) and 3.3976 (1) Å] are observed in the crystal packing

(E)-1-[2-(Methyl­sulfan­yl)phen­yl]-2-({(E)-2-[2-(methyl­sulfan­yl)phen­yl]hydrazinyl­idene}(nitro)­meth­yl)diazene

In the title compound, C15H15N5O2S2, the phenyl rings make dihedral angles of 4.03 (4) and 9.77 (5)° with the plane defined by the central N—N—C—N—N atoms (r.m.s. deviation = 0.010 Å). The C—S—C—C torsion angles of the methyl­sulfanyl groups with their respective phenyl rings are −7.47 (13) and −72.07 (13)°. The shortest centroid–centroid distance of 3.707 Å occurs between the two π-systems N—N—C—N—N and the benzene ring in the diazene 1-position. The H atom bound to the N atom is involved in intra­molecular N—H⋯N and N—H⋯S contacts, while the nitro O atoms are involved in inter­molecular C—H⋯O contacts

Vegetation Change from the Euro-American Settlement Era to the Present in Relation to Environment and Disturbance in Southwest Oregon

Faced with landscapes degraded by fire suppression, logging, and grazing, land managers in the interior western US are attempting to restore habitat structure and function. In southwest Oregon, landscape-scale fuels treatments are being implemented with goals including recreating historic vegetation structure, despite poor understanding of the nature of the landscape prior to widespread Euro-American influence, or the patterns and processes of vegetation change over time. We compared a General Land Office-based reconstruction of Euro-American settlement era (1850s) vegetation in southwest Oregon's interior valleys and foothills with modern vegetation interpreted from aerial orthoimages to determine patterns of vegetation distribution in both eras, trajectories of vegetation change, and environmental and disturbance factors related to these themes. We found that this landscape was primarily occupied by closed plant community types in both eras, with a comparatively minor proportion in open types; vegetation was distributed along a dominant environmental gradient that ran from prairies in xeric lowlands to conifer forests in steeper, cooler uplands. Temporal shifts from open to closed vegetation were consistent with expected effects of fire suppression in many cases, but in other cases, the long-term persistence of open vegetation in the absence of recorded fire indicated that other mechanisms were also in operation. Human encroachment into wildlands, particularly in valleys, has also been a major driver of landscape-level change in the past 150 yr. Our results suggest that conservation should focus on lowlands, particularly where uncommon vegetation types such as savanna, shrubland, and prairie still exist.Keywords: vegetation distribution, Klamath-Siskiyou region, General Land Office surveys, southwest Oregon, environmental gradient

Ultrasound promoted synthesis, characterization and computational studies of some thiourea derivatives

Synthesis of some thiourea derivatives have been achieved by using ultrasound, the compounds have been characterised using IR, NMR, GC-MS and elemental analysis. The single crystal X-ray structure of N-[(benzyloxy)methanethioyl]benzamide (IV), 1-benzoyl-3-(2-hydroxyethyl)thiourea (V) and 3-benzoyl-1-(1-benzylpiperidin-4-yl)thiourea (VI) has been presented and the bond lengths and bond angles contrasted with computed results. The HOMO and LUMO energy levels as well as the global chemical reactivity descriptors of the compounds have also been computed and discussed. Two comformers were obtained for compounds IV to VI in the molecular Electrostatic potential and the vibrational frequency computations and these have been discussed