Copper(II)-salicylaldehydate/-methoxy(pyridine-2-yl)methanolate complexes via in-situ hydrolysis of Schiff bases

Structural and Electronic (Absorption and Fluorescence) Properties of a Stable Triplet Diphenylcarbene: A DFT Study

A triplet diphenylcarbene, bis[3-bromo-5-(trifluoromethyl)[1,1'-biphenyl]-4-yl]methylidene (B3B), with exceptional stability was discovered by chemists from Japan's Mie University. To investigate its different quantum chemical features, a theoretical analysis was predicated on Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) based technique. According to the findings, the singlet-triplet energy gap (ES-T), as well as HOMO-LUMO energy bandgap (E_H-L), was found to be diminished when nucleophilicity (N) rose. We looked at the geometrical dimensions, molecular orbitals (MOs), electronic spectra, electrostatic potential, molecular surfaces, reactivity characteristics, and thermodynamics features of the title carbene (B3B). Its electronic spectra in different solvents were calculated using TD-DFT and Polarizable Continuum Model (PCM) framework. The estimated absorption maxima of B3B were seen between 327 and 340 nm, relying on the solvents, and were attributed to the S⁰ → S¹ transition. Estimated fluorescence spectral peaks were found around 389 and 407 nm with the S¹ and S⁰ transitions being identified. Its fluorescence/absorption intensities revealed a blue shift change when the solvent polarity was increased. The least exciting state has been discovered to be the π → π^* charge-transfer (CT) phase. According to the Natural Bonding Orbital (NBO) exploration, ICT offers a significant role in chemical system destabilization. Furthermore, several hybrid features were used to determine the NLO (nonlinear optical) features (polarizability, first-order hyperpolarizability, and dipole moment). The calculated values suggest that B3B is a promising candidate for further research into nonlinear optical properties.

Revisiting salicylidene-based anion receptors

Several salicylidene-based colorimetric and fluorimetric anion sensors are known in the literature. However, our ¹H-NMR experimental results (in DMSO-d₆) showed hydrolysis of imine (–N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH–) bonds in salicylidene-based receptors (SL, CL1 and CL2) in the presence of quaternary ammonium salts (n-Bu₄N⁺) of halides (Cl⁻ and Br⁻) and oxo-anions (H₂PO₄⁻, HSO₄⁻ and CH₃COO⁻). The mono-salicylidene compound CL1 showed the most extensive –NCH– bond hydrolysis in the presence of anions. In contrast, the di-salicylidene compound CL2 and the tris-salicylidene compound SL showed comparatively slow hydrolysis of –NCH– bonds in the presence of anions. Anion-induced imine bond cleavage in salicylidene compounds could easily be detected in ¹H-NMR due to the appearance of the salicylaldehyde –CHO peak at 10.3 ppm which eventually became more intense over time, and the –NCH– peak at 8.9–9.0 ppm became considerably weaker. Furthermore, the formation of the salicylidene O–H⋯X⁻ (X⁻ = Cl⁻/Br⁻) hydrogen-bonded complex, peak broadening due to proton-exchange processes and keto–enol tautomerism have also been clearly observed in the ¹H-NMR experiments. Control ¹H-NMR experiments revealed that the presence of moisture in the organic solvents could result in gradual hydrolysis of the salicylidene compounds, and the rate of hydrolysis has further been enhanced significantly in the presence of an anion. Based on ¹H-NMR results, we have proposed a general mechanism for the anion-induced hydrolysis of imine bonds in salicylidene-based receptors.

Salicylidene Schiff bases undergo imine bond hydrolysis in the presence of halides and oxo-anions in aprotic media, raising fundamental questions on the applicability of salicylidene-based receptors as anion sensors.

Pseudotetrahedral copper(II)-complexes with enantiopure (R or S)-2-(((aryl)ethylimino)ethyl)phenolate Schiff base ligands

Condensation of 2-hydroxy-benzophenone (HL') with (R or S)-(Ar)ethylamine yields the enantiopure Schiff bases (S or R)-2-((E)-1-(1-(Ar)ethylimino)ethyl)phenol {Ar = C6H5 (S- or R-HL1), p-CH3OC6H4 (S- or R-HL2)}. These Schiff bases react with copper(ii) acetate under reflux to give green microcrystals of bis[(R or S)-2-((E)-1-(1-(Ar)ethylimino)ethyl)phenolato-κ2N,O]-Λ/Δ-copper(ii), {Ar = C6H5 (Λ/Δ-Cu-R- or S-L1), p-CH3OC6H4 (Λ/Δ-Cu-R- or S-L2)} with induction of Λ/Δ-chirality at-metal. The presence of Schiff base ligands in the paramagnetic green microcrystals is confirmed by decomplexation reaction with NaCN via reduction of Cu(ii) to Cu(i) in DMSO-d6 solution. Crystallization attempts of the green microcrystalline Schiff-base Cu complexes provide deep-green block-shaped crystals of an about equal admixture of bis[2-oxo-benzophenonato-κ2O,O']-copper(ii), (CuL'2) and bis[2-(imino(phenyl)methyl)phenolato-κ2N,O]copper(ii), (CuL''2) via in situ hydrolysis of the coordinated Schiff base ligands back to 2-hydroxy-benzophenone (HL') and to 2-(imino(phenyl)methyl)phenol (HL''), which in-turn bind with the copper(ii) ion. Powder X-ray diffraction (PXRD) patterns of R-HL1 and Cu-R-L1 allowed their structure determinations using the program Expo-2014 followed by Rietveld refinement. The Cu structures refined to four-coordinated Λ/Δ-copper(ii)-complexes by the two phenolate-oxygen and two imine-nitrogen atoms from two Schiff base ligands in a pseudotetrahedral geometry. DFT optimized structures (at gas-phase) reveal the Δ-Cu-S-L1 or Λ-Cu-R-L1 diastereomer as slightly more stable than the corresponding Λ-Cu-S-L1 or Δ-Cu-R-L1 by ca. 7.60 kcal mol-1, resulting from diastereoselectively induced Λ vs. Δ-chirality at-metal. Electronic circular dichroism (ECD) spectra display mirror-image relationships and comparisons of experimental and simulated ECD spectra by TDDFT suggest an excess of the Δ-Cu-S-L1 or Λ-Cu-R-L1 diastereomer in solution. The cyclic voltammograms demonstrate two one electron charge transfer processes for Cu2+/Cu+ and Cu+/Cu0 couples in acetonitrile, respectively.

New mixed amino acids complexes of iron(III) and zinc(II) with isonitrosoacetophenone: Synthesis, spectral characterization, DFT study and anticancer activity

New mixed Fe(III) and Zn(II) complexes with isonitrosoacetophenone (HINAP) and l-amino acids (such as l-histidine, l-phenylalanine and l-proline) have been synthesized and characterized by elemental analyses, UV-Vis, IR and ESR spectroscopy and thermal analyses. The values of molar conductance of the complexes in DMSO solution at 10^-3 M concentration indicate their non-electrolyte nature. IR spectroscopy has revealed the coordination of deprotonated ligands to metal through nitrogen and oxygen atoms in an N₂O₂ arrangement. Density functional theory (DFT) calculations were performed using the hybrid functional of Truhlar and Zhao (M06) with basis set of double zeta quality LANL2DZ to evaluate the cis and trans coordination modes and to ascertain dipole moment, HOMO-LUMO energy gap, chemical hardness, softness and electrophilicity. The magnetic moments and ESR measurements suggest that there is an admixture of S = 5/2 and S = 1/2 spins in Fe(III) complexes. UV-Visible spectra indicate a distorted octahedral geometry around the metal ions. Thermal analyses show the presence of hydrated and coordinated water. The antimicrobial activity was investigated against (G⁺ and G^-) bacteria (Staphylococcus aureus, bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa) and fungi (Candida albicans). The iron and zinc complexes were found to be more active against Gram-positive than Gram negative bacteria. They also show considerable growth inhibition against the fungi tested. In vitro antitumor activity assayed against cancer cell lines of the HEP2 type (cancer cells of the larynx) exhibited significant toxicity of the ligands and their mixed complexes.

Decanuclear FeIII clusters with hemiacetal ligands: a new {M10(μ3-O)8} cluster core

The characterization of a Fe^III₁₀ cluster with α-methyl-2-pyridinemethanolate lead us to explore the direct syntheses of medium nuclearity Fe^III clusters with aldehydes in methanol. The complexes exhibit an unprecedented {Fe₁₀(μ₃-O)₈} cluster core.