Synthesis, structure and magnetic characterization of a dinuclear and two mononuclear iron(III) complexes with N,O-donor Schiff base ligands

Enantiomeric pairs of copper(II) complexes with tridentate Schiff bases derived from R- and S-methionine: the role of decorating organic groups of the ligand in crystal packing and biological activity

Three enantiomeric pairs consisting of copper(II) complexes with tridentate Schiff bases have been synthesized for employing in biological assessments: 1∞[Cu₂(R/S-salmet)₂(H₂O)] (1-R/S·H2O), 1∞[Cu(R/S-3-HOMe-5-Me-salmet)] (2-R/S), and 1∞[Cu(R/S-3-MeO-salmet)] (3-R/S) (where R/S-salmetH₂, R/S-3-HOMe-5-Me-salmetH₂, and R/S-3-MeO-salmetH₂ result from the condensation of R/S-methionine with salicylaldehyde, 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde, and 3-methoxy-salicylaldehyde, respectively, in a 1 : 1 molar ratio). The crystal structures of 1-R·H2O and 2-R/S are reported. Moreover, the 1-R/S·H2O enantiomers have been subjected to a single-crystal-to-single-crystal (SC-SC) transformation by heating at 160 °C to afford their dehydrated forms, 1∞[Cu₂(R/S-salmet)₂] (1-R/S), whose structures have also been crystallographically determined. The coordination polyhedra of the metal centers, the binding modes of the ligands, and the 1-D double chain assemblies generated by the chiral mononuclear units are comparatively described. The diffuse reflectance UV-Vis and circular dichroism (CD) spectra of compounds 1-R/S·H2O, 1-R/S, and 2-R/S are analysed with respect to their structural peculiarities and compared to those of 3-R/S. The UV-Vis and CD spectra of solutions of 1-R/S, 2-R/S, and 3-R/S point to the collapse of the double chains via dissolution. Biological tests performed on the model eukaryote Saccharomyces cerevisiae indicated low toxicity for 1-R/S, 2-R/S, and 3-R, and moderate toxicity for 3-S. The S-type complexes were accumulated by cells in higher quantity compared to their R-type counterparts due to selective transport via the high-affinity S-methionine transporter, Mup1. A chemogenomic analysis of 3-S toxicity performed on a collection of yeast knockout mutants revealed that most of the deleted genes identified in the screen were involved in the cell response to oxidative stress, calcium-mediated response, or metal homeostasis. Altogether, it was concluded that 3-S accumulation may perturb the redox state of the cell, also interfering with the calcium-mediated response to oxidative stress or metal-related oxidative stress.

Hydrogen bond mediated intermolecular magnetic coupling in mononuclear high spin iron(iii) Schiff base complexes: synthesis, structure and magnetic study with theoretical insight

The crystal structure and magnetic properties of two mononuclear iron(iii) Schiff base complexes, [FeL¹(NCS)₂] (1), HL¹ = 2-[1-[[2-[(2-aminoethyl)amino]ethyl]imino]ethyl]phenol and [FeL²(N₃)Cl] (2), HL² = 2-(-1-(2-(2-aminoethylamino)ethylimino)ethyl)-4-methylphenol are reported. Each complex contains a Fe(iii) ion surrounded by a N₃O Schiff base ligand and two NCS⁻ ligands (in 1) or one N₃⁻ and one Cl⁻ ligands (in 2). The magnetic properties can be well reproduced with zero field splittings in the high spin S = 5/2 Fe(iii) ions and weak intermolecular Fe–Fe interactions mediated by hydrogen bonds. This intermolecular antiferromagnetic interaction has been validated by using DFT calculations in complex 2. Moreover, the interaction energies of the H-bonded dimers in both complexes have been estimated using DFT calculations and characterized using a combination of QTAIM and NCI plot computational tools. Complexes 1 and 2 constitute two rare examples of Fe(iii) complexes with magnetic interactions through H-bonds.

H-Bond mediated magnetic interactions in mononuclear iron(iii) Schiff base complexes were studied experimentally and validated by using DFT calculations.

Insight into the formation of H-bonds propagating the monomeric zinc complexes of a tridentate reduced Schiff base to form an infinite chain

The formation of an infinite 1D assembly is governed by the H-bonding interactions in the solid state structure of the two zinc complexes. It has been analyzed energetically using DFT calculations and several computational tools.

Insight into non-covalent interactions in two triamine-based mononuclear iron(iii) Schiff base complexes with special emphasis on the formation of Br⋯π halogen bonding

The nature and characteristics of noncovalent interactions that play important roles in the crystal packing of two iron(iii) complexes have been discussed.

Differentiating intramolecular spodium bonds from coordination bonds in two polynuclear zinc(ii) Schiff base complexes

Two new zinc(ii) complexes have been synthesized and characterized. Theoretical study is devoted to distinguish between conventional coordination bonds and spodium bonds between the zinc and oxygen centers.

Design and catalytic studies of structural and functional models of the catechol oxidase enzyme

The catechol oxidase activity of three copper/bicompartmental salen derivatives has been studied. One mononuclear, [CuL] (1), one homometallic, [Cu₂L(NO₃)₂] (2), and one heterometallic, [CuMnL(NO₃)₂] (3) complexes were obtained using the ligand H₂L = N,N'-bis(3-methoxysalicylidene)-1,3-propanediamine through different synthetic methods (electrochemical, chemical and solid state reaction). The structural data indicate that the metal ion disposition models the active site of type-3 copper enzymes, such as catechol oxidase. In this way, their ability to act as functional models of the enzyme has been spectrophotometrically determined by monitorization of the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butyl-o-benzoquinone (3,5-DTBQ). All the complexes show significant catalytic activity with ratio constants (k_obs) lying in the range (223-294) × 10^-4 min^-1. A thorough kinetic study was carried out for complexes 2 and 3, since they show structural similarities with the catechol oxidase enzyme. The greatest catalytic activity was found for the homonuclear dicopper compound (2) with a turnover value (k_cat) of (3.89 ± 0.05) × 10⁶ h^-1, which it is the higher reported to date, comparable to the enzyme itself (8.25 × 10⁶ h^-1).

Synthesis, characterization, self-assembly and non-ohmic Schottky barrier diode behaviors of two iron(iii) based semiconductors with theoretical insight

Schottky barrier diodes have been fabricated using two iron(iii) Schiff base complexes. The total and partial DOS values have been calculated using DFT to calculate the band gaps in these complexes.

Phosphatase-mimicking activity of a unique penta-nuclear zinc(ii) complex with a reduced Schiff base ligand: assessment of its ability to sense nitroaromatics

A penta-nuclear zinc(ii) complex has been synthesized and characterized. The complex has shown good phosphatase-mimicking activity, which has been evaluated spectrophotometrically. The complex also behaves as a sensor for the detection of nitroaromatics via turn-off fluorescence response.

σ-Hole halogen bonding interactions in a mixed valence cobalt(iii/ii) complex and anti-electrostatic hydrogen bonding interaction in a cobalt(iii) complex: a theoretical insight

Supramolecular interactions in the solid state structures of a mixed valence cobalt(ii/iii) complex and a cobalt(iii) complex have been studied using DFT calculations.

One pot synthesis of two cobalt(iii) Schiff base complexes with chelating pyridyltetrazolate and exploration of their bio-relevant catalytic activities

Two new cobalt(iii) tetrazolato complexes [Co(L¹)(PTZ)(N₃)] (1) and [Co(L²)(PTZ)(N₃)] (2) {where H₂L¹ = 2((3-(methylamino)propylimino)methyl)-6-methoxyphenol, H₂L² = 2((3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole}, have been synthesized via in situ 1,3-dipolar cycloaddition reaction of 2-cyanopyridine and sodium azide in the presence of cobalt(ii) nitrate hexahydrate and respective Schiff bases in the open atmosphere. The structures of both complexes have been confirmed by single crystal X-ray diffraction studies. Features of noncovalent interactions in the solid state of both complexes have been studied by means of DFT and MEP calculations and characterized using Bader's theory of “atoms in molecules” (AIM). These complexes act as biomimetic catalysts promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding o-benzoquinone at room temperature. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers of ∼0.030 s⁻¹ in an acetonitrile–methanol (2 : 1) mixture. Both complexes are also reactive towards aerobic oxidation of o-aminophenol in acetonitrile–methanol (2 : 1) with turnover numbers ∼0.095 s⁻¹.

Two cobalt(iii) tetrazolato complexes have been synthesized and characterized. Noncovalent interactions have been analysed by DFT and MEP calculations and characterized using Bader's theory of AIM. Both complexes catalyze the aerial oxidation of 3,5-DTBC and OAPH.