Iron(III) and cobalt(III) complexes with pentadentate pyridoxal Schiff base ligand – structure, spectral, electrochemical, magnetic properties and DFT calculations

Water Serving as Cocatalyst for the Highly Efficient Homogeneously Catalyzed Conversion of N2O/H2 Mixtures with Optimized Rhodium NHC Complexes

Nitrous oxide (N2O) is a valuable oxygen/nitrogen transfer reagent but reactions with N2O are challenging due to its inertness. Consequently, it accumulates in the atmosphere, and because it is both an ozone-depleting reagent and potent green-house gas, effective mitigation methods become important. This study presents rhodium(I) amido bis(olefin) N-heterocyclic carbene complexes [Rh(trop2N)(NHC)] as robust homogeneous catalysts for the direct hydrogenation of N2O. Kinetic experiments and DFT calculations show that increasing π-acidity of the NHC and the presence of water significantly enhance the catalytic efficiency. The rhodium-amido bond facilitates cooperative H2-cleavage and oxygen atom transfer from N2O. The catalyst is regenerated with the loss of water from the hydroxide intermediate [Rh(OH)(trop2NH)(NHC)], which forms a dimeric complex with a central bridging hydrated hydroxide ligand [H3O2]-. Water facilitates dinitrogen (N2) loss from an intermediate containing an oxy-diazene ligand [H─N═N─O]-. The optimized catalyst achieves a TON > 230 000 and TOF > 1300 h-1.

Effects of changing ions on the crystal design, non-covalent interactions, antimicrobial activity, and molecular docking of Cu(II) complexes with a pyridoxal-hydrazone ligand

The present work reports the influence of the presence of different ions (Cl-, Br-, NO3 -, or SO4 2-) on the formation and proprieties of Cu(II) complexes with pyridoxal-benzoylhydrazone (PLBHZ). Four new complexes were successfully synthesized, [CuCl2(PLBHZ)] (1), [CuBr2(PLBHZ)] (2), [CuCl(PLBHZ)H2O]⋅NO3⋅H2O (3), and [CuSO4(PLBHZ)H2O]⋅3H2O (4), and characterized by spectroscopic and physicochemical methods. A single-crystal X-ray study reveals the Schiff base coordinated to the metal center tridentate by the ONS-donor system, resulting in distorted square pyramidal coordination geometries. Noncovalent interactions were investigated by 3D Hirshfeld surface analysis by the d norm function, 2D fingerprint plots, and full interaction maps. The ion exchange is important in forming three-dimensional networks with π⋅⋅⋅π stacking interactions and intermolecular hydrogen bonds. The in vitro biological activity of the free ligand and metal complexes was evaluated against Gram-positive and Gram-negative bacterial strains and the free pyridoxal-hydrazone ligand showed higher activity than their Cu(II) complexes. Molecular docking was used to predict the inhibitory activity of the ligand and complexes against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria.

Reactions of cobalt(ii) chloride and cobalt(ii) acetate with hemisalen-type ligands: ligand transformation, oxidation of cobalt and complex formation. Preliminary study on the cytotoxicity of Co(ii) and Co(iii) hemisalen complexes

Several molecular cobalt(ii) complexes, one Co(ii) coordination polymer and one ionic cobalt(iii) complex with imine hemisalen ligands were synthesized. The hemisalen ligands were synthesized from o-vanillin (oVP) and diverse aminopyridines (compounds HL1-HL4) or aminophenol (compound HL5). It was observed that cobalt(ii) chloride in dry acetonitrile catalyzes a transformation of HL1 and HL3 instead of complex formation. The conversion of these imines proceeded via self-cyclization to N-2''-pyridyl-2,6-dioxo-9-aza-[c,g]di-2'-methoxybenzo nonan or its methyl derivative as the major product. The remaining reactions were performed using imines HL1-HL5 and cobalt(ii) acetate Co(Ac)₂ in methanol or DMSO/acetonitrile resulting in forming a series of cobalt complexes. The following series of compounds was obtained: two similar tetrahedral molecular Co(ii) complexes [Co(L1)₂] and [Co(L3)₂], one trinuclear, mixed-ligand Co₃(Ac)₂(L4)₂(oVP)₂, one coordination polymer {Co(L2)₂}_∞ and finally one octahedral anionic Co(iii) complex [HNEt₃][Co(L5)₃]. The latter complex formed in a cobalt(ii) acetate reaction with a hemisalen HL5 derived from oVP and 2-aminophenol. The molecular structures of all compounds were confirmed by X-ray diffraction, and the cytotoxicity of Co(ii) and Co(iii) complexes towards cancer cell lines HCT116, HL-60 and normal cell line MRC-5 was studied.