Mehdi Salehi

Crystal structure, electrochemistry, and catalytic studies of a series of new oxidovanadium(IV) Schiff-base complexes derived from 1,2-diphenyl-1,2-ethylenediamine

New derivatives of N2O2 tetradentate Schiff bases, from condensation of meso-1,2-diphenyl-1,2-ethylenediamine and salicylaldehyde derivatives (X-salicylaldehyde; Xu2009=u20093-OMe,u20094-OMe, 5-OMe,u20096-OMe,u20095-Cl,u20095-Me), and oxidovanadium(IV) complexes were synthesized and characterized by 1H NMR, UV-Vis, IR spectroscopy, and elemental analysis. Crystal structure of 5-OMe; H2L3 and two of the complexes (VOL2 and VOL3) were also obtained. In the crystals, the molecule of H2L3 is Ci symmetrical, as it occupies the special position on the center of symmetry; its conformation is partially determined by classical intramolecular O–H···N hydrogen bonds. The complexes have monomeric structures with a distorted square pyramid of vanadium, with the oxo ligand in the apical position. Cyclic voltammetry studies show quasi-reversible VIV/VV redox for which the presence of electron-withdrawing groups on salicylaldehyde derivatives shifts the E° to more positive values. The complexes were used as catalysts for selective epoxidation of cyclooctene with tert-butylhydroperoxide as oxidant, in various solvents and reaction conditions. High catalytic activities and excellent selectivity was found. The catalytic activity of the complexes increased increasing E°, a consequence of the presence of electronegative substituents. This epoxidation process with the new catalysts was also studied under solvent-free condition and excellent reactivity was observed.

Synthesis, crystal structures, spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H2L1), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H2L2); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H2L3), namely [CoIII(L1)(N-MeIm)3]PF6 (1), [CoIII(L1)(py)3]ClO4 (2), [Co(L1)(py)3][Co(L1)2] (3) and [CoIII(L2)(N-MeIm)3]PF6 (4) and [Co(L3)(N-MeIm)2]PF6 (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.

Synthesis, Antibacterial Studies and Crystal Structures of Tridentate Schiff Base Ligand and It’s Cobalt(III) Complex

The crystal structures of 4-[(2-hydroxyphenyl)imino]-2-pentanone (H2hpac, 1) and its cobalt(III) complex [CoIII(hpac)py3]+·PF6− (2) have been determined by X-ray diffraction. The ligand 1 crystallizes in orthorhombic chiral P212121 space group, with axa0=xa08.8405(4)xa0Å, bxa0=xa010.5349(8)xa0Å, cxa0=xa011.2292)7(xa0Å), and the complex 2—in the centrosymmetric monoclinic P2/n space group, with axa0=xa016.496(5)xa0Å, bxa0=xa010.171(2)xa0Å, cxa0=xa016.646(5)xa0Å, and βxa0=xa095.53(3)°. In the ligand molecule quite strong intramolecular hydrogen bond closes six-membered ring. The bond length pattern within this ring suggests the significant conjugation and the structure might be therefore regarded as the intermediate between keto-enamine and zwitterionic forms, and the intramolecular hydrogen bond falls into category of resonance-assisted hydrogen bonds. In turn, intermolecular O–H···O hydrogen bonds connect the molecules of the ligand into infinite chains along [100] direction. In the complex, the Co(III) ion is hexa-coordinated, by two oxygen and one nitrogen atoms of the doubly-deprotonated ligand 1 and by three nitrogen atoms from three pyridine ligands. The coordination polyhedron is close to a slightly distorted octahedron. The in vitro antimicrobial activity of the Schiff base ligand and its corresponding complex have been tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli.Graphical AbstractResonance-assisted intramolecular hydrogen bond increases the degree of delocalization within the NCCCO fragment of the Schiff base.

Synthesis, crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N2O2 type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H2L4 and its corresponding complex VOL4 were determined by X-ray crystallography.

Crystal structures, electrochemical properties, antioxidant screening and in vitro cytotoxic studies on four novel Cu(II) complexes of bidentate Schiff base ligands derived from 2-methoxyethylamine

Abstract Four novel Schiff base ligands and their copper(II) complexes, [Cu(L1)2] (1), [Cu(L2)2] (2), [Cu(L3)2] (3), and [Cu(L4)2] (4), were synthesized and characterized by elemental analyses, FT-IR, and UV–Vis spectroscopy. The ligands were synthesized from the condensation of 2-methoxyethylamine with various salicylaldehyde derivatives (x-salicylaldehyde for HLn, x = H (n = 1), 5-Br (n = 2), 3-OMe (n = 3), and 4-OMe (n = 4)). The molecular structures of 1, 2, and 3 were determined by the single crystal X-ray diffraction technique. The redox behavior studies of the complexes in acetonitrile display the electronic effects of the groups on the redox potential. The antioxidant activity of the Schiff base ligands and their Cu(II) complexes was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging method and FRAP assay. Furthermore, the in vitro anticancer activity of compounds was screened, including MTT and migration assays against gastric cancer cell line (MKN-45). The results show that all ligands and complexes have antioxidant and anticancer activity in a concentration-dependent way.

Syntheses, crystal structures, and antibacterial activities of two cobalt(III) complexes

Syntheses, structures, and antimicrobial activities of cobalt(III) complexes with two tetradentate Schiff-base ligands, (BA)2enu2009=u2009bis(benzoylacetone)ethylenediimine dianion and (acac)2enu2009=u2009bis(acetylacetone)ethylenediimine dianion, and two axial pyridines (py) have been investigated. These complexes were characterized by FT-IR, 1H-NMR, UV-Vis spectroscopy, and elemental analysis. The crystal structures of the complexes were determined by X-ray crystallography. Single-crystal X-ray diffraction analyses revealed that both complexes have distorted octahedral environments, Schiff-base ligand coordinates cobalt in four equatorial positions, and the two axial positions are occupied by pyridines. The pyridines and Schiff-base ligands are involved in N–H···O hydrogen bonds with perchlorate. Biological activities of the ligands and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, and Bacillus subtilis by the well diffusion method. The activity data show the metal complexes to be more potent than the parent ligand against two bacterial species.

Synthesis, characterization, and crystal structures of α, α′-bis(substituted-benzylidene)cycloalkanone derivatives by nano-TiO2/HOAc

A new and economical synthesis of α, α′-bis(substituted-benzylidene)cycloalkanones has been achieved by the reaction of cycloalkanones with different aromatic aldehydes using nano-TiO2/acetic acid as a catalyst in ethanol under reflux conditions with excellent yields. Five new products and three new single crystal structures are reported.

Nickel versus copper: enhanced antibacterial activity in a series of new nickel(II) Schiff base complexes

Abstract Five new Ni(II) Schiff base complexes [NiLx(Solv)2] denoted by NiLx, x = 1–5, were synthesized and characterized. The Schiff base ligands were synthesized from the condensation of 5-bromo-2-hydroxy-3-nitrobenzaldehyde with different aliphatic and aromatic diamines. The X-ray crystal structure of NiL3 was determined. The ligands and complexes were tested as antibacterial agents against two gram(+) and two gram(−) human pathogenic bacteria. The complexes showed moderate antibacterial activity against both gram type bacteria. The new Ni(II) complexes showed enhanced antibacterial activity compared to the previously reported Cu(II) complexes of the same ligands.

{2,2′-[1,1′-(Ethane-1,2-diyldinitrilo)­diethyl­idyne]diphenolato}bis­(pyrrolidine)cobalt(III) perchlorate p-xylene hemisolvate

In the mononuclear title complex, [Co(C18H18N2O2)(C4H9N)2]ClO4·0.5C8H10, the CoIII ion has a slightly distorted octahedral coordination geometry. In the Me–salen ligand, the benzene rings are almost parallel, making a dihedral angle of 0.48u2005(13)°, but the torsion angle along the central C—C bond is 41.1u2005(2)°·The pyrrolidine rings are in slightly distorted chair conformations. The N atoms of the pyrrolidine axial ligands are involved in N—H⋯O hydrogen bonds with the perchlorate anions, and these hydrogen bonds connect the ionic species into infinite chains along the b axis. Some relatively short C—H⋯π interactions are also present in the crystal structure and C—H⋯O interactions occur. The guest solvent p-xylene molecule lies on a special position at the inversion centre.

Highly efficient and recyclable phosphoric acid functionalized zirconia encapsulated-Fe3O4 nanoparticles: clean synthesis of 1,4-dihydropyridine and 1-amidoalkyl-2-naphthol derivatives

A novel type of magnetically recoverable acid nanocatalyst was synthesized by means of grafting phosphoric acid groups on the surface of core–shell zirconia-coated magnetite nanoparticle (nano-Fe3O4@ZrO2). The active nano-Fe3O4@ZrO2 supported phosphoric acid (n-Fe3O4@ZrO2–H3PO4) catalyst was studied in detail by the aid of various analyses, e.g. pH measurement, Fourier transform infrared spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and vibrating sample magnetometry. Additionally, the reactivity, reusability, and stability of the new catalyst were probed in the multicomponent one-pot reactions for the synthesis of dihydropyridines as well as 1-amidoalkyl-2-naphthols. The significant merits of the catalyst were related to its facile recyclability using an external magnetic field, reusability for at least five reaction cycles, excellent activity, high stability, mild reaction conditions and high isolated yields of the products.