Tridentate ONS Ligand Research Articles

Thiosemicarbazone ligand, nickel(II) and ruthenium(II) complexes based on vitamin B6 vitamer: The synthesis, different coordination behaviors and antioxidant activities

Mixed ligand nickel(II) and ruthenium(II) complexes were synthesized from pyridoxal-N-allyl-thiosemicarbazone hydrochloride and triphenylphosphine. The structures of the complexes have been characterized by elemental analysis, IR, 1H and 31P NMR, conductivity, magnetic moment measurements and single-crystal X-ray diffraction technique. Based on X-ray crystallographic studies, a square-planar structure has been proposed for the Ni(II) complex, in which the thiosemicarbazone ligand acts as dianionic tridentate ONS ligand. In the case of the Ru(II) complex, the thiosemicarbazone is coordinated to metal atom as a monoanionic bidentate NS donor ligand in an octahedral geometry. Antioxidant activities of the ligand and its metal complexes were calculated as their trolox equivalent antioxidant capacities (TEAC) by CUPRAC method and DPPH assay. Both the ligand and its metal complexes were found to be antioxidant and are much more antioxidant at least 2.1 times than trolox, even, ligand is 3.5 times greater than that of trolox according to CUPRAC. A linear correlation (correlation coefficient R2 = 0.9997) appeared between the obtained TEAC values by the two antioxidant assays.

Mononuclear oxovanadium(Iv) complex containing VO(ONS) basic core: Synthesis, structure, thermal gravimetric analysis, and catalytic property

ABSTRACTReaction of vanadyl(IV)-acetylacetonate with 3-ethoxy-2-hydroxybenzaldehyde 4-methylthiosemicarbazone and 2,2′-bipyridyl in methanol affords a mononuclear oxovanadium(IV) complex containing VO(ONS) basic core. The complex has been characterized by various physicochemical techniques (UV–Vis, IR, and elemental analysis), and single-crystal X-ray diffraction. X-ray crystal structure determination reveals that the complex crystallizes as triclinic space group P, with unit cell dimensions a = 10.073(2) Å, b = 11.272(3) Å, c = 11.338(3) Å, α = 87.291(2)°, β = 83.440(2)°, γ = 64.003(2)°, V = 1149.5(5) Å3, Z = 2, R1 = 0.0356, wR2 = 0.0867, S = 1.052. The V atom in the complex is octahedrally coordinated, with the tridentate ONS ligand occupying the meridional sites. The nitrogen donor of 2,2′-bipyridyl ligand, occupying an apical position has a trans-labilizing influence, resulting in elongation of the V=O terminal bond. Thermal gravimetric analysis was performed to understand the stability of the complex. The complex shows high catalytic property and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide as oxidant.

Nonoxido Vanadium(IV) Compounds Involving Dithiocarbazate-Based Tridentate ONS Ligands: Synthesis, Electronic and Molecular Structure, Spectroscopic and Redox Properties.

A new series of nonoxido vanadium(IV) compounds [VL2] (L = L(1)-L(3)) (1-3) have been synthesized using dithiocarbazate-based tridentate Schiff-base ligands H2L(1)-H2L(3), containing an appended phenol ring with a tert-butyl substitution at the 2-position. The compounds are characterized by X-ray diffraction analysis (1, 3), IR, UV-vis, EPR spectroscopy, and electrochemical methods. These are nonoxido V(IV) complexes that reveal a rare distorted trigonal prismatic arrangement around the "bare" vanadium centers. Concerning the ligand isomerism, the structure of 1 and 3 can be described as intermediate between mer and sym-fac isomers. DFT methods were used to predict the geometry, g and (51)V A tensors, electronic structure, and electronic absorption spectrum of compounds 1-3. Hyperfine coupling constants measured in the EPR spectra can be reproduced satisfactorily at the level of theory PBE0/VTZ, whereas the wavelength and intensity of the absorptions in the UV-vis spectra at the level CAM-B3LYP/gen, where "gen" is a general basis set obtained using 6-31+g(d) for S and 6-31g for all the other elements. The results suggest that the electronic structure of 1-3 can be described in terms of a mixing among V-dxy, V-dxz, and V-dyz orbitals in the singly occupied molecular orbital (SOMO), which causes a significant lowering of the absolute value of the (51)V hyperfine coupling constant along the x-axis. The cyclic voltammograms of these compounds in dichloroethane solution display three one-electron processes, two in the cathodic and one in the anodic potential range. Process A (E1/2 = +1.06 V) is due to the quasi-reversible V(IV/V) oxidation while process B at E1/2 = -0.085 V is due to the quasi-reversible V(IV/III) reduction, and the third one (process C) at a more negative potential E1/2 = -1.66 V is due to a ligand centered reduction, all potentials being measured vs Ag/AgCl reference.

Tridentate ONS vs. ONO salicylideneamino(thio)phenolato [MoO2L] complexes for catalytic solvent-free epoxidation with aqueous TBHP

Comparison of molybdenum precatalysts with salicylideneaminothiophenolato (SATP; a tridentate ONS ligand) and salicylideneaminophenolato (SAP; a tridentate ONO ligand) in the solvent-free epoxidation of cyclooctene with aqueous TBHP yields better activity for the former. The DFT study of the catalytic cycle shows that the SATP catalyst follows the same pathway recently established for the SAP analogue and with a slightly smaller activation barrier in agreement with the experimental results.

Nickel(II) complexes of polyhydroxybenzaldehyde N4-thiosemicarbazones: synthesis, structural characterization and antimicrobial activities

Nickel(II) complexes with 2,3-dihydroxybenzaldehyde N4-substituted thiosemicarbazone ligands (H3L1–H3L4) have been synthesized and characterized with the aim of evaluating the effect of N4 substitution in the thiosemicarbazone moiety on their coordination behavior and biological activities. Two series of nickel(II) complexes with the general formulae [Ni(H3L)(H2L)]ClO4 and [Ni2(HL)2] were characterized by analytical and spectral techniques. The molecular structure of one of the complexes, namely, [Ni(H3L4)(H2L4)]ClO4 was established by single crystal X-ray diffraction studies. The crystal structure of this complex revealed that two H3L4 ligands are coordinated to nickel(II) in different modes; one as a neutral tridentate ONS ligand and the other is as a monoanionic tridentate (ONS−) ligand. The antimicrobial activities of the compounds were tested against 25 bacterial strains via the disc diffusion method, and their minimum inhibitory concentration (MIC) and minimum microbicidal concentration were evaluated using microdilution methods. With a few exceptions, most of the compounds exhibited low-to-moderate inhibitory activities against the tested bacterial strains. However, the complexes [Ni2(HL3)2] (7) and [Ni2(HL4)2] (8) indicated higher inhibitory activity against Salmonella enterica ATCC 9068 (MIC values 15.7 and 50 μg/ml). The toxicities of the compounds were tested on brine shrimp (Artemia salina), where no meaningful toxicity level was noted for both the free ligands and the complexes. The cytotoxicities of the compounds on cell viability were determined on MCF7, PC3, A375, and H413 cancer cells in terms of IC50; complexes [Ni(H3L3)(H2L3)]ClO4 (3), [Ni2(HL3)2] (7) and [Ni2(HL4)2] (8) exhibited significant cytotoxicity on the tested cell lines.

Binary and ternary copper(II) complexes of a tridentate ONS ligand derived from 2-aminochromone-3 carboxaldehyde and thiosemicarbazide: Synthesis, spectral studies and antimicrobial activity

A tridentate ONS donor ligand, HL, was synthesized by the condensation of 2-aminochromone-3-carboxaldehyde with thiosemicarbazide. The structure of the ligand was elucidated by elemental analyses, IR, 1H and 13C NMR, electronic and mass spectra. Reaction of the ligand with several copper(II) salts, including AcO−, NO3-, SO42-, Cl−, Br− and ClO4- afforded different metal complexes that reflect the non-coordinating or weakly coordinating power of the ClO4- and Br− anions as compared to the strongly coordinating power of AcO−, SO42-, Cl− and NO3- anions. Also, the ligand was allowed to react with Cu(II) ion in the presence of a secondary ligand (L′) [N,O-donor; 8-hydroxyquinoline or N,N-donor; 1,10-phenanthroline]. Characterization and structure elucidation of the prepared complexes were achieved by elemental and thermal analyses, IR, electronic, mass and EPR spectra as well as conductivity and magnetic susceptibility measurements. The EPR spin Hamiltonian parameters of some complexes were calculated. The metal complexes exhibited octahedral and square planar geometrical arrangements depending on the nature of the anion. The ligand and most of its metal complexes showed antibacterial activity towards Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram-negative bacteria (Salmonella typhimurium and Escherichia coli), yeast (Candida albicans) and fungus (Aspergillus fumigatus).

Synthesis, spectroscopy, and X-ray crystal structures of copper(II) complexes of the tridentate ONS ligand formed by condensation of 4,4,4-trifluoro-1-(2-thienyl)-2,4-butanedione with S-benzyldithiocarbazate

A new tridentate ONS ligand, H2L, has been synthesized by condensing thenoyltrifluoroacetone(4,4,4-trifluoro-1-(2-thienyl)-2,4butaneanedione) with S-benzyldithiocarbazate and its structure determined by X-ray diffraction. In the solid state, the Schiff base exists as the ketoamine-thioketo tautomer but in solution and in the presence of copper(II), it converts to the enol-thiol form and deprotonates to give copper(II) complexes of formula, [CuL] and [CuLL1] (L = doubly deprotonated form of the ligand; L1 = py, bipy or phen] which have been characterized by magnetic, spectroscopic, and X-ray diffraction studies. An X-ray crystallographic analysis shows that [CuL(py)] has a square-planar geometry with the ligand coordinated to the copper(II) center via the enolate oxygen, the azomethinic nitrogen and the thiolate sulfur, the fourth coordination position being occupied by pyridine. The [CuL(bipy)] complex is five-coordinate with a structure close to square-pyramidal in which the Schiff base acts as a doubly deprotonated tridentate ONS ligand and bipy is bidentate.

Preparation and structural characterization of nickel(II), cobalt(II), zinc(II) and tin(IV) complexes of the isatin Schiff bases of S-methyl and S-benzyldithiocarbazates

The molecular structures of the isatin Schiff bases of S-methyldithiocarbazate (Hisasme) and S-benzyldithiocarbazate (Hisasbz) have been determined by X-ray diffraction and their complexes of general formula [ML 2]· n(solvate) [M = Co 2+, Ni 2+, Zn 2+; L = anionic forms of Hisasme or Hisasbz; solvate = DMF, DMSO; n = 1, 2] and [Sn(L)Ph 2Cl]· nMeOH ( n = 0, 1) have been synthesized and characterized by a variety of physicochemical techniques and X-ray diffraction. The bis-ligand complexes, [Ni(isasbz) 2]·2DMSO and [Co(isasme) 2]·DMF have a six-coordinate, distorted octahedral geometry with the two uninegatively charged tridentate ONS ligands coordinated to the metal ions meridionally via the amide O-atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. By contrast, the crystal structure of [Zn(isasbz) 2]·2DMF shows a four-coordinate distorted tetrahedral geometry with the two Schiff bases coordinated as NS bidentate ligands via the azomethine nitrogen atoms and the thiolate sulfur atoms. Steric constraints of the rigid tridentate ligands lead to unusual ‘pseudo-coordination’ of the O-donors which occupy sites close to the metal but too distant to be considered as true coordinate bonds. The crystal structures of the tin(IV) complexes [SnLPh 2Cl]· nMeOH (L = isasme and isasbz; n = 0, 1) also show that the Schiff bases act as monoanionic bidentate NS chelating agents coordinating the tin(IV) ion via the azomethine nitrogen atoms and the thiolate sulfur atoms, the tin atom in each complex is five-coordinate with a highly distorted geometry intermediate of square pyramidal and trigonal bipyramidal. Again Sn⋯O contacts are weak and do not qualify as coordinate bonds.

Spontaneous assembly of a polymeric helicate of sodium with LVO(2) units forming the strand: photoinduced transformation into a mixed-valence product.

The anionic cis-dioxovanadium(V) complex species LVO(2)(-) of a tridentate ONS ligand (H(2)L) can bind sodium ion in a bis-monodentate fashion like a bridging carboxylate group. The product [LVO(2)Na(H(2)O)(2)](infinity) (1) is a water soluble polymeric compound in which the complementary units are held together by the simultaneous use of hydrogen bonding and Coulombic interactions. Crystallographic characterization reveals that 1 is a single stranded helicate with LVO(2)(-) units forming the strand which surrounds the labile sodium ions that occupy the positions on the axis. In solution of protic solvents, viz. water and methanol, 1 is quite stable as indicated by electrical conductivity and (1)H NMR measurements. In aprotic solvents, viz. CH(3)CN, DMF, or DMSO, however, the extended hydrogen bonded network in 1 breaks apart and the helical structure collapses when irradiated with visible light. The product is a mixed-oxidation vanadium(IV/V) species obtained by photoinduced reduction as confirmed by EPR, time dependent (1)H NMR, and electronic spectroscopy. Compound 1 is a rare example of a nonnatural helix where hydrogen bonding interactions play a crucial role in stabilizing the single stranded polymeric structure such as that frequently observed in the biological world.

Preparation, characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N -methyl- S -methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN]·H 2 O complex

Nickel(II) complexes of general empirical formula, NiLX·nH2O (L = deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxybenzaldehyde; X = Cl−, Br−, NCS−, AcO− or CN−; n = 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN]·H2O complex (ONMeS = anionic form of the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands.

Mono- and dinuclear oxovanadium (IV) compounds containing VO(ONS) basic core: synthesis, structure and spectroscopic properties

Reaction of [VO(acac) 2] with S-methyl 3-(2-hydroxyphenyl) methylenedithiocarbazate (H 2L 1) and its nitro- (H 2L 2) and bromo derivatives (H 2L 3) as tridentate heterodonor (ONS) 2− ligands offers a basic VO(ONS) core. In the presence of bidentate (N,N′) donor ancillar ligands, various mono- and dinuclear oxovanadium(IV) complexes [VOL(2,2′-bipy)] ( 1–3), [VOL(Phen)] ( 4, 5) and [LOV(μ-4,4′-bipy)VOL] ( 4, 5) and [LOV(μ-4,4′-bipy)VOL] ( 6–8) were obtained. The compounds have been characterized by EPR, electronic and FAB mass spectroscopic studies. The X-ray crystal structure of a representative compound [VOL 2(2,2′-bipy)] ( 2) is reported and shows the presence of the tridentate ONS ligand occupying the meridional sites leading to distorted octahedral geometry. The nitrogen donor, occupying an apical position has a trans-labilizing influence, resulting in elongation of the VO terminal bond. Magnetic susceptibility and EPR spectral studies indicate non-interacting nature ( vbJ vb ≈ 0) of the vanadium(IV) unpaired electrons in the dinuclear complexes ( 6–8).

X-Ray Structures of Several Bis(N-alkylsalicylaldiminato)zinc(II) Complexes

Abstract X-ray structures of five bis(N - R-salicylaldiminato)zinc(II) complexes with R = ethyl, n-propyl, i-propyl, n-butyl and 4-thia-n-hexyl were determined. The N2O2 coordination geometry is in all cases quasi-tetrahedral with the dihedral angle between the planes of the two chelate rings ranging from 84 to 89°. Bond lengths and angles in the coordination sphere are not affected by the nature of R or by a methoxy substituent in 4-position of the salicylaldimine. The potentially tridentate ONS ligand N(4-thia-n-hexyl)salicylaldimine is also coordinated only in a bidentate NO fashion.

Nickel(II) complex with a tridentate ONS-Schiff base ligand: X-ray structure, VIS and NIR solution spectra and kinetics of ligand substitution

The ligand N-(3-thia-n-pentyl)salicylaldimine (Hsalen-SEt) and its green nickel(II) complex Ni(salen-SEt) 2 was prepared. The complex crystallizes in the orthorhombic space group Pbca with a a = 2538.3(4) pm, b = 1490.0(3) pm, c = 1163.5(2) pm and Z = 8. The coordination sphere of the nickel is a distorted octahedron with two oxygen atoms in a cis-position, two nitrogen atoms in a trans-position and two sulfur atoms in a cis-position. The two NiO distances were 197.8 and 198.1 pm, the two NiN distances 201.8 and 200.6 pm, whereas the two NiS distances are 272.0 and 266.3 pm. The magnetic susceptibility of Ni(salen-SEt) 2 was measured in the temperature range 2.6-281 K, the magnetic moment being μ eff=3.02μ B. The VIS and NIR solution spectra of the complex in different solvents indicate that the two tridentate ONS-ligands are coordinated as bidentate ON-ligands, the coordination geometry being square-planar ( trans- N 2O 2) in non-coordinating solvents ( e.g., toluene) and octahedral in coordinating solvents ( e.g., pyridine), due to addition of two solvent molecules. From spectrophotometric titration the individual complex formation constants for the species Ni(salen-SEt) 2·py ( K 1 and Ni(salen-SEt) 2·2py ( K 2) were found to be K 1 = 1.76 ± 0.40 M -1 and K 2 = 145 ± 34 M -1. The kinetics of the reaction Ni(salen-SEt) 2 + H 2salen → Ni(salen) + 2Hsalen-SEt as studied in acetone by stopped-flow spectrophotometry follow the rate law, rate = ( k S = k H 2 salen H 2salen]) × [Ni(salen-SEt) 2] with k S = 0.038 ± 0.013 s -1 and k H 2 salen = 17.2 ± 0.4 M -1 s -1 at 25°C. The spectroscopic and kinetic properties of Ni(salen-SEt) 2 are compared with those of bis(N-alkyl-salicylaldiminato)nickel(II) complexes

Magnetic and spectroscopic studies on nickel(II) and copper(II) complexes of some neutral tridentate ONS ligands

New Schiff base ligands formed from 2-methoxybenzaldehyde and 2,4-dimethoxybenzaldehyde with N-methyl-S-alkyldithiocarbazates and their nickel(II) and copper(II) complexes have been prepared and characterised by elemental analysis and magnetic and spectroscopic measurements. The Schiff bases behave as neutral tridentate chelating agents forming stable nickel(II) complexes of stoichiometry NiLX2•xC2H5OH (L = 2-methoxy- or 2,4-dimethoxybenzaldehyde Schiff bases of N-methyl-S-methyldithiocarbazate; X = I−, SCN−; x = 0, 1). Conductivity, magnetic, and spectral data support an octahedral structure for the nickel(II) complexes. The CuLCl2 complexes were also isolated. Magnetic and spectral evidence are in accord with a chloro-bridged dimeric structure. The chloro-complex of copper(II) with the 2-methoxybenzaldehyde Schiff base displays a room-temperature magnetic moment of 1.81 BM, which remains virtually constant over the temperature range 343–123 K.Hydrated copper(II) chloride promotes complete hydrolysis of the 2,4-dimethoxybenzaldehyde and 2-methoxybenzaldehyde Schiff bases of N-methyl-S-benzyldithiocarbazate with the concomitant formation of copper(II) complexes of the parent N-methyl-S-benzyldithiocarbazate of general formula, Cu(N—SR)Cl2 (R = C6H5CH2—).