Aderoju A. Osowole

Synthesis, Physicochemical, and Biological Properties of Nickel(II), Copper(II), and Zinc(II) Complexes of an Unsymmetrical Tetradentate Schiff Base and Their Adducts

Nickel(II), copper(II) and zinc(II) complexes of unsymmetrical Schiff base derived from 2-hydroxy-1-naphthaldehyde, 2,4-pentanedione and p-phenylenediamine of the general formula [M(C10H6OCH:N(C6H4)N:C(CH3)CH:C(CH3)O)], [ML], and their adducts with 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) have been synthesized and characterized by elemental analyses, conductance, room temperature magnetic susceptibility, and infrared and electronic spectral measurements. The ligand is tetradentate, coordinating via the imine N and enolic O atoms. The magnetic moments and electronic spectra corroborate octahedral geometry for Ni(II) and Cu(II) complexes whereas the Zn(II) Schiff base complex analyzed 4-coordinate and the adduct 6-coordinate. The Ni(II) and Cu(II) complexes incorporated two water molecules each. The antimicrobial properties of the ligand and compounds against Staphylococcus aureus, Streptococcus faecalis, Bacillus sp, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Klebsiella pneumoniae, Acinetobacter sp, Flavobacterium sp, Enterococcus faecalis and Candida albicans are reported. The compounds generally exhibited good activity against the selected organisms. The compound [CuLphen] has comparable activity to gentamycin. The minimum inhibitory concentrations (MICs) of the sensitive compounds are between 1.0–12.0 mg/mL.

Synthesis, characterization and biological studies on unsymmetrical Schiff-base complexes of nickel(II), copper(II) and zinc(II) and adducts with 2,2′-dipyridine and 1,10-phenanthroline

A series of metal(II) unsymmetrical Schiff-base complexes, {M(C10H6OCH:N(CH2)2N : C(CH3)CH : C(CH3)O), where M=Ni(II), Cu(II) and Zn(II)}, and their 2,2′-dipyridine (bipy) and 1,10-phenanthroline (phen) adducts are synthesized and characterized by microanalysis, magnetic susceptibility, conductance, IR and UV-Vis spectra. The ligand coordinates using the N2O2 chromophore to give a two-metal-center four-coordinate square-planar geometry. IR and UV-Vis spectra are consistent with octahedral adducts. The compounds are non-electrolytes in nitromethane and magnetic moments indicate that the complexes are magnetically dilute. The antimicrobial activity of the compounds against ten bacteria and one fungus are reported. The Cu(II) and Zn(II) complexes showed good activity against many of the organisms while their adducts are generally not sensitive. The minimum inhibitory concentrations (MICs) of the sensitive compounds are between 3.0–13.0 mg mL−1.

SYNTHESIS AND CHARACTERISATION OF SOME NICKEL(II) β-KETOAMINES AND THEIR ADDUCTS WITH 2,2′-BIPYRIDINE AND 1,10-PHENANTHROLINE

ABSTRACT A series of nickel(II) β-ketoimine complexes, {Ni[CH3-C(O)CHC(CH3)NR]2, R=CH3, C4H9}, and ketoiminates, {Ni[CH3C(O)CH(CH3)C(-N(CH2)nN-)C(CH3)CHC(O)CH3], n=2, 6, 8, 9}, and their adducts with 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) have been synthesized and characterized using elemental analyses, magnetic susceptibility, conductivity, infrared and electronic spectral measurements. The ketoimine ligands coordinate to the nickel atom in a bidentate fashion using the N2O2 chromophore. A range of stereochemistries was observed for the nickel(II) ketoiminates from four-coordinate tetrahedral and square-planar geometry to six-coordinate octahedral geometry. Conductivity measurements indicate that the compounds are non-electrolytes. The influence of bridging chain lengthening on the adopted geometry is discussed and possible structures for the compounds are suggested.

Synthesis and characterization of some metal(II) complexes of isomeric unsymmetrical Schiff bases and their adducts with triphenylphosphine

We report the isolation of two unsymmetrical isomeric Schiff bases obtained from condensation of 2,4-pentanedione/1-phenyl-1,3-butanedione and 2-hydroxy-4-methoxyacetophenone/2-hydroxy-4-methoxybenzophenone with ethylenediamine and their VO(IV), Co(II), Ni(II), and Cu(II) complexes. Further reaction of each complex with triphenylphosphine resulted in formation of 1 : 1 adducts, with water occupying the sixth position in some, except copper and cobalt formed 1 : 2 adducts with [ML1]. The purities of the ligands and complexes were established by microanalyses and the complexes were characterized by magnetic susceptibility, conductance, infrared and electronic spectral measurements. The involvement of the azomethine N and phenolic O in bonding resulted in an N2O2 chromophore around the central metal atom. Infrared and electronic spectral data are consistent with square-planar/tetrahedral geometry for Ni(II), Co(II), and Cu(II) complexes and a five-coordinate, square-pyramidal geometry for the VO(IV) complexes. Evidence for triphenylphosphine adducts is adduced from microanalyses, spectral changes, and magnetic susceptibility measurements.

Syntheses and Characterization of Some Tetradentate Schiff-Base Complexes and Their Heteroleptic Analogues

VO(IV), Ni(II) and Cu(II) complexes of the asymmetric Schiff base [(HOC6H3(OCH3)C(C6H5):N(CH2CH2)N:C(CH3)CH:C(C6H5)OH)], and their heteroleptic analogues with triphenyl phosphine and 2,2’-bipyridine have been synthesized and characterized by elemental analyses, conductance, magnetic, infrared and electronic spectral measurements. The ligand is tetradentate coordinating via the imine N and enolic O atoms. The Ni(II) and Cu(II) complexes adopt a four coordinate square planar geometry, the VO(IV) complex is five coordinate square-pyramidal and the heteroleptic complexes are 6-coordinate, octahedral. The assignment of geometry is collaborated by magnetic moments and electronic spectra measurements. The compounds are non-electrolyte in nitromethane and are magnetically dilute.

Spectral, thermal stability and antibacterial studies of copper, nickel and cobalt complexes of N-methyl-N-phenyl dithiocarbamate

Copper(II), cobalt(II) and nickel(II) bis(N-methyl-N-phenyl dithiocarbamate) complexes having the general formula [M{S2CN(MePh)}2] (where M = Cu, Co and Ni) have been prepared and characterized by spectral and thermal analysis. The IR spectra suggest that coordination of dithiocarbamate (DTC) occurred through the two sulfur atoms in a symmetrical bidentate fashion. The electronic spectra, conductance measurement and magnetic moment analysis support the proposed geometry for the electronically dilute complexes. The results of the thermal analysis showed that after dehydration, a one-step decomposition pattern leading to the formation of respective metal sulfide as the end-product occurred. The results are consistent with the proposed composition of the complexes. The in vitro antibacterial activity of the complexes was investigated against strains of gram-negative Escherichia coli, Klebsiella oxytoea and Pseudomonas aureginosa, and gram-positive Bacillus cereus, Staphylococcus aureus and Protues mirabilis. The antibacterial activity of the complexes compared favorably with that of streptomycin and augmentine against S. aureus and B. cereus. The cobalt complex had the best antibacterial activity against the test compounds with inhibitory zone range of 11–14.5 mm. GRAPHICAL ABSTRACT

Synthesis and Physico‐Chemical Properties of Some Copper(II) β‐Ketoamines and Their Adducts with 2,2′‐Bipyridine and 1,10‐Phenanthroline

The copper(II) β‐ketoamine complexes, {Cu[CH3C(O)C(Cl)C(CH3)NR]2, R=CH3, C4H9} and ketoiminates, {Cu[CH3C(O)C(Cl)(CH3)C(‐N(CH2)nN‐)C(CH3)(Cl)CC(O)CH3], n=2, 6, 8, 9} and their 2,2‐bipyridine (bipy) and 1,10‐phenanthroline (phen) adducts have been synthesized and characterized by elemental analyses, conductance, magnetic susceptibility, infrared and electronic spectral measurements. The available conductance data in nitromethane indicate that the compounds are non‐electrolytes while the room temperature magnetic moments (1.88–2.20 B.M.) suggests the absence of magnetic interaction between the Cu(II) ions. The ketoimine ligands coordinate to the copper atom in a bidentate fashion using the N2O2 chromophore to give a four‐coordinate square‐planar geometry. Infrared and electronic spectra results are consistent with the adoption of a six‐coordinate octahedral arrangement for the adducts of the copper(II) complexes with 2,2′‐bipyridine and 1,10‐phenanthroline. Probable structures for the compounds are suggested.

Synthesis, Biological, and Quantum Chemical Studies of Zn(II) and Ni(II) Mixed-Ligand Complexes Derived from N,N-Disubstituted Dithiocarbamate and Benzoic Acid

Some mixed-ligand complexes of Zn(II) and Ni(II) derived from the sodium salt of N-alkyl-N-phenyl dithiocarbamate and benzoic acid have been prepared. The complexes are represented as ZnMDBz, ZnEDBz, NiMDBz, and NiEDBz (MD: N-methyl-N-phenyl dithiocarbamate, ED: N-ethyl-N-phenyl dithiocarbamate, and Bz: benzoate); and their coordination behavior was characterized on the basis of elemental analyses, IR, electronic spectra, magnetic and conductivity measurements, and quantum chemical calculations. The magnetic moment measurement and electronic spectra were in agreement with the four proposed coordinate geometries for nickel and zinc complexes and were corroborated by the theoretical quantum chemical calculations. The quantum chemically derived thermodynamics parameters revealed that the formation of N-methyl-N-phenyl dithiocarbamate complexes is more thermodynamically favourable than that of the N-ethyl-N-phenyl dithiocarbamate complexes. The bioefficacy of the mixed-ligand complexes examined against different microbes showed moderate to high activity against the test microbes. The anti-inflammatory and antioxidant studies of the metal complexes showed that the ethyl substituted dithiocarbamate complexes exhibited better anti-inflammatory and antioxidant properties than the methyl substituted dithiocarbamate complexes.

Coordination behaviours of new (bidentate N,O-chelating) Schiff bases towards copper(II) and nickel(II) metal ions: synthesis, characterization, antimicrobial, antioxidant, and DFT studies

Two Schiff bases, HL1 and HL2, were synthesized in two different reactions involving 2-hydroxynaphthaldehyde with 2-amino-6-methylbenzothiazole and 2-amino-6-florobenzothiazole respectively. Copper(II) and nickel(II) complexes of the Schiff bases were subsequently prepared in 1:1 metal-to-ligand stoichiometric reactions. The compounds were characterized extensively by 1H NMR, 13C NMR, Dept-90, UV–Vis, and IR spectroscopic techniques, magnetic susceptibility, TGA, DTG, and molar conductivity analysis. The spectroscopic results confirm bidentate nature of the Schiff bases and a four coordinate geometry for all the complexes: [CuL1ClH2O], [NiL1ClH2O], [Cu(L2)2], and [NiL2ClH2O]. Quantum chemical studies gave fully optimized geometries of the Schiff bases and metal complexes using the 6-31+g(d,p) basis set. The compounds were studied for their in vitro antibacterial activities against some selected Gram-positive and Gram-negative bacteria, using agar well diffusion. The metal complexes exhibited better antibacterial activities compared to the free ligand due to the effects of chelation, which improved the lipophilicity. Furthermore, the antioxidant potentials of the compounds were ascertained using DPPH radical scavenging and ferrous chelating assay. The copper complexes had the best antioxidant properties of all the tested compounds. The results of the biological analysis were in agreement with the theoretical data from quantum chemical calculations. The study presented biologically active coordination compounds with benzothiazole moiety that could be used as compounds of interest in the drug discovery processes.

Synthesis, Spectroscopic, Thermal, and In Vitro Anticancer Properties of Some M(II) Complexes of 3-(-1-(4,6-Dimethyl-2-pyrimidinylimino)methyl-2-naphthol

Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes of the Schiff base 3-(-1-(4,6-dimethyl-2-pyrimidinylimino)methyl-2-naphthol have been synthesized and characterized by infrared (IR), electronic, nuclear magnetic resonance (1H-NMR), and mass spectroscopies, elemental and thermal analyses, and room-temperature magnetic, powder x-ray diffraction, and conductance measurements. The involvement of the azomethine N and enol O atoms in bonding resulted in an N2O2 chromophore around the central metal atom. The room-temperature magnetic data, IR, and electronic spectral measurements are corroborative of a 4-coordinate square planar/tetrahedral geometry for the Ni(II), Cu(II), and Zn(II) complexes, and a 6-coordinate octahedral geometry for the Mn(II) and Co(II) complexes with water occupying the fifth and sixth coordination sites. All the complexes are high spin and nonelectrolyte in dimethylformamide (DMF). The metal complexes generally have mild to very good anticancer activity in vitro against HL 60 (leukemia) and 518A2 (melanoma) carcinomas, with IC50 in the range 7.67–20.67 μm, respectively. [CuL2] has the best cytotoxic activities against both HL60 (leukemia) and melanoma (518A2) carcinomas with IC50 of 7.67 and 11.20 μm, respectively, which is half as sensitive as and three times more sensitive than CDDP.