Applied Chemistry

Synthesis, spectroscopic (IR and electronic) and in-vitro antibacterial properties of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Pd(II) complexes of the enolimines derived from condensation of p-nitroaniline and benzoyl trifluoroacetone (HL1) / theonyltrifluoroacetone (HL2) were reported. The ligands coordinated to the metal ions through the azomethine N and enol O atoms in ratio 1M: 1L, resulting in complexes of the type [ML1NO3].xH2O, [ML2(CH3COO)].xH2O and [PdL(Cl)H2O]. The IR and electronic spectral measurements were consistent with the adoption of a 4-coordinate square planar/ tetrahedral geometry for the metal complexes. The in-vitro antibacterial studies of the Schiff bases and their metal(II) complexes against Bacillus subtilis, Staphylococcus aureus, Proteus mirabilis, Klebsiella oxytoca, Pseudomonas aeruginosa, and Escherichia coli revealed that HL1 and its metal complexes were generally more active than HL2 and its complexes. Interestingly, [Zn(L1)NO3].½H2O, [Pd(L1)Cl(H2O)] and [Ni(L2)2] had broad-spectrum antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli with inhibitory zones range of 12.5-22.0 mm proving their potential usefulness as broad-spectrum antibacterial agents.

Oxovanadium(IV) and Dioxouranium(VI) complexes of Schiff bases derived from 3-substituted-4-animo-5-mercapto-1,2,4-triazole and glyoxal/biacetyl /benzyl have been synthesized and characterized on the basis of analytical and spectroscopic studies. The elemental analysis agrees well with the 1:1 stoichiometry of the type VO.L.So4 and UO2.L.(CH3COO)2 respectively. The IR data suggests that, ligands have coordinated to the metal ion through azomethine nitrogen atoms in a bidentate fashion by keeping sulphur atom of mercapto groups away from coordination. Thermograimetric measurements and XRD pattern have also been done on some oxovanadium (IV) complexes. Some of the VO(IV) and UO2(IV) complexes have been screened for their antimicrobial and antifungal activity. One of the VO(IV) complex has been evaluated for its oxytocic and antihistaminic activity.

A new series of Cr(III) and Fe(III) complexes with the Flavone ligand were prepared and spectroscopic method and elemental analysis verified their structures. All the prepared complexes have been identified by available spectroscopic tools (UV-Visible and IR) in addition the structure of complexes was characterized by magnetic moments and molar conductance in DMSO solution .From the above of these studies and measurements suggest an octahedral geometry around Cr(III) and Fe(III). A theoretical treatment of the formation of complexes in the gas phase was studied, this was done using the HYPERCHEM-6 program for the Molecular mechanics and Semi-empirical calculations. 

The novel ligand, 2-(6-(2-hydroxy phenyl)-[1,2,4] triazolo [3,4-b][1,3,4] thiadiazol-3-yl)-N-phenyl benzamide (TTS) (2) was prepared from 2-(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)-N-phenylbenzamide (1) with salicyldehyde. The transition metal ions were used to synthesize various metal chelates of ligand (2).The synthesized ligand and its metal chelates were analyzed by elemental analysis, spectral study, ratio of M:L and magnetic characterization. Antifungal activities of the entire novel synthesized ligand and its metal chelates were screened.

Isomeric Nickel (II) complexes of toluic acid hydrazide-hydrazone, HL have been synthesized through one pot synthesis. The ligand, HL and the complexes were characterized with FTIR, Uv-Vis, NMR and Mass Spectroscopies, Melting point, solubility, metal conductance, percentage metal and elemental analyses and magnetic susceptibility. The solubility test revealed that the compounds were generally soluble in DMSO hence the molar conductance of the complexes in DMSO showed that the complexes are electrolytic in nature. The mass spectroscopy, percentage metal and elemental analyses conformed with the formulated masses, while the compounds were stable at room temperature. The FTIR spectra of the ligand proved it to be bidentate and the ligand, HL coordinated to the Ni(II) ions through while the electronic spectra peaks showed that Ni(II) complex isomer I and Ni(II) complex isomer II assumed tetrahedral and square planar geometries respectively. The NMR spectra of Ni(II) complex isomer I gave broad bands due to paramagnetism while Ni(II) complex isomer II revealed the relevant peaks. The antibacterial activities of the compounds showed the complexes are more active against the ligand, with Ni(II) complex isomer 1 showing greater activity against k.pneumoniea.

The tridentate Schiff base, 3-{[(6-methoxypyridin-3-yl)imino]methyl}naphthalen-2-ol, formed by condensation of 5-amino-2-methoxypyridine and 2-hydroxy-1-napthaldehyde coordinates to some Metal(II) ions, forming complexes of the type [M(L2)]½H2O {where M = Mn, Co, Ni, Cu, Zn, Pd}. These complexes are characterized by percentage metal, melting point, conductance measurements, electronic and IR spectroscopies. The IR data confirms that coordination is via the imine nitrogen and napthanenol oxygen atoms; while electronic data support a 4-coordinate tetrahedral/squareplanar geometry for the metal complexes. The complexes are air-stable solids which melt/decompose on heating in the temperature range 196-232oC; and none is an electrolyte in nitromethane. The in-vitro antibacterial activities of the complexes against Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella oxytoca are reported. Notably, the Pd(II) complex exhibits broad-spectrum antibacterial activity against these bacteria with the exception of Pseudomonas aeruginosa with inhibitory zones range in the range 8.0-12.0 mm.

The Schiff base, 3-{[(6-methoxypyridin-3-yl)imino]methyl}-5-nitrophenol, formed by condensation of 5-amino-2-methoxypyridine and 2-hydroxy-5-nitrophenol; and its metal(II) complexes{where M = Mn, Co, Ni, Cu, Zn, Pd} have been synthesized and characterized by %metal, melting points, IR and electronic spectroscopies. The complexes analyse as [ML(NO3)] with the exception of the Ni(II), Cu(II) and Pd(II) complexes which analyse as [MLCl(H2O)] respectively. The IR data confirm that the Schiff base coordinates via the imine nitrogen and phenol oxygen atoms; while the electronic data support a 4-coordinate tetrahedral/squareplanar geometry for the metal complexes. The metal complexes are air-stable solids, which melt/decompose on heating in the temperature range 228-390 oC; while the metal–free Schiff base melts at 208-210 oC. The in-vitro antibacterial studies reveal that the Schiff base, its Co(II) and Zn(II) complexes have a broad-spectrum antibacterial activity against Bacillus cereus, Pseudomona aeuriginosa, Staphylococcus aureus and Proteus mirabilis with inhibitory zones range of 14.0-22.0mm.

Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) ions form complexes of the type [ML₂]xH₂O with the  Schiff  base, [{4-(methylsulfanyl)phenyl]imino}methyl]benzene-2,4-diol, using the phenolic O and imine N atoms. These compounds are characterized by microanalysis, conductance, ¹H NMR, infrared and electronic spectral measurements. The IR measurements reveal that the Zn(II) complex is in the trans-isomeric form while electronic measurements are corroborative of a four coordinate, tetrahedral/square-planar geometry for the metal complexes. None is an electrolyte in nitromethane, and all the complexes are air stable but decomposed on heating in the temperature range 210-330^oC. The antibacterial studies show that the ligand, the Mn(II), Co(II), and Zn(II) complexes are active against Staphylococcus aureus with inhibitory zones range of 9.0-17.0 mm.  The cytotoxic study shows that the Cu(II) complex has the best in-vitro anticancer activity against HT-29 (colon carcinoma) cells with an IC₅₀ value of 30.17 ?M, which is  about a quarter as active as Cis-platin.

The Cu(II) , Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Mn(II) and Fe(III) complexes of Schiff base 6-bromo-N’-(1-(5-chloro-2-hydroxyphenyl)ethylidine)-2-oxo-2H-chromen -3-carbohydrazide has been synthesized and characterized by various spectral techniques. The complexes were prepared by reacting the ligand and metal chloride of Cu(II), Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Mn(II) and Fe(III) in ethanol to get a series of mononuclear complexes. The complexes were characterized by CHN analysis, conductivity measurements, magnetic susceptibility, IR, NMR, ESR, UV-Vis and X-ray Powder diffraction studies. By these spectral studies it is found that Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) complexes have exhibited octahedral geometry where as the other Zn(II), Cd(II), and Hg(II), complexes have exhibited square pyramidal geometry. The ligand and its metal complexes have been screened for their antimicrobial activities. The prepared ligand shows low activity and its metal complexes shows moderate to good activity.

Polystyrene-anchored Cu(II), Zn(II), Cd(II), Ni(II), Mn(II), MoO₂(II), UO₂(II), Fe(III) and Zr(IV), complexes of unsymmetrical dibasic tetradentate ONNO donor Schiff base derived from the condensation of chloromethylated polystyrene, 3-formylsalicylic acid, ethylenediamine and 2-hydroxy-1-naphthaldehyde (PS–LH₂) have been synthesized. The polystyrene anchored complexes have the formulae: PS–LM (where M = Cu, Zn, Cd, Ni, MoO₂, UO₂), PS–LFeCl×DMF, PS–LMn×2DMF and PS–LZr(OH)₂×DMF. The polystyrene-anchored coordination compounds have been characterized by elemental analysis, IR, reflectance, ESR and magnetic susceptibility measurements. The per cent reaction conversion of polystyrene anchored Schiff base to polystyrene supported coordination compounds lies between 24.0–77.9. The coordinated dimethylformamide is completely lost on heating the complexes. The shifts of the n(C=N)(azomethine) and n(C–O)(phenolic) stretches have been monitored in order to find out the donor sites of the ligands. The Cu(II) complex is paramagnetic with square planar structure; the Ni(II) complex is diamagnetic with square planar structure; the Zn(II) and Cd(II) complexes are diamagnetic and have tetrahedral structure; the Mn(II) and Fe(III) complexes are paramagnetic and have octahedral structure; the MoO₂(II) and UO₂(II) complexes are diamagnetic and have octahedral structure and the Zr(IV) complex is diamagnetic and has pentagonal bipyramidal structure.