E. Offiong

STEREOCHEMISTRY AND ANTITUMOUR ACTIVITY OF PLATINUM METAL COMPLEXES OF 2-ACETYLPYRIDINE THIOSEMICARBAZONES

Complexes, [M(HL)2], where M = PdII, PtII and HL = neutral 2-acetylpyridine-(2-methylthiosemicarbazone), 2-acetylpyridine-(4-methylthiosemicarbazone) and 2-acetylpyridine-(4-phenylthiosemicarbazone), as well as [M(HL)2]Cl3, where M = RuIII, RhIII and IrIII, have been prepared and characterized by elemental analyses, conductivity measurements, magnetic susceptibility measurements and spectroscopic (i.r., Raman, u.v.-vis. and 1H and 13C-n.m.r) studies. The ligands behave as neutral bidentate components in the PdII and PtII complexes, whereas in RuIII, RhIII and IrIII complexes the ligands exist as neutral tridentates. Various ligand and nephelauxetic parameters have been calculated for the metal complexes. The RuIII, RhIII and IrIII complexes are six-coordinate distorted octahedral, whereas PdII and PtII are four coordinated. The ligands and their platinum group complexes exhibit a potent cytotoxic activity against Ehrlich ascites tumour cells in vitro but appear to be more in vivo.

Synthesis, spectral and cytotoxicity studies of palladium(II) and platinum(II) amino acid Schiff base complexes

Novel PdII and PtII complexes of substituted o-hydroxyacetophenone-glycine have been synthesized, and characterized by conductivity measurements, i.r., electronic and 1H-n.m.r. spectra. The spectral data indicate that the ligands are monobasic bidentate, coordinating through imino nitrogen and the carboxylate group. A four coordinate square planar configuration has been proposed for all the complexes. The ligands, as well as their PdII and PtII complexes, exhibit potent cytotoxic activity against Ehrlich ascites tumour cells in vitro, but appear to be more active in vivo.

The inhibition of mild steel corrosion in hydrochloric acid by 2,2′-pyridil and α-pyridoin

Abstract The effect of closely related α-pyridoin and 2,2′-pyridil on the corrosion behaviour of mild steel in hydrochloric acid solution has been studied. Weight loss and hydrogen evolution measurements reveal that α-pyridoin gives a better inhibition effect than 2,2′-pyridil. The inhibition effect is more pronounced with increasing temperature as well as inhibitor concentration. Chemical adsorption mechanism has been proposed for the two inhibitors. α-Pyridoin and 2,2′-pyridil obey the Freundlich adsorption isotherm equation at all concentrations and temperatures. The higher efficiencies of the α-pyridoin have been explained in terms of high solubility of the compound facilitated by hydrogen bonding with solvent molecules. α-Pyridoin is also considered to form a more stable bond with mild steel.

Synthesis and spectral studies of platinum metal complexes of benzoin thiosemicarbazone

Abstract The platinum metal chelates of benzoin thiosemicarbazone obtained with Ru(III), Rh(III), Ir(III), Pd(II) and Pt(II) were prepared from their corresponding halide salts. The complexes were characterized by elemental analysis, conductance measurement, IR, Raman, 1H-NMR, 13C-NMR and UV-visible spectra studies. Various ligand field parameters and nephelauxetic parameters were also calculated. The mode of bonding and the geometry of the ligand environment around the metal ion have been discussed in the light of the available data obtained. Complexes of Ru(III), Rh(III) and Ir(III) are six-coordinate octahedral, while Pd(II) and Pt(II) halide complexes are four-coordinated with halides bridging.

Formation constants and thermodynamic parameters of α-pyridoin thiosemicarbazones with divalent metal ions

The proton–ligand stability constants of α-pyridoin thiosemicarbazone, α-pyridoin 2–methylthiosemicarbazone, α-pyridoin 4–methylthiosemicarbazone and α-pyridoin (4–phenylthiosemicarbazone) as well as the formation constants of their chelates with CuII, NiII, CoII, ZnII and MnII have been determined. The Calvin–Bjerrum pH titration techniques, as modified by Irving and Rossotti, were employed in aqueous media at different ionic strengths and temperatures. The stability constants of the complexes follow the order: CuII > NiII > CoII > ZnII >MnII which is in accord with the Irving–Williams series. The chelates derived from α-pyridoin 4–phenylthiosemicarbazone have relatively higher stability constants, which may be attributed to the presence of the benzene ring in the chain.

Studies on the stereochemistry of diphenyl diketone monothio-semicarbazone and its transition metal complexes

SummaryThe stereochemistry and complexation behaviour of diphenyl diketone monothiosemicarbazone (DKTS) with CuII, CoII, NiII, CdII, ZnII, PdII, PtII, RuIII, RhIII and IrIII have been investigated by means of chemical, magnetic and spectral (i.r., Raman, 1H- and 13C-n.m.r. and electronic) studies. The ligand forms complexes of the M(DKTS)2 type with NiII, CuII and CoII having a distorted octahedral geometry. The absence of a v(M—X) band in the i.r. spectra, coupled with their 1:1 electrolytic conductances, suggests that RuIII, RhIII and IrIII form octahedral complexes of the [M(DKTS)2]Cl type. A four-coordinate structure involving bridging halides is proposed for the ZnII, CdII, PdII and PtII complexes, which have relatively low v(M—X) vibration modes.

Nickel (II) and Iron (II) Complexes with Azole Derivatives: Synthesis, Crystal Structures and Antifungal Activities

Two new complexes of nickel (II) with 4-amino-3, 5-bis(pyridyl)-1, 2, 4-triazole (abpt) and iron (II) with 2-(3-phenyl-1H-pyrazole-5-yl) pyridine (phpzpy) have been synthesized and characterized by elemental analysis and IR spectroscopy. The crystal structures of the complexes have been determined by single crystal X-ray diffraction techniques. In the nickel and iron complexes, the ligands are coordinated through nitrogen atoms in bidentate manner. The ligands and their respective complexes have been tested for their antifungal activity against Aspergillus niger, Aspergillus flavus, and Candida albicans. From the study, the complexes showed enhanced activities against the tested organisms compared to the ligands.

Copper(II) malonate coordination frameworks with amino-1,2,4-triazole: Crystal structures and magnetic properties of [Cu2(mal)2(datz)2(H2O)]·5H2O and [Cu2(mal)2(atz)2(H2O)]·3H2O

Two new malonato-bridged copper(II) complexes of the composition [Cu2(mal)2(datz)2(H2O)]·5H2O (1) and [Cu2(mal)2(atz)2(H2O)]·3H2O (2) (mal = malonate, atz = 4-amino-1,2,4-triazole, datz = 3,5-diamino-1,2,4-triazole) are prepared and characterized by X-ray crystal structure determination and magnetic studies. The environment of each copper atom in 1 and 2 has distorted square pyramidal and octahedral geometries. The intrachain copper-copper separation is 6.305 Å and 3.640 Å across the carboxylates and trizolates bridges respectively for complexes 1 and 2. The magnetic properties of 1 and 2 are investigated in the temperature range 2–300 K. The overall antiferromagnetic behavior is observed in both cases.

Solvent-Mediated Synthesis of M(II)-Coordination Polymer Part 1: Crystal Structure of Poly(1,2-di(4-pyridyl)ethylene-k2N,N')-bis(1,4-benzenediacetato-k4O,O′,O′′,O′′')zinc(II)], C22H18ZnN2O4

An interaction of water-methanol solution of sodium1,4-benzenediacetate (bda) and 4,4′-bipyridylethelene (bpee) with aqueous solution of Zn(NO3)2·6H2O at room temperature yielded colourless crystals of 1 after three weeks in a sealed glass tube. The compound with composition C22H18ZnN2O4 crystallizes in monoclinic space group P21/c, with the following cell dimensions: a = 10.4566(2), b = 13.3085(2), c = 13.7189(2) A, β = 101.491(1)°. In the structure of 1, two Zn(II) neighbours are connected by two bda ligands adopting chelating and bidentate-bridging coordination modes to form a dimeric unit (Zn2O8N4) with the Zn–Zn distance of 4.0432(6) A. The carboxyl-bridged dimeric units are extended along the [001] direction by bpee co-ligands and further linked by bda ligand to form a three-dimensional network structure. The IR shows the characteristic bands of the carboxylates at 1611/1507 cm−1 and 1424/1373 cm−1, respectively, for asymmetric and symmetric stretching −CO2− vibrations. The separation ∆[νasym(CO2−) − νsym(CO2−)] values of 187 and 134 cm−1 are indicative of chelating and bidentate bridging coordination modes of the carboxylate to the metal centre.

Mixed-Ligand Complexes Of Nickel (II) With 2-Acetylpyridine Thiosemicarbazone And Some N/S Monodentate Ligands: Synthesis, Structural Characterization And Biological Activity

The preparation and spectral properties of five nickel (II) mixed-ligands complexes (Ni [2-Actsc.Y]CI2), derived from 2-acetylpyridinethiosermicarbazones and some nitrogen/sulphur monodentate ligands such as thiophene, ammonia, picoline, pyridine and aniline are described. The complexes have been characterized on the basis of 1H and 13C-NMR, IR and electronic spectra. These revealed the primary ligand to be a tridentate thiosemicarbazone that coordinate in a square planar conformation to nickel (II) via azomethine N, pyridyl N and thiolate S atoms and a monodentate donor molecuole. The antimicrobial activities of these mixed-ligands complexes were investigated. Nickel (II) mixed-ligands complexes derived from 2-acetylpyridinethiosemicarbazones and aniline or ammonia seem to be most efficient inhibitors among these tested compounds. Keywords : mixed-ligands complexes, square planar geometry, thiosemicarbazones, electronic spectra, biological activity. Global Journal or Pure and Applied Sciences Vol. 14 (4) 2008: pp. 411-416