2-formylpyridine Thiosemicarbazone Research Articles

Copper(II) Complexes with Isomeric Morpholine-Substituted 2-Formylpyridine Thiosemicarbazone Hybrids as Potential Anticancer Drugs Inhibiting Both Ribonucleotide Reductase and Tubulin Polymerization: The Morpholine Position Matters.

The development of copper(II) thiosemicarbazone complexes as potential anticancer agents, possessing dual functionality as inhibitors of R2 ribonucleotide reductase (RNR) and tubulin polymerization by binding at the colchicine site, presents a promising avenue for enhancing therapeutic effectiveness. Herein, we describe the syntheses and physicochemical characterization of four isomeric proligands H2L3-H2L6, with the methylmorpholine substituent at pertinent positions of the pyridine ring, along with their corresponding Cu(II) complexes 3-6. Evidently, the position of the morpholine moiety and the copper(II) complex formation have marked effects on the in vitro antiproliferative activity in human uterine sarcoma MES-SA cells and the multidrug-resistant derivative MES-SA/Dx5 cells. Activity correlated strongly with quenching of the tyrosyl radical (Y•) of mouse R2 RNR protein, inhibition of RNR activity in the cancer cells, and inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity, supported by experimental results and molecular modeling calculations, are presented.

New iron(III) complexes with 2-formylpyridine thiosemicarbazones: Synthetic aspects, structural and spectral analyses and cytotoxicity screening against MCF-7 human cancer cells

2-Formylpyridine thiosemicarbazone - iron (III) chelates [FeL2] Cl•2H2O {L = L1 (C1) [HL1 = 4-(4-Nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide] and L = L2 (C2) [HL2 = 4-(2,5-Dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide]} were prepared. The two ligand anions in each complex resulted in saturation of the iron coordination number and consequently the existence of these complexes as 1:1 electrolytes. As well, the iron in these complexes exhibits low-spin electronic configuration. X-ray crystallography of complex C1 indicated its triclinic crystal system and P 1‾ space group. In addition, it proved the ligation through a thiol sulfur atom and two nitrogen atoms of pyridine and azomethine groups. This is while the presence of two water molecules of crystallization in the complex structure was also indicated. The ligand HL1 was selected for cytotoxicity screening against human MCF-7, A-549, HEPG-2 and HCT-116 cancer cells and the most enhanced activities were detected against the breast cells. Against these cells, the compounds HL1, HL2, C1 and C2 induced cytotoxicity, respectively, with IC50 values of 52.4, 145.4, 34.3 and 62.0 μM. However, against the healthy BHK cells, HL1 and HL2 caused cytotoxicity, respectively, with IC50 values of 54.8 and 110.6 μM and cytotoxicity with percent viabilities of 56.7 and 55.4% of the BHK cells by the complexes (137.4 μM of C1 and 131.9 μM of C2) was determined. These activities against MCF-7 cells are less significant compared with the measured value for doxorubicin. But this standard is more toxic to normal cells than the thiosemicarbazones (IC50 (doxorubicin) = 9.66 μM against MCF-7 cells and 36.42 μM against BHK cells).

A comparative study of α- N -pyridyl thiosemicarbazones: Spectroscopic properties, solution stability and copper(II) complexation

Abstract The effects of methyl substituents at different positions on the 2-formylpyridine thiosemicarbazone (FTSC) core structure on various physico-chemical properties were investigated. Proton dissociation processes, aqueous solution stability, isomer distribution in different solvents, fluorescence properties and lipophilic character of FTSC, pyridine-2-carboxaldehyde N 4 , N 4 -dimethylthiosemicarbazone (PTSC), 2-acetylpyridine thiosemicarbazone (AcFTSC) and 2-acetylpyridine N 4 , N 4 -dimethylthiosemicarbazone (AcPTSC) were studied and compared under the same conditions. There are more and more indications that Cu(II) ions play an important role in the biological activity of anticancer thiosemicarbazones. Therefore, the complex formation equilibria of FTSC with Cu(II) ions were studied by pH-potentiometry, UV–visible spectrophotometry and electron paramagnetic resonance (EPR) spectroscopy to determine stoichiometry, stability constants and solution structures of the complexes formed in aqueous solution (with 30% DMSO). Mono-ligand complexes in different protonation states were identified such as [CuLH] 2+ , [CuL] + and [CuL(OH)] with (N pyridyl ,N,S)(H 2 O), (N pyridyl ,N,S − )(H 2 O) and (N pyridyl ,N,S − )(OH) coordination modes, respectively. At ligand excess two kinds of isomers of a bis complex [CuL 2 ] were detected at pH > 7, in which binding of the ligands via (N pyridyl ,N,S − )(N) and (N pyridyl ,N,S − )(S − ) donor sets is probable at the equatorial positions. Based on the stability data, [CuL] + complexes of the α- N -pyridyl thiosemicarbazones are predominant at pH 7.4 at 1:1 metal-to-ligand ratio possessing such high solution stability that their decomposition is not likely even at biologically relevant micromolar concentrations. In addition, FTSC and all methylated derivatives investigated show similar Cu(II) binding abilities which is in contrast to the respective Fe(II)/(III) complexes where terminal dimethylation distinctly increases the solution stabilities.

Abnormal Magnetic Moment and Zero Field Splitting of Some Nickel (II) Complexes

<em>Some complexes of Ni(II) have been prepared with 2-thio-3-acetyl hydantoin (TAHN) and 2-formyl pyridine thiosemicarbazone (FPTS). On the basis of elemental analysis and molar conductivity, the complexes have been formulated as NiL<sub>2</sub>X<sub>2</sub>, where L = TAHN or FPTS and X = Cl<sup>–</sup>, Br<sup>–</sup>, NCS<sup>–</sup>, ClO<sub>4</sub><sup>–</sup>. The infrared spectra of complexes and free ligand reveal that the ligand TAHN is co-ordinated through sulphur and acetyl oxygen, while FPTS ligand co-ordinates through heterocyclic nitrogen and sulphur to Ni(II) metal ion. The magnetic moment of these complexes are found to be 3.20-3.25 B.M. The values are greater than value (2.828 B.M) corresponding to two unpaired electrons of a d<sup>8</sup>-system. The appearance of four absorption bands in their electronic spectra reveal, the tetragonal distortion in the octahedral symmetry of complexes. The zero field splitting parameter(D) and the other crystal field parameters like Dq<sub>(xy)</sub>, Dq<sub>(z)</sub>, Dt have been calculated. The results show that, the tetragonal distortion parameter (Dt) increases in the order of NCS<sup>– </sup>< Cl<sup>–</sup> < Br<sup>–</sup> while the zero field splitting parameter (D) also increases in the same order for both the planer ligands.</em>

Palladium complexes of 2-formylpyridine thiosemicarbazone and two related ligands: Synthesis, structure and, spectral and catalytic properties

Thiosemicarbazones of 2-formylpyridine, 2-aceylpyridine and 2-benzoylpyridine, abbreviated in general as HL-R (where H depicts the acidic hydrogen and R the fragment (R=H, Me and Ph) linked to the imine-carbon) react with [Pd(PPh3)2Cl2] in refluxing ethanol in the presence of triethylamine to afford complexes of the type [Pd(L-R)(PPh3)]Cl (1, R=H; 2, R=Me, 3, R=Ph). Structures of the complexes 1 and 3 have been determined by X-ray crystallography, and the structure of complex 2 has been optimized by DFT. In all three the thiosemicarbazone ligand binds to the metal center as a monoanionic tridentate NNS-donor forming two adjacent five-membered chelate rings, the triphenylphosphine occupies the fourth coordination site on palladium. Complexes 1–3 display intense absorptions in the visible and ultraviolet regions, which have been analyzed by TDDFT calculations. All the complexes are found to efficiently catalyze Suzuki, Heck and Sonogashira type C–C cross-coupling, and C–N coupling reactions of aryl halides with primary and secondary amines. All the catalytic reactions are found to proceed under ligand-free condition.

Mechanisms underlying reductant-induced reactive oxygen species formation by anticancer copper(II) compounds

Intracellular generation of reactive oxygen species (ROS) via thiol-mediated reduction of copper(II) to copper(I) has been assumed as the major mechanism underlying the anticancer activity of copper(II) complexes. The aim of this study was to compare the anticancer potential of copper(II) complexes of Triapine (3-aminopyridine-2-carboxaldehyde thiosemicarbazone; currently in phase II clinical trials) and its terminally dimethylated derivative with that of 2-formylpyridine thiosemicarbazone and that of 2,2'-bipyridyl-6-carbothioamide. Experiments on generation of oxidative stress and the influence of biologically relevant reductants (glutathione, ascorbic acid) on the anticancer activity of the copper complexes revealed that reductant-dependent redox cycling occurred mainly outside the cells, leading to generation and dismutation of superoxide radicals resulting in cytotoxic amounts of H(2)O(2). However, without extracellular reductants only weak intracellular ROS generation was observed at IC(50) levels, suggesting that cellular thiols are not involved in copper-complex-induced oxidative stress. Taken together, thiol-induced intracellular ROS generation might contribute to the anticancer activity of copper thiosemicarbazone complexes but is not the determining factor.

Impact of Metal Coordination on Cytotoxicity of 3-Aminopyridine-2-carboxaldehyde Thiosemicarbazone (Triapine) and Novel Insights into Terminal Dimethylation

The first metal complexes of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (Triapine) were synthesized. Triapine was prepared by a novel three-step procedure in 64% overall yield. In addition, a series of related ligands, namely, 2-formylpyridine thiosemicarbazone, 2-acetylpyridine thiosemicarbazone, 2-pyridineformamide thiosemicarbazone, and their N(4)-dimethylated derivatives (including the N(4)-dimethylated analogue of Triapine) were prepared, along with their corresponding gallium(III) and iron(III) complexes with the general formula [M(L)(2)](+), where HL is the respective thiosemicarbazone. The compounds were characterized by elemental analysis, (1)H and (13)C NMR, IR and UV-vis spectroscopies, mass spectrometry, and cyclic voltammetry. In addition, Triapine and its iron(III) and gallium(III) complexes were studied by X-ray crystallography. All ligands and complexes were tested for their in vitro antiproliferative activity in two human cancer cell lines (41M and SK-BR-3), and structure-activity relationships were established. In general, the coordination to gallium(III) increased the cytotoxicity while the iron(III) complexes show reduced cytotoxic activity compared to the metal-free thiosemicarbazones. Selected compounds were investigated for the capacity of inhibiting ribonucleotide reductase by incorporation of (3)H-cytidine into DNA.

Synthesis, Spectroscopic, and Antimicrobial Studies on Bivalent Zinc and Mercury Complexes of 2‐Formylpyridine Thiosemicarbazone

A series of metal complexes of Zn(II) and Hg(II) having the general composition [M(L)2]X2 [where L = 2-formylpyridine thiosemicarbazone; M = Zn(II) and Hg(II); X = Cl−, NO3 − and 1/2SO4 2−] have been prepared and characterized by elemental chemical analysis, molar conductance, and spectral (IR and mass) studies. The IR spectral data suggests the involvement of sulphur and azomethane nitrogen in coordination to the central metal ion. On the basis of spectral studies, a tetrahedral geometry has been assigned for Zn(II) and Hg(II) complexes. The free ligand and its metal complexes have been tested in vitro against a number of microorganisms in order to assess their antimicrobial properties.

The electrochemical reduction of 2-formylpyridine thiosemicarbazone monitored by SERS and UV–vis spectroscopies

Surface-enhanced Raman scattering (SERS) and UV–vis absorption techniques were used to monitor the faradaic reduction of 2-formylpyridine thiosemicarbazone (PATS2) at a silver electrode in methanol solution. Using these spectroscopic techniques coupled with cyclic voltammetry it was possible to identify the reduction products of PATS2 as thiourea and 2-picolylamine, giving support for one of the proposed mechanisms presented in the literature.

Synthesis and characterisation of new homoleptic rhenium thiosemicarbazone complexes

A series of new rhenium(III) complexes, [ReL2]+, where LH = a 2-formylpyridine thiosemicarbazone have been synthesised and characterised. The complexes have been synthesised from the Re(V) starting material [ReOCl3(PPh3)2] and from [ReO4]− in the presence of triphenylphosphine. All of the new compounds have been characterised by X-ray crystallography, NMR and mass spectroscopy. In all cases the Re atom is in a distorted octahedral environment with two tridentate deprotonated thiosemicarbazones binding as monoanionic ligands through the sulfur, pyridyl nitrogen and azamethinic nitrogen in a mer (azomethine nitrogen atoms trans) configuration. Electrochemical measurements show that the complexes undergo two reversible reductions at biologically accessible potentials. Under certain conditions the 2-formylpyridine thiosemicarbazone ligands undergo reductive cleavage of the hydrazinic N–N bond resulting in the formation of a rhenium complex of methyl(2-pyridyl)methyleneimine which has been characterised by X-ray crystallography.

Equilibrium and kinetic studies of iron(II) and iron(III) complexes of some α(N)-heterocyclic thiosemicarbazones. Reduction of the iron(III) complexes of 2-formylpyridine thiosemicarbazone and 2-acetylpyridine thiosemicarbazone by cellular thiol-like reducing agents

α(N)-heterocyclic thiosemicarbazones have been shown to possess antitumor properties in mammalian cells through the inhibition of DNA synthesis; the ability to provide the inhibitory action is probably due to coordination of iron. This paper deals with equilibrium and kinetic studies involving 2-formylpyridine thiosemicarbazone (HFPT) and 2-acetylpyridine thiosemicarbazone (HAPT) coordinated to Fe(II) and Fe(III) cations in aqueous solution. The formation constants of all species present in equilibrium were determined. Kinetic measurements of the reduction of the Fe(III) complex of both ligands by thiolic reducing agents, that can act as structural models of cellular thiols, i.e., N-acetyl-L-cysteine (ACCIS) and dithiothreitol (DTT), were carried out. The experimental data lead to a rate law of the type v = k 1[A] + k 2[A][B], where [A] represents the concentration of the complex and [B] that of the reducing agent, indicating the coexistence of two reaction pathways. One pathway depends only on the complex concentration and occurs even in the absence of the reducing agent, and the other involves both the complex and ACCIS or DTT.

Organotin(IV) complexes with tridentate ligands—III. Synthesis and characterization of some organotin(IV) complexes with N-(2-pyridinylmethylene)hydrazinecarbothioamide: the X-ray crystal structure of dimethylmonochloro[ N-(2-pyridinylmethylene)hydrazinecarbothioamidato) NS(—1)]Tin(IV) hemihydrate

Three organotin(IV) complexes with 2-formylpyridine thiosemicarbazone (HFPT) of formulae [Sn(CH 3)(FPT)Cl 2] and [SnR 2(FPT)Cl] (R = CH 3 and C 2H 5) were prepared and characterized by elemental analysis as well as IR and mass spectral techniques. The X-ray crystal structure of [Sn(CH 3) 2(FPT)Cl]·0.5H 2O has been determined. In this complex, the FPT − anion acts as a mononegative NS bidentate ligand, while the pyridine nitrogen remains uncoordinated. The tin(IV) is in a strongly distorted trigonal bipyramidal configuration where the thiol sulphur and the two methyl carbons occupy the equatorial plane while the chloride and the azomethine nitrogen occupy the apical positions. The 1H and 13C NMR spectra as well as the electronic absorption spectra of these complexes are discussed.

The reaction of 2-formylpyridine thiosemicarbazone (HFPT) with tin tetrahalides. Crystal and molecular structure of [SnCl 3(FPT)

2-Formylpyridine thiosemicarbazone (HFPT) reacts with the tin tetrahalides (X=Cl, Br, I) with abstraction of HX and the formation of tridentate N,N,S-bonded hexacoordinated species [SnX 3(FPT)]. A single crystal X-ray diffraction study of the chloro complex establishes mer-isomerism. Mössbauer data of the products correlate very well with a rehybridization of tin from sp 3 to d 2sp 3 upon complexation.

The reaction of the pyrophosphate ion with the antitumour complex [{CuL(CH 3COO)} 2] (HL=2-formylpyridine thiosemicarbazone) and the single-crystal X-ray structure of [(CuL) 4P 2O 7]· nH 2O

The preparation of the complex [(CuL) 4P 2O 7]· nH 2O (HL=2-formylpyridine thiosemicarbazone; n=9–12) from the reaction of Na 4P 2O 7 with [{CuL(CH 3COO)} 2] is described. The complex has been characterized by a variety of physiochemical techniques and its crystal and molecular structure determined. Crystals of [(CuL) 4P 2O 7]· nH 2O are monoclinic, space group C2/ c, with a=29.074(6), b=28.021(3), c=13.374(3) Å, β=102.93(2)° and Z=8. The complex is tetranuclear, containing four CuL + moieties linked by a bridging P 2O 7 4− anion. Each copper atom is in an approximately square pyramidal environment. The equatorial positions are occupied by a pyrophosphate oxygen, a pyridine nitrogen, an imine nitrogen and a thioamide sulfur, the latter three from the same L ligand. A weakly bound S atom from an adjacent L ligand, is in an axial position, thus completing the coordination sphere. Each tetranuclear [(CuL) 4P 2O 7] molecule may be considered as a pair of dinuclear (CuL +) 2 units linked by a P 2O 7 4− anion. Each dinuclear unit is further linked by the axial CuS bonds. The pyrophosphate ion, which displays a staggered conformation, plays an important role in the hydrogen bonding network involving phosphate oxygens, the thioamide and amine nitrogens of L, and the watet molecules in the structure. The variable temperature magnetic susceptibility of [(CuL) 4P 2O 7]· nH 2O is compared with that of [{CuL(CH 3COO)} 2] and in both cases the results are interpreted in terms of very weak antiferromagnetic coupling between the copper atoms. In the case of the pyrophosphate complex, the fact that the structure contains dinuclear (CuL +) 2 units linked in pairs required that an interaction between the dinuclear units as well as the intramolecular J value be included to fit the magnetic data.

Synthesis and Characterization of Potential Antitumor and Antiviral Gallium(III) Complexes of α-(N)-Heterocyclic Thiosemicarbazones

Abstract Gallium(III) complexes of six α-(N)-heterocyclic thiosemicarbazones were synthesized and characterized by elemental analysis, conductivity measurements, infrared spectroscopy and 1H NMR spectroscopy. Mass spectrometry was carried out with two complexes and a X-ray single-crystal study performed with one complex - dichloro-[(2-acetylpyridine)-4, 4-(3-methyl pentamethylene) thiosemicarbazonato-N1, N2, S]gallium(III). The gallium(III) complexes had the general formula LGaCL2 (LH [ligand acid] = 2-formylpyridine thiosemicarbazone, 2-acetylpyridine thiosemicarbazone, 2-aceryl-pyridine-4, 4-dimethyl thiosemicarbazone, 2-acetylpyridine-4, 4-hexamethylene thiosemicarbazone, 2-acetylpyridine-4, 4-(cyclohexane-l, 4-bismethylene) thiosemicarbazone, 2-acetylpyridine-4, 4-(3-methyl pentamethylene) thiosemicarbazone). The galhum(III) complexes of 2-formylpyridine and 2-acetylpyridine thiosemicarbazone seem to have a cis-configurated trigonal bipyramidal structure whereas the galhum(III) complexes of the N4-dis...

Preparation and characterization of complexes of the antitumour copper(II) 2-formylpyridine thiosemicarbazone (HL) system and the single-crystal X-ray structures of [{Cu(HL)(CF3CO2)}2][CF3CO2]2and [Cu(HL)(H2O)(CLO4)2]·2H2O

The complexes [{Cu(HL)X2·nH2O (HL = 2-formylpyridine thiosemicarbazone, X = CF3CO2, F or I, n= 0; X = Br, n= 2) and [Cu(HL)(H2O)X2]·nH2O (X = ClO4, n= 2; X = NO3, n= 0) have been prepared from the reaction of [{CuL(MeCO2)}2] with the appropriate acid, HX. Also prepared were the deprotonated ligand complexes [(CuLX)2]·nH2O from the reaction of NaL with the appropriate copper(II) salt (X = F, n= 5.5; X =½SO4, n= 3) or by the reaction of [{CuL(MeCO2)}2] with the appropriate sodium salt, NaX (X = N3, n= 1; X = CN, n= 2). The complexes have been characterized by a variety of physicochemical techniques and the crystal and molecular structures of [{Cu(HL)(CF3CO2)}2][CF3CO2]2 and [Cu(HL)(H2O)(ClO4)2]·2H2O determined by single-crystal X-ray diffraction studies. Crystals of [{Cu(HL)(CF3CO2)}2][CF3CO2]2 are triclinic, space group P, with a= 9.6015(7), b= 10.837(1), c= 8.811(2)Å, α= 100.71(1), β= 117.06(1), γ= 80.877(7)°, and Z= 1. The complex cation is a centrosymmetric dimer, the monomeric units being bridged by two CF3CO2– anions. The copper atoms have a distorted square-pyramidal co-ordination geometry with three donor atoms (NNS) coming from HL and the fourth donor (an oxygen) from the bridging anion. The fifth position is occupied by a less strongly bound oxygen from the second bridging anion. Crystals of [Cu(HL)(H2O)(ClO4)2]·2H2O are monoclinic, space group P21/c, with a= 12.9615(5), b= 9.7638(4), c= 14.9964(8)Å, β= 111.580(4)°, and Z= 4. The complex is monomeric with a distorted tetragonal co-ordination around the copper atom. The four in-plane donor atoms are provided by HL (NNS) and an oxygen from a co-ordinated water molecule. Two weakly bound ClO4– ions occupy the fifth and sixth positions. In both complexes hydrogen-bonding schemes appear to be important in stabilizing them in the solid state. The differences in the bonding parameters for the Cu(HL)2+ and CuL+ systems are discussed and related to the fact that the S→CuII ligand-to-metal charge-transfer absorption (at ca. 400 nm) is always observed at higher energies for the HL complexes.

Reaction of nitrogen and sulphur donor ligands with the antitumour complex [{CuL(MeCo2)}2](HL = 2-formylpyridine thiosemicarbazone) and the single-crystal X-Ray structure of [CuL(bipy)]ClO4(bipy = 2,2′-bipyridyl)

The preparation of N- and S-donor ligand adducts with CuL+(HL = 2-formylpyridine thiosemicarbazone) is described. The N-donors, 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen) and 4-dimethylaminopyridine (dmap) give the complexes [CuL(bipy)]X (X = ClO4 or PF6), [CuL(bipy)]2SO4·8H2O, [CuL(phen)]PF6 and [CuL(dmap)2]PF6, which have been characterized by physical and spectroscopic techniques. The structure of one of the complexes, [CuL(bipy)]ClO4, has been determined by the single-crystal X-ray diffraction method: triclinic, space group P with a= 8.560(3), b= 9.452(4), c= 13.078(4)A, α= 106.35(3), β= 94.66(3), γ= 95.27(3)° and Z= 2. The complex contains discrete [CuL(bipy)]+ cations and ClO4– anions. The copper atom environment exhibits a distorted five-co-ordinate geometry. Three donor atoms (NNS) from L form a tricyclic ligating system with the remaining positions being occupied by bipy N atoms giving significantly different Cu–N distances of 1.986(4) and 2.179(4)A. Pentafluoro-(pftp), pentachloro-(pctp) and 4-nitro-thiophenolate (ntp) give S-donor complexes [{CuL(SR)}2]·nH2O (SR = pftp, n= 4; pctp, n= 0; ntp, n= 6). Thiolato co-ordination is proposed on the basis of spectroscopic evidence. With 2-mercaptobenzothiazole (Hmbt), 2-mercaptoimidazole (Hmi), 2-mercapto-1-methylimidazole (Hmmi) and 3-mercapto-4-methyl-1,2,4-triazole (Hmmt), either deprotonated ligand adducts of the type [CuL(A)](A = mbt, mi or mmt) or neutral ligand adducts [CuL(HA)2]PF6(HA = Hmmi or Hmi) are isolated. It is suggested that the thioamides co-ordinate via the imine nitrogen atom. The relevance of the results to proposed mechanisms for the antitumour activity of CuL+ is discussed.

Spectroscopic studies of metal complexes containing π-delocalized sulfur ligands. Mössbauer and kinetic studies of iron(II) and iron(III) complexes of the antitumor agent 2-formylpyridine thiosemicarbazone

Mössbauer studies on the Fe(II) and Fe(III) complexes of 2-formylpyridine thiosemicarbazone (FPT) showed the complexes to be low spin and provided evidence of the reducing character of the ligand. In addition, kinetic measurements of the Fe(III) complex reduction by the ligand gave an expression for the initial rate of the type v i = k′A + k″AB, in which A stands for the concentration of the Fe(III) complex and B for the concentration of the reducing agent. From this equation one may infer the coexistence of two mechanisms, one expressed by the first term and occurring even in the absence of FPT. For the second term we propose an inner sphere mechanism in which the ligand is the reducing agent.

The characterization of both the coordinated and non-coordinated saccharinate ion. The syntheses and crystal structures of aqua(2-formylpyridine thiosemicarbazonato)(saccharinato- N)copper(II) hemihydrate and 2,2′-bipyridyl-(2-formylpyridine thiosemicarbazonato)copper(II) saccharinate dihydrate

The preparation of the complex [CuL(sacc)- (H 2O)]·0.5H 2O (HL=2-formylpyridine thiosemicarbazone, Hsacc = saccharin) from the reaction of Na(sacc) with [{CuL(CH 3COO)} 2] is described. The complex [CuL(bpy)](sacc)·2H 2O (bpy = 2,2′- bipyridyl) is obtained if the reaction is carried out in the presence of 2,2′-bipyridyl. The complexes have been characterized by a variety of physicochemical techniques and their crystal and molecular structures determined. Crystals of [CuL(sacc)(H 2O)]·0.5H 2O are monoclinic, space group P2 1/n, with a = 7.465(7), b = 9.245(7), c = 26.209(33) Å, β = 97.18(9)° and Z = 4. Crystals of [CuL(bpy)](sacc)·2H 2O are triclinic, space group P 1 , a = 9.243(1), b = 12.393(1), c = 13.323(1) Å, α = 75.511(5), β = 67.751(5), λ = 73.294(7)° and Z = 2. Both complexes contain five coordinate copper with three donor atoms (NNS) contributed by L, which forms a tricyclic ligating system. For [CuL(sacc)(H 2O)]·0.5H 2O the coordination sphere is completed by a monodentate N-bound saccharinate ion and a more weakly bound water molecule giving a distorted square-pyramidal geometry. For the complex [CuL(bpy)](sacc)-2H 2O the remaining coordination sites are occupied by two N atoms from 2,2′-bipyridyl, resulting in a geometry intermediate between square-pyramidal and trigonal- bipyramidal. The saccharinate ion is a non- coordinated anion.

A study of ruthenium complexes of some selected N—S donors Part II. Ligational behaviour of 2-formylpyridine(4-phenyl) thiosemicarbazone towards ruthenium

Ru(II) and Ru(III) complexes of the biologically active tridentate NNS donors 2-formylpyridine(4- phenyl) thiosemicarbazone (L 1H) and 2-formylpyridine thiosemicarbazone (LH) have been synthesized and characterized by elemental analysis, conductance and magnetic susceptibility measurements, as well as by spectroscopic techniques such as UV—Vis, IR and NMR. A series of mononuclear bis chelates of the formulae [Ru(L 1H) 2](SCN) 2, [Ru(L 1H)(L 1)] Cl, [Ru(L 1) 2], [Ru(L)(LH)]ClO 4·2H 2O and mononuclear mixed ligand complexes such as [Ru(L 1H)Cl 2(CH 3OH)], [Ru(L 1H)(imz)Cl 2], [Ru(L 1H)(2-pico)(imz)]ClO 4, [Ru(L 1H)(TTSC)]Cl· 1 2 (C 2H 5) 2O, [Ru(L 1H)(imz)(thiosal)]Cl·CH 3OH, [Ru(L 1H)(bipy)Cl]Cl 2·CH 2Cl 2 have been isolated and characterized. Binuclear complexes [Ru 2(L 1) 2(OH) 2], [Ru 2(L 1) 2Cl 4]·4H 2O, [Ru 2(L 1) 2(SCN) 4]·H 2O, [Ru 2(L 1)(imz)Cl 4]·3CH 3OH, [Ru 2(L 1)(H 2O)Cl 4] have also been synthesized and characterized. From the analysis of spectroscopic and magnetic data the donor sites of the ligands have been located and the geometries of the donor environment around the Ru(II)/Ru(III) acceptor centre have been proposed.