Thiolate Sulfur Atoms Research Articles

Synthesis, spectroscopic, thermal and antimicrobial studies of neodymium(III) and samarium(III) complexes derived from tetradentate ligands containing N and S donor atoms

Trivalent lanthanide complexes of the type [Ln(L)Cl(H2O)2] (where Ln=Nd(III) or Sm(III) and LH2=Schiff bases derived by the condensation of 3-(phenyl/substitutedphenyl)-4-amino-5-mercapto-1,2,4-triazole with diacetyl/benzil) have been synthesized by the reactions of anhydrous lanthanide(III) chloride with Schiff bases in methanol. The structures of the complexes have been proposed on the basis of elemental analysis, electrical conductance, magnetic moment, spectroscopic measurements (IR, 1H, 13C NMR and UV–vis spectra) and X-ray diffraction studies. The spectral data reveal that the Schiff base ligands behave as dibasic tetradentate chelating agents having coordination sites at two thiol sulfur atoms and two azomethine nitrogen atoms. The presence of coordinated water in metal complexes was confirmed by thermal and IR data of the complexes. All the Schiff bases and their metal complexes have also been screened for their antibacterial activity against Bacillus subtilis, Staphylococcus aureus and antifungal activities against Aspergillus niger, Curvularia pallescens and Colletotrichum capsici.

New palladium(II) complexes containing 3-mercapto-1,2,4-triazole ligands: synthesis, characterization, crystal structure, and density functional theory calculations

Two new palladium(II) complexes of 4-amino-3-methyl-1,2,4-triazol-5-thione (H3L) have been synthesized and characterized. The reaction of H3L, palladium(II) chloride, and sodium acetate in a molar ratio 2:1:2 gave the homoleptic binuclear palladium(II) complex [Pd2(H2L)4]·2DMSO (1), while its treatment with palladium(II) chloride, sodium acetate, and triphenylphosphane in a molar ratio 4:4:7:4 gave the tetranuclear palladium(II) complex [Pd4(H2L)2(HL)(L)(PPh3)4]Cl·7MeOH·3H2O (2) with terminal phosphane ligands. All complexes have been characterized by a combination of IR, 1H and 31P NMR spectroscopy, ESI(+) mass spectrometry, and elemental analysis as well as X-ray diffraction studies. On the basis of determined molecular structures, each triazole moiety in the binuclear complex is singly deprotonated, whereas the centrosymmetric tetranuclear complex contains three different 3-mercapto-1,2,4-triazolate moieties, namely singly, twofold, and threefold deprotonated in its solid state. In the binuclear complex, the triazolate ligands act as N,S-bidentate bridging ones and coordinate with the metal centers in a trans-(2,2) fashion. In the tetranuclear complex, the four triazolate ligands act as bridging agents between four metal centers through their thiol sulfur atoms and their endocyclic nitrogen atoms in a head-to-head fashion. In addition, each deprotonated NH2 group of the ligand acts as bridging agent between two adjacent palladium metals. According to density functional theory calculations, the structural constraints imposed by the bridging deprotonated NH2 groups are responsible for the observed close Pd–Pd distance in this complex. No indication for metallophilic interactions was found.

Dimeric nickel(II) and copper(II) complexes of the pentadentate N3S2 chelating agents derived from S-alkyl/aryl esters of dithiocarbazic acid

The helical dimeric copper(II) complex, [Cu(dapsbz)]2 (dapsbz=doubly deprotonated form of the 2,6-diacetylpyridine Schiff base of S-benzyldithiocarbazate) has been synthesized and structurally characterized. Each Schiff base in the dimer acts as a doubly negatively charged N3S2 pentadentate chelating agent, providing three donor atoms, viz. the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom, to one copper ion and the azomethine nitrogen atom and thiolate sulfur atom to the second copper(II) ion. The stereochemistry adopted by each copper(II) ion in the dimer is five-coordinate, approximately square-pyramidal, with a CuN3S2 coordination core. In the dimeric nickel(II) complex, [Ni(dapsme)]2 (dapsme=doubly deprotonated form of the 2,6-diacetylpyridine Schiff base of S-methyldithiocarbazate), the Schiff base also coordinates with the two nickel(II) ions as pentadentate N3S2 chelating agent, but here the pyridine nitrogen atom of each ligand acts as a bridging donor atom. The azomethine nitrogen and thiolate sulfur atoms of one arm of a ligand coordinate with one nickel ion whereas the azomethine nitrogen and thiolate sulfur atoms of the other arm of the same ligand coordinate with a second nickel atom, the stereochemistry adopted by each nickel atom in the dimer being distorted octahedral with a NiN4S2 coordination sphere.

Mixed-ligand metal complexes containing an ONS Schiff base and imidazole/benzimidazole ligands: synthesis, characterization, crystallography and biological activity

Salicylaldehyde-4-methylthiosemicarbazone (H2MTSali) has been prepared via the condensation reaction of 4-methyl-3-thiosemicarbazide and salicylaldehyde. Four new mixed-ligand copper(II) and nickel(II) complexes with a general formula [M(MTSali)L] (M = Cu2+ or Ni2+; L = co-ligand) were synthesized, where L is either imidazole (im) or benzimidazole (bzim). The Schiff base and its mixed-ligand complexes were characterized by IR and UV/Vis spectroscopy, and the complexes by molar conductivity and magnetic susceptibility measurements. The spectroscopic data indicated that the Schiff base behaves as a tridentate ONS donor ligand coordinating via the phenoxide-oxygen, azomethine-nitrogen, and thiolate-sulphur atoms. Magnetic data indicate a square planar environment for the nickel(II) complexes while molar conductance values indicate that the metal complexes are essentially non-electrolytes in DMSO solution. X-ray crystallography shows Cu(MTSali)bzim (1) and Ni(MTSali)bzim (3) to be isostructural, with the metal(II) ions being coordinated by a N2OS donor set that defines an approximate square planar geometry; in both cases, the benzimidazole is splayed with respect to the coordination plane. The copper(II) complexes were active against MDA-MB-231 and MCF-7 breast cancer cell lines, more so than H2MTSali, whereas the nickel(II) complexes were inactive.

Synthesis, spectroscopy and X-ray crystal structures of some zinc(II) and cadmium(II) complexes of the 2-pyridinecarboxaldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazates

The Schiff bases formed by condensation of S-methyl- and S-benzyldithiocarbazate with 2-pyridinecarboxaldehyde react with zinc(II) and cadmium(II) acetates to form stable metal complexes of general formulas, [Zn(NNS)(CH3COO)]2 and [M(NNS)2] (M=Zn2+, Cd2+; NNS−=anionic forms of the 2-pyridinecarboxaldenhdye Schiff bases of S-methyl- and S-benzyldithiocarbazate, respectively) which have been characterized by a variety of physico-chemical techniques and X-ray crystallographic structure analysis. The complexes, [Zn(NNS)(CH3COO)]2 are acetate anion-bridged centrosymmetric dimers in which each of the Schiff bases is coordinated to the zinc(II) ions as a uninegatively charged NNS tridentate chelating agent coordinating via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The acetate anion acts as a bridging bidentate ligand coordinating with the two zinc atoms in a syn–syn manner. Each zinc(II) ion in the dimer adopts an approximately square-pyramidal geometry. The bis-ligand complexes, [M(NNS)2] (M=Zn2+, Cd2+) have distorted octahedral structures in which the two anionic Schiff bases are coordinated to the metal ions meridionally as NNS tridentate chelating agents via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom.Both the mono- and bis-ligand zinc(II) complexes exhibit strong cytotoxic activity against the HELA (human cervical cancer) cell lines. Some of these compounds exhibit stronger cytotoxicity against HELA than the commercially important anticancer drug, Tamoxifen.

The first nickel(II) complexes of disubstituted diphenyldithiophosphates: Synthesis, spectroscopic, electrochemical, antifungal and single crystal X-ray analysis

Five novel nickel(II) complexes of disubstituted diphenyldithiophosphates, [{(ArO)2PS2}2Ni] [Ar=2,4-(CH3)2C6H3 (1), 2,5-(CH3)2C6H3 (2), 3,4-(CH3)2C6H3 (3), 3,5-(CH3)2C6H3 (4) and 4-Cl-3-CH3C6H3 (5)], have been synthesized in aqueous medium and structurally characterized by IR, heteronuclear NMR (1H, 13C and 31P) spectroscopic and single crystal X-ray analyses. Complexes 1 and 5 crystallize in the triclinic space group P1¯, whereas complex 4 crystallizes in the monoclinic space group P21/n. In these complexes, the ligands are coordinated to the nickel ion as a bidentate chelating agent via the two thiolate sulfur atoms, leading to a spirocyclic system. Crystal structure determination of complexes 1, 4 and 5 reveals that the complexes consist of mononuclear units with the nickel(II) ion coordinated in a bis-bidentate fashion with a distorted square planar coordination environment. A cyclic voltammetry experiment was used to probe the redox capabilities of complex 4. The investigated complexes, along with the ligands, have been screened for in vitro antifungal activities against the fungus Penicillium chrysogenum.

Synthesis and Crystal Structures of Copper(II) Complexes with Schiff Base Ligands: [Cu2(acpy-mdtc)2(HBA)(ClO4)]·H2O and [Cu2(acpy-phtsc)2(HBA)]·ClO4

Two new Cu(II) complexes, (1) (acpy-mdtc- = 2-acetylpyridine S-methyldithiocarbamate and = benzilic acid anion) and (2) (acpy- = 2-acetylpyridine 4-phenyl-3-thiosemicarbazate) have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single crystal X-ray diffraction. The X-ray analysis reveals that the structures of 1 and 2 are dinuclear copper(II) complexes bridged by two thiolate sulfur atoms of Schiff base ligand and bidentate bridging anion. For 1, each of the two copper atoms has different coordination environments. Cu1 adopts a five-coordinate square-pyramidal with a donor, while Cu2 exhibits a distorted octahedral geometry in a manner. For 2, two Cu(II) ions all have a five-coordinate square-pyramidal with a donor. In each complex, the Schiff base ligand is coordinated to copper ions as a tridentate thiol mode.

Synthesis and characterization of mixed-ligand copper(II) saccharinate complexes containing tridentate NNS Schiff bases. X-ray crystallographic analysis of the free ligands and one complex

Four new Schiff bases containing N and S heteroatoms (HL1–HL4) have been prepared and characterized, including determination of the X-ray crystal structures of HL1 and HL3. Spectroscopic evidence indicates that these Schiff bases behave as uninegatively charged tridentate NNS ligands in complexes of general formula [Cu(Ln)sac] (Ln is the anionic form of NNS, and sac represents saccharinate anion). Crystals of both HL1 and [Cu(L4)sac)(H2O)]·Hsac crystallized in triclinic system with P\( \bar{1} \) space group, while HL3 crystallized in monoclinic system with P 21/c space group. [Cu(L4)sac)(H2O)]·Hsac has a distorted square-pyramidal structure with a non-bonded saccharin molecule present in the outer coordination sphere. The tridentate NNS ligands are coordinated to Cu through pyridine nitrogen, azomethine nitrogen and thiolate sulfur atoms, while the fourth and fifth coordination positions are occupied by the N-bonded saccharinate anion and a water ligand, respectively.

Vanadium Thiolate Complexes for Efficient and Selective Sulfoxidation Catalysis: A Mechanistic Investigation

The structural and electronic properties as well as the catalytic activity toward sulfoxidation of two new vanadium complexes have been investigated. They both possess in their coordination sphere two alkyl thiolate ligands: a dioxido V(V) complex [VO2L(NS2)](HNEt3) (1) (L(NS2) = 2,2'-(pyridine-2,6-diyl)bis(1,1'-diphenylethanethiol)) and an oxido V(IV) complex [VOL(N2S2)] (2) (L(N2S2) = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1'-diphenylethanethiol)). The X-ray structure of 1 has revealed that the V(V) metal ion is at the center of a distorted trigonal bipyramid. The optimized structure of 2 obtained by DFT calculations displays a square-pyramidal geometry, consistent with its EPR spectrum characterized by an axial S = 1/2 signal (g⊥ = 1.988, g∥ = 1.966, Ax(V) = 45 × 10(-4) cm(-1), Ay(V) = 42 × 10(-4) cm(-1), Az(V) = 135 × 10(-4) cm(-1)). DFT calculations have shown that the HOMO (highest occupied molecular orbital) of 1 is notably localized on the two thiolate sulfur atoms (56% and 22%, respectively), consistent with the expected covalent character of the V(V)-S bond. On the other hand, the SOMO (singly occupied molecular orbital) of 2 is exclusively localized at the V(IV) ion (92%). Complexes 1 and 2 have shown an ability to catalytically oxidize sulfide into sulfoxide. The oxidation reactions have been carried out with thioanisole as substrate and hydrogen peroxide as oxidant. Yields of 80% and 75% have been obtained in 10 and 15 min for 1 and 2, respectively. However, in terms of conversion, 1 is more efficient than 2 (81% and 44%, respectively). More importantly, the reaction is completely selective with no trace of sulfone produced. While 1 displays a poor stability, catalyst 2 shows the same efficiency after five successive additions of oxidant and substrate. The difference in reactivity and stability between both complexes has been rationalized through a mechanism study performed by means of experimental data ((51)V NMR and EPR spectroscopy) combined with theoretical calculations. It has been shown that the structure of the cis-oxo peroxo V(V) intermediate species, which is related to its stability, can partly explain these discrepancies.

Tin and lead phosphinothiolate derivatives. Crystal structures of [Ph3Sn{Ph2PC6H4S-2}], [Sn{PhP(C6H4S-2)2}2] and [Pb{Ph2P(O)C6H4S-2}2]·1/2CH3OH·2H2O complexes

The coordination capability of the phosphinothiol ligands Ph2PC6H4SH-2 and PhP(C6H4SH-2)2, towards two organotin (Ph3SnCl, Ph2SnCl2) and the organolead Ph2PbCl2 was studied. The complexes were characterized by microanalysis, FAB mass spectrometry, IR and NMR spectroscopy. Also, crystal structures of [Ph3Sn{Ph2PC6H4S-2}], [Sn{PhP(C6H4S-2)2}2] and [Pb{Ph2P(O)C6H4S-2}2]·1/2CH3OH·2H2O complexes have been determined. The structure of [Ph3Sn{Ph2PC6H4S-2}] complex shows the triphenyltin fragment coordinated to one monoanionic phosphinothiol ligand acting as monodentate through the thiolate sulfur atom with the tin ion in a tetrahedral environment. The crystal structure of [Sn{PhP(C6H4S-2}2] shows the metal ion in a distorted octahedral geometry. The geometry about the Pb in [Pb{Ph2P(O)C6H4S-2}2]·1/2CH3OH·2H2O complex is best described as distorted ψ−trigonal bipyramidal with the five position occupied by the active lone pair of metal. Intermolecular weak Pb-(η6-C6H5) interactions between the lead electron pair and phenyl rings are also observed.

Mixed Tridentate π -Donor and Monodentate π -Acceptor Ligands as Chelating Systems for Rhenium-188 and Technetium-99m Nitrido Radiopharmaceuticals

A new molecular metallic fragment for labeling biologically active molecules with 99mTc and 188Re is described. This system is composed of a combination of tridentate π-donor and monodentate π-acceptor ligands bound to a [M Ξ N]2+ group (M = (99m)Tc, 188Re) in a pseudo square-pyramidal geometry. A simple structural model of the new metallic fragment was obtained by reacting the ligand 2, 2'-iminodiethanethiol [H2NS2 = NH(CH2CH2SH)2] and monodentate tertiary phosphines with the [M Ξ N]2+ group (M = (99m)Tc, (188)Re). In the resulting complexes (dubbed3+1complexes), the tridentate ligand binds the [M Ξ N]2+ core through the two deprotonated, negatively charged, thiol sulfur atoms and the neutral, protonated, amine nitrogen atom. The residual fourth position of the five-coordinated arrangement is occupied by a phosphine ligand. The chemical identity of these model (99m)Tc and (188)Re compounds was established by comparison with the chromatographic properties of the corresponding complexes obtained at the macroscopic level with the long-lived (99)Tc and natural Re isotopes. The investigation was further extended to comprise a series of ligands formed by simple combinations of two basic amino acids or pseudo-amino acids to yield potential tridentate chelating systems having [S, N, S] and [N, N, S] as sets of π-donor atoms. Labeling yields and in vitro stability were investigated using different ancillary ligands. Results showed that SNS-type ligands afforded the highest labeling yields and the most robust 3+1 nitrido complexes with both (99m)Tc and (188)Re. Thus, the new chelating system can be conveniently employed for labeling peptides and other biomolecules with the [M Ξ N]2+ group.

Novel synthesis of palladium (II) complexes derived from 3-arylsydnone-4-carbaldehyde N(4)-phenylthiosemicarbazones and biological activity

The aim of this research is to investigate whether the oxygen atom O(6) in the sydnone ring of 3-arylsydnone-4-carbaldehyde N(4)-phenylthiosemicarbazones (HArSYTSCs, 3a-d) is a good electron donor atom upon metal complexation. Furthermore, ligands 3a-d and the corresponding palladium complexes (Pd(ArSYTSC)Cl, 4a-d) would be expected to find their potent biological activities. The desired palladium complexes 4a-d were first synthesized from thiosemicarbazones 3a-d. Then, the antiproliferative activity of ligands 3a-d and complexes 4a-d were tested against human hepatocellular carcinoma and human cervical epithelioid carcinoma (HeLa) cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl trazolium bromide (MTT) assay. According to X-ray analyses, ligands 3a-d are bonded to the Pd (II) center in an O, N, S-tridentate coordination mode through sydnone carbonyl oxygen O(6), azomethine nitrogen and the thiolate sulfur atom. The carbonyl oxygen of the sydnone ring is found to be a good electron donor site upon metal complexation. Moreover, MTT assay results reveal that the palladium complexes 4a-d have greater antiproliferative activity than 5-fluorouracil. In particular, the complexes exhibit obvious better activity than the corresponding ligands 3a-d against HeLa cell. The results indicate that the synthesized novel palladium complexes have greater antiproliferative activity than both 5-fluorouracil and the corresponding ligands against HeLa cell. Accordingly, the study of sydnonyl complexes bearing anticancer activities may support the development of coordination chemistry.

Synthesis and Characterization of Novel Methyl 2-(1,7,7-Tri methylbicyclo[2.2.1]hept-2-yieldene)hydrazinecarbodithioate Schiff Bases Derived From Methylhydrazine carbodithioate And Their Bi(III) And Ag(II) Complexes

Novel bidentate Schiff bases having nitrogen-sulphur donor sequence was synthesized from condensation of racemate camphor, (R)-camphor and (S)-camphor with Methyl hydrazinecarbodithioate (SMDTC). Its metal complexes were also prepared through the reaction of these ligands with silver and bismuth salts. All complexes were characterized by elemental analyses and various physico-chemical techniques. These Schiff bases behaved as uninegatively charged bidentate ligands and coordinated to the metal ions via ?-nitrogen and thiolate sulphur atoms. The NS Schiff bases formed complexes of general formula, [M(NS)2] or [M(NS)2.H2O] where M is BiIII or AgI, the expected geometry is octahedral for Bi(III) complexes while Ag(I) is expected to oxidized to Ag(II) forming square planner complexes.

Synthesis and Characterization of Novel Methyl 2-(1,7,7-Tri methylbicyclo[2.2.1]hept-2-yieldene)hydrazinecarbodithioate Schiff Bases Derived From Methylhydrazine carbodithioate And Their Bi(III) And Ag(II) Complexes

Novel bidentate Schiff bases having nitrogen-sulphur donor sequence was synthesized from condensation of racemate camphor, (R)-camphor and (S)-camphor with Methyl hydrazinecarbodithioate (SMDTC). Its metal complexes were also prepared through the reaction of these ligands with silver and bismuth salts. All complexes were characterized by elemental analyses and various physico-chemical techniques. These Schiff bases behaved as uninegatively charged bidentate ligands and coordinated to the metal ions via ?-nitrogen and thiolate sulphur atoms. The NS Schiff bases formed complexes of general formula, [M(NS)2] or [M(NS)2.H2O] where M is BiIII or AgI, the expected geometry is octahedral for Bi(III) complexes while Ag(I) is expected to oxidized to Ag(II) forming square planner complexes.

Preparation and characterization of rhenium(I) complexes with thiosemicarbazone ligands derived from resorcinol

New neutral tricarbonylrhenium(I) complexes with bidentate thiosemicarbazone ligands derived from resorcinol have been prepared. Ligands were obtained by condensation reactions of 2,4-dihydroxybenzaldehyde (dhb) and 2,4-dihydroxyacetophenone (dha) with thiosemicarbazide derivatives. The metal complexes have been characterized by elemental analysis, mass spectrometry, spectroscopic methods (IR, 1H NMR) and the crystal structures for eight of these compounds have been elucidated. The Re(I) metal centers are coordinated through the azomethine nitrogen and the sulfur atoms establishing five-membered chelate rings (κ-S,N(3)). The deprotonation of the ligand HL6 and the labilization of the halogen produces the formation of the dimeric complex [Re2(L6)2(CO)6] by Re–S–Re bridges, where S is the thiolate sulfur atom from a κ-S,N(3)-bidentate thiosemicarbazonate ligand.

Silver(I) complex formation with cysteine, penicillamine, and glutathione.

The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and δ((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and δ((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ∼11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ∼10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution.

Synthesis, spectroscopic characterization, structural studies and antibacterial and antitumor activities of diorganotin complexes with 3-methoxysalicylaldehyde thiosemicarbazone

Three organotin(IV) complexes, Ph2Sn(mstsc) (1), Me2Sn(mstsc) (2) and Bu2Sn(mstsc) (3), have been synthesized from reaction of R2SnCl2 (R=Ph, Me and Bu) with 3-methoxysalicylaldehyde thiosemicarbazone (H2mstsc). The synthesized complexes have been characterized by elemental analysis and FT-IR, 1H, 13C and 119Sn NMR spectroscopy. The structures of 2 and 3 have been also confirmed by X-ray crystallography. On the basis of spectral and structural data thiosemicarbazone acts as a tridentate dianionic ligand and coordinates to tin through phenolic oxygen, the azomethine nitrogen and thiolate sulfur atoms. The metal coordination geometry for 2 and 3 is described as distorted square pyramid and the crystal lattices are stabilized by intermolecular hydrogen bands. On the basis of 119Sn NMR data, coordination number of tin retains five in solution. The in vitro antibacterial activity of ligand and its complexes has been evaluated against one Gram-positive and three Gram-negative bacteria. Complex 2 exhibited good activity along with the standard antibacterial drugs. The in vitro cytotoxicities of the synthesized compounds against Jurkat cells were evaluated by the standard WST-1 assay. The activity decreases in the order 3>1>2=H2mstsc.

A Functional [NiFe]-Hydrogenase Model Compound That Undergoes Biologically Relevant Reversible Thiolate Protonation

Two model compounds of the active site of [NiFe]-hydrogenases with an unusual {S(2)Ni(μ-S)(μ-CO)Fe(CO)(2)S}-coordination environment around the metals are reported. The neutral compound [Ni(xbsms)(μ-CO)(μ-S)Fe(CO)(2)('S')], (1) (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) is converted to [1H][BF(4)] by reversible protonation using HBF(4)·Et(2)O. The protonation takes place at the terminal thiolate sulfur atom that is coordinated to nickel. Catalytic intermediates with a protonated terminal cysteinate were suggested for the native protein but have not yet been confirmed experimentally. [1H][BF(4)] is the first dinuclear [NiFe] model compound for such a species. Both complexes have been synthesized and characterized by X-ray crystallography, NMR-, FTIR-, and (57)Fe-Mössbauer spectroscopy as well as by electronic absorption and resonance Raman spectroscopy. The experimental results clearly show that the protonation has a significant impact on the electronic structure of the iron center, although it takes place at the nickel site. DFT calculations support the interpretation of the spectroscopic data and indicate the presence of a bonding interaction between the metal ions, which is relevant for the enzyme as well. Electrochemical experiments show that both 1 and [1H][BF(4)] are active for electrocatalytic proton reduction in aprotic solvents.

Template synthesis and X-ray structural characterization of nickel(II) and zinc(II) complexes of tetradentate SNNS ligands formed by condensation of phthalaldehyde with S-methyldithiocarbazate and 4N-methyl-3-thiosemicarbazide

The reaction of phthalaldehyde (1,2-benzenedialdehyde) with S-methyldithiocarbazate does not lead to the formation of the expected open-chain linear Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) but a cyclic diazine dithiocarbazate is obtained which has been characterized by spectroscopic and X-ray diffraction. However, if the reaction of phthalaldehyde with S-methyldithiocarbazate is carried out in the presence of nickel(II) and zinc(II) acetate salts, stable metal complexes of empirical formula, [M(phthalsme)] (M=Ni, Zn; phthalsme=doubly deprotonated form of the Schiff base, phthalaldehyde bis(S-methyldithiocarbazonate) are obtained. Likewise, the reaction of 4N-methyl-3-thiosemicarbazide with phthaladehyde in the presence of nickel(II) acetate also yields a crystalline nickel(II) complex, [Ni(phthaltsc)] (phthaltsc=doubly deprotonated form of the teradentate phthaladehyde bis(4N-methyl-3-thiosemicarbazone) ligand. The complexes, [Ni(phthalsme)], [Ni(phthaltsc)] and [Zn(phthalsme)(DMF)] have been characterized by a variety of physico-chemical techniques and their structures have been determined by X-ray diffraction. In these complexes, the ligands are coordinated to the metal ion as dinegatively charged tetradentate chelating agents via the two thiolate sulfur atoms and the azomethine nitrogen atoms. The nickel complexes, [Ni(phthalsme)] and [Ni(phthaltsc)] exhibit a distorted square–planar geometry whereas the zinc complex, [Zn(phthalsme)(DMF)] is five-coordinate and square-pyramidal with the dianionic Schiff base occupying the basal plane of the square-pyramid and the oxygen atom of dimethylformamide in the apical coordination site.

Synthesis, characterization and X-ray crystal structures of thiolate sulfur-bridged dimeric copper(II) complexes of the 2-aminoacetophenone Schiff base of S-methyldithiocarbazate

Copper(II) complexes of general empirical formula, Cu(apsme)X (apsme=monodeprotonated form of the 2-aminoacetophenone Schiff base of S-methyldithiocarbazate (Hapsme); X=Cl−, Br−, NCS−) have been prepared and characterised by a variety of physico-chemical techniques. The crystal and molecular structures of the Schiff base, Hapsme (1), [Cu(apsme)Br] (2), [Cu(apsme)(NCS)] (3) and [Cu(apsme)Cl] (4) have been determined by X-ray diffraction. In the solid state the copper(II) complexes 2, 3 and 4 are dimers in which the anionic Schiff base, (apsme−) coordinates with a copper(II) ion as a tridentate NNS chelating agent via the amino nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom. The fourth and fifth coordination positions of a copper atom are occupied by a co-ligand and bridging thiolate sulfur atoms, respectively.