Exocyclic Sulfur Atom Research Articles

Use of an Evaporated Gold SERS Substrate to Detect 2-Mercaptobenzothiazole on Sulfide Mineral Surfaces

The interaction of 2-mercaptobenzothiazole (MBT) with the sulfide mineral surfaces, chalcopyrite (CuFeS2), chalcocite (Cu2S) and synthetic copper sulfide (CuxS) thin films, was investigated by Raman spectroscopy. Gold was evaporated onto the sulfide surface to facilitate surface enhancement of Raman scattering. Raman and gold-induced SERS spectra from mineral surfaces exposed for various times to solutions of different MBT concentrations, recorded before and after gold decoration, were used to elucidate the mechanism of collector adsorption. Spectra were identified with MBT bonded to copper atoms in the mineral surface and not to bonding to the gold overlayer. Spectra obtained from each sulfide surface displayed the band arising from the NCS ring stretch vibration of MBT downshifted from its position from CuMBT. The shift was similar to that found previously for MBT chemisorbed on a copper metal electrode. MBT chemisorbs to copper atoms in the mineral surfaces through the exocyclic sulfur atom.

Copper(I) halide chelates of the wide bite angle diphosphane xantphos: Crystal structures of [CuBr(xantphos)(dmpymtH)] and [CuI(xantphos)(imdtH 2)] · CH 3CN

Copper(I) halide complexes containing the diphosphane xantphos (4,5-bis(diphenylphosphano)-9,9-dimethyl-xanthene) and some heterocyclic thione ligands have been synthesized and characterized by 1H NMR, IR spectroscopy, elemental analyses and melting point determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in acetonitrile/methanol solution. The molecular structures of [CuBr(xantphos)(dmpymtH)] and [CuI(xantphos)(imdtH 2)] · CH 3CN have been established by single-crystal X-ray diffraction. Each of these structures features a tetrahedral copper(I) center with two phosphorus atoms from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. Rapid decomposition of the mixed-ligand complexes via ligand dissociation occurs upon standing of their acetonitrile solutions at room temperature for several days. The resulting colored crystals, which not only on elemental analysis but also on the basis of their NMR and IR spectra, are found to be phosphane-free coordination polymers of composition [CuX(thione)].

Wurster's Thiacrown Ethers: Synthesis, Properties, and Pt(II)-Coordination Chemistry

Two isomeric redox-responsive azathiacrown ethers, based on p-phenylenediamine, have been synthesized in traditional crown (L1) and crownophane (L2) architectures. Each of these "Wurster's crowns" was designed to target the encapsulation of transition or heavy metal ions. The solid-state structures of these ligands show binding cavities defined by three exocyclic sulfur atoms and either a N donor atom (L1) or the electron-rich pi face of the phenylenediamine subunit (L2). The ability of these ligands to form complexes with platinum(II) was investigated by various techniques including 1H NMR spectroscopy, electrospray mass spectrometry, cyclic voltammetry, and single-crystal X-ray analysis. The traditional crown geometry proved to be better at forming stable endocyclic complexes with Pt(II) than the crownophane geometry. The square-planar Pt(II) crown complex includes direct bonding to the redox center (Pt1-N1 = 2.125 angstroms and Pt1-S(av) = 2.278 angstroms) with concomitant polarization of the phenylenediamine moiety. This results in the crown complex oxidizing 916 mV more anodically than the free ligand. In contrast, modest shifts in the oxidation potential of the crownophane isomer indicate poor interaction between the redox center and complexed Pt(II) ion.

Synthesis of 2,3-Diaryltetrazole-5-thiones and Theoretical Studies on Atomic Charge Distributions of 2,3-Diphenyltetrazole-5-thione

Four 2,3-diaryltetrazole-5-thiones have been synthesized in high yields using a new synthetic method under mild reaction conditions. Theoretical calculations of the structure, vibrational frequencies, and natural population analysis (NPA) of atomic charge distributions on 2,3-diphenyltetrazole-5-thione 1 have been performed by DFT-B3LYP, HF, and MP2 methods using several basis sets. According to the NPA results a new resonance hybrid structure of 1 has been proposed with an exocyclic sulfur atom and a tetrazole ring carrying negative charges and two phenyl rings having positive charges. On the basis of this new proposed structure, the calculated results can explain experimental facts logically. In addition, a new chemical property of 1 has been predicted: the protonation should occur not only on the exocyclic S atom, but also on the N atoms having negative charges.

Copper(I) bromide complexes from 1,2-bis(diphenylphosphano) benzene and some heterocyclic thiones

The synthesis, characterization and solid state emission properties of a series of mixed-ligand copper(I)bromide complexes containing 1,2-bis(diphenylphosphano)benzene (dppbz) and some heterocyclic thiones (L) are reported. The complexes are readily synthesized by the addition of the appropriate thione to a CuBr-diphosphane adduct in acetonitrile/methanol or acetone solution. The molecular structures of [CuBr(dppbz)(py2SH)], [CuBr(dppbz)(pymtH)] and [CuBr(dppbz)(imdtH 2)] were established by single-crystal X-ray diffraction. Each of these structures features a tetrahedral copper(I) centre with two phosphorus atoms from the chelating diphos ligand, one bromine and the exocyclic sulfur atom of the heterocyclic thioamide unit. Slow decomposition of the mixed-ligand complexes via ligand dissociation occurs when their chloroform solutions are left to stand at room temperature for several weeks. On the basis of elemental analysis, NMR and IR spectra, the resulting coloured crystals are found to contain phosphane-free coordination polymers of composition [CuBr(L)]. At room temperature, some of the molecular complexes in the solid state exhibit strong emission assigned to a metal–ligand charge transfer of type Cu(I) → π*(PPh 2).

Experimental and Density Functional Theory Calculational Studies on 2,3‐Diaryl‐tetrazole‐5‐thione

Abstract2,3‐Diaryl‐tetrazole‐5‐thione (diaryl=diphenyl, di(p‐methylphenyl) and di(p‐chlorophenyl)) has been synthesized and characterized by elemental analysis, IR and electronic absorption spectroscopy. Two of them have also been characterized by X‐ray diffraction analysis. Density functional theory calculations of the structures, charge distribution, natural bond orbital and topological analysis of the three compounds were performed at B3LYP/6‐31G* level. The calculational results are in good agreement with the X‐ray data and show that different substitute group results in different charge distribution, the exocyclic sulfur atom has the biggest negative charge value and this site is the most likely site of protonation and methylation as well as the potential coordination site with metallic ions. The predicted harmonic vibration frequencies were compared with the experimental values. On the basis of vibrational analyses, the thermodynamic properties of these compounds at different temperatures were calculated, which reveal that $ S^{0}_{\rm m} $, $ H^{0}_{\rm m} $ and temperatures have good linear correlations. The calculations of second order optical nonlinearity have also been carried out and relatively high molecular hyperpolarizability values of 1.0913×10‐29‐1.6518×10‐29 esu were predicted.

Coordination Polymers of Copper(I) Halides and Neutral Heterocyclic Thiones with New Coordination Modes

Reaction of copper(I) chloride or bromide with equimolar amounts of the neutral pyrimidine-2-thione ligand (pymtH) afforded linear chain polymers [Cu(pymtH)X]n (X = Cl, Br) with the pymtH ligand acting as a bridging N, S donor. In contrast, copper(I) iodide under the same conditions gave the dimeric complex [Cu(pymtH)2I]2 with the pymtH ligand adopting monodentate coordination mode through the exocyclic sulfur atom in terminal and bridging modes. Reactions of the heterocyclic thione ligand 2,4,6-trimercaptotriazine (H3TMT) with copper(I) halides afforded novel three-dimensional polymers, which crystallized in the cubic space group Pa. Each copper(I) ion is coordinated by three S atoms of three distinct H3TMT ligands, and each H3TMT acts as a tridentate bridging ligand linking three copper(I) ions through its sulfur atoms, thus forming two independent three-dimensional (3D) networks. The network belongs to a three-connected (10, 3)-a topology, which is enantiometric and interpenetrating. In all complexes the ligands are present in the thione form, and all halides are terminally coordinated to copper(I) ions. The photoluminescent and thermal properties of the complexes have also been investigated.

Complexes of heterocyclic thiones and group 12 metals: Part VI. Preparation and characterisation of complexes of cadmium(II) halides with 1-methylimidazoline-2(3H)-thione, 1,3-thiazolidine-2-thione and 1,3-benzothiazoline-2-thione. Crystal structures of polymeric (1,3-thiazolidine-2-thione)cadmium(II) chloride, bis(1,3-thiazolidine-2-thione)cadmium(II) iodide and monomeric bis(1-methylimidazoline-2(3H)-thione)cadmium(II) bromide

Reactions of 1-methylimidazoline-2(3H)-thione (meimz2SH), 1,3-thiazolidine-2-thione (tzdSH) and 1,3-benzothiazoline-2-thione (bztzSH) with cadmium(II) halides in ethanol solutions result in the formation of 1:1 complexes for the chloride, both 1:1 and 2:1 complexes for the bromide, and only 2:1 complexes for the iodide. Spectroscopic evidence confirms the exocyclic sulfur atom to be the donor in all cases. Cadmium(II) acetate and the heterocyclic ligands in the presence of triethylamine form the insoluble deprotonated complexes. The structure of (tzdSH)CdCl 2 consists of double halogen-bridged chains, linked into sheets via NH⋯Cl interactions and with the heterocycle coordinated to the metal via the exocyclic sulfur atom. Thus each cadmium is approximately octahedrally surrounded by one sulfur, 2 two-coordinate and 3 three-coordinate chlorine atoms. In contrast (tzdSH) 2CdI 2 forms chains via I⋯S interactions; the metal is tetrahedrally coordinated by two sulfur and two iodine atoms. The structure of (meimz2SH) 2CdBr 2 consists of discrete complex molecules with essentially tetrahedrally coordinated Cd and no significant intermolecular interactions; the six molecules in the asymmetric unit are related by pseudo-symmetry and are very similar except for variation in the orientation of the heterocyclic substituents.

The reaction of [{Co(η5-C5H5)}2{Fe(CO)2(PPh3)}(μ3-S)(μ3-CS)] and related complexes with carbon disulfide. Synthesis, structure and reactivity of [{Co(η5-C5H5)}2{Fe(CO)(L)}(μ3-S)(μ3-C2S3)] derivatives (L = PR3and CNR)

[{Co(η5-C5H5)}2{Fe(CO)(L)2}(μ3-S)(μ3-CS)] complexes 1 where (L)2 = (a) (CO)(PPh3), (b) (CO){P(OPh)3}, (c) (CO)(PBun3), (d) (CNMe)2 and (e) (CNMes)2 (Mes = 2,4,6-Me3C6H2), but not (CO)(CNMes), react with CS2 under reflux to give [{Co(η5-C5H5)}2{Fe(L)2}(μ3-S)(μ3-C2S3)], 2, in which a CS2 molecule has been incorporated into a FeSC(S*)SC heterocycle with a trithiocarbonate moiety bridging the Fe–C cluster edge. Clusters 2 react with incoming ligands either by simple ligand substitution, or by displacement of CS2 to form clusters of type 1. The exocyclic sulfur atom S* is nucleophilic and with electrophiles E forms [{Co(η5-C5H5)}2{Fe(L)2}(μ3-S)(μ3-C2S3E] adducts which contain S*→E bonds where E = Me+ [3]+, Et+ [4]+, HgCl2 [5], and I4 (or I+) [6]. The clusters 2a–c and the [3]+ and [4]+ derived from them are chiral as indicated by their NMR spectra, and do not racemize on the NMR timescale. The structures of 2a·2C6H6 and [3a]I·C6H6·CHCl3 are reported. Cluster 2a contains a very short Fe–Cμ bond as compared with 1a, and it is suggested that in many respects the FeSC(S)SCμ ring is best regarded as a metallo-1,3-dithiole-2-thione (or metallovinyl trithiocarbonate) with a Fe–Cμ double bond which, on alkylation at the exocyclic S*, adopts a more delocalised electronic structure with a longer Fe–Cμ bond. Spectroscopic and electrochemical data for the new compounds are discussed.

Transmethylation of 2‐(methylthio)benzothiazole on silver sols: a SERS investigation

AbstractDiscrepancies between the SERS and the normal Raman spectra of 2‐(methylthio)benzothiazole (MTBT) led to an extension of the SERS study to include an investigation of the reactivity of this molecule on a silver surface. Experimental evidence indicates a surface reaction of MTBT on silver sol. In particular, it undergoes an intramolecular transmethylation, rearranging to 3‐methylbenzothiazoline‐2‐thione. Experimental data suggest that this transmethylation takes place only because of the presence of the silver surface, which acts as a catalyst. In contrast, the hypothesis of a reaction photo‐induced by the silver surface seems very unlikely. 3‐Methylbenzothiazoline‐2‐thione adsorbs on the silver surface via the lone pairs of the exocyclic sulphur atom and, to some extent, also via the π‐system of the benzene ring. The molecular orientation is inclined with respect to the metal surface. Copyright © 2002 John Wiley & Sons, Ltd.

NEW ORGANOSILICON DERIVATIVES OF NITROGEN- CONTAINING HETEROCYCLES*

Results are summarized of investigations carried out by the authors on the synthesis and study of the reactivity of organosilicon derivatives of nitrogen-containing heterocycles YCH2SiX3, where X = OMe, F, 1/3 (OCH2CH2)3N; Y = a heterocyclic substituent linked by a CH2 group with an endocyclic nitrogen atom or an exocyclic sulfur atom.

Surface enhanced raman scattering spectroscopic studies of the adsorption of flotation collectors

Surface enhanced Raman scattering (SERS) spectroscopy at surfaces under electrochemical control has been applied to elucidate the adsorption of thiol collectors. Voltammetry has shown that charge transfer chemisorption of ethyl, isopropyl, isobutyl and isoamyl xanthates occurs on silver surfaces at potentials below the reversible value for the formation of the silver xanthate. SERS spectroscopy has identified the species formed at underpotentials to be xanthate bonded to silver atoms through the sulfur atoms. Application of this technique has also shown that the adsorption of O-isopropyl-N-ethylthionocarlpamate on copper involves a charge transfer process and rest potential measurements indicate that this adsorption occurs at underpotentials. SERS spectra also establish that 2-mercaptobenzothiazole undergoes charge transfer chemisorption on copper, silver and gold over a wide potential range by bonding through the exocyclic sulfur atom.

A SERS spectroelectrochemical investigation of the interaction of 2-mercaptobenzothiazole with copper, silver and gold surfaces

The interaction of the sulfide mineral flotation collector, 2-mercaptobenzothiazole, with silver, copper and gold surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. 2-mercaptobenzothiazole, the copper, silver and gold compounds of this species, and the dithiolate, 2,2′-dithiobis(benzothiazole) were characterised by 13C NMR and Raman spectroscopy to provide a basis for identifying surface species. SERS investigations showed that, at pH 4.6 where the solution species is in the protonated form, and at 9.2, where it is present as the ion, adsorption on each metal occurs over a wide potential range. Attachment of the organic compound occurs through bonding between the exocyclic sulfur atom and metal atoms in the surface. X-ray photoelectron spectroscopy confirmed that the adsorbed layer was of monolayer thickness. Adsorption of the protonated 2-mercaptobenzothiazole occurs on copper at pH 4.6 at potentials below that at which charge transfer adsorption commences.

Coordination Chemistry, Structure, and Reactivity of Thiouracil Derivatives of Tungsten(0) Hexacarbonyl: A Theoretical and Experimental Investigation into the Chelation/Dechelation of Thiouracil via CO Loss and Addition.

The synthesis of 2-thiouracil and 6-methyl-2-uracil derivatives of tungsten carbonyl from the reaction of photogenerated W(CO)(5)(solvent) (solvent = MeOH or THF) and the corresponding [Et(4)N][thiouracilate] is described. The crystal structure of the [Et(4)N][W(CO)(5)(2-thiouracilate)], 1, derivative is reported where the thiouracilate is found to be bound to the tungsten center via the exocyclic sulfur atom. In the solid-state structure of 1 two anions are associated by means of two hydrogen bonds between the metal bound nucleobases. These pentacarbonyl complexes stereoselectively lose cis carbonyl ligands, as is apparent from (13)C-labeling studies, to provide the endocyclic nitrogen N(1)-chelated tungsten tetracarbonyl derivatives, e.g., [Et(4)N][W(CO)(4)(2-thiouracilate)], 3. The kinetics of the loss of CO from the pentacarbonyl anions to afford the metal tetracarbonyls, and the reverse of that process, were monitored by means of in situ infrared spectroscopy in the nu(CO) region as a function of temperature. These studies reveal that the tetracarbonyl anions in CO-saturated acetonitrile ([CO] approximately 6 x 10(-)(3) M) are unstable with respect to the formation of the pentacarbonyl derivatives, i.e., the equilibrium 1 right harpoon over left harpoon 3 + CO lies to the left under an atmosphere of carbon monoxide. From the activation parameters determined for the dissociative CO loss process (DeltaH() = 82.0 +/- 3.6 kJ mol(-)(1) and DeltaS() = -44.9 +/- 9.6 J mol(-)(1) K(-)(1) for complex 1) it is apparent that the sulfur-bound thiouracilate ligand is serving as a pi-donor during CO dissociation, i.e., behaving as a cis-labilizing ligand. Ab initio geometry optimizations carried out for the process 1 right harpoon over left harpoon 3 + CO at the Hartree-Fock and DFT levels support these experimental observations. For example, complex 1 is shown to be more stable than 3 + CO and chelation via the endocyclic N(1) donor is favored over N(3) binding. Finally, the "16-electron" intermediate resulting from CO dissociation in 1 was found to possess a significantly shortened W-S interaction, presumably due to the pi-donating ability of the thiouracilate ligand.

Solution structures of stromelysin complexed to thiadiazole inhibitors.

Unregulated or overexpressed matrix metalloproteinases (MMPs), including stromelysin, collagenase, and gelatinase. have been implicated in several pathological conditions including arthritis and cancer. Small-molecule MMP inhibitors may have therapeutic value in the treatment of these diseases. In this regard, the solution structures of two stromelysin/ inhibitor complexes have been investigated using 1H, 13C, and 15N NMR spectroscopy. Both-inhibitors are members of a novel class of matrix metalloproteinase inhibitor that contain a thiadiazole group and that interact with stromelysin in a manner distinct from other classes of inhibitors. The inhibitors coordinate the catalytic zinc atom through their exocyclic sulfur atom, with the remainder of the ligand extending into the S1-S3 side of the active site. The binding of inhibitor containing a protonated or fluorinated aromatic ring was investigated using 1H and 19F NMR spectroscopy. The fluorinated ring was found to have a reduced ring-flip rate compared to the protonated version. A strong, coplanar interaction between the fluorinated ring of the inhibitor and the aromatic ring of Tyr155 is proposed to account for the reduced ring-flip rate and for the increase in binding affinity observed for the fluorinated inhibitor compared to the protonated inhibitor. Binding interactions observed for the thiadiazole class of ligands have implications for the design of matrix metalloproteinase inhibitors.

Crystal structure of bis(tetraphenylphosphonium) hexathiotetraarsenate, [Ph4P]2[As4S6

Source of material: Arsenic oxide, sulfur, manganese and tetraphenylphosphoniumbromide (molar ratio: 1:5:1:1 ) in 5 ml of 2m ammonia solution were reacted in teflon coated steal autoclaves at 398 К for 6 days. The product was filtered off and washed with deionized water. The structure of the title compound is built up of well-separated Ph4P' -cations and [As4S6]^~-anions. The tetraphenylphosphonium cations form pairs with sixtuple embracements of the phenyl rings with the midpoint located on a centre of inversion and relatively short Ρ···Ρ distances of 6.331(3) Â and 6.351(3) Â. These pairs are arranged in corrugated sheets parallel to ((Ю1) with a honey-comb like arrangement of the Ρ atoms, a pattern which is found in many compounds containing tetraphenylphosphonium cations. The [As4S6]^~-anion forming a bicyclic ring system of alternating As and S atoms consists of two five-membered rings with the two common arsenium centers As3 and As4. The structure of the [As4S6]^-anion is related to that of AS4S4 (see ref. 1 ) by replacement of an As-As bond by two As-S~ units. The As3-As4 bond length of 2.621(2) Â is significantly longer than that in elemental As by about 0.12 Â. The other two arsenium atoms Asl and As2 are each bound to an additional exocyclic sulfur atom. All arsenium atoms have trigonal pyramidal coordination with sums of angles around Asl and As2 of 3(Ю.7(9)° and 298.4(9)° and around As3 and As4 of 308.1(8)° and 307.2(8)°. The As-S bond lengths to As3 and As4 are shorter than those to Asl and As2 by about 0.1 Â. The longer As-S distances as well as the stronger pyramidalization of Asl and As2 suggest that the negative charge is predominantely located on these centers. It is noted that the geometrical parameters of the [As4S6]^~-anion are comparable to those in piperidinium hexathiotetraarsenate (see ref. 2). C48H40AS4P2S6, orthorhombic, Pbca (No. 61), α =11.1998(6) Â, b =19.657(1) Â, с =44.177(5) Â, V=9725.5 Â^Z=8,R{F) =0.050, A w f f ^ ) = 0 . 1 1 6 .

Gold(I) complexes with biologically active thiolate ligands

The reaction of ethanolic solutions of Na(SR) (SR=4-oxo-2-thioxopyrimidines) with [AuClL] (LPPh 3, PPh 2Me and AsPh 3) gives [Au(SR)L]; when PPN[AuCl 2] or NBu 4[AuBr(C 6F 5)] are used instead, PPN[Au(SR) 2] and NBu 4[Au(C 6F 5)(SR)] are obtained. The structure of [Au(SR 1)(PPh 3)] has been established by X-ray diffraction, and shows a linear coordination at gold involving the phosphine phosphorus and the exocyclic sulfur atom of the organic ligand.

ChemInform Abstract: Regio‐ and Stereoselective Oxidations of the Exocyclic Sulfur Atom of Two Endocyclic Ketene Dithioacetals.

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Bimetallic reactivity: unusual change in the coordination mode of the bridging ligands arising from an oxidative addition process

The reactions of the dinuclear complex [{Rh(μ-C 7H 4NS 2)(CO)(PPh 3)}2] ( 1) (C 7H 4NS 2 = benzothiazole-2-thiolate) with electrophilic agents have been studied. Iodomethane reacts with 1 to give the diacetyl complex [{Rh(μ-C 7H 4NS 2)(COCH 3) (I)(PPh 3)}2] ( 2) as the result of the addition of one MeI molecule to each metal atom followed by the insertion of the carbonyl groups into the RhMe bonds. Monitoring this reaction by 31P{ 1H} NMR and IR shows that it goes through a dinuelear pathway. The crystal structure analysis of 2 shows a significant change in the coordination mode of the bridging benzothiazol-2-thiolates relative to the parent compound 1. In 2 each bridging ligand bonds through the exocyclic sulphur atom to both rhodium atoms, and the azolate nitrogen maintains a weak bonding interaction with one metal as shown by the long RhN distance, 2.588(3) Å. A further rearrangement is observed in solution, since spectroscopic studies show that 2 is in equilibrium with an acyl-mononuclear complex arising from the fragmentation of the dinuclear unit. Iodine also reacts with 1 to give the insoluble rhodium(III) complex [{Rh(C 7H 4NS 2)I 2(CO)(PPh3)} n ] whereas HgI 2 and methyl triflate react with 1 to give the heterotrinuclear and homotrinuclear aggregates [(PPh 3) 2(CO) 2Rh 2(μ 3-C 7H 4NS 2) 2HgI] [HgI 3]( 4) and [Rh 3(μ 3-C 7H 4NS 2) 2(CO) 3(PPh 3) 3] + respectively, as a result of the attack of the electrophiles on the exocyclic sulphur atoms of the benzothiazole-2-thiolates.

The vibrational spectra of some 2-mercaptopyrimidine complexes of mercury(II)

Abstract The IR and Raman spectra of a series of complexes of the type HgX 2 (2MP), where X = Cl, Br or I and 2MP = 2-mercaptopyrimidine, have been obtained in the solid state. The spectra show that all three species possess a trans dimeric halogen-bridged structure of C 2 h molecular symmetry and that the organic ligand is bonded to mercury by its exocyclic sulfur atom. The above conclusion is also supported by an SCF—MO—MNDO calculation on the HgI 2 (2MP) dimer, which shows that the trans structure is ca 100 kcal/mol more stable than any other intermediate possible structure.