Thiolate Ligands Research Articles

Facet-Specific Ligand Interactions on Ternary AgSbS2 Colloidal Quantum Dots.

Silver dimetal chalcogenide (Ag-V-VI2 ) ternary quantum dots (QDs) are emerging lead-free materials for optoelectronic devices due to their NIR band gaps, large absorption coefficients, and superior electronic properties. However, thin film-based devices of the ternary QDs still lag behind due to the lack of understanding of the surface chemistry, compared to that of lead chalcogenide QDs even with the same crystal structure. Herein the surface ligand interactions of AgSbS2 QDs, synthesized with 1-dodecanethiol used as a stabilizer, are studied. For nonpolar (1 0 0) surfaces, it is suggested that the thiolate ligands are associated with the crystal lattices, thus preventing surface oxidation by protecting sulfur after air-exposure, as confirmed through optical and surface chemical analysis. Otherwise, silver rich (1 1 1) surfaces are passivated by thiolate ligands, allowing ligand exchange processes for the conductive films. This in-depth investigation of the surface chemistry of ternary QDs will prompt the performance enhancement of their optoelectronic devices.

One-pot hydrothermal synthesis of thioglycolic acid-capped CdSe quantum dots-sensitized mesoscopic TiO2 photoanodes for sensitized solar cells

In this work, colloidal CdSe QDs capped with a short chain thiol ligand thioglycolic acid (TGA) were prepared using a one-pot synthesis route in aqueous medium. This method integrates colloidal QDs synthesis and assembly of QDs in a single step due to the use of TGA, which serves as a stabilizer to control the formation of QDs and a linker to tether CdSe QDs to TiO2 during the synthesis of QDs, and it could achieve high surface coverage of high-quality QDs on TiO2 electrodes. The hydrothermal temperature is found to play an important role in determining the size of CdSe QDs and photovoltaic properties of the resulting TiO2/CdSe photoanodes. To further improve the fill factor and efficiency of solar cells, PbS/CuS films were prepared with chemical bath deposition method and used instead of the usual Pt as counter electrodes (CEs). PbS/CuS CEs show superior electrocatalytic activity for the reduction of polysulfide than Pt. An optimized TiO2/CdSe based QDSSC in combination with the PbS/CuS CEs achieved a champion PCE of 4.18% under one sun illumination (100mWcm−2).

Competitive Hole Transfer from CdSe Quantum Dots to Thiol Ligands in CdSe-Cobaloxime Sensitized NiO Films Used as Photocathodes for H2 Evolution

Quantum dot (QD) sensitized NiO photocathodes rely on efficient photoinduced hole injection into the NiO valence band. A system of a mesoporous NiO film co-sensitized with CdSe QDs and a molecular proton-reduction catalyst was studied. While successful electron transfer from the excited QDs to the catalyst is observed, most of the photogenerated holes are instead quenched very rapidly (ps) by hole trapping at the surface thiols of the capping agent used as linker molecules. We confirmed our conclusion by first using a thiol free capping agent and second varying the thiol concentration on the QD’s surface. The later resulted in faster hole trapping as the thiol concentration increased. We suggest that this hole trapping by the linker limits the H2 yield for this photocathode in a device.

Effect of surface modification with various thiol compounds on colloidal stability of gold nanoparticles

Gold nanoparticles (AuNPs) are attractive materials due to their special optical and electronic properties. However, they tend to aggregate particularly in the presence of thiol‐containing compounds. In this study, to investigate the effect of surface conjugation with thiol‐containing compounds on colloidal stability, thiol compounds with various structures as modifying agents were used. To this end, AuNPs were synthesized and stabilized by trisodium citrate in aqueous solution, and then modified with thiol‐containing compounds, namely cysteamine hydrochloride (MEA, containing primary amine groups), 2‐mercaptoethanol (BME, containing hydroxyl groups), 1‐dodecanthiol (LCA, containing long‐chain alkyl groups) and thioglycolic acid (TGA, containing carboxylic acid groups). We studied the effect of thiol ligands on solution stability of colloidal AuNPs and on the formation of aggregates originating from the modification process using UV–visible spectroscopy, dynamic light scattering, field emission scanning electron microscopy and transmission electron microscopy. Results showed that surface modification with MEA, BME and LCA led to the formation of aggregates. However, conjugation with TGA showed a concentration‐dependent behaviour: surface modification with low concentration resulted in the formation of aggregates whereas that with high concentration of TGA did not disturb the colloidal stability of AuNPs. Finally, the effect of surface modification on temperature increase of solutions originating from infrared light irradiation was studied, where the temperature increase depends on the surface‐modifying compound.

Crystal Structure of Faradaurate-279: Au279(SPh-tBu)84 Plasmonic Nanocrystal Molecules.

We report the discovery of an unprecedentedly large, 2.2 nm diameter, thiolate protected gold nanocrystal characterized by single crystal X-ray crystallography (sc-XRD), Au279(SPh-tBu)84 named Faradaurate-279 (F-279) in honor of Michael Faraday's (1857) pioneering work on nanoparticles. F-279 nanocrystal has a core-shell structure containing a truncated octahedral core with bulk face-centered cubic-like arrangement, yet a nanomolecule with a precise number of metal atoms and thiolate ligands. The Au279S84 geometry was established from a low-temperature 120 K sc-XRD study at 0.90 Å resolution. The atom counts in core-shell structure of Au279 follows the mathematical formula for magic number shells: Au@Au12@Au42@Au92@Au54, which is further protected by a final shell of Au48. Au249 core is protected by three types of staple motifs, namely: 30 bridging, 18 monomeric, and 6 dimeric staple motifs. Despite the presence of such diverse staple motifs, Au279S84 structure has a chiral pseudo-D3 symmetry. The core-shell structure can be viewed as nested, concentric polyhedra, containing a total of five forms of Archimedean solids. A comparison between the Au279 and Au309 cuboctahedral superatom model in shell-wise growth is illustrated. F-279 can be synthesized and isolated in high purity in milligram quantities using size exclusion chromatography, as evidenced by mass spectrometry. Electrospray ionization-mass spectrometry independently verifies the X-ray diffraction study based heavy atoms formula, Au279S84, and establishes the molecular formula with the complete ligands, namely, Au279(SPh-tBu)84. It is also the smallest gold nanocrystal to exhibit metallic behavior, with a surface plasmon resonance band around 510 nm.

Synthesis of Au38(SCH2CH2Ph)24, Au36(SPh-tBu)24, and Au30(S-tBu)18 Nanomolecules from a Common Precursor Mixture.

Phenylethanethiol protected nanomolecules such as Au25, Au38, and Au144 are widely studied by a broad range of scientists in the community, owing primarily to the availability of simple synthetic protocols. However, synthetic methods are not available for other ligands, such as aromatic thiol and bulky ligands, impeding progress. Here we report the facile synthesis of three distinct nanomolecules, Au38(SCH2CH2Ph)24, Au36(SPh-tBu)24, and Au30(S-tBu)18, exclusively, starting from a common Aun(glutathione)m (where n and m are number of gold atoms and glutathiolate ligands) starting material upon reaction with HSCH2CH2Ph, HSPh-tBu, and HStBu, respectively. The systematic synthetic approach involves two steps: (i) synthesis of kinetically controlled Aun(glutathione)m crude nanocluster mixture with 1:4 gold to thiol molar ratio and (ii) thermochemical treatment of the purified nanocluster mixture with excess thiols to obtain thermodynamically stable nanomolecules. Thermochemical reactions with physicochemically different ligands formed highly monodispersed, exclusively three different core-size nanomolecules, suggesting a ligand induced core-size conversion and structural transformation. The purpose of this work is to make available a facile and simple synthetic method for the preparation of Au38(SCH2CH2Ph)24, Au36(SPh-tBu)24, and Au30(S-tBu)18, to nonspecialists and the broader scientific community. The central idea of simple synthetic method was demonstrated with other ligand systems such as cyclopentanethiol (HSC5H9), cyclohexanethiol(HSC6H11), para-methylbenzenethiol(pMBT), 1-pentanethiol(HSC5H11), 1-hexanethiol(HSC6H13), where Au36(SC5H9)24, Au36(SC6H11)24, Au36(pMBT)24, Au38(SC5H11)24, and Au38(SC6H13)24 were obtained, respectively.

Selectivity in Physiological Action of Nitric Oxide: A Hypothetical Mechanism.

The study showed that dinitrosyl iron complex (NO)2Fe(RS)2 containing the thiolate ligands, which is the basic physiological donor of NO, can transfer NO to other molecule only at the moment of rearrangement. This rearrangement can occur during interaction of the complex with more effective iron chelators than the thiolate ligands. In the absence of NO trap, a new complex is formed with a new ligand. NO transfer to a trap can also occur under the action of the agents such as mercury salts or ROS, which interact with the thiolate ligands. Probably, the ligands in the dinitrosyl iron complexes are the structures responsible for interaction of these complexes with physiological targets and for specificity and effectiveness of this interaction.

Catalytic Activity Control via Crossover between Two Different Microstructures.

Metal nanocatalysts hold great promise for a wide range of heterogeneous catalytic reactions, while the optimization strategy of catalytic activity is largely restricted by particle size or shape control. Here, we demonstrate that a reversible microstructural control through the crossover between multiply twinned nanoparticle (MTP) and single crystal (SC) can be readily achieved by solvent post-treatment on gold nanoparticles (AuNPs). Polar solvents (e.g., water, methanol) direct the transformation from MTP to SC accompanied by the disappearance of twinning and stacking faults. A reverse transformation from SC to MTP is achieved in nonpolar solvent (e.g., toluene) mixed with thiol ligands. The transformation between two different microstructures is directly observed by in situ TEM and leads to a drastic modulation of catalytic activity toward the gas-phase selective oxidation of alcohols. On the basis of the combined experimental and theoretical investigations of alcohol chemisorption on these nanocatalysts, we propose that the exposure of {211}-like microfacets associated with twin boundaries and stack faults accounts for the strong chemisorption of alcohol molecules on MTP AuNPs and thus the exceptionally high catalytic activity.

Bulky Surface Ligands Promote Surface Reactivities of [Ag141X12(S-Adm)40]3+ (X = Cl, Br, I) Nanoclusters: Models for Multiple-Twinned Nanoparticles.

Surface ligands play important roles in controlling the size and shape of metal nanoparticles and their surface properties. In this work, we demonstrate that the use of bulky thiolate ligands, along with halides, as the surface capping agent promotes the formation of plasmonic multiple-twinned Ag nanoparticles with high surface reactivities. The title nanocluster [Ag141X12(S-Adm)40]3+ (where X = Cl, Br, I; S-Adm = 1-adamantanethiolate) has a multiple-shell structure with an Ag71 core protected by a shell of Ag70X12(S-Adm)40. The Ag71 core can be considered as 20 frequency-two Ag10 tetrahedra fused together with a dislocation that resembles multiple-twinning in nanoparticles. The nanocluster has a strong plasmonic absorption band at 460 nm. Because of the bulkiness of S-Adm, the nanocluster has a low surface thiolate coverage and thus unusually high surface reactivities toward exchange reactions with different ligands, including halides, phenylacetylene and thiols. The cluster can be made water-soluble by metathesis with water-soluble thiols, thereby creating new functionalities for potential bioapplications.

Effects of Noncovalent Interactions on the Catalytic Activity of Unsupported Colloidal Palladium Nanoparticles Stabilized with Thiolate Ligands.

This article presents the systematic evaluation of colloidal palladium nanoparticles functionalized with well-defined small organic ligands that provide spatial control of the geometric and electronic surface properties of nanoparticle catalysts. Palladium nanoparticles stabilized with thiolate ligands of different structures and functionalities (linear alkyl vs cyclohexyl vs phenyl) are synthesized using the thiosulfate protocol in a two-phase system. The structure and composition of palladium nanoparticles are characterized using transmission electron microscopy, thermogravimetric analysis, NMR, and UV-vis spectroscopies. The catalysis studies show that the chemical and structural compositions of monolayers surrounding the nanoparticle core greatly influence the overall activity and selectivity of colloidal palladium nanoparticle catalysts for the hydrogenation, isomerization, and hydrogenolysis of allylic alcohols. Especially, noncovalent interactions between surface phenyl ligands and incoming aromatic substrates are found to have a profound influence on the selectivity of colloidal palladium nanoparticles.

New monoclinic form of {O-Ethyl N-(4-nitro-phen-yl)thio-carbamato-κS}(tri-4-tolyl-phosphane-κP)gold(I): crystal structure and Hirshfeld surface analysis.

The title phosphanegold(I) thiol-ate compound, [Au(C9H9N2O3S)(C21H21P)], is a second monoclinic polymorph (space group P21/c) that complements a previously reported Cc polymorph [Broker & Tiekink (2008 ▸). Acta Cryst. E64, m1582]. An SP donor set defines an approximately linear geometry about the gold atom in both forms. The key distinguishing feature between the present structure and the previously reported polymorph rests with the relative disposition of the thiol-ate ligand. In the title compound, the orientation is such to place the oxygen atom in close contact with the gold atom [Au⋯O = 2.915 (2) Å], in contrast to the aryl ring in the original polymorph. In the crystal, linear supra-molecular chains along the a-axis direction mediated by C-H⋯π and nitro-O⋯π inter-actions are found. These pack with no directional inter-actions between them. The analysis of the Hirshfeld surfaces for both forms of [Au(C9H9N3O3S)(C21H21P)] indicates quite distinctive inter-action profiles relating to the differences in inter-molecular contacts found in their respective crystals.

Controlled Synthesis of CuInS2/ZnS Nanocubes and Their Sensitive Photoluminescence Response toward Hydrogen Peroxide.

We synthesized uniform CuInS2/ZnS nanocubes by adjusting reaction parameters at the ZnS growth stage. Higher temperature and zinc concentration were shown to drive resultant crystals to have cubic morphology, which could be ascribed to the facet-dependent ligand dynamics on the crystal surface and concomitantly preferred directions of crystal growth. It was found that these nanocubes exhibit sensitive responses, as of photoluminescence quenching, toward hydrogen peroxide, compared to pyramid-shaped nanocrystals. The origin of quenching was further analyzed to be the oxidation of thiolate ligands that leaves the quenching center on the surface. It was noted that the quenched photoluminescence could be fully recovered by introducing additional ligand molecules into the system. Being adopted in the shape-controlled crystal growth, the ligand-to-crystal interaction was shown to still govern the interfacial reaction, the oxidation by hydrogen peroxide, of faceted crystals in our system. It turns out that the reactivity at the crystal surface depends on the exposed facets, especially induced by shape control, and the weak ligand-binding nature of the nanocube renders it vulnerable to the surface reaction.

On the stability of noble-metal nanoclusters protected with thiolate ligands(a)(a)Contribution to the Focus Issue Self-assemblies of Inorganic and Organic Nanomaterials edited by Marie-Paule Pileni.

Noble metal nanoclusters (NCs) protected with thiolate ligands have been of interest because of their long-term stability that makes them suitable as building blocks for diverse assembled systems with emergent and improved functions. Despite the advances in synthesis and characterization, the mechanisms that contribute to their stability are still poorly understood. In this article, we review the different criteria that have been used to explain the experimental stability of NCs with a well-defined number of atoms that are protected with thiolate ligands. We discuss why these criteria are not enough to explain the stability. We conclude that there are other physical factors that should be included when explaining the stability of these systems and could be important for the discovery of new noble-metal NCs.

Revisiting the Electronic Structure of FeS Monomers Using ab Initio Ligand Field Theory and the Angular Overlap Model.

Iron-sulfur (FeS) proteins are universally found in nature with actives sites ranging in complexity from simple monomers to multinuclear sites from two up to eight iron atoms. These sites include mononuclear (rubredoxins), dinuclear (ferredoxins and Rieske proteins), trinuclear (e.g., hydrogenases), and tetranuclear (various ferredoxins and high-potential iron-sulfur proteins). The electronic structure of the higher-nuclearity clusters is inherently extremely complex. Hence, it is reasonable to take a bottom-up approach in which clusters of increasing nuclearity are analyzed in terms of the properties of their lower nuclearity constituents. In the present study, the first step is taken by an in-depth analysis of mononuclear FeS systems. Two different FeS molecules with phenylthiolate and methylthiolate as ligands are studied in their oxidized and reduced forms using modern wave function-based ab initio methods. The ab initio electronic spectra and wave function are presented and analyzed in detail. The very intricate electronic structure-geometry relationship in these systems is analyzed using ab initio ligand field theory (AILFT) in conjunction with the angular overlap model (AOM) parametrization scheme. The simple AOM model is used to explain the effect of geometric variations on the electronic structure. Through a comparison of the ab initio computed UV-vis absorption spectra and the available experimental spectra, the low-energy part of the many-particle spectrum is carefully analyzed. We show ab initio calculated magnetic circular dichroism spectra and present a comparison with the experimental spectrum. Finally, AILFT parameters and the ab initio spectra are compared with those obtained experimentally to understand the effect of the increased covalency of the thiolate ligands on the electronic structure of FeS monomers.

Modeling of the Passive Permeation of Mercury and Methylmercury Complexes Through a Bacterial Cytoplasmic Membrane.

Cellular uptake and export are important steps in the biotransformation of mercury (Hg) by microorganisms. However, the mechanisms of transport across biological membranes remain unclear. Membrane-bound transporters are known to be relevant, but passive permeation may also be involved. Inorganic HgII and methylmercury ([CH3HgII]+) are commonly complexed with thiolate ligands. Here, we have performed extensive molecular dynamics simulations of the passive permeation of HgII and [CH3HgII]+ complexes with thiolate ligands through a model bacterial cytoplasmic membrane. We find that the differences in free energy between the individual complexes in bulk water and at their most favorable position within the membrane are ∼2 kcal mol-1. We provide a detailed description of the molecular interactions that drive the membrane crossing process. Favorable interactions with carbonyl and tail groups of phospholipids stabilize Hg-containing solutes in the tail-head interface region of the membrane. The calculated permeability coefficients for the neutral compounds CH3S-HgII-SCH3 and CH3HgII-SCH3 are on the order of 10-5 cm s-1. We conclude that small, nonionized Hg-containing species can permeate readily through cytoplasmic membranes.

Electrocatalytic proton reduction by [Fe(CO)2(κ2-dppv)(κ1-SAr)2] (dppv = cis-1,2-bis(diphenylphosphino)ethylene; Ar = C6F5, C6H5, C6H4CH3-p)

Electrocatalytic reduction of protons to hydrogen by mononuclear iron complexes which are developed as models of the distal iron center of [FeFe]-hydrogenase active site are described. A series of iron(II) bis(thiolate) complexes [Fe(CO)2(κ2-dppv)(κ1-SAr)2] (1, Ar=C6F5; 2, Ar=C6H4; 3, Ar=C6H4CH3-p; dppv=cis-1,2-bis(diphenylphosphino)ethylene) have been prepared from direct reactions between the corresponding hexacarbonyl [Fe2(CO)6(μ-SAr)2] and dppv at elevated temperatures. Structurally they are similar being coordinated by a chelating dppv, two carbonyls and two thiolate ligands bonded in an all cis-arrangement. Solution spectroscopic data indicate that they exist in two isomeric forms in solution. All reversibly protonate at sulphur atom(s) upon addition of HBF4·Et2O and lose a thiolate ligand as thiol. They show a common quasi-reversible reductive feature (attributed to the FeII/FeI couple) in their CVs in addition to other redox responses and are able to catalyze reduction of protons to hydrogen at their Fe(I) oxidation state in presence of HBF4·Et2O. Complex 1 is the most efficient catalyst and catalyzes proton reduction at ca. −1.5V showing icat/ip ≥46 in the presence of ten equivalents of HBF4·Et2O.

Plasmonic Particles – Now Tailored to Your Needs

Plasmonic Particles – Now Tailored to Your Needs

NO-donating and hemolytic activity of tetranitrosyl iron complexes with ligands of the 2-mercaptopyridine series

The NO-donating and hemolytic activity of the binuclear tetranitrosyl iron complexes (TNIC) with thiolate ligands of the composition [Fe2(SR)2(NO)4], where R is pyridin-2-yl and 5-nitropyridin-2-yl, was studied. The NO-donating and hemolytic activities of the com- plex with the nitrosubstituted ligand are approximately two and three times higher than the corresponding characteristics of the complex with unsubstituted 2-mercaptopyridine, respectively. Symbate changes in these parameters confirm the conclusion made earlier on the peroxynitrite-dependent mechanism of erythrocyte hemolysis under the action of TNIC. The NO-donating activity of TNIC with ligands of the 2-mercaptopyridine series, unlike the previously studied complexes containing thioderivatives of other nitrogenous heterocycles as S-ligands, did not decrease with an increase in the concentration of erythrocytes. This allows one to consider them as promising NO-donating substances for the preparation of pharma- cological remedies.

Quantum chemical assessment of the ligand effect on the properties and structure of protected gold clusters

A procedure based on density functional theory is proposed for calculation of Au20(ХCH3)16 (Х = S, Se, Te) isomers. It is established that the most stable isomer for all X has a core‒shell structure: Au7@(AuXCH3)8(XCH3(AuXCH3)3)(XCH3AuXCH3)2. Optical and IR spectra, ionization potential, and electron affinity are calculated for the first time for all clusters. It is shown that a cluster protected by thiolate ligands has the greatest electronic and thermodynamic stability.

Tailoring the Structure of 58-Electron Gold Nanoclusters: Au103S2(S-Nap)41 and Its Implications.

We report the synthesis and crystal structure determination of a gold nanocluster with 103 gold atoms protected by 2 sulfidos and 41 thiolates (i.e., 2-naphthalenethiolates, S-Nap), denoted as Au103S2(S-Nap)41. The crystallographic analysis reveals that the thiolate ligands on the nanocluster form local tetramers by intracluster interactions of C-H···π and π···π stacking. The herringbone pattern formation via intercluster interactions is also observed, which leads to a linearly connected zigzag pattern in the single crystal. The kernel of the nanocluster is a Marks decahedron of Au79, which is the same as the kernel of the previously reported Au102(pMBA)44 (pMBA = -SPh-p-COOH); this is a surprise given the much bulkier naphthalene-based ligand than pMBA, indicating the robustness of the decahedral structure as well as the 58-electron configuration. Despite the same kernel, the surface structure of Au103 is quite different from that of Au102, indicating the major role of ligands in constructing the surface structure. Other implications from Au103 and Au102 include (i) both nanoclusters show similar HOMO-LUMO gap energy (i.e., Eg ≈ 0.45 eV), indicating the kernel is decisive for Eg while the surface is less critical; and (ii) significant differences are observed in the excited-state lifetimes by transient absorption spectroscopy analysis, revealing the kernel-to-surface relaxation pathway of electron dynamics. Overall, this work demonstrates the ligand-effected modification of the gold-thiolate interface independent of the kernel structure, which in turn allows one to map out the respective roles of kernel and surface in determining the electronic and optical properties of the 58e nanoclusters.