Cationic Ag Research Articles

In-situ exploration of divergent methane coupling pathways in dry and aqueous environments on silver and palladium heteropolyacid-titania photocatalysts

Methane, abundant but inert, contributes significantly to greenhouse gases, primarily through combustion, which emits vast amounts of CO2. Photocatalytic methane coupling at ambient temperature offers a method to convert it into ethane, a more versatile hydrocarbon. This study examines selective methane-to-ethane coupling using heterogeneous photocatalysts comprising silver and palladium salts dispersed on titania. Through a combination of ex-situ and in-situ techniques along with DFT simulations, distinct mechanisms and active phases in these catalysts are revealed. In silver catalysts, dispersed cationic Ag+ species are crucial for methane activation, while in palladium catalysts, palladium primarily exists in metallic form during coupling. Water strongly enhances coupling rates with both catalysts. DFT modeling identified methane adsorption sites, suggesting methane activation via •OH radicals, experimentally supported by EPR under in-situ conditions.

Silver catalyzed substitution of allylic and benzylic alcohols having unactivated hydroxy groups

The catalytic Friedel-Crafts substitution of allylic and benzylic alcohols having free hydroxy groups was regioselectively catalyzed by cationic Ag(I) salts. No precautions to exclude moisture or atmosphere were necessary, making the reaction highly robust and facile. Substitution of allylic alcohols with electron rich aromatic nucleophiles favored products with alkenes conjugated to aromatic substituents. Benzylic substitution was impacted by the electronics of the alcohol aryl group, whereas allylic substitution was not. The use of a bromoindole nucleophile allowed for a formal total synthesis of echinosulfonic acid D, where the penultimate synthetic intermediate was synthesized in half the steps previously needed.

Single-Atom Cationic Ag and Metallic Ag Nanoparticles Supported on Al2O3 as Catalysts for Water-Resistant and CO2-Selective HCHO Oxidation

Ag-based catalysts have been extensively investigated in HCHO oxidation on account of the low price of the Ag precursor and their considerable low-temperature activity. It is known that H2 pretreatment has a remarkable promotion effect on Pt- and Pd- catalysts for HCHO oxidation, whereas the effect of H2 reduction on Ag-based catalysts has been rarely reported, probably due to the coexistence of multiple states of Ag species resulting from the high Ag loading. Herein, we prepared a 1% Ag/Al2O3 (Ag/Al-fresh) catalyst with Ag species in a uniform state and then reduced Ag/Al-fresh with H2 at 600 °C to obtain the Ag/Al-600H2 catalyst. We observed that H2 reduction had a significant influence on the performance of Ag/Al2O3 nanocatalysts in HCHO oxidation. In a dry reaction atmosphere, Ag/Al-fresh and Ag/Al-600H2 exhibited comparable HCHO conversion levels, but Ag/Al-600H2 showed much higher CO2 selectivity than Ag/Al-fresh. The presence of water vapor severely suppressed the HCHO conversion of the Ag/Al-fresh catalyst, while Ag/Al-600H2 showed high water resistance, maintaining high HCHO conversion and CO2 selectivity at 35% RH. Characterization results showed that the Ag species on Ag/Al-fresh and Ag/Al-600H2 were single-atom cationic Ag and metallic Ag nanoparticles, respectively. It was revealed that the Ag0 nanoparticles were more conducive than single-atom Ag+ to formate decomposition, as well as O2 and H2O activation, thus accelerating the conversion of HCOO– and CO intermediates to CO2 and contributing to the higher activity and water resistance of the Ag/Al-600H2 catalyst.

Dinuclear silver(I)‐ and gold(I)‐ N heterocyclic carbene complexes; Synthesis, structural characterizations, photoluminescence and theoretical studies

Herein, a new family of cationic Ag(I)- and Au(I)-, complexes ligated to a novel C∩N donor N- heterocyclic carbene (NHC) ligand 3-methyl-1-(1-methyl-2-methylbenzoyl)imidazolin-2-ylidene, (1) are described. Compound 3-methyl-1-(1-methyl-2-methylbenzoyl)imidazolium hexafluorophosphate (1.HPF6) essentially serves as a carbene precursor that delivers the NHC carbene to Ag(I) and Au(I). The corresponding complex [{Ag(1)}{PF6}]2,(2), was prepared using mild base Ag2O and 3-methyl-1-(1-methyl-2-methylbenzoyl)imidazolium hexafluorophosphate (1.HPF6). Transmetallation method was capitalized to synthesize [{Au(1)}{PF6}]2,(3). All the novel compounds were characterized by elemental analysis, 1H NMR, 13C NMR, HR mass spectroscopic studies, and finally by single crystal X-ray studies. X-ray crystallographic studies revealed that the dinuclear complex 2 and 3 adopt linear geometry (Ccarbene-Ag/Au-Nimi) where strong Ag–Ag and Au–Au interaction present. The structural assignments were further supported by DFT calculations. TDDFT studies have been performed to inside into the electronic properties.

Interaction of the Silver(I) Cation with [2.2]Paracyclophane: Experimental and Theoretical Study

AbstractElectrospray ionization mass spectrometry was used to investigate the cation‐π interaction of Ag+ cation with [2.2]paracyclophane. It was found that cationic Ag.([2.2]paracyclophane)+ and Ag.([2.2]paracyclophane)2+ complex species are formed in the gas phase. Further, applying quantum mechanical calculations in the frame of the density functional theory, using B3LYP functional with Def2TZVP basis set, the most probable structures of the proved Ag+ ‐ [2.2]paracyclophane complexes were derived. In the Ag.([2.2]paracyclophane)+ complex, the cation Ag+ is bounded to three carbon atoms of one benzene ring of [2.2]paracyclophane ligand via cation‐π interaction. Quite analogously is bonded also second [2.2]paracyclophane molecule in Ag.([2.2]paracyclophane)2+ complex. The interaction energy, E(int), of Ag.([2.2]paracyclophane)+ complex was calculated to be −220.79 kJ/mol, E(int) of Ag.([2.2]paracyclophane)2+ complex is −362.67 kJ/mol. It is consistent with the formation of the considered Ag+ ‐ [2.2]paracyclophane complex species.

Facile construction of Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction with narrow band gaps for efficient visible-light photocatalysis

It is of great importance to fabricate photocatalyst with high photocatalytic activity, and the formation of Z-scheme heterojunction photocatalyst has been proved to be an effective way to restrain the recombination of photo-induced carriers. In this work, Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction is synthesized via a two-step process involving appropriate amount of cationic Ag ion doping into the imidazole ring of ZIF-8 framework and the precipitation of AgCl onto this Ag-doped-ZIF-8. The successful doping of ZIF-8 which decreases the band gap energy, enhances the light harvesting. Besides, the separation efficiency of photo-induced carriers is further improved due to the formation of Z-scheme AgCl/Ag-doped-ZIF-8 heterojunction, which is confirmed by photoelectrochemical experiments. As a result, the as-prepared AgCl/Ag-doped-ZIF-8 photocatalyst possesses excellent photocatalytic activity under visible light illumination. This work will provide a novel perspective for the design and construction of Z-scheme heterojunction for highly efficient photocatalysis.

Gas-phase synthesis and deposition of metal-bipyridine complex [M-bpy1-2]+ (M = Ag, Cu).

Controllable synthesis of organometallic clusters in the gas phase is a topic of reasonable interest with precisely tunable properties depending on sizes, compositions, and intra-cluster charge-transfer interactions. Here, we have prepared small Agn+ and Cun+ clusters by using a customized magnetron sputtering (MagS) source and observed the gas-phase reactions with 2,2'-bipyridine. It is found that the small silver and copper clusters readily react with bipyridine and form products of [M-bpy1-2]+ (M = Ag, Cu). Quantum chemistry calculations reveal that the bipyridine in both [Ag-bpy1-2]+ and [Cu-bpy1-2]+ takes on cis-conformation with altered N-C-C-N dihedral angles, which is in contrast to the trans-conformation of a free 2,2'-bipyridine molecule itself. In order to unveil the principle of conformational transition, we have fully studied the interactions between the nitrogen atoms of bipyridine and the cationic Ag+ and Cu+, calculated the donor-acceptor orbital overlaps, and analyzed the correlation of their frontier molecular orbital energy levels. Furthermore, by using a soft-landing strategy, we have managed to deposit the [Cu-bpy2]+ complex onto the glass substrates coated with Ag nanoparticles, and recorded the surface-enhanced Raman scattering spectra.

Stability of cationic silver doped gold clusters and the subshell-closed electronic configuration of AgAu14.

Silver doping is a valuable route to modulate the structural, electronic, and optical properties of gold clusters. We combine photofragmentation experiments with density functional theory calculations to investigate the relative stability of cationic Ag doped Au clusters, AgAuN-1 + (N ≤ 40). The mass spectra of the clusters after photofragmentation reveal marked drops in the intensity of AgAu8 +, AgAu14 +, and AgAu34 +, indicating a higher relative stability of these sizes. This is confirmed by the calculated AgAuN-1 + (N ≤ 17) dissociation energies peaking for AgAu6 +, AgAu8 +, and AgAu14 +. While the stability of AgAu6 + and AgAu8 + can be explained by the accepted electronic shell model for metal clusters, density of states analysis shows that the geometry plays an important role in the higher relative stability of AgAu14 +. For this size, there is a degeneracy lifting of the 1D shell, which opens a relatively large HOMO-LUMO gap with a subshell-closed 1S21P41P21D6 electronic configuration.

Absence of temperature effect on elution profiles on anionic and cationic ion-exchange resins from 4°C to 28°C.

In labs devoted to the geochemistry of non-traditional isotopes, chemical elution is necessary to purify the element of interest. Elution is always performed in over-pressured and air-conditioned clean rooms. We took advantage of an air-conditioning failure in our lab during summer 2018 to study the effect of temperature on the characteristics of the elution profiles of ion-exchange resins. We performed the ion-exchange separation of copper, iron and zinc on macroporous anionic AG MP-1 resin and that of calcium on cationic AG 50W-X12 resin, at 28°C, prior to the measurement of their isotopic ratios by mass spectrometry. We further performed these experiments in a clean hood in a cold room at 4°C. The elution curves were processed on biological standards, i.e. bovine liver (SRM-1577c), fetal bovine serum (FBS), bone meal (SRM-1486) and the seawater IAPSO standard. The elution profiles of major elements for each matrix, and those of copper, iron, zinc and calcium, were compared with those classically achieved at 20°C in air-conditioned conditions. The results show that the elution profiles preserve their characteristics whatever the temperature, suggesting that partitioning coefficients between resin and solution are thermo-independent in the range of temperature from 4°C to 28°C. If generalized to other matrices, notably inorganic, and to other elements, notably the extreme case of the separation of Rare Earth Elements, the present results suggest that clean labs may not have to be air-conditioned. This would reduce installation and operating costs and have a positive effect on the environment, paving the way for the development of a "green geochemistry".

Indirect Nano-sensing approach: A universal potentiometric silver ion selective sensor for inline quantitative profiling of the kinetics and thermodynamics of formation and decay of silver nanoparticles

Indirect Nano-sensing are indispensable chemical sensory points that make use of the unique properties of nanoparticles to derive information about it to our macroscopic world. Precious Silver nanoparticles have become more attractive in many areas of healthcare and life sciences leading to massive industrial production and increase of environmental exposure which may lead to Nanotoxicity accompanied by the release of Ag+ ions. A reversible silver selective screen-printed electrode was fabricated, optimized, and validated. A wide linearity range of 1 × 10−6 – 1 × 10−2 M was obtained, with a LOD that reaches 1.5 × 10−7 M and a typical slope of monovalent cationic compounds of 59.6 mV/decade. It showed high selectivity towards the cationic Ag+ ion activity in presence of the negatively charged citrate capped silver nanoparticles (Cit-AgNPs). The fabricated sensor has been used for tracking the decrease of Ag+ activity during the reduction of AgNO3 with tri-sodium citrate during the Bottom-up synthesis of Cit-AgNPs at different temperature (60, 70 and 80 °C). The kinetic parameters (Activation energy (Ea) and Reaction rate (K)) and the thermodynamic characteristics (free activation energy (ΔG), entropy (ΔS), enthalpy (ΔH)) have been calculated. Furthermore, it has been used for tracking the release of Ag+ during the spontaneous and stimulated decay of Cit-AgNPs. The present work could be a junction between nanotechnology and recent advances in design of a reproducible, portable real-time analyzer for in-process monitoring of the production of Cit-AgNPs and its environmental hazards with many advantages in comparison to the reported techniques in terms of portability, simplicity, cost-efficient, fast inline tracking, no sampling, real-time profiles at high temperatures and it does not need professional operators.

A Highly Efficient Coordination Polymer for Selective Trapping and Sensing of Perrhenate/Pertechnetate.

A porous cationic Ag(I) coordination polymer, [Ag(1,2,4,5-p4b)](SbF6) (TJNU-302) with the ligand 1,2,4,5-p4b (1,2,4,5-tetra(pyridin-4-yl)benzene), is reported that shows high sorption capacity (211 mg g-1) and distribution coefficient Kd (5.8 × 105 mL g-1) as well as outstanding selectivity in 500 times excess of CO32- or PO43- anion for perrhenate removal. TJNU-302 can act as a crystalline turn-off sensor for perrhenate upon UV radiation. In this way, a test paper strip for sensing ReO4- could be produced. In water solution, TJNU-302 shows an efficient fluorescence quenching response to ReO4- ion, with the highest quenching percentage (86%) among all reported ReO4- sensors. These results could be elucidated by the bonding properties of single-crystal structures of TJNU-302 before and after perrhenate sorption, as well as density functional theory (DFT) calculations.

Mechanism-Property Correlation in Coordination Polymer Crystals toward Design of a Superior Sorbent.

A methodology was developed to design superior sorbents of oxoanions. To integrate the high efficiency of chemisorption, selectivity, and recyclability into one sorbent, understanding the nature of oxoanions-sorbent interactions and the structural evolution of the sorbents is essential. Three cationic Ag(I) coordination polymers (CPs) are synthesized for dichromate (Cr2O72-) removal, and three distinct oxoanion-exchange mechanisms are identified, namely, the replacement, breath, and reconstruction processes, depending on the degree of framework distortion induced by the dichromate-CP interactions. The single crystal to single crystal transformation during the oxoanion exchange has been investigated by using single-crystal X-ray diffraction and energy-dispersive X-ray microanalysis. The replacement process, due to a weak chemisorption, shows excellent recyclability at the cost of reduction of efficiency and selectivity of adsorption. The reconstruction process may achieve a high efficiency and selectivity, but it loses recyclability. Due to the formation of a Ag-O(dichromate) bond and the breathing effect of the framework, the sorbent with the breath mechanism shows both superior efficiency and high recyclability in dichromate removal. The study of perrhenate (ReO4-) removal using the same CPs demonstrates that one CP performing the reconstruction process during dichromate removal turns to the breath process in removal of perrhenate anions. These results of mechanism-property correlation provide an insight into improvement of the methodology to fabricate a superior CP sorbent for oxoanion removal.

A new cationic silver(I)/melamine coordination polymer, [Ag2(melamine)]n2n+: Synthesis, characterization and potential use for aqueous contaminant anion exchange

A new cationic Ag(I)-melamine coordination polymer (AgM-CP), [Ag2(melamine)(CH3CO2)(NO3)]n, was synthesized in acidic aqueous solution and characterized via FTIR, Raman, SEM/EDX, SC-XRD, PXRD, and BET. SC-XRD and Raman reveal that melamine acts as tridentate ligand towards three different Ag (I) through the three triazine-nitrogen atoms. Raman results confirm the crystalline nature of AgM-CP as given by SC-XRD. Raman and FTIR, together, confirm the formation of coordination bonds between the electron-donor nitrogen atoms and the electron-acceptor silver(I). SEM shows that AgM-CP has a bar-like macro-structure with considerably large dimensions, e.g. 220 μm. AgM-CP structure is suggested to be cationic, and highly water-stable as concluded from weight loss calculations, PXRD, and Raman analyses. Due to these properties, AgM-CP was examined for the selective removal of anionic methyl orange (MO−) competitively with the cationic methylene blue (MB+) using aqueous solution of these synthetic dyes. MO− was almost completely removed (95 mg g−1 under the specified initial concentration) with no significant removal of MB+, which encourages its use as a material for the selective removal of the anionic contaminants from wastewater.

Weinreb Amide Directed Versatile C-H Bond Functionalization under (η5 -Pentamethylcyclopentadienyl)cobalt(III) Catalysis.

The (η5 -pentamethylcyclopentadienyl)cobalt(III) (Cp*CoIII )-catalyzed C-H bond functionalization of aromatic, heteroaromatic, and α,β-unsaturated Weinreb amides was explored. C-H allylation reactions with the use of allyl carbonate and a perfluoroalkene, oxidative alkenylation reactions with the use of ethyl acrylate, iodination reactions with the use of N-iodosuccinimide, and amidation reactions with the use of dioxazolones were catalyzed by Cp*Co(CO)I2 in the presence of a cationic Ag salt and AgOAc to afford various synthetically useful building blocks. Mechanistic studies of the C-H allylation disclosed that the C-H activation step was rate determining and virtually irreversible.

Substrate Specific Silver(I)-Catalyzed Cycloisomerization of Diene Involving Alkyl Rearrangements: Syntheses of 1,2,5,6-Tetrahydrocuminic Acid, p-Menth-3-en-7-ol, and p-Menth-3-en-7-al.

The novel cationic Ag(I)-catalyzed cycloisomerization, which is associated with alkyl rearrangements, from dimethyl 2-allyl-2-prenylmalonate (1) to dimethyl 4-isopropylcyclohex-3-ene-1,1-dicarboxylate (2) has been developed. Derivatization from the diester 2 into the diol 3 and its X-ray crystallographic analysis determined the structure. The mechanisms of the novel reaction were investigated by isotopic experiments, which supported the unusual alkyl shifts. In addition, the product 2 was used for the total syntheses of three natural products, 1,2,5,6-tetrahydrocuminic acid (12), p-menth-3-en-7-ol (13), and p-menth-3-en-7-al (14) in short steps.

Core-polarization-corrected random-phase approximation with exact exchange for dipole surface plasmons in silver clusters

The surface plasmon in silver clusters is red shifted with respect to standard jellium random-phase approximation (RPA) predictions that work well for simple metal clusters. The reason for the deviation arises primarily from the non-negligible polarization interaction between the valence electrons and ionic cores. In order to quantify this effect in the jellium approximation we introduce a modified RPAE (RPA with exact exchange). The jellium background of Ag cores is treated as a polarizable sphere. This model predicts a dipole surface resonance in excellent agreement with published experimental data. Moreover it yields the blue shift (red shift) with decreasing sizes for cationic (anionic) Ag clusters as observed experimentally.

Efficient visible light photocatalytic NOx removal with cationic Ag clusters-grafted (BiO)2CO3 hierarchical superstructures

A facile method was developed to graft cationic Ag clusters on (BiO)2CO3 hierarchical superstructures (BHS) surface to improve their visible light activity. Significantly, the resultant Ag clusters-grafted BHS displayed a highly enhanced visible light photocatalytic performance for NOx removal due to the direct interfacial charge transfer (IFCT) from BHS to Ag clusters. The chemical and coordination state of the cationic Ag clusters was determined with the extended X-ray absorption fine structure (EXAFS) and a theoretical structure model was proposed for this unique Ag clusters. The charge transfer process and the dominant reactive species (OH) were revealed on the basis of electron spin resonance (ESR) trapping. A new photocatalysis mechanism of Ag clusters-grafted BHS under visible light involving IFCT process was uncovered. In addition, the cationic Ag clusters-grafted BHS also demonstrated high photochemical and structural stability under repeated photocatalysis runs. The perspective of enhancing photocatalysis through combination of microstructural optimization and IFCT could provide a new avenue for the developing efficient visible light photocatalysts.

A simple Ag(I)-enyne cation

A simple cationic Ag(I)-1,3-enyne complex was synthesized and characterized. In the solid state, single crystal X-ray crystallography showed the Ag(I) centre bonded in an asymmetric manner exclusively to the alkyne portion of the substrate. NMR spectroscopy studies showed this structure is maintained in solution over the temperature range of −90 to +60 °C.

High-efficiency solution-processed OLEDs based on cationic Ag6Cu heteroheptanuclear cluster complexes with aromatic acetylides

Strongly phosphorescent cationic Ag6Cu cluster complexes show highly efficient electroluminescence from solution-processed OLEDs with a current efficiency of 42.5 cd A−1 and an external quantum efficiency of 13.9% at a low bias voltage (4.5 V).

Impact of reaction variables and PEI/l-cysteine ratio on the optical properties and cytocompatibility of cationic Ag2S quantum dots as NIR bio-imaging probes

Near-infrared emitting semiconductor quantum dots (NIRQDs) are popular fluorescent probes due to better penetration depth and elimination of tissue autofluorescence.