Peripheral metal-ion binding to tris(thia-oxo crown) porphyrazines

We report the preparation and solution properties of metal-free [1b(H(2))] and cobalt [1c(Co)] porphyrazines (pz's), where three pyrroles are functionalized with a S(2)O(3) crown ether for metal-ion binding and the fourth pyrrole is appended with two long-chain alcohols (bis((11-hydroxyundecyl)thio)) for potential use as surface anchors. Compounds 1b(H(2) and 1c(Co) exhibit ion-specific optical changes in the presence of Ag(+) and Hg(2+). Binding of Ag(+) to 1b(H(2)) is described by a 1:1 binding isotherm, with K(D) approximately 147 microM, whereas binding of Hg(2+) to 1b(H(2)) appears more complex. For 1c(Co), binding of Ag(+) and Hg(2+) also can be fit to a 1:1 isotherm, with K(D) approximately 109 and 83 microM, respectively. All four titrations show nonisosbesticity, including those apparently describable by the 1:1 isotherm, which indicates that there are intermediate stages as multiple ions bind. Neither 1b(H(2)) or 1c(Co) gives optical responses to Ni(2+), Zn(2+), Pb(2+), or Cu(2+) or to alkali (Li(+), Na(+), K(+), and Cs(+)) and alkaline earth (Mg(2+), Ca(2+), and Ba(2+)) metal ions. Nonetheless, "hard" ions are sensed electrochemically: Na(+) and Li(+) strongly shift the pz/pz(-) couple of 1b(H(2)()) and Co(III)/Co(II) couple of 1c(Co). For the addition of 4 equiv of Li(+) to 1c(Co), the Co(III)/Co(II) shifts +40 mV, and for the addition of 4 equiv of Na(+) to 1c(Co), the shift is +155 mV. The shifted redox waves of 1c(Co) all retain their reversibility. In contrast, for the addition of either 4 equiv of Li(+) or Na(+) to 1b(H(2)), the shifts of the pz/pz(-) couple are essentially the same, approximately 170 mV, and the shifted redox waves become broadened and less reversible, due to ion-induced aggregation. For 1c(Co) the shape of the titration curves [M]/[1b(H(2))] versus E(1/2) is concave to the x-axis, implying cooperative binding of multiple M(+) ions as part of the redox/binding system of equilibria.     

Elucidation of the redox behavior of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrodes and application of the DMcT-PEDOT composite cathodes to lithium/lithium ion batteries

The redox reactions of DMcT at PEDOT-modified glassy carbon electrodes (GCEs) in acetonitrile (AN) have been investigated via cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM) in order to elucidate the redox reaction mechanism. A redox couple at -0.29 V versus Ag/Ag+ was assigned to the dimerization process of singly protonated DMcT (DMcT-1H), and a second couple observed at +0.42 V was assigned to the polymerization process of the protonated DMcT dimer. Our investigations revealed further that the anodic current response at +0.55 V (polymerization process) has a shoulder at +0.38 V ascribed to the dimerization process of doubly protonated DMcT (DMcT-2H), indicating that the redox couple at +0.42 V is the overlapping response of the polymerization of the protonated DMcT dimer and the dimerization of the DMcT-2H monomer. It was also confirmed that the dimerization process of DMcT-1H at -0.29 V proceeded not only at the surface of a PEDOT film but also inside the film as previously suggested. Moreover, the thermodynamics of these redox reactions at PEDOT-modified GCEs are dependent on the basicity (or acidity) of the solution, as anticipated and previously shown at unmodified GCEs. The oxidation of DMcT occurs at less positive potentials and the reduction occurs at more negative potentials in the presence of base. On the basis of the results obtained, the full redox reaction scheme for DMcT at a PEDOT-modified GCE is proposed.     

Electronic structure and solvation of copper and silver ions: a theoretical picture of a model aqueous redox reaction

Electronic states and solvation of Cu and Ag aqua ions are investigated by comparing the Cu(2+) + e(-)--> Cu(+) and Ag(2+) + e(-)--> Ag(+) redox reactions using density functional-based computational methods. The coordination number of aqueous Cu(2+) is found to fluctuate between 5 and 6 and reduces to 2 for Cu(+), which forms a tightly bound linear dihydrate. Reduction of Ag(2+) changes the coordination number from 5 to 4. The energetics of the oxidation reactions is analyzed by comparing vertical ionization potentials, relaxation energies, and vertical electron affinities. The model is validated by a computation of the free energy of the full redox reaction Ag(2+) + Cu(+) --> Ag(+) + Cu(2+). Investigation of the one-electron states shows that the redox active frontier orbitals are confined to the energy gap between occupied and empty states of the pure solvent and localized on the metal ion hydration complex. The effect of solvent fluctuations on the electronic states is highlighted in a computation of the UV absorption spectrum of Cu(+) and Ag(+).     

Synthesis and photochromism of spirobenzopyrans and spirobenzothiapyran derivatives bearing monoazathiacrown ethers and noncyclic analogues in the presence of metal ions

Spirobenzopyrans bearing monoazathiacrown ethers and noncyclic analogues were synthesized, and their ion-responsive photochromism depending on the dual metal ion interaction with the crown ether and the phenolate anion moieties was examined using alkali and alkaline-earth metal ions, Ag(+), Tl(+), Pb(2+), Hg(2+), and Zn(2+). The prepared spirobenzopyrans showed a selective binding ability to Mg(2+) and Ag(+) with negative and positive photochromism, respectively. Among the metal ions, only Ag(+) facilitated photoisomerization to the corresponding merocyanine form. Depending on the ring size of the monoazathiacrown ether moieties, soft metal ions such as Hg(2+) and Ag(+) showed significant shifts in the UV-vis absorption spectra, while hard metal ions such as Mg(2+), Zn(2+), and Pb(2+) did not afford any meaningful shift. This result reflects that the monoazathiacrown ether and phenolate anion moieties prefer soft and hard metal ions, respectively. Therefore, the Mg(2+) and Ag(+) selectivities are mainly derived from the phenolate anion and monoazathiacrown ether moieties, respectively. On the other hand, a spirobenzothiapyran bearing 3,9-dithia-6-monoazaundecane showed a remarkable selectivity to Ag(+).     

The voltammetric behaviour of solid 2,2-diphenyl-1-picrylhydrazyl (DPPH) microparticles

The electrochemical behaviour of 2,2-diphenyl-1-picrylhydrazyl (DPPH) microparticles, attached to a graphite electrode and adjacent to an aqueous electrolyte solution, has been studied by cyclic voltammetry. DPPH exhibits one reversible redox couple with a formal potential of 0.340 V versus Ag|AgCl (pH=7.0). At more positive potentials, a redox couple appears with a formal potential E_f=0.733 V versus Ag|AgCl. The oxidation at this potential is followed by an irreversible chemical reaction generating a product which gives a redox couple with a formal potential at 0.177 V versus Ag|AgCl. The reduction process of this couple is followed by a slow chemical reaction in the course of which DPPH is reformed.     

Silver nanocluster redox-couple-promoted nonclassical electron transfer: an efficient electrochemical Wolff rearrangement of alpha-diazoketones

In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag(n), mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-diazoketones. More specifically, the presence of a Ag(n) (0)/Ag(n) (+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag(n)) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag(n) as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.     

Diabatic free energy curves and coordination fluctuations for the aqueous Ag+Ag2+ redox couple: a biased Born-Oppenheimer molecular dynamics investigation

Biased Born-Oppenheimer molecular dynamics simulations are performed to compute redox potential and free energy curves for the redox half reaction Ag(+)-->Ag(2+)+e(-) in aqueous solution. The potential energy surfaces of reactant and product state are linearly coupled and the system transferred from the reduced state to the oxidized state by variation of the coupling parameter from 0 to 1. The redox potential is obtained by thermodynamic integration of the average ionization energy of Ag(+). Diabatic free energy curves of reduced (R) and oxidized (O) states are obtained to good statistical accuracy by reweighting and combining the set of biased distributions of the ionization energy. The diabatic free energy curves of Ag(+) and Ag(2+) are parabolic over a wide range of the reaction coordinate in agreement with the linear response assumption that underlies Marcus theory. However, we observe deviations from parabolic behavior in the equilibrium region of Ag(+) and find different values for the reorganization free energy of R (1.4 eV) and O (0.9 eV). The computed reorganization free energy of Ag(2+) is in good agreement with the experimental estimate of 0.9-1.2 eV obtained from photoelectron spectroscopy. As suggested by our calculations, the moderate deviation from linear response behavior found for Ag(+) is likely related to the highly fluxional solvation shell of this ion, which exhibits water exchange reactions on the picosecond time scale of the present molecular dynamics simulation.     

Influence of anionic sulfonate-containing co-ligands on the solid structures of silver complexes supported by 4,4'-bipyridine bridges

In this paper, ten new silver compounds, namely [Ag(bipy)](L1).H2O (1), [Ag(bipy)](L2).2H2O (2), [Ag2(bipy)2(H2O)2](L3).H2O (3), [Ag(L4)(bipy)].H2O (4), [Ag(L5)(bipy)] (5), [Ag(L6)(bipy)].0.5CH3CN (6), [Ag3(L7)2(bipy)2].2(H2O) (7), [Ag2(L8)(bipy)1.5(H2O)].H2O (8), [Ag2(L9)(bipy)2(H2O)2] (9) and [Ag3(L10)(bipy)2][(bipy)(H2O)2].(H2O)3.5 (10) (where bipy = 4,4'-bipyridine, L1 = 6-amino-1-naphthalenesulfonate anion, L2 = 2-naphthalenesulfonate anion, L3 = sulfosalicylate anion, L4 = p-aminobenzenesulfonate anion, L5 = 4-dimethyaminoazobenzenen-4'-sulfonate anion, L6 = 2,5-dichloro-4-amino-benzenesulfonate anion, L7 = 8-hydroxyquinoline-5-sulfonate anion, L8 = 2-nitroso-1-naphthol-4-sulfonate anion, L9 = 2,6-naphthalenedisulfonate anion and L10 = 1,3,5-naphthalenetrisulfonate anion), have been synthesized and characterized by elemental analyses, IR spectroscopy and X-ray crystallography. In compounds 1-6, Ag(I) centers are linked by bipy ligands to form 1D Ag-bipy chain structures, in which the sulfonate anions of compounds 1-3 act as counter ions. The sulfonate anions of compounds 4 and 5 connect Ag-bipy chains to form 1D double chain structures, respectively. The sulfonate anions of compound 6 connect Ag-bipy chains to form a 2D layer structure. Unexpectedly, compound 7 shows a hinged chain structure, and these chains interlace with each other through hydrogen bonds and pi-pi interactions to generate a 3D structure with channels along the c axis. Compounds 8 and 9 show 1D ladder-like structures. In compound 10, the Ag-bipy chains are connected by sulfonate anions to generate a 3D poly-threaded network, in which an isolated Ag-bipy chain is inserted. The results indicate that the anionic sulfonate-containing co-ligands play an important role in the final structures of the Ag(I) complexes. Additionally, the luminescent properties of these compounds were also studied.     

Halogen-Bonding Strapped Porphyrin BODIPY Rotaxanes for Dual Optical and Electrochemical Anion Sensing

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. ¹H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P^+. redox couple.     

Simple electrochemical method for deposition and voltammetric inspection of silver particles at the liquid-liquid interface of a thin-film electrode

A novel experimental methodology for depositing and voltammetric study of Ag nanoparticles at the water-nitrobenzene (W-NB) interface is proposed by means of thin-film electrodes. The electrode assembly consists of a graphite electrode modified with a thin NB film containing decamethylferrocene (DMFC) as a redox probe. In contact with an aqueous electrolyte containing Ag(+) ions, a heterogeneous electron-transfer reaction between DMFC((NB)) and Ag(+)((W)) takes place to form DMFC(+)((NB)) and Ag deposit at the W-NB interface. Based on this interfacial reaction, two different deposition strategies have been applied. In the uncontrolled potential deposition protocol, the electrode is immersed into an AgNO(3) aqueous solution for a certain period under open circuit conditions. Following the deposition step, the Ag-modified thin-film electrode is transferred into an aqueous electrolyte free of Ag(+) ions and voltammetrically inspected. In the second protocol the deposition was carried out under controlled potential conditions, i.e., in an aqueous electrolyte solution containing Ag(+) ions by permanent cycling of the electrode potential. In this procedure, DMFC((NB)) is electrochemically regenerated at the electrode surface, hence enabling continuation and voltammetric control of the Ag deposition. Hence, the overall electrochemical process can be regarded as an electrochemical reduction of Ag(+)((W)) at the W-NB interface, where the redox couple DMFC(+)/DMFC acts as a mediator for shuttling electrons from the electrode to the W-NB interface. Ag-particles deposited at the W-NB interface affect the ion transfer across the interface, which provides the basis for voltammetric inspection of the metal deposit at the liquid-liquid interface with thin-film electrodes. Voltammetric properties of thin-film electrodes are particularly sensitive to the deposition procedure, reflecting differences in the properties of the Ag deposit. Moreover, this methodology is particularly suited to inspect catalytic activities of metal particles deposited at the liquid-liquid interface toward heterogeneous electron-transfer reactions occurring at the at the liquid-liquid interface.     

Mechanistic study of photomediated triangular silver nanoprism growth

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.     

Activation of the C-I and C-OH bonds of 2-iodoethanol by gas phase silver cluster cations yields subvalent silver-iodide and -hydroxide cluster cations

The gas phase ion-molecule reactions of silver cluster cations (Ag(n)(+)) and silver hydride cluster cations (Ag(m)H(+)) with 2-iodoethanol have been examined using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. These clusters exhibit size selective reactivity: Ag(2)H(+), Ag(3)(+), and Ag(4)H(+) undergo sequential ligand addition only, while Ag(5)(+) and Ag(6)H(+) also promote both C-I and C-OH bond activation of 2-iodoethanol. Collision induced dissociation (CID) of Ag(5)HIO(+), the product of C-I and C-OH bond activation by Ag(5)(+), yielded Ag(4)OH(+), Ag(4)I(+) and Ag(3)(+), consistent with a structure containing AgI and AgOH moieties. Ag(6)H(+) promotes both C-I and C-OH bond activation of 2-iodoethanol to yield the metathesis product Ag(6)I(+) as well as Ag(6)H(2)IO(+). The metathesis product Ag(6)I(+) also promotes C-I and C-OH bond activation.DFT calculations were carried out to gain insights into the reaction of Ag(5)(+) with ICH(2)CH(2)OH by calculating possible structures and their energies for the following species: (i) initial adducts of Ag(5)(+) and ICH(2)CH(2)OH, (ii) the subsequent Ag(5)HIO(+) product, (iii) CID products of Ag(5)HIO(+). Potential adducts were probed by allowing ICH(2)CH(2)OH to bind in different ways (monodentate through I, monodentate through OH, bidentate) at different sites for two isomers of Ag(5)(+): the global minimum "bowtie" structure, 1, and the higher energy trigonal bipyramidal isomer, 2. The following structural trends emerged: (i) ICH(2)CH(2)OH binds in a monodentate fashion to the silver core with little distortion, (ii) ICH(2)CH(2)OH binds to 1 in a bidentate fashion with some distortion to the silver core, and (iii) ICH(2)CH(2)OH binds to 2 and results in a significant distortion or rearrangement of the silver core. The DFT calculated minimum energy structure of Ag(5)HIO(+) consists of an OH ligated to the face of a distorted trigonal bipyramid with I located at a vertex, while those for both Ag(4)X(+) (X = OH, I) involve AgX bound to a Ag(3)(+) core. The calculations also predict the following: (i) the ion-molecule reaction of Ag(5)(+) and ICH(2)CH(2)OH to yield Ag(5)HIO(+) is exothermic by 34.3 kcal mol(-1), consistent with the fact that this reaction readily occurs under the near thermal experimental conditions, (ii) the lowest energy products for fragmentation of Ag(5)HIO(+) arise from loss of AgI, consistent with this being the major pathway in the CID experiments.     

Reactivity of ammonia ligands of the antitumor agent cisplatin: a unique dodecanuclear Pt4,Pd4,Ag4 platform for four cytosine model nucleobases

The reaction of a potential mono(nucleobase) model adduct of cisplatin, cis-[Pt(NH(3))(2)(1-MeC-N3)(H(2)O)](2+) (6; 1-MeC: 1-methylcytosine), with the electrophile [Pd(en)(H(2)O)(2)](2+) (en: ethylenediamine) at pH approximately 6 yields a kinetic product X which is likely to be a dinuclear Pt,Pd complex containing 1-MeC(-)-N3,N4 and OH bridges, namely cis-[Pt(NH(3))(2)(1-MeC(-)-N3,N4)(OH)Pd(en)](2+). Upon addition of excess Ag(+) ions, conversion takes place to form a thermodynamic product, which, according to (1)H NMR spectroscopy and X-ray crystallography, is dominated by a mu-NH(2) bridge between the Pt(II) and Pd(II) centers. X-ray crystallography reveals that the compound crystallizes out of solution as a dodecanuclear complex containing four Pt(II), four Pd(II), and four Ag(+) entities: [{Pt(2)(1-MeC(-)-N3,N4)(2)(NH(3))(2)(NH(2))(2)(OH)Pd(2)(en)(2)Ag}(2){Ag(H(2)O)}(2)](NO(3))(10) 6 H(2)O (10) is composed of a roughly planar array of the 12 metal ions, in which the metal ions are interconnected by mu-NH(2) groups (between Pt and Pd centers), mu-OH groups (between pairs of Pt atoms), and metal-metal donor bonds (Pt-->Ag, Pd-->Ag). The four 1-methylcytosinato ligands, which are stacked pairwise, as well as the four NH(3) ligands and parts of the en rings, are approximately perpendicular to the metal plane. Two of the four Ag ions (Ag2, Ag2') of 10 are labile in solution and show the expected behavior of Ag(+) ions in water, that is, they are readily precipitated as AgCl by Cl(-) ions. The resulting pentanuclear complex [Pt(2)Pd(2)Ag(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(4)7 H(2)O (11) largely maintains the structural features of one half of 10. The other two Ag(+) ions (Ag1, Ag1') of 10 are remarkably unreactive toward excess NaCl. In fact, the pentanuclear complex [Pt(2)Pd(2)AgCl(1-MeC(-))(2)(NH(2))(2)(OH)(NH(3))(2)(en)(2)](NO(3))(3)4.5 H(2)O (12), obtained from 10 with excess NaCl, displays a Cl(-) anion bound to the Ag center (2.459(3) A) and is thus a rare case of a crystallized "AgCl molecule".     

Photoreduction of catalytic platinum particles using immobilized multilayers of Photosystem I

Using the abundance of available electrons generated by immobilized multilayers of the photoactive protein complex Photosystem I (PSI), we have photoreduced platinum particles that are catalytically active for the H(2)/H(+) redox couple. The resulting platinized PSI films were optimized using electrochemical measurements and then characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and scanning electrochemical microscopy (SECM). These results demonstrate a novel method for generating immobilized platinum catalysts that are readily available on the surface of a photoactive PSI multilayer.     

Cation and pressure effects on the electrochemistry of 12-tungstocobaltate and 12-tungstophosphate ions in acidic aqueous solution

The effects of supporting electrolytes and of pressure on the electrode reactions of the aqueous CoW(12)O(40)(5-/6-) couple at 25 degrees C are reported, together with limited data on PW(12)O(40)(3-)/4-) and PW(12)O(40)(4-/5-). The half-wave potentials E(1/2) for the CoW(12) couple become moderately more positive with increasing electrolyte concentration and cationic charge, and also in the sequences Li(+) approximately Na(+) < NH(4)(+) < or = H(+) < K(+) < Rb(+) < Cs(+) and Na(+) < Mg(2+) < Ca(2+) < Eu(3+). The mean diffusion coefficients for CoW(12) with the 1:1 electrolytes are independent of electrolyte concentration and rise only slightly from Li(+) to Cs(+), averaging (2.4 +/- 0.3) x 10(-6) cm(2) s(-1). Neither the volumes of activation for diffusion Delta V(diff)(++) (average -0.9 +/- 1.1 cm(3) mol(-1)) nor the electrochemical cell reaction volumes Delta V(Ag/AgCl) (average -22 +/- 2 cm(3) mol(-1)) for the CoW(12) couple show significant dependence on electrolyte identity or concentration. For the PW(12)(3-/4-) and PW(12)(4-/5-) couples, Delta V(Ag/AgCl) = -14 and -26 cm(3) mol(-1), respectively, suggesting a dependence on Delta(z(2)) (z = ionic charge number) as predicted by the Born-Drude-Nernst theory of electrostriction of solvent, but comparison with Delta V(Ag/AgCl) for CoW(12) and other anion-anion couples shows that the Born-Drude-Nernst approach fails in this context. For aqueous electrode reactions of CoW(12), as for other anionic couples such as cyanometalates, the standard rate constants k(el) show specific cation catalysis (Na(+) < K(+) < Rb(+) < Cs(+)), and Delta V(el++) is invariably positive, in the presence of supporting electrolytes. For the heavier group 1 cations, Delta V(el++) is particularly large (10-15 cm(3) mol(-1)), consistent with a partial dehydration of the cation to facilitate catalysis of the electron-transfer process. The positive values of Delta V(el++) for the CoW(12) couple cannot be attributed to rate control by solvent dynamics, which would lead to Delta V(el++) < or = Delta V(diff++), i.e., to negative or zero Delta V(el++) values. These results stand in sharp contrast to those for aqueous cationic couples, for which k(el) shows relatively little influence of the nature of the counterion and Delta V(el++) is always negative.     

Infrared spectroscopy of Cu+(H2O)(n) and Ag+(H2O)(n): coordination and solvation of noble-metal ions

M(+)(H(2)O)(n) and M(+)(H(2)O)(n)Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions. These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer. Density functional theory calculations are also carried out for analyzing the experimental IR spectra. Partially resolved rotational structure observed in the spectrum of Ag(+)(H(2)O)(1) x Ar indicates that the complex is quasilinear in an Ar-Ag(+)-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M(+)(H(2)O)(2) are consistent with twofold coordination with a linear O-M(+)-O arrangement for these ions, which is stabilized by the s-d hybridization in M(+). Hydrogen bonding between H(2)O molecules is absent in Ag(+)(H(2)O)(3) x Ar but detected in Cu(+)(H(2)O)(3) x Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H(2)O attaches directly to Ag(+) in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu(+). The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag(+), in contrast to the extensive 4s-3d hybridization in Cu(+) which retains the dicoordination. This is most likely because the s-d energy gap of Ag(+) is much larger than that of Cu(+). The fourth H(2)O occupies the second shells of the tricoordinated Ag(+) and the dicoordinated Cu(+), as extensive hydrogen bonding is observed in M(+)(H(2)O)(4) x Ar. Interestingly, the Ag(+)(H(2)O)(4) x Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag(+)(H(2)O)(3) x Ar but revived at n=4. Size dependent variations in the spectra of Cu(+)(H(2)O)(n) for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu(+)(H(2)O)(2) subunit is surrounded by four H(2)O molecules. The gas-phase coordination number of Cu(+) is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes.     

Mechanistic study on adsorptive removal of tert-butanethiol on Ag-Y zeolite under ambient conditions

The dynamics and surface chemistry of tert-butanethiol (TBT) adsorptive removal over silver-exchanged Y zeolite (Ag-Y) were studied under ambient conditions. Saturation uptake on Ag-Y was higher than that on H-Y and Na-Y. The structural analyses by a combination of X-ray diffraction, Ag K-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structures (EXAFS), Ag L(III)-edge XANES, S K-edge XANES, and in situ UV-vis show that the AgSH molecule, Ag(2)S monomer, and Ag(4)S(2) cluster are the dominant silver species in TBT-saturated Ag-Y. Dynamic changes in adsorbed intermediates, gas-phase products, and the silver sulfides were followed by in situ FTIR, mass spectroscopy and in situ UV-vis, respectively. The results show the following reaction mechanism: (1) formation of iso-butene and adsorbed H(2)S on the Ag(+) site via C-S cleavage of hydrogen-bonded TBT initially adsorbed on the Ag(+) site; (2) conversion of the adsorbed H(2)S to AgSH and H(+) on zeolite; (3) the reaction of two Ag-SH species to yield Ag(2)S and H(+) on zeolite.     

Syntheses of copper(I)cis-1,3,5-tri-iminocyclohexane complexes

Copper(I) complexes of the ligand cis-1,3,5-tris(cinnamylideneamino)cyclohexane (L) have been prepared from a versatile precursor complex, [Cu(I)(L)NCMe]BF4, which incorporates a labile acetonitrile ligand that can be exchanged to give a range of new Cu(L)X complexes (where X = Cl, Br, NO2, SPh). 1H NMR spectra and X-ray structures of the Cl, Br and NO2 complexes show L coordinated in a symmetric fashion about the copper centre. The complexes have been further characterised using UV/Visible spectroscopy and cyclic voltammetry. CuLCl shows an electrochemically reversible Cu(I/II) redox couple at 0.51 V (vs. Ag/AgCl) while the CuLNO2 complex shows an analogous quasi-reversible wave at 0.41 V (vs. Ag/AgCl).     

Wolff rearrangement of alpha-diazoketones using in situ generated silver nanoclusters as electron mediators

[reaction: see text] We report Wolff rearrangement of alpha-diazoketones by in situ generated silver nanoclusters (Ag(n)(), 2-4 nm) from silver(I) oxide (Ag(2)O) involving a nonclassical electron-transfer process. Our results show that Ag(n)()(+)/Ag(n)()(0) redox couple allows the initial removal of an electron from alpha-diazoketone and its back-donation after chemical reaction(s). Controlled potential coulometry (CPC) of various alpha-diazoketones results in the realization of Wolff-rearranged carboxylic acids in excellent yields.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.