Through-Space Spin Coupling in a Silver(II) Porphyrin Dimer upon Stepwise Oxidations: AgII⋅⋅⋅AgII,AgII⋅⋅⋅AgIII,and AgIII⋅⋅⋅AgIII Metallophilic Interactions

Metallophilic interactions between closed-shell metal ions are becoming a popular tool for a variety of applications related to high-end materials. Heavier d⁸ transition-metal ions are also considered to have a closed shell and can be involved in such interactions. There is no systematic investigation so far to estimate the structure and energy characteristics of metallophilic interactions in Ag^II/Ag^II (d⁹/d⁹), Ag^III/Ag^III (d⁸/d⁸), and mixed-valent Ag^II/Ag^III (d⁹/d⁸) complexes, which have been demonstrated in the present study. Both interporphyrinic and intermetallic interactions were investigated on stepwise oxidation by using a rigid ethene-bridged cis silver(II) porphyrin dimer and the results compared with those for highly flexible ethane-bridged analogues. By controlling the nature of chemical oxidants and their stoichiometry, both 1e and 2e oxidations were done stepwise to generate Ag^II/Ag^III mixed-valent and Ag^III/Ag^III porphyrin dimers, respectively. Unlike all other ethene-bridged metalloporphyrin dimers reported earlier, in which 2e oxidation stabilizes only the trans form, such an oxidation of silver(II) porphyrin dimer stabilizes only the cis form because of the metallophilic interaction. Besides silver(II) ⋅⋅⋅ silver(II) interactions in cis silver(II) porphyrin dimer, stepwise oxidations also enabled us to achieve various hitherto-unknown silver(II) ⋅⋅⋅ silver(III) and silver(III) ⋅⋅⋅ silver(III) interactions, which thereby allow significant modulation of their structure and properties. The strength of Ag ⋅⋅⋅ Ag interaction follows the order Ag^II/Ag^II (d⁹/d⁹)<Ag^II/Ag^III (d⁹/d⁸)<Ag^III/Ag^III (d⁸/d⁸). Single-crystal XRD, X-ray photoelectron spectroscopy (XPS), ¹H NMR and EPR spectroscopy, and variable-temperature magnetic investigations revealed various oxidation states of silver and metallophilic interactions, which are also well supported by computational analysis.     

Use of Ag(II) as a removable template in porphyrin chemistry: diol cleavage products of [meso-tetraphenyl-2,3-cis-diolchlorinato]silver(II)

The use of Ag^II as a removable template in synthetic porphyrin chemistry is described. Mild procedures for the insertion of Ag^II into chlorins and the demetallation of the [chlorinato]Ag^II complexes are delineated. The UV-vis spectra of the novel [chlorinato]Ag^II complexes are discussed. The diol cleavage products of [meso-tetraphenyl-2,3-diolchlorinato]silver(II) under a number of conditions are characterized and compared to those resulting from the cleavage of the corresponding free base diol chlorin or its Ni^II complex, highlighting the unique templating effect of Ag^II. The scopes and limits of electrospray ionization mass spectrometry (ESI-MS) for the analysis of Ag^II chlorins is described. The use of Ag^II as a templating metal is superior over Ni^II or Zn^II for the preparation of free base pyrrole-modified porphyrins along metal templated pathways.     

Colloidal copper in aqueous solutions: radiation-chemical reduction,mechanism of formation,and properties

Colloidal copper has been obtained by -irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When Cu^II is not entirely incorporated into the complex with PEI, disproportionation of Cu^I aqua complexes formed affords the metal, along with Cu₂O. Reduction of the PEI complex of Cu^I by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–30, January, 1994.     

Silver(III)⋅⋅⋅Silver(III) Interactions that Stabilize the syn Form in a Porphyrin Dimer Upon Oxidation

The interaction between two Ag^II porphyrins, connected covalently through a highly flexible ethane bridge, in a metalloporphyrin dimer has been investigated upon stepwise oxidation. X‐ray structure determination of one and two‐electron oxidized complexes has clearly revealed only metal‐centered oxidation that results in short Ag−N (porphyrin) distance with large distortion in the porphyrin macrocycle. The 2e‐oxidized complex exhibits significant metallophilic interaction in the form of a close Ag^III⋅⋅⋅Ag^III contact that brings two porphyrin rings more cofacial with syn ‐conformation, which would otherwise stabilize in an anti ‐form. The interaction also leads to an intense emission peak at 546 nm at 77 K in the photoluminescence study.     

Remarks on the reactions of a tetracarboxylic porphyrin with gold and silver ions: A spectrophotometric,TEM and SEM study

The coproporphyrin-I (CPI) behaves as a reducing agent for silver and gold metal ions and as stabilizing agent for the formed colloidal metallic nanoparticles. The peculiarity of silver and gold nanoparticles obtained in the reactions of monomeric form of CPI with their metal ions has been studied. The optical properties of the colloidal forms of these metals have been investigated by UV–Vis spectrophotometry, and their morphology by TEM and SEM measurements. The structures and the size distributions of Ag and Au particles have been characterized and determined by computerized TEM images.     

SERS and DFT study of nitroarenes adsorbed on metal nanoparticles

A combined SERS and DFT investigation has been performed for 2-amino,5-nitropyridine (ANP) adsorbed on silver colloidal nanoparticles in order to get a better insight into the adsorption mechanism of ANP on the silver surface. Both B3LYP and B3PW91 functionals were used in the DFT calculations on ANP in the anionic form (ANP⁻) and on different models of ANP⁻/silver surface complexes. A mixed basis set 6-311++G^**/LANL2DZ was used in the case of the ANP⁻/Ag⁺ complexes. From the comparison between the experimental and the computational data, it was evinced that ANP is adsorbed on the silver surface in the anionic form with a quinonoid electronic structure through the nitrogen atom of the imino group.     

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Peripheral and non-peripheral-designed multifunctional phthalocyanines; synthesis, electrochemistry, spectroelectrochemistry and metal ion binding studies

A novel type of ionophore ligands, 3′-(2,3-dihydroxypropylthio)-phthalonitrile and 4′(2,3-dihydroxypropylthio)-phthalonitrile, and their α- and β-tetrasubstituted metallo phthalocyanines, (MPc), (M = Zn^II, Co^II, Mn^IIICl, Fe^IIIAc, Cu^II) have been prepared and fully characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR, and MS (ESI and Maldi-TOF). The complexes are soluble in both polar and non-polar solvents, such as MeOH and EtOH, THF, CHCl₃ and CH₂Cl₂. The spectroscopic properties of the complexes are affected strongly by the electron-donating sulfanyl units on the periphery of the phthalocyanines. The cation binding properties of the complexes, for example using Ag^I and Pd^II, were evaluated by UV-Vis spectroscopy and the results show the formation of polynuclear phthalocyanine complexes. Functional donors on the periphery of the zinc and copper complexes coordinate to Ag^I and Pd^II to give ca. a 2:1 metal-phthalocyanine complex binding ratio for the concentration of 2.5 × 10⁻⁵ M (Pc) and 1.0 × 10⁻³ M (Metal ions). Voltammetric and in-situ spectroelectrochemical studies were performed to characterize the redox behavior of the complexes. An in-situ electrocolorimetric method was applied to investigate the colors of the electro-generated anionic and cationic forms of the complexes.     

Design of Ratiometric Fluorescent Probes Based on Arene–Metal‐Ion Interactions and Their Application to CdII and Hydrogen Sulfide Imaging in Living Cells

Non‐coordinative interactions between a metal ion and the aromatic ring of a fluorophore can act as a versatile sensing mechanism for the detection of metal ions with a large emission change of fluorophores. We report the design of fluorescent probes based on arene–metal‐ion interactions and their biological applications. This study found that various probes having different fluorophores and metal binding units displayed significant emission redshift upon complexation with metal ions, such as Ag^I, Cd^II, Hg^II, and Pb^II. X‐ray crystallography of the complexes confirmed that the metal ions were held in close proximity to the fluorophore to form an arene–metal‐ion interaction. Electronic structure calculations based on TDDFT offered a theoretical basis for the sensing mechanism, thus showing that metal ions electrostatically modulate the energy levels of the molecular orbitals of the fluorophore. A fluorescent probe was successfully applied to the ratiometric detection of the uptake of Cd^II ions and hydrogen sulfide (H₂S) in living cells. These results highlight the utility of interactions between arene groups and metal ions in biological analyses.     

Silver(III)⋅⋅⋅Silver(III) Interactions that Stabilize the syn Form in a Porphyrin Dimer Upon Oxidation

The interaction between two Ag^II porphyrins, connected covalently through a highly flexible ethane bridge, in a metalloporphyrin dimer has been investigated upon stepwise oxidation. X-ray structure determination of one and two-electron oxidized complexes has clearly revealed only metal-centered oxidation that results in short Ag−N (porphyrin) distance with large distortion in the porphyrin macrocycle. The 2e-oxidized complex exhibits significant metallophilic interaction in the form of a close Ag^III⋅⋅⋅Ag^III contact that brings two porphyrin rings more cofacial with syn-conformation, which would otherwise stabilize in an anti-form. The interaction also leads to an intense emission peak at 546 nm at 77 K in the photoluminescence study.     

Complex formation equilibria between mercury(II) complexes of pencillamine and glutathione and transition metal ions

Summary The interaction between Hg^II complexes of the thiols pencillamine and glutathione and some transition metal ions has been investigated potentiometrically. Mixedmetal complexes of the forms Hg(ps)₂M and Hg(gs)₂M (where M=Co or Ni), were detected. The complexes formed between glutathione disulphide with bivalent metal ions Zn^II, Ni^II, Co^II and Cd^II have also been studied. Zn^II and Ni^II form the complexes M(gssg)H and M(gssg), while Co^II and Cd^II form only the fully deprotonated complex M(gssg). The formation constants of the complexes were determined at 25°C and I=0.1 M (NaNO₃). The concentration distribution of various complex species as a function of pH was evaluated.     

Interaction of Silver(II) and Gold(III) meso-Tetraphenylporphine Complexes with Concentrated Sulfuric Acid

The reaction of meso-tetraphenylporphine (H₂TPP) with Ag(OAc) or KAuCl₄in boiling acetic acid affords Ag^IITPP and (Cl)Au^IIITPP complexes. The complexes are purified by column chromatography and identified by thin layer chromatography and IR and electronic absorption spectroscopy. The transfer of a proton to the porphyrin macrocycle and dissociation of the complexes via the metal–nitrogen bonds in concentrated H₂SO₄at different temperatures and H₂SO₄concentrations are studied by spectrophotometric and kinetic methods. The formation of the stable ion-molecular H-associate of the metalloporphyrin with a doubly-charged metal cation is found for the first time for silver(II) tetraphenylporphine. Gold(III) tetraphenylporphine exists in a sulfuric acid solution in the monomolecular form. The numeric values of true rates and activation parameters of the complex dissociation are determined. The stability, state in solution, and mechanism of dissociation of the silver(II) and gold(III) tetraphenylporphine complexes are determined by the metal electronic configuration of the complex cation and, especially, by the contribution of the component to the donor–acceptor M–N interaction.     

Sorption of silver ions by Chelex 100 chelating resin

Sorption of Ag⁺, Ag(NH₃) _n ⁺ , and anionic complexes of silver with chloride and thiocyanate ions by Chelex 100, a chelating resin, were investigated systematically. The results are utilized to interpret the seemingly contradictory data available in the literature     

Surface enhanced Raman spectroscopic studies on 1H-1,2,4-triazole adsorbed on silver colloidal nanoparticles

1H-1,2,4-triazole is a very effective corrosion inhibitor for copper. The adsorption of this compound on silver colloidal nanoparticles has been studied by means of surface enhanced Raman scattering (SERS). SERS data are interpreted with the help of DFT calculations of models of the surface complex formed by 1H-1,2,4-triazole on the silver colloidal nanoparticles surface. It was found that this compound is adsorbed on metal surface in its anionic form and that it interacts with silver through the N₁ and N₂ atoms. The molecular plane assumes a tilted orientation with respect to the silver surface.     

Synthesis and antibacterial activity of metal complexes of cefazolin

Cefazolin (Hcefaz) interacts with transition metal(II) ions to give [M(cefaz)Cl] complexes (M = Mn^II, Co^II, Ni^II, Cu^II, Zn^II, Pd^II) and [Ag₂(cefaz)₂Cl₂] which were characterized by physicochemical and spectroscopic methods. Their i.r. and the ¹H-n.m.r. spectra suggest that cefazolin behaves as a monoanionic tetradentate ligand. The complexes have been screened for antibacterial activity and the results are compared with the activity of cefazolin.     

Self‐Assembly of Spheroidal Structures: The Coordination Chemistry of Pentacyanocyclopentadienide

Modelling studies show that the anion pentacyanocyclopentadienide, 1 , can complex linearly coordinating cations such as silver(I) and copper(I) to form a spheroidal complex [M₃₀( 1 )₁₂]¹⁸⁺ with minimum distortion. The anion 1 complexes transition metal ions to give species which appear to be polymers in the solid state. The structure of Ag( 1 ) was determined by powder diffraction and shows a one‐dimensional polymeric structure with three coordinate Ag^I and two CN functions of the ligand 1 non‐coordinated. No evidence for the formation of the spheroidal complex was found.     

Kinetics of the mediatory reduction ofgem-dichlorocyclopropanes

The effect of the nature of organic electron transfer agents and of Pt^II, Pd^II, Rh^II, Co^II, Ni^II, Cu^II, Cr^III, Mn^II, Ti^III, V^III, Zn^II, and Ag^I metal ions on the kinetics of the homogeneous reduction ofgem-dichlorocyclopropanes has been studied. Pt^II, Pd^II, Rh^III, Co^II, and Ni^II ions accelerate this process, V^III and Ag^I ions exert practically no effect on the reduction rate, and the rest of the metal ions exhibit inhibitor properties.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1407–1410, August, 1993.     

Copper(II) and zinc(II) chemistry of a new hexadentate cyclam-based bis-di-2-pyridylmethanamine ligand

In the endo-conformation of the substituted cyclam derivative L, with two trans-disposed di-2-pyridylmethanamine (dipa) coordination sites (endo: both dipa subunits on the same face of cyclam), the bis-dipa-substituted cyclam platform may form hexacoordinate mononuclear complexes with the two dipa subunits coordinated to one metal ion or dinuclear complexes, when the two dipa subunits are coordinated to two metal ions (oligonuclear linear chain complexes with exo-configured ligands L and metal ions coordinated to the cyclam unit have not been observed so far). Here, the structures, relative stabilities and spectroscopic properties of the mononuclear complexes of Cu^II and Zn^II, which are formed in preference to other structural possibilities, are discussed, and the preference for their formation is also evaluated.     

Displacement-dispersive liquid-liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of trace silver in environmental and geological samples

A novel displacement-dispersive liquid-liquid microextraction method was developed for the selective determination of trace silver in complicated samples by graphite furnace atomic absorption spectrometry. This method involves two steps of dispersive liquid-liquid microextraction (DLLME). Firstly, copper ion reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex and extracted with DLLME procedure using carbon tetrachloride (extraction solvent) and methanol (dispersive solvent); then, the sedimented phase was dispersed into the sample solution containing silver ion with methanol and another DLLME procedure was carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag⁺ can displace Cu²⁺ from the pre-extracted Cu-DDTC and thus the preconcentration of Ag⁺ was achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu²⁺ from Cu-DDTC complex. The tolerance limits for the co-existing ions were increased by a long way compared with conventional DLLME. Under the optimal conditions, the limit of detection was 20 ng L⁻¹ (3σ) for silver with a sample volume of 5.0 mL, and an enhancement factor of 72 was achieved. The proposed method was successfully applied to determine of trace silver in some environmental and geological samples with satisfactory results.     

The selectivity of active carbons modified by fullerenes with respect to mixtures of metal cations in aqueous solutions

The separating ability of active carbons and active carbons modified with fullerenes with respect to mixtures of nonferrous metal cations was studied. The selectivity series for the extraction of cations from aqueous solutions was Ag⁺ > Cu²⁺ > Pb²⁺. The selectivity of adsorption by active carbon modified with fullerenes was higher than that characteristic of the initial adsorbent, especially for the extraction of silver ions from a mixture of silver and copper cations.