Electrochemical capacitances of well-defined carbon surfaces

Reported is the capacitive behavior of homogeneous and well-defined surfaces of pristine carbon nanofibers (CNFs) and surface-modified CNFs. The capacitances of the well-defined CNFs were measured with cyclic voltammetry to correlate the surface structure with capacitance. Among the studied pristine CNFs, the edge surfaces of platelet CNFs (PCNF) and herringbone CNFs were more effective in capacitive charging than the basal plane surface of tubular CNF by a factor of 3-5. Graphitization of PCNF (GPCNF) changed the edge surface of PCNF into a domelike basal plane surface, and the corresponding capacitances decreased from 12.5 to 3.2 F/g. A chemical oxidation of the GPCNF, however, recovered a clear edge surface by removal of the curved basal planes to increase the capacitance to 5.6 F/g. The difference in the contribution of the edge surface and basal-plane surface to the capacitance of CNF was discussed in terms of the anisotropic conductivity of graphitic materials.     

Electrochemical and electrochromic properties of rare-earth metal diphthalocyanine complexes

The electrochemical and spectroelectrochemical properties of several new rare-earth metal diphthalocyanine complexes with different substituents containing both electron-withdrawing and -donating substituents in the phthalocyanine rings were studied. The influence of structural modification of the phthalocyanine complexes (viz., the nature of the central metal atom and substituents in the phthalocyanine rings and the number of phthalocyanine rings in the complexes) on the total number of redox transitions, their potentials, and spectral characteristics of anionic and cationic forms of the complexes was examined. The potentials of the first anodic and cathodic redox transitions of the diphthalocyanine complexes are in a good linear correlation with the ionic radii of lanthanides. The potentials of the observed redox transitions of the complexes under study correlate well with the sums of Hammett constants for the substituents and the minimum molecular electrostatic potential of the benzene rings in the phthalocyanine moiety, which serves as a measure of electron perturbations introduced by the substituents. The revealed regularities allow the prediction of the redox properties and structure of rare-earth element diphthalocyanine complexes, which are redox-active in a specified potential range.     

Synthesis and spectral studies of new N2S2 and N2O2 Mannich base ligands and their metal complexes

New Mannich bases bis(thiosemicarbazide methyl) phosphinic acid H₃L¹ and bis(1-phenylsemicarbazide methyl) phosphinic acid H₃L² were synthesized from condensation of phosphinic acid and formaldehyde with thiosemicarbazide and 1-phenylsemicarbazide, respectively. Monomeric complexes of these ligands, of general formula K₂[Cr^III(L ⁿ )Cl₂], K₃[Fe^II(L¹)Cl₂], K₃[Mn^II(L²)Cl₂], and K[M(L ⁿ )] (M = Co(II), Ni(II), Cu(II), Zn(II) or Cd(II); n = 1, 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II), and Fe(II) complexes, square planar for Co(II), Ni(II), and Cu(II) complexes and tetrahedral for the Zn(II) and Cd(II) complexes. Complex formation via molar ratio in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M : L) as (1 : 1).     

Electrochemical behaviour of a series ofN,N′-1,2-Phenylenebis(salicylideneimin)ato transition metal complexes

Summary The electrochemistry of a series of nickel(II), copper(II), cobalt(II), manganese(II) and oxovanadium(IV) complexes with theN,N-1,2-phenylenebis(salicylideneimin)ate ligand has been studied in dimethyl sulfoxide solution. Kinetic and thermodynamic aspects of the electron-transfer processes are discussed, also with respect to those of the correspondingN,N-ethylenebis(salicylideneimin)ate and bis(salicylideneiminate-3-propyl)amine derivatives     

A N,N′-diacetate benzodioxotetraazamacrocycle and its transition metal complexes

Reaction of 2,9-dioxo-1,4,7,10-tetraazabicyclo[1.10.1]hexadeca-1(11),13,15-triene-4,7-diacetic acid (H₂L1) with CuCl₂ · 2H₂O in ethanol at pH 6 led to the monomeric benzodioxochlorocomplex [Cu(L′1)Cl] (1) (HL′1 = monoethylesther of H₂L1). X-ray structural analysis has shown that in complex 1 the Cu is five-coordinated by two nitrogen and two oxygen atoms of the macrocycle and by a chloride, displaying a square pyramidal coordination geometry. One of the acetate arms does not coordinate to the Cu and has suffered an in situ ethanolic esterification reaction. The protonation constants of H₂L1 and the stability constants of its complexes with Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were determined by potentiometric methods and in some cases by ¹H NMR spectroscopy. The stability constants of the complexes follow the trend [Ni(H₋₁L1)]⁻ > [Cu(H₋₁L1)]⁻ ≫ [Pb(H₋₁L1)]⁻ > [Zn(H₋₁L1)]⁻ > [Cd(H₋₁L1)]⁻, probably due to steric requirements. Spectroscopic measurements (absorption and EPR) at different pH values have shown the effect of the pH on the coordination sphere of the Cu complexes.     

Transition metal dinitrogen complexes supported by a versatile monoanionic [N2P2] ligand

By adjusting to the steric and electronic requirements of differing metal centers, the new multidentate monoanionic ligand [N(2)P(2)] has demonstrated a unique ability to stabilize a range of transition metal-dinitrogen complexes in a variety of oxidation states and coordination geometries.     

Electrochemical synthesis of benzoylglycine and ethylphthaloyl-glycine complexes of transition metal ions

Summary The direct electrochemical oxidation of metallic iron, cobalt, nickel and copper in Me₂CO solution of benzoylglycine and/or ethylphthaloylglycine gave products with high yields. For each of the complexes, the electrochemical efficiency is commensurate with the metals being divalent. Conventional physical and chemical studies were used to characterize the isolated complexes and octahedral geometry was suggested for them on the basis of magnetic and electronic spectral studies. The i.r. spectra show that the ligands coordinate in a bidentate fashion; the carboxylate ion is monodentate. The molar conductances agree with the complexes being non-electrolytes.     

Synthesis and characterization of metal complexes of 3-( N -phenyl)-thiourea-pentanone-2

Copper and cobalt complexes derived from 3-(N-phenyl)-thiourea-pentanone-2 were characterized by elemental, XRD, FTIR, UV–Vis, SEM and ¹H NMR spectroanalytical studies. The X-ray diffraction studies indicate that 3-(N-phenyl)-thiourea-pentanone-2 and complexes with copper and cobalt are crystalline in nature with simple cubic lattice structure. IR spectroscopic data were used to assign characteristic vibrational frequencies of groups present in these compounds. Scanning electron micrograms were used to assign morphology and particle size.     

Electrochemical potential tuned solar water splitting

As a fundamental step towards a clean, renewable source of H2, a novel physical chemical process within molten NaOH in which an external single, small bad gap photosentizer, such as Si, can drive the energetics of water cleavage is demonstrated, and is accomplished by tuning (decreasing) the water splitting electrochemical potential, EH2O, rather than tuning the photosensitizer band gap; this diminished potential is due to (i) a thermodynamic temperature induced decrease of EH2O with increasing temperature, and (ii) a partial recombination of the cleavage products.     

Electrochemical and theoretical study of the redox properties of transition metal complexes with [Pt2S2] cores

The oxidation processes undergone by the [Pt2(mu-S)2] core in [Pt2(P[intersection]P)2(mu-S)2](P[intersection]P = Ph2P(CH2)nPPh2, n= 2,3) complexes have been analysed on the basis of electrochemical measurements. The experimental results are indicative of two consecutive monoelectronic oxidations after which the [Pt2(mu-S)2] core evolves into [Pt2(mu-S2)]2+, containing a bridging disulfide ligand. However, the instability of the monoxidised [Pt2(P[intersection]P)2(mu-S)2]+ species formed initially, which converts into [Pt3(P[intersection]P)3(mu-S)2]2+, hampered the synthesis and characterisation of the mono and dioxidised species. These drawbacks have been surpassed by means of DFT calculations which have also allowed the elucidation of the structural features of the species obtained from the oxidation of [Pt2(P[intersection]P)2(mu-S)2] compounds. The calculated redox potentials corresponding to the oxidation processes are consistent with the experimental data obtained. In addition, calculations on the thermodynamics of possible processes following the degradation of [Pt2(P[intersection]P)2(mu-S)2]+ are fully consistent with the concomitant formation of monometallic [Pt(P[intersection]P)S2)] and trimetallic [Pt3(P[intersection]P)3(mu-S)2]2+ compounds. Extension of the theoretical study on the [Pt2Te2] core and comparisons with the results obtained for [Pt2S2] have given a more general picture of the behaviour of [Pt2X2](X = chalcogenide) cores subject to oxidation processes.     

N2 activation by iron-sulfur complexes

Inspired by the determination of the structure of the nitrogenase enzyme cofactor by Rees et al., the binding of an N₂ molecule to some model iron-sulfur compounds was investigated usingab initio calculations. Side-on and end-on coordination to one two and four iron centers were investigated. In most cases, the N₂ is loosely bound and retains its internal triple bond, but a few examples are found where the N₂ is “activated” and has a longer N-N bond length.     

Transition metal complexes of 13- and 14-membered N2O2 macrocycles: synthesis and characterization

Two novel series of 13- and 14-membered diazadioxamacrocyclic complexes [ML¹Cl₂] and [ML²Cl₂] (M=Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) have been synthesized via the condensation reaction of o-aminophenol and 1,2-dibromoethane with a dialdehyde or a diketone in the presence of transition metal ions as templates in ethanol. The mode of bonding and overall geometry of the complexes have been inferred through IR, ¹H NMR, EPR, and electronic spectral studies, conductivity, and magnetic moment measurements. An octahedral geometry is proposed for all the complexes.     

Electrochemical CO2 reduction with earth-abundant metal catalysts

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Design of well-defined shell–core covalent organic frameworks/metal sulfide as an efficient Z-scheme heterojunction for photocatalytic water splitting

Development of a covalent–organic framework (COF)-based Z-scheme heterostructure is a promising strategy for solar energy driven water splitting, but the construction of a COF-based Z-scheme heterostructure with well-defined architecture, large contact area and intimate contact interfaces is scarce. Herein, we fabricated a direct Z-scheme heterostructure COF–metal sulfide hybrid (T-COF@CdS) with shell–core architecture by self-polymerization of 1,3,5-benzenetricarboxaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in situ on CdS. The formed C–S chemical bonding between T-COF and CdS could provide a very tight and stable interface. Owing to the properly staggered band alignment, strong interfacial interaction and large interfacial contact area between T-COF and CdS, a Z-scheme route for charge separation and transfer is realized, resulting in electron accumulation in CdS for H₂O reduction. The obtained Z-scheme heterostructure T-COF@CdS-3 exhibits a high apparent quantum efficiency of 37.8% under 365 nm monochromatic light irradiation, and long-term stability arising from shell–core structures in which the T-COF shell protects the catalytic centers of CdS against deactivation, as well as acts as oxidation sites to avoid the photocorrosion of CdS. This work provides a strategy for the construction of a shell–core direct Z-scheme heterostructure photocatalyst for water splitting with high performance.

A stable Z-scheme with well-defined architecture by in situ growth of COFs on CdS for photocatalytic water splitting is constructed. The T-COF shell can protect the catalytic center of CdS from deactivation and photocorrosion.     

Stability constants of 2-mercaptohistamine metal complexes

Summary Stability constants of 2-mercaptohistamine (2-MH) with a number of transition metal ions were determined by a potentiometric titration method and the coordination mode of (2-MH) metal complexes were thereby characterized. With Mn^II, Fe^ll, Co^II, and Ni^II, coordination occurred through both the imidazole-nitrogen and amino groups, while with Zn^II, Cd^II, Pb^II, and Hg^II, both thiolate and amino groups, contribute to the coordination. in the 2-MH copper complex, polymer formation is suggested on the basis of visible absorption and e.p.r. spectra.     

Electrochemical synthesis and properties of δ-fluoroacyl and δ-perfluoroalkyl transition metal complexes

The electrochemical synthesis of δ-fluoroacyl complexes [M]-δ-COR_f(M=C₅H₅(CO)₃W or (CO)₅Mn; R_f=CF₃ or C₄F₉) was performed according to two procedures: (1) the preliminary electrochemical synthesis of [M]⁻ from [M]₂ followed by reaction with a fluorine-containing compound and (2) the electrochemical synthesis of [M]⁻ in the presence of a fluorine-containing compound. Trifluoroacetic anhydride was demonstrated to be the best acylating agent in these reactions. The electrochemical properties of the resulting complexes were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 373–375, February, 2000.     

Transition metal complexes derived from 2-mercaptobenzothiazole

Summary Complexes of ethyl S-(2-benzothiazolyl)mercaptoacetate (e.s.m.) with Mn^II, Co^II, Ni^II, Cu^II and Zn^II have been prepared and their structures assigned on the basis of analytical, spectral (i.r., electronic, e.p.r. and XPS), magnetic data, molar conductance and t.g.-d.t.a. methods.     

Transition metal complexes of 2-formylthiophene S-methyldithiocarbazate

Transition metal complexes of 2-formylthiophene S-methyldithiocarbazate have been synthesized and characterized. Analytical data show that the complexes are of the type [ML3], where M = Fe3+, and [ML2], where M=Ni2+, Cu2+ or Zn2+. The i.r. spectra suggest coordination to the metal through the azomethine nitrogen and thiolate sulfur. The magnetic and spectroscopic data indicate a square planar geometry for the complexes, except for the Fe3+ complex, which is octahedral. The e.s.r. parameters are indicative of a square planar N2S2 system for the Cu2+ complex.     

The thermal decomposition of group iib metal halide complexes: Part II. N,N,N′,N′-tetramethylethylenediamine and 1,2-diphenylphosphinoethane complexes

The preparation and pyrolysis procedures for 1/1 complexes MX₂·L (where M = Group IIB metal, XCl, Br or I and LN,N,N′,N′-tetramethylethylene-diamine (TMED) or 1,2-diphenylphosphinoethane (DPE))is reported. The decomposition of the cadmium chloride and bromide TMED complexes afford intermediates of varying stability. From far infrared spectrophotometry we conclude that the chloride intermediate is a four coordinate polymeric complex. Differential scanning calorimetry has been used to determine selected latent heats of fusion.