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1Author    S. Volkov, N. Tumanova, S. Kothetova, N. BuryakRequires cookie*
 Title    The Polysurface Mechanism of Ta and Ti Anodic Dissolution in Low-Temperature Carbamide-NH4CL Melt  
 Abstract    In this work the peculiarities o f the electrochemical dissolution of tantalum and titanium in carbamide containing low temperature melts were studied. 
  Reference    Z. Naturforsch. 56a, 761—763 (2001); received August 8 2001 
  Published    2001 
  Keywords    Carbamide, Tantalum, Titanium, Electrochemistry, Passivation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0761.pdf 
 Identifier    ZNA-2001-56a-0761 
 Volume    56 
2Author    Ute Honrath, Heimich VahrenkampRequires cookie*
 Title    zur Natur einfach arsenverbrückter Metall-Metall-Bindungen Electrochemical and Electron Spectroscopic Measurements on the Nature of Singly Arsenic Bridged Metal-Metal Bonds  
 Abstract    For a series of singly arsenic bridged dinuclear metal carbonyl complexes with metal-metal bonds electronic spectra and dc-voltammograms in 1,2-dichloroethane were recorded. There is a reasonable correlation between the a ->cr* transitions and the first reduction potentials which can both be taken as measures of the relative strength of the metal-metal bonds. The a ^ a* excitation energy and the negative reduction potential increase (a) with increasing atomic weight of the connected metal atoms, (b) with in-creasing number of CO groups present, (c) with decreasing intramolecular steric hindrance. Steric and electronic factors cannot be cleanly separated. There seems to be no correlation with metal-metal bond lengths. Terminal phosphine ligands decrease all redox potentials but hardly change the electronic absorptions. Die Stärke von Metall-Metall-Bindungen ist sehr schwierig zu bestimmen. Da thermochemische Methoden nur in besonders einfachen Fällen heran-gezogen werden können [1], bedient man sich meist indirekter Messungen [2]. Von den dazu verwend-baren Verfahren haben in jüngster Zeit zwei an Be-deutung gewonnen. Dies ist einmal die Elektro-chemie [3], deren Bedeutung darauf beruht, daß in mehrkernigen metallorganischen Komplexen die HOMOs und LUMOs die Metall-Metall-Wechsel-wirkungen betreffen [2, 4, 5]. Das andere ist die Elektronenspektroskopie, seit entdeckt wurde, daß mit der Metall-Metall-Bindung ein <x->cx*-Übergang im nahen UV verknüpft ist [6], und daß dessen Energie sich mit der Metall-Metall-Bindungsstärke verknüpfen läßt [7]. Wir haben eine Serie einfach phosphor-bzw. arsen-verbrückter Metallcarbonyl-Zweikernkomplexe ge-wonnen, die sich vorteilhaft auf die Eigenschaften von Metall-Metall-Bindungen untersuchen lassen. Denn die Brückenfunktion bewirkt, daß nach einer Spaltung der Metall-Metall-Bindung die beiden Organometall-Einheiten zusammen in einem Kom-plex verbleiben. Nach einer ausführlichen chemi-schen [8] und kristallographischen [9] Bearbeitung dieser Verbindungen erschien es daher auch lohnend, sie weiter physikalisch zu charakterisieren. Wir * Sonderdruckanforderungen an Prof. Dr. H. Vahren-kamp. 0340-5087/79/0900-1190/5 01.00/0 wählten dazu die elektrochemischen und elektronen-spektroskopischen Messungen, einerseits wegen ihrer erwähnten Vorteile, andererseits weil wir bei einer Untersuchung sehr einfacher Zweikernkomplexe [10] die gute Vergleichbarkeit der jeweiligen Meßergeb-nisse festgestellt hatten. Messungen Es wurden von den unsubstituierten arsenver-brückten Metallcarbonyl-Zweikernkomplexen mit Metall-Metall-Bindungen die bekannten Vertreter 1-5 und dazu vier ausgewählte phosphinsubstitu-ierte Derivate 6 vermessen. Die elektrochemischen Messungen geschahen mit Platin-Scheibenelektroden und Ag/AgCl/Cl --Bezugs-elektrode. Als Lösungsmittel diente 1.2-Dichlor-ethan, das die gleichen Vorzüge hat wie Methylen-Me2 As / \ (C0)5Cr M 1 Me2 As / \ (C0)< Fe M Me2 As /\ ICOLCW M Me2 As / \ Cp(C0)Co M Me2 As / \ Cp(C0)2Mn M Me2 As / \ L-(CO),Fe Mn(C0),-L l-5:M = Cr(CO)2Cp: a Mo(CO)2Cp: b W(CO)2Cp: c Mn(CO)4 Re(CO)4 Co(CO)3 6: L/L'=CO/PMe3: a PMe3/CO: b 
  Reference    Z. Naturforsch. 34b, 1190—1194 (1979); eingegangen am 5. Juni 1979 
  Published    1979 
  Keywords    Electrochemistry, Electron Spectroscopy, Metal-Metal Bonds 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-1190.pdf 
 Identifier    ZNB-1979-34b-1190 
 Volume    34 
3Author    Michael Neumann-Spallart, K. KalyanasundaramRequires cookie*
 Title    On the One and Two-Electron Oxidations of Water-Soluble Zinc Porphyrins in Aqueous Media  
 Abstract    The one and two-electron oxidations of water soluble ionic zinc porphyrins (Zinctetra-methylpyridylporphyrin, ZnTMPyP, Zinc-tetra-p-sulfonato-phenyl-porphyrin, ZnTPPS, and Zinc-tetra-p-carboxy-phenylporphyrin, ZnTPPC) leading to the porphyrin /7-cations and /7-dications have been investigated in water by electrochemical (cyclic voltammetry and controlled potential electrolysis) and chemical methods. The half-wave potentials for the oxidation are shown to be markedly dependent on the charge on the /?-substituents. While the one-electron oxidations for all these porphyrins are reversible, the dication formation leads to labile isoporphyrins as intermediates. 
  Reference    Z. Naturforsch. 36b, 596—600 (1981); received December 1 1980/February 19 1981 
  Published    1981 
  Keywords    Redox Potentials, yr-Cation Radicals, Electrochemistry 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0596.pdf 
 Identifier    ZNB-1981-36b-0596 
 Volume    36 
4Author    Emerich Eichhorn, Anton Rieker, Bernd Speiser, Jürgen Sieglen, Joachim SträhleRequires cookie*
 Title    Electrochemistry of Oxygenation Catalysts, Part 2 + Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N-Bis(salicylidene)ethylenediaminatocobalt(III) Chloride  
 Abstract    N,N'-Bis(salicylidene)ethylenediaminatocobalt(III) hydroxide is treated with chloroform in methanol to yield the corresponding chloride in pure, crystalline form. Results of the crystal structure determination compare well with those in earlier reports of dimeric [Co(salen)Cl]2 units and incorporated CHC13 molecules. Electrochemical experiments in D M F and pyridine show that the chloride fully dissociates in these donor solvents. Thus, the quasireversible one-electron reduction to Co(salen) is observed in cyclic voltammograms. 
  Reference    Z. Naturforsch. 48b, 418—424 (1993) 
  Published    1993 
  Keywords    Oxygenation Catalyst, Cobalt Schiff-Base Complex, Crystal Structure, Electrochemistry 
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 TEI-XML for    default:Reihe_B/48/ZNB-1993-48b-0418.pdf 
 Identifier    ZNB-1993-48b-0418 
 Volume    48 
5Author    Conny Vogler, Wolfgang Kaim, H.-D HausenRequires cookie*
 Title    Zweikernige Bisphosphankupfer(I)-Komplexe mit dem 2,2 -Bipyrimidin-Brückenliganden: Strukturelle Analogie zu "Blauen" Kupferzentren und Reduktion zu paramagnetischen Spezies Dinuclear Bis(phosphane)copper(I) Complexes with 2,2'-Bipyrimidine as Bridging Ligand: Structural Analogy to " Blue" Copper Centers and Reduction to Paramagnetic Species  
 Abstract    Dinuclear complexes [(PR3)2C u(//:/74-bpym)Cu(PR3)2](BF4)2 with the bis-chelating bridging ligand 2,2'-bipyrimidine (bpym) and various m onodentate and bidentate phosphanes were synthesized via a four com ponent "self assembly" reaction. The reversible electrochemical reduction to m onocationic radical complexes was studied by cyclic voltammetry and electron spin resonance (ESR). Highly resolved ESR spectra revealed the presence o f the bpym anion radical ligand via resolved hyperfine coupling with 'H, 14N , 31P, 63Cu and 65Cu nuclei. The variation o f phosphane ligands was accompanied by significant changes o f electrochemical potentials which were rationalized considering electronic and structural effects. The configura­ tional flexibility o f Cu(I) in this environment is evident from the X-ray crystal structure ana­ lysis o f [(PPh3)2C u(//:^4-bpym)Cu(PPh3)2](BF4)2 H2O C H 3OH for which the coordination at the metal can be described as 3 + 1 (N N'P + P'), qualitatively similar to the (NN'S + S') arrange­ ment around the type 1 Cu centers o f "blue" copper proteins. Intramolecular cooperative n donor/;: acceptor/^ donor "Sandwich" interactions provide parts o f the driving force for this highly distorted coordination geometry which illustrates the proclivity o f Cu(I) towards such an "entatic state" arrangement. 
  Reference    Z. Naturforsch. 48b, 1470—1480 (1993); eingegangen am 5. Mai 1993 
  Published    1993 
  Keywords    Copper Complexes, Structure, Electrochemistry, ESR Spectra, Phosphane Ligands 
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 TEI-XML for    default:Reihe_B/48/ZNB-1993-48b-1470.pdf 
 Identifier    ZNB-1993-48b-1470 
 Volume    48 
6Author    Oliver Heilmann, Hans-Dieter Hausen, Wolfgang KaimRequires cookie*
 Title      
 Abstract    The crystal structure determination of the new rhodium(III)-complex [(DM L)(C5Me5)ClRh](PF6). DML = 1,3-dimethyllumazine, reveals 0 4,N5 coordination of the metal to DML with not very different bond lengths of 213.0(2) pm (R h -N) and 219.2(2) pm (R h -O). This result stands in contrast to the previously reported structure of a cationic dihydrobiopterin bound to [Mo(0)C13] which exhibited a very unsymmetrical chelate ar­ rangement. Chemical and electrochemical two-electron reduction of the Rh(III) complex led to a very labile Rh(I) species (DM L)(C5Me5)Rh which is distinguished by an intense charge transfer band in the visible. The results confirm the characterization of DML as a weak o donor In acceptor ligand with a rather low-lying tc* orbital. 
  Reference    Z. Naturforsch. 49b, 1554—1560 (1994); received July 8 1994 
  Published    1994 
  Keywords    Crystal Structure, Pteridine Heterocycles, Rhodium, Electrochemistry, Coordination 
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 TEI-XML for    default:Reihe_B/49/ZNB-1994-49b-1554.pdf 
 Identifier    ZNB-1994-49b-1554 
 Volume    49 
7Author    Wolfgang Kaim, Jörg FeesRequires cookie*
 Title    The New Tetrafunctional i t Acceptor Ligand 3,6-Bis(2'-pyrimidyl)-l,2,4,5-tetrazine (bmtz): Diruthenium Complexes of bmtz and of its 1,4-Dihydro Form  
 Abstract    Synthesis, physical properties and the coordination with two [Ru(bpy)2]2+ complex frag­ ments are described for 3,6-bis(2'-pyrimidyl)-l,2,4,5-tetrazine (bmtz), the first compact ligand which offers four equivalent a-diimine chelate sites. Spectroelectrochemistry of intensely blue {(a-bmtz)[Ru(bpy)2]2}"+, n = 4, reveals a very facile reduction (n -3) at -0 .4 0 V vs. FeCp2+/o and a metal oxidation (n = 5) at +1.18 V to a diruthenium (II/III) mixed-valent form which exhibits an intervalence transfer absorption at 1490 nm. The corresponding complex {(M-H2bm tz)[Ru(bpy)2]2}4+ with the 1,4-dihydro form H 2bmtz of the tetrafunctional ligand is oxidized in two steps at 0.58 and 1.07 V vs. FeCp2+/°. 
  Reference    (Z. Naturforsch. 50b, 123—127 [1995]; received August 26 1994) 
  Published    1995 
  Keywords    Heterocycles, Complex Ligands, Ruthenium Compounds, Electrochemistry, Mixed Valency 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-0123.pdf 
 Identifier    ZNB-1995-50b-0123 
 Volume    50 
8Author    JohannW. Buchler, Wolfgang Kokisch, PaulD. Smith, Bernhard TonnRequires cookie*
 Title    Metallkomplexe mit Tetrapyrrol-Liganden, XIX [1] Synthese und elektrochemische Charakterisierung der Kohlenmonosulfid-Metalloctaethylporphyrine mit Eisen(II) oder Osmium(II) im Zentrum. Ein Beitrag zur "Bathochromie-Regel"  
 Abstract    The preparation and spectroscopic characterization of thiocarbonyl metalloporphyrins M(OEP)CS(L') (e.g. 2e: M = Fe, L' = Py, le: M = Os, L' = Py** are described. Especially noteworthy is the existence of a pentacoordinate, diamagnetic, air-stable heme Fe(OEP)CS (2f: M = Fe, no L'). A linear correlation of the a-band frequencies (expressed as Va) in the optical spectrum and the metal(II/IH) redox potentials (E1/2) taken from cyclic voltam-metry experiments suggests (Abb. 3) that in complexes of the type M(OEP)LL' (1, 2) K is bathochromically shifted as the 7r-acceptor capacity of L increases ("Rule of Batho-chromism"). The strong 71-acceptor capacity of carbon monosulphide renders the attack of dioxygen to the thiocarbonyl heme unfavourable; O2 and CS seem to be comparable in their jr-acceptor strength. 
  Reference    Z. Naturforsch. 33b, 1371—1380 (1978); eingegangen am 29. Juni 1978 
  Published    1978 
  Keywords    Hemes, Osmium Porphyrins, Thiocarbonyl Complexes, Electrochemistry, Electronic Absorption Spectra 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-1371.pdf 
 Identifier    ZNB-1978-33b-1371 
 Volume    33 
9Author    Conny Vogler, Wolfgang KaimRequires cookie*
 Title    Einkernige Bis(triphenylphospin)kupfer(I)-Komplexe der Bidiazine M ononuclear Bis(triphenylphosphine)copper(I) Complexes of the Bidiazines  
 Abstract    The cationic d 10 metal complexes [(bdz)Cu(PPh3).J+ o f the n accepting bidiazine (bdz) che­ late ligands 3,3'-bipyridazine, 2,2'-bipyrazine, 2,2'-and 4,4'-bipyrimidine were synthesized and compared with the analogous com plex o f 2,2'-bipyridine. The long wavelength metal-to-ligand charge transfer (M LCT) absorption maxima and the reduction potentials indicate relatively little 7i* orbital stabilization by +Cu(PPh3)2. The particular d orbital splitting in a tetrahedral ligand field results in an additional contribution from J , to the energy difference between the first and second MLCT band. Only the most easily reduced com plexes o f 4,4'-bipyrimidine and 2,2'-bipyrazine yield neutral radical complexes ("Cu(0)") which were characterized by ESR spectroscopy. 
  Reference    Z. Naturforsch. 47b, 1057—1062 (1992); eingegangen am 11. März 1992 
  Published    1992 
  Keywords    Copper Complexes, Heterocyclic Ligands, Electrochemistry, Absorption Spectroscopy, ESR Spectra 
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 TEI-XML for    default:Reihe_B/47/ZNB-1992-47b-1057.pdf 
 Identifier    ZNB-1992-47b-1057 
 Volume    47 
10Author    Martin Köckerling, Gerald HenkelRequires cookie*
 Title    Nickelkomplexe  
 Abstract    mit Thioether-Chelatliganden: Elektrochemische Eigenschaften und Kristallstrukturen von [Ni(MeSCH2CH2SMe)2 (NCS)2], [Ni(EtSCH2CH2SEt)2(NCS)2] und [Ni(MeSCH2CH2SMe)2Br2] Nickel Complexes with Chelating Thioether Ligands: Electrochemical Properties and Crystal Structures of [Ni(MeSCH2CH2SMe)2(NCS)2], [Ni(EtSCH2CH,SEt)2(NCS)2] and [Ni(MeSCH2CH2SMe)2Br2] interest in nickel complexes with sulfur donor ligands as models for the active sites of nickel-containing hydrogenases has prompted us to investigate the structural and elec­ trochemical behaviour of nickel complexes with bifunctional thioether ligands. Crystals of [Ni(MeSCH,CH,SMe),(NCS),] (1) and [Ni(EtSCH2CH,SEt)2(NCS)2], (2) are triclinic, space group Pi, Z = 1, 1: a = 7.293(3) A, b = 7.567(3) A, c = 8.784(3) A, a = 72.81(3)°, ß = 78.41(3)°, 7 = 85.14(3)°; 2: a = 8.611(1) A, b = 8.101(1) Ä, c = 9.163(1) ßrbÄ, a = 66.54(1)°, ß = 76.19(1)°, 7 = 67.88(1)ßrb°. [Ni(MeSCH2CH2SMe^Br2] (3) crystallizes in the mono­ clinic space group P2,/n, a = 6.757(2) A, b = 7.881(2) A, c = 14.674(4) Ä, ß = 94.05(2)°, Z = 2. In crystals of 1, 2 and 3 mononuclear neutral complex molecules are observed which have pseudo-octahedral rran5-NiS4L2 coordination sites. The cyclovoltammograms of 1 and 3 in MeCN (Ag/AgCl/KCl, 3 mol/1) show only irreversible oxidation waves at +837 mV for 1 and +846 mV for 3, respectively, which are characteristic features of NCSe and Bre ions. In addition, a reduction wave at +393 mV is observed in 3. No redox response is found in the potential region between -700 and +100 mV which is used by the NiFe hydrogenase enzymes. 
  Reference    Z. Naturforsch. 51b, 178—186 (1996); eingegangen am 18. Juli 1995 
  Published    1996 
  Keywords    Nickel-Sulfur Complexes, Thioether Ligands, Crystal Structure, Electrochemistry, Bioinorganic Chemistry Current 
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 TEI-XML for    default:Reihe_B/51/ZNB-1996-51b-0178.pdf 
 Identifier    ZNB-1996-51b-0178 
 Volume    51