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  • Aryl-diselenadiazoles  (1)
  • Chromium(III) alkyls  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Metal-Metal Bonding in Paramagnetic Chromium(III) Complexes - An MO-Theoretical Case Study (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 631-643 
    Details
    ISSN: 0009-2940
    Keywords: Chromium(III) alkyls ; Paramagnetism ; Calculations, MO ; Metal - Metal bonding ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structures of the edge-sharing bioctahedral chromium(III) dimers {C5H5Cr(CH3)(μ1-Cl)}2 (2) and {Me5C5Cr(CH3)(μ1-CH3)}2 (4* (Cp* derivative), 4 (Cp derivative)), the trinuclear complex {C5H5Cr(μ1-Cl)}3(μ1-CH) (3), and the face-sharing bioctahedral chromium(III) compounds {Me5C5Cr}2(μ1-CH2) (6*, 6) [{Me5C5Cr}2(μ1-CH3)3]+ (7*, 7) have been studied MO-theoretically by the extended Hückel method. Proceeding from 2 over 3 to 4*, or from 6* to 7* a 3-center/4-electron chloride or methylene bridge is replaced by a 3-center/2-electron methyl group (a methylidyne cap in the trimer). The 3c/2e bridges give rise to an increased metal - metal overlap population due to Cr - Cr bonding within the core levels. In the series of 2 - 3 - 4* this is accompanied by a decrease in the Cr - Cr distance (329 - 284 - 260 pm) and effective magnetic moment, μeff (2.53 - 2.05 - 1.53 μB per Cr at room temp.). The latter can be ascribed to an increased splitting within the chromium d-block because of the shorter metal-metal separation. The bioctahedra 6* and 7* feature even shorter Cr - Cr contacts than 4* (239 and 242 pm), primarily because of their face-sharing geometry. However, their effective magnetic moments (per Cr) are 2.33 and 1.32 μB at room temp. The high magnetic moment for 6* can be understood from the orbital interactions in the frontier orbital metal d block: A face-sharing bioctahedron shows one σ, two δ, and no π type overlap, while an edge-sharing bioctahedron (4) has σ, π, and δ interaction between the metals. In the former this destabilizes only σ* sufficiently to prevent occupation by electrons (leaving five orbitals for six electrons, possible spin multiplicities S=0, 1, 2) while for the latter both σ* and π* are destabilized beyond electron occupation (leaving four MOs for six electrons, possible spin multiplicities S=0, 1). 4*, 6* and 7* are unusual examples of metal - metal bonded complexes containing octahedral CrIII ions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260313
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  • 2
    Electronic Resource
    Electronic Resource
    Electrochemical evidence for the existence of three stable oxidation states for heterocycles of the type X—C6H4—CN2E2 (E = S, Se). X-ray crystal structure of the dimer with X = Cl, E = S (1994)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 1589-1598 
    Details
    ISSN: 0044-2313
    Keywords: Aryl-dithiadiazoles ; Aryl-diselenadiazoles ; π radicals ; cyclic voltammetry ; crystal structure of (4-Cl—C6H4—CN2S)2 ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Elektrochemische Nachweise zur Existenz von drei stabilen Oxidationsstufen der Heterocyclen des Typs X—C6H4—CN2E2 (E = S, Se). Kristallstruktur des Dimeren mit X = Cl, E = SDie Darstellung und Isolierung von fünf Aryl-1,2,3,5-dithia- und -diselenadiazolylen wird mitgeteilt. Die Kristallstruktur des Dimeren von 4-Cl—C6H4—CN2S2 wird bestimmt: monoklin, Raumgruppe C2/c, Z = 8, a = 20,982(10), b = 10,058(3), c = 15,867(6) Å, β = 93,34(4)°, R = 0,066, Rw = 0,053 für 1 099 Parameter. Cyclovoltammetrische Messungen zeigen reversible Oxidation zu einem 6π-Kation für alle 10 Verbindungen in CH2Cl2 und CH3CN; reversible Reduktion zu einem 8π-Anion wird in CH2Cl2 für alle Verbindungen außer bei X = CF3, E = S beobachtet. Die Reduktionen sind in CH3CN nur quasi-reversibel bei E = Se. Der Oxidationsprozeß ist unabhängig vom Chalkogen; der Reduktionsprozeß ist um 0,2 V negativer für E = S gegenüber E = Se.
    Notes: The preparation and isolation in the solid state of five aryl 1,2,3,5-dithia- and diselenadiazolyls is reported. The structure of the dimer of 4-Cl—C6H4—CN2S2 in the solid state was obtained: monoclinic, C2/c with Z = 8, a = 20.982(10), b = 10.058(3), c = 15.867(6) Å, β = 93.34(4)°, R = 0.066, Rw = 0.053 for 1 099 data. Cyclic voltammetry shows reversible oxidation to a 6π cation for all 10 compounds in both CH2Cl2 and CH3CN; reversible reduction to an 8π anion is observed in CH2Cl2 for all except X = CF3, E = S. The reductions are only quasi-reversible in CH3CN for E = Se. The oxidation process is independent of chalcogen type; the reduction process is found to be about 0.2 V more negative for E = S vs E = Se.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19946200916
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    Paper (German National Licenses)
    Fulltext
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