Cis‐/Trans‐Isomerie bei Bis‐(trisalkoxy)‐hexavanadaten: cis‐Na2[V 6IVO7(OH)6{(OCH2)3CCH2OH}2] · 8 H2O, cis‐(CN3H6)3[VIVV 5VO13{(OCH2)3CCH2OH}2] · 4,5 H2O und trans‐(CN3H6)2[V 6VO13{(OCH2)3CCH2OH}2] · H2O

Die beschriebenen Trisalkoxy-polyoxovanadate mit verzerrter Lindqvist-Struktur, in der sechs der zwolf μ2-verbruckenden Sauerstoffatome formal durch die Sauerstoffatome von zwei koordinierten Pentaerythritolliganden ((HOCH2)3CCH2OH) ersetzt wurden, konnen auf einfache Weise im wasrigen Medium dargestellt werden. Durch UV/VIS-, IR- und ESR-Spektroskopie sowie durch magnetische Messungen, Cyclovoltammetrie und Rontgenstrukturanalyse wurden die „vollstandig reduzierte”, sechsfach protonierte Verbindung cis-Na2[VO7(OH)6{(OCH2)3CCH2OH}2] ·8 H2O (1), das gemischtvalente, ein lokalisiertes V(IV)-Zentrum enthaltende Derivat cis-(CN3H6)3[VIVVO13{(OCH2)3CCH2OH}2] · 4,5 H2O (2) sowie die „vollstandig oxidierte” Verbindung trans-(CN3H6)2[VO13{(OCH2)3CCH2OH}2] · H2O (3) charakterisiert. Da die organischen {(CH2)3CCH2OH}3+-Gruppen, formal betrachtet, die jeweils aus drei μ2-O-Atomen gebildeten Flachen der zentralen, angenahert oktaedrischen {V6O19}-Einheit uberdachen, konnen die Anionen der Bis-(trisalkoxy)-hexavandate sowohl in einer trans-Form als auch in einer stellungsisomeren cis-Form bezuglich einer aus vier Vanadiumatomen des {V6}-Oktaeders gebildeten „Basis”-Ebene auftreten. Die unterschiedliche Anordnung der Liganden hat einen signifikanten Einflus auf die Redoxpotentiale der Verbindungen. 1 : cis-Na2[VIO7(OH)6{(OCH2)3CCH2OH}2] · 8 H2O: Raumgruppe P1, a = 987,2(2) pm, b = 1 080,6(2) pm, c = 1 654,3(3) pm, α = 94,83(1)°, β = 98,73(2)°, γ = 116,05(1)°, V = 1,5443(5) nm3, Z = 2, R = 0,067 fur 5 913 unabhangige Reflexe [F > 4σ(F)]. 2 : cis-(CN3H6)3[VIVVO13{(OCH2)3CCH2OH}2] · 4,5 H2O: Raumgruppe Pbca, a = 1 569,5(3) pm, b = 1 652,3(3) pm, c = 2 758,2(6) pm, V = 7,153(2) nm3, Z = 8, R = 0,126 fur 2 698 unabhangige Reflexe [F > 4σ(F)]. 3 : trans-(CN3H6)2[VO13{(OCH2)3CCH2OH}2] · H2O: Raumgruppe C2/c, a = 2 293,4(3) pm, b = 1 102,6(2) pm, c = 1 368,6(2) pm, β = 120,87(1)°, V = 2,9705(8) nm3, Z = 4, R = 0,046 fur 2 206 unabhangige Reflexe [F > 4σ(F)] . Cis-/Trans-Isomerism of Bis-(trisalkoxy)-hexavanadates: cis-Na2[VO7(OH)6{(OCH2)3CCH2OH}2] · 8 H2O, cis-(CN3H6)3[VIVVO13{(OCH2)3CCH2OH}2] · 4.5 H2O and trans-(CN3H6)2[VO13{(OCH2)3CCH2OH}2] · H2O Polyoxovanadates with distorted Lindquist-structure, in which six of the twelve μ2-oxygen atoms are formally replaced by the oxygen atoms of two coordinated pentaerythritol ligands, can be prepared by a simple method in an aqueous medium. The “fully reduced”, six-fold protonated compound cis-Na2[VO7(OH)6{(OCH2)3CCH2OH}2] · 8 H2O (1), the mixed valence species cis-(CN3H6)3[VIVVO13{(OCH2)3CCH2OH}2] · 4.5 H2O (2) containing one localized VIV centre and the “fully oxidized” compound trans-(CN3H6)2[VO13{(OCH2)3CCH2 · OH}2] · H2O (3) have been synthesized and characterized by UV/VIS-, IR- and EPR-spectroscopy, by magnetic measurements, cyclic voltammetry and by a single-crystal X-ray structure analysis. The organic {(CH2)3CCH2OH}3+-groups tend to cap the triangular faces formed by μ2-oxygen atoms of the central approximately octahedral {V6O19}-unit. Therefore the anions of bis-(trisalkoxy)-hexavanadates can exist in a trans-form as well as in an isomeric cis-form referring to a “basic” plane of four vanadium atoms of the {V6}-octahedron. The different relative positions of the ligands have a significant influence on the redox potentials of the compounds. For structural details see “Inhaltsubersicht”.

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