Structural, Spectroscopic, and Electrochemical Studies of Binuclear Manganese(II) Complexes of Bis(pentadentate) Ligands Derived from Bis(1,4,7-triazacyclononane) Macrocycles

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• 作者：Suzanne J. Brudenell ; Leone Spiccia ; Alan M. Bond ; Gary D. Fallon ; David C. R. Hockless ; George Lazarev ; Peter J. Mahon ; and Edward R. T. Tiekink
• 刊名：Inorganic Chemistry
• 出版年：2000
• 出版时间：March 6, 2000
• 年：2000
• 卷：39
• 期：5
• 页码：881 - 892
• 全文大小：224K
• 年卷期：v.39,no.5(March 6, 2000)
• ISSN：1520-510X

文摘

Structural, electrochemical, ESR, and H₂O₂ reactivity studies are reported for [Mn(dmptacn)Cl]ClO₄ (1, dmptacn= 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane) and binuclear complexes of bis(pentadentate) ligands, generatedby attaching 2-pyridylmethyl arms to each secondary nitrogen in bis(1,4,7-triazacyclononane) macrocycles andlinked by ethyl (tmpdtne, [Mn₂(tmpdtne)Cl₂](ClO₄)₂·2DMF, 2), propyl (tmpdtnp, [Mn₂(tmpdtnp)Cl₂](ClO₄)₂·3H₂O, 3), butyl (tmpdtnb, [Mn₂(tmpdtnb)Cl₂](ClO₄)₂·DMF·2H₂O, 4), m-xylyl (tmpdtn-m-X, [Mn₂(tmpdtn-m-X)Cl₂](ClO₄)₂, 5) and 2-propanol (tmpdtnp-OH, [Mn₂(tmpdtnp-OH)Cl₂](ClO₄)₂, 6) groups. 1 crystallizes in theorthorhombic space group P2₁2₁2₁ (No. 19) with a = 7.959(7) Å, b = 12.30(1) Å, and c = 21.72(2) Å; 2, in themonoclinic space group P2₁/c (No. 14) with a = 11.455(4) Å, b = 15.037(6) Å, c = 15.887(4) Å, and =96.48(2); 3, in the monoclinic space group P2₁/c (No. 14) with a = 13.334(2) Å, b = 19.926(2) Å, c = 18.799(1) Å, and = 104.328(8); and [Mn₂(tmpdtnb)Cl₂](ClO₄)₂·4DMF·3H₂O (4'), in the monoclinic space groupP2₁/n (No. 14) with a = 13.361(3) Å, b = 16.807(5) Å, c = 14.339(4) Å, and = 111.14(2). Significantdistortion of the Mn(II) geometry is evident from the angle subtended by the five-membered chelate (ca. 75) andthe angles spanned by trans donor atoms (<160). The Mn geometry is intermediate between octahedral andtrigonal prismatic, and for complexes 2-4, there is a systematic increase in M···M distance with the length ofthe alkyl chain. Cyclic and square-wave voltammetric studies indicate that 1 undergoes a 1e^- oxidation fromMn(II) to Mn(III) followed by a further oxidation to Mn^IV at a significantly more positive potential. The binuclearMn(II) complexes 2-5 are oxidized to the Mn(III) state in two unresolved 1e^- processes {Mn^II₂ Mn^IIMn^III Mn^III₂} and then to the Mn^IV state {Mn^III₂ Mn^IIIMn^IV Mn^IV₂}. For 2, the second oxidation process waspartially resolved into two 1e^- oxidation processes under the conditions of square-wave voltammetry. In the caseof 6, initial oxidation to the Mn^III₂ state occurs in two overlapping 1e^- processes as was found for 2-5, but thiscomplex then undergoes two further clearly separated 1e^- oxidation processes to the Mn^IIIMn^IV state at +0.89 Vand the Mn^IV₂ state at +1.33 V (vs Fc/Fc⁺). This behavior is attributed to formation of an alkoxo-bridged complex.Complexes 1-6 were found to catalyze the disproportionation of H₂O₂. Addition of H₂O₂ to 2 generated anoxo-bridged mixed-valent Mn^IIIMn^IV intermediate with a characteristic 16-line ESR signal.