Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: Combined effects of steric substitution and chelate ring size variations on structural, spectroscopic, and electrochemical properties
Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: Combined effects of steric substitution and chelate ring size variations on structural, spectroscopic, and electrochemical properties
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DOI：
10.1021/ic020131w
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发表时间：
2003-03-24
影响因子：
4.6
通讯作者：
Butcher, RJ
中科院分区：
文献类型：
--
作者：
Gultneh, Y;Yisgedu, TB;Butcher, RJ
介绍了三脚配体三（6-甲基-2-吡啶基甲基）胺（L-1）和双（6-甲基-2-吡啶基甲基）（2-（2-吡啶基）乙基）胺（L-2）和双（2-（2-吡啶基）乙基）胺（L-3）的Mn（II）配合物（2-（2-吡啶基）乙基）胺（L-3）的合成、结构、光谱和电化学表征。将H2O2水溶液加入到L-1和l2的Mn（II）配合物的甲醇溶液中，在快速反应中产生绿色溶液，随后分别析出二氧桥接双核配合物1和2的棕色固体，其通式为[LMnIII(mu-O)(2)(MnL)-L-III](CIO4)(2)。L-3的Mn（II）配合物([(MnL3)-L-II(CH3CN)(H2O)](CIO4)（2)(3)）的甲醇溶液中加入30%的H2O2水溶液，变化非常缓慢，逐渐析出不溶的黑色胶状固体，但没有生成二氧桥接的锰配合物。相比之下，据报道配体双（2-（2-吡啶基）乙基）（2-吡啶基甲基）胺（L-3a）的Mn（II）配合物与H2O2水溶液反应形成二氧桥接(MnMnIV)-Mn- iii配合物。在乙腈溶液的循环伏安实验中，配合物I在E-1/2 = 0.87和1.70 V （vs Ag/AgCI）处显示出两个可逆峰，分别属于Mn-2(III) (MnMnIV)-Mn-III和(MnMnIV)- Mn-2（IV）过程。配合物2也显示出两个可逆峰，一个峰在E-1/2 = 0.78 V，另一个峰在E-1/2 = 1.58 V (vs Ag/AgCI)，分别属于Mn-2(III) (MnMnIV)-Mn-III和Mn11IMnIV Mn-2（IV）氧化还原过程。这些电位是迄今为止观察到的最高的二氧桥式双核锰配合物的三脚配体类型。配合物1和2在控制的阳极电位为1.98 V （vs Ag/AgCI）下进行大量电解氧化，生成了绿色的Mn-2（IV）配合物，并对其进行了光谱表征。L-3的Mn（II）配合物在E-p，E-a为1.96 V （vs Ag/AgCI）的阳极电位下显示出准可逆峰，分配给Mn（II）到Mn（III）的氧化配合物。它比L-3a的Mn（II）配合物的Ep，a高约0.17 V。较高的氧化电位是由于L-3的吡啶基给体的6位甲基取代基的空间效应。
The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mu-O)(2)MnL](CIO4)(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L-1) and bis(6-methyl2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L-2), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L-3) are described. Addition of aqueous H2O2 to methanol solutions of the Mn(II) complexes of L-1 and L 2 produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMnIII(mu-O)(2)(MnL)-L-III](CIO4)(2). Addition of 30% aqueous H2O2 to the methanol solution of the Mn(II) complex of L-3([(MnL3)-L-II(CH3CN)(H2O)](CIO4)(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L-3a) has been reported to react with aqueous H2O2 to form the dioxo-bridged (MnMnIV)-Mn-III complex. In cyclic voltammetric experiments in acetonitrile solution, complex I shows two reversible peaks at E-1/2 = 0.87 and 1.70 V (vs Ag/AgCI) assigned to the Mn-2(III) (MnMnIV)-Mn-III and the (MnMnIV)-Mn-III Mn-2(IV) processes, respectively. Complex 2 also shows two reversible peaks, one at E-1/2 = 0.78 V and a second peak at E-1/2 = 1.58 V (vs Ag/AgCI) assigned to the Mn-2(III) (MnMnIV)-Mn-III and Mn11IMnIV Mn-2(IV) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCI), produced the green Mn-2(IV) complexes that have been spectrally characterized. The Mn(II) complex of L-3 shows a quasi reversible peak at an anodic potential of E-p,E-a of 1.96 V (vs Ag/AgCI) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the Ep,a of the Mn(II) complex of L-3a. The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-positon of the pyridyl donor of L-3.