Hureau Christelle, Blondin Geneviève, Charlot Marie-France, Philouze Christian, Nierlich Martine, Césario Michèle, Anxolabéhère-Mallart Elodie
Laboratoire de Chimie Inorganique, UMR 8613, LCR-CEA No. 33V, Institut de Chimie Moléculaire et des Matériaux d'Orsay, Université Paris-Sud, France.
Inorg Chem. 2005 May 16;44(10):3669-83. doi: 10.1021/ic050243y.
Two Mn(II) complexes are isolated and X-ray characterized, namely, cis-[(L(2))Mn(II)(Cl)(2)] (1) and (L(3))Mn(II)Cl(OH(2)) (2(ClO(4))), where L(2) and L(3) are the well-known tetradentate N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine and N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)propane-1,3-diamine ligands, respectively. The crystal structure reveals that whereas the ligand L(2) is in the cis-alpha conformation in complex 1, the ligand L(3) is in the more unusual cis-beta conformation in 2. EPR spectra are recorded on frozen solutions for both complexes and are characteristic of Mn(II) species. Electrochemical behaviors are investigated on acetonitrile solution for both complexes and show that cation 2 exists as closely related Mn(II) species in equilibrium. For both complexes exhaustive bulk electrolyses of acetonitrile solution are performed at oxidative potential in various experimental conditions. In the presence of 2,6-lutidine and after elimination of chloride ligands, the formation of the di-mu-oxo mixed-valent complexes (L(2))Mn(III)(mu-O)(2)Mn(IV)(L(2)) (3a) and (L(3))Mn(III)(mu-O)(2)Mn(IV)(L(3)) (4) is confirmed by UV-vis and EPR spectroscopies and cyclic voltammetry. In addition crystals of 4(ClO(4))(3) were isolated, and the X-ray structure reveals the cis-alphaconformation of L(3). In the absence of 2,6-lutidine and without elimination of the exogenous chloride ions, the electrochemical oxidation of 1 leads to the formation of the mononuclear Mn(III) complex, namely, (L(2))Mn(III)(Cl)(2) (5), as confirmed by UV-vis as well as parallel mode EPR spectroscopy and cyclic voltammetry. In the same conditions, the electrochemical oxidation of complex 2 is more intricate, and a thorough analysis of EPR spectra establishes the formation of the binuclear mono-mu-oxo mixed-valent (L(3))ClMn(III)(mu-O)Mn(IV)Cl(L(3)) (6) complexes. Electrochemical conversion of Mn(II) complexes into mixed-valent Mn(2)(III,IV) oxo-bridged complexes in the presence of 2,6-lutidine is discussed. The role of the chloride ligands as well as that of L(3) in the building of oxo bridges is discussed. Differences in behavior between L(2) and L(3) are commented on.
分离出两种锰（II）配合物并通过X射线进行表征，即顺式-[(L(2))Mn(II)(Cl)(2)]（1）和(L(3))Mn(II)Cl(OH(2))（2(ClO(4))），其中L(2)和L(3)分别是著名的四齿N,N'-二甲基-N,N'-双（2-吡啶甲基）乙烷-1,2-二胺和N,N'-二甲基-N,N'-双（2-吡啶甲基）丙烷-1,3-二胺配体。晶体结构表明，配合物1中的配体L(2)处于顺式-α构象，而配合物2中的配体L(3)处于更不寻常的顺式-β构象。对两种配合物的冷冻溶液记录了电子顺磁共振（EPR）光谱，其为锰（II）物种的特征光谱。在乙腈溶液中研究了两种配合物的电化学行为，结果表明阳离子2以密切相关的锰（II）物种处于平衡状态。在各种实验条件下，对两种配合物的乙腈溶液在氧化电位下进行了彻底的本体电解。在2,6-二甲基吡啶存在下并消除氯配体后，通过紫外可见光谱、电子顺磁共振光谱和循环伏安法确认形成了二-μ-氧混合价配合物(L(2))Mn(III)(μ-O)(2)Mn(IV)(L(2))（3a）和(L(3))Mn(III)(μ-O)(2)Mn(IV)(L(3))（4）。此外，分离出了4(ClO(4))(3)的晶体，X射线结构揭示了L(3)的顺式-α构象。在不存在2,6-二甲基吡啶且未消除外源氯离子的情况下，1的电化学氧化导致形成单核锰（III）配合物，即(L(2))Mn(III)(Cl)(2)（5），这通过紫外可见光谱、平行模式电子顺磁共振光谱和循环伏安法得到证实。在相同条件下，配合物2的电化学氧化更为复杂，对电子顺磁共振光谱的深入分析确定形成了双核单-μ-氧混合价(L(3))ClMn(III)(μ-O)Mn(IV)Cl(L(3))（6）配合物。讨论了在2,6-二甲基吡啶存在下锰（II）配合物向混合价锰（2）（III,IV）氧桥联配合物的电化学转化。讨论了氯配体以及L(3)在氧桥构建中的作用。对L(2)和L(3)之间行为的差异进行了评论。
