Eilers Gerriet, Zettersten Camilla, Nyholm Leif, Hammarström Leif, Lomoth Reiner
Department of Physical Chemistry, Uppsala University, Box 579, S-75123 Uppsala, Sweden.
Dalton Trans. 2005 Mar 21(6):1033-41. doi: 10.1039/b415148h. Epub 2005 Feb 15.
The structural rearrangements triggered by oxidation of the dinuclear Mn complex [Mn(2)(bpmp)(mu-OAc)2]+(bpmp = 2,6-bis[bis(2-pyridylmethyl)amino]methyl-4-methylphenol anion) in the presence of water have been studied by combinations of electrochemistry with IR spectroscopy and with electrospray ionization mass spectrometry (ESI-MS). The exchange of acetate bridges for water (D2O) derived ligands in different oxidation states could be monitored by mid-IR spectroscopy in CD(3)CN-D(2)O mixtures following the v(as(C-O)) bands of bound acetate at 1594.4 cm(-1)(II,II), 1592.0 cm(-1)(II,III) and 1586.5 cm(-1)(III,III). Substantial loss of bound acetate occurs at much lower water content (< 0.5% v/v) in the III,III state than in the II,II and II,III states (> or = 10%). The ligand-exchange reactions do not initially reduce the overall charge of the complex but facilitate further oxidation by proton-coupled electron transfer as the water-derived ligands are increasingly deprotonated in higher oxidation states. In the IR spectra deprotonation could be followed by the formation of acetic acid (DOAc, approximately 1725 cm(-1), v(C-O)) from the released acetate (1573.6 cm(-1), v(as(C-O))). By the on-line combination of an electrochemical flow cell with ESI-MS several product complexes could be identified. A di-mu-oxo bridged III,IV dimer Mn(2)(bpmp)(mu-O)(2)(m/z 335.8) can be generated at potentials below the III,III/II,III couple of the di-mu-acetato complex (0.61 V vs. ferrocene). The ligand-exchange reactions allow for three metal-centered oxidation steps to occur from II,II to III,IV in a potential range of only 0.5 V, explaining the formation of a spin-coupled III,IV dimer by photo-oxidation with [Rubpy)(3) in previous EPR studies.
通过电化学与红外光谱以及电喷雾电离质谱（ESI-MS）相结合的方法，研究了双核锰配合物[Mn(2)(bpmp)(μ-OAc)2]+（bpmp = 2,6-双[双(2-吡啶甲基)氨基]甲基-4-甲基苯酚阴离子）在水存在下氧化引发的结构重排。在CD(3)CN-D(2)O混合物中，通过中红外光谱跟踪1594.4 cm(-1)(II,II)、1592.0 cm(-1)(II,III)和1586.5 cm(-1)(III,III)处结合醋酸根的v(as(C-O))谱带，可以监测不同氧化态下醋酸根桥被水（D2O）衍生配体取代的情况。在III,III态中，结合醋酸根的大量损失发生在水含量低得多（< 0.5% v/v）的情况下，而在II,II和II,III态中（>或 = 10%）则不然。配体交换反应最初不会降低配合物的总电荷，但随着水衍生配体在更高氧化态下越来越多地去质子化，通过质子耦合电子转移促进进一步氧化。在红外光谱中，去质子化可以通过从释放的醋酸根（1573.6 cm(-1)，v(as(C-O))）形成醋酸（DOAc，约1725 cm(-1)，v(C-O)）来跟踪。通过将电化学流通池与ESI-MS在线结合，可以鉴定出几种产物配合物。在低于双核μ-醋酸根配合物的III,III/II,III偶合电位（相对于二茂铁为0.61 V）下，可以生成二μ-氧桥联的III,IV二聚体Mn(2)(bpmp)(μ-O)(2)(m/z 335.8)。配体交换反应允许在仅0.5 V的电位范围内发生从II,II到III,IV的三个以金属为中心的氧化步骤，这解释了在先前的电子顺磁共振研究中用Ru(bpy)(3)光氧化形成自旋耦合的III,IV二聚体的原因。
