SYNTHESIS, STRUCTURE, AND CHARACTERIZATION OF A MIXED-VALENCE MANGANESE(III) MANGANESE(IV) BIS(MU-OXO) COMPLEX WITH A MACROCYCLIC TETRAAZA LIGAND
SYNTHESIS, STRUCTURE, AND CHARACTERIZATION OF A MIXED-VALENCE MANGANESE(III) MANGANESE(IV) BIS(MU-OXO) COMPLEX WITH A MACROCYCLIC TETRAAZA LIGAND
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DOI：
10.1021/ic00324a007
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发表时间：
1989-12-13
影响因子：
4.6
通讯作者：
SPREER, LO
中科院分区：
文献类型：
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作者：
BREWER, KJ;CALVIN, M;SPREER, LO
合成并表征了[（14-aneN 4）MnO] 23+（14-aneN 4 = 1，4，8，11-四氮杂环十四烷）配合物。该混合价（III，IV）化合物的晶体结构显示离散的Mn（III）和Mn（IV）中心。将我们的晶体学数据与之前报道的三种Mn（III）-Mn（IV）双（u-oxo）配合物的数据进行比较表明，虽然外部配体不同，但Mn 2 O2核心中的Mn-O距离保持相对不变（±0.03 Á）。在4 K的X波段EPR实验表现出一个16线的光谱中心在g= 2。这16线的光谱是由于重叠的超精细分裂与两个化学性质不同的Mn核（I= 5/2），其中一个超精细耦合常数约为另一个的两倍。该配合物为Robin和Day Ⅱ类混合价物种。详细的研究表明，这种双核锰物种的形成，桥氧来自溶剂水和桥的形成发生both锰离子在III氧化态。该配合物的循环伏安法表现出可逆的单电子氧化（ε m=+1.0 V vs SCE）至IV、IV能级以及可逆的单电子还原（ε l/2=-0.12 V vs SCE）至III、III能级。进行了光谱电化学实验，确定了Ⅲ、Ⅳ络合物的电子光谱归属。III，IV复合物在可见光区（1= 538（sh），550，650 nm）以及延伸到近红外区的尾部表现出三个主要的吸收最大值。在538和550 nm处的谱带分别归属于涉及Mn（IV）和Mn（III）中心的dd跃迁。650 nm处的谱带归属于配体到金属的电荷转移跃迁，氧代-*· Mn（IV）。进入近红外区域的尾部是由于一个价间跃迁，这是强烈的650 nm电荷转移带的基础。复合物，如1是感兴趣的多电子氧化还原催化剂，如光系统II中的放氧复合物（OEC）的模型。
The complex [(14-aneN4) MnO] 23+(14-aneN4= 1, 4, 8, 11-tetraazacyclotetradecane) has been prepared and characterized. The crystal structure of this mixed-valence (III, IV) compound shows discrete Mn (III) and Mn (IV) centers. Comparison of our crystallographic data with the data for the three previously reported Mn (III)-Mn (IV) bis (u-oxo) complexes indicates that while the external ligands are varied, the Mn-O distances in the Mn202 core remain relatively unchanged (±0.03 Á). The X-band EPR experiments at 4 K exhibit a 16-line spectrum centered at g= 2. This 16-line spectrum is attributed to the overlap of hyperfine splitting with two chemically differentMn nuclei (I= 5/2) with one hyperfine coupling constant being roughly twice the magnitude of the other. This complex is a Robin and Day class II mixed-valence species. Detailed studies of the formation of this binuclear Mn species indicate that the bridging oxygens come from solvent water and that the bridge formation occurs with bothmanganese ions in the III oxidation state. Cyclic voltammetry of the complex exhibits a reversible one-electron oxidation (£ m=+ 1.0 V vs SCE) to the IV, IV level as well as a reversible one-electron reduction (£ l/2=-0.12 V vs SCE) to the III, III level. Spec-troelectrochemical experimentshave been performed that help to establishthe assignments of the electronic spectrum of the III, IV complex. The III, IV complex exhibits three main absorption maxima in the visible region (1= 538 (sh), 550, 650 nm) as well as a tail that extends into the near-infrared region. The bands at 538 and 550 nm are assigned to dd transitions involving the Mn (IV) and Mn (III) centers, respectively. The band at 650 nm is assigned to a ligand-to-metal charge-transfer transition, oxo-*· Mn (IV). The tail into the near-infrared region is due to an intervalence transition, which underlies the intense 650-nm charge-transfer band. Complexes such as 1 are of interest as models for multiple-electron redox catalysts like the oxygen-evolving complex (OEC) in photosystem II.