STRUCTURAL AND MAGNETIC EFFECTS OF SUCCESSIVE PROTONATIONS OF OXO BRIDGES IN HIGH-VALENT MANGANESE DIMERS
STRUCTURAL AND MAGNETIC EFFECTS OF SUCCESSIVE PROTONATIONS OF OXO BRIDGES IN HIGH-VALENT MANGANESE DIMERS
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DOI：
10.1021/ja00104a014
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发表时间：
1994-12-14
影响因子：
15
通讯作者：
PECORARO, VL
中科院分区：
文献类型：
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作者：
BALDWIN, MJ;STEMMLER, TL;PECORARO, VL
报道了第一个双(羟基)桥联锰(IV)二聚体[Mn-IV(Salpn)(Mu-OH)](2)(CF3SO3)(2)，1H(2)(CF3SO3)(2)的合成和表征。与以前报道的配合物[Mn-IV(Salpn)(Mu-O)](2)，1和[Mn-IV(Salpn)](2)(Mu-O)(Mu-OH)(CF3SO3)，1H(CF3SO3)一起，这提供了第一系列矿桥锰配合物，它们被分离在桥的三个不同的质子化状态中，而不改变其他配体或锰的氧化态。利用该系列络合物研究了氧桥质子化对这些Mn(IV)二聚体结构和磁性的影响。氧桥的每一次连续质子化都会导致最低能量(可能是酚-锰)电荷转移跃迁的能量降低2200厘米(-1)，延长了锰-锰距离，并显著降低了反铁磁耦合，而对锰的X射线吸收边能量没有显著的影响。边缘能量都在0.3 eV以内，约为6553 eV。扩展的X射线吸收精细结构谱表明，随着质子化的进行，Mn-Mn距离从1级的2.73埃增加到2.83埃和2.93埃。随温度变化的磁化率测量表明，1的反铁磁耦合在第一次质子化时从J=-92 cm(-1)减小到J=-48 cm(-1)，在第二次质子化时J=-6 cm(-1)。在1H(2)(CF3SO3)(2)中发现的如此低的耦合对于Mn(IV)二聚体来说是前所未有的。了解质子化对高价Mn-2(IV)(Mu-O)(2)单元电子结构和几何结构的影响是很重要的，因为这个核心被认为存在于光系统II的放氧复合体中。讨论了质子化状态变化对S态推进的可能影响以及提出的S-1和S-2的不同组态。
The preparation and characterization of [Mn-IV(salpn)(mu-OH)](2)(CF3SO3)(2), 1H(2)(CF3SO3)(2), the first bis-(hydroxo)-bridged manganese(IV) dimer, is reported. Along with the previously reported complexes [Mn-IV(salpn)(mu-O)](2), 1, and [Mn-IV(salpn)](2)(mu-O)(mu-OH)(CF3SO3), 1H(CF3SO3), this provides the first series of ore-bridged manganese complexes which are isolated in three different protonation states of the bridges without a change in the other ligands or the manganese oxidation state. The effects of oxo bridge protonations on the structure and magnetism of these Mn(IV) dimers are studied using this series of complexes. Each successive protonation of the oxo bridges results in a 2200 cm(-1) decrease in the energy of the lowest energy (presumably, phenolate-to-manganese) charge transfer transition, a lengthening of the Mn-Mn distance, and a dramatic decrease in the antiferromagnetic coupling, without a significant change in the manganese X-ray absorption edge energies. The edge energies an all within 0.3 eV of each other, at ca. 6553 eV. The extended X-ray absorption fine structure spectra indicate that the Mn-Mn distance increases from 2.73 Angstrom for 1 to 2.83 and 2.93 Angstrom with successive protonations. Temperature-dependent magnetic susceptibility measurements show that the antiferromagnetic coupling of 1 decreases from J = -92 cm(-1) to J = -48 cm(-1) upon the first protonation, and to J = -6 cm(-1) upon the second protonation. Such a low coupling as found for 1H(2)(CF3SO3)(2) is unprecedented for Mn(IV) dimers. Understanding the effects of protonation on the electronic and geometric structure of high-valent Mn-2(IV)(mu-O)(2) units is important, as this core has been proposed to exist in the oxygen-evolving complex (OEC) of photosystem II. The possible effects of protonation state changes on S-state advancement and the proposed different configurations of S-1 and S-2 are discussed.