Department of Photochemistry and Molecular Science, Uppsala University, P.O. Box 523, S-75120 Uppsala, Sweden.
Inorg Chem. 2012 Feb 20;51(4):2332-7. doi: 10.1021/ic202323b. Epub 2012 Jan 25.
The carboxylate stretching frequencies of two high-valent, di-μ-oxido bridged, manganese dimers has been studied with IR spectroscopy in three different oxidation states. Both complexes contain one monodentate carboxylate donor to each Mn ion, in one complex, the carboxylate is coordinated perpendicular to the Mn-(μ-O)(2)-Mn plane, and in the other complex, the carboxylate is coordinated in the Mn-(μ-O)(2)-Mn plane. For both complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequencies decrease for both the Mn(2)(IV,IV) to Mn(2)(III,IV) transition and the Mn(2)(III,IV) to Mn(2)(III,III) transition, with only minor differences observed between the two arrangements of the carboxylate ligand versus the Mn-(μ-O)(2)-Mn plane. The IR spectra also show that both carboxylate ligands are affected for each one electron reduction, i.e., the stretching frequency of the carboxylate coordinated to the Mn ion that is not reduced also shifts. These results are discussed in relation to FTIR studies of changes in carboxylate stretching frequencies in a one electron oxidation step of the water oxidation complex in Photosystem II.
两个高氧化态、二μ-氧桥接的锰二聚体的羧酸酯伸缩频率已通过红外光谱在三种不同的氧化态下进行了研究。两个配合物都有一个单齿羧酸根供体与每个 Mn 离子配位，在一个配合物中，羧酸根垂直于 Mn-(μ-O)(2)-Mn 平面配位，而在另一个配合物中，羧酸根在 Mn-(μ-O)(2)-Mn 平面内配位。对于两个配合物，不对称和对称羧酸酯伸缩频率之间的差异随着 Mn(2)(IV,IV)到 Mn(2)(III,IV)的转变和 Mn(2)(III,IV)到 Mn(2)(III,III)的转变而减小，两种羧酸酯配体相对于 Mn-(μ-O)(2)-Mn 平面的排列仅观察到微小差异。红外光谱还表明，每个电子还原都会影响两个羧酸酯配体，即，未还原的 Mn 离子配位的羧酸酯的伸缩频率也会发生位移。这些结果与 PSII 中水氧化复合物在单电子氧化步骤中羧酸酯伸缩频率变化的 FTIR 研究有关。
