Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd MC 127-72, Pasadena, California 91125, United States.
J Am Chem Soc. 2023 Jul 12;145(27):14592-14598. doi: 10.1021/jacs.3c04464. Epub 2023 Jun 27.
The S state of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) shows high-spin (HS) and low-spin (LS) EPR signals attributed to distinct structures based on computation. Five-coordinate Mn centers are proposed in these species but are absent in available spectroscopic model complexes. Herein, we report the synthesis, crystal structure, electrochemistry, SQUID magnetometry, and EPR spectroscopy of a MnMnO cuboidal complex featuring five-coordinate Mn. This cluster displays a spin ground state of = 5/2, while conversion to a six-coordinate Mn upon treatment with water results in a spin state change to = 1/2. These results demonstrate that coordination number, without dramatic changes within the MnO core, has a substantial effect on spectroscopy.
氧释放复合体(OEC)的 S 态表现出高自旋(HS)和低自旋(LS)电子顺磁共振(EPR)信号,这些信号归因于基于计算的不同结构。在这些物种中提出了五配位 Mn 中心,但在现有的光谱模型配合物中不存在。本文报道了一种具有五配位 Mn 的 MnMnO 立方体形配合物的合成、晶体结构、电化学、超导量子干涉磁强计(SQUID)磁测量和 EPR 光谱。该配合物显示自旋基态为 = 5/2,而用水分处理转化为六配位 Mn 导致自旋状态变为 = 1/2。这些结果表明,配位数在 MnO 核内没有明显变化,对光谱有很大影响。