Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, California 91125, United States.
Inorg Chem. 2023 Feb 6;62(5):1791-1796. doi: 10.1021/acs.inorgchem.2c01612. Epub 2022 Jul 13.
Synthetic complexes provide useful models to study the interplay between the structure and spectroscopy of the different S-state intermediates of the oxygen-evolving complex (OEC) of photosystem II (PSII). Complexes containing the Mn core corresponding to the S state, the last observable intermediate prior to dioxygen formation, remain very rare. Toward the development of synthetic strategies to stabilize highly oxidized tetranuclear complexes, ligands with increased anion charge were pursued. Herein, we report the synthesis, electrochemistry, SQUID magnetometry, and electron paramagnetic resonance spectroscopy of a stable MnO cuboidal complex supported by a disiloxide ligand. The substitution of an anionic acetate or amidate ligand with a dianionic disiloxide ligand shifts the reduction potential of the MnMn/Mn redox couple by up to ∼760 mV, improving stability. The = 3 spin ground state of the siloxide-ligated MnO complex matches the acetate and amidate variants, in corroboration with the Mn assignment of the S state of the OEC.
合成配合物为研究光合作用系统 II（PSII）放氧复合物（OEC）中不同 S 态中间态的结构和光谱之间的相互作用提供了有用的模型。含有与 S 态对应的 Mn 核的配合物，即在形成氧气之前最后一个可观察到的中间态，仍然非常罕见。为了开发稳定高度氧化的四核配合物的合成策略，人们寻求具有增加的阴离子电荷的配体。在此，我们报告了一种由二硅氧烷配体支撑的稳定 MnO 立方配合物的合成、电化学、SQUID 磁强计和电子顺磁共振波谱。用二阴离子二硅氧烷配体替代阴离子乙酸盐或酰胺配体，可将 MnMn/Mn 氧化还原对的还原电位移动高达约 760 mV，从而提高稳定性。硅氧烷配体 MnO 配合物的 = 3 自旋基态与乙酸盐和酰胺变体相匹配，这与 OEC 的 S 态的 Mn 分配相吻合。
