Chen Hongyu, Tagore Ranitendranath, Olack Gerard, Vrettos John S, Weng Tsu-Chien, Penner-Hahn James, Crabtree Robert H, Brudvig Gary W
Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA.
Inorg Chem. 2007 Jan 8;46(1):34-43. doi: 10.1021/ic060499j.
MnIII/IV2(-O)2(terpy)2(OH2)23 (1, where terpy = 2,2':6'2' '-terpyridine) + oxone (2KHSO5 x KHSO4 x K2SO4) provides a functional model system for the oxygen-evolving complex of photosystem II that is based on a structurally relevant Mn-(-O)2-Mn moiety (Limburg, J.; et al. J. Am. Chem. Soc. 2001, 123, 423-430). In this study, electron paramagnetic resonance, ultraviolet-visible spectroscopy, electrospray ionization mass spectrometry, X-ray absorption spectroscopy, and gas-phase stable isotope ratio mass spectrometry were utilized to identify the title compounds in the catalytic solution. We find that (a) O2 evolution does not proceed through heterogeneous catalysis by MnO2 or other decomposition products, that (b) O atoms from solvent water are incorporated into the evolved O2 to a significant extent but not into oxone, that (c) the MnIII/IV2 title compound 1 is an active precatalyst in the catalytic cycle of O2 evolution with oxone, while the MnIV/IV2 oxidation state is not, and that (d) the isotope label incorporation in the evolved O2, together with points a-c above, is consistent with a mechanism involving competing reactions of oxone and water with a "MnV=O" intermediate in the O-O bond-forming step.
MnIII/IV2(-O)2(terpy)2(OH2)23（1，其中terpy = 2,2':6'2''-三联吡啶）与过一硫酸氢钾复合盐（2KHSO5·KHSO4·K2SO4）构成了一个用于光系统II析氧复合物的功能模型体系，该体系基于一个结构相关的Mn-(-O)2-Mn部分（林堡，J.；等人，《美国化学会志》，2001年，123卷，423 - 430页）。在本研究中，利用电子顺磁共振、紫外可见光谱、电喷雾电离质谱、X射线吸收光谱以及气相稳定同位素比质谱来鉴定催化溶液中的目标化合物。我们发现：（a）氧气析出并非通过MnO2或其他分解产物的非均相催化进行；（b）溶剂水中的氧原子在很大程度上被并入析出的O2中，但未并入过一硫酸氢钾复合盐中；（c）MnIII/IV2目标化合物1在与过一硫酸氢钾复合盐的析氧催化循环中是一种活性预催化剂，而MnIV/IV2氧化态的化合物则不是；并且（d）析出的O2中的同位素标记掺入，连同上述a - c点，与一种机制相符，该机制涉及在O - O键形成步骤中过一硫酸氢钾复合盐和水与“MnV = O”中间体的竞争反应。
