Petrie Simon, Stranger Robert
Department of Chemistry, The Faculties, The Australian National University, Canberra ACT 0200, Australia.
Inorg Chem. 2004 Aug 23;43(17):5237-44. doi: 10.1021/ic049967k.
Density functional theory (DFT) calculations, using the Becke-Perdew gradient-corrected functional with a triple-zeta-plus-polarization basis set, have been used to characterize the (H(2)O)(H(3)N)(3)Mn(mu-O)(2)Mn(NH(3))(3)(OH(2))(+) (q = 2-5) complexes. This structure has been proposed as a possible model for the oxygen-releasing site of the photosystem II (PSII) reaction center. We have performed full optimizations to locate stationary points in various spin states for each of the +2 to +5 charge states. Our calculations indicate that O(2) release from the vacuum-phase +5 charge state complex is barrier inhibited, in contrast to the results of a recent DFT study. We report several new di-mu-oxo-bridged stationary points with spin multiplicities of S = (1)/(2), (3)/(2), and (5)/(2) and effective metal oxidation states of Mn(IV)Mn(V) for the +5 charge state. Finally, calculations employing the 'conductorlike screening model' (COSMO), to address the inclusion of solvent effects, indicate that dissociative O(2) release from the +5 charge state model complex is inhibited by a major barrier and is therefore apparently highly disfavored.
采用含三重ζ加极化基组的Becke-Perdew梯度校正泛函的密度泛函理论（DFT）计算，对[(H₂O)(H₃N)₃Mn(μ-O)₂Mn(NH₃)₃(OH₂)]ⁿ⁺（n = 2 - 5）配合物进行了表征。该结构已被提议作为光系统II（PSII）反应中心氧释放位点的一种可能模型。我们对 +2至 +5电荷态的每种自旋态进行了完全优化以确定驻点。我们的计算表明，与最近一项DFT研究的结果相反，真空相 +5电荷态配合物的O₂释放受到势垒抑制。我们报告了几个新的双μ-氧桥连驻点，其自旋多重度为S = 1/2、3/2和5/2，对于 +5电荷态，有效金属氧化态为Mn(IV)Mn(V)。最后，采用“类导体屏蔽模型”（COSMO）进行的计算，以考虑溶剂效应，结果表明 +5电荷态模型配合物的离解性O₂释放受到主要势垒的抑制，因此显然极不受青睐。
