Ryeng Hege, Gonzalez Emmanuel, Ghosh Abhik
Department of Chemistry, University of Tromsø, 9037 Tromsø, Norway.
J Phys Chem B. 2008 Nov 27;112(47):15158-73. doi: 10.1021/jp805486b.
DFT calculations, using the PW91, OLYP, and B3LYP functionals, have provided some of the first estimates of the relative energies of the Ni(I) and Ni(II) ligand anion radical states of hydroporphyrin complexes. Although the three functionals chosen sometimes yield discordant results, the results of this study are essentially functional-independent. For isobacteriochlorin derivatives, our calculations predict that the Ni(I) state may be favored by 0.5 eV or more, relative to the ligand anion radical state. For other hydroporphyrins, however, electrochemical studies indicate a much finer balance, which may be tipped one way or the other, depending on the substituents. DFT calculations nicely capture these rather subtle substituent effects. In particular, our results support and extend Bruckner and co-workers' finding (from electrochemical studies) that the most rigid, strongly ruffled nickel chlorins prefer to reduce on the macrocycle, whereas their more flexible congeners undergo metal-centered reduction.
采用PW91、OLYP和B3LYP泛函进行的密度泛函理论（DFT）计算，首次对氢卟啉配合物的Ni(I)和Ni(II)配体阴离子自由基态的相对能量进行了一些估算。尽管所选用的这三种泛函有时会得出不一致的结果，但本研究的结果基本上与泛函无关。对于异菌叶绿素衍生物，我们的计算预测，相对于配体阴离子自由基态，Ni(I)态可能更稳定0.5 eV或更多。然而，对于其他氢卟啉，电化学研究表明其平衡更为精细，这可能会因取代基的不同而向某一方向倾斜。DFT计算很好地捕捉到了这些相当微妙的取代基效应。特别是，我们的结果支持并扩展了布鲁克纳及其同事（来自电化学研究）的发现，即最刚性、强烈褶皱的镍卟啉倾向于在大环上发生还原，而其更灵活的同类物则发生以金属为中心的还原。
