How a [CoIV-O]2+ Fragment Oxidizes Water: Involvement of a Biradicaloid [CoII-(•O•)]2+ Species in Forming the O-O Bond

被引:46
作者
Crandell, Douglas W. [1 ]
Ghosh, Soumya [1 ]
Berlinguette, Curtis P. [2 ]
Baik, Mu-Hyun [1 ,3 ]
机构
[1] Indiana Univ, Dept Chem, Bloomington, IN 47405 USA
[2] Univ British Columbia, Dept Chem, Vancouver, BC V6T 1Z1, Canada
[3] Korea Univ, Dept Chem Mat, Jochiwon Eup 339700, Sejong Si, South Korea
基金
美国国家科学基金会;
关键词
cobalt; density functional theory; photocatalysis; solar fuels; water oxidation; DENSITY-FUNCTIONAL THEORY; EFFECTIVE CORE POTENTIALS; SOLVATION FREE-ENERGIES; OXIDATION CATALYST; MOLECULAR CALCULATIONS; ELECTRONIC-STRUCTURE; REDOX PROPERTIES; RUTHENIUM COMPLEX; OXYGEN EVOLUTION; EFFICIENT;
D O I
10.1002/cssc.201403024
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The mechanism of water oxidation performed by a recently discovered cobalt complex [Co(Py5)(OH2)](ClO4)(2) (1; Py5=2,6-(bis(bis-2-pyridyl)-methoxymethane)pyridine) was examined using quantum chemical models based on density functional theory. The computer models were first benchmarked against the experimental cyclic voltammetry data to identify the catalytically competent resting state of the catalyst, which was thought to contain a Co-IV-oxyl complex. The electronic structure calculations suggest that the low-spin doublet state is energetically most favorable, but the catalytically most active species is the intermediate-spin quartet complex that is almost isoenergetic with the doublet state. The electronic structure of the quartet state shows significant spin polarization on the terminal oxygen atom, which is consistent with an intramolecular electron transfer from the oxygen to the metal. Based on the calculated spin densities, the formally [Co-IV - O] can be viewed as a biradicaloid [Co-II(O)](2+), that is, a cobalt-oxene moiety. This electronic structure is reminiscent of many other systems where similar electronic patterns were proposed to be responsible for the oxidative reactivity. In this context, this first-row transition-metal system constitutes a logical extension, because the oxyl-radical character is maximized by using the more easily accessible high-spin configurations in which two half-filled Co-d pi orbitals can work in concert to maximize the oxyl-radical character to ultimately afford a new reactive intermediate that can be characterized as carrying a biradicaloid oxene moiety with a formal oxidation state of zero. This conceptual proposal for the catalytically active species provides a plausible rationale for the remarkable oxidative reactivity.
引用
收藏
页码:844 / 852
页数:9
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