The hydrogen catalyst cobaloxime: a multifrequency EPR and DFT study of cobaloxime's electronic structure.
The hydrogen catalyst cobaloxime: a multifrequency EPR and DFT study of cobaloxime's electronic structure.
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DOI：
10.1021/jp209395n
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发表时间：
2012-03-08
影响因子：
3.3
通讯作者：
Poluektov, Oleg G.
中科院分区：
文献类型：
--
作者：
Niklas, Jens;Mardis, Kristy L.;Rakhimov, Rakhim R.;Mulfort, Karen L.;Tiede, David M.;Poluektov, Oleg G.
太阳能燃料研究的目的是模仿光合作用，并设计出能够以高能分子键的形式捕获、转换和储存太阳能的集成系统。分子氢通常被认为是理想的太阳能燃料，因为它的燃烧基本上是无污染的。钴肟是地球上最有前途的将质子还原为分子氢的催化剂之一。我们已经使用多频EPR光谱在X波段，Q波段，和D波段结合DFT计算，以揭示电子结构和建立这些配合物的结构，环境和催化活性之间的相关性。为了评估配体钴相互作用的强度和性质，在各种不同的溶剂中研究了BF 2封端的钴肟Co（dmgBF 2）2，所述溶剂具有钴离子的一系列极性和化学计量量的潜在配体。这使得分化的不稳定和强烈的协调轴向配体的Co（II）配合物。不稳定或弱配位的配体如甲醇比强配位的配体如吡啶导致更大的g-张量各向异性。此外，对于具有单连接的LCo（dmgBF 2）2和双连接的L2 Co（dmgBF 2）2的强配位配体，观察到配位数效应。两个强配位轴向配体的存在导致最小的g-张量各向异性。讨论了轴向配体的强度与Co（dmgBF 2）2催化效率的关系。最后，研究了分子氧对Co（III）超氧自由基LCo（dmgBF 2）2 O2·形成的影响。实验结果进行了比较与一套全面的DFT计算Co（dmgBF 2）2模型系统与各种轴向配体。与实验值的“关键”的磁性参数，如g-张量和59钴超精细耦合张量的比较允许轴向连接的Co（dmgBF 2）2复合物的构象的测定。这里提供的数据对于理解溶剂和配体配位对钴肟催化效率的影响至关重要。
Solar fuels research aims to mimic photosynthesis and devise integrated systems that can capture, convert, and store solar energy in the form of high-energy molecular bonds. Molecular hydrogen is generally considered an ideal solar fuel as its combustion is essentially pollution-free. Cobaloximes rank among the most promising earth-abundant catalysts for the reduction of protons to molecular hydrogen. We have used multifrequency EPR spectroscopy at X-band, Q-band, and D-band combined with DFT calculations to reveal electronic structure and establish correlations between structure, surroundings and catalytic activity of these complexes. To assess the strength and nature of ligand cobalt interactions, the BF2-capped cobaloxime, Co(dmgBF2)2, was studied in a variety of different solvents with a range of polarities and stoichiometric amounts of potential ligands to the cobalt ion. This allows the differentiation of labile and strongly coordinating axial ligands for the Co(II) complex. Labile, or weakly coordinating, ligands like methanol result in larger g-tensor anisotropy than strongly coordinating ligands like pyridine. Additionally, a coordination number effect is seen for the strongly coordinating ligands with both singly-ligated LCo(dmgBF2)2 and doubly-ligated L2Co(dmgBF2)2. The presence of two strongly coordinating axial ligands leads to the smallest g-tensor anisotropy. The relevance of the strength of the axial ligand(s) to the catalytic efficiency of Co(dmgBF2)2 is discussed. Finally, the influence of molecular oxygen and formation of Co(III) superoxide radicals LCo(dmgBF2)2O2• is studied. The experimental results are compared with a comprehensive set of DFT calculations on Co(dmgBF2)2 model systems with various axial ligands. Comparison with experimental values for the “key” magnetic parameters like g-tensor and 59Co hyperfine coupling tensor allows the determination of the conformation of the axially ligated Co(dmgBF2)2 complexes. The data presented here are vital for understanding the influence of solvent and ligand coordination on the catalytic efficiency of cobaloximes.
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影响因子：
3
作者：
Baker, Jon;Wolinski, Krzysztof;Pulay, Peter
通讯作者：
Pulay, Peter
DOI：
10.1039/dt9900003311
发表时间：
1990-11-01
期刊：
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS
影响因子：
--
作者：
DECASTRO, B;RANGEL, M;RAYNOR, JB
通讯作者：
RAYNOR, JB
影响因子：
15
作者：
Dempsey, Jillian L.;Winkler, Jay R.;Gray, Harry B.
通讯作者：
Gray, Harry B.
影响因子：
16.6
作者：
Fihri, Aziz;Artero, Vincent;Fontecave, Marc
通讯作者：
Fontecave, Marc
影响因子：
1
作者：
Hyde, J. S.;Pasenkiewicz-Gierula, M.;Antholine, W. E.
通讯作者：
Antholine, W. E.