ELECTRONIC AND GEOMETRIC STRUCTURE DETERMINATION OF NI-O2 COMPLEXES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 过渡金属氧配合物在生物和化学领域具有重要意义，包括好氧氧化、氧化催化、生物氧活化等。然而，关于Ni-O2络合物的报道很少，部分原因是很难分离出具有O2反应活性的目标Ni氧化态的NiI络合物。最近，我们合成并表征了一种Ni-O2配合物(1)([Ni(14-tmc)O2](OTf)；(14-tmc)=1，4，8，11-tetramethyl-1，4，8，11-tetraazacyclotetradecane；(OTf)=CF3SO3)，其O-O伸缩频率为1131 cm-1。NiK边XAS和EXAFS数据与光学光谱相结合，得到NiII-超氧化物的描述为1。在没有晶体结构的情况下，EXAFS和DFT计算被用来预测O2以末端方式结合。用改进的轴向配体系统进行的实验得出了令人惊讶的结果。例如，选择13-TmC(1，4，7，10-tetramethyl-1，4，7，10-tetraazacyclotridecane)作为配体得到的物种(2)具有与1相似的光谱特征，而12-TmC(1，4，7，10-tetramethyl-1，4，7，10-tetraazacyclododecane)得到的物种(3)具有类似的光谱特征。3具有独特的侧面结合的Ni-O2构象，并进行了结晶学表征。3还表现出截然不同的光谱性质，O-O伸缩频率降低(1002厘米-1)。O-O频率的下降表明3中具有更多的过氧化氢性质，这表明与1中的NiII样特征相比，3中具有NiIII样特征。很可能是1(14-TMC)到12-TMC(3)中轴向配体的变化调节了中心Ni原子与氧之间的成键。为了了解不同的TMC配体在Ni-O2成键中的作用，我们建议在1、2和3上进行Ni K边XAS实验(用于比较)。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Transition metal dioxygen complexes are important in several fields of biology and chemistry, which include aerobic oxidation, oxidative catalysis, and biological O2 activation. However, very few reports of Ni-O2 complexes are available, partly due to the difficulty in the isolation of NiI complexes, which have the target Ni oxidation state for O2 reactivity. Recently, we synthesized and spectroscopically characterized a Ni-O2 complex (1) ([Ni(14-tmc)O2](OTf);(14-tmc)=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; (OTf)=CF3SO3), with an O-O stretching frequency of 1131 cm-1. Ni K-edge XAS and EXAFS data were combined with optical spectroscopies to arrive at a NiII-superoxide description of 1. In the lack of a crystal structure, EXAFS and DFT calculations were used to predict that O2 binds in an end-on fashion. Experiments with modified axial ligand systems have led to surprising results. For example, the choice of 13-tmc (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) as a ligand results in a species (2) with similar spectroscopic features as 1, while 12-tmc (1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) results in a species (3). 3 has been crystallographically characterized and has a unique side-on bound Ni-O2 conformation. 3 also demonstrates starkly different spectroscopic properties with a decreased O-O stretching frequency (1002 cm-1). The decrease in O-O frequency indicates a more peroxide like character in 3, which would suggest a NiIII-like character in 3 compared to a NiII-like character in 1. It is likely that the change in the axial ligand in 1 (14-tmc) to 12-tmc (3) tunes the bonding between the central Ni atom and dioxygen. To understand the role of the different tmc ligands in Ni-O2 bonding, we propose to undertake Ni K-edge XAS experiments on 1(for comparison purposes), 2 and 3.