ELECTRONIC AND GEOMETRIC STRUCTURE DETERMINATION OF NI-O2 COMPLEXES

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 研究中心，而研究中心不一定是研究者所在的机构。 过渡金属双氧配合物在生物学和化学的许多领域都有重要的应用，包括有氧氧化、氧化催化和生物氧气活化。然而，Ni-O2络合物的报道很少，部分原因是NiI络合物的分离困难，NiI络合物具有用于O2反应性的目标Ni氧化态。最近，我们合成了一种镍氧配合物（1）（[Ni（14-tmc）O2]（OTf）;（14-tmc）= 1，4，8，11-四甲基-1，4，8，11-四氮杂环十四烷;（OTf）= CF 3SO 3），并对其进行了光谱表征，其O-O伸缩频率为1131 cm-1。镍K-边XAS和EXAFS数据与光学光谱相结合，以达到镍超氧化物的描述1。在缺乏晶体结构的情况下，EXAFS和DFT计算被用来预测O2以末端方式结合。用改性的轴向配体系统的实验已经导致了令人惊讶的结果。例如，选择13-tmc（1，4，7，10-四甲基-1，4，7，10-四氮杂环十三烷）作为配体产生具有与1类似的光谱特征的物质（2），而12-tmc（1，4，7，10-四甲基-1，4，7，10-四氮杂环十二烷）产生物质（3）。3已被晶体学表征，并具有独特的侧上结合的Ni-O2构象。3还显示出明显不同的光谱性质，具有降低的O-O伸缩频率（1002 cm-1）。O-O频率的降低表明3中的过氧化物样特征更强，这表明3中的NiIII样特征与1中的NiIII样特征相比。很可能是1（14-tmc）到12-tmc（3）中轴向配体的变化调整了中心Ni原子和分子氧之间的键合。为了了解不同的TMC配体在Ni-O2键合中的作用，我们建议对1（用于比较目的）、2和3进行Ni K边XAS实验。

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.