Integrated Paramagnetic Resonance of High-Spin Co(II) Systems

在这个由化学部化学结构、动力学和机制项目资助的项目中，新墨西哥大学的Tierney教授将系统地研究具有混合N/O/S供体集的高自旋（hs） Co（II）配位化合物库，包括4-、5-和6-配位化合物。这项工作建立在顺磁共振的综合方法上，同时应用冷冻溶液多频电子顺磁共振（EPR）和流体溶液核磁共振（NMR）来绘制电子-核超精细相互作用的场依赖性和温度依赖性。基于epr的技术用于将基态电子-核超精细相互作用映射到三维结构上。激发态效应通过紫外可见近红外光谱，由场和温度依赖的核磁共振弛豫和NMRD详细检查。由此产生的信息将定义在这些电子复杂系统中控制电子动力学的因素。脉冲EPR技术（在X和q波段的ENDOR和ESEEM）和异核核的NMR，包括吡唑酸酯配合物中的11B和结合到配体中的19F，将用于帮助溶液形成。目标是深入了解激发态混合如何决定基态电子特性和溶液动力学。目标分子包括一系列自旋交叉配合物，研究结构动力学在转化为功能材料所需的磁滞中的作用。高自旋钴（II）配合物对金属的生物化学研究以及现代磁性材料和催化剂具有重要意义。例如，这些配合物可用作酶促反应机理的光谱探针。此外，它们还可以用于在分子或纳米尺度上构建可切换磁铁。这种材料处于现代计算机小型化研究的前沿。广泛的磁共振技术将被用于确定这些有趣分子的结构特征。这项研究为早期职业科学家以及研究生和本科生研究人员提供了培训机会。参与这项研究的许多学生都在当地介绍了他们的研究，有几个人在区域和国家会议上做了报告。该研究项目的成果已被纳入本科化学课程，包括利用低温EPR、顺磁核磁共振和x射线结构测定的实验。

In this project, funded by the Chemistry Division's Chemical Structure, Dynamics and Mechanisms Program, Professor Tierney of the University of New Mexico will systematically investigate a large library of high-spin (hs) Co(II) coordination compounds with mixed N/O/S donor sets, encompassing 4-, 5- and 6-coordination. The work is founded on an integrated approach to paramagnetic resonance, simultaneously applying frozen-solution multi-frequency electron paramagnetic resonance (EPR) and fluid-solution nuclear magnetic resonance (NMR), to map the field- and temperature-dependence of electron-nuclear hyperfine interactions. EPR-based techniques are used to map ground state electron-nuclear hyperfine interactions onto three-dimensional structure. Excited state effects are examined in detail by UV-vis-NIR spectroscopy, by field- and temperature-dependent NMR relaxation and by NMRD. The resulting information will define the factors controlling electron dynamics in these electronically complex systems. Pulsed EPR techniques (ENDOR and ESEEM at both X- and Q-bands) and NMR of heteronuclei, including 11B in pyrazolylborate complexes and 19F incorporated into ligands, will be utilized to aid in solution speciation. The goal is to develop a deeper understanding of how excited state mixing determines ground state electronic properties and solution dynamics. Target molecules include a series of spin-crossover complexes, examining the role of structural dynamics in the magnetic hysteresis required for translation into functional materials.Complexes of high-spin cobalt(II) are important to the study of metals in biochemistry, as well as to modern magnetic materials and catalysts. For example, these complexes can be used as spectroscopic probes of the mechanisms of enzymatic reactions. Also, they can used to construct switchable magnets on the molecular or nano-scale. Such materials are at the frontier of research in modern computer miniaturization. A wide range of magnetic resonance techniques will be employed for determining the structural features of these interesting molecules. This research provides training opportunites for early-career scientists, as well as graduate and undergraduate researchers. Many students involved in this research have presented their research locally, and several have made presentations at regional and national meetings. Results from this research program have been incorporated into the undergraduate chemistry curriculum, including experiments that utilize low-temperature EPR, paramagnetic NMR, and X-ray structure determination.