Experimental and Theoretical Studies of Paramagnetic Transient Reaction Intermediates

顺磁瞬态反应中间体的实验与理论研究

• 批准号: 1955-2007
• 负责人: Mattar, Saba
• 金额: $ 3.82万
• 依托单位: University of New Brunswick
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2010
• 资助国家: 加拿大
• 起止时间: 2010-01-01 至 2011-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=449348
• 关键词: Experimental; Theoretical; Studies; Paramagnetic; Transient

Our research program involves the study of the formation mechanisms, structure-bonding relationships, properties and chemical reactivity of selected paramagnetic reaction intermediates. They are sulfur-nitrogen heterocycles and organometallic transition metal half-sandwich complexes. These intermediates are fundamental building blocks that react to form important new magnetic, conducting and spin-electronic materials. We would like to understand how their structure and bonding influences their magnetic, electronic, chemical and physical properties. This will be done by generating the intermediates and determining their experimental parameters, such as hyperfine (A) and g tensors by electron paramagnetic resonance (EPR), vibrational frequencies by Raman and infrared (IR) spectroscopy and their electronic excitation energies by ultraviolet-visible (UV-VIS) spectroscopy. These parameters will also be calculated by hybrid density functional, CAS-SCF or configuration interaction (CI) methods. The agreement between the computed and experimental parameters results in a comprehensive clear bonding picture from which concrete conclusions are made about the role of the intermediate in the mechanism of the overall formation reaction. We have successfully used this technique in the past. Organic semiquinone free radical intermediates that are involved in single electron transfer reactions of biological importance will also be studied by the same methods. When the reactive intermediates are short-lived, they will be trapped in rare-gas matrices at low temperatures (8-12 K). By matrix-isolating them, their experimental parameters are determined, via EPR, IR and UV-VIS spectroscopy, without the necessity of expensive ultra-fast techniques. EPR spectroscopy is our most important tool and we will continue to develop new methods of improving our home-built pulsed and conventional multi-frequency (4.5 - 35.0 GHz) EPR spectrometers. These include new pulsed electron-spin-echo techniques, phase-modulation detection and dielectric resonator probes that increase the spectrometers' sensitivities by a factor of 30. This will enhance their spectral resolution and the detection of smaller amounts of intermediates.

我们的研究项目涉及选定的顺磁反应中间体的形成机制，结构键关系，性质和化学反应性的研究。它们是硫氮杂环和有机金属过渡金属半夹层配合物。这些中间体是形成重要的新型磁性、导电性和自旋电子材料的基本组成部分。我们想了解它们的结构和成键如何影响它们的磁性、电子、化学和物理性质。这将通过生成中间体并确定其实验参数来完成，例如通过电子顺磁共振（EPR）确定超精细(A)和g张量，通过拉曼和红外（IR）光谱确定振动频率，以及通过紫外-可见（UV-VIS）光谱确定其电子激发能。这些参数也将通过混合密度泛函、CAS-SCF或配置相互作用（CI）方法计算。计算参数和实验参数之间的一致导致了一个全面清晰的键合图，从中可以得出关于中间体在整个生成反应机制中的作用的具体结论。我们过去曾成功地使用过这种技术。有机半醌自由基中间体是参与生物重要性的单电子转移反应也将通过相同的方法进行研究。当反应中间体寿命较短时，它们将在低温（8-12 K）下被困在稀有气体基质中。通过基质分离，可以通过EPR， IR和UV-VIS光谱测定它们的实验参数，而不需要昂贵的超快速技术。EPR光谱是我们最重要的工具，我们将继续开发新的方法来改进我们自制的脉冲和传统的多频率（4.5 - 35.0 GHz） EPR光谱仪。其中包括新的脉冲电子自旋回波技术、相位调制检测和介电谐振器探针，这些技术将光谱仪的灵敏度提高了30倍。这将提高它们的光谱分辨率和检测更少量的中间产物。