Experimental and Theoretical Studies of Paramagnetic Transient Reaction Intermediates

我们的研究项目包括研究选定的顺磁性反应中间体的形成机理、结构-键关系、性质和化学反应活性。它们是硫氮杂环化合物和有机金属过渡金属半夹心配合物。这些中间体是反应形成重要的新型磁性、导电和自旋电子材料的基本构件。我们想了解它们的结构和成键如何影响它们的磁性、电性、化学性质和物理性质。这将通过生成中间体并确定它们的实验参数来实现，如用电子顺磁共振(EPR)测定超精细(A)和g张量，用拉曼光谱和红外光谱(IR)测定振动频率，用紫外可见光谱(UV-Vis)测定它们的电子激发能。这些参数也将通过混合密度泛函、CAS-SCF或组态相互作用(CI)方法计算。计算参数和实验参数之间的一致性导致了一幅全面而清晰的成键图，从中可以得出中间体在整个生成反应的机理中所起的作用的具体结论。我们在过去已经成功地使用了这项技术。涉及生物意义的单电子转移反应的有机半喹自由基中间体也将用相同的方法进行研究。当反应中间体寿命短时，它们会在低温(8-12K)下被捕获在稀有气体基质中。通过基质分离，通过EPR、IR和UV-Vis光谱确定了它们的实验参数，而不需要昂贵的超快技术。EPR光谱学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多频率(4.5-35.0 GHz)EPR光谱仪。这些技术包括新的脉冲电子自旋回波技术、相位调制检测和介质谐振器探头，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对较少量中间体的检测。

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.