IDENTIFICATION OF TRANSITION METAL ION COMPOUNDS BY ESR SPECTROSCOPY

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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. Prof Chirik is interested in studying low-valence transition metal ion compounds (Ti, Zr, Hf, Nb) for nitrogen fixation. For this purpose he synthesized and studied a number of compounds, such as bis(cyclopentadienyl)zirconium complexes and used a variety of methods including ESR for their identification. As an important service/training component of the center activity, ACERT staff trained a number of graduate students from Chirik's group to use the Bruker EMX ESR machine and helped them with analyzing the spectra. ESR spectroscopy clearly demonstrated that the reaction products consisted of two nitrogen atoms each bearing a free electron. Synthesis of 13C substituted compounds and analysis of the additional ESR spectral splitting via 13C nuclei provided further structural details. Along with the main product, ESR detects substantial amounts of other products. Based on their g-factors and their anisotropy, isotope satellite lines etc. the products were identified as Zr(III) compounds. ESR was also used to quantify the ratio of reaction products (radical vs. non-radical, Zr(IV) vs. Zr(III)) and helped in choosing conditions favoring the desired reaction path. Similar work is now in progress for niobium organic compounds.