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Electron Paramagnetic Resonance

Preamble
The structure-activity relationship is one of the important aspects to have control over the property of the targeted complexes and to fine-tune the structure of the complexes to realize the improved activity in many research areas such in Chemistry, Biology, solid-state physics, semi-conductors, display materials, catalysis, spin Tapping, etc. For example, to understand the mechanism of a catalytic reaction (either a radical or non-radical pathway), nature of the excited state involved in the various bio-mimetic and metalloenzyme oxidation reaction need to be understood. The transient intermediates that are generated in many reactions, protein folding, display devices (light or temperature or pressure-induced) are some of of the cutting-edge research areas. Electron Paramagnetic Resonance (EPR) spectrometer helps to study these intermediates and various associated processes

The instrument
EPR instrument is mainly used to characterize the paramagnetic complexes with unpaired electrons and organic radicals. Unlike nuclear magnetic resonance (NMR), there is always an element of hesitation and hurdle among the students to understand, analyze and interpret the data that arises from the EPR, due to the complication arising from the g-anisotropy, hyperfine interaction, and magnetic anisotropy in certain transition metal complexes such as Fe(II). Therefore, we aim to introduce this sophisticated analysis at their preliminary level to make the students realize the potential applications of these instruments besides teaching the basic principles, analysis, and interpretation of the EPR data. The generic instrument consists of four major components 1) Microwave resonator 2) Microwave bridge 3) Magnet system 4) Control electronics.

Experiments
Among the many experiments planned for UG/PG/Ph.D., students, one illustrative example is the temperature-dependent spin state change of the Fe(II) complex i.e. temperature assisted spin Crossover (SCO) of [Fe(NH₂tra)₃]Br₂ (where NH₂trz = 4-amino-1,2,4-triazole) phenomenon. The SCO complexes are envisaged as molecular-based information storage devices, molecular switches, and display materials, etc.,. At room temperature, the Fe(II) complex exists as a high spin (S =2), paramagnetic while at low temperature (77 K) the same complex exists as a low spin (S = 0), diamagnetic complex. EPR instrument is aimed at teaching how to determine the electronic structure of both spin states from their EPR spectral features, besides the fundamental theories of the instrument.