Joshua Telser | Associate Professor at Roosevelt University
________
ADVANCED PARAMAGNETIC RESONANCE SPECTROSCOPY OF HIGH-SPIN TRANSITION METAL ION COMPLEXES
ABSTRACT:
We will discuss the inorganic chemistry applications of advanced paramagnetic resonance techniques. These techniques include electron paramagnetic resonance (EPR), but rather than being performed at a fixed, low frequency (typically X-band, ~9 – 9.5 GHz) and a modest field sweep (typically 0 – 600 mT), the technique of interest involves variable, high frequencies (up to 1 THz) and field sweeps from zero up to 36 T This technique is referred to as high-frequency and -field EPR (HFEPR). Another technique is far-infrared magnetic resonance (FIRMS), which involves fixed external fields from 0 – 7 T, with FIR frequencies in the range of 20 – 200 cm-1 (or higher using a conventional FTIR). HFEPR and FIRMS are applied to high-spin (defined here for EPR purposes as S > 1/2) mononuclear transition metal ion complexes. Particular emphasis will be placed on those ions that belong to the non-Kramers (integer-spin) class and are typically “EPR-silent” at X-band due to large magnitude zero-field splitting (zfs). Classic examples of this type include: V3+ (3d2, S = 1), Mn3+ (3d4, S = 2), Fe2+ (3d6, S = 2), and Ni2+ (3d8, S = 1). From among these ions, Mn3+ will be the primary example (see Figure 1). HFEPR is also useful for investigating high-spin Kramers-type (half integer-spin) ions characterized by large zero-field splitting. Examples of these are Cr3+ (3d3, S = 3/2), Fe3+ (3d5, S = 5/2), and Co2+ (3d7, S = 3/2), of which the last will be used for illustration. The meaning and utility of the parameters extracted by HFEPR/FIRMS will be explained. This information, in concert with quantum chemical theory, helps understand the electronic structure transition metal ion complexes both as models for enzymatic active sites and as building blocks for molecular (single ion) magnets.
The Catalyst 