title: Electron spin relaxation of a boron-containing heterocyclic radical.
abstract: Preparation of the stable boron-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), by frustrated Lewis pair chemistry has been reported recently. Electron paramagnetic resonance measurements of this radical were made at X-band in toluene:dichloromethane (9:1) from 10 to 293K, in toluene from 180 to 293K and at Q-band at 80K. In well-deoxygenated 0.1mM toluene solution at room temperature hyperfine splittings from11B, four pairs of1H, and 5 pairs of19F contribute to an EPR spectrum with many resolved lines. Observed hyperfine couplings were assigned based on DFT calculations and account for all of the fluorines and protons in the molecule. Rigid lattice g values are gx=2.0053, gy=2.0044, and gz=2.0028. Near the melting point of the solvent 1/Tmis enhanced due to motional averaging of g and A anisotropy. Increasing motion above the melting point enhances 1/T1due to contributions from tumbling-dependent processes. The overall temperature dependence of 1/T1from 10 to 293K was modeled with the sum of contributions of a process that is linear in T, a Raman process, spin rotation, and modulation of g anisotropy by molecular tumbling. The EPR measurements are consistent with the description of this compound as a substituted aromatic radical, with relatively small spin density on the boron.
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Eaton
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
authors.forename: Kirby
authors.initials: K
authors.lastname: Huber
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
authors.forename: Hanan
authors.initials: H
authors.lastname: Elajaili
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: McPeak
authors.affiliation: Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA. Electronic address: geaton@du.edu.
authors.forename: Gareth R
authors.initials: GR
authors.lastname: Eaton
authors.affiliation: University of Toronto, 80 St. George St, Toronto, ON M5S 3H6, Canada.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Longobardi
authors.affiliation: University of Toronto, 80 St. George St, Toronto, ON M5S 3H6, Canada.
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Stephan
keywords: Boron; Hyperfine coupling constants; Spin lattice relaxation; Spin-spin relaxation