A magnetic resonance study of complex formation between the neutral phenalenyl radical and alkali metal ions in dilute alcohol solutions

In previous work from our laboratories we have characterized the molecular motion of phenalenyl in the supercage of cation-exchanged X- and Y-zeolites using continuous wave-electron paramagnetic resonance (CW-EPR) and pulsed- EPR techniques. The trends in activation energies with cation size and Lewi s acidity and in EPR line widths provided circumstantial evidence for a wea k covalent interaction between the neutral phenalenyl alpha-system and the cations. This work on phenalenyl and alkali metal cations in solution provi des Li-7 nuclear magnetic resonance (NMR) and CW-EPR spectroscopic evidence for this type of interaction. Moreover, to our knowledge it is the first e xample of a neutral radical-alkali metal ion complex in solution. In rigoro usly dried alcohol solutions this interaction results in the formation of a complex between neutral phenalenyl and Li+ or Na+, which is in equilibrium with solvated phenalenyl and the respective cation. The forward and revers e rates for this equilibrium for Li+ and phenalenyl in methanol allow for a n analysis of Li-7 NMR data acquired at 320 K in the fast exchange limit, w hich yields an equilibrium constant of 29 +/- 4 M-1. Analysis of the CW-EPR data for Na+ and phenalenyl in methanol at 295 K in the slow exchange limi t produces an isotropic Na hyperfine frequency for the phenalenyl-Na+ compl ex of 4.2 +/- 0.1 MHz. This hyperfine frequency reflects a Fermi contact wi th the Na nucleus of ca. 0.5% of the nonbonding pi-electron spin density fr om phenalenyl.