Electron Spin Resonance and Structure of the BF2 Radical

The BF₂ radical has been detected and its structure determined from observation of the electron spin resonance of >γ‐irradiated molecules of BF₃ trapped in the xenon matrix at 4.2°K. Hyperfine structure of both B and F was resolved and analyzed. The isotropic coupling constants are: for ¹⁰B, 277.98 Mc/sec; for ¹¹B, 826.24 Mc/sec; and for ¹⁹F, 532 Mc/sec. Analysis of the hyperfine structure shows that the unpaired electron is in the $\sigma$ system, that 93% of the electron spin density is in a nonbonding ${\mathrm{sp}}_2$ hybrid on the B, and that the remaining 7% is in hybridized bonding orbitals of the two F atoms. The ${\mathrm{sp}}_2$ hybrid of the unpaired electron on the B has 44% $\text{2s}$ character and 56% $\text{2p}$ character. This orbital is in the molecular plane. The bond angle derived from the hybridization is 112°.