Isolation and X‑ray Crystal Structures of Triarylphosphine Radical Cations

Salts containing triarylphosphine radical cations 1•+ and 2•+ have been isolated and characterized by electron paramagnetic resonance (EPR) and UV–vis absorption spectroscopy as well as single-crystal X-ray diffraction. Radical 1•+ exhibits a relaxed pyramidal geometry, while radical 2•+ becomes fully planar. EPR studies and theoretical calculations showed that the introduction of bulky aryl groups leads to enhanced p character of the singly occupied molecular orbital, and the radicals become less pyramidalized or fully flattened.