Singlet-triplet ground state degeneracy of phosphoryl biradicals

Summary form only given. We present the preparation and characterization of a phosphoryl biradical with a low-energy triplet state. Biradical 1 is prepared via photoinduced reduction of the corresponding bisphosphinic chloride and represents a first example of a high-spin molecule consisting of a m-phenylene unit with pendant radical centers on a second-row atom. The zero-field splitting parameters determined by ESR spectroscopy are |D/hc|=0.0120 cm/sup -1/ and |E/hc|=0.0015 cm/sup -1/. Variable temperature experiments reveal that the singlet-triplet energy gap is less than 10 cal/mol and demonstrate the versatility of m-phenylene as a ferromagnetic coupling unit, even for second row radical centers.