EPR spectra of bis(nitroxyl) adducts of bis(hexafluoroacetylacetonato)manganese(II)

The EPR spectra of the bis(nitroxy1) adducts Mn(F6acac)2(tempo)2(I ) and Mn(F&CaC)2(prOXyl)2 (11) (F6acac = hexafluoroacetylacetonato; tempo = 2,2,6,6-tetramethylpiperidinyl-1 -oxy; proxyl = 2,2,5,5-tetramethylpyrrolidinyl- 1 -oxy) were recorded in the range of temperature 4.2-300 K. The spectra are temperature-dependent, in agreement with previous magnetic susceptibility data, which indicated the thermal population of one S = 3/2, two S = 5 / 2 , and one S = 7/2 total spin states. At low temperature, single-crystal spectra were obtained at both X- and Q-band frequencies, which allowed us to obtain the D tensors for the quartet states of both I and 11. Polycrystalline powder spectra of the two compounds at room temperature provided an estimate of D and E/D for the first excited sextuplet. These data are used to discuss the isotropic exchange and the anisotropic spin-spin interaction in I and 11.