Moderate ferromagnetic exchange between copper(II) and a nitronyl nitroxide in a square-pyramidal adduct. MO interpretation of the mechanism of exchange in copper(II)-nitroxide complexes

Bis(trifluoroacetylacetonato)copper(II), Cu(tfac),, reacts with the nitronyl nitroxide radical 2,4,4,5,5-pentamethyl-4,5-dihydro- 1 H-imidazolyl-I-oxy 3-oxide, NITMe, to yield a square-pyramidal adduct of formula C~(tfac)~.N1TMeT. he X-ray crystal structure shows that it crystallizes in the space group Pi, with a = 10.1 19 (5) 4, b = 12.159 (6) A, c = 11.814 (5) A, a = 115.13 (I)O, /3 = 85.30 (I)O, y = 68.42 (1)O, and Z = 2. The distance of the copper ion from the oxygen of the axial NITMe is 2.303 A. The magnetic data shows that the coupling is ferromagnetic, with a singlet-triplet splitting of 65 * 5 cm-I. Structural-magnetic correlations for copper(I1)-nitroxide complexes have been established through extended Hiickel calculations.