Crystal structure and ferromagnetic behavior of a cis-Co(II) complex with nitronyl nitroxide

Bis(hexafluoroacetylacetonate)cobalt(II), Co(hfac)(2), reacted with the nit ronyl nitroxide radical 2-(4-methylphenyl)-4,4,5,5-tetramethylimidazoline-1 -oxyl-3-oxide, NITPhMe, to yield an octahedral adduct of formula Co(hfac)(2 )(NITPhMe)(2). The X-ray crystal structure shows that it crystallizes in th e space group <P(1)over bar>, with a = 9.837(3), b = 11.618(3), c = 20.502( 4) Angstrom, alpha = 81.22(2), beta = 87.93(2), gamma = 72.24(3)degrees, V = 2205(1) Angstrom(3), Z = 2. The mechanism of ferromagnetic exchange betwe en cobalt(II) and the radical can be qualitatively understood in terms of a charge-transfer interaction (J being 25.7 cm(-1), the Hamiltonian is writt en in the form H = -2J(S-Rad1. S-Co + S-Co. S-Rad2)).