Metal complexation reactions of N-t-butyl-N-oxidanyl-2-amino(nitronyl nitroxide) diradical (1) with M-(hfac)(2) (M: Mn or Cu) were investigated. These reactions were found to be very sensitive to the type of metal ion employed. Complex [Mn(hfac)(2)center dot 1], consisting of Mn(hfac)(2) and diradical 1, was readily prepared by mixing the components. However, the reaction of Cu(hfac)(2) with 1 or N-t-butyl-N-oxidany1-2-amino(iminonitroxide) diradical (2) involved the reduction of the diradical to the N-t-butyl-Noxidanide-2-amino(iminonitroxide) radical anion (3) and finally produced the polymer-chain complex [Cu-2(hfac)(2)center dot 3(2)center dot Cu(hfac)(2)](n). The structures of these complexes were elucidated by X-ray analysis, and their magnetic properties were investigated in detail. The temperature dependence of chi T-p (chi(p): magnetic susceptibility) for [Mn(hfac)(2)center dot 1] exhibited a strong antiferromagnetic interaction (H = -2JS(1)center dot S-2, J/k(B) = -217 K) between the Mn(II) spin (S = 5/2) and the diradical 1 spin (S = 1). However, the chi T-p-T plots for [Cu-2(hfac)(2)center dot 3(2)center dot Cu(hfac)(2)](n) indicated the presence of several magnetic interactions: a large ferromagnetic interaction (f/k(B) = 510 K) between iminonitroxide 3 and the imino-coordinating Cu(II) atom, a moderately large ferromagnetic interaction (j/k(B) = 58 K) between the iminonitroxide and (iminonitroxide oxygen)-coordinating Cu(hfac)(2), and a weak antiferromagnetic interaction (j/k(B) = -1.4 K) between the two Cu(hfac)-3 moieties within a Cu2O2 square.