With the radical 2,5-dihydro-4,5,5-trimethyl-2,2-bis(2-pyridyl)imidazole-l-oxyl (L) a series of transition metal complexes have been prepared : [ML(2)](SbF6)(2) with M(2+) = Mn2+ (1), Fe2+ (2), Co2+ (3), Ni2+ (4), CU2+ (5), and Zn2+ (6), Cu(L)(Cl)(2)(MeOH) (7), and Cu(L)SO4 . H2O (8). The structures of 1, 3, and 6 were determined by X-ray structural analyses. In these compounds the tridendate L is coordinated to the metal ion by the two pyridine nitrogen donors and by the oxygen atom of the nitroxide group. The N-O bond distances are 1.25(2) Angstrom (1), 1.267(13) Angstrom (3), and 1.260(11) Angstrom (6). The M-O-N angles are 117.0(10)degrees (1), 114.5(8)degrees (3), and 114.2(7)degrees (6). Crystal data : space group P2(l)/n, for 1, 3, and 6; compound 1, a = 10.806(3) Angstrom, b = 14.101(6) Angstrom, c 14.253(4) Angstrom, beta = 108.82(2)degrees, V = 2055.7(12) Angstrom, Z = 2, R(1) = 0.0677, wR(2) = 0.1512. Compound 3, a = 10.761(4) Angstrom, b = 14.253(6) Angstrom, c = 14.108(5) Angstrom, beta = 111.16(3)degrees, V = 2017.9(13) Angstrom(3), Z = 2, R(1) = 0.0702, wR(2) = 0.1460; compound 6, a = 10.788(2) Angstrom, b = 14.147(3) Angstrom, c = 14.196(3) Angstrom, beta = 109.93(3)degrees, V = 2036.8(7) Angstrom(3), Z = 2, R(1) = 0.0573, wR(2) = 0.1194. Magnetic measurements of 1, 2, 5, and 8 show strong antiferromagnetic interaction between the spin of the metal ion and the spin of the radical which increases at lower temperatures. For 6 the magnetic moment corresponds to two noninteracting spins in the temperature range 60-300 K.