The first two transition metal compounds incorporating triazole-nitronyl-nitroxide radicals as ligands have been synthesized. These compounds are [Cu(4-Me-3-Nit-trz)(4)](ClO4)(2) (1) and [Ni(4-Me-3-Nit-trz)(4)](ClO4)2 (2) with 4-Me-3-Nit-trz = 2-(3-[4-methyl-1,2,4-triazolyl])-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide. Compound 1 crystallizes in the triclinic system, space group P (1) over bar. The lattice parameters are a = 9.742(2) Angstrom, b = 12.214(12) Angstrom, c = 12.981(4) Angstrom, alpha = 67.19(4)degrees, beta = 81.48(2)degrees, and gamma = 79.24(4)degrees, with Z = 1. The structure consists of centrosymmetrical [Cu(4-Me-3-Nit-trz)(4)]](2+) cations and noncoordinated perchlorate anions. The Cu-II ion is in an N4O2 elongated tetragonal environment with two oxygen atoms of two nitroxide groups occupying the apical positions. Within the lattice the cations form infinite chains with short intermolecular contacts involving the nitronyl-nitroxide moieties of two adjacents cations. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization at 2 K have been investigated. Both intermolecular antiferromagnetic and intramolecular ferromagnetic interactions are operative. A theoretical model has been developed to interpret quantitatively the magnetic data, which allows us to determine the values of the interaction parameters.