The complex Mn(NITImH)3(CIO4)2[NITImH═2-(2-imidazolyl)-4,4,5,5,-tetramethyl-4,5-dihydro- 1H-imidazolyl-1-oxy)] has been synthesized. It crystallizes in the monoclinic space group P2t/n, with a=15.832(3)Å b = 10.346(3)Å, c = 26.029(4)Å β = 106.78(1)° and Z = 4. The crystal structure consists of [Mn(NITImH)3]2+cations and non-coordinated perchlorate anions. Each NITImH nitronyl nitroxide radical is bis-chelated to the manganese(II) ion through an oxygen atom of one of its NO groups and a nitrogen atom of the imidazolyl substituent. The coordination geometry around the manganese(II) ion is slightly distorted from octahedral. The perchlorate anions weakly hydrogen bond the [Mn(NITImH)3]2+cations in a tridimensional network. Cryomagnetic investigations in the range 2–300K revealed a strong antiferromagnetic behavior. The χT product is 2.9 lcm3.K.mol−1at 300K, reaches a plateau (1.00 cm3.K.mol−1) between 65 and 15K, then decreases abruptly. The experimental magnetic data were fit assuming identical nitroxide-manganese(II) coupling J = −53cm−1based on the isotropic model H= −2ΣJijSiSjassociated with an intermolecular antiferromagnetic interaction Z'J' = −1.4cm−1based on the molecular field approximation and g = 2.06.