The complex Mn(NITImH)(3)(ClO4)(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 P21/n, with a=15.832(3)Angstrom, b=10.346(3)Angstrom, c=26.029(4)Angstrom, beta=106.78(1)degrees 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 T-chi product is 2.91cm(3).K.mol(-1) at 300K, reaches a plateau (1.00 cm(3).K.mol(-1)) between 65 and 15K, then decreases abruptly. The experimental magnetic data were fit assuming identical nitroxide-manganese(II) coupling J=-53cm(-1) based on the isotropic model H=-2 Sigma J(ij)S(i)S(j) associated with an intermolecular antiferromagnetic interaction Z’J’=-1.4cm(-1) based on the molecular field approximation and g=2.06.