Syntheses, structural characterization, crystal engineering, and variable-temperature magnetic study at fixed field strength of a novel dicyanamide bridged three-dimensional manganese(II)-nitronyl nitroxide compound, [Mn-II(NIT-tz)(dca)(2)] (1), (NIT-tz = 2-(2-thiazole)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide, a new Ullman type radical) have been described. The compound crystallizes in the orthorhombic P2(1)2(1)2(1) space group with the following unit cell parameters: a = 11.015(2) Angstrom, b = 12.6134(14) Angstrom, c = 13.7652(9) Angstrom, and Z = 4. In this complex, the radical behaves as a bidentate chelating ligand, while four single end-to-end dicyanamide (dca) units construct the three-dimensional structure. Inside the structure, there exist diamond-shaped channels, spiral networks, and helical chains. Variable-temperature (5-300 K, 1 T) magnetic susceptibility data reveal the existence of antiferromagnetic interaction in this molecule. The magnetic behavior is explained by considering the exchange-coupled manganese(Il)-radical system, which is subjected to the Mn-II-dca-Mn-II intermolecular interactions (H = -2JS(1)(.)S(2) - 2zJS). The least-squares fitting of the data results J = -73 cm(-1), g = 1.99, and J = -0.17 cm(-1) (z = 4).