Abstract Co(II), Ni(II), Zn(II), and Cd(II) complexes of sulfadiazine (HSD) were prepared and characterized by spectroscopic data. For [Cd(SD) 2]·2H 2O the crystal and molecular structure is reported. The compound crystallizes in the monoclinic C2/c space group with Z = 4, in a cell of dimensions a = 19.879(3), b = 8.730(3), c = 16.538(3) Å, β = 122.15(2)°. Least-squares refinement of 2019 reflections [I⩾2σ(I)] gave a final R = 0.034. The structure consists of a monodimensional polymeric chain running along the b axis in which the cadmium atom is coordinated to two sulfonamido and two amino nitrogens from four symmetry-related SD anions. The coordination geometry around the metal is distorted tetrahedral. Hydrogen bonds involving the water molecule contribute to crystal stability.