Cobalt(III) complexes, of two potentially pyrazole-derived bidentate ligands (with one ambidentate donor site), 3,5-dimethyl-1-(N-methyl/ethyl)thiocarbamylpyrazole (HL 1 for N-methyl, HL 2 for N-ethyl) have been synthesized and characterized by elemental analyses, IR, UV-Vis and 1 H NMR spectral studies. The structure of Co(L 2 ) 3 has been determined by single-crystal X-ray diffraction studies. The complex (triclinic, space group P1) has a distorted octahedral structure with the ambidentate ligands coordinated to the Co(III) ion as uninegative bidentate chelating agents via the pyrazole ring nitrogen (tertiary) and the thiocarbamyl iminyl nitrogen atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar bidentate ligands. © 2000 Elsevier Science B.V.