New iron(III) and nickel(II) chelates were synthesized by template reaction of 2,4-dihydroxy- and 2-hydroxy-4-methoxy-benzophenone S-methylthiosemicarbazones with 2-hydroxy- and 5-bromo-2-hydroxy-benzaldehydes. The template complexes were isolated as stable solids and characterized by elemental analysis, conductivity and magnetic measurements, IR, 1H NMR, UV-Visible, and mass spectra. The crystal structure of N1-(2-hydroxy-4-methoxyphenyl)(phenyl)methylene-N4-(2-hydroxy-phenyl)methylene-S-methyl-thiosemicarbazidato-Fe(III) was determined by X-ray diffraction. A five-coordinate, distorted square-pyramidal geometry was established crystallographically for the iron(III) complex. Cytotoxicity and proliferation properties were determined using human erythromyeloblastoid leukemia and HL-60 mouse promyelocytic leukemia cell lines. For K 562 and HL-60 cells, compounds 1a and 2b were found to be cytotoxic at concentrations of 10 and 20 g mL-1.