1. Introduction Cisplatin, cis-[Pt(NH 3 ) 2 Cl 2 ], is one of the most important chemotherapeutic agents used in the treatment of a wide variety of solid tumors. Despite the important contribution of cisplatin in cancer therapy, its use presents some limitations such as development of resistance and severe side effects, such as, nephrotoxicity, ototoxicity and neurotoxicity [1,2]. These considerations have stimulated the search for new platinum complexes to be used as anticancer agents. Thus, in an attempt to reduce toxicity and widen the spectrum of activity of cisplatin and its analogous, thousands of platinum complexes have been prepared by varying the nature of the leaving groups and the carrier ligands [1-3]. The use of different types of organic ligands can modify the biological activity of the complexes and, for this reason, the use of hydrazides is very interesting. The properties of hydrazides are of interest due to their biological activities and their use as metal extracting agents. The formation of metal complexes plays an important role in the growth of their biological activity [4-7]. Hydrazides successfully provide various active potential donor sites (C=O, NH and NH 2 ) and, therefore, many coordination compounds containing hydrazides have been synthesized and characterized [8-11]. Hydrazides and their metallic complexes show fungicide and antibacterial activity [12-14]. Particularly, platinum complexes with hydrazides derived from benzoic acid showed strong growth inhibitory effect in leukemia cells in vitro, not verifed with the free ligands [12]. In view of the biological activities of hydrazides and their metallic compounds, this paper reports on the synthesis and characterization of new complexes. The compounds were characterized by elemental analysis, NMR, IR and UV-Vis. The cytotoxic activity of the synthesized compounds was also evaluated. Central European Journal of Chemistry * E-mail: wg@iqufu.ufu.br 1 Chemistry Institute, Federal University of Uberlândia, Campus Santa Mônica, 38.400-902 Uberlândia - MG, Brazil 2 Chemistry Department, Federal University of Minas Gerais, Campus Pampulha, 31.270-901 Belo Horizonte - MG, Brazil Gustavo D. de Souza 1 , Mônica A. Rodrigues 1 , Lucianno E. Fernandes 1 , Priscila P. Silva 2 , Reinaldo Ruggiero 1 , Elene C. Pereira-Maia 2 , Wendell Guerra 1* Complexes of platinum and palladium with 4-nitrobenzoic hydrazide: synthesis and cytotoxic activity Research Article Abstract: © Versita Sp. z o.o. Received 8 June 2012; Accepted 4 October 2012 Keywords: Platinum complexes • Palladium complexes • Hydrazones • Cytotoxic activity New complexes of platinum and palladium were isolated with 4-nitrobenzoic hydrazide (4-NH) and characterized by spectroscopic techniques. Results show that the ligand is coordinated to metallic ions by the basic nitrogen of NH 2 group and have the general structure cis-[M(4-NH) 2 X 2 ] where M= Pt or Pd and x = Cl or I. The compound III, [Pt(4-NH) 2 I 2 ], was found to display cytotoxicity (IC 50 = 0.96 µmol L -1 ) against the K562 tumoral cell line. This complex is signifcantly more cytotoxic than cisplatin. Cent. Eur. J. Chem. • 11(2) • 2013 • 290-294 DOI: 10.2478/s11532-012-0156-5 290