Synthesis, Characterization, and Biological Activity of Some Transition Metal Complexes of N-Benzoyl-N′-2-thiophenethiocarbohydrazide

In the present study, Mn(II), Fe(II), Ni(II), and Cu(II) complexes of N-benzoyl -N′-2-thiophenethiocarbohydrazide (H2 BTTH) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, infrared, NMR, electronic, and ESR spectral studies. The complexes were found to have compositions [Mn(H BTTH)2], [Ni(BTTH)(H2O)2], [Cu(BTTH)], and [Fe(H BTTH)2EtOH]. The antibacterial and antifungal properties of H2 BTTH and its metal complexes have been screened against several bacteria and fungi. 1. Introduction The expansion of research in the coordination chemistry of nitrogen-sulphur donor ligands such as substituted thiosemicarbazides [1], thiosemicarbazones [2–4], and dithiocarbazates [5], during the recent years has been due to their remarkable antineoplastic activity against a variety of tumors [6] in addition to their applicable antifungal [7] and antibacterial [8] activities. Sulphur and nitrogen containing ligands and their transition metal complexes were also used as corrosion inhibitors [9, 10] and extreme pressure lubricant additives [11]. Keeping in view the above biological activity of the sulfur and nitrogen containing ligands, we planned to undertake the synthesis, characterization, antibacterial, and antifungal activity of N-benzoyl-N′-2-thiophenethiocarbohydrazide (H2 BTTH) (Figure 1) and its Mn(II), Fe(II), Ni(II), and Cu(II) complexes. This ligand is expected to form addition complexes without loss of protons, and deprotonated complexes by loss of one or both the hydrazinic protons. Figure 1: Structure of H 2BTTH. 2. Experimental 2.1. Starting Materials All the chemicals used were of analytical grade. Ammonium polysulphide [12] and carboxymethyl-2-thiophenedithioate [13] were prepared by literature methods. 2.2. Preparation of N-benzoyl-N′-2-thiophenethiocarbohydrazide (H2 BTTH) N-benzoyl-N′-2-thiophenethiocarbohydrazide (H2 BTTH) was prepared by mixing solutions of benzoic acid hydrazide (20？mmol) and carboxymethyl-2-thiophenedithioate (20？mmol) each dissolved separately in 50？mL of 0.5？N NaOH and allowing the mixture to stand at room temperature for 2？hrs. The product precipitated by adding dilute AcOH dropwise to the above ice-cold mixture, was filtered off, washed with H2O, dried, and recrystallized from EtOH. 2.3. Synthesis of [Mn(H BTTH)2] The complex [Mn(H BTTH)2] was prepared by boiling together the methanolic solutions (25？mL) of Mn(OAc)2 · nH2O (1？mmol) and H2BTTH (2？mmol) for 1？h under reflux. The precipitated complexes were filtered, washed with methanol, and dried in vacuo. 2.4. Synthesis of [Ni