Zinc and mercury complexes of benzil bis(4-methyl-3- thiosemicarbazone) David G. Calatayud 1 , Elena López-Torres, M. Antonia Mendiola ⇑ Departamento de Química Inorgánica, C/Francisco Tomás y Valiente 7, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain article info Article history: Received 22 July 2015 Accepted 6 September 2015 Available online 12 September 2015 Keywords: Bis(thiosemicarbazone) ligands Mercury(II) complexes Zinc(II) complexes X-ray crystallography 199 Hg NMR abstract The ligand benzil bis(4-methyl-3-thiosemicarbazone), LMe 2 H 4 , reacts with zinc and mercury nitrates, both in the presence or in the absence of lithium hydroxide. Complexes containing a neutral or a doubly deprotonated ligand, depending on the reaction conditions, have been prepared. In all the complexes, the bis(thiosemicarbazone) acts as a N 2 S 2 tetradentate ligand and in complex 4 probably also as a bridge through the sulfur atom leading to a dinuclear structure, while complex 3 is a monomer with a water molecule coordinated to the zinc atom in a penta-coordinated environment. Complexes 1 and 2 contain monodentate nitrato ligands in a hexa-coordinated structure, which is confirmed by the crystal structure of complex 2, [Hg(LMe 2 H 4 )(NO 3 ) 2 ]. The complexes have been thoroughly characterized by elemental analysis, mass spectrometry, FTIR and 1 H, 13 C and 199 Hg NMR spectroscopy and in the case of complex 2, also by single crystal X-ray diffraction. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Thiosemicarbazones, TSCs, are ligands of great interest, due to their versatility as donor systems, the variety of chemical species that form [1,2], the wide and important type of reactions that can lead and their biological, structural and optical properties [3– 5], which are normally increased in bis(thiosemicarbazones), since they form very stable complexes with metal ions due to its capac- ity to form several five-member chelate rings. All of this makes that their pharmacological properties and coordinative behavior towards transition metal ions are widely studied. Moreover, cop- per(II) bis(thiosemicarbazonate) complexes have been explored as radiopharmaceuticals for positron emission tomography (PET) over the last decade [6–8]. The selective detection of heavy and toxic metal ions in the background of biologically relevant metal ions is important with respect to human health and the environ- ment. Therefore, development of chemical turn-on sensors for the selective and sensitive determination of toxic metals [9], such as copper [10] or mercury [11–13] in aqueous medium is of crucial importance. However, very few mercury(II) complexes with thiosemicarbazones are known, although they are potentially good candidates to give stable complexes with this soft and toxic ion. Following our interest in the coordinating behavior of symmet- ric and dissymmetric bis(thiosemicarbazone) ligands with different metals with potential biological applications such as nickel [14], copper [15], zinc [14,16] or tin [17] or with demon- strated toxicity as cadmium [14,18,19], lead [20] and mercury [21,22], in this paper we report an extension of our previous work with the symmetric ligand benzil bis(4-methyl-3-thiosemicar- bazone), LMe 2 H 4 . This ligand has shown a versatile behavior with toxic metals such as PbPh 2 2+ and cadmium(II) and, depending of the pH, it acts as neutral or doubly deprotonated ligand. In all the complexes behaves as a tetradentate quelate donor and in some complexes also as a bridge through a sulfur atom, leading to the formation of dimeric species [17,19,20]. In this paper, the synthesis and spectroscopic characterization of four new complexes from zinc(II) and mercury(II) nitrates, and the crystal structure of the mercury complex, [Hg(LMe 2 H 4 ) (ONO 2 ) 2 ], 2, are reported. 2. Experimental 2.1. Materials and general methods All reagents were obtained from standard commercial sources and were used as received. Caution! Mercury is highly toxic cumu- lative poison, and their compounds should be handled carefully. Microanalyses were carried out using a LECO CHNS-932 Elemental Analyzer. FTIR spectra in the 4000–400 cm À1 range were recorded as KBr pellets on a Jasco FT/IR-410 spectrophotometer. Fast atom bombardment mass spectra were recorded on a VG Auto Spec instrument using Cs as the fast atom and m-nitrobenzylalcohol http://dx.doi.org/10.1016/j.poly.2015.09.016 0277-5387/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 91 497 4844; fax: +34 914974833. E-mail address: antonia.mendiola@uam.es (M.A. Mendiola). 1 Present address: Department of Chemistry, University of Bath, Claverton Down, BA2 7AY, United Kingdom. Polyhedron 101 (2015) 133–138 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly