Homobimetallic organotin(IV) complexes with hexadentate Schiff base: Synthesis, crystal structure and antimicrobial studies Shaukat Shujah a, * , Zia-ur-Rehman b , Niaz Muhammad c , Afzal Shah b , Saqib Ali b, ** , Auke Meetsma d , Zahid Hussain e a Department of Chemistry, Kohat University of Science & Technology, Kohat 26000, Pakistan b Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan c Department of Chemistry, Abdul Wali Khan University, Mardan, Pakistan d Crystal Structure Center, Chemical Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands e Institute of Industrial Biotechnology, G.C. University, Lahore, Pakistan article info Article history: Received 18 October 2013 Received in revised form 24 January 2014 Accepted 18 February 2014 Keywords: Homobimetallic Pentacoordinated diorganotin(IV) Supramolecular Hexadentate Schiff base Biological activity abstract This article describes the synthesis of four new homobimetallic organotin(IV) complexes: [Et 2 Sn] 2 L(1), [Bu 2 Sn] 2 L(2), [Oct 2 Sn] 2 L(3) and [BuClSn] 2 L(4)(H 4 L ¼ N 10 ,N 60 -bis(5-bromo-2-hydroxybenzylidene)adi- podihydrazide) and their structural elucidation by means of elemental analysis, mass spectroscopy, FT-IR, NMR ( 1 H, 13 C, 119 Sn) and single crystal X-ray analysis. Spectroscopic studies indicate coordination of hexadentate ligand to the diorganotin(IV) moieties via ONOeONO donor sites and pentacoordinated tin centers. Single crystal X-ray analysis of (1) and (2) revealed homobimetallic nature of complexes with each Sn atom in a distorted square pyramidal coordination geometry. Packing diagrams suggest the seminal role of Sn/N and Br/p interactions in generating supramolecular assembly. The synthesized compounds were screened for their antimicrobial activity and cytotoxicity. Compound (2) exhibit highest activity against several pathogenic microbes. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The study of organotin(IV) complexes of Schiff bases has been a subject of interest mainly due to their wide applications in various fields like catalysis, biotechnology, analytical and medicinal chemistry [1e6]. Several organotin(IV) hydrazones have been investigated for their structural diversity [7,8]. The tin atom in these complexes is usually pentacoordinate with a trigonal bipyramidal or square pyramidal geometry and can act as a Lewis acid. The coordination number can be increased by addition of molecules with donor atoms and the geometry around tin changes to pentagonal bipyramidal [9]. Moreover, supramolecular architec- tures can be achieved through self-assembly of molecules by hydrogen bonding, hydrophobic, hydrophilic effects, electrostatic and pep interactions etc. [10,11]. The metal complexes of diacylhydrazones exhibit pronounced biological and pharmaceutical activities as antitumor, antimicro- bial, antituberculosis and antimalarial agents [12e17]. The presence of two coordinating units connected by hydrocarbon linkers with varying degrees of flexibility in the ligand may yield supramolec- ular architectures such as double helices, grids, racks or coordina- tion polymers [18]. However, few studies have been reported for the synthesis of bis-diorganotin(IV) complexes of diacylhydrazones with double set of ONO donor atoms [19]. The diacylhydrazones can either act as monobasic bis-bidentate, monobasic bis-tridentate, dibasic bis-tridentate chelators or they may form polymeric chain [20]. In continuation with our studies on diorganotin(IV) complexes derived from ONO donor ligands [21,22], and triggered by the need for potent antimicrobial agents to mitigate or eliminate the in- fections, we report herein the synthesis, spectroscopic character- ization and antimicrobial activities of four new centrosymmetric homobimetallic organotin(IV) derivatives of N 10 ,N 60 -Bis(5-bromo- 2-hydroxybenzylidene)adipodihydrazide, a potential tetrabasic * Corresponding author. Tel.: þ92 0333 5203621. ** Corresponding author. Tel.: þ92 5190642208; fax: þ92 51 2873869. E-mail addresses: shaukat.shujah@yahoo.com (S. Shujah), drsa54@yahoo.com (S. Ali). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.02.010 0022-328X/Ó 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 759 (2014) 19e26