New di- and triorganotin(IV) complexes of tripodal Schiff base ligand containing three imidazole arms: Synthesis, structural characterization, anti-inflammatory activity and thermal studies Mala Nath a, * , Pramendra Kumar Saini a , Ashok Kumar b a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, Uttarakhand, India b Department of Pharmacology, LLRM Medical College, Meerut 250004, India article info Article history: Received 23 December 2009 Received in revised form 5 February 2010 Accepted 10 February 2010 Available online 16 February 2010 Keywords: Tripodal Schiff base Organotin(IV) compounds Anti-inflammatory activity Thermal studies abstract Some new tri- and diorganotin(IV) complexes of the general formula, R 3 Sn(H 2 L) and R 0 2 Sn(HL) [where R = Me, n-Pr, n-Bu and Ph; R 0 = Me, n-Bu, Ph and n-Oct; H 3 L = Schiff base (abbreviated as tren(4-Me-5- ImH) 3 ) derived from condensation of tris(2-aminoethyl)amine (tren) and 4-methyl-5-imidazolecarboxal- dehyde (4-Me-5-ImH)] have been synthesized. The coordination behaviour of Schiff base towards organotin(IV) moieties is discussed on the basis of infrared and far-infrared, 119 Sn Mössbauer and multi- nuclear ( 1 H, 13 C and 119 Sn) magnetic resonance (NMR) spectroscopic studies. Thermal studies of all of the synthesized organotin(IV) complexes have been carried out using TG, DTG and DTA techniques. The res- idues thus obtained from pyrolysis of the studied complexes have been characterized by X-ray powder diffraction analysis and IR. The newly synthesized complexes have been tested for their anti-inflamma- tory activity and toxicity (LD 50 ). Ó 2010 Published by Elsevier B.V. 1. Introduction There has been considerable interest in the synthesis of ligands containing an imidazole moiety because of its biological signifi- cance in a variety of metalloproteins, especially heme proteins. Tri- podal hexadentate Schiff base ligands formed by the condensation of polyfunctional amine such as tris(2-aminoethyl)amine (tren) and imidazolecarboxaldehyde are capable of chelating a transition metal via imine and deprotonated imidazole N donors. The presence of ionizable protons on the imidazole rings of the several imidazolecarboxaldehyde precursors and substituted imidazole- carboxaldehyde precursors afforded an opportunity to synthesize the complexes of transition metals in various combinations of oxi- dation and spin states of metal atom and protonation states of the ligands [1–6]. The tripodal Schiff base ligand containing three imidazole groups is the first ligand affording spin-cross over (SCO) behavior for both the Fe II and Fe III oxidation states, and 2D extended network structure based on imidazole–imidazolate hydrogen bonds produces elastic interactions between SCO sites. These ligands can bind to iron with or without ionization of the imidazole ring. It has also been reported that the degree of depro- tonation at imidazole moiety and the substituent effect control the oxidation and spin states [1–9]. A number of iron(II, III) complexes of tripodal ligands formed by condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 2-imidazolecarboxaldehyde/1-methyl-2- imidazolecarboxaldehyde/2-methyl-4-imidazolecarboxaldehyde/ 4-methyl-5-imidazolecarboxaldehyde have been reported to show low-spin–high-spin cross over phenomenon [1–10]. Further, the counter anion has been reported to modify the SCO behavior of these 2D complexes through interlayer elastic interactions [8]. Asymmetric tripodal iron complexes of tren and mixtures of alde- hydes have also been synthesized and characterized [11]. Re- cently, Cu(II) and Ni(II) complexes of the type, [MH 3 L](ClO 4 ) 2 (where M = Cu(II) and Ni(II), H 3 L = Schiff base derived from the condensation of tren and 4-methyl-5-imidazole-carboxaldehyde) have also been reported [12]. The structures of these two com- plexes are isomorphous with each other and with the iron(II) complex [6]. Further, a neutral complex CuHL and the ionic com- plex Na[NiL] have also been reported [12]. However, complexes of this type of tripodal Schiff base ligands with main group metals have not been synthesized, and also organotin(IV) complexes of such ligands have not been reported so far. Recently, the chemistry of organotin(IV) complexes of Schiff bases has stemmed from their antitumour [13–17], antimicrobial [17–20], antinematicidal [21], anti-insecticidal [21] and anti- inflammatory activities [19]. Several organotin(IV) derivatives of dipeptides have been found to exhibit potent anti-inflammatory activity [22–28]. Since fast and effective relief of pain and inflam- mation in humans with minimum side effects continues to be a 0022-328X/$ - see front matter Ó 2010 Published by Elsevier B.V. doi:10.1016/j.jorganchem.2010.02.009 * Corresponding author. Tel.: +91 1332 285797; fax: +91 1332 73560. E-mail address: malanfcy@iitr.ernet.in (M. Nath). Journal of Organometallic Chemistry 695 (2010) 1353–1362 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem