ORGANOTIN(IV) COMPLEXES OF BIOLOGICALLY RELEVANT SCHIFF BASES AND HACROCYCLES

Abstract

Organotincompounds have been found to show a vast array of structural possibilities and multiple applications in various fields. The largest application of organotin compounds is as stabilizers for polyvinyl chloride (PVC) plastics where they act as an acid scavenger as well as antioxidant. Triorganotin(IV) compounds have been used as surface disinfectants, bacteriostates, antimicrobials, rodent-repellent, and hospital and veterinary disinfectants. Organotin(IV) compounds find extensive uses as catalysts in the manufacture of polyurethane foams and as curing agents for room temperature 'Vulcanization' of silicon rubbers. Organotin(IV) compounds have been used as agricultural biocides. A new dimension in the field of organotin chemistry is emergence of these compounds as potential metallopharmaceuticals among the class of metal-based non-platinum chemotherapeutics. Therefore, several organotin derivatives of the ligands having N, O or S donor atoms have been reported to exhibit antitumor activity, viz. carboxylic acid derivatives, pyrazoles, lupinylsulfide hydrochloride, heterocyclic thioamide and cyanooximates, etc. Furthermore, to explain the biological activity of organotin(IV) compounds, several studies revealed that the biological activity of these compounds may be due to the presence of easily hydrolysable groups (easily dissociable chelating ligands) yielding intermediates such as, RnSn(4-n)+ (n= 2 or 3) moieties, which may bind with DNA or proteins. Recently, organotin(IV) compounds are explored as single source precursors to produce nanoscale semiconducting materials, viz. tin particles/ tin sulfides/ tin(IV) oxide, by their pyrolysis. However, the nanoscale, semiconducting tin(IV) oxide, has its own technological importance. Schiff bases are the most important nitrogen donor ligands and are used towards a wide variety of metal ions. Schiff base ligands are one of the most widely used ligands due to ease of their formation, diverse properties, medicinal, biochemical and industrial applications, and therefore, they have played an important role in the development of coordination chemistry. Schiff base-metal complexes find importance in the number of interdisciplinary areas that include bioinorganic chemistry, magnetochemistry, catalysis, analytical chemistry, modification of polymers, 02 carrier and functional materials. In the n area of bioinorganic chemistry, Schiffbase-metal complexes represent synthetic models for the metal-containing sites in metalloproteins and enzymes. The field of macrocyclic chemistry has undergone enormous expansion in recent years and the coordination chemistry of macrocyclic ligands has evolved in to a fascinating area of current research interest. Complexes of porphyrins, corrins, and phthalocyanines have been investigated because of their relationto important naturally occurring species such as heme, cytochromes, and chlorophyll. The considerable interest in the field of macrocyclic chemistry in order to design new macrocyclic ligands with N, O, S-donor atoms is due to their high synthetic possibilities, greater coordination sites and their technological applications. In view of the wide range of applications of organotin(IV) compounds and the versatile coordination behavior of Schiff bases and tetraazamacrocyclic ligands, it was considered significant to synthesize, characterize, and biological activity of new organotin(IV) derivatives of these ligands. Further, it is important to study their thermal behaviour followed by the surface morphology determination of resulted residue in order to explore the synthesized compounds as single source precursors for the preparation of nanoscale semiconducting tin(IV) oxide. In order to maintain the clarity in the presentation, the work embodied in the thesis is systematically divided into the following chapters. First chapter of the thesis presents the general introduction and an overview of some important applications of organotin(IV) compounds, Schiffbases and macrocycles. A critical and comprehensive review of the available literature on the organotin(IV) complexes of Schiff bases and tetraazamacrocycles (nonporphyrin and nonphthalocyanine) with special reference to their synthetic methods, structural characterization and biological activity, if any, has also been presented. In addition to this, the applications of nanoscale Sn02 and important methods employed for the preparation of these nanoscale materials have also been included. Second chapter incorporates the details of make, purity and other specifications of the materials used in the present study. For the spectroscopic studies, viz. DART-mass, multinuclear and multidimensional NMR and 119Sn Mossbauer, of the synthesized organotin(IV) derivatives, the compounds have been sent to various Institutes/Universities in India/Abroad. Some of the synthesized compounds were sent to L. L. R. M. Medical College, Meerut (India) for their antiinflammatory and toxicity studies. The specifications of the instruments and the procedures used therein have been included. The details of procedure and equipments used for thermal studies of synthesized compounds have also been described. Third chapter deals with the synthesis and characterization of some new tri- and diorganotin(IV) complexes of the general formulae RnSn(L)m (n = 3, m = 1, R = Me, w-Bu and Ph; n = 2, m = 2, R = Me, n-Bu, n-Oct and Ph; HL = Schiff base derived from the condensation of 2-aminomethylbenzimidazole (ambmz) and salicylaldehyde) (Hsal-ambmz). The probable structure of the synthesized derivatives have been proposed on the basis of physico-chemical studies, viz., elemental analysis, molar conductance and UV-visible, infrared (IR), far-infrared (far-IR), multinuclear (!H, 13C and 119Sn) magnetic resonance spectral studies. On the basis of spectral studies, a fac- or wer-c/s-trigonal-bipyramidal structure, in which ligand is bidentate coordinating through phenolic oxygen and azomethine nitrogen atom, has been proposed for all triorganotin(IV) derivatives. Whereas a distorted octahedral environment around tin has been tentatively proposed for Ph3Sn(IV) derivatives in which either the ligand may act tridentate and coordinating also through N(imidazoie) along with Nfazomethine) and 0(Phenoiic) or one solvent molecule interact to the central tin atom. However, a distorted octahedral structure for R2Sn(L)2 (R = Me, n-Bu, n-Oct and Ph) have been proposed in which ligand coordinate through both the azomethine nitrogen and phenolic oxygen atom. Thermal studies of the synthesized complexes have been carried out in the temperature range 25-1000 °C using TG, DTG and DTA techniques. Mass loss consideration at main decomposition stages indicates the conversion of the complex to tin(IV) oxide, which have been characterized by IR and powder X-ray diffraction analysis. The data obtained for in vivo antiinflammatory activity (% inhibition) and toxicity (LD50 in mg/kg) of synthesized compounds have been compiled. The complexes have shown considerable activity in comparison to the ligand. Fourth chapter of the thesis includes the synthesis and results of spectroscopic investigations of some new tri- and diorganotin(IV) derivatives of the general formulae iv R3Sn(H2L')/R'2Sn(HL') (where R = Me, «-Pr, n-Bu and Ph; R' = Me, «-Bu, n-Oct and Ph; H3L' = Schiff base (tren(meim)3) derived by the condensation of tris(2-aminoethyl)amine (tren) and 4-methyl-5-imidazolecarboxaldehyde (meim)). A detailed interpretation of the coordination modes of the Schiff base towards organotin(IV) moieties have been discussed on the basis of UV/Vis, IR and far-IR, multinuclear (!H, 13C and 119Sn) NMR spectroscopic studies. The six-coordinated tri- and diorganotin(IV) derivatives have been proposed to exhibit a distorted cw-octahedral geometry around tin atom as supported from their spectral studies. In the triorganotin(IV) derivatives of type, R3Sn(H2L') (R = Me, n-Pr, n-Bu and Ph), Schiff base acts as a monoionic tridentate ligand, coordinating through two azomethine nitrogen and one imidazole ring nitrogen. However, IR, *H and 13C spectral studies revealed that the ligand acts as biionic tetradentate ligand in diorganotin(IV) derivatives of type, R'2Sn(HL') (R' = Me, «-Bu, «-Oct and Ph) and coordinating through two azomethine nitrogen and two imidazole ring nitrogen to give a highly distorted octahedral geometry/skew trapezoidal-bipyramidal structure. 119Sn NMR spectral data of Ph2Sn(HL') reveal that the weak interaction between central tin and central N(triethyiamine) or third azomethine nitrogen or one solvent molecule in solution, leading to fast interchange of octahedral to pentagonal-bipyramidal species in the solution. TG, DTG and DTA of the synthesized derivatives have been carried in air. The residues thus obtained of are characterized by IR and X-ray powder diffraction analysis. The results obtained for the antiinflammatory activity and toxicity (LD50) of the synthesized derivatives are discussed and the activity has been found to increase on complexation. Fifth chapter enumerates the different synthetic strategies that have been followed in order to isolate diorganotin(IV) derivatives of tetraazamacrocyclic ligands. The synthesis and characterization of diorganotin(IV) derivatives of tetradendate macrocyclic ligands, of general formula [R2Sn(L-l)/ R2Sn(L-2)] (R = Me, n-Bu and Ph; H2L-1 = 5,12-dioxa-7,14- dimethyl-l,4,8,ll-tetraazacyclotetradeca-l,8-diene and H2L-2 = 6,14-dioxa-8,16-dimethyll, 5,9,13-tetraazacyclohexadeca-l,9-diene) have been carried out. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state 13C-NMR, 119mSn Mossbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidalbipyramidal environment around tin centre. Thermal decomposition of the synthesized derivatives have been carried out, which provides a simple route to prepare nanosized semiconducting Sn02 grains in the temperature range -500-800 °C. The residues thus obtained are characterized by IR, X-ray diffraction and FESEM-EDX analysis. X-ray line broadening shows that the particle size varies in the range of 36-57 nm. The particle size of the residues obtained by pyrolysis is also determined by transmission electron microscope (TEM) and found in the range of -5-20 nm. The surface morphology of these residues has been investigated by scanning electron microscopy (SEM). Mathematical analysis of TGA data shows that the first step of decomposition in n-Bu2Sn(L-2) follows first order kinetics for which kinetic and thermodynamic data, such as energy of activation (E*), preexponential factor (A), entropy of activation (S*), free energy of activation (G*) and enthalpy of activation (H*) have also been calculated using two different methods such as Horowitz and Metzger and Coats and Redfern methods. Sixth chapter of thesis incorporates the template synthesis and characterization of diorganotin(IV) tetraazamacrocyclic complexes, viz. R2Sn(L-5)/(L-6) (R = Me, «-Bu and Ph; H2L'-l/H2L'-2 = 3-oxo-l,2-benzo-4,7,10,13-tetraazacyclotridecane/3-oxo-l,2-benzo-4,7,10, 14-tetraazacyclotetradecane). The geometry and the mode of bonding of the resulting 1 1 ^ complexes are inferred from elemental analysis, UV-Vis, IR, far-IR, DART-mass, ( H, C and 119Sn) NMR and 119mSn Mossbauer spectral studies. The observed spectroscopic data have been consisted with a structure in which R2Sn(IV) moiety is bonded to the four nitrogen atoms resulting in a six-coordinated geometry around the tin centre in its usual saddle conformation and the two subsitituent groups (R) may be cis. Thermal studies of all of the studied complexes have been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques and provided a simple route to prepare nanosized semiconducting Sn02 grains, identified by infrared, X-ray diffraction and FESEM-EDX analysis. The crystal average size of Sn02 calculated by Scherrer equation is in the range of 38-48 nm, whereas, the size measured by SEM and TEM are in the range of -20-200 nm and -3-20 nm respectively, in diameter.