Organotin(IV) Complexes of O, N, O and S, S Donor Ligands Derived from Dibasic Acids for Biological Applications

Abstract

Herein we reports the synthesis of new mono and diorganotin(IV) complexes of Schiff baes/hydrazones with [O, N, O] and dithiocarbamates with [S, S] donor ligands. The methodologies described herein includes; the synthesis of five versatile Schiff bases/hydrazones ligands; N', N'-4-bis(2-hydroxybenzylidene)oxalohydrazide (H4L1), N', N'-4-bis(2-hydroxylbenzylidene)malonohydrazide (H4L2), N′, N′-4-bis(2- hydroxybenzylidene)succinohydrazide (H4L3), N′, N′-4-bis(2-hydroxybenzylidene)glutarohydrazide (H4L4) and N′, N′-4-bis(2-hydroxybenzylidene)adipohydrazide (H4L5). Herein the thesis also embodied another series of five dithiocarbamates ligands of the types; dipotassium-2, 2-oxalylbis(hydrazine-1-carbodithioat) (K2L1), dipotassium-2, 2-malonylbis(hydrazine-1-carbodithioate) (K2L2), dipotassium2, 2'-succinylbis(hydrazine-1-carbodithioate) (K2L3), dipotassium-2, 2'-glutaroylbis(hydrazine-1-carbodithioate) (K2L4) and dipotassium-2, 2'-adipoylbis(hydrazine-1carbodithioate) (K2L5). For the synthesis of organotin(IV) complexes the reaction between Schiff bases/ hydrazone ligands with [O, N,O] donor sites, mono- and diorganotin(IV) chlorides/oxides were carried out at various reaction conditions and obtained fifty new organotin Schiff bases/hydrazone complexes. The reaction between dithiocarbamae ligands with [S, S] binding sites, mono- and diorganotin(IV) chlorides were unsuccessful and end up with desulfurized isothiocynates. The structural and coordination chemistry of ligands with O, N, O and S, S binding mode/sites and thier organotin(IV) complexes were investigated by using FT-IR and single crystallographic studies in the solid sate. The solution chemistry of these complexes was investigated through mass spectrometry and some multinuclear (1H, 13C and 119Sn) spectal studies. The results revealed that Schiff bases/hydrazones coordinate to tin through a tridentate mode using [O, N, O] binding mode. The structural analysi of single crystal by X-ray technique showed that organotin complexes procured from hydrazone with tridentate lignads (O, N, O), mono- and diorganotin(IV) chlorides exhibited distorted octahedral (oh) and distorted trigonal bipyramidal (tbp) geometry respectively. Based on the computational studies; the trigonal bipyramidal complexes showed a Sn···O tetrel bonding/interaction in the solid state. A computational study, in combination with the quantum theory of atoms in molecules (QTAIM) shows that the Sn···O interactions involved here are purely electrostatic in nature with little covalent character and leads to a shorter Sn···O [3.480(2 Å)] inter-atomic bond distance as compare to the reported “sum of van der Waals radii (3.92 Å)”. However, these types of interaction cannot be seen in the compounds when the phenyl /butyl groups or when the methylene spacer (-CH2-) between the two-hydrazone fragments is increased replaces the methyl groups. Finally, all the complexes were screened for anticancer activities using carbopaltin as a standard drug. The diorgantotin hydrazone complexes; where methyl and phenyl groups are attached to tin(IV) showed reasonable activities due to solubility problems but the dibutyltin(IV) complexes of the hydrazone [O, N, O] ligands showed excellent activities and have been used as representative sample (compounds) against various cancer cell lines (HL-60, MCF-7 and HeLa ) obtained from human being. It is assumed that the high cytotoxic activities of the dibutyl tin(IV) complexes are due to its lipophilic character and can be compared with the activity of the standard drug (carboplatin). These results might be helpful in the rational drug designing of those complexes containing the dibutyl moiety.