Organotin(IV)n+ complexes formed with biologically active ligands: equilibrium and structural studies, and some biological aspects

Schiff bases are the most widely used versatile ligands, able to coordinate many elements and to stabilize them in various oxidation states. Recently, this class of compounds has been employed as models for biological systems, and in control of stereochemistry in six-coordinate transition metal complexes. Recently, the chemistry of organotin(IV) complexes of Schiff bases has also stemmed from their antitumour, antimicrobial, antinematicidal, anti-insecticidal and anti-inflammatory activities. Furthermore, organotin(IV) complexes of Schiff bases present a wide variety of interesting structural possibilities. Both aliphatic and aromatic Schiff bases in their neutral and deprotonated forms have been used to yield adducts and chelates with variable stoichiometry and different modes of coordination. This critical review (>155 references) focuses upon the chemistry and biological applications of organotin(IV) complexes of Schiff bases reported in the past 15 years. Thermal behavior of these complexes is also discussed.

Chemistry and applications of organotin(IV) complexes of Schiff bases

Synthesis and characterisation of tin(IV) and organotin(IV) derivatives 2-{[(2-hydroxyphenyl)imino]methyl}phenol

Tin(IV) complexes 2a—q derived from pyridine Schiff bases were prepared and characterized. Four complexes of this series were evaluated in vitro against different carcinogenic cell lines; besides their anti-inflammatory and antioxidant properties were also tested. Combination of mass spectrometry, multinuclear NMR and X-ray diffraction techniques evidenced the formation of heptacoordinated monomeric species. The X-ray diffraction analysis of 2a, 2b, 2i, 2j and 2n led to establish the heptacoordination around the tin atom in solid state and also revealed that the ligand occupies the equatorial positions of the distorted pentagonal bipyramidal geometry and the two alkyl or aryl groups the axial positions. The in-vitro study for complexes 2a—d against six tumor cell lines showed varied antiproliferative activity, the IC50 for all tested complexes was lower than that of the cis-platin. Compounds 2a—d also exhibited anti-inflammatory activity where complex 2c resulted to be more active (IC50=0.11 μM) than the indomethacin IC50=0.27 μM which was used as reference. The antioxidant activity in rat brain homogenate on inhibition of thiobarbituric acid reactive substances (TBARS) indicated that 2c (IC50=1.77 μM) is more active than the quercetine (4.11 μM) and α-tocopherol (IC50=569.09 μM).

Heptacoordinate tin(IV) compounds derived from pyridine Schiff bases: synthesis, characterization, in vitro cytotoxicity, anti-inflammatory and antioxidant activity.

Synthesis, characterisation and X-ray structures of diorganotin(IV) and iron(III) complexes of dianionic terdentate Schiff base ligands

Inner coordination sphere tin(IV) complexes with some O,N,N-terdentate {N-(2-hydroxybenzaldehyde)-1-amino-2-phenyleneimine and N-(2-hydroxy-1-naphthaldehyde)-1-amino-2-phenyleneimine} and O,N,N,O-quadridentate {N,N′-bis(2-hydroxybenzaldehyde)-1,2-phenylenediimine and N,N′-bis(2-hydroxy-1-naphthaldehyde)-1,2-phenylenediimine} Schiff bases

Ching-Ching Loh

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