Biologically relevant metal complexes with mixed O, S donor ligands

• Main Author: Monga, Vishakha
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/16082

Thio analogues of two 3-hydroxy-4-pyrones (Hma, Hema) and two 3-hydroxy-4- pyridinones (Hmpp, Hdpp) have been synthesized as a new class of ligand precursors. Reacting 3-hydroxy-4-pyrones with P₂ S₅ led to the formation of the respective 3- hydroxy-4-pyranthiones (Htma, Hetma) in reasonable yields. One of these pyranthiones, thiomaltol (Htma), was further reacted with aqueous NH₄OH and MeNH₂ to yield 3- hydroxy-4-pyridinethiones, Hmppt and Hdppt, respectively. During the synthesis of the 3-hydroxy-4-pyridinethiones, their dimeric forms Hmppt-dimer and Hdppt-dimer were also isolated and characterized. Solution studies of the monomeric compounds established that these thio compounds have lower pKa values than the corresponding oxygen analogues, as expected. X-ray crystallographic analyses of Htma and Hetma confirmed that only the carbonyl oxygen (C=0) had been substituted with a sulfur atom and C=S bond lengths in the resulting molecules are longer than the C=0 bond lengths in their synthetic precursors. X-ray crystallographic analysis of Hdppt-dimer demonstrated the presence of a disulfide bond in the dimeric organic compounds. The four monomeric ligand precursors were complexed with vanadium to yield eight complexes: four oxovanadium(IV) and four vanadium(III) complexes. Solution studies (potentiometric and spectrophotometric) of the four oxovanadium(IV) compounds indicated the formation of reasonably stable complexes with (VO)L₂ and (VO)L₂(OH) as the dominant species at physiological pH. X-ray crystallographic analysis demonstrated the presence of cis and trans isomers of VO(tma)₂. For both isomers, the two ligands are in the equatorial plane with the V=0 bond perpendicular to the ligands, forming a square pyramidal structure. Reaction of the four monomeric ligand precursors with Ga³⁺and In³⁺ ions yielded new tris(bidentate ligand) complexes. X-ray quality crystals of the/ac-isomer of Ga(tma)₃ were also obtained; two of the ligated S atoms were found in a cis configuration with respect to each other with the third sulfur atom and one of the oxygen atoms occupying the perpendicular axis. New complexes with a range of lanthanides (Ln³⁺) were also synthesized with the two pyranthiones, Htma and Hetma. The synthesis reactions yielded complexes of the type LnL₃•xH₂0 and LnL₂(OH) •xH₂0, supported by elemental analysis and spectroscopic evidence such as mass spectral data and IR and NMR spectra. === Science, Faculty of === Chemistry, Department of === Graduate