| Summary: | 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
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