Structural, Spectral, Biological and Electrochemical Studies Of Some ...

thione thiol
Fig 1.1
The existence of two forms of E isomer viz E l and Ell is reported. The E l
isomer has more intermolecular hydrogen bonding than Ell [18]. The isomers are
represented in the Figure.l.2
The E and Z isomers of 2-formylpyridine thiosemicarbazones as well as those
of other heterocyclic thiosemicarbazones have been separated and characterized [19].
The subtle difference in stereochemistry between isomers was based upon the degree
of shielding observed for the 2N proton ofthe Z isomer, (8= 14.15 ppm).
However in most complexes thiosemicarbazones coordinate as bidentate
ligand via the azomethine nitrogen and thione-thiol sulphur. When additional
coordination functionality is present in the proximity of the donating centers, the
ligands will coordinate in a tridentate manner. This either can be accomplished by
the neutral molecule or by the monobasic anion upon loss ofhydrogen.
Besides the denticity variation, consideration of the charge distribution is
complicated in thiosemicarbazones due to the existence of thione and thiol tautomers.
Although the thione form predominates in the solid state, solutions of
thiosemicarbazone molecules show a mixture of both tautomers. As a result,
depending upon the preparative conditions, the metal complex can be cationic neutral
or anionic. Most of the earlier investigations of metal thiosemicarbazone complexes
have involved ligands in the uncharged thione form, but a number of recent reports
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