ThioneThiol Tautomerism

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Thione-Thiol Tautomerism in Cobalt(II) Complexes
Objectives --Synthesize Co complexes of an
ambidentate ligand --Characterize with IR and
electronic spectroscopy Determine geometry and
exact coordination sphere
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MIMT Ambidentate Tautomeric Ligand
1,3-dihydro-1-methyl-2H-imidazole-2-thione
2-mercapto-1-methylimidazole
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Tautomerism
--Tautomers structural isomers --Interconversion
always involves bond breaking and forming
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Ambidentate
--Can bind to metal with different donor atoms
M-S bond
M-N bond
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Co Complexes of MIMT
(A) Co(MIMT)4(NO3)2 and (B)
Co(MIMT)2 (NO3)2

Which tautomer is ligated?
--all thione or all thiol, no mixed-ligand
complexes
--both thione complexes, both thiols, or one of
each
--complex obtained depends on -quantity of
MIMT added -solvent can cause interconversion
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Co Complexes of MIMT
(A) Co(MIMT)4(NO3)2 and (B) Co(MIMT)2
(NO3)2
What is coordination sphere and geometry of A?
(B) nitrates bound coordination sphere
L2O2 Td
However (A) nitrates bound or
counterions?
coordination sphere L4O2 Oh
or coordination sphere L4 Td
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Characterization of Products

• UV-VIS spectroscopy
• probes crystal field gap

• IR spectroscopy
• probes atomic motion

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IR Spectrum Free MIMT
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Safety

• Aqueous Co2 complexes liquid waste bottle.
• Wear gloves when working with MIMT

MIMT used when treating hyperthyroidism at
some dose dangerous
Paracelsus, 16th century All substances are
poisons. There is no substance that is not a
poison. The only difference between a poison and
a remedy is the dose.
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Summary
--Synthesize Co(II) complexes of an ambidentate,
tautomeric, ligand
Use IR and electronic spectroscopy to determine
geometries and exact coordination spheres