Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 2
carbonyl compounds [22]. So the energy difference between 7! and 7r* orbitals in
thiocarbonyl compounds is smaller. Also, because of the lesser ionization potential of
sulfur compared to oxygen the n electrons in the thiocarbonyl compounds are of
higher energy and the n -—> It * transition requires less energy in these compounds
than in carbonyls. So the absorption maxima in thiocarbonyl compounds occur at
longer wavelengths.
The thiosemicarbazone HL7 shows " n —> rr * transitions at 29410 and 28330
cm", while that of HL8 are seen at 29590 and 23580 cm" (Fig. 2.7). The other bands
12- ­
are assigned intra-ligand 72‘ -—> Ir * transitions.
2.0­
10­
16­
08­
0_Q 1 , t , . * I + | * | ' I ' | * 1
250 300 350 400 450 300 350 400 450 500 550
Wavelgngth (nm) Wavelength (nm)
HL7 in 10-5 M DMF sglutign HL8 in 10*‘ M DMF solution
2.3.3. NMR spectral studies
Fig. 2.7. Electronic spectra of thiosemicarbazones.
For the identification of organic compounds NMR spectroscopy is considered
as inevitable in conjunction with other spectrometric techniques. Considering the
NMR spectra of semicarbazones or thiosemicarbazones the solution spectra of
carbohydrazones and thiocarbohydrazones are much complicated. The
thiocarbohydrazone ligands having better solubility in CDCI3 or DMSO-db are found
to show well-resolved peaks compared to their oxygen counterparts.
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