Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 2
The carbohydrazone and thiocarbohydrazone compounds show some common
features, and it is found that the main difference as carbohydrazones HZL4, HZLS and
H2L6 show strong bands in the range 1696-1704 cm" of C=O stretching vibrations
instead of the strong bands seen in the range 1209-1225 cm" assigned to stretching
mode of C=S vibrations for thiocarbohydrazones H2L', HZLZ and HZL3. Apart from
this, the spectra of carbohydrazones and thiocarbohydrazones show some marginal
differences in the mixing patterns of common group frequencies. Many bands in the
region 1400 to 1600 cm" are consistent with v(C=N) and v(C=C) mixing patterns. The
v(SH) band usually seen at ~2600 cm" is absent in the IR spectra of H2L', HZLZ and
H2L3, clear indication of the absence of thiol tautomers in the solid form of these
compounds [11,21]. The strong bands at ~l7O0 cm" for carbohydrazones suggest the
presence of ketone form in their solid state. These ketone and thione form in the solid
state of compounds are in agreement with XRD studies of HZL3 and HZL4, will be
discussed shortly. The broad bands at ~3400 cm" of NH protons are indicative of the
presence of hydrogen bonding interactions as seen in the single crystal X-ray studies
of HZLZ [11], H21.’ and HZL‘ [16]. 11 is found that bands at ~1120 cm" are common in
carbohydrazone, thiocarbohydrazone and thiosemicarbazone ligands, assigned to v(N—
N). Selected IR spectra of ligands are given in Figs 2.1 to 2.3.
100­
­
80­_
20-
, 5
"
1 40- _'< 1 -,
@­
. (“I1
46
0'1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm")
Fig. 2.1. IR spectrum of thiocarbohydrazone HZL3.