Self-assembled Transition Metal Coordination Frameworks of ...

3.3.2. IR and electronic spectral studies of square complexes
Ni(II) complexes
The IR spectral features of molecular square grids are different from that of
their metal free ligands. The significant IR bands with tentative assignments of the
Ni(II) square complexes are listed in Table 3.1. The absence of v(SH) bands at ~2600
cm" fiom the IR spectra of complexes 1 and 2 are clear indication of the absence of
thiol tautomers in free or coordinated form in these compounds [8,29]. The change in
frequencies for assigned bands and differences in mixing patterns of common group
frequencies may be attributed to the coordination to metal center. For carbohydrazone
complexes the carbonyl band at ~l7OO cm" of free ligands disappear, confirming the
absence of free ketonic group in the complexes, attributed to oxygen coordination. All
the complexes show common broad bands in the region at ~342O cm", confirming the
presence of lattice water [30], and the shift and broadness are attributable to possible
hydrogen bonds. The v(P—F) band for all the four compounds are seen as sharp strong
bands at ~842 cm" [8,l6]. The spectra in the far IR region is rich with bands
attributable to coordination to Ni(II) by pyridyl/quinolyl N (at ~260 cm"), azomethine
N (at ~43O cm") and sulfur/oxygen (at ~350 cm"). Selected IR and far IR spectra are
given in Figs. 3.10 to 3.13.
100­
W‘
80­‘ |
60­
1..
20­
0 "i ' I ' I ' | ' a ' | ' 1 ' s
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm'1)
Fig. "3.10. IR spectrum of Ni(II) thiocarbohydrazone complex 1.
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