Self-assembled Transition Metal Coordination Frameworks of ...

Chapter 5
5.3.3. IR and electronic spectral studies
The IR spectra of manganese complexes show marginal differences from their
corresponding ligands. The IR spectral assignments of the Mn(H) complexes are listed
in Table 5.1. The square complex 19 shows both C=S and C—S stretching bands
suggesting the presence of both thione and thiolate coordination. Absence of bands at
~ 2600 cm" for 19 and 20 are indicative of absence of of thiol tautomers in free or
coordinated form in these complexes [40]. Similarly, the carbohydrazone grid
complexes 21, 22 and 23 show both C=O and C-0 stretching bands. These are in
agreement with other results. The change in frequencies for assigned bands and
differences in mixing patterns of common group frequencies of complexes compared
to their respective metal free ligands are attributed to the coordination to metal center.
The spectra in the far IR region is also rich with bands attributable to coordination of
pyridyl N, azomethine N and sulfur/oxygen to Mn(lI). The sulfur metal coordination
is supported by strong bands at 350 and.354 cm" for complexes 19 and 20, assigned
to v(Mn-S). The v(Mn-Nm) and v(Mn-Npy/qu) frequencies for all the complexes are
seen at ~420 and ~280 cm" respectively. For 21, 22 and 23, clear indication of ionic
form of perchlorate is seen. The broad bands at 1100s, 1090s, 1100s cm" for 21, 22
and 23 respectively are attributed to v3(ClO4), while unsplit bands at 625 cm" for
these three compounds are assigned to v4(ClO4). These indicate presence of ionic
perchlorate species (T ,1 symmetry) [41]. The other bands at ~935 cm" for these
compounds, assignable to v |(ClO4), are very week For the azido complex 20, a sharp
band at 2058 and a strong band at 1294 cm" are assigned as asymmetric and
symmetric stretching of coordinated azido group [42]. The weak band at 630 cm" may
be of 5(NNN). The band at 324 cm" in the far IR region is attributed to v(Mn-Nam.)
[42], also supporting the azide coordination to metal. Selected IR and far IR spectra
are given in Figs. 5.11 to 5.15.
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