134
S. Materazzi et al. / Thermochimica Acta 397 (2003) 129–134
This behaviour, which is observed for both the
M(AIC) and the M(AIC)2 complexes, is the conse-
quence of the breakdown of both the coordination
sites, followed by complete oxidation to the metal
oxide as the final product. The loss of the side chains
in a well defined TG step verifies the proposed double
in at least two different processes. Moreover, once
the breakdown is started, all the complexes decom-
pose in a sharp temperature range as shown in the
Fig. 3.
Evidence of the coordination shown in the Scheme 1
is also supported by the UV–VIS spectra. The spec-
troscopic parameters suggest coordination via two
imidazole nitrogens and two amide oxygens forming
six membered chelate rings. The Cu(AIC)2 complex,
for example, shows a d–d transition band at 644 nm,
with strong CT transition (shoulder) at 400 nm (dark
green solution).
4. Conclusions
The solid-state complexes of AIC with Co(II),
Ni(II) and Cu(II), synthesized and characterized in
this study, confirmed the coordination reported in the
literature for the complexes in solution, and showed a
thermal stability in inverse order to the stability range
coordination via imidazole nitrogen and acetate group
was investigated by DSC and coupled TG–FT-IR. The
polymeric structure of the {M(AIC)·2.5H2O}n com-
plexes is suggested by the DSC analysis, and the cou-
pling of thermogravimetry and infrared spectroscopy
(TG–FT-IR) gives the qualitative characterization of
the gases evolved during the thermal decomposition.
Acknowledgements
From previous studies [5,6], EPR parameters in a
frozen solution of the Cu(AIC)2 complex support the
double 2N,2O coordination, with distorted octahedral
structure.
This work resulted from an exchange program be-
tween the University of Rome “La Sapienza” and the
University of Houston.
It is interesting to compare the thermal behaviour
of the M(AIC)2 with the M(IAA)2 complexes [13].
Both are realistic models for studying the coordina-
tion behaviour of the imidazole ring in presence of
oxygen donors. Due to the very different substituents
on the imidazole ring, comparative data between ba-
sicity and metal binding properties can be achieved.
The different coordinations of IAA and AIC com-
plexes are reflected in the thermal profiles. The AIC
complexes decompose in a well defined temperature
range, loosing both ligand molecules in two steps
separated by 30 ◦C. The IAA complexes show two
separate well defined thermogravimetric steps, sep-
arated by 150 ◦C. The first ligand molecule is lost
at 50 ◦C lower than AIC complexes and the second
molecule is lost 100 ◦C greater than AIC complexes.
This new compound, resulting from the loss of one
ligand molecule, can be described as M(IAA). It was
not described previously [13], but is more stable of
the M(IAC) compound previously described. The high
stability can be again explained by the possibility of
the IAA ligand to rearrange a mono-chelate complex
via imidazole nitrogen and carboxyl group, being ther-
mally more stable than the corresponding bis-chelate
complex.
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