In this study, we analyzed influence of the type
of the syntheses used: hydrothermal and non-hydrothermal
on pyridine-2,3-dicarboxylic acid ($2,3pydcH_{2}$) coordina-
tion fashion. Two manganese(II) complexes: $[Mn(H_{2}O)_{3}(2,3pycd)]_{n}$ and $[Mn(H_{2}O)_{6}][Mn(2,3pydcH)_{3}]_{2}$ were
successfully synthesized from the non-hydrothermal reac-
tion system containing organic ligand and different Mn(II)
salts. The received complexes have been prepared and
characterized by spectroscopic (IR, Raman), structural
(X-ray single crystal), and thermogravimetric methods.
The results of the crystal study give some evidence that
ligand exhibits various topological structures and interest-
ing properties. Pyridine-2,3-dicarboxylic acid acts as
monodicarboxylate N,O-chelating anion (complex
2
) or a
doubly deprotonated three-dentate-
N,O,O' dicarboxylate
ion (complex 1). In the $[Mn(H_{2}O)_{6}][Mn(2,3pydcH)_{3}]_{2}$
the
coordination geometry around Mn(1) ion can be considered
as being distorted octahedron ${MnN_{3}O_{3}}$. The Mn(2) cation possesses the same coordination polyhedron (octahedral). We have also analyzed influence of furnace
atmosphere on the thermal behavior and the kind of final
product. The sample of (1) decomposes in four stages in $N_{2}$
(368–1073 K) and the final residue is $MnO_{2}$. The thermogram of (2) exhibits three main distinct decomposition
steps (383–973 K). A residue of MnO is remained. In both air and nitrogen atmosphere, Mn(II) complexes (1) and (2)
keep unchanged over all steps of decomposition. Only the
final residues are different ($Mn_{2}O_{3}$ are formed). The course
of pyrolysis and molecular structure of the complexes lead
to the same conclusion about the strength of metal–ligand
bonds. On the basis of the above results, it is concluded that
the thermal stability of the manganese(II) compounds is
slightly different.
keywords in English:
manganese(II) complexes, IR and Raman spectra, pyridine-2 3-dicarboxylic acid, TG/DTG analysis, X-ray studies, magnetic properties