SYNTHESIS AND STRUCTURE OF IRON(III) COMPLEX WITH
2-ACETYLPYRIDINE-AMINOGUANIDINE
Mirjana M. Radanović, Ljiljana S. Vojinović-Ješić, Marko V.
Rodić,
Vukadin M. LeovacUniversity of Novi Sad, Faculty of Sciences,
Trg Dositeja Obradovića 3, 21000 Novi Sad, Serbia
MEĐUNARODNA NAUČNA KONFERENCIJA „SAVREMENI MATERIJALI“
10. I 11. SEPTEMBAR 2020.
The aim of this study was to examine the synthesis and structure
of a novel Fe(III) complex with the Schiff base of aminoguanidine
and 2-acetylpyridine and the
physicochemical properties of the novel complex compound.
Bis(ligand) complex of iron(III), of the formula
[Fe(L–H)2]2(NCS)Cl, was obtained by the reaction of FeCl3 and the
thiocyanate ligand salt in a mole ratio 1:1 in the
presence of lithium-acetate as a deprotonating agent. The
complex is obtained in the form of brown single crystals and is
characterized by elemental analysis data,
conductometric measurements, IR spectra, and X-ray analysis. The
latter revealed that the chelating ligand is coordinated in its
monoanionic form via pyridine,
azomethine, and nitrogen atoms of the aminoguanidine fragment,
forming octahedral environment..
Abstract
Introduction
Schiff bases are a promising class of compounds because of easy
synthetic routes and a wide range of applications. Some of these
compounds show significant
antioxidant [1], anticonvulsant [2], and diuretic activities
[3], while the others are used for the preparation of drugs, as
catalysts, sensors, for gas storage and purification,
etc. These structures are often stabilized by hydrogen and
halogen bonds, as well as π…π stacking interactions, thus could be
used as thermo-resistant materials,
pharmaceutical products, optoelectronic devices [3]. The
presence of metal ion in these structures could enhance the
properties of the ligands themselves, especially the
biological activity [4]. In the paper [5] this ligand class is
called ‘‘exclusive ligands” because they can coordinate to
different metals and have rich coordination
chemistry.
All of the above led to necessity of thorough investigation of
the coordination chemistry of Schiff bases of aminoguanidine. As
the continuation of that research, the
synthesis and characterization of iron(III) complex with the
Schiff base of aminoguanidine and 2-acetylpyridine are described in
this paper.
Results and Discussion
Bis(ligand) complex of iron(III) was obtained in the reaction of
FeCl3 and the thiocyanate ligand salt in molar ratio 1:1, in the
presence of LiOAc as deprotonating agent
(Scheme 1). The obtained complex shows good solubility in DMF,
while it is poorly soluble in MeOH and EtOH.
Scheme 1. Synthesis of the complex
Formula
(sum formula)Found (calculated), %
λM
[Scm2mol-1]
C H N(DMF)
[Fe(L-H)2]2(NCS)Cl
(Fe2C33H40N21SCl)
43.28 4.20 32.18
291
(43.57) (4.40) (32.33)
Table 1. Elemental analysis and molar conductivity data
The molar conductivity of the complex corresponds to 3:1 type of
electrolyte, which is in concordance with the coordination formula
(Table 1).
A similar reaction with chloride ligand salt and with ammonia
used for deprotonation of the ligand yielded in the formation of
the complex of the formula
[Fe(L–H)2]Cl∙6H2O [6]. It was interesting to compare the
structure parameters of those two complexes. The latter complex
crystallizes in the tetragonal crystal system,
i.e. has higher symmetry, probably due to the presence of only
one sort of counter-ion.
Figure 1. Structure of the complex
(counter-ions are omitted due to clarity)Figure 2. Packing of
the structural units of the complex [Fe(L-H)2]2(NCS)Cl
Bond
Lengths, Å
Bond
Angles, °
[Fe(L–H)2]Cl∙6H2O [Fe(L-H)2]2(NCS)Cl [Fe(L–H)2]Cl∙6H2O
[Fe(L-H)2]2(NCS)Cl
Fe–N1 1.884(5)-1.932(5) 1.879(4)-1.893(5) C3–N5–C7
119.4(5)-120(5) 119.2(4)-120.3(4)
Fe–N3 1.889(5)-1.911(6) 1.892(3)-1.900(3) C1–N2–N3
107.1(3)-108.3(5) 106.6(4)-108.3(4)
Fe–N5 1.529(7)-1.578(4) 1.964(4)-1.976(4) N3B–Fe–N3A178.5(2)
177.7(2)
C1–N1 1.305(9)-1.324(7) 1.316(6)-1.356(6) N5B–Fe–N1B160.8(2)
160.9(2)
C1–N2 1.346(7)-1.360(7) 1.347(6)-1.356(6) N1A–Fe–N5A161.1(2)
161.4(2)
C1–N4 1.327(7)-1.340(7) 1.346(5)-1.364(7)
N2–N3 1.335(9)-1.369(6) 1.347(4)-1.364(7)
C2–N3 1.287(9)-1.322(7) 1.288(6)-1.314(6)
Table 2. Selected bond lengths and angle values
The asymmetric unit of the complex [Fe(L-H)2]2(NCS)Cl consists
of two complex cations [Fe(L–H)2]+, and one chloride and one
thiocyanate as counterions. In this
complex chelating ligand is coordinated in the usual tridentate
NNN mode, through pyridine (N5), azomethine (N3) and, the imino
nitrogen atom of aminoguanidine
moiety (N1), forming two five-membered metallocycles (Fig
1).
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All hydrogen-donors of the chelating ligand are involved in the
formation of weak H-bonds with chloride ion, sulfur atom of
thiocyanate ion, and the hydrazine nitrogen
atom of the neighboring ligand molecule.
The packing of the structural units of the complex is presented
in Fig. 2.
In the complex [Fe(L–H)2]2(NCS)Cl all Fe–N bond lengths are in
the range of 1.879(4)–1.976(4) Å, with the longest distance between
the metal ion and pyridine nitrogen
atom (N5), as it was found in the structure of [Fe(L–H)2]Cl∙6H2O
as well.
The Fe(III) ion is situated in the slightly distorted octahedral
environment of two monoanions of the chelating ligand. Even though
bis(ligand) complex is obtained, the
ligand preserved the high degree of planarity. The values of
trans angle N3B-Fe-N3A are near the theoretical value, while the
others deviate from this value for ca. 10 °.
Due to the presence of LiOAc as a deprotonating agent, the
Schiff base is deprotonated, thus coordinated in its monoanionic
form. The deprotonation of the pyridine N-
atom, which takes place prior to coordination, causes the
shrinkage of the C3–N5–C7, which has a value of 123.7(2) ° in the
structure of the ligand [7] for ca. 4 °. Similarly, the
deprotonation of N2 atom as well as the coordination of the
aminoguanidine residue leads to shrinkage of C1–N2–N3 angle for
10-11 °. It should be mentioned that this change in angle value is
less pronounced in the complexes containing the neutral form of the
ligand with the protonated N2 atom [7].
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References
Conclusion
In the reaction of FeCl3 and the thiocyanate ligand salt in
molar ratio 1:1, in the presence of LiOAc as deprotonating agent,
bis(ligand) Fe(III) complex of the formula
[Fe(L–H)2]2(NCS)Cl was obtained. Physicochemical properties of
the complex were examined and X-ray analysis done..
The asymmetric unit of the complex [Fe(L-H)2]2(NCS)Cl consists
of two complex cations [Fe(L–H)2]+, and one chloride and one
thiocyanate as counterions. In this
complex chelating ligand is coordinated in the usual tridentate
NNN mode, through pyridine (N5), azomethine (N3) and, the imino
nitrogen atom of aminoguanidine
moiety (N1). Bond lengths and angle values correspond to all the
previously described structures with this ligand, with differences
which are a consequence of the
ligand deprotonation.
Future research should be broadened with the investigation of
antioxidant activity, but also the possibility of synthesis and
characterization of the complexes with other
metal ions.
