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COORDINATION INTERACTION BETWEEN ANTHRANILIC LIGAND AND D-
ELEMENT SALTS DURING CRYSTAL FORMATION: A STRUCTURAL AND
SPECTROSCOPIC APPROACH
Jiemuratova Aynura Amangeldievna
1
Pardayev Ulug‘bek Xayrullo o‘g‘li
1
Bobojonov Jamshid
Shermatovich
Uzbek-Finnish Pedagogical Institute. E-mail:
jiyemuratovaaynura@gmail.com
Abstract:
This study focuses on the crystallization of coordination complexes formed
between anthranilic acid ligand and d-block metal salts (Fe(III), Cu(II), Ni(II), Co(II)). The
coordination occurs via the ligand’s carboxylic and amino groups, resulting in the formation of
stable chelate complexes. The crystalline structure of the compounds was characterized by X-ray
diffraction analysis, while bonding characteristics were examined through IR and UV-Vis
spectroscopy. The results suggest that these crystalline complexes hold potential for use in
pharmaceuticals, catalysis, and biosensor technologies.
Keywords
:
Anthranilic acid, coordination complex, d-block metal ions, chelation,
crystallization, bidentate ligand, thermal stability, ligand field, transition metals.
Introduction:
Anthranilic acid (2-aminobenzoic acid) serves as a structurally versatile ligand
due to its functional groups – the carboxylic acid (-COOH) and amino (-NH2). These groups enable
bidentate coordination to metal centers, especially d-block elements which are known for their
variable oxidation states and coordination geometries. Investigating the crystallization behavior of
such complexes provides insights into structure–property relationships critical for applied
chemistry.
Literature review:
The coordination chemistry of aromatic amino acids, particularly
anthranilic acid (2-aminobenzoic acid), has been widely investigated due to the ligand’s dual donor
sites — the amino group (-NH
₂
) and the carboxylic acid group (-COOH). Early studies by Cotton
and Wilkinson (1999) established the foundational principles of bidentate ligand behavior in d-
block metal coordination complexes, emphasizing the importance of geometric preferences and
ligand field stabilization.
Nakamoto (2009) further elaborated on the spectroscopic signatures of coordinated
carboxylate and amine functionalities in metal-organic complexes, providing a reference framework
for interpreting IR and UV-Vis spectral data. In particular, shifts in the ν(C=O) band and changes in
ligand field transition bands have been extensively used as indicators of coordination. The use of
anthranilic acid in forming stable chelate rings has been documented in studies by Housecroft &
Sharpe (2012), where its coordination to transition metals such as Cu(II), Fe(III), and Ni(II) was
shown to result in thermally stable crystalline complexes. These studies confirmed that the
crystallization behavior is highly dependent on the metal’s ionic radius, electronic configuration,
and the nature of the solvent environment. More recent research has shifted toward application-
focused analysis. Complexes of anthranilic acid with transition metals have been reported as
potential precursors in catalysis (Lever, 1984), biosensor fabrication, and even drug delivery
systems, owing to their structural predictability and functional group compatibility.Despite this
foundational work, detailed investigations of the crystal structure variations among different metal
RESPUBLIKA ILMIY-AMALIY KONFERENSIYASI 7-8-MAY 2025-YIL
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complexes of anthranilic acid remain limited. The present study aims to bridge this gap by
systematically analyzing the crystallization outcomes, structural motifs, and spectroscopic
characteristics of anthranilic acid complexes with Fe(III), Cu(II), Ni(II), and Co(II) under controlled
experimental conditions.
Materials and Methods:
The experiments were conducted using anthranilic acid and four
transition metal salts: FeCl
₃
·6H
₂
O, CuCl
₂
·2H
₂
O, NiSO
₄
·6H
₂
O, and CoCl
₂
·6H
₂
O. Stoichiometric
ratios of 1:2 metal to ligand were reacted in ethanol–water solution (1:1 v/v) under ambient
temperature with continuous stirring. Crystallization was achieved through slow evaporation over a
period of 7–14 days.
Characterization was performed using the following methods:
X-ray diffraction (XRD):
to confirm the formation of crystalline structures and determine unit
cell parameters.
UV-Visible spectroscopy:
to identify metal–ligand charge transfer bands and ligand field
transitions, typically observed between 510–580 nm.
Infrared spectroscopy (IR):
to detect shifts in vibrational frequencies, especially the C=O
stretch moving from 1700 cm
⁻
¹ in free ligand to 1620 cm
⁻
¹ upon coordination, and NH
₂
vibrations
near 3300 cm
⁻
¹.
Results and Discussion:
The resulting complexes formed distinct crystalline phases. XRD
analysis revealed that Fe and Co complexes crystallized in a monoclinic system, whereas Cu and Ni
complexes preferred a triclinic arrangement. These differences suggest a metal-dependent influence
on lattice packing and symmetry.
UV-Vis spectra showed distinct absorption bands for each metal complex, indicating
successful coordination and electronic interaction between the metal center and the ligand. IR
spectra confirmed the involvement of both amino and carboxyl groups in coordination, as evidenced
by the characteristic shifts. The thermal behavior of the crystals, inferred from decomposition onset
points above 250 °C, supports their stability. This aspect is particularly promising for practical
applications requiring durable coordination frameworks.
Conclusion:
The anthranilic acid ligand forms stable crystalline complexes with a variety of
d-block metal salts through bidentate coordination. Spectroscopic and structural analyses validate
the formation of well-defined compounds with potential application in fields such as catalysis,
biosensors, and pharmaceutical formulations. The metal-specific crystallization behavior highlights
the role of ionic radius and electronic configuration in directing the final crystal structure, offering a
basis for targeted synthesis of functional coordination compounds.
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