Diverse coordination of aroylhydrazones toward iron(III) in solid state and in solution: spectrometric, spectroscopic and computational study

The coordination properties of N ′-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L1 ), N ′-(2-hydroxy-4-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L2 ) and N ′-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L3 ) toward Fe(III) ions were st...

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Published in:Molecular diversity 2020-11, Vol.24 (4), p.1253-1263
Main Authors: Benković, Tomislav, Kontrec, Darko, Kazazić, Saša, Chiş, Vasile, Miljanić, Snežana, Galić, Nives
Format: Article
Language:English
Subjects:
Biochemistry
Biomedical and Life Sciences
Chloroform
Iron
Life Sciences
Ligands
Organic Chemistry
Original Article
Pharmacy
Polymer Sciences
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Summary:The coordination properties of N ′-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L1 ), N ′-(2-hydroxy-4-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L2 ) and N ′-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbohydrazide ( H 2 L3 ) toward Fe(III) ions were studied by computational, spectrometric (MS) and spectroscopic methods (UV–Vis, IR and Raman spectroscopy) in solid state and in solution. Free ligands were present in keto-amine form with intramolecular H-bond. In MeOH:H 2 O 1:1 system, the 1:1 complexes with Fe(III) were formed, characterized by lg K  ≥ 6. The coordination to the metal ion was achieved via oxygen and azomethine nitrogen since the hydrolysis of hydrazone bond was suppressed. Unlike the 1:1 stoichiometry in methanolic solution, the composition of the complexes extracted to chloroform was Fe( L )( HL ). The release of three protons upon complexation was determined by independent spectrophotometric measurements. The complexes isolated from MeOH/EtOH solution have also stoichiometry 1:2. However, depending on the position of the methoxy substituent, two types of complexes were formed. In Fe( H 2 L1 ) 2 Cl 3 and Fe( H 2 L3 ) 2 Cl 3 , hydrazones acted as neutral ligands, while in Fe( HL2 ) 2 Cl the keto-enol tautomeric interconversion and release of one proton per ligand took place. All complexes were analyzed in gas phase as well, using triple quadrupole, ion trap and H/D exchange for determination of labile hydrogens. Based on the fragmentation pathways, the structural isomers were distinguished. Graphic abstract
ISSN:1381-1991
1573-501X
DOI:10.1007/s11030-019-09989-6