Water soluble Eu(III) complexes of macrocyclic triamide ligands: Structure, stability, luminescence and redox properties

Water soluble Eu(III) complexes of macrocyclic triamide ligands: Structure, stability, luminescence and redox properties

Two water soluble Eu(III) nine coordinate complexes of macrocyclic triamide chelators were synthesized and characterized by several spectroscopic techniques, and their pKa values were determined by potentiometric titration. Both complexes were structurally characterized by means of X-ray diffraction...

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Bibliographic Details
Published in:Inorganica Chimica Acta Vol. 486; pp. 252 - 260
Main Authors: Pradhan, Rabindra N., Hossain, Sayed M., Lakma, Avinash, Stojkov, Dragana D., Verbić, Tatjana Ž., Angelovski, Goran, Pujales–Paradela, Rosa, Platas–Iglesias, Carlos, Singh, Akhilesh K.
Format: Journal Article
Language:English
Published: Amsterdam Elsevier B.V 24-02-2019
Elsevier Science Ltd
Subjects:
Aqueous solutions
Binding
Coordination compounds
Crystals
DFT calculation
Eu(III) macrocyclic complexes
Glassy carbon
Ligands
Luminescence
pKa & stability constant
Redox properties
Silver chloride
Single crystals
Solvents
Spectrophotometry
Structural stability
Synthesis
Titration
Water chemistry
X-Ray
X-ray diffraction
X-Ray
DFT calculation
Eu(III) macrocyclic complexes
Redox properties
Luminescence
pKa & stability constant
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Summary:Two water soluble Eu(III) nine coordinate complexes of macrocyclic triamide chelators were synthesized and characterized by several spectroscopic techniques, and their pKa values were determined by potentiometric titration. Both complexes were structurally characterized by means of X-ray diffraction. Luminescence measurements confirm the presence of a water molecule coordinated to Eu(III) in aqueous solution. Cyclic voltammetric studies of these Eu(III) complexes show reversible, one electron reductive response corresponding to Eu(III)/Eu(II) redox couple. [Display omitted] •Water soluble Eu(III) nine coordinate macrocyclic complexes.•X-ray structure, pKa values and stability constants, Weak CEST effect.•Luminescence and DFT calculation.•Cyclic voltammetric studies of Eu(III)/Eu(II) redox couple. Two macrocyclic triamide octadentate chelator scaffolds L1 and L2 were synthesized, characterized by several spectroscopic techniques, and their pKa values were determined by potentiometric titration. Using these ligands, two water soluble paramagnetic Eu(III) complexes, [EuL1(OH2)](NO3)3·H2O (EuL1) and [EuL2(OH2)](NO3)3·H2O (EuL2) were synthesized and characterized in the solid state and in solution. Single crystal X ray diffraction measurement of [EuL1(OH2)](NO3)3.H2O (EuL1) reveals octadentate binding of the ligand to Eu(III) and ninth coordination being completed by an oxygen atom of a solvent molecule (H2O). X-ray diffraction data of [EuL2(OH2)](NO3)3·H2O (EuL2) were severely disordered and hence its chloride analogue [EuL2(DMF)]Cl3·H2OMeOH (EuL2-Cl) was synthesized and characterized using single-crystal X-ray diffraction measurements. The crystal data of [EuL2(DMF)](Cl)3·H2OMeOH (EuL2-Cl) reveal octadentate binding of the ligand to Eu(III), with the ninth coordination being completed by an oxygen atom of a solvent molecule (DMF). Luminescence measurements confirm the presence of a water molecule coordinated to Eu(III) in aqueous solution. The stability of the Eu(III) complexes was investigated using spectrophotometric molar ratio method. Cyclic voltammetry studies obtained from aqueous solutions of the Eu(III) complexes show reversible one electron reduction processes at the glassy carbon electrode with E1/2 = −0.799 V and −0.777 V (versus Ag/AgCl) for the complexes of L1 and L2.
ISSN:0020-1693
1873-3255
DOI:10.1016/j.ica.2018.10.050