Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Syntheses, characterization, biological activity and fluorescence properties of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base ligand and its lanthanide complexes
Graphical abstract
New lanthanide metal complexes [LnL(NO3)2]NO3 {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La and Er, L = bis-(salicylaldehyde)-1,3-propylenediimine} are described and discussed. Luminescent spectra of Sm, Tb and Dy complexes exhibit characteristic metal-centered fluorescence.
Highlights
• Eight new complexes [LnL(NO3)2]NO3 {Ln = Nd, Dy, Sm, Pr, Gd, Tb, La, Er}are synthesized. • Sm, Tb and Dy complexes exhibit characteristic luminescence emissions of Ln(III) ions. • Most of the Ln(III) complexes exhibit good antibacterial activity.
Introduction
Schiff bases are considered as a very important class of organic compounds because of their ability to form stable complexes with many different transition metal and rare-earth metal ions in various oxidation states via N and O atoms [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15]. They have the potential to be used in different areas such as electrochemistry, bioinorganic, catalysis, metallic deactivators, separation processes, and environmental chemistry. Moreover they are becoming increasingly important in the pharmacological, dye, and plastic industries as well as in the field of liquid crystal technology [16], [17]. Since the first report of their metal complexes, simple di-, ter-, tetra-, and penta-dentate Schiff base ligands have been extensively studied and used for the metal complexation. The tetradentate salen-type Schiff base ligands derived from salicylaldehyde and diamine complexes with transition metal ions have been synthesized and investigated using different chemical techniques. Their chemical analysis showed the formation of 1:1 [M:L] ratio complexes where the Schiff base ligands were coordinated to the metal ion in a tetradentate manner with N2O2 donor sites of the two phenol-O and two azomethine-N [5], [6], [7].
In the last decades, the luminescent properties of lanthanides have attracted much attention for their wide applications in light emitting diodes (OLEDs), liquid crystal, fluoroimmunoassays, biophysics, laser technology, and optical telecommunication systems [18], [19]. Mainly due to their very narrow emission bands, long excited-state lifetimes and large Stokes shifts. Since f–f electronic transitions of lanthanides in their “+3” oxidation state are Laporte forbidden, the direct photo-excitation of lanthanide ions is difficult [20]. Therefore, it is necessary to sensitize the lanthanide ions with chelating organic chromophores such as aromatic carboxylic acids, aromatic phenols, cryptand and heterocyclic ligands. Subsequently the absorbed light by the ligands can be transferred to the lanthanide ion (antenna effect) by an intra-molecular energy transfer [20]. The luminescent intensities of the lanthanide metal complexes are strongly dependent on the efficiency of the organic ligand to absorb UV light, the efficiency of energy transfer from the ligand to metal, and the efficiency of lanthanide metal luminescence. This work focuses on the use of a tetradentate salene-type ligand which has selective ability to coordinate to lanthanide ions thus protect them from deactivation caused by interaction with solvent molecules and enhance their luminescence by providing proper conjugate absorption groups suitable for energy transfer. Structurally characterized salen-type lanthanide complexes are rare. Depending on the preparative procedures, different compositions salen-type Ln(III) have been reported such as [Ln(H2salen)(NO3)3], [Ln2(H2salen)3(NO3)4](NO3)2(H2O)3, and [Ln2(H2salen)1.5(NO3)3]n [Ln2(salen)3] [9], [10], [11], [12], [13], [14], [15].
In this context, we have studied the interaction of [Ln(NO3)3·xH2O] {Ln(III) = Nd, Dy, Sm, Pr, Gd, Tb, La, Er, x = 6 except for Tb = 5} with bis-(salicyladehyde)-1,3-propylenediimine tetradentate Schiff base ligand L. The coordination behaviors have been investigated by correlating with their elemental analysis, thermal properties, 1H NMR, FT-IR, UV–vis, and molar conductivity measurements. Moreover, the antimicrobial efficiency of these complexes has been screened against three different microorganisms. The photoluminescence properties of these complexes have been explored in solutions at room temperature through detailed photophysical investigation.
Section snippets
Materials and methods
[Ln(NO3)3·6H2O] {Ln = Sm, Nd, Er, Gd, Pr}, [Tb(NO3)3·5H2O] and [Dy(NO3)3·xH2O] were purchased from Sigma Aldrich Chemical company. Salicylaldehyde and 1,3-propyldiamine were purchased from Merck Schuchardt. All other solvents and reagents were of analytical grade purchased from TEDIA Company, OH, USA and used without further purification. The elemental analysis (C, H and N) was performed on Euro EA elemental analyzer 3000. The metal content of the complexes was determined by titration with EDTA
Results and discussions
In the present investigations, the ligand L and its new eight Ln(III) complexes were synthesized and characterized by different physical and chemical techniques. Scheme 1 summarizes the multi-step procedure leading to the target complexes. The ligand L was synthesized by a conventional one-step condensation of salicylicaldehyde and 1,3-propyldiamine and characterized by 1H NMR (Fig. 1SM), IR, 13C NMR (Fig. 2SM), TGA (Fig. 3SM) and elemental analysis [22].
All Ln(III) complexes were synthesized
Conclusions
In this work the tetradentate Schiff base ligand L and its corresponding lanthanide complexes [LnL(NO3)2]NO3 are synthesized and characterized. It is concluded from analytical and spectral data that the ligand L is a tetradentate chelate and coordinates to the central Ln(III) ion by the two imine nitrogen atoms and the two phenolic oxygen atoms with 1:1 stoichiometry. IR spectral, conductivity and thermal data showed that two nitrate groups are bound in a bidentate manner to the central Ln(III)
Acknowledgment
The authors are grateful to the Deanship of Scientific Research at Jordan University of Science and Technology for the financial support of this work, grant number (48/2008).
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O atoms from 8-hydroxyquinoline Schiff base ligands, leading to a parallelogram Ln2O2 core. The magnetism investigation shows that compound 2 display slow magnetic relaxation behavior under zero dc field (ΔE/kB = 19.77 K and τ0 = 1.35 × 10−6 s). Subsequent studies strongly suggested that the four Ln2 compounds binded to Calf thymus DNA (CT-DNA) through intercalative mode and have pBR322 plasmid DNA cleavage ability. This work will provide more insights for the design and investigation of lanthanide-based SMMs, and has certain reference value to study the interaction between compound and DNA.