Tuning the Coordination Sphere around Highly Luminescent Lanthanide Complexes

Abstract

A series of three ligands designed for the formation of water-soluble luminescent lanthanide complexes is described. All ligands are based on a 6''-carboxy-2,2':6',2''-terpyridine framework linked via a methylene bridge to n-butylamine. The second negatively charged arm consists of a 6-carboxy-2-methylenepyridine for L1, a 6'-carboxy-6-methylene-2,2'-bipyridine for L2, and a 6''-carboxy-6-methylene-2,2':6',2''-terpyridine for L3. The photophysical properties of the Eu and Tb complexes were studied in aqueous solutions by means of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy. Luminescence excited-state lifetimes were recorded and led to the determination of two water molecules in the first coordination sphere. The europium complexes were characterized by means of (1)H NMR spectroscopy in D 2O and DFT calculations performed at the B3LYP level both in vacuo and in aqueous solution. Finally, the influence of different phosphorylated anions such as HPO 4 (2-), ATP (4-), ADP (3-), and AMP (2-) on the luminescence properties of the [Eu L X (H 2O) 2] (+) complexes ( X = 1-3) was investigated in buffered aqueous solutions (0.01 M TRIS, pH 7.0), showing a significant interaction of ATP (4-) with [Eu( L2)(H 2O) 2] (+). The coordination of anions was understood in terms of partial decomplexation of one arm of the ligands and water displacement, with formation of ternary species, and it was rationalized on the basis of the structural models of the complexes obtained from DFT calculations.

Phosphonated Podand Type Ligand for the Complexation of Lanthanide CationsPhosphonated Podand Type Ligand for the Complexation of Lanthanide Cations

“…It also resulted in a flattening of the angles formed by the two opposite pyridyl strands. Considering the three atoms composing a tridentate unit (the tertiary N atom, the N atom of the pyridyl and the O atom of the carboxylate or phosphonate units), the average angles between the planes of the coordinating arms in opposite directions are 21.4° for the phosphonated complex (44.1° for the carboxylated one), with an almost planar pentadentate unit formed by these opposite strands as observed in disubstituted 6,6′′‐terpyridyl pentadentate ligands …”

“…Considering the three atoms composing a tridentate unit (the tertiary N atom, the N atom of the pyridyl and the O atom of the carboxylate or phosphonate units), the average angles between the planes of the coordinating arms in opposite directions are 21.4°f or the phosphonated complex (44.1°for the carboxylated one), with an almost planar pentadentate unit formed by these opposite strands as observed in disubstituted 6,6′′-terpyridyl pentadentate ligands. [25] Figure 7. Views along the N tert -Eu bonds of the coordination spheres of Eu for the carboxylated analogue (a) [24] and the phosphonated one (b).…”

Luminescence behaviour in acetonitrile and in the solid state of a series of lanthanide complexes with a single helical ligand

“…[22][23][24][25][26] Moreover, the enhanced ff emission may be induced, if the ligands act as a shield from the outer-sphere with a stable structure in solution 23,[27][28][29][30] or in the solid state. 24,[31][32][33][34][35] A chelate effect provides a fundamental but most useful technique to design stable metal complexes, and the coordination number of the chelate ring contributes to the stability constant of the coordination in solution. There are some manuscripts for metal complexes, e.g.…”

Supramolecular Luminescent Lanthanide Dimers for Fluoride Sequestering and Sensing

“…In our approach to fluoride sensing by metal coordination, we hypothesized that hard lanthanide cations (Ln) could be the targets of choice, and we intended to take advantage of their well-documented luminescence that is sensitive to water quenching [11] or anion binding. [12] However, the interaction of fluoride anions with lanthanide complexes in water was reported to be weak (log K % 2-4) [13] and hardly compatible with a high sensitivity. We recently demonstrated that europium complexes of DOTA derivatives (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) having a water molecule at the ninth coordination site could be very effective and selective fluoride sensors; [14] the complexation of fluoride displaces the coordinated water molecule with a concomitant enhancement of the europium-based luminescence.…”