Lanthanide complexes based on a diazapyridinophane platform containing picolinate pendants

Area of Science:

• Coordination Chemistry
• Lanthanide Complexes
• Macrocyclic Ligands

Background:

• Macrocyclic ligands are crucial in coordinating metal ions, influencing their properties.
• Lanthanide complexes have applications in imaging and sensing.

Purpose of the Study:

• To synthesize and characterize a new macrocyclic ligand, H(2)BPDPA.
• To investigate the coordination properties of H(2)BPDPA with lanthanide(III) ions.
• To evaluate the structural, dynamic, and thermodynamic properties of these complexes.

Main Methods:

• Synthesis of H(2)BPDPA ligand.
• Luminescence lifetime measurements for hydration number determination.
• NMR spectroscopy ((1)H, (13)C, (17)O) and NMRD for structural and dynamic studies.
• Density functional theory (DFT) calculations for conformational analysis.
• pH-potentiometric titration for stability constant determination.

Main Results:

• The Eu(III) and Tb(III) complexes show one inner-sphere water molecule.
• DFT calculations accurately predict the solution structure of the Yb(III) complex.
• Gd(III) complex exhibits a fast water exchange rate (k(ex)(298) = 63 × 10(6) s(-1)).
• Stability constants (logK(LnL) = 12.5-14.2) indicate relatively low complex stability.
• Low ligand basicity is identified as the primary reason for reduced complex stability.

Conclusions:

• H(2)BPDPA forms lanthanide complexes with interesting dynamic properties, including fast water exchange.
• The ligand's low basicity limits the thermodynamic stability of the resulting complexes.
• These findings provide insights into the design of macrocyclic ligands for lanthanide coordination.