Unsymmetrical Tripodal Ligand for Lanthanide Complexation: Structural, Thermodynamic, and Photophysical Studies

Abstract

Two tridentate and one bidentate binding strands have been anchored on a carbon atom to provide a new unsymmetrical tripodal ligand L for Ln(III) coordination. The ligand itself adopts a single conformation in solution stabilized by intramolecular hydrogen bonds evidenced in the solid state. The reaction of L with trivalent lanthanides provides different coordination complexes depending on the metal/ligand ratio. The speciation studies with selected lanthanides were performed in solution by means of NMR, ESMS, and spectrophotometric titrations. Differences in coordination properties along the lanthanide series were evidenced and may be associated with the changes in the ionic size. However, thermodynamic stability constants for the species of the same stoichiometry do not significantly vary. In addition, the structure of the dinuclear complex [Eu(2)L(2)](6+) has been elucidated in the solid state, where the complex crystallizes predominantly as an M-isomer. The crystal structure shows the coordination of two different ligands to each europium cation through tridentate strands, and the europium nine-coordinate sphere is completed with three solvent molecules. Finally, the results of photophysical investigations of [Eu(2)L(2)](6+) are in close agreement with the structural parameters determined by crystallography.

Effect of Counteranions on the Extraction and Complexation of Trivalent Lanthanides with Tetradentate Phenanthroline-Derived Phosphonate Ligands

“…NMR titration is an effective approach to determining the stoichiometries of the complexes formed between organic ligands and a diamagnetic metal ion solution. − In this work, diamagnetic Lu­(III), with the best extraction results, has been chosen to uncover the complexation properties of trivalent lanthanides with C4-POPhen in the systems of NO 3 – , Cl – , and ClO 4 – by 1 H and 31 P NMR spectroscopic titrations.…”

Thermodynamics, Structure and Properties of Polynuclear Lanthanide Complexes with a Tripodal Ligand: Insight into their Self‐Assembly

“…This finding gives quantitative evidence for unfavourable intramolecular reactions within the self‐assembly and translates in a drastic decrease in thermodynamic stability. In addition to entropic factors, the introduction of structural constraints, that is, shortening of the spacer length between the anchoring atom and binding sites ( L9 ,21 L10 22), and a mismatch between the ligand denticity and the Ln III coordination number14 may prevent the formation of mononuclear tripodal complexes. Consequently, self‐assembly leads to polynuclear structures with opened binding strands of a tripodal ligand (a trefoil form) that coordinate to different metal ions…”

Utilizing electronic effects in the modulation of BTPhen ligands with respect to the partitioning of minor actinides from lanthanides

“…NMR spectroscopic titrations of ligands with diamagnetic metal salts were used to determine the stoichiometries of the complexes in solution. [18][19][20][21] NMR titrations of the C5-BTPhen 7a with a number of trivalent lanthanide (lanthanum and lutetium) salts were thus performed in deuterated acetonitrile (CD 3 CN). La(III) (ionic radius = 116 pm) 15 and Lu(III) (ionic radius = 98 pm) 15 were chosen to give the greatest difference in of the Ln(III) radius.…”