Synthesis and Photophysical Properties of Lanthanide Pyridinylphosphonic Tacn and Pyclen Derivatives: From Mononuclear Complexes to Supramolecular Heteronuclear Assemblies
Nadège Hamon, Léna Godec, Elsa Jourdain, Fátima Lucio-Martínez, Carlos Platas-Iglesias, Maryline Beyler , Loïc Charbonnière, Raphaël Tripier
Inorg. Chem. 2023, 62, 46, 18940–18954, doi: 10.1021/acs.inorgchem.3c02522

Synthetic methodologies were developed to achieve the preparation of ligands L1 and L2 consisting of tacn- and pyclen-based chelators decorated with pyridinylphosphonic pendant arms combined with ethylpicolinamide or acetate coordinating functions, respectively. Phosphonate functions have been selected for their high affinity toward Ln³⁺ ions compared to their carboxylated counterparts and for their steric hindrance that favors the formation of less-hydrated complexes. Thanks to regiospecific N-functionalization of the macrocyclic backbones, the two ligands were isolated with good yields and implicated in a comprehensive photophysical study for the complexation of Eu³⁺, Tb³⁺, and Yb³⁺. The coordination behavior of L1 and L2 with these cations has been first investigated by means of a combination of UV–vis absorption spectroscopy, steady-state and time-resolved luminescence spectroscopy, and ¹H and ³¹P NMR titration experiments. Structural characterization in solution was assessed by NMR spectroscopy, corroborated by theoretical calculations. Spectroscopic characterization of the Ln³⁺ complexes of L1 and L2 was done in water and D₂O and showed the effective sensitization of the lanthanide metal-centered emission spectra, each exhibiting typical lanthanide emission bands. The results obtained for the phosphonated ligands were compared with those reported previously for the corresponding carboxylated analogues.