Phosphonated Podand Type Ligand for the Complexation of Lanthanide Cations

C. Charpentier (1) , J. Salaam (1) , A. Lecointre (1) , O. Jeannin (2) , A. Nonat (1) , L.J. Charbonnière (1)

1 IPHC - Institut Pluridisciplinaire Hubert Curien
2 ISCR - Institut des Sciences Chimiques de Rennes

A new tripodal ligand, based on a central nitrogen atom tris‐functionalized with 6‐methylene‐2‐pyridyl phosphonic acid was synthesized and characterized, in particular by its X‐ray crystal structure. The coordination behaviour of the tripod with lanthanide cations in aqueous solutions was studied by means of UV/Vis electronic absorption spectroscopy and steady‐state and time‐resolved luminescence spectroscopy, revealing the formation of a [LnL] complex followed by polynuclear species with 2:1 and 3:1 metal/ligand stoichiometries. The [LnL] complexes (Ln = Eu, Tb and Yb) were isolated and characterized and the solid‐state structure of the Eu complex was determined by X‐ray diffraction analysis on monocrystals, revealing the observation of dimeric species, in which the Ln3+ cations are firmly held in the cavity formed by the three pyridylphosphonate arms, the coordination of the cations being completed by a water molecule and a phosphonate function of the second complex, allowing for the formation of the dimers, which are further stabilized by π–π stacking interactions between one pyridyl unit of each adjacent monomer. The spectroscopic properties of the complexes in aqueous solutions were studied, showing an impressive 16 µs excited state lifetime for the Yb complex in D2O, despite the presence of a water molecule in the first coordination sphere.

Keywords: Luminescence; phosphonate; Lanthanides; Coordination chemistry; Spectroscopy

Domains: Chemical Sciences

C. Charpentier, J. Salaam, A. Lecointre, O. Jeannin, A. Nonat, et al.. Phosphonated Podand Type Ligand for the Complexation of Lanthanide Cations. European Journal of Inorganic Chemistry, 2019, 2019 (16), pp.2168-2174. ⟨10.1002/ejic.201900069⟩. ⟨hal-02122174⟩