Photophysical studies of coordination polymers and composites based on heterometallic lanthanide succinate

Abstract

This work reports the synthesis and characterization of heterometallic Tb/Eu lanthanide-succinate coordination polymers (CPs) under hydrothermal conditions. Compounds were obtained inserting different quantities of Eu3+ ions into the terbium succinate structure, named here xEuyTbSuc (x and y are the percentage of the respective lanthanide ions). Composites with these heterometallic CPs and activated carbon (CP@AC, AC = activated carbon) were obtained using one-pot hydrothermal reactions. Bimetallic CPs with or without presence of AC crystallize in monoclinic system, isostructural to [Ln2(Suc)3(H2O)2]•0.5H2O (Ln = Eu or Tb), already described in the literature, confirmed by X-ray powder diffraction (XRPD) data. Scanning electron microscopy (SEM) images show the CP crystals inside the carbon pores. Luminescence spectroscopy measurements (excitation, emission and lifetime) were conducted to explore photophysical properties of these new materials. Lifetime data indicates all Eu3+ ions are in the same chemical environment. Even at low concentration (1%), Eu3+ transitions (5D0→7FJ (J = 0–4)) were observed in the emission spectrum, along transitions related to the Tb3+ cations (5D4→7FJ (J = 6–3)), due to the metal-to-metal charge transfer (MMCT) between the lanthanide ions. Similar results are found in the composites. Increasing the Eu3+ concentration, a more intense MMCT process took place, suppressing the terbium emission.