Ln2M complexes (M = Ru, Re) derived from a bismacrocyclic ligand containing a 4,4′-dimethyl-2,2′-bipyridyl bridging unit

Abstract

Homodinuclear lanthanide complexes derived from a ligand featuring two DO3A chelating sites linked by a 4,4′-dimethyl-2,2′-bipyridyl spacer were prepared and characterized. The bipyridyl coordination site of 1 was used to introduce Ru(Bpy)₂ and Re(CO)₃Cl moieties, leading to the formation of heterometallic d–f₂ complexes with general formulae [Ln₂·1·Ru(Bpy)₂]²⁺ (Ln = Nd, Eu, Tb, Yb and Lu) and [Ln₂·1·Re(CO)₃Cl] (Ln = Nd, Yb and Lu). The luminescence properties of the complexes were investigated by means of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy covering the visible and NIR regions. Both Ru and Re chromophores were shown to act as efficient sensitizers of the NIR emission of Yb and Nd in aqueous solutions. We also consider the unsaturated coordination spheres of the Ln cations in the Ln₂·1 complexes, which form ternary complexes with bidentate anions without showing particular synergistic effects for polyanionic species.