Self-Assembly Synthesis, Structural Features, and Photophysical Properties of Dilanthanide Complexes Derived from a Novel Amide Type Ligand: Energy Transfer from Tb(III) to Eu(III) in a Heterodinuclear Derivative

A novel amide type ligand benzyl-N,N-bis­[(2′-furfurylaminoformyl)­phenoxyl)­ethyl]-amine (L) has been designed and applied for the self-assembly generation of homodinuclear lanthanide coordination compounds [Ln₂(μ₂-L)₂(NO₃)₆(EtOH)₂] [Ln = Eu (1), Tb (2), and Gd (3)] and a heterodinuclear derivative [EuTb­(μ₂-L)₂(NO₃)₆(EtOH)₂] (4). All the complexes have been characterized by the X-ray single-crystal diffraction analyses. They are isostructural, crystallize in a monoclinic space group P2₁/c, and form [2 + 2] rectangular macrocycle structures. Compound 4 is the first example of a [2 + 2] rectangular macrocycle heterodinuclear EuTb complex assembled from an amide type ligand. In 4, the discrete 0D dimeric [EuTb­(μ₂-L)₂(NO₃)₆(EtOH)₂] units are extended, via the multiple N–H···O hydrogen bonds, into a 2D supramolecular network that has been topologically classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology. The triplet state (³ππ*) of L studied by the Gd­(III) complex 3 demonstrated that the ligand beautifully populates Tb­(III) emission (Φ = 52%), whereas the corresponding Eu­(III) derivative 1 shows weak luminescence efficiency (Φ = 0.7%) because the triplet state of L has a poor match with ⁵D₁ energy level of Eu­(III). Furthermore, the photoluminescent properties of heterodinuclear complex 4 have been compared with those of the analogous homodinuclear compounds. The quantum yield and lifetime measurements prove that energy transfer from Tb­(III) to Eu­(III) is being achieved, namely, that the Tb­(III) center is also acting to sensitize the Eu­(III) and enhancing Eu­(III) emission in 4.