Near-infrared luminescence and RNA cleavage ability of lanthanide Schiff base complexes derived from N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine ligands

A complete series of lanthanide Schiff base salen-type complexes were prepared with trivalent lanthanide ions (Ln³⁺) and the N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine ligand (Ln³⁺=La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺). Three unique crystal structures of La³⁺ and Pr³⁺N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine complexes, with the La³⁺ complex prepared in two different synthetic approaches, are reported, namely a dimeric [La(H₂L)(NO₃)₃]₂ (H₂L=N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine) complex, an asymmetric two-centered [La₂(H₂L)₂(NO₃)₆] complex and a discrete mononuclear [Pr(H₂L)(NO₃)₂(H₂O)₂] complex. For Nd³⁺ and Sm³⁺, an isotypic mononuclear [Nd(H₂L)(NO₃)₃] and 1D polymeric [Sm(H₂L)(NO₃)₃(MeOH)]_n structure was obtained, respectively. The whole series of complexes was tested for their ability to cleave the 20-mer RNA oligonucleotide 5'-AGC-GAU-AAG-AUU-CAU-AUA-UC-3'. Additionally three complexes (Ln³⁺=Nd³⁺, Sm³⁺, Ho³⁺) were tested for the cleavage of the 12-mer RNA oligonucleotide 5'-GCA-CCC-UGU-CAG-3'. A detailed luminescence study was additionally carried out and revealed that the Eu³⁺ complex emitted bright red light upon excitation at both 285.8nm and 394.4nm. The Nd³⁺, Er³⁺, and Yb³⁺ complexes showed strong emission in the near-infrared region after excitation at 380nm.