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 (Ln) and the N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine ligand (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). Three unique crystal structures of La and PrN,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine complexes, with the La complex prepared in two different synthetic approaches, are reported, namely a dimeric [La(HL)(NO)] (HL=N,N'-bis-(3-methoxysalicylidene)ethylene-1,2-diamine) complex, an asymmetric two-centered [La(HL)(NO)] complex and a discrete mononuclear [Pr(HL)(NO)(HO)] complex. For Nd and Sm, an isotypic mononuclear [Nd(HL)(NO)] and 1D polymeric [Sm(HL)(NO)(MeOH)] 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 (Ln=Nd, Sm, Ho) 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 Eu complex emitted bright red light upon excitation at both 285.8nm and 394.4nm. The Nd, Er, and Yb complexes showed strong emission in the near-infrared region after excitation at 380nm.