Tunable ligand emission of napthylsalophen triple-decker dinuclear lanthanide(iii) sandwich complexes

The fluorescent ligand 1,1'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene)) bis(naphthalen-2-ol) (H₂L) was used to prepare lanthanide(iii) metal complexes. These were found to self-assemble as triple decker sandwich complexes of the type (Ln₂L₃), where Ln = Pr(iii), Nd(iii), Sm(iii), Eu(iii), Gd(iii), Tb(iii), Dy(iii), Ho(iii), Er(iii), Yb(iii), or Lu(iii). The structures of the complexes Nd₂L₃, Gd₂L₃, Tb₂L₃, Dy₂L₃, Ho₂L₃, Yb₂L₃, and Lu₂L₃ are structurally characterized by single crystal X-ray diffraction. In the Nd₂L₃ complex, both metals are 8 coordinate. Yb₂L₃, Tb₂L₃, Dy₂L₃, and Lu₂L₃ are isostructural. In these, as in the Gd₂L₃ and Ho₂L₃ complexes, one metal is 8 coordinate, one 7 coordinate. The ligand was found to have tunable emission in the solid state across the lanthanide series with a maximum at 556 nm for the Sm₂L₃ complex to 617 nm for Er₂L₃. Of these, most demonstrate only ligand-centered fluorescence at room temperature. The ligand was found to have much greater fluorescence in the complex Lu₂L₃. Here, we describe these distinctive triple decker complexes and their absorption and emission properties as both solids and solutions.