Helix-mediated over 1 nm-range chirality recognition by ligand-to-ligand interactions of dinuclear helicates.

Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances ( = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes ( and , respectively) used as mediators. Both and form one-dimensional (1D) helical structures upon terminal binding of two chiral guest co-ligands (L or L ). Long-range chiral self-recognition is achieved in self-assembly of with L and L to preferentially form homochiral assemblies, -L ·L and -L ·L , whereas there is no direct molecular interaction between the two guest ligands at the terminal edges. X-ray crystal structure analysis and density functional theory studies reveal that long-range chiral recognition is achieved by terminal ligand-to-ligand interactions between the bis-diketonate ligands and chiral guest co-ligands. Conversely, in self-assembly of with a longer helix length, statistical binding of L and L occurs, forming heterochiral (-L ·L ) and homochiral (-L ·L and -L ·L ) assemblies in an almost 1 : 1 ratio. When phenyl side arms of the chiral guest co-ligands are replaced by isopropyl groups (L' and L' ), chiral self-recognition is also achieved in the self-assembly process of with the longer helix length to generate homochiral (-L' ·L' and -L' ·L' ) assemblies as the favored products. Thus, subtle modification of the chiral guests is capable of achieving over 1.4 nm-range chirality recognition.