Ligand-to-Ligand Interactions That Direct Formation of D2‑Symmetrical Alternating Circular Helicate

This work demonstrates that ligand-to-ligand interactions between achiral bis-β-diketonate (BTP) and chiral bis­(4-phenyl-2-oxazolinyl)­pyridine [(R)- or (S)-Ph-Pybox] are successfully directed to the fabrication of a D2-symmetrical alternating circular helicate with the general formula [(R)- or (S)-Ph-Pybox]4(LnIII)4(BTP)6. The lanthanide­(III) LnIII assemblies (LnIII4-RRRR and LnIII4-SSSS) have a nanometer-size squarelike grid (interatomic distances > 10 Å). X-ray structure analysis revealed that the circular helicate contains two double helicate LnIII2L2 units, where both show (M)-helicity for LnIII4-RRRR and (P)-helicity for LnIII4-SSSS, where π–π stacking interaction is present between the side arm of (R)-Ph-Pybox (Ph1) and the adjacent BTP ligand around the EuIII metal center (dππ = 3.636 Å: the diketonate plane···Ph1 distance). The newly obtained circular lanthanide­(III) helicate exists as single and homochiral diastereomers in solution (LnIII4-RRRR and LnIII4-SSSS), exhibiting circularly dichroism (CD) and circularly polarized luminescence (CPL). Conversely, the circular helicate favors the heterochiral arrangement (i.e., LnIII4-RRRR/LnIII4-SSSS).