Self-assembled Tetranuclear EuIII Complexes with D 2- and C 2h-Symmetrical Square Scaffold

Three new tetranuclear europium­(III) alternating circular helicates, (2- Ph RRRR/ 2- Ph SSSS) [(R)- or (S)-Ph-Pybox]4EuIII 4(BPP)6, (2- iPr RRRR/2- iPr SSSS) [(R)- or (S)-iPr-Pybox]4EuIII 4(BPP)6, and (3- Ph RRRR/ 3- Ph SSSS) [(R)- or (S)-Ph-Pybox]4EuIII 4(BHP)6, are presented with their structural and chiroptical characterization (BPP and BHP = bis-β-diketonates; Pybox = chiral bis­(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-β-diketonates and Pybox ligands produce different bis-β-diketonates arrangements around four EuIII ions and, thus, their specific symmetry in the final tetranuclear complexes. 2- Ph RRRR/ 2- Ph SSSS and 3- Ph RRRR/ 3- Ph SSSS are recognized as D 2-symmetry, while 2- iPr RRRR/2- iPr SSSS self-assemblies possess pseudo C 2h-symmetry. Due to different molecular symmetry, 2- Ph RRRR/ 2- Ph SSSS and 2- iPr RRRR/2- iPr SSSS crystals display different ligands orientation in their EuIII coordination spheres. The presence of pseudo σh-mirror symmetry in 2- iPr RRRR/2- iPr SSSS promotes a pair of distinguishable EuIII geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f–f transitions in the EuIII core. The EuIII self-assemblies exhibit intense CPL with different observed |g lum| values (2- Ph RRRR/ 2- Ph SSSS ∼ |0.31|, 2- iPr RRRR/2- iPr SSSS ∼ |0.08|, 3- Ph RRRR/ 3- Ph SSSS ∼ |0.31| in chloroform).