A hydrogen-bond-stabilized chiral tetrakis Eu(iii) complex with strong circularly polarized luminescence

Abstract

We report the synthesis and properties of a hydrogen-bond-stabilized chiral tetrakis Eu(III) complex with enhanced circularly polarized luminescence (CPL). It is based on a Eu(III) tris[3-(heptafluoropropylhydroxymethylene)-camphorate] complex modified with tetrabutylammonium and imidazolium counterions. While the bulky tetrabutylammonium cation preserves the parent tris-diketonate framework, the smaller imidazolium cation forms a novel chiral tetrakis Eu(III) complex through stable NH⋯OC hydrogen bonding between the imidazolium N–H donor and the diketonate carbonyl acceptor. A single-crystal X-ray diffraction study indicates a square-antiprismatic geometry. CPL spectra, recorded with a Raman optical activity (ROA) spectrometer under 532 nm excitation, reveal an extremely high dissymmetric factor of 1.26 at 595 nm. In chloroform solution, additional ROA signals were detected, attributed to CPL-induced Raman scattering from the solvent. These properties highlight the convenience of hydrogen-bond-assisted stabilization. The results document an efficient approach for tuning CPL-active lanthanide complexes and demonstrate the methodological advantage of ROA-based CPL detection.