Synthesis, crystal structure, luminescent properties, and magnetic properties of lanthanide(III) complexes containing the chiral (S,S/R,R)-N,N'-bis(3,5-dinitrosalicylidene)-1,2-cyclohexanediamine ligand

In this work, we report novel enantiopure mononuclear complexes (teaH)[Ln((S,S)-dnsalcd)₂] and (teaH)[Ln((R,R)-dnsalcd)₂] (Ln = Eu³⁺ for 1 and 4, Tb³⁺ for 2 and 5, and Sm³⁺ for 3 and 6), where teaH = triethylammonium and (S,S/R,R)-H₂dnsalcd = (S,S/R,R)-N,N'-bis(3,5-dinitrosalicylidene)-1,2-cyclohexanediamine. Their unique structural features have been studied by single crystal diffraction and chiral and magnetic properties have been investigated by circular dichroism and susceptibility, respectively. Notably, 1 and 3 were found to be isomorphous and exhibited a single intramolecular π-π interaction between two (S,S)-dnsalcd^2- ligands. In contrast, 2 and 5 were found to be isomorphous and displayed two intramolecular π-π interactions between two (S,S/R,R)-dnsalcd^2- ligands. Interestingly, strong Eu³⁺/Sm³⁺-based emissions in the solid and solution states were observed by efficient antenna effects due to the π-π interaction modes of the coordinated ligands. Furthermore, density functional theory calculations indicated that 1 contained a single localized benzene group in the highest occupied molecular orbital (HOMO), whereas 2 exhibited full delocalization via π-π interactions in the HOMO.