The Underexplored Field of Lanthanide Complexes with Helicene Ligands: Towards Chiral Lanthanide Single Molecule Magnets

Abstract

The effective combination of chirality and magnetism in a single crystalline material can lead to fascinating cross-effects, such as magneto–chiral dichroism. Among a large variety of chiral ligands utilized in the design and synthesis of chiral magnetic materials, helicenes seem to be the most appealing ones, due to the exceptionally high specific rotation values that reach thousands of deg×cm3×g−1×dm−1, which is two orders of magnitude higher than for compounds with chiral carbon atoms. Despite the sizeable family of transition metal complexes with helicene-type ligands, there are only a few examples of such complexes with lanthanide ions. In this mini-review, we describe the most recent developments in the field of lanthanide-based complexes with helicene-type ligands and summarize insights regarding the further exploration of this family of compounds towards multifunctional chiral lanthanide single molecule magnets (Ln-SMMs).

Multifunctional Helicene‐Based Ytterbium Coordination Polymer Displaying Circularly Polarized Luminescence, Slow Magnetic Relaxation and Room Temperature Magneto‐Chiral Dichroism**

“…However, generating helicene‐based metal‐organic 1D polymeric architectures remains challenging and very few examples are described in the literature [35] . Recently, we have shown that 3‐(2‐pyridyl)‐4‐aza[6]‐helicene (H6bpy) bearing a 2,2′‐bipyridine coordinating unit can accommodate a lanthanide ion and combine the inherent properties of the helicenic ligand with those of the lanthanide to create unprecedented chiral SMMs ( 1 ) (Figure 1a), [36–39] efficient singlet oxygen sensitizers, [40] and strong MChD response in the NIR range of the electromagnetic spectrum [41–43] . Despite their pertinent chiroptical properties, chiral emissive Yb III complexes are still scarce [18, 19, 44–49] .…”

Multifunctional Helicene‐Based Ytterbium Coordination Polymer Displaying Circularly Polarized Luminescence, Slow Magnetic Relaxation and Room Temperature Magneto‐Chiral Dichroism**

“… [35] Recently, we have shown that 3‐(2‐pyridyl)‐4‐aza[6]‐helicene (H6bpy) bearing a 2,2′‐bipyridine coordinating unit can accommodate a lanthanide ion and combine the inherent properties of the helicenic ligand with those of the lanthanide to create unprecedented chiral SMMs ( 1 ) (Figure 1a ),[ 36 , 37 , 38 , 39 ] efficient singlet oxygen sensitizers, [40] and strong MChD response in the NIR range of the electromagnetic spectrum. [ 41 , 42 , 43 ] Despite their pertinent chiroptical properties, chiral emissive Yb III complexes are still scarce. [ 18 , 19 , 44 , 45 , 46 , 47 , 48 , 49 ] Herein, we describe the synthesis of the first homochiral monodimensional coordination polymer (1D‐CP), namely M ‐ and P ‐[H6(py) 2 Yb(hfac) 3 ] n 2 and its structural features.…”

Get under the Umbrella: A Comprehensive Gateway for Researchers on Lanthanide‐Based Single‐Molecule Magnets

“…In 2021, [289] D. Pinkowicz et al. reviewed recent results on helicene‐ 4 f complexes in the framework of chiral lanthanide complexes, while in 2023 [280] the already mentioned review by S. Chorazy et al.…”