Unprecedented three-dimensional hydrogen-bonded hex topological chiral lanthanide–organic frameworks built from an achiral ligand

Abstract

The design and preparation of chiral metal–organic frameworks (CMOFs) from achiral ligands are a big challenge. Using 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid (HL) as a new linker, a total of eight chiral lanthanide–organic frameworks (LOFs), namely poly[diaquatris[μ2‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ2O:O′]lanthanide(III)], l‐ and d‐[Ln(C12H7N2O4)3(H2O)2]n [(1), Ln = Eu; (2), Ln = Gd; (3), Ln = Dy; (4), Ln = Tb], were hydrothermally synthesized without chiral reagents and determined by X‐ray crystallography. Crystal structure analyses show that l‐(1)–(4) crystallize in the hexagonal P65 space group and are isomorphous and isostructural, while the enantiomers d‐(1)–(4) crystallize in the hexagonal P61 space group. All LnIII ions are octacoordinated by six carboxyl O atoms of six 3‐nitro‐4‐(pyridin‐4‐yl)benzoate ligands and two water molecules in a dodecahedral geometry. A one‐dimensional neutral helical [Ln2(CO2)3]n chain is observed in (1)–(4) as a chiral origin. These helical chains are further interconnected via directional hydrogen‐bonding interactions between pyridyl groups and water molecules to construct a three‐dimensional (3D) homochiral network with hex topology. The present CMOF structure is the first chiral 3D hydrogen‐bonded hex‐net and shows good water stability. Solid‐state circular dichroism (CD) signals revealed that (1)–(4) crystallized through spontaneous resolution. Furthermore, (1) and (4) display a strong red and green photoluminescence at room temperature, respectively, but their intensities reduce to almost half at 200 °C. Notably, upon excitation under visible light (463 nm), a circularly polarized luminescence (CPL) of (1) in the solid state is observed for the first time, with a glum value of 2.61 × 10−2.

Two topologically different 3D CuII metal–organic frameworks assembled from the same ligands: control of reaction conditions

“…Very few MOFs are stable in both acidic and basic solutions (Wang, Jin et al, 2013;Zhu et al, 2018). The superior water and chemical stabilities of (1) may be ascribed to the synergistic effect of robust 3D structure, different coordination abilities between the hard-base carboxylate and sulfonate groups and the soft-base N-atom donors of the 4,4 0 -bpy coligands (Qin et al, 2018) and abundant hydrogen-bond interactions.…”

Chiral Lanthanide Complexes with l- and d-Alanine: An X-ray and Vibrational Circular Dichroism Study

“…There is a persistent interest in the chiral complexes of metals with the 4 f n electron configuration [ 50 , 51 , 52 , 53 , 54 , 55 ]. Nowadays, not only electronic circular dichroism (ECD) can be used for the chiroptical characterization of such species.…”

Three novel topologically different metal–organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid

“…Our current interest is to incorporate one nitro group into the pba backbone, expecting that the resulting ligand can create robust MOFs with variable topological structures. In our recent work, a series of unprecedented 3D hydrogenbonded hex topological chiral lanthanide-organic frameworks built from 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) have been reported to show solid-state circularly polarized luminescence upon excitation under visible light (Qin et al, 2018). As a continuation of our investigation on this new ligand, herein three novel MOFs, namely [CdL 2 (DMF)]ÁDMFÁ-CH 3 OH, (1), [Cd 2 L 3 (CH 3 CO 2 )]Á2DMAÁH 2 O, (2), and [NiL 2 -(H 2 O) 2 ]Á2DMA, (3), have been synthesized by solvothermal methods (DMF = N,N-dimethylformamide and DMA = N,Ndimethylacetamide) (see Scheme 1).…”