Synthesis of Metal-Organic Zeolites with Homochirality and High Porosity for Enantioselective Separation.

Using lactic acid derivatives as chiral ligands, a pair of unprecedented homochiral metal-organic zeolites have been synthesized that feature zeotype CAN topology and have high porosity for enantioselective separation of racemates.

Catenation of Homochiral Metal-Organic Nanocages or Nanotubes.

Catenation based on homochiral metal-organic nanocages or nanotubes is realized in this work for the first time. A flexible enantiopure ligand is employed to assemble metal ions, with the structure-directing effect of an auxiliary ligand, a triangular-prism-like nanocage, and a nanotube successfully built. Further 0D → 3D catenation is achieved by interlocking the nanocages, and 1D → 3D catenation based on nanotubes is also presented. This work reveals extraordinary catenating architectures from molecular cages and tubes.

Size-Dependent Enantioselective Adsorption of Racemic Molecules through Homochiral Metal-Organic Frameworks Embedding Helicity.

Homochiral metal-organic frameworks (HMOFs) are efficient materials for enantioselective adsorption. However, the combination of size selectivity and enantioselectivity is still a major challenge in the field of HMOFs. Herein, two enantiomorphic HMOFs built from predesigned proline-derived ligands are presented. Both of them show multiple homochiral features: they contain four different helical chains and three types of helical channels. Due to the size effect of the helical channels, each HMOF can enantioselectively adsorb methyl lactate with high ee. The results reveal a new approach toward size-dependent enantioselective separation of racemic compounds by using HMOFs built from inexpensive proline derivatives.

Homochiral metal-organic frameworks with enantiopure proline units for the catalytic synthesis of ß-lactams.

Two enantiopure organic ligands integrating flexible proline units and rigid isophthalate units have been rationally designed and employed for the construction of four homochiral porous metal-organic frameworks (MOFs), respectively. One pair of these MOFs is used as heterogeneous catalysts to construct ß-lactam derivatives by oxidative coupling reactions.

3D semiconducting Co-MOFs based on 5-(hydroxymethyl)isophthalic acid and imidazole derivatives: syntheses and crystal structures.

Two three-dimensional cobalt-based metal-organic frameworks with 5-(hydroxymethyl)isophthalic acid (H2HIPA), namely poly[[µ2-1,4-bis(2-methyl-1H-imidazol-1-yl)benzene-κ2N3:N3'][µ2-5-(hydroxymethyl)isophthalato-κ2O1:O3]cobalt(II)], [Co(C9H6O5)(C14H14N4)]n (1), and poly[tris[µ2-1,4-bis(1H-imidazol-1-yl)benzene-κ2N3:N3']bis[µ3-5-(hydroxymethyl)isophthalato-κ2O1:O3:O5]dicobalt(II)], [Co2(C9H6O5)2(C12H10N4)3]n (2), were synthesized under similar hydrothermal conditions. Single-crystal X-ray diffraction analyses revealed that 5-(hydroxymethyl)isophthalate (HIPA2-) and 1,4-bis(2-methyl-1H-imidazol-1-yl)benzene (1,4-BMIB) are simple linkers connecting cobalt centres to build a fourfold interpenetration dia framework in complex 1. However, complex 2 is a pillared-layer framework with a (3,6)-connected network constructed by 1,4-bis(1H-imidazol-1-yl)benzene (1,4-DIB) linkers, 3-connected HIPA2- ligands and 6-connected CoII centres. The above significant structural differences can be ascribed to the introduction of the different auxiliary N-donor ligands. Moreover, UV-Vis spectroscopy and Mott-Schottky measurements confirmed that complexes 1 and 2 are typical n-type semiconductors.

Temperature-induced solid-to-solid transformation in helical homochiral coordination polymers.

The reactions of (R)- and (S)-4-(1-carboxyethoxy)benzoic acid (H2CBA) with 1,3-bis(2-methyl-1H-imidazol-1-yl)benzene (1,3-BMIB) ligands afforded a pair of homochiral coordination polymers (CPs), namely, poly[[[µ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][µ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate], {[Zn(C10H8O5)(C14H14N4)]·H2O}n or {[Zn{(S)-CBA}(1,3-BMIB)]·H2O}n (1-L), and poly[[[µ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][µ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate] (1-D). Three kinds of helical chains exist in compounds 1-D and 1-L, which are constructed from ZnII atoms, 1,3-BMIB ligands and/or CBA2- ligands. When the as-synthesized crystals of 1-L and 1-D were further heated in the mother liquor or air, poly[[µ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][µ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)], [Zn(C10H8O5)(C14H14N4)]n or [Zn{(S)-CBA}(1,3-BMIB)]n (2-L), and poly[[µ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][µ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] (2-D) were obtained, respectively. The single-crystal structure analysis revealed that 2-L and 2-D only contained one type of helical chain formed by ZnII atoms and 1,3-BMIB and CBA2- ligands, which indicated that the helical chains were reconstructed though solid-to-solid transformation. This result not only means the realization of helical transformation, but also gives a feasible strategy to build homochiral CPs.

Enantiopure anion templated synthesis of a zeolitic metal-organic framework.

Utilizing (R)-H3CIA as a chiral template, an unprecedented homochiral metal-organic framework (MOF) with zeotype GIS topology is obtained from achiral 1.4-DIB ligands and Zn(II) ions, which opens up a feasible approach to create zeolitic MOFs with homochirality.

Asymmetric induction in homochiral MOFs: from interweaving double helices to single helices.

Two three-dimensional (3D) homochiral metal-organic frameworks, integrating double helical chains based on enantiopure ligands and single helical structures braided by 4,4'-bipyridine (bipy) and cadmium clusters, have been synthesized successfully, as a result of complete asymmetric induction between the two types of helix.

Integration of a semi-rigid proline ligand and 4,4'-bipyridine in the synthesis of homochiral metal-organic frameworks with helices.

A pair of 3-D homochiral metal-organic frameworks (HMOFs) based on a mixed semi-rigid 5-(2-carboxypyrrolidine-1-carbonyl)isophthalate (PIA) ligand and rigid 4,4'-bipyridine (bipy), [Co3((R)-PIA)2(bipy)3]·6H2O (1-D) and [Co3((S)-PIA)2(bipy)3]·6H2O (1-L) are synthesized and structurally characterized. They are enantiomers and exhibit three-dimensional open frameworks. In each structure, the PIA ligands link the Co centers into homochiral frameworks with large open channels that are occupied by the bipy ligands. Interesting helical chains built from the connectivity between PIA ligands and Co centers are presented. Antiferromagnetic coupling is observed in 1-D. These results demonstrated that the mixed ligand approach is successful for the construction of HMOFs.

Integration of rigid and flexible organic parts for the construction of a homochiral metal-organic framework with high porosity.

Presented is a pair of homochiral metal-organic frameworks built from mixed ligands integrating rigid and flexible organic parts, and each compound shows high porosity and can be used for enantioselective separation of racemic 1-phenethylalcohol and methyl lactate.