as a Versatile and Predictable Chiral Stationary Phase for the Resolution of Racemic Mixtures

Metal-organic frameworks (MOFs) have become promising materials for multiple applications due to their controlled dimensionality and tunable properties. The incorporation of chirality into their frameworks opens new strategies for chiral separation, a key technology in the pharmaceutical industry as each enantiomer of a racemic drug must be isolated. Here, we describe the use of a combination of computational modeling and experiments to demonstrate that high-performance liquid chromatography (HPLC) columns packed with TAMOF-1 as the chiral stationary phase are efficient, versatile, robust, and reusable with a wide array of mobile phases (polar and non-polar). As proof of concept, in this article, we report the resolution with TAMOF-1 HPLC columns of nine racemic mixtures with different molecular sizes, geometries, and functional groups. Initial in silico studies allowed us to predict plausible separations in chiral compounds from different families, including terpenes, calcium channel blockers, or P-stereogenic compounds. The experimental data confirmed the validity of the models and the robust performance of TAMOF-1 columns. The added value of in silico screening is an unprecedented achievement in chiral chromatography.

Chiral Metal-Organic Frameworks

In the past two decades, metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) assembled from metal ions or clusters and organic linkers via metal-ligand coordination bonds have captivated significant scientific interest on account of their high crystallinity, exceptional porosity, and tunable pore size, high modularity, and diverse functionality. The opportunity to achieve functional porous materials by design with promising properties, unattainable for solid-state materials in general, distinguishes MOFs from other classes of materials, in particular, traditional porous materials such as activated carbon, silica, and zeolites, thereby leading to complementary properties. Scientists have conducted intense research in the production of chiral MOF (CMOF) materials for specific applications including but not limited to chiral recognition, separation, and catalysis since the discovery of the first functional CMOF (i.e., d- or l-POST-1). At present, CMOFs have become interdisciplinary between chirality chemistry, coordination chemistry, and material chemistry, which involve in many subjects including chemistry, physics, optics, medicine, pharmacology, biology, crystal engineering, environmental science, etc. In this review, we will systematically summarize the recent progress of CMOFs regarding design strategies, synthetic approaches, and cutting-edge applications. In particular, we will highlight the successful implementation of CMOFs in asymmetric catalysis, enantioselective separation, enantioselective recognition, and sensing. We envision that this review will provide readers a good understanding of CMOF chemistry and, more importantly, facilitate research endeavors for the rational design of multifunctional CMOFs and their industrial implementation.

Homochiral metal-organic frameworks for enantioseparation

Obtaining homochiral compounds is of high importance to human health and environmental sustainability. Currently, enantioseparation is one of the most effective approaches to obtain homochiral compounds. Thanks to their controlled synthesis and high efficiency, homochiral metal-organic frameworks (HMOFs) are one of the most widely studied porous materials to enable enantioseparation. In this review, we discuss the chiral pocket model in depth as the key to unlock enantioselective separation mechanisms in HMOFs. In particular, we classify our discussion of these chiral pockets (also regarded as "molecular traps") into: (a) achiral/chiral linker based helical channels as a result of packing modality; and (b) chiral pores inherited from chiral ligands. Driven by a number of mechanisms of enantioseparation, conceptual advances have been recently made in the design of HMOFs for achieving high enantioseparation performances. Herein, these are systematically categorised and discussed. Further we elucidate various applications of HMOFs as regards enantioseparation, systematically classifying them into their use for purification and related analytical utility according to the reported examples. Last but not the least, we discuss the challenges and perspectives concerning the rational design of HMOFs and their corresponding enantioseparations.

CFA-18: a homochiral metal-organic framework (MOF) constructed from rigid enantiopure bistriazolate linker molecules

In this work, we introduce the first enantiopure bistriazolate-based metal-organic framework, CFA-18 (Coordination Framework Augsburg-18), built from the R-enantiomer of 7,7,7',7'-tetramethyl-6,6',7,7'-tetrahydro-3H,3'H-5,5'-spirobi[indeno[5,6-d]-[1,2,3]triazole] (H2-spirta). The enantiopurity and absolute configuration of the new linker were confirmed by several chiroselective methods. Reacting H2-spirta in hot N,N-dimethylformamide (DMF) with manganese(ii) chloride gave CFA-18 as colorless crystals. The crystal structure with the composition [Mn2Cl2(spirta)(DMF)2] was solved using synchrotron single-crystal X-ray diffraction. CFA-18 shows a framework topology that is closely related to previously reported metal-azolate framework (MAF) structures in which the octahedrally coordinated manganese(ii) ions are triazolate moieties, and the chloride anions form crosslinked one-dimensional helical chains, giving rise to hexagonal channels. In contrast to MAFs crystallizing in the centrosymmetric space group R3[combining macron], the handedness of the helices found in CFA-18 is strictly uniform, leading to a homochiral framework that crystallizes in the trigonal crystal system within the chiral space group P3121 (no. 152).

Syntheses, crystal structures, dye degradation and luminescence sensing properties of four coordination polymers

Four coordination polymers based on the pyridyl-carboxyl ligand have been solvothermally synthesized and characterized. The heterogeneous catalytic oxidation activities of 1–3 and luminescence titration experiments for 4 have been studied.

Two-step chiral transfer from d-penicillamine to metallosupramolecular ionic crystals

Treatment of a racemic RhIII4ZnII4 complex, (Δ)4/(Λ)4-[Zn4O{Rh(aet)3}4]6+ (aet = 2-aminoethanethiolate), with d-penicillaminate (d-pen) gave optically pure ionic crystals composed of (Λ)4-[Zn4O{Rh(aet)3}4]6+ and ΛD-[Rh(d-pen)3]3-via intramolecular and intermolecular chiral transfers from d-pen.

Stacking changes of KLi[Sb2(C4H2O6)2] homochiral layers mediated by interlayer solvent molecules

A new compound KLi[Sb2(C4H2O6)2]·4H2O, 1, was synthesized in single crystal form by slowly evaporating an aqueous solution of potassium antimony tartrate and lithium nitrate. The structure of 1 consists of homochiral layers of antimony tartrate dimers linked by LiO4 tetrahedra. The interlayer water molecules can be reversibly driven out by heating or exchanged by small alcohol molecules under ambient conditions, occurring via single-crystal to single-crystal transformations. To accommodate different interlayer molecules, the interlayer space is changed by adjusting the relative lateral shift of neighboring layers. A similar adjustment in the layer stacking also occurs in a structural phase transition caused by order-disorder transformation of the arrangement of interlayer methanol molecules at low temperature.

Two 3D nonlinear optical and luminescent lanthanide-organic frameworks with multidirectional helical intersecting channels

Two chiral 3D lanthanide-organic frameworks with multidirectional helical intersecting channels, [Ln(Hpzc)(Hida)]_n were hydrothermally synthesized and characterized.

Molecular tectonics: gas adsorption and chiral uptake of (l)- and (d)-tryptophan by homochiral porous coordination polymers

The combination of an enantiomerically pure tecton with a Cu(ii) cation yields robust porous homochiral crystals displaying preferential adsorption ofl-tryptophan.