Chiral Metal-organic Frameworks Research Articles

A pair of 3D enantiotopic zinc(ii) complexes based on two asymmetric achiral ligands.

Enantiomorphism and enantioselectivity are critical in biology and many other applications. Herein, we report two 3D chiral MOFs {[Zn6(MIDPPA)3(1,2,4-btc)3(NO2)3(H2O)3](H2O)7}n (1L and 1R) based on achiral ligands with high enantiomeric excess and a novel topological type. The internal mechanism of spontaneous chiral symmetry breaking, during the crystallization of chiral MOFs based on achiral ligands, is elucidated for the first time from both structural and theoretical aspects. Hydrogen bonds are found to play a key role in the spontaneous symmetry breaking of chiral MOFs. Also, DFT calculations support our findings from the aspects of total energies and HOMO-LUMO energy gaps. Both 1L and 1R, exhibiting green fluorescence, present a non-centrosymmetric polar packing arrangement, resulting in good ferroelectric behaviors and second-order nonlinear optical effects.

The first porphyrin-salen based chiral metal-organic framework for asymmetric cyanosilylation of aldehydes.

The first porphyrin-salen based chiral metal-organic framework (ps-CMOF) constructed by judiciously incorporating metalloporphyrin and metallosalen struts into one MOF structure is reported, which can serve as an effective heterogeneous catalyst for the asymmetric cyanosilylation of aldehydes owing to the synergistic function between Lewis acid activation (from metalloporphyrin) and chiral induction (from metallosalen).

Control of bulk homochirality and proton conductivity in isostructural chiral metal-organic frameworks.

We have demonstrated for the first time that isostructural homochiral metal-organic frameworks (MOFs) can be synthesized directly from chiral ligands and indirectly from achiral ligands via spontaneous resolution combined with cooperative chirality induction, respectively. Moreover, the usage of different ligands leads to distinct proton conduction behaviors.

Solid-phase extraction with metal-organic frameworks for the analysis of chiral compounds.

Metal-organic frameworks (MOFs) are excellent porous materials with nanoscale cavities and high surface areas, which make them promising as novel adsorbents in solid-phase extraction (SPE). In this article we report a new application of the chiral MOF [Zn2 (D-Cam)2 (4,4'-bpy)]n in SPE used for the measurement of the enantiomeric excess (ee) of (±)-1,1'-bi-2-naphthol. Several important experimental parameters that may influence the extraction efficiency were investigated and optimized. Under the optimum conditions, a good linearity (R2 >0.999) was found between the ee value and the reciprocal of the peak areas. When compared with the actual ee measured using chiral HPLC, the SPE-based assay also showed good accuracy and precision. The results showed that SPE based on chiral MOFs as adsorbents is a simple and effective method for the determination of the ee values of chiral compounds.

Polymer-based monolithic column with incorporated chiral metal-organic framework for enantioseparation of methyl phenyl sulfoxide using nano-liquid chromatography.

A new approach to the preparation of enantioselective porous polymer monolithic columns with incorporated chiral metal-organic framework for nano-liquid chromatography has been developed. While no enantioseparation was achieved with monolithic poly(4-vinylpyridine-co-ethylene dimethacrylate) column, excellent separations of both enantiomers of (±)-methyl phenyl sulfoxide were achieved with its counterpart prepared after admixing metal-organic framework [Zn2 (benzene dicarboxylate)(l-lactic acid)(dmf)], which is synthesized from zinc nitrate, l-lactic acid, and benzene dicarboxylic acid in the polymerization mixture. These novel monolithic columns combined selectivity of the chiral framework with the excellent hydrodynamic properties of polymer monoliths, may provide a great impact on future studies in the field of chiral analysis by liquid chromatography.

Chiral Metal–Organic Framework as a Platform for Cooperative Catalysis in Asymmetric Cyanosilylation of Aldehydes

In this work, we demonstrate cooperative asymmetric catalysis by a metal–organic framework (MOF) as exemplified in the context of catalyzing cyanation of aldehydes with a VO(salen)-MOF, which after oxidation affords remarkably increased stereoselectivity (up to >99% ee) compared to the homogeneous VO(salen) counterpart as a result of the pairs of VO(salen) units in close proximity within its open channels. The cooperative asymmetric catalysis has been evidenced by the significantly decreased stereoselectivity and activity when one VO(salen) in such pairs of VO(salen) units is replaced with one Cu(salen), which results in blocking the VO–VO synergistic pathway while prompting unimolecular activation of substrates. The heterogeneous nature of VO(salen)-MOF has been verified by the fact that it can be easily recycled and reused without significant loss of catalytic activity and enantioselectivity, and its practical utility as asymmetric cyanation catalysist has been illustrated in the gram-scale synthesis of...

Recent progress of chiral stationary phases for separation of enantiomers in gas chromatography.

Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal-organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced.

Coordinative alignment of molecules in chiral metal-organic frameworks.

A chiral metal-organic framework, MOF-520, was used to coordinatively bind and align molecules of varying size, complexity, and functionality. The reduced motional degrees of freedom obtained with this coordinative alignment method allowed the structures of molecules to be determined by single-crystal x-ray diffraction techniques. The chirality of the MOF backbone also served as a reference in the structure solution for an unambiguous assignment of the absolute configuration of bound molecules. Sixteen molecules representing four common functional groups (primary alcohol, phenol, vicinal diol, and carboxylic acid), ranging in complexity from methanol to plant hormones (gibberellins, containing eight stereocenters), were crystallized and had their precise structure determined. We distinguished single and double bonds in gibberellins, and we enantioselectively crystallized racemic jasmonic acid, whose absolute configuration had only been inferred from derivatives.

Stop wiggling and hold that pose

Crystallography X-ray crystallography can be the definitive method for determining the structure and chirality of small organic molecules, but orientational disorder in the crystal can limit its resolution. Lee et al. used a chiral metal-organic framework containing formate ligands that can bind and align molecules covalently to reduce this motion (see the Perspective by Ohrstrom). The structure and absolute configuration—i.e., which spatial arrangement of atoms is the R or S isomer—of several organic molecules can thus be measured. These range from small molecules, such as methanol, to complex plant hormones, such as gibberellins that have eight stereocenters or jasmonic acid, whose absolute configuration had not previously been directly established. Science , this issue p. [808][1]; see also p. [754][2] [1]: /lookup/doi/10.1126/science.aaf9135 [2]: /lookup/doi/10.1126/science.aah5367

Structural Studies on a New Family of Chiral BioMOFs

The use of a family of dinuclear copper(II) complexes, prepared from enantiopure disubstituted oxamidato ligands derived from the natural amino acids l-alanine, l-valine, and l-leucine, as metalloligands toward barium(II) cations leads to the formation of three novel three-dimensional (3D) chiral metal–organic frameworks (MOFs). They exhibit different architectures, which serve as playground to study both how the chiral information contained in the starting enantiopure ligands is ultimately transmitted to the 3D structure and the effect of the size of the aliphatic residue of the amino acid on the final architecture.

Metal-Organic Framework [Cd(LTP)2]n for Improved Enantioseparations on a Chiral Cyclodextrin Stationary Phase in GC.

Metal-organic frameworks (MOFs) are a class of novel porous materials consisting of clusters or chains of metal ions and organic linkers. The chiral MOF [Cd(LTP)2]n (LTP = l(-)-thiazolidine-4-carboxylic acid) possesses infinite extension three-dimensional supramolecular reticular structure with right-handed helix. In this work, three capillary columns (A, B and C) containing MOF [Cd(LTP)2]n, permethylated β-cyclodextrin (CD) and sodium chloride, and MOF [Cd(LTP)2]n and permethylated β-CD, respectively, have been prepared and their respective enantioseparation abilities have been investigated. The polarities of all of the MOFs and permethylated β-CDs are moderate. The numbers of theoretical plates (plate m-1) of the three columns have been measured using n-dodecane at 120°C, which followed an increasing order of A (3100) < B (3800) < C (4300). Some racemates were separated with different resolutions on Columns A, B and C. The results indicated that the incorporated MOF [Cd(LTP)2]n enhanced the separations of racemates on a permethylated β-CD stationary phase with high column efficiency and good reproducibility in gas chromatography.

Crystal structure of poly[(4-amino-pyridine-κN)(N,N-di-methyl-formamide-κO)(μ3-pyridine-3,5-di-carboxyl-ato-κ(3) N:O (3):O (5))copper(II)

The title compound, [Cu(C7H3NO4)(C5H6N2)(C3H7NO] n , is an amino-function-alized chiral metal-organic framework with (10,3)-a topology. It has been constructed via the assembly of the achiral triconnected pyridine-3,5-di-carboxyl-ate (3,5-PDC) building block and a triconnected Cu(II) atom. Each Cu(II) ion is coordinated by two O atoms and one N atom, respectively, of three crystallographically independent 3,5-PDC ligands. The square-pyramidal (CuN2O3) coordination geometry of the Cu(II) ion is completed by an N atom of a terminal 4-amino-pyridine (4-APY) ligand and the O atom of a terminal N,N-di-methyl-formamide (DMF) ligand to give a triconnected 'T'-shaped secondary building unit, which becomes trigonal in the resulting (10,3)-a topology. In the three-dimensional structure, weak N-H⋯O hydrogen bonds are observed in which the donor N-H groups are provided by the 4-APY ligands and the acceptor O atoms are provided by the non-coordinating carboxylate O atoms of the 3,5-PDC ligands.

A 3D Homochiral MOF [Cd2(d-cam)3]•2Hdma•4dma for HPLC Chromatographic Enantioseparation.

Up to now, some chiral metal-organic frameworks (MOFs) have been reported for enantioseparation in liquid chromatography. Here we report a homochiral MOF, [Cd2(d-cam)3]·2Hdma·4dma, used as a new chiral stationary phase for high-performance liquid chromatographic enantioseparation. Nine racemates of alcohol, naphthol, ketone, and base compounds were used as analytes for evaluating the separation properties of the chiral MOF packed column. Moreover, some effects such as mobile phase composition, column temperature, and analytes mass for separations on this chiral column also were investigated. The relative standard deviations for the resolution values of run-to-run and column-to-column were less than 2.1% and 3.2%, respectively. The experimental results indicate that the homochiral MOF offered good recognition ability, which promotes the application of chiral MOFs use as stationary phase for enantioseparation.

ChemInform Abstract: Progress in the Synthetic and Functional Aspects of Chiral Metal‐Organic Frameworks

AbstractReview: 125 refs.

Three chiral metal organic frameworks used as stationary phases for the separation of racemates by open tubular capillary electrochromatography

Three chiral metal organic frameworks used as stationary phases for the separation of racemates by open tubular capillary electrochromatography

A new type of surface-enhanced Raman scattering sensor for the enantioselective recognition of d/l-cysteine and d/l-asparagine based on a helically arranged Ag NPs@homochiral MOF.

For the first time, we report the synthesis of Ag nanoparticles (NPs) arranged in a helical structure on a chiral metal-organic framework via a facile process at room temperature. This material can serve as a new type of surface-enhanced Raman scattering sensor for the efficient recognition of d/l-cysteine and d/l-asparagine enantiomers.

Constructing chiral MOFs by functionalizing 4,2′:6′,4′′-terpyridine with long-chain alkoxy domains: rare examples of neb nets

Three chiral 3D MOFs with uncommon neb topologies assemble from Co(NCS)2 and 4′-(4-nalkyloxyphenyl)-4,2′:6′,4′′-terpyridines (alkyl = hexyl or nonyl).

Sorption discrimination between secondary alcohol enantiomers by chiral alkyl-dicarboxylate MOFs

The coordination polymers withtrans-(S,S)-1,2-cyclopropane dicarboxylate or (1R,3S)-camphorate contain only one polar group in close proximity to the asymmetric C atom but show different sorption of (R) or (S) isomers of 2-butanol.

Single-handed helical framework material [{Cu(sala)}n] incorporated peramylated β-cyclodextrin for improving gas chromatography enantioseparation

Metal-organic frameworks (MOFs) as a new generation of functional molecular materials, have broad application prospects in enantioselective catalysis and chiral separation areas due to their unusual properties, such as high surface area, rich topologies, permanent microporous, availability of outer-surface modification and so on. A single-handed helical three-dimensional metal-organic framework material [{Cu(sala)}n] (H2sala=N-(2-hydroxybenzyl)-L-alanine) was incorporated with peramylated β-cyclodextrin for the preparation of novel capillary gas chromatography stationary phase. To investigate whether the use of a chiral MOF can enhance enantioseparation on peramylated β-cyclodextrin, three chiral columns were fabricated using different stationary phases for comparison, including column A ([{Cu (sala)}n]), column B (peramylated β-cyclodextrin) and column C ([{Cu(sala)}n]+peramylated β-cyclodextrin). The results of comparing the resolving abilities of the three columns for the same chiral compounds demonstrated that column C showed better enantioselectivity and higher resolution. The use of MOF [{Cu(sala)}n] can improve enantioseparation on peramylated β-cyclodextrin.

Preparation and characterization of Ni2(mal)2(bpy) homochiral MOF membrane

AbstractAs an important subclass of metal‐organic frameworks (MOFs), homochiral MOFs show special ability of asymmetric catalysis and enantioselective separation via the open chiral channels or cavities. A new homochiral MOF membrane [Ni2(mal)2(bpy)]•2H2O (Ni‐MB) was synthesized by a secondary growth technique, in which high energy ball milling was employed to prepare nanosized MOF seeds, and their synthesis condition were optimized. X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and thermal gravimetric analysis were used to measure physicochemical properties of the MOF crystals and membranes. In particular, the homochiral MOF membranes were characterized by nano‐indentation/scratch technique with high‐resolution mechanical property analysis. The SEM results indicated that the membrane was continuous and integrated without observable defects; the permeation measurements of single gas show that the permeate flux of nitrogen was independent on the transmembrane pressure, further confirming the absence of macroporous defects in the as‐prepared chiral MOF membranes. It is expected that the proposed chiral MOF membrane can be potentially applied to enantioselective separation in the future. © 2015 Curtin University of Technology and John Wiley &amp; Sons, Ltd.