Spontaneous Resolution of a Mixed-Ligand Nickel(II) Coordination Polymer with Achiral Precursors

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.

Coordination-induced spontaneous resolution of a TPPE-based MOF and its use as a crystalline sponge in guest determination

In this work, by virtue of a coordination-induced fixation of the propeller-like conformation of the tetraphenylethylene (TPE) backbone, we achieved a spontaneous resolution of conglomerate-forming enantiomers of [Co(TPPE)Cl2]·4DMF (1M and 1P), as unambiguously probed by single-crystal X-ray crystallography. Benefitting from the robust, accessible, and electron-rich 1D channels, the chiral MOF turned out to be a good 'crystalline sponge' to adsorb and determine six liquid guests, of which two (2-butanol and 2-butylamine) are crystallized in an enantiospecific manner.

Spontaneous resolution of a Δ/Λ-chiral-at-metal pseudo-tetrahedral Schiff-base zinc complex to a racemic conglomerate with C–H⋯O organized 41- and 43-helices

Weak supramolecular interactions can be decisive!

Synthesis and structural diversity of d10 metal coordination polymers constructed from new semi-rigid bis(3-methyl-1H-pyrazole-4-carboxylic acid)alkane ligands

Three isomeric ligands, and four d¹⁰ metal CPs were synthesized, varying from 1D to 2D, together with achirality to chirality variation.

Achiral aromatic solvent-induced assembly of 3-D homochiral porous 3d–4f heterometallic-organic frameworks based on isonicotinic acid

Via induction of achiral aromatic solvents, two 3-D monochiral 3d–4f MOFs (1 and 2) from the ligand HIN without any chiral auxiliary are uncommonly constructed. And the results show homochirality of 1 and 2 are enantiopurity rather than enantiomeric excess.

A pair of homochiral porous metal–organic frameworks with a helical metal-carboxylate layer

By employment of predesigned proline derivative ligands ((R)-PIA and (S)-PIA) to assemble with bipy and Cd²⁺ ion, a pair of porous homochiral metal–organic frameworks (HMOFs) with a wavy Cd-PIA layer has been synthesized.

Spontaneous resolution, asymmetric catalysis, and fluorescence properties of δ- and λ-[cu(tzmp)]N enantiomers from in situ [2 + 3] cycloaddition synthesis

Although a number of acentric or chiral tetrazole complexes were synthesized from Sharpless reaction, there are no spontaneous resolution Cu(I)-tetrazole compounds from in situ [2 + 3] cycloaddition synthesis that have been reported before. The first enantiomers Δ- and Λ- of metal tetrazole compound [Cu(Tzmp)]n (1) (HTzmp = 3-tetrazolemethylpyridine) were obtained and isolated from in situ [2 + 3] cycloaddition reactions of a flexible organic nitrile (3-cyanomethylpyridine) with sodium azide in the presence of CuCl2 as the Lewis acid. Δ-1 and Λ-1 feature a homochiral helical coordination polymeric system and {4(4).6(2)} two-dimensional framework. The photoluminescence study suggests 1 exhibits strong green fluorescence in solid state with maximal emission peaks around 535 nm. Remarkably, the Δ- and Λ- of [Cu(Tzmp)]n (1) catalyzes the enantioselective Henry reaction with high yield (more than 96%) and certain enantioselectivity (up to 69%).

A homochiral magnet based on D3 symmetric [(NaO3)Co3] clusters: from spontaneous resolution to absolute chiral induction

A pair novel 3D chiral magnets have been synthesized using the achiral ligand imidazole-4-acrylate via spontaneous resolution, in which the D₃ symmetric chiral [(NaO₆)Co₃] clusters act as nodes. By using chiral induction agent, they are driven to controllable homochiral crystals.

Structural studies and detection of nitroaromatics by luminescent 2D coordination polymers with angular dicarboxylate ligands

The solvothermal synthesis and crystal structures of 2D coordination polymers involving an SDB linker with Cd(ii)/Zn(ii) nodes, and the luminescence properties of these activated compounds for the detection of nitroaromatics, have been investigated.

Chiral or achiral: four isomeric Cd(ii) coordination polymers based on phenylenediacrylate ligands

The isomeric coordination polymers derived fromp- andm-phenylenediacrylates contain similar homochiral motifs (hydrogen-bonded layers or μ-O_carboxylatebridged helical chains), but only themligand, with assistance of hydrogen bonds, induces spontaneous resolution to generate 3D homochiral networks.

Syntheses, structures, photoluminescence and photocatalysis of chiral 3D Cd(ii) frameworks from achiral mixed flexible ligands by spontaneous resolution

Two three-interpenetrating chiral cadmium MOF enantiomers with good photocatalytic activities for degradation of dyes were constructed from achiral flexible ligands.

A homochiral Cu(i) coordination polymer based on achiral precursors and its photocatalytic properties

A homochiral three-dimensional framework material has been successfully synthesized by solvothermal reaction, which is generated through an unusual spontaneous asymmetrical crystallization from achiral precursors without any enantiopure additive.

A series of coordination polymers based on varied polycarboxylates and different imidazole-containing ligands: syntheses, crystal structures and physical properties

To investigate the effect of organic ligands on the coordination frameworks, seven nickel(ii) coordination polymers, based on varied polycarboxylates and different imidazole-containing ligands, are synthesized under hydrothermal method.

A Zn-oxalate helix linked by a water helix: spontaneous chiral resolution of a Zn helical coordination polymer

Two enantiomers of a Zn helical coordination polymer have been obtained from spontaneous resolution. In this compound, homochiral Zn-oxalate helices are linked by water helices comprising coordinated and guest water.

Solvothermal synthesis, structure, and fluorescence properties of three d10 polymers assembled from semi-rigid V-shaped aza-bridged multicarboxylate

Hydrothermal reactions of azanediyldibenzoic acid and M(OH)₂ with different ancillary ligands afford three polymers. These polymers show great different structures and properties originated from the variation of second ligands and coordination modes.

Chiral template induced homochiral MOFs built from achiral components: SHG enhancement and enantioselective sensing of chiral alkamines by ion-exchange

A homochiral anionic framework built from achiral components was synthesized for enantioselective sensing of chiral alkamines. Ion-exchange with polar or chiral organic cations leads to the enhancement of the SHG efficiency.

Stereospecific generation of homochiral helices in coordination polymers built from enantiopure binaphthyl-based ligands

The novel enantiopure spacer 2,2′-dimethoxy-1,1′-binaphthyl-3,3′-bis(4-pyridyl-amido) has been designed to prepare helical coordination polymers here investigated by means of experimental and theoretical data.

Synthesis, characterisation, water adsorption and proton conductivity of three Cd(ii) based luminescent metal–organic frameworks

Three Cd(ii) based H-bonded 3D MOFs show a significant amount of uptake for water vapor and an impedance measurement indicates that they show proton conductivity at a higher temperature (358 K) at 95% relative humidity.

Strong intermolecular exciton couplings in solid-state circular dichroism of aryl benzyl sulfoxides

A series of 13 enantiopure aryl benzyl sulfoxides () with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed.