Three-Dimensional Homochiral Covalent Organic Frameworks with Intrinsic Chiral Topology

Although a variety of chiral porous framework materials have been reported, there are few examples known to combine molecular chirality, helicity, and three-dimensional (3D) intrinsically chiral topology in one structure, which is beneficial for chirality transfer and amplification. Here, we report the synthesis of the first two 3D covalent organic frameworks (COFs) with an intrinsic chiral qzd topology, which exhibit unusual integration of various homochiral and homohelical features. By imine condensation of 4-connected porphyrin tetraamines and 2-connected enantiopure diene dialdehyde, we prepared two isostructural COFs with a noninterpenetrated qzd topology. The specific geometry and conformation flexibility of the V-shaped diene linker control the alignment of square-planar porphyrin units with rotational linkages and facilitate the creation of homochiral extended porous structures that feature a helical arrangement of porphyrins. Post-synthetic metalation of CCOF 23 with Rh(I) affords a heterogeneous catalyst for the asymmetric Michael addition reaction of aryl boronic acids to 2-cyclohexenone, which shows higher enantioselectivities compared to their homogeneous counterparts, presumably due to the confined effect of helical channels. This finding will provide an impetus to explore multichirality materials, offering new insights into the generation and control of helicity, homochirality, and enantioselectivity in the solid state.

A novel 3D Cu(i) coordination polymer based on Cu6Br2 and Cu2(CN)2 SBUs: in situ ligand formation and use as a naked-eye colorimetric sensor for NB and 2-NT

A novel 3D Cu(i) coordination polymer based on Cu₆Br₂ and Cu₂(CN)₂ SBUs shows strong green light emission and sensing properties for NB and 2-NT.

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.

Self-triggered conformations of disulfide ensembles in coordination polymers with multiple metal clusters

Five coordination polymers containing manganese(ii) ions, 6,6′-dithiodinicotinate, and/or N-donor coligands display mononuclear, trinuclear cluster and polymeric metal oxide wire and exhibit intrinsic biomimetic characteristics.

A two-dimensional Cd(II) coordination polymer with 2,2'-(disulfanediyl)dibenzoate and 1,10-phenanthroline ligands

In poly[[μ3-2,2'-(disulfanediyl)dibenzoato-κ(5)O:O,O':O'',O'''](1,10-phenanthroline-κ(2)N,N')cadmium(II)], [Cd(C14H8O4S2)(C12H8N2)]n, the asymmetric unit contains one Cd(II) cation, one 2,2'-(disulfanediyl)dibenzoate anion (denoted dtdb(2-)) and one 1,10-phenanthroline ligand (denoted phen). Each Cd(II) centre is seven-coordinated by five O atoms of bridging/chelating carboxylate groups from three dtdb(2-) ligands and by two N atoms from one phen ligand, forming a distorted pentagonal-bipyramidal geometry. The Cd(II) cations are bridged by dtdb(2-) anions to give a two-dimensional (4,4) layer. The layers are stacked to generate a three-dimensional supramolecular architecture via a combination of aromatic C-H···π and π-π interactions. The thermogravimetric and luminescence properties of this compound were also investigated.

Preparation and topological properties of two structures with p-sulfobenzoic ligands and Zn2+ and Mn2+ ions

There has been recent interest in coordinated polymers due to their structural and topological properties; therefore, the search for efficient synthesis processes to construct these materials by exploiting different organic ligands has intensified.

A series of novel zinc(II) entangled coordination polymers based on carboxyphenyl-terpyridine ligands

Hydrothermal synthesis has afforded five divalent zinc coordination polymers containing 4-(4-carboxyphenyl)-2,2':6',2''-terpyridine (HL1) or its isomer 4-(4-carboxyphenyl)-2,2':4',4''-terpyridine (HL2), with or without the addition of auxiliary ligands, 1,3,5-benzenetricarboxylic acid (H3btc) and 1,4-benzenedicarboxylic acid (H2bdc). Their structures have been characterized by single crystal X-ray analyses and further characterized by infrared spectra, elemental analyses, powder X-ray diffraction, thermogravimetric analyses and photoluminescent spectra. Across this series, the π···π interactions have a dramatic impact on the self-assembly of these entanglement structures, in either case it can exert an important structure-directing role. In addition, the disposition of pyridine nitrogen atoms in ligands also plays a large role in structure direction in this system. Complex 1 is a 2D + 2D→3D inclined polycatenated coordination polymer based on the resulting array of 2D (6,3) layers constructed by 1D→2D π···π directed self-assembly. Complex 2 is assembled into a 3D framework by means of 1D + 1D→3D mutual interdigitation based on 1D→1D self-assembly driven by π···π stacking interactions. Complex 3 shows a 2D + 2D→3D interdigital network involving 2D + 2D→2D parallel interpenetrated and 2D + 2D→2D interdigital (4,4) layer motifs. Complex 4 displays a 2D + 2D→3D polythreaded framework based on a 2D (4,4) network comprised of alternating rings and rods. Complex 5 is a (3,4)-connected 3D framework with topology (4.8(2).10(3))(4.8(2)). In comparison with covalently connected entanglements, such π···π directing self-assembly of entanglements are far less explored, especially, polycatenane based on 1D chain motifs and polythread based on 2D layer motifs are rarely reported. Furthermore, the luminescent properties of complexes 1-5 at room temperature have also been studied in detail herein.

Syntheses, Photoluminescent Properties, and Structural Investigation of Five Complexes based on a New T-Shaped 2-(Pyridin-3-yl)-4,6-Pyrimidine Dicarboxylic Acid Ligand: Structure Evolution from One-dimensional Chains to Three-dimensional Architectures

A series of structurally diverse coordination polymers, [Mn(ppmdc)(H2O)2]n (1), [Cu(ppmdc)(H2O)2]n (2), {[Co(ppmdc)][Co(ppmdc)(H2O)]}n (3), [Zn(ppmdc)(H2O)]n (4), and [Cd(ppmdc)]n (5) (H2ppmdc = 2-(pyridin-3-yl)-4,6-pyrimidine dicarboxylic acid) were obtained from metal salts and H2ppmdc under hydrothermal conditions. Single crystal X-ray structural analysis reveals that complexes 1–5 have different structures, ranging from one- to three-dimensions, which are mainly due to the different metal ions, and especially the coordination mode of the H2ppmdc ligand. Complexes 1 and 2 are 1D coordination polymers, in which the ppmdc2– ligand adopts a bis-(bidentate) mode to link metal ions. Complexes 3 and 4 feature a 2D metal-organic framework with Schläfli topologies of (4.62) (42.62.82) and (4.82), respectively, in which the metal ions are bridged by μ3-ppmdc2– ligands. Complex 5 possesses a 3D nanotubular metal-organic framework with a point symbol of (49.66) topology built up from the 6-connected ppmdc2– ligands and Cd(ii) ions. The thermal properties of complexes 1–5 have been determined. Moreover, investigation of photoluminescent properties reveals that the configuration of ppmdc2– resulting from metal-directed coordination has a profound effect on the fluorescence emissions of complexes 4 and 5.