A homochiral 3D covalent framework assembled from vertical chiral layers with achiral bridging ligands

A novel metal-organic coordination polymer, [Cd(HPT)₂(4,4′-bpy)]_n (PT=phthalate), has been hydrothermally synthesized and characterized by elemental analysis, IR, TG and single crystal X-ray diffraction. Colorless crystals crystallized in the tetragonal system, space group I4₁22, a=8.294(5), b=8.294(5), c=33.7535(17) Å, V=2321.8(18) Å³, Z=4 and R=0.0207. The structure of the compound exhibiting a homochiral 3D covalent framework based on achiral bridging ligands has been constructed by an alternating assembly of vertical chiral layers consisting of homochiral helices.     

Interlocked chiral nanotubes assembled from quintuple helices

Homochiral helical chains were rationally synthesized from C2-symmetric 1,1-binaphthyl-6,6'-bipyridine ligands and linear metal-connecting points, Ni(acac)2. Five such homochiral helices associate in parallel to form nanotubes of 2 x 2 nm in dimensions which further intertwine to form periodically ordered, interlocked nanotubular architectures that possess nanometer-scale open channels and have high affinity for aromatic molecules. Chiral crown ethers have also been successfully incorporated into the walls of these nanotubes, which promises to lead to novel chiral zeolitic materials applicable in enantioselective processes.     

Spontaneous resolution of chiral polyoxometalate-based compounds consisting of 3D chiral inorganic skeletons assembled from different helical units

Four enantiomerically pure 3D chiral POM-based compounds, [Ni(2)(bbi)(2)(H(2)O)(4)V(4)O(12)]2 H(2)O (1 a and 1 b) and [Co(bbi)(H(2)O)V(2)O(6)] (2 a and 2 b) (bbi=1,1'-(1,4-butanediyl)bisimidazole) based on the achiral ligand, different vanadate chains, and different metal centers have been synthesized by hydrothermal methods. Single-crystal X-ray diffraction analyses revealed that 1 a and 1 b, and 2 a and 2 b, respectively, are enantiomers. In 1 a and 1 b two kinds of vanadate chains with different screw axes link Ni cations to generate 3D chiral inorganic skeletons, which are connected by the achiral bbi ligands to form complicated 3D 3,4-connected chiral self-penetrating frameworks with (7(2)8)(7(2)8(2)9(2))(7(3)8(2)10) topology. They represent the first examples of chiral self-penetrating frameworks known for polyoxometalate (POM) systems. Contrary to 1 a and 1 b, in 2 a and 2 b the vanadate chains link Co(II) cations to generate 3D chiral inorganic skeletons, which are assembled from two kinds of heterometallic helical units of opposite chirality along the c axes. The chiral inorganic skeletons are connected by bbi to form 3D 3,4-connected chiral POM-based frameworks with (6(2)8)(2)(6(2)8(2)10(2)) topology. It is believed that the asymmetrical coordination modes of the metal cations in 1 a-2 b generate the initial chiral centers, and that the formation of the various helical units and the hydrogen bond interactions are responsible for preservation of the chirality and spontaneous resolution when the chirality is extended into the homochiral 3D-networks. This is the first known report of chiral POM-based compounds consisting of 3D chiral inorganic skeletons being obtained by spontaneous resolution upon crystallization in the absence of any chiral source, which may provide a rational strategy for synthesis of chiral POM-based compounds by using achiral ligands and POM helical units.     

Two luminescent enantiomorphic 3D metal-organic frameworks with 3D homochiral double helices

Two enantiomorphic Cd(II) coordination polymers with three-dimensional homochiral double helices have been assembled respectively from two tripodal enantiopure amino acid derivatives, which exhibit (3,4)-connected (6(3))(6(3).10(3)) topology and strong purple fluorescence.     

Spontaneously resolved homochiral 3D lanthanide-silver heterometallic coordination framework with extended helical Ln-O-Ag subunits

Two novel homochiral lanthanide-silver heterometallic coordination polymers LnAg(OAc)(IN)3 [Ln = Nd (1), Eu (2), HIN = isonicotinic acid, HOAc = acetic acid] have been prepared under hydrothermal conditions, which were characterized by elemental analysis, infrared, thermogravimetric analysis, and single-crystal X-ray diffraction. Both complexes are isostructural and crystallize in a hexagonal system, chiral space group P6(1)22. Both polymers are constructed from infinite right-handed homochiral helical chains with Ln-O-Ag connectivity, representing the first examples of homochiral lanthanide-transition metal heterometallic coordination polymers with a 3D coordination framework based on spontaneous resolution. Furthermore, the luminescent properties of 2 were studied.     

A homochiral luminescent 2D porous coordination polymer with collagen-type triple helices showing selective guest inclusion

A homochiral luminescent porous coordination polymer, [Cd(L)(H(2)O)]·3H(2)O, with interconnected collagen like triple-helical chains has been synthesized solvothermally by using cadmium(II) salt and a newly designed d-isosorbide-based, enantiomerically pure chiral ligand. The framework is a 2D porous material and forms a 1D channel along the a axis, with the channel dimensions ~6.2 × 4.4 ?(2). The compound has high selectivity in the uptake of water and methanol over other solvents (e.g., tetrahydrofuran, ethanol, benzene, and cyclohexane) inside the channels.     

Construction of two 3D homochiral frameworks with 1D chiral pores via chiral recognition

The reactions of a pair of enantiomers of macrocyclic nickel(II) complexes with racemic penicillamine generated two 3D hydrogen-bonded homochiral frameworks of {[Ni(f-(SS)-L)](2)(l-pends)(ClO(4))(2)}(n) (Λ-1) and {[Ni(f-(RR)-L)](2)(d-pends) (ClO(4))(2)}(n) (Δ-1). The frameworks possess 1D tubular pores and opposite right/left-handed helical porous surfaces (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; pends(2-) = penicillaminedisulfide anion).     

Spontaneous resolution of a 3D chiral polyoxometalate-based polythreaded framework consisting of an achiral ligand

Two enantiomerically 3D chiral POM-based architectures have been constructed based on the achiral ligand bbi, [V10O26](4-) polyoxoanion and mixed valence Cu(I/II) without a chiral auxiliary, and they represent the first examples of enantiomerically 3D POM-based compounds using achiral ligands.     

Double-stranded helices and molecular zippers assembled from single-stranded coordination polymers directed by supramolecular interactions

Using three nonlinear dicarboxylates, isophthalate (ipa), 4,4'-oxybis(benzoate) (oba), and ethylenedi(4-oxybenzoate) (eoba), we have prepared five neutral infinite copper(II) dicarboxylate coordination polymers containing lateral aromatic chelate ligands, namely [Cu(ipa)(2,2'-bpy)]n.2nH2O (1), [Cu2(ipa)2(phen)2H2O]n (2), [Cu(oba)(phen)]n (3), [Cu(oba)(2,2'-bpy)]n (4), and [Cu(eoba)(phen)]n (5; 2,2'-bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) by hydrothermal synthesis. X-ray single-crystal structural analyses of these complexes reveal that the nonlinear flexible or V-shaped dicarboxylates can induce the helicity or flexuousity of the polymeric chains and aromatic chelate ligands are important in providing potential supramolecular recognition sites for pi-pi aromatic stacking interactions. An appropriate combination of the bridging dicarboxylate and aromatic chelate can induce a pair of single-stranded helical or flexuous chains to generate a double-stranded helix or molecular zipper through supramolecular interactions, respectively.     

A 2D homochiral inorganic-organic framework exhibiting a spin-flop transition

A 2D homochiral inorganic-organic framework {[Mn(NPTA)(4,4'-bpy)(H(2)O)]·(H(2)O)(2)}(n) was prepared by assembling achiral polar 4-nitrophthalic acid, manganese ions, and ancillary 4,4'-bipyridine ligands (NPTA = 4-nitrophthalate) (4,4'-bpy = 4,4'-bipyridine). The isomorphous Zn(ii) compound was also prepared as a diamagnetic analogue. Adjacent manganese spin centres are linked by the syn-anti carboxylate to form a helical chain, and chains of the same chirality are connected by 4,4'-bpy ligands to generate a homochiral layered framework. Edge-to-face aromatic interactions between neighboring layers lead to a 3D homochiral supramolecular structure. Magnetization and heat capacity measurements indicate that the framework is a weak antiferromagnet at low applied field. The magnetic interactions between adjacent manganese ions in the helical chain can be fitted using the 1D Fisher model, with 2J/k = -0.68 K and g = 2.00. Moreover, the compound displays a unique field-dependent spin-flop transition in high magnetic fields, with a critical field of 23.6 kOe at 1.9 K.     

A nanoporous chiral metal-organic framework material that exhibits reversible guest adsorption

Assembly of the novel homochiral ligand L(S) (where L(S) is 1,4-benzylidene-bis(S,S)-4-yl-3,5-bis(1-hydroxyethyl)-1,2,4-triazole) and AgNO3 generates a robust, porous, chiral and cationic framework that exhibits reversible guest adsorption.     

Homochiral 3D open frameworks assembled from 1- and 2-D coordination polymers

Homochiral 3D open frameworks have been assembled from 1- and 2-D coordination structures via hydrogen bonding and are stable towards the removal of included guest molecules.     

A homochiral triple helix constructed from an axially chiral bipyridine

A homochiral triple helix was self-assembled from an axially chiral bipyridine and a linear metal-connecting point, which further assembles into a 2D network via infinite pi...pi stacking interactions and acts as a host for the inclusion of guest molecules.     

1D and 2D homochiral metal-organic frameworks built from a new chiral elongated binaphthalene-derived bipyridine

Six homochiral coordination polymers 1-6 based on a new enantiopure elongated (S)-2,2'-diethoxy-1,1'-binaphthyl-6,6'-bis(4-vinylpyridine) ligand (L) and divalent metal (Zn, Cd, and Ni) connecting points were synthesized and characterized by single-crystal X-ray diffraction studies. These new homochiral coordination polymers adopt two distinct framework structures: a one-dimensional infinite chain structure with bridging L ligands occupying the axial positions of the metal centers and a two-dimensional rhombic grid structure formed by linking octahedrally coordinated metal centers with four pyridyl groups of bridging L ligands in the equatorial positions. The structures of these coordination polymers are sensitive to the nature of the anions as well as the solvents from which the coordination polymer crystals were grown. Powder X-ray diffraction studies showed that the two-dimensional chiral rhombic grids exhibited porosity, which could potentially find applications in enantioselective separations and catalysis.     

New 3D and chiral 1D CuIICrIII coordination polymers exhibiting ferromagnetism

The reaction of K3[Cr(CN)6] and the copper(II) bis-diamino complex of the ligand 1,3-diaminopropane (tn) led to the new cyanide-bridged 3D polymer ([(Cu(tn)2)3(Cr(CN)6)][Cr(CN)6]) infinity (1). Crystallographic data for 1: trigonal space group R3, a = b = 15.4908(11), c = 16.7699(13) angstroms, Z = 3, V = 3485.0(4) angstroms3. By the same reaction using trans-cyclohexane-(1R,2R)-diamine [1R,2Rchxn] or trans-cyclohexane-(1S,2S)-diamine [1S,2Schxn] as ligands, the chiral 1D polymers ([Cu(1R,2Rchxn)2]3[Cr(CN)6]2.4.75H2O) infinity (2) and ([Cu(1S,2Schxn)2]3[Cr(CN)6]2.4.25H2O} infinity (3), respectively, were obtained. 2 and 3 are isostructural and crystallize in the triclinic space group P1, with a = 8.5421(6), b = 12.6379(9), c = 16.1571(11) angstroms, alpha = 104.594(5) degrees , beta = 98.425(6) degrees , gamma= 97.440(5) degrees , Z = 1, V = 1644.3(2) angstroms3 for 2, and a = 8.5435(8), b = 12.6309(12), c = 16.1711(17) angstroms, alpha = 104.632 degrees , beta = 98.429(8) degrees , gamma = 97.375(8) degrees , Z = 1, and V = 1645.1(3) angstroms3 for 3. The complexes have been characterized by X-ray crystallography, IR, and magnetic susceptibility measurements. The chirality of 2 and 3 has been confirmed by circular dichroism measurements in the solid state. From the magnetic point of view, 1 shows 3D ferromagnetic ordering at ca. 4K, and 2 shows a weak intrachain ferromagnetic exchange, as a result of magnetic orbital orthogonality between Cr(III) and Cu(II) in the chain, with very long Cu-N(cyano) distances (2.665(5) and 2.671(5) angstroms) due to the long Jahn-Teller axis of the copper(II) ions.     

Synthesis,characterization and NLO properties of a new 3D coordination polymer assembled from p-aminobenzoic acid

Reaction of Zn(NO₃)₂·6H₂O with p-aminobenzoic acid in a 1:2 molar ratio under ethanol medium at room temperature affords a new three dimensional (3D) coordination polymer [Zn(PABA)₂]·H₂O (1) (PABA = p-aminobenzoic acid). Single-crystal X-ray diffraction reveals that 1 crystallizes in the orthorhombic system, space group P2₁2₁2₁, a = 7.614(2), b = 11.133(3), c = 16.869(4). 1 adopts a 3D open framework with H₂O molecules in the cavities. PABA, acting as bridging ligand as well as coordinating ligand, adopts a different coordination mode to bridge Zn atoms and form the 3D supramolecular structure which is further stabilized by N–H?O, O–H?O hydrogen bonding and π–π stacking interactions. Powder second-harmonic generation (SHG) efficiency measurement with Nd:YAG laser (1064 nm) radiation shows that the SHG efficiency of 1 is equivalent to KDP crystal. The present work also demonstrates that the framework of 1 is retained after removal of the guest H₂O molecules, and the H₂O molecules can be reintroduced into the framework, indicating that this complex may also be used to generate porous materials.     

1D, 2D and 3D luminescent zinc(II) coordination polymers assembled from varying flexible thioether ligands

Using a series flexible thioether ligands, 4-(2-pyridylmethylthio)benzoic acid (HL(1)), 4-(4-pyridylmethylthio)benzoic acid (HL(2)) and 4-(3-pyridylmethylthio)benzoic acid (HL(3)), a 1D infinite chain [Zn(3)(L(1))(6)](n) (), a 2D interpenetrating sheet [Zn(L(2))(2)](n) (), and a chiral 3D framework [Zn(L(3))(2)H(2)O](n) () were obtained. Luminescent properties of these compounds were also studied.     

A chiral, heterometallic metal-organic framework derived from a tris(chelate) coordination complex

A novel tris(chelate) metalloligand has been used to synthesize a chiral, heterometallic metal-organic framework that is robust to solvent removal and shows selective uptake of nitroaromatic compounds.