Xi-He Huang

Enantioselective Synthesis of a Chiral Coordination Polymer with Circularly Polarized Visible Laser

Circular dichroism is known to be the feature of a chiral agent which has inspired scientist to study the interesting phenomena of circularly polarized light (CPL) modulated molecular chirality. Although several organic molecules or assemblies have been found to be CPL-responsive, the influence of CPL on the assembly of chiral coordination compounds remains unknown. Herein, a chiral coordination polymer, which is constructed from achiral agents, was used to study the CPL-induced enantioselective synthesis. By irradiation with either left-handed or right-handed CPL during the reaction and crystallization, enantiomeric excesses of the crystalline product were obtained. Left-handed CPL resulted in crystals with a left-handed helical structure, and right-handed CPL led to crystals with a right-handed helical structure. It is exciting that the absolute asymmetric synthesis of a chiral coordination polymer could be enantioselective when using CPL, and provides a strategy for the control of the chirality of chiral coordination polymers.

Structural variation from 1D to 3D: effect of metal centers on the construction of metal–organic coordination polymers with N-(1H-tetrazol-5-yl)benzamide ligand

A new multifunctional semirigid acylamide ligand comprising a tetrazole ring, N-(1H-tetrazol-5-yl)benzamide (HL), has been synthesized, with which five coordination polymers of different metal ions, namely, CdL2 (1), AgL (2), MnL2 (3), CuL2 (4), PbL2 (5), have been prepared and characterized by elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction. The X-ray diffraction analysis reveals that compound 1 crystallized in a chiral space group and is a 3D non-interpenetrated diamondoid framework with Cd(II) centers in tetrahedral geometry. Compound 2 is a 2D coordination polymer with a 3-connected 4·82-fes topology. Compounds 3 and 4 are isomorphous, and both of them exhibit an interesting 2D 44-sql network while compound 5 shows 1D zigzag chains. Thermal stabilities, photoluminescence and NLO properties have also been studied.

Two lanthanide metal–organic frameworks as sensitive luminescent sensors for the detection of Cr2+ and Cr2O72− in aqueous solutions

Two lanthanide–organic frameworks [Ln(HPIDC)(m-bdc)·1.5H2O]n (Ln = Eu 1 or Tb 2; H3PIDC = 2-(4-pyridyl)-1H-imidazole-4,5-dicarboxylic acid; m-H2bdc = 1,3-benzenedicarboxylic acid) were synthesized under hydrothermal conditions. Compounds 1 and 2 are all of a 3D 6-connected pcu topology. There are uncoordinated nitrogen atoms in the molecule, indicating that the uncoordinated pyridine groups and imidazole groups can serve as functional groups. We tested their luminescence detection ability for cations and anions. Fluorescence measurements show that two compounds (1 and 2) can detect Cr2+ ions and Cr2O72− anions with high selectivity and sensitivity, which suggests that the two Ln-MOFs are promising functional luminescent sensor materials for sensing metal ions and anions.

Ammonia-modulated reversible gel–solution phase transition and fluorescence switch for a salicylhydrazide-based metal–organic gel

Based on a multi-dentate salicylhydrazide-derived ligand, a Zn-contained metal–organic gel that could stand for months has been prepared. The driving force within the supramolecular assembly was discussed by studying the gelation conditions, optical spectra, dynamic rheology and mass spectra. These studies revealed that both the coordination bonds and hydrogen bonds participate in the supramolecular assembly. In addition, electrostatic force also played as a key role in stabilizing the gel phase. The charge nature of the colloidal particle is negative charged. Consequently, the xerogel shows significant adsorption behavior that favors positively charged dye molecules, such as methyl violet and methylene blue. The title gel exhibits gelation-induced fluorescence enhancement property. When the gel was exposed to ammonia vapor, a gel–solution transition occurred, accompanied by a great weakening of fluorescence. The phase transition and fluorescence switching were found to be reversible for at least seven cycles. The mechanism involved was studied and discussed.

μ2-Acetato-κ2O:O′-tris(μ2-ferrocenecarboxylato-κ2O:O′)bis[(N,N-dimethylformamide-κO)copper(II)]

The title compound, [Cu(2)Fe(3)(C(5)H(5))(3)(C(2)H(3)O(2))(C(6)H(4)O(2))(3)(C(3)H(7)NO)(2)], belongs to the classic dimeric paddle-wheel structure type. It is an unusual example in that it contains two different carboxylate groups, viz. ferrocenecarboxylate and acetate. With three ferrocenecarboxylate groups and only one acetate group bridging the two Cu centres, a noncentrosymmetric molecular arrangement results.

catena-Poly[zinc(II)-μ3-{hydrogen [1-hydr­oxy-2-(3-pyridinio)ethane-1,1-di­yl]diphospho­nato}]

In the polymeric title compound, [Zn(C7H9NO7P2)]n, the zinc(II) centre displays a tetrahedral coordination geometry provided by four O atoms from three different phosphonate groups. The crystal structure consists of ladder chains parallel to the b axis built up from vertex-sharing of ZnO4 and PO3C tetrahedra. The chains are linked by strong intra- and interchain O—H⋯O and N—H⋯O hydrogen bonds, forming a three-dimensional supramolecular assembly.

Poly[(μ2-aqua-κ2O:O)(μ3-azido-κ3N1:N1:N3)(μ2-isonicotinato-κ2O:O′)­lead(II)]

In the title compound, [Pb(C(6)H(4)NO(2))(N(3))(H(2)O)](n), the Pb ion is seven-coordinated by three N atoms from three azide ligands, two O atoms from two isonicotinate (inic) ligands and two O atoms from two coordinated water molecules, forming a distorted monocapped triangular prismatic coordination geometry. Each azide ligand bridges three Pb(II) ions in a mu(1,1,3) coordination mode to form a two-dimensional three-connected 6(3) topology network extending in the bc plane. The carboxylate group of the inic unit and the aqua ligand act as coligands to bridge Pb(II) ions. Adjacent two-dimensional layers are connected by hydrogen-bonding interactions between the isonicotinate N atom and the water molecule, resulting in an extended three-dimensional network. The title complex is the first reported coordination polymer involving a p-block metal, an azide and a carboxylate.

New organically templated vanadium tellurites: (H2pn)[V2TeO8] (pn is propane-1,3-diamine)

The title compound, poly[propane-1,3-diaminium hexa-mu-oxido-dioxidotellurium(IV)divanadium(V)], (C3H12N2)[V2O8Te] or (H2pn)[V2TeO8] (pn is propane-1,3-diamine), contains a two-dimensional anionic layer and the diprotonated pn cation for charge compensation. The anionic layer consists of pyrovanadates and [TeO3] pyramids, which are linked alternately through corner-sharing to form a one-dimensional chain. These one-dimensional chains are crosslinked through two weak Te-O bonds, constructing an anionic layer. Hydrogen bonds are observed involving the diprotonated pn cation and the O atoms of the anionic framework.

Two pseudo-polymorphic copper-benzene-1,2,4,5-tetracarboxylate complexes.

Two pseudo-polymorphic polymers, poly[ethylenediammonium [[aquacopper(II)]-micro(4)-benzene-1,2,4,5-tetracarboxylato] dihydrate], [(C(2)H(10)N(2))[Cu(C(10)H(2)O(8))(H(2)O)].2H(2)O](n), (I), and poly[ethylenediammonium [copper(II)-micro(4)-benzene-1,2,4,5-tetracarboxylato] 2.5-hydrate], [(C(2)H(10)N(2))[Cu(C(10)H(2)O(8))].2.5H(2)O](n), (II), contain two-dimensional anionic layers, ethylenediammonium (H(2)en) cations acting as counter-ions and free water molecules. Although the topological structures of the two anionic layers are homologous, the coordination environments of the Cu(II) centres are different. In (I), the Cu(II) centre, sitting on a general position, has a square-pyramidal environment. The two independent benzene-1,2,4,5-tetracarboxylate (btc) anions rest on centres of inversion. The Cu(II) cation in (II) is located on a twofold axis in a square-planar coordination. The H(2)en cation is on an inversion centre and the btc ligand is split by a mirror plane. Extensive hydrogen-bonding interactions between the complexes, H(2)en cations and water molecules lead to the formation of three-dimensional supramolecular structures.

A new three-dimensional neutral framework of lanthanum oxalate: [La2(C2O4)3(DMF)(H2O)3]n.

In the title complex, poly[triaquabis(dimethylformamide)di-mu3-oxalato-mu2-oxalato-dilanthanum(III)], [La2(C2O4)3(C3H7NO)(H2O)3]n, both La ions are coordinated by nine O atoms, forming slightly distorted tricapped trigonal prisms. The two La ions, the terminal water O atom, and the O and N atoms of the dimethylformamide molecule reside on twofold rotation axes, giving the two La-centered coordination geometries twofold or pseudo-twofold symmetries. The two oxalate ligands, one of which rests on a center of inversion at the mid-point of the C-C bond, adopt different bridging modes, connecting with the La ions to form two types of lanthanide oxalate chains, i.e. anionic {[La(C2O4)2(DMF)(H2O)2]n-}(n) (DMF is dimethylformamide) and cationic zigzag {[La(C2O4)(H2O)]n+}n, respectively. Each zigzag cationic chain is linked to four adjacent anionic chains via the bridging oxalate anions, and each anionic chain connects with four zigzag cationic chains, constructing a three-dimensional neutral framework.