Ming Dai

Construction of Cd(II) coordination polymers used as catalysts for the photodegradation of organic dyes in polluted water

Four Cd(II) coordination polymers formulated as {[Cd3(tpcb)2)(η,η-μ-SO4)2(H2O)6]SO4·16H2O}n (1), {[Cd(tpcb)0.75(OH)(H2O)2](NO3)}n (2), {[Cd2(tpcb)(SO4)2(H2O)6]·2MeOH·3H2O}n (3), and {[Cd(tpcb)(NO3)(H2O)2](NO3)}n (4) were synthesized by reactions of CdSO4 or Cd(NO3)2 with tetrakis(4-pyridyl)cyclobutane (tpcb) under solvothermal conditions or at ambient temperature. Compounds 1–4 were characterized by elemental analysis, IR spectroscopy, thermal analysis, powder X-ray diffraction analysis and single crystal X-ray diffraction. Compounds 1, 2, and 4 possess three different complicated 3D frameworks with the Schlafli symbols of (46)(412·54·64·88), (63)4(62·84)3 and (83)(86), respectively, while 3 presents a 1D chain structure. Compounds 1–4 exhibited relatively good photocatalytic activity towards the degradation of methyl orange (MO), methyl blue (MB) and rhodamine B (RhB) in aqueous solution. These results offered a good insight into the temperature effects on the assembly of Cd(II) coordination polymers and their photocatalytic applications.

Cracking the framework of bulk CuCN with flexible bipyrazolyl-based ligands to assemble [CuCN]n-based coordination polymers

Solvothermal reactions of CuCN with a set of flexible bipyrazolyl-based ligands with different spacer lengths [(dmpz)(CH(2))(n)(dmpz)] (dmpz = 3,5-dimethyl-pyrazolyl; n = 1-6) gave rise to six [CuCN](n)-based coordination polymers [(CuCN)(3)L](n) (1: L = dmpzm; 2: L = dmpze), [(CuCN)(2)L](n) (3: L = dmpzpr; 4: L = dmpzb; 5: L = dmpzp; 6: L = dmpzh). Compounds 1-6were characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffraction. 1 or 2 exhibits a 1D scolopendra-like chain assembled from a rare 1D zigzag [CuCN](n) chain with [CN-Cu-CN-Cu-L] (1: L = dmpzm; 2: L = dmpze) side arms. 3 or 4 shows a 2D (6,3) wave-like layer in which [Cu(6)(mu-CN)(6)L(2)](n) (L = dmpzpr or dmpzb) double chains are interconnected by pairs of L bridges. 5 consists of two [CuCN](n) single chains that are linked by dmpzp bridges to form a rare 1D chain with an oblong channel. has a 3D network in which the 2D [Cu(10)(mu-CN)(10)(dmpzh)(3)](n) layers are interconnected by pairs of dmpzh bridges. In addition, the photoluminescent properties of 1-6 in the solid state at ambient temperature were investigated.

New approaches to the degradation of organic dyes, and nitro- and chloroaromatics using coordination polymers as photocatalysts

Industrial wastewater with organic pollutants has become one of the most serious problems related to our human environment. One possible treatment is to develop environmentally friendly and efficient photocatalysts. Coordination polymers (CPs) with a structural regularity and synthetic stability provide an important possibility to perform photodegradation. Doping CPs with metal ions or loading CPs on carbon nanomaterials can extend their photoresponse region and thus enhance their catalytic activity toward the photodegradation of organic dyes. In this article, we briefly highlight some of the latest progress in the photodegradation of organic dyes using modified CP-based catalysts. The decomposition of nitro- and chloroaromatics using CPs as photocatalysts is also described.

Multi-dimensional iodocuprates of 4-cyanopyridinium and N,N′-dialkyl-4,4′-bipyridinium: syntheses, structures and dielectric properties

Solvothermal reactions of CuI with 4-cyanopyridine (4-cypy) or 4,4′-bipyridine (4,4′-bipy) and alcohols (methanol, ethanol, propanol, isopropanol) in the presence of I2 and a trace amount of water in acetonitrile gave rise to a family of multi-dimensional iodocuprate complexes of 4-cyanopyridinium and N,N′-dialkyl-4,4′-bipyridinium including {[MC]2[Cu4(μ3-I)4(μ-I)2]}n (MC+ = N-methyl-4-cyanopyridium) (1), {[PC][(Cu2I4)1/4(Cu2I4)1/4]}n (PC+ = N-propyl-4-cyanopyridinium) (2), {[iPC][(Cu2I4)1/4((Cu1/2)4I4)1/4]}n (iPC+ = N-isopropyl-4-cyanopyridium) (3), {[EV]1/4[((Cu1/2)4I4)1/4]}n (EV2+ = N,N′-diethyl-4,4′-bipyridinium) (4) and {[PV]1/2[(Cu2I4)1/4((Cu1/2)4I4)1/4]}n (PV2+ = N,N′-dipropyl-4,4′-bipyridinium) (5). The resulting 4-cyanopyridinium and viologen cations were generated in situ via the cleavage of the C–O bond of alcohols followed by alkylation of 4-cypy or 4,4′-bipy. X-ray analysis revealed that compound 1 consists of a unique three-dimensional anionic [Cu4I6]n2n− framework while compounds 2–5 contain one-dimensional anionic [Cu2I4]n2n− chains that are enclosed into different cationic channels formed by either 4-cyanopyridinium or N,N′-dialkyl-4,4′-bipyridinium. The dielectric properties of 1–5 were investigated.

Luminescent Zn(II) Coordination Polymers for Highly Selective Sensing of Cr(III) and Cr(VI) in Water

Three photoluminescent zinc coordination polymers (CPs), {[Zn2(tpeb)2(2,5-tdc)(2,5-Htdc)2]·2H2O}n (1), {[Zn2(tpeb)2(1,4-ndc)(1,4-Hndc)2]·2.6H2O}n (2), and {[Zn2(tpeb)2(2,3-ndc)2]·H2O}n (3) (tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene, 2,5-tdc = 2,5-thiophenedicarboxylic acid, 1,4-ndc = 1,4-naphthalenedicarboxylic acid, and 2,3-ndc = 2,3-naphthalenedicarboxylic acid) were prepared from reactions of Zn(NO3)2·6H2O with tpeb and 2,5-H2tdc, 1,4-H2ndc, or 2,3-H2ndc under solvothermal conditions. Compound 1 has a two-dimensional (2D) grid-like network formed from bridging 1D [Zn(tpeb)]n chains via 2,5-tdc dianions. 2 and 3 possess similar one-dimensional (1D) double-chain structures derived from bridging the [Zn(tpeb)]n chains via pairs of 1,4-ndc or 2,3-ndc ligands. The solid-state, visible emission by 1-3 was quenched by Cr3+, CrO42-, and Cr2O72- ions in water with detection limits by the most responsive complex 3 of 0.88 ppb for Cr3+ and 2.623 ppb for Cr2O72- (pH = 3) or 1.734 ppb for CrO42- (pH = 12). These values are well below the permissible limits set by the USEPA and European Union and the lowest so far reported for any bi/trifunctional CPs sensors. The mechanism of Cr3+ luminescence quenching involves irreversible coordination to free pyridyl sites in the CP framework, while the Cr6+ quenching involves reversible overlap of the absorption bands of the analytes with those of the excitation and/or emission bands for 3.

Construction of Zn(II) and Cd(II) metal–organic frameworks of diimidazole and dicarboxylate mixed ligands for the catalytic photodegradation of rhodamine B in water

A set of four metal–organic frameworks, namely, [Zn(1,3-BDC)(bmimb)]n (1), [Zn(1,4-BDC)(bmimb)]n (2), [Cd(1,3-BDC)(bmimb)]n (3), and [Cd(1,4-BDC)(bmimb)]n (4), have been prepared under solvothermal conditions (1,3-BDC = 1,3-benzenedicarboxylate; 1,4-BDC = 1,4-benzenedicarboxylate; bmimb = 4,4′-bis(4-methyl-1-imidazolyl)biphenyl). The long bmimb ligand (N⋯N separation of ca. 14.1 A) induces interpenetration of 1, 2 and 4 to increase both the framework stability and the density of effective catalytic metal centers. Compounds 1, 2 and 4 are interpenetrated 3D structures while 3 features a 2D structure. Compound 1 exhibits a parallel 2D → 3D polycatenation while 2 and 4 are isomorphous and feature 3D → 3D interpenetration. Compounds 1–4 fluoresce in the range of 350–372 nm in the solid state, whereas compounds 2 and 3 catalyze the almost complete photodegradation of rhodamine B (RhB) in water within ca. 4 h and can be recycled at least five times without loss in their crystallinity.

Novel Zn and Cd coordination polymers of 1,1′-(1,6-hexanediyl)bis-1H-benzimidazole: solvothermal synthesis, crystal structures and photoluminescence properties

Solvothermal reactions of 1,1′-(1,6-hexanediyl)bis-1H-benzimidazole (hbbm) with Zn(II), or Cd(II) salts yielded six coordination polymers, [MX2(hbbm)]n (1: M = Zn, X = Cl; 2: M = Zn, X = Br), {[CdI2(hbbm)]·0.5H2O}n (3), [CdCl2(hbbm)2]n (4), [Cd3(η,μ-OAc)2(μ-OAc)2(OAc)2(hbbm)2]n (5), and [Zn2(μ-OAc)4(hbbm)]n (6). Compounds 1–6 were characterized by elemental analysis, IR, powder X-ray diffraction, and single crystal X-ray diffraction. Compounds 1–3 contain a 1D zigzag chain in which [MX2] units are linked by hbbm bridges. For 4, each [Cd4Cl8(hbbm)4] unit acting as a planar four-connecting node connects other four equivalent ones via eight hbbm molecules to form a 2D (4,4) network. For 5, each linear [Cd3(η,μ-OAc)2(μ-OAc)2(OAc)2] unit is linked by two pairs of hbbm bridges to afford a 1D double chain. For 6, each [Zn2(μ-OAc)4] unit is connected by hbbm bridges to form a 1D U-type chain, which further interweaves with other adjacent chains to form a unique 3D net. The solid state luminescent properties of 1–6 at ambient temperature were also investigated.

Formation of Zn(II) and Pb(II) coordination polymers of tetrakis(4-pyridyl)cyclobutane controlled by benzene and toluene

Reactions of Zn(NO3)2·6H2O with tetrakis(4-pyridyl)cyclobutane (tpcb) in MeOH followed by addition of benzene or toluene gave rise to two two-dimensional (2D) coordination polymers {[Zn(tpcb)(NO3)2]·2S}n (1: S = benzene; 2: S = toluene). The analogue reactions of Pb(NO3)2 with tpcb in similar solvent systems resulted in the formation of {[Pb(tpcb)0.5(NO3)2(MeOH)]·benzene}n (3) and [Pb(tpcb)(NO3)2(MeOH)]n (4), respectively. Slow evaporation of the MeOH solution containing Pb(NO3)2 and tpcb generated [Pb(tpcb)(NO3)2(H2O)]n (5). Compounds 1 and 2 show similar 2D networks but differ in their packing modes, namely “overlapping” and “crisscross” modes. Compound 3 exhibits a 3D porous framework in which its 1D channels are occupied by benzene molecules. Compound 4 consists of 1D [Pb(tpcb)(NO3)2(MeOH)]n chains which are linked by weak Pb⋯N secondary interactions to form a 2D gridlike network. Compound 5 has a 3D structure constructed by dinuclear [Pb2(tpcb)6(NO3)4(H2O)2] units and tpcb bridges with a Schlafli symbol of (4·62)·(42·610·82). The solvent effects may be ascribed to the formation of the five 2D and 3D coordination polymers 1–5. The inclusion of benzene and toluene molecules in the frameworks of 1 and 2 along with the time lengths of their crystal growth may provide an interesting approach to the selective separation of benzene and toluene.

Capturing the Organic Species Derived from the C–C Cleavage and in Situ Oxidation of 1,2,3,4-Tetra(pyridin-4-yl)cyclobutane by [CuCN]n-Based MOFs

The solvothermal cycloreversion and in situ oxidation of 1,2,3,4-tetra(pyridin-4-yl)cyclobutane (tpcb) within [CuCN] n-based MOFs were investigated. The radical mechanism for the cycloreversion of tpcb ligands was supported by capturing a 1,3-butadiene species 1,2,3,4-tetra(4-pyridyl)-1,3-butadiene (tpyb) into {[Cu18(μ-CN)18(tpcb)4(tpyb)2]·H2O} n in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Without TEMPO, a furan-based ligand 2,3,4,5-tetra(4-pyridyl)furan (tpyf) was generated within {[Cu4(μ-CN)4(tpyf)]·4MeCN} n via the C-C cleavage, followed by in situ oxidation in acidic condition.

Post-synthetic Modification of a Two-Dimensional Metal–Organic Framework via Photodimerization Enables Highly Selective Luminescent Sensing of Aluminum(III)

Reaction of Cd(NO3)2·4H2O with 5-fluoro-1,3-bis[2-(4-pyridyl)ethenyl]benzene (5-F-1,3-bpeb) and 1,3-benzenedicarboxylic acid (1,3-H2BDC) under the solvothermal conditions gave rise to a two-dimensional metal-organic framework (MOF) [{Cd2(5-F-1,3-bpeb)2(1,3-BDC)2}·0.5DMF·2H2O] n (1). Compound 1 was postmodified by a photodimerization reaction between 5-F-1,3-bpeb ligands to yield [{Cd2( syn-dftpmcp)(1,3-BDC)2}·0.5DMF·H2O] n ( syn-dftpmcp = syn-3,4,12,13-tetrakis(4-pyridyl)-8,17-bisfluoro-1,2,9,10-diethano[2.2]metacyclophane) (2). Compounds 1 and 2 have 2D networks built from linking one-dimensional [Cd2(1,3-BDC)2] n chains via 5-F-1,3-bpeb or syn-dftpmcp bridges. After such a post-synthetic modification, compound 2, relative to 1, can probe Al3+ by using a luminescent quenching approach with much higher selectivity and sensitivity.