Zilu Chen

Controlling the dimensionalities and structures of homochiral Zn(II) and Cd(II) compounds of N-(p-tosyl)-S-carboxymethyl-L-cysteinevia tuning the connecting modes of metal ions and chiral linkers by different kinds of ancillary ligands

A new ligand of N-(p-tosyl)-S-carboxymethyl-L-cysteine (Ts-cmc) was prepared. The reactions of Ts-cmc with Zn(II) or Cd(II) salts in the absence or presence of ancillary ligands provided five homochiral coordination polymers [Cd(Ts-cmc)]n (1), [Cd(Ts-cmc)(4,4′-bipy)(H2O)]n (2), [Zn2(Ts-cmc)2(4,4′-bipy)2(H2O)2]n (3), [Cd(Ts-cmc)(Im)(H2O)]n (4) and [Zn(Ts-cmc)(Im)(H2O)]n (5) and one discrete dinuclear compound [Zn2(Ts-cmc)2(2,2′-bipy)2(H2O)2]·2H2O (6) (4,4′-bipy = 4,4′-bipyridine, Im = imidazole and 2,2′-bipy = 2,2′-bipyridine). Complexes 1–4 crystallize in a chiral space groupP21, but 5 and 6 in chiral space groupsP212121 and C2, respectively. The interaction of 5-connected Cd(II) ions and Ts-cmc ligands of 1 without the help of any ancillary ligands led to the construction of a 2D network with 1D helices. With the aid of the bridging ancillary ligand of 4,4′-bipy another kind of 2D homochiral network was established for 2 and 3 with 4-connected metal ions and 2-connected Ts-cmc ligands. However the introduction of a monodentate ancillary ligand of imidazole into the reaction system gave a 1D double-chain made from 3-connected Cd(II) ions and Ts-cmc ligands for 4 and a 1D helix constructed from 2-connected metal ions and Ts-cmc ligands for 5. Furthermore, the chelating ancillary ligand of 2,2′-bipy resulted in the formation of a chiral discrete dinuclear structure (6) with 2-connected metal ions and Ts-cmc ligands. It was revealed that the introduction of bridging, monodentate or chelating ancillary ligands into the reaction system leads to the change of connecting modes for metal ions and Ts-cmc linkers from 5- to 2-connected modes reaching the goal of controlling the growth of dimensionalities and structures of homochiral metal-frameworks. An investigation of the fluorescence of the Cd(II) compounds as well as the free ligands indicates the emission bands of the Cd(II) compounds are due to the intraligand transmission.

Structure and fluorescent properties of mercury(II) pyridine-2,3-dicarboxylate coordination polymers tuned by ancillary ligands and alkaline-earth metal ions

The reactions of pyridine-2,3-dicarboxylic acid (2,3-PyDCH2) with Hg(CH3COO)2, tuned by ancillary ligands and alkaline-earth metal ions, gave [Hg2(2,3-PyDC)2]n (1), {[Hg(phen)(2,3-PyDC)]·2H2O}n (2), [CaHg(2,3-PyDC)(SCN)2(H2O)]n (3), [SrHg(2,3-PyDC)(SCN)2(H2O)]n (4) and [BaHg(2,3-PyDC)(SCN)2(H2O)]n (5). Compound 1 presents a three-dimensional topological network with the Schlafli symbol (42.64)(42.63.8)(43.66.8) (4.62), formed by two kinds of 2,3-PyDC2− ligands (five-connecting and three-connecting) and two kinds of four-connecting Hg(II) ions. The introduction of chelating 1,10-phenanthroline ancillary ligands in 2 gave one-dimensional chains. The addition of alkaline-earth metal ions and the ancillary ligand SCN− to the Hg2+–2,3-PyDC2− system gave a three-dimensional topological network with the Schlafli symbol (46.69.84)(32.42.5.65)(32.4.63)(46.62) for 3 and two-dimensional structures formed by the connection of one-dimensional Sr(II)/Ba(II)–carboxylate chains via dinuclear units [Hg2(SCN)2]2+ with the Schlafli symbol (3.82)(34.45.5.64.7)(3.42.5.6.7) for compounds 4 and 5. The photoluminescent properties of free 2,3-PyDCH2 and complexes 1–5 were investigated. They reveal no fluorescent emission (fluorescence “off” state) for free 2,3-PyDCH2 in the absence of metal ions. However, an emission band (fluorescence “on” state) was found upon the coordination of 2,3-PyDC2− to Hg2+ in 1 to giva a 3D structure. Interestingly, the addition of ancillary ligands and alkaline earth metal ions to the Hg2+–2,3-PyDC2− system results in the disappearance of the fluorescence (fluorescence “off” state) in compounds 2–5.

Heterometallic coordination polymers containing unique inorganic chain of [LnIII2CuII3(OH)4]: syntheses, structures and magnetism

Heterometallic compounds of [Ln2Cu3(OH)4(pyba)8(H2O)2]n (1–5) (Hpyba = 4-(4-pyridyl)benzoic acid, Ln = La 1, Pr 2, Sm 3, Eu 4, Gd 5) were hydrothermally synthesized by using lanthanide oxides, Hpyba, and copper halide as raw materials. Structurally, the two-dimensional frameworks of 1–5 possess the very original heterometallic chain moiety of [LnIII2CuII3(μ3-OH)4], which is the first inorganic chain in 3d–4f chemistry. Variable temperature magnetic susceptibility studies show that 5 displays weak antiferromagnetic coupling between the neighboring Gd(III) and Cu(II) ions.

Synthesis, crystal structure and spectroscopic characterization of silver(I), cadmium(II) complexes with the Schiff base derived from pyridine-2-carboxaldehyde and 4-[(E)-2-phenyldiazenyl]aniline

The bidentate Schiff-base L is synthesized by condensation of pyridine-2-carboxaldehyde with 4-[(E)-2-phenyldiazenyl]aniline. Hydrothermal reaction of L with AgNO3 and Cd(ClO4)2·6H2O afforded complexes AgLNO3 (1) and [CdL2(H2O)ClO4]ClO4 (2), respectively, which are characterized by elemental analysis and IR spectroscopy. The single crystal X-ray diffraction analyses reveal that both 1 and 2 are mononuclear. In 1, Ag(I) is coordinated by two N atoms from the Schiff-base ligand and one O atom from group in a distorted trigonal geometry. In 2, the cadmium(II) is coordinated in a distorted octahedral geometry, with an equatorial plane composed of four nitrogen atoms from two bidentate Schiff-base ligands, and the apical position occupied by one O atom from aqua ligand and one O atom from perchlorate.

Structural diversity of transition-metal complexes derived from N-propionic acid functionalized 1,4,7-triazacyclononane: From enchanting cluster motifs to unprecedented homometallic polymeric networks

Self-assembly between perchlorate salts of Cu(II), Zn(II) and Cd(II) with tri-substituted N-propionic acid functionalized 1,4,7-triazacyclononane (H33L11) or the mono-substituted one (HL22) results in the formation of four novel complexes [Cu5(H2O)6(L11)2](ClO4)4 (1), [Zn9(L11)4(H2O)18](ClO4)6·9H2O (2), [Cd2(H22L11)2](ClO4)2 (3) and [Cd(L22)]ClO4·CH3OH (4) with different aggregation modes. All these complexes were structurally characterized by solid state X-ray diffraction measurement. Complex 1 belongs to a homometallic 2D polymer, where each [Cu(L11)]− complex entity acts as a three-connected node joined to three Cu(II) ions through μ2 bridged propionate arms to afford a puckered honeycomb framework. In complex 2, two face-to-face arranged [Zn(L11)]− moieties clip three Zn(II) ions by virtue of pendant propionate arms generating a macrotricyclic metallacryptate. Two such metallacryptates are fused via co-sharing one lateral Zn(II) ion into an unprecedented nonazinc cluster with a double-cage architecture. Complex 3 exhibits a discrete centrosymmetric dinuclear unit [Cd2(H22L11)2]2+ consisting of two pendant propionate groups linked to a [Cd2O2] core. Complex 4 reveals Cd(II) centers are associated through the unique propionate bridge of the L22− ligand leading to an infinite 1D zig–zag polymeric chain of [Cd(L22)]+ cations. Deduced from the structural investigations, the linkage patterns of the selected macrocyclic ligands towards metal centers may be exquisitely tuned according to the type of metals and the number of the coordinating pendant arms present in the macrocyclic ligands, and then the architectural variation of these metal–organic coordination species is achieved. In addition, magnetic studies for complex 1 show a weak Cu⋯Cu antiferromagnetic coupling in the 2D honeycomb layer with a Weiss temperature of −4.31 K.

Metal-controlled structural variations of coordination architectures constructed from flexible 1H-benzimidazole-1-propionic acid

Treatment of a flexible bifunctional ligand 1H-benzimidazole-1-propionic acid (Hbiap) with appropriate transition metal salts led to the formation of six new complexes, [Co(biap)2]n (1), [Cu2(biap)4(H2O)]n·7n(H2O) (2), [Ag(H0.5biap)2]n·2n(H2O) (3), [Zn(biap)2]n (4), [Cd12(biap)24]·8H2O (5) and [Hg(Hbiap)Cl2] (6). X-ray crystallographic studies reveal that complexes 1 and 2 exhibit two different 1D chain structures due to the distinct coordination geometries of central Co(II) and Cu(II). Complex 3 consists of a 1D zigzag [Ag(H0.5biap)2]n chain constructed via O⋯H⋯O interactions. In 4, two sets of 1D [Zn(biap)]n chains along two perpendicular directions are interwoven at the Zn(II) nodes to afford a 2D puckered sheet with a (4,4) topology. The crystal structure of 5 manifests an unprecedented nano-sized dodecanuclear Cd(II) cage in a garland-like appearance, which can be thought of as a head-to-tail 1D looped chain enclosing a hollow cavity. Complex 6 features a 1D infinite wavy chain generated by the linkage of [Hg(Hbiap)2] and HgCl2 fragments through μ2-Cl− groups. Of these complexes, the flexible organic ligand is in favor of the gauche conformation in 1–5, and the anti conformer can only be observed in 6. A comparison of the structural features for these complexes suggests that the coordination preferences of the metals, connectivity of the metal nodes as well as the binding modes and protonation behavior of Hbiap are responsible for the interesting architectural variations. The four coordination complexes with d10 metal centers display solid-state luminescent emissions at room temperature, which originate from either intraligand π–π* transitions (4 and 5) or ligand to metal charge transfer (LMCT) transitions (3 and 6).

Preparation and characterization of four polymeric metal complexes based on the flexible ligand 1H-1,2,4-triazole-1-propionic acid in different conformations

Three 2-D layered coordination polymers with (4,4) topology, {[Cu(trzp)2(H2O)]·1.18H2O} n (1), {[Co(trzp)2(H2O)2]·2H2O} n (2), and {[Cd(trzp)2(H2O)]·2H2O} n (3), have been synthesized with the flexible, bifunctional ligand 1H-1,2,4-triazole-1-propionate (trzp−) as a two-connected bridge. In addition, a complicated 3-D MOF [Ag3(trzp)2(NO3)] n (4) has been obtained with the help of Ag⋯Ag interactions and trzp− as a four-connected linker. Htrzp and 1–4 have been characterized by single-crystal X-ray diffraction, elemental analysis, and infrared spectroscopy. The structural analysis showed that Htrzp has a gauche conformation in the solid state. However, both gauche and trans conformers of trzp− are observed in the crystals of 1; only one conformer of trzp− exists in the other three compounds (trans conformation in 2 and 3, and gauche conformation in 4). The thermal behaviors of 1–4 have been examined by thermal gravimetric analysis under nitrogen, which revealed that metal cyanide salts M(CN) n (M = Cu(II), Co(II), Cd(II), and Ag(I), n = 1 or 2) may be an intermediate pyrolytic decomposition product of the corresponding compounds.

Synthesis, structure and properties of an octahedral dinuclear-based Cu12 nanocage of trimesoyltri(L-alanine)

The reaction of a three-armed ligand of trimesoyltri(L-alanine) (TMTAH3) with CuCl2 gave [Cu12(TMTA)8(H2O)12]·8CH3CH2OH·40H2O (1) as expected. It features paddlewheel dinuclear secondary building blocks, six of which are connected by eight TMTA3− linkers, forming a Mo6C184+-like dinuclear-based octahedral nanocage. The magnetic studies revealed the presence of antiferromagnetic interactions between the Cu(II) ions in 1. The desolvated sample of 1 presents nice selectivity on the adsorption of H2 and CO2 over CH4.

Manganese clusters of aromatic oximes: synthesis, structure and magnetic properties

With the aim of tuning the structures by using oxime ligands with different non-coordinating groups, three aromatic oxime ligands were designed by fusing oxime groups ([double bond, length as m-dash]N-OH) onto different non-coordinating groups. Their reactions with the corresponding Mn(ii) salts gave five manganese clusters [Mn(μ3-O)(L1)3(DMF)(H2O)3Cl]·2DMF·CH3OH (1), [Mn(μ3-O)(L2)3(OAc)(CH3OH)2] (2), [Mn(μ3-O)2(L2)6(H2O)(py)7](ClO4)2·py·0.5CH3OH·2H2O (3), [MnO4(L2)8(DMF)4]·DMF·6CH3CN (4), and [MnMnO4(L3)12]·3DMF·6H2O (5), in which H2L1, H2L2 and HL3 represent indane-1,2,3-trione-1,2-dioxime, acenaphthenequinone dioxime, and 9,10-phenanthrenedione-9-oxime, respectively. Their structures were determined and studied in detail. 1 and 2 show planar triangular trinuclear Mn structures. 3 has a hexanuclear Mn skeleton formed from two Mn triangular units through inter-trinuclear mutual coordination. 4 and 5 present octanuclear skeletons constructed from planar triangular Mn3O and tetrahedral Mn4O secondary building units, respectively, with different symmetries and different oxidation states of the manganese ions. Their structural studies reveal a significant contribution of the parent rings for fusing oxime groups, different non-coordinating groups and anions to the formation of different cluster skeletons. Their magnetic properties were investigated and simulated, which revealed the presence of dominant antiferromagnetic interactions between the metal ions in these compounds.

Synthesis, Structure, and Properties of a Chiral Zinc(II) Metal-Organic Framework Featuring Linear Trinuclear Secondary Building Blocks

A chiral metal-organic framework formulated as [Zn3(L-TMTA)2(4,4′-bpy)4]·24H2O (1) was prepared from the reaction of Zn(NO3)2·6H2O with trimesoyltri(L-alanine) (L-TMTAH3) in the presence of 4,4′-bipyridine (4,4′-bpy). Compound 1 features linear trinuclear secondary building blocks [Zn3(syn-syn-COO)2(μ2,η3-COO)2]2+. Each linear trinuclear secondary building block is further linked to another eight ones around it by four L-TMTA3– ligands and eight 4,4′-bpy ligands, leading to the construction of a uninodal three-dimensional framework with triangular prism-like one-dimensional channels. Dehydrated compound 1 displays remarkable adsorption selectivity on CO2 and water vapour over N2 gas.