Sheng-Run Zheng

Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework

Despite the high charge-carrier mobility in covalent organic frameworks (COFs), the low intrinsic conductivity and poor solution processability still impose a great challenge for their applications in flexible electronics. We report the growth of oriented thin films of a tetrathiafulvalene-based COF (TTF-COF) and its tunable doping. The porous structure of the crystalline TTF-COF thin film allows the diffusion of dopants such as I2 and tetracyanoquinodimethane (TCNQ) for redox reactions, while the closely packed 2D grid sheets facilitate the cross-layer delocalization of thus-formed TTF radical cations to generate more conductive mixed-valence TTF species, as is verified by UV-vis-NIR and electron paramagnetic resonance spectra. Conductivity as high as 0.28 S m−1 is observed for the doped COF thin films, which is three orders of magnitude higher than that of the pristine film and is among the highest for COF materials.

Assembly of CdI2-type coordination networks from triangular ligand and octahedral metal center: topological analysis and potential framework porosity

Reaction of a rigid triangular ligand 2,4,6-tris[4-(1H-imidazole-1-yl)phenyl]-1,3,5-triazine (TIPT) with Cd2+ ions affordedrare non-interpenetrating CdI2-type networks which display high thermostability and potential porosity; the topological character of the CdI2-type networks have been analyzed in comparison with three common uniform (4,4), (6,3) and (3,6) plane nets.

The construction of coordination networks based on imidazole-based dicarboxylate ligand containing hydroxymethyl group

Reaction of Cd(II), Fe(II), and Cu(II) with a new ligand 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) and 4,4′-bipyridine (bpy) affords three coordination polymers of {[Cd(H2hmIDC)(bpy)]·0.5bpy·H2O}n (1), [Fe2(HhmIDC)2]n (2), and {[Cu2(ITC)(bpy)(H2O)3]·2.5H2O}n (3) (ITC = imidazole-2,4,5-tricarboxylic acid), respectively. Complex 1 and complex 3 are (4,4) nets in topological view and display in different packing mode, while hydroxymethyl group in complex 3 is oxidized to carboxylic groupin situ. Complex 2 is a rare example of a cdl-e network containing both tetrahedral and square nodes. The hydroxymethyl groups act as a precursor and undergo different reactions directed by metal ions.

An unusual 3D coordination polymer assembled through parallel interpenetrating and polycatenating of (6,3) nets

Reaction of AgClO4 with a bulky semi-flexible tripodal ligand 2,4,6-tris(4-((pyridin-4-ylthio)methyl)phenyl)-1,3,5-triazine (tppt) affords highly undulating (6,3) honeycomb networks [Ag3(tppt)2](ClO4)3·8DMSO which display unusual net entanglement. Three (6,3) nets interweave in parallel to give rise to a 3-fold interpenetrating basic layer (2D → 2D parallel). In addition, every such layer interlocks four other layers, two above and two below (2D → 3D parallel). Therefore, totally fifteen (6,3) nets are involved in entanglement with respect to each basic layer, in which each single (6,3) net shows 11-fold interpenetration and 5-fold catenation, thus resulting in a novel 3D coordination polymer containing both interpenetration and polycatenation.

Self-assembly of triple helical and meso-helical cylindrical arrays tunable by bis-tripodal coordination converters.

The synergistic interplay of coordination and hydrogen-bonding interactions leads to assembly of isomorphous compounds of the general formula [Ln(ntb) 2](ClO 4) 3.(BDA4BPy) 3.2MeCN} infinity (Ln = La, Sm and Pr, ntb = tris(2-benzimidazoylmethyl)amine, and BDA4BPy = N (1), N (4)-bis(pyridin-4-ylmethylene)-benzene-1,4-diamine), of which polymorphic crystals can be isolated in a different solvent system. In acetonitrile (MeCN) solution, the compounds crystallize as a red color (Ln = La, meso -1, Ln = Pr, meso -2), while in an acetonitrile-benzonitrile (MeCN-PhCN) mixture, yellow crystals are obtained (Ln = Pr, helical - 2). The single-crystal X-ray diffraction analyses of these crystals reveal that the structures display similar cylindrical arrays containing polycompartmental cavities for guest inclusion. Occurrence of polymorphism is due to formation of helical and meso-helical arrays, giving rise to a way to tune the helicity through the solvent effects on the helix propensity of the bis-tripodal coordination converters.

Tubular metal-organic framework-based capillary gas chromatography column for separation of alkanes and aromatic positional isomers.

In this work, a tubular metal-organic framework, MOF-CJ3, with a large one-dimensional channel was chosen as stationary phase to prepare a capillary gas chromatographic column via a verified dynamic coating procedure. The column offered good separations of linear and branched alkanes, as well as aromatic positional isomers (ethylbenzene, xylene, cresol, hydroquinone, dichlorobenzene, bromobenzonitrile, chloronitrobenzene, and nitrotoluene) based on a combination of host-guest interactions and adsorption effects. Elution sequence of most of the analytes followed an increasing order of their boiling points, except for the separation of n-heptanes/isooctane, cresol, and hydroquinone isomers. Separation behavior of the column upon different organic substances may be related to the tubular pore structure of MOF-CJ3, in which the van der Waals forces between the alkanes and the hydrophobic inner surfaces might have great effect on separation of n-heptanes and isooctane, whereas the separation of cresol and hydroquinone isomers were affected by (OH⋯O) hydrogen bonds formed between the analytes and the 1,3,5-benzenetricarboxylate ligands on the pore wall. The effects of temperature on separation of aromatic positional isomers were investigated to elucidate entropy and enthalpy controlling of the separation process.

An unprecedented (3,4,14)-connected 3D metal–organic framework based on planar octanuclear lead(II) clusters as a secondary building unit

An unprecedented trinodal (3,4,14)-connected 3D metal–organic framework formed by planar octanuclear lead(II) clusters as 14-connected nodes and 2-(Pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate ligands as 3- and 4-connected nodes has been hydrothermally made. It provides a novel topological structure of metal–organic frameworks.

Anion-dependent assembly and solvent-mediated structural transformations of three Cd(II) coordination polymers based on 1H-imidazole-4-carboxylic acid

Three new Cd(II) coordination polymers with 1H-imidazole-4-carboxylic acid (Himc), [Cd(Himc)2(H2O)]n (1), [Cd(Himc)2]n (2) and [Cd2(Himc)2(SO4)(H2O)2]n (3) were perpared by solvothermal reactions and structurally characterized, which all comprised metal–negative ligand systems. Compound 1 exhibit a 1D zigzag chain; compound 2 features a 3D diamondoid work; while compound 3 possesses a 2D layer structure consisting of rhomboid grids. When 1 or 2 was left in a water/ethanolic solution of Na2SO4, their 1D or 3D framework was transformed into a 2D framework of 3. All compounds also displayed structure-related photoluminescent properties in the solid state.

Assembly of Cd(II) coordination polymers: structural variation, supramolecular isomers, and temperature/anion-induced solvent-mediated structural transformations

The reactions of Cd(II) salts and 5-(3-(1H-imidazol-1-yl)phenyl)-1H-tetrazolate (3-HIPT) resulted in eight new coordination polymers (CPs), namely, {[Cd(3-IPT)2(H2O)2]·H2O}n (1 and 2), {[Cd(3-IPT)2(H2O)2]·2H2O}n (3), [Cd(3-IPT)(H2O)Cl]n (4), [Cd(3-IPT)Cl]n (5), [Cd(3-HIPT)I2]n (6), [Cd(3-IPT)I]n (7), and [Cd(3-HIPT)2]n (8). Single-crystal X-ray analysis revealed that compound 1 is a 1D beaded chain, whereas compounds 2 and 3 are made of 2D networks. Compounds 1–3 are supramolecular isomers; their synthesis can be controlled under different temperatures and concentrations. The results showed that compounds 1 and 3 are the most thermodynamically and kinetically favored products, respectively. The thermodynamic stability of compound 1 may be attributed to the formation of the smallest M2L2 ring in the compound. Compounds 4–7 were obtained at higher Cl−/I− concentrations. Compound 4 is a 2D net composed of 1D [Cd(3-IPT)]n chains and μ2-Cl and μ2-H2O connectors. Compound 5 is a (3,6)-connected 3D framework with rtl topology. Compound 6 possesses a 1D chain with 3-HIPT ligands on both sides. Compound 7 is a 2D (4·82) net. Compound 8, a 3D pcu framework based on trinuclear linear SBUs, was formed when Cd(CF3CO2)2 was introduced at 170 °C. Based on a temperature-changing cycle, compounds 1 and 3 display crystal-to-amorphous-to-crystal phase transitions accompanying the dehydration–rehydration process, whereas compound 2 only displays crystal-to-amorphous phase transition when the temperature is increased and cannot go back to the crystal phase again. Interestingly, solvent-mediated structural transformations were accomplished among the selected compounds. When compounds 2, 3, 6, 7, or 8 were left in a water and NaCl solution at 170 °C, they were partly/fully transformed into compounds 1 and 5, respectively. When compound 5 was recrystallized in water at 120 and 170 °C, it was partly and fully transformed into compounds 2 and 1, respectively. Such transformations were induced by the temperature or an anion. In addition, the thermal stabilities and luminescence properties of selected compounds have also been studied in detail. The complexes exhibit intense solid-state fluorescence emission at room temperature.

The construction of Cu(I)/Cu(II) coordination polymers based on pyrazine–carboxylate: Structural diversity tuned by in situ hydrolysis reaction

The reaction of a new ligand, N,N′-(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c′]dipyrrole-2,6(1H,3H)-diyl)bis-(9CI)-3-pyrazinecarboxamide (L), with CuCl2·2H2O, CuI, or Cu(ClO4)·2H2O yields five coordination polymers. Among these polymers are three new coordination polymers, [CuII2(μ3-pzc)2(μ1-Cl)2]n (1), [CuICuII(μ2-pzc)2(μ2-Cl)(H2O)]n (2a), and {[CuI2CuII(μ2-pzc)2(μ3-I)2(H2O)]·H2O}n (3), as well as two previously reported coordination compounds, [CuICuII(μ2-pzc)2(μ2-Cl)(H2O)]n (2b) and [CuII(pzc)2] (4), in which 2-pyrazinecarboxylate (Hpzc) was obtained from in situ hydrolysis of the L ligand. Compound 1 is a two-dimensional (2D) double-layer structure, which can be viewed as a binodal (3,3)-connected network with the Schlafli symbol of (62·10) (6·102). Compounds 2a and 2b are two supramolecular isomers, both of them are (4,4) nets in topological view but showing different packing modes. Compound 3 has a 3D open framework constructed from the linkages of 1D sawtooth chains of iodide copper(I) clusters with [CuII(μ2-pzc)] subunits. Compound 4 is a mononuclear complex. Interestingly, except for compounds 2b and 4, all the other compounds cannot be directly synthesized using Hpzc and the corresponding Cu ions as initial reactants under the same reaction conditions. This finding indicates that the structural diversity of this system is tuned by the in situ hydrolysis reactions.