Mesoscopic superstructures of flexible porous coordination polymers synthesized via coordination replication

The coordination replication technique is employed for the direct conversion of a macro- and mesoporous Cu(OH)₂–polyacrylamide composite to three-dimensional superstructures consisting of the flexible porous coordination polymers, Cu₂(bdc)₂(MeOH)₂ and Cu₂(bdc)₂(bpy) (bdc^2– = 1,4-benzenedicarboxylate, bpy = 4,4′-bipyridine). Detailed characterization of the replicated systems reveals that the structuralization plays an important role in determining the adsorptive properties of the replicated systems, and that the immobilization of the crystals within a higher-order architecture also affects its structural and dynamic properties. The polyacrylamide polymer is also found to be crucial for maintaining the structuralization of the monolithic systems, and in providing the mechanical robustness required for manual handling. In all, the results discussed here demonstrate a significant expansion in the scope of the coordination replication strategy, and further confirms its utility as a highly versatile platform for the preparation of functional three-dimensional superstructures of porous coordination polymers.     

Two d 10-metal coordination polymers constructed from flexible ligands: Syntheses, crystal structures, and luminescent properties

Two new complexes, Zn(Glut)(Bix) · 2H₂O (I) and Cd(Pda)(Bimb) (II) (H₂Glut = glutaric acid, H₂Pda = 1,3-phenylenediacetic acid, Bix = 1,4-bis(imidazol-1-ylmethyl)benzene and Bimb = 1,4-di(1H-imidazol-1-yl)butane) were obtained under hydrothermal conditions by employing mixed ligands with metal salts and characterized by elemental analysis, IR, TGA, and Single crystal X-ray diffraction. Complex I presents a two-dimensional 2-fold interpenetrating layer structure. Whereas complex II is a two-dimensional layer network and exhibits a typical (4,4) topological net. The infrared spectra, thermogravimetric and luminescent properties were also investigated in detail for two complexes.     

Reversible assembly of enantiomeric helical polymers: from fibers to gels

A novel class of stereocomplexes is described by the interaction of helically complementary poly(phenylacetylene)s (PPAs) carrying an α-methoxy-α-trifluoromethylphenylacetamide pendant group. The formation of the stereocomplex requires the presence of cis amide bonds on the external crest of the polymer to provide efficient cooperative supramolecular hydrogen bonding between matching enantiomeric helical structures. The interlocking of the chains gives rise to supramolecular fiber-like aggregates that, at higher concentrations, result in gels. The modification of the cis–trans amide conformation at the pendant groups allows the controlled formation and cleavage of the stereocomplex due to a dramatic change between the intermolecular and intramolecular hydrogen bond interactions.     

Bis(dipyrrinato)metal(ii) coordination polymers: crystallization,exfoliation into single wires,and electric conversion ability

One-dimensional coordination polymers (1D-CPs) tend either to dissociate into constitutive ligands and metals readily in solution, or to aggregate randomly and amorphously, which prevents them from widespread application. In the present research, 1D-CPs comprising bridging dipyrrin ligands and divalent metal ions (Zn²⁺, Ni²⁺, and Cu²⁺) are synthesized. A liquid/liquid interfacial reaction gives rise to single crystals suitable for X-ray diffraction analysis: A dichloromethane solution of the ligand is layered with aqueous metal(ii) acetate, such that the coordination reaction proceeds at the liquid/liquid interface. Isolated single fibers of the zinc coordination polymer may be exfoliated from the single crystal or bulk solid upon ultrasonication. Atomic force microscopy (AFM) detects the isolated fibers with lengths of more than several μm. The exfoliated 1D-CP wires feature good processability, realizing a conjugate with single-wall carbon nanotubes (SWCNTs), and a thin film on a transparent SnO₂ electrode. The processed materials show electric conversion ability: For example, the modified SnO₂ electrode serves as a photoanode for a photoelectric conversion system. The designability and tunability of the present 1D-CPs is demonstrated by a ligand modification, affording a luminescent property and an extension of the photoelectric conversion response to longer wavelengths.     

Two helical coordination polymers constructed from V-shaped and chelate ligands

The synthesis and X-ray characterization of two supramolecular isomers, [Co(oba)(2,2′-bpy)] _n (1 and 2) (oba?=?4,4′-oxybis(benzoate), 2,2′-bpy?=?2,2′-bipyridine) are reported. Crystal data for 1: a?=?12.026(2), b?=?15.120(3), c?=?11.361(2)?Å, β?=?91.46(3)°, Z?=?4, R ₁?=?0.0330, wR ₂?=?0.0949. Crystal data for 2: a?=?16.171(3), b?=?19.162(4), c?=?22.914(5)?Å, α?=?107.66(3), β?=?91.46(3), γ?=?98.99(3)°, Z?=?2, R ₁?=?0.0388, wR ₂?=?0.0456. They are conformational supramolecular isomers without solvent molecules in the structures, and exhibit different one-dimensional helical structures that are further assembled into distinct two-dimensional layers via π–π stacking interactions. The results indicate that the geometry of ligand is one of the most important factors for the construction of a helical motif.     

pH-dependent binding of guests in the cavity of a polyhedral coordination cage: reversible uptake and release of drug molecules

A range of organic molecules with acidic or basic groups exhibit strong pH-dependent binding inside the cavity of a polyhedral coordination cage. Guest binding in aqueous solution is dominated by a hydrophobic contribution which is compensated by stronger solvation when the guests become cationic (by protonation) or anionic (by deprotonation). The Parkinson''s drug 1-amino-adamantane (‘amantadine’) binds with an association constant of 10⁴ M^–1 in the neutral form (pH greater than 11), but the stability of the complex is reduced by three orders of magnitude when the guest is protonated at lower pH. Monitoring the uptake of the guests into the cage cavity was facilitated by the large upfield shift for the ¹H NMR signals of bound guests due to the paramagnetism of the host. Although the association constants are generally lower, guests of biological significance such as aspirin and nicotine show similar behaviour, with a substantial difference between neutral (strongly binding) and charged (weakly binding) forms, irrespective of the sign of the charged species. pH-dependent binding was observed for a range of guests with different functional groups (primary and tertiary amines, pyridine, imidazole and carboxylic acids), so that the pH-swing can be tuned anywhere in the range of 3.5–11. The structure of the adamantane-1-carboxylic acid complex was determined by X-ray crystallography: the oxygen atoms of the guest form CH···O hydrogen bonds with one of two equivalent pockets on the internal surface of the host. Reversible uptake and release of guests as a function of pH offers interesting possibilities in any application where controlled release of a molecule following an external stimulus is required.     

Copper(II) coordination polymers constructed from aromatic polycarboxylate and flexible triazole ligands with different spacer lengths: syntheses,structures, and properties

{[Cu₂(btm)₂(Hbtc)(H₂btc)₂(H₂O)]·9.5H₂O}_n (1), [Cu(bte)(H₂btc)₂]_n (2) {[Cu(btp)(H₂btc)₂]·0.25H₂O}_n (3) (btm?=?bis(1,2,4-triazol-1-yl)methane, bte?=?bis(1,2,4-triazol-1-yl)ethane, btp?=?bis(1,2,4-triazol-1-yl)propane, H₃btc?=?benzene-1, 3, 5-tricarboxylic acid) have been synthesized and structurally characterized. 1 features a 1-D double chain, which is interconnected by classical hydrogen-bonding (O–H?O) and π–π interactions to lead to a 3-D supramolecular architecture. 2 and 3 are both 1-D single chains, which are interconnected by π–π interactions to 2-D layer architectures. Elemental analysis, XRD, IR, TG and EPR spectra have been carried out and discussed.     

Studies on coordination polymers : Part I. Coordination polymers of 8,8'-dihydroxy-5,5'-biquinolyl

Coordination polymers of 8,8'-dihydroxy-5,5'-biquinolyl(I) with Cu(II), Zn(II), Cd(II), Ni(II), Co(II) and Mn(II) were prepared and studied. The polymers were all powders, very insoluble in all the common organic solvents, apparently of low molecular weight and all began to decompose between 250–300°. The polymers of cobalt and nickel were amorphous, whereas the polymers of copper, zinc, cadmium and manganese were crystalline. Infrared studies confirmed the chelation reaction between metal and (I). As a spot test reagent, (I)gave instant color reactions with 14 common ions but the sensitivity of the reagent is not particularly impressive. The most interesting result is the detection of 2 μg of gallium.     

Extending N-heterocyclic carbene ligands into the third dimension: a new type of hybrid phosphazane/NHC system

A simple, “click” synthetic approach to a new type of hybrid phosph(III)azane/NHC system is described. The presence of the phosphazane P₂N₂ ring unit, with P atoms flanking the NCN fragment and with this ring perpendicular to the binding site of the NHC, provides unique opportunities for modifying the electronic and steric character of these carbenes.     

Self-assembly of 2D-->2D interpenetrating coordination polymers showing polyrotaxane- and polycatenane-like motifs: influence of various ligands on topological structural diversity

A series of mixed-ligand coordination complexes, namely, [Cd 2(bimb) 2(L (1)) 2] ( 1), [Cd(bpimb) 0.5(L (2))(H 2O)] ( 2), [Zn 5(bpib) 2(L (3)) 4(OH) 2(H 2O) 2] ( 3), [Zn(bpib) 0.5(L (4))] ( 4), and [Cd(bib)(L (4))] ( 5), where bimb = 1,4-bis((1 H-imidazol-1-yl)methyl)benzene, bpimb = 1,4-bis((2-(pyridin-2-yl)-1 H-imidazol-1-yl)methyl)benzene, bpib = 1,4-bis(2-(pyridin-2-yl)-1 H-imidazol-1-yl)butane, bib = 1,4-bis(1 H-imidazol-1-yl)butane, H 2L (1) = 4-((4-(dihydroxymethyl)phenoxy)methyl)benzoic acid, H 2L (2) = 4,4'-methylenebis(oxy)dibenzoic acid, H 2L (3) = 3,3'-methylenebis(oxy)dibenzoic acid, and H 2L (4) = 4,4'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In 1, (L (1)) (2-) anions link the metal-neutral ligand subunits to generate a 2-fold parallel interpenetrating net with the 6 (3) topology. In 2- 4, neutral ligands connect the various metal-carboxylic ligand subunits to give a 2-fold parallel interpenetrating net with (4,4) topology in 2, a 2-fold parallel interpenetrating net with (3,6)-connected topology in 3, and a 3-fold parallel interpenetrating net with (4,4) topology in 4. Compounds 1- 4 display both polyrotaxane and polycatenane characters. Compound 5 is a 5-fold parallel interpenetrating net with (4,4) topology. By careful inspection of these structures, we find that different topological structures showing both polyrotaxane and polycatenane characters have been achieved with increase of the carboxylic ligand length. It is believed that various carboxylic ligands and N-donor ligands with different coordination modes and conformations are important for the formation of the different structures. In addition, the luminescent properties of these compounds are discussed.     

Synthesis and characterization of redox-active coordination polymers generated from ferrocene-containing bridging ligands

Coordination polymers showing redox activity have been constructed by using ferrocene-based bidentate ligands, 1,1'-(4-dipyridinethio)ferrocene (1) and 1,1'-(2-dipyridinethio)ferrocene (2). The ligand of 1 formed an Ag(I) coordination polymer, 1 x AgPF(6) x (CH(3)CN)(2) (3). This complex showed a 1-D double-chain structure, with a weak interchain Ag...Ag interaction. Combination of 1 with M(hfac)(2) (M = Mn, Cu, Zn) afforded 1-D chain complexes, 1 x M(hfac)(2) (M = Mn (5), Cu (6), Zn (7)). The complex 2 x CuPF(6) (8) showed a 1-D twisted helix-like chain structure.     

Development of peptoid-based ligands for the removal of cadmium from biological media

Cadmium poisoning poses a serious health concern due to cadmium''s increasing industrial use, yet there is currently no recommended treatment. The selective coordination of cadmium in a biological environment—i.e. in the presence of serum ions, small molecules, and proteins—is a difficult task. To address this challenge, a combinatorial library of peptoid-based ligands has been evaluated to identify structures that selectively bind to cadmium in human serum with minimal chelation of essential metal ions. Eighteen unique ligands were identified in this screening procedure, and the binding affinity of each was measured using metal titrations monitored by UV-vis spectroscopy. To evaluate the significance of each chelating moiety, sequence rearrangements and substitutions were examined. Analysis of a metal–ligand complex by NMR spectroscopy highlighted the importance of particular residues. Depletion experiments were performed in serum mimetics and human serum with exogenously added cadmium. These depletion experiments were used to compare and demonstrate the ability of these peptoids to remove cadmium from blood-like mixtures. In one of these depletion experiments, the peptoid sequence was able to deplete the cadmium to a level comparable to the reported acute toxicity limit. Evaluation of the metal selectivity in buffered solution and in human serum was performed to verify minimal off-target binding. These studies highlight a screening platform for the identification of metal–ligands that are capable of binding in a complex environment. They additionally demonstrate the potential utility of biologically-compatible ligands for the treatment of heavy metal poisoning.     

Homochiral self-assembly of biocoordination polymers: anion-triggered helicity and absolute configuration inversion

The different natures of the weakly coordinating anions – triflate or perchlorate – in the Cu²⁺-mediated self-assembly of cytidine monophosphate nucleotide play a fundamental role in the homochiral resolution process, yielding one-dimensional copper(ii) coordination polymers of opposite helicity that can be easily inverted, in a reversible way, by changing the nature of the anion as revealed by circular dichroism experiments both in solution and in the solid state.     

One‐ and two‐dimensional CdII coordination polymers incorporating organophosphinate ligands

Reaction of cadmium nitrate with diphenylphosphinic acid in dimethylformamide solvent yielded the one‐dimensional coordination polymer catena‐poly[[bis(dimethylformamide‐κO)cadmium(II)]‐bis(μ‐diphenylphosphinato‐κ²O:O′)], [Cd(C₁₂H₁₀O₂P)₂(C₃H₇NO)₂]_n, (I). Addition of 4,4′‐bipyridine to the synthesis afforded a two‐dimensional extended structure, poly[[(μ‐4,4′‐bipyridine‐κ²N:N′)bis(μ‐diphenylphosphinato‐κ²O:O′)cadmium(II)] dimethylformamide monosolvate], {[Cd(C₁₂H₁₀O₂P)₂(C₁₀H₈N₂)]·C₃H₇NO}_n, (II). In (II), the 4,4′‐bipyridine molecules link the Cd^II centers in the crystallographic a direction, while the phosphinate ligands link the Cd^II centers in the crystallographic b direction to complete a two‐dimensional sheet structure. Consideration of additional π–π interactions of the phenyl rings in (II) produces a three‐dimensional structure with channels that encapsulate dimethylformamide molecules as solvent of crystallization. Both compounds were characterized by single‐crystal X‐ray diffraction and FT–IR analysis.     

Self-catenated and interdigitated layered coordination polymers constructed from kinked dicarboxylate and organodiimine ligands

Hydrothermal combination of divalent nickel or cobalt nitrates with the kinked carboxylic acid 4,4'-oxybis(benzoic acid) (H2oba) and the kinked and hydrogen-bonding capable organodiimine 4,4'-dipyridylamine (dpa) under basic conditions has afforded a pair of coordination polymers with a formulation of {[M(oba)(dpa)] x H2O} (M = Ni, 1; M = Co, 2). Both materials were characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The structures of 1 and 2 are isomorphous and manifest intriguing self-catenated two-dimensional layered motifs with very rare non-diamond 66 topology constructed from the direct covalent linkage of [M(oba)]n double helices through [M(dpa)]n undulating chains. Adjacent self-catenated layers engage in mutual interdigitation to form double-layer patterns that further aggregate via supramolecular hydrogen-bonding patterns imparted by the central amine of the dpa ligand. These coordination polymers are very thermally robust, with decomposition occurring only above 400 degrees C.     

Synthesis,structural characterization,and photocatalytic study of transition metal coordination polymers constructed from mixed ligands

Three 3-D coordination polymers, [Cu(cca)(4,4′-bipy)]_n (1), [Co₃(pda)₃(1,10′-phen)₂]_n (2), and [Co(pda)(1,10′-phen)]_n (3), have been synthesized from 4-carboxycinnamic acid (cca), 1,4′-phenylenediacrylic acid (pda), 4,4′-bipyridine (4,4′-bipy), 1,10′-phenanthroline (1,10′-phen), and Cu and Co salts under different conditions. The X-ray crystal structures of these three complexes are presented. Complex 1 exhibits a threefold 3-D α-Po interpenetration network. Complex 2 with a 3-D framework with six-connected single α-Po framework constructed from Co₃ unit has been synthesized and characterized. Complex 3 shows a 3-D framework with bcu topology composed of 1-D rod-shaped secondary building units. Furthermore, the photocatalytic properties of 2 were studied. When excited by UV light, 2 exhibits photocatalytic activity, in 300?min, about 71% Rhodamine B decomposes.     

Syntheses,crystal structures,and photoluminescence of two new coordination polymers derived from dicarboxylate and N-donor ligands

Two metal-organic coordination polymers, [Co(tda)(ip)(H₂O)₂] _n (1) and [Mn(tda)(ip)(H₂O)] _n (2) [H₂tda?=?thiophene-2,5-dicarboxylic acid, ip?=?1H-imidazo[4,5-f][1,10]-phenanthroline], have been synthesized and characterized by elemental analyses, IR, PXRD, and X-ray diffraction. Single-crystal X-ray analyses reveal that 2,5-tda is a bridging ligand, exhibiting two coordination modes to link metal ions: μ₁-η¹?:?η⁰/μ₁-η¹?:?η⁰ and μ₂-η¹?:?η¹/μ₁-η¹?:?η⁰. Compound 1 demonstrates a 1-D structure in which Co²⁺ centers are connected via tda anions into 1-D chains; the chains are further connected via hydrogen-bonding and π?···?π interactions. Compound 2 displays a 2-D structure in which tda connects two Mn ions forming a dinuclear molecule. In 2 the 3-D supramolecular structure arrays through hydrogen-bonding and π?···?π interactions. In addition, photoluminescence for 1 and 2 is also investigated in the solid state at room temperature.     

MM quadruply bonded complexes supported by vinylbenzoate ligands: synthesis,characterization, photophysical properties and application as synthons

From the reactions between M₂(TⁱPB)₄ compounds and meta and para-vinylbenzoic acids (2 equiv.) in toluene at room temperature the compounds trans-M₂(TⁱPB)₂L₂, where L = m-vinylbenzoate 1A (M = Mo) and 1B (M = W) and TⁱPB = 2,4,6-triisopropylbenzoate, and where L = p-vinylbenzoate 2A (M = Mo) and 2B (M = W) have been isolated. Compounds 1A and 2A have been shown to undergo Heck carbon–carbon coupling reactions with phenyliodide to produce trans-Mo₂(TⁱPB)₂(O₂CC₆H₄-m-CHCH–C₆H₅)₂, 3A and trans-Mo₂(TⁱPB)₂(O₂CC₆H₄-p-CHCH–C₆H₅)₂, 4A. The molybdenum compounds 1A and 2A have been structurally characterized by single crystal X-ray crystallography. All the new compounds have been characterized by ¹H NMR, IR, UV-visible absorption and emission spectroscopy, high resolution MALDI-TOF MS, fs- and ns-transient absorption spectroscopy and fs-time-resolved IR spectroscopy. Electronic structure calculations employing density functional theory, DFT, and time-dependent DFT have been employed to aid in the interpretation of spectral data. All compounds show intense absorptions in the visible region corresponding to M₂δ to Lπ* charge transfer transitions. The lifetimes of the ¹MLCT state fall in the range of 1–10 ps and for the molybdenum complexes the T₁ states are ³δδ* with lifetimes ∼50 μs while for the tungsten complexes the T₁ are ³MLCT with lifetimes in the range of 3–10 ns.