Metal complexation induced supramolecular gels for the detection of cyanide in water

ABSTRACT

The role of metal salts in inducing supramolecular gel network formation was analysed by reacting two pyridyl-N-oxide amides with various diamagnetic zinc(II) and cadmium(II) salts. Metal induced supramolecular gelation was observed for zinc(II) and cadmium(II) chloride complexes in water and the morphologies of the xerogels were analysed by scanning electron microscopy (SEM). The relative gel strength was corroborated with various non-bonding interactions observed in the solid-state structures of zinc(II) complexes using X-ray diffraction. The non-bonding interactions of the pyridyl-N-oxide amides and the metal complexes were compared to find the key interactions responsible for metallogel formation. The anion induced stimuli-responsive property of the metallogels was studied in the presence of halides and cyanide anions. The cadmium(II) gels were stable in presence of two equivalents of halides but the network collapsed in presence of cyanide anion in water and this property can be used to detect cyanide anions in water.     

A zinc(II) coordination polymer, [Zn4( o -bda)4( p -pbim)4] n,with strong blue fluorescence

A zinc(II) coordination polymer, [Zn₄(o-bda)₄(p-pbim)₄] _n (1) (p-pbim = 4-pyridylbenzimidazole, o-bda^2? = o-phenylenediacetic acid dianion), has been synthesized by hydrothermal method and characterized by elemental analysis, IR, TG, photoluminescence and X-ray single crystal diffraction. Complex 1 crystallizes in a monoclinic system and space group P2₁ /n, with a = 14.231(3) Å, b = 16.257(4) Å, c = 16.794(4) Å, β = 100.262(1)°, and Z = 8; R ₁ for 6475 observed reflections [I > 2σ(I)] was 0.0420. Complex 1 shows a bi-chain structure fabricated by the tetranuclear zinc unit. Two zinc(II) ions are five coordinate with distorted trigonal-bipyramid geometry; the other two zinc(II) ions are four coordinate with distorted tetrahedral geometry. Complex 1 builds the 1-D bi-chain structure with two different subrings A and B, which are 32-member and 14-member rings, respectively. There exists a 2-D supramolecular network linked by hydrogen-bonding interactions (2.695 and 2.807 Å). A 3-D supramolecular network is further constructed by non-covalent interactions between the 1-D bi-chain structure. The TG/DTG shows that the chain skeleton is thermally stable to 356°C. Blue fluorescent emission of the complex was determined at 404 nm in the solid state with short decay lifetime of 1.67 ns.     

A novel dicyanamide-bridged zinc(II) complex incorporating the 4,4′-azopyridine ligand

A novel complex {[Zn(azpy)₂(dca)(H₂O)₂]·ClO₄·azpy·2H₂O}_n (1) has been synthesized and structurally and spectroscopically characterized, where azpy is the 4,4′-azopyridine and dca the dicyanamide. The crystal structure analysis of 1 shows that in 1 the dca ligands act as μ _1,5-bridges linking the zinc(II) ions into 1D covalent bonding chains. The zinc(II) ion lies in a distorted octahedral environment completed by two nitrogen atoms from two terminal azpy groups, two nitrogen atoms from two dca bridges, and two water molecules. The most striking feature of 1 is that the 1D covalent bonding chains are linked through O–H·N hydrogen bonds and π–π stacking interactions into a 3D supramolecular structure.     

Aggregation of two different coordination polymers by reacting zinc nitrate and cadmium chloride with N,N′-ethylenebisacetamide

Two different coordination polymers are obtained from d¹⁰ metal ions [Zn(II) and Cd(II)] and N,N′-ethylenebisacetamide (EBA). {[Zn(EBA)_1.5(NO₃)]?·?(NO₃)} _n (1) is a 1-D coordination polymer assembled from zinc ions and EBA molecules acting as a bridging ligand. Cd(H₂O)₂Cl₂(EBA) (2) is constructed from 1-D inorganic polymeric chains {Cd(OH₂)₂Cl₂} _n and uncoordinated N,N′-ethylenebisacetamide molecules. These chains are interconnected through hydrogen bonds resulting in a 3-D supramolecular network. The luminescent properties of the organic molecule EBA, as well as of the coordination polymers 1, and 2 have been investigated.     

Synthesis and characterization of light‐emitting main‐chain metallo‐polymers containing bis‐terpyridyl ligands with various lateral substituents

A series of conjugated monomers ( 5a‐5d ) with various lateral substituents were symmetrically synthesized by the Sonogashira coupling reaction, in which central aromatic units (i.e. 9,9‐dipropylfluorenes) were linked to 2,2′:6′,2′‐terpyridyl (tpy) units via phenylene/ethynylene fragments. These light‐emitting monomers were further reacted with zinc(II) ions and subsequently anion exchanged to produce supramolecular main‐chain metallo‐polymers ( 6a‐6d ). The formation of polymers 6a‐6d was confirmed by the increased viscosities (up to 1.5–1.83 times) relative to those of their analogous monomers. The results of ¹H NMR titration and UV‐Vis spectral titration revealed a detailed complexation process of metallo‐polymers by varying the molar ratios of zinc(II) ions to monomers. After coordination with zinc(II) ions, the luminescent and thermal properties of the polymers were enhanced by the formation of metallo‐supramolecular structures in contrast to their monomer counterparts. PLED devices employing these metallo‐polymers as emitters gave yellow to orange electroluminescence (EL) emissions with turn‐on voltages around 6 V. The maximum power efficiency, external quantum yield, and brightness of the PLED device containing polymer 6c were 0.33 cd A^?1 (at 14 V), 1.02%, and 931 cd m^?2 (at 14 V), respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3243–3255, 2007     

Syntheses,crystal structures,and characterization of three metal–organic complexes with 2,2′-biphenyldicarboxylic acid and phenanthroline ligands

Three complexes constructed with 2,2′-biphenyldicarboxylic acid, multidentate nitrogen donors, and metal salts, {[Cd(2,2′-dpdc)(tppp)(H₂O)]₂?·?2H₂O} _n (1), {[Pb(2,2′-dpdc)(pyphen)]₂} _n (2), and {[Pb(2,2′-dpdc)(dppz)]} _n (3) (H₂dpdc = 2,2′-diphenyldicarboxylic acid; tppp = 4-(1H-1,3,7,8-tetraazacyclopenta[l]phenanthren-2-yl)phenol; pyphen?=?pyrazino[2,3-f]-[1,10]phenanthroline; and dppz = dipyrido[3,2-a:2′,3′-c]phenazine), are synthesized under hydrothermal conditions. These complexes are characterized by single-crystal X-ray diffraction, elemental analysis, IR, TGA, and photoluminescence. In 1, two 2,2′-dpdc ions bridge two Cd(II) ions to form an isolated cluster with Cd?···?Cd distance of 5.023(4)?Å. These clusters are further linked by intermolecular hydrogen bonds, yielding a 2-D supramolecular structure. Complex 2 contains two crystallographically independent Pb(II) ions in the asymmetric unit. Pb1 ions are bridged by 2,2′-dpdc anions to form a chain along the x-axis. Two Pb2 ions are coordinated by two 2,2′-dpdc anions and two pyphen ligands to form a cluster. These clusters are linked by π–π interactions to yield a 1-D supramolecular chain along the y-axis. In 3, neighboring Pb(II) atoms are bridged by 2,2′-dpdc anions to form a 1-D chain structure. Further, the chains are linked into a 3-D supramolecular network through aromatic π–π interactions.     

Synthesis,crystal structure and fluorescence properties of two dinuclear zinc(II) complexes incorporating tridentate (NNO) Schiff bases

Reactions of hydrated zinc(II) trifluoroacetate and sodium azide with two tridentate Schiff bases HL¹ (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-chlorophenol) and HL² (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-bromophenol) under the same reaction conditions yielded two dinuclear isostructural zinc(II) complexes, [Zn(L¹)(N₃)]₂ (1) and [Zn(L²)(N₃)]₂ (2), respectively. The complexes were characterized systematically by elemental analysis, UV–Vis, FT-IR, and ¹H NMR spectroscopic methods. Single-crystal X-ray diffraction studies reveal that each of the dinuclear complexes consists of two crystallographically independent zinc(II) ions connected by double bridging phenoxides. All zinc(II) ions in 1 and 2 are surrounded by similar donor sets and display distorted square–pyramidal coordination geometries. The ligands and complexes reveal intraligand ¹(π → π*) flourescence. The enhancement of the fluorescence intensities for the complexes compared to the ligands indicates their potential to serve as photoactive materials.     

A Schiff-base cross-linked supramolecular polymer containing diiminophenol compartments and its interaction with copper(II) ions

We report here the preparation of a Schiff-base linked organic polymer 1 based on linkages containing the potent supramolecular aggregator benzene-1,3,5-tricarboxamide, connected through 2,6-diiminophenol metal binding pockets into a cross-linked polymer. The morphological and physical properties of this material are studied using electron microscopy techniques, thermal analysis, NMR, fluorescence spectroscopy and gas adsorption studies. The interaction of the polymer 1 with Cu^II ions is then investigated by soaking the material with methanolic copper acetate solution, and studying the resulting aggregates using EDX microscopy and FTIR spectroscopy. A small-molecule model compound 2 is also prepared and crystallographically characterised to act as a spectroscopic comparison, providing strong evidence that 1 interacts with copper ions through a nucleation/seeding mechanism for the growth of microcrystalline copper acetate deposits, rather than via chemisorption of the copper ions within the diiminophenol binding pockets. Preliminary results suggest a similar mechanism for Co^II adsorption, while Zn^II ions exhibit a separate interaction mode.     

Formation of the aggregates of actinocin derivatives containing 4′-benzo-15-crown-5 radicals in amide groups and their interaction with a DNA molecule

Methods of spectrophotometry, spectropolarimetry, and viscometry are used to study the self-organization in the solution of crown-containing actinocin derivative (I) exhibiting antitumor activity and the interaction of the formed aggregates with a DNA molecule. The presence of the 4′-benzo-15-crown-5 radical in the structure of the studied compound determines the observed differences in its complexation with Na⁺ and K⁺ ions. The process of aggregation in the presence of K⁺ ions is accompanied by a shift of the long-wave band in the absorption spectrum to short-wave (the formation of H type aggregates) or long-wave (the formation of J type aggregates) regions depending on the K⁺ ion concentration in the solution. In the presence of Na⁺ ions, regardless of their concentration in the solution, J type aggregates form. A scheme of complex formation and their mutual transformations with changes in the ionic composition of the medium is proposed. A study of the interaction of this compound with DNA shows that in the presence of K⁺ ions it binds to the DNA molecule in the form of monomers and/or dimers without producing large supramolecular aggregates. The H and J structures formed in K⁺-containing solutions of compound I are broken in the interaction with DNA. If a solution of compound I is added to a DNA solution containing Na⁺ ions, the J type aggregates are formed directly on the surface of the DNA molecule. At the same type, the J structures originally formed in the Na⁺-containing solution of compound I practically do not interact with DNA. A study of this system shows that the introduction of the crown group in the compound molecule with a heterocyclic chromophore provides the opportunity to affect its affinity and binding to the DNA molecule by means of the ionic composition of the medium.     

Synthesis,structure, magnetism and antibacterial properties of a 2-D nickel(II) metal–organic framework based on 3-nitrophthalic acid and 4,4′-bipyridine

A 2-D nickel(II) mixed-ligand metal–organic framework [Ni(NPTA)(4,4′-bipy)(H₂O)]_n (1) was synthesized by reaction of 3-nitrophthalic acid (H₂NPTA) and 4,4′-bipyridine (4,4′-bipy) with Ni(II) under hydrothermal condition and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. Compound 1 possesses a 2-D layer structure constructed from dinuclear nickel(II) building blocks in which two crystallographically equivalent Ni ions are bridged by two NPTA ligands. Furthermore, the layers are connected into 3-D supramolecular network by hydrogen bonds. The magnetism and antibacterial activity of 1 were investigated.     

Self-Assembly of Synthetic Zinc Chlorins in Aqueous Microheterogeneous Media to an Artificial Supramolecular Light-Harvesting Device

Self-assembled aggregates of a synthetic zinc chlorin in an aqueous suspension with either α-lecithin or Triton X-100 exhibit unique structural and functional properties. Absorption, circular dichroism, fluorescence, and resonance Raman spectra indicate that the supramolecular structure in an aqueous microheterogeneous medium is very similar to that of the bacteriochlorophyll c aggregates in non-polar organic solvents and in chlorosomes, the main light-harvesting antennae of green photosynthetic bacteria. The nature of the aggregates is controlled by structure and/or concentration of the added surfactants. When a small amount of metal-free bacteriochlorin is present it acts as an efficient energy acceptor from the aggregated zinc chlorins. Thus, self-assembly of synthetic zinc chlorins, doped with appropriate energy acceptors and surrounded with surfactants, affords an artificial supramolecular light-harvesting device in aqueous environment.     

Multidentate bis(pyrazolylmethyl)pyridine ligands: coordination chemistry and binding properties with zinc(II) and cadmium(II) cations

The coordination chemistry and cationic binding properties of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L1), 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L2), and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L3) with zinc(II) and cadmium(II) have been investigated. Reactions of L2 with zinc(II) and cadmium(II) nitrate or chloride salts produced monometallic complexes [Zn(NO₃)₂(L2)] (1), [ZnCl₂(L2)] (2), [Cd(NO₃)₂(L2)] (3), and [CdCl₂(L2)] (4). Solid state structures of 1 and 3 confirmed that L2 binds in a tridentate mode. While the nitrates in the zinc complex (1) adopt monodentate binding fashion, in cadmium complex (3), they exhibit bidentate mode. L1–L3 show binding efficiencies of 99% for zinc(II), 60% for lead(II), and 30% for cadmium(II) cations from aqueous solutions of the metal ions. Theoretical studies using Density Functional Theory were consistent with the observed extraction results.     

Supramolecular Assembly: A Comparative Structural Study of the Incorporation of Bis(2-guanidinobenzimidazolo)nickel(II) into Supramolecular Arrays

The structural effects of incorporating a non-planar neutral metal complex, bis(2-guanidinobenzimidazolo)nickel(II), into three supramolecular arrays are described. The complex has a donor-acceptor-donor (DAD) hydrogen bonding motif on each ligand and this motif is used to link it to bis(biureto)nickelate(II) ions, or to 1,8-naphthalimide or phthalimide molecules, all of which incorporate a complementary acceptor-donor-acceptor (ADA) hydrogen bonding motif. The geometry about the metal ion as well as the nature of the network of hydrogen bonds formed have significant influences on the supramolecular structure adopted. An interesting combination of intramolecular hydrogen bonding and close ~ -stacking interactions also occur in each species.     

A Thermodynamic Study Of N,N,N',N'-Tetrakis(2-Hydroxyethyl)-Ethylenediamine Complexes With Nickel(II), Copper(II), And Zinc (II)

Abstract

Thermodynamic parameters have been determined by poten-tiometric techniques for complex ions formed by N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine TKED, with nickel (II), copper(II), and zinc(II) ions. The formation constants, enthalpy, and free energy data for the complexes exhibited values qualitatively consistent with predicted ligand field stabilization trends for these cations. The general expected stability of the complexes in the order Ni(II) < Cu(II) > Zn(II) is observed.     

Synthesis and structural characterization of three supramolecular coordination polymers constructed from different metal ions and 2,2′-bipyridyl-3,3′-dicarboxylic acid

Three new supramolecular coordination polymers based on 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) and Mn(II), Fe(II), and Zn(II) were synthesized under hydrothermal conditions and characterized with single-crystallographic X-ray analysis and IR spectrum. Complex 1 exhibits a 1-D, chain-like structure, which is further connected to 2-D supramolecular layer structure through hydrogen bonds. Complex 2 exhibits a 3-D supramolecular structure constructed from 1-D chains through hydrogen bonds and π–π interactions. Like 1, 3 also shows 2-D supramolecular layer structure based on 1-D chains. Furthermore, the fluorescence of 3 was studied.     

Metal-induced supramolecualr chirality in an optically active polythiophene aggregate

Chiral polythiophenes (PTs), in sharp contrast to other optically active polymers, exhibit optical activity in the pi-pi* transition region which is derived from the chirality of the main chain when they self-assemble to form a supramolecular pi-stacked aggregate with intermolecular interactions in a poor solvent or in a film. We now report that the regioregular, optically active PT poly[(R)-3-[4-(4-ethyl-2-oxazolin-2-yl)phenyl]thiophene] (poly-1) exhibits unique split-type induced circular dichroism (ICD) in the pi-pi* transition region of the main chain upon complexation with various metal salts such as trifluoromethanesulfonates of copper(I), copper(II), silver(I), and zinc(II), and iron(II) perchlorate in chloroform, which is a good solvent for poly-1. The appearance of ICD and slight changes in the UV/Vis spectra (no color change), except for the zinc salts, indicated that the chirality may not be induced by chiral pi-stacked aggregates of poly-1, but by the chirality of the main chain, for example, a predominantly one-handed helical structure induced by intermolecular coordination of the oxazoline groups to metal ions. The sign of the Cotton effect depends on the metal salt; most metal salts induced ICDs with similar Cotton-effect patterns, while zinc salts caused an inversion of the signs of the Cotton effect of poly-1 accompanied by a gradual red shift in the absorption of up to 125 nm. The changes in the conformation and the size of the poly-1 aggregates induced by different metal salts were also investigated by (1)H NMR titrations, static light scattering (SLS), atomic force microscopy (AFM), and membrane filtration. On the basis of these results, we propose a possible model for the chiral supramolecular aggregates of poly-1 with metal salts.     

1D and 3D supramolecular structures exhibiting weak ferromagnetism in three Cu(II) complexes based on malonato and di-alkyl-2,2’-bipyridines

Three new Cu(II) complexes composed of malonato (mal), methylmalonato (memal), 4,4′-di-tert-butyl-2,2′-bipyridine (tbpy) and 5,5′-dimethyl-2,2′-bipyridine (mebpy) ligands, Cu(H₂O)(mal)(tbpy) (1), Cu(H₂O)(memal)(tbpy) (2) and Cu₄(H₂O)₄(memal)₄(mebpy)₄·11H₂O (3) were synthesized by simple one-pot solution reactions at ambient conditions. Single-crystal X-ray diffraction analyses reveal that the Cu(II) ions exhibit a distorted five-coordinate square pyramidal geometry. These three complexes display supramolecular arrays due to hydrogen-bonding interactions. Complexes 1 and 2 show 1-D supramolecular structures; 1 forms a double-ion chain, unlike 2, which only generates a single-ion chain. In 3, there are two identical monomers in the asymmetric unit with Z″ = 2; its high number of noncoordinated water molecules, along with hydrogen-bonding interactions between aqua ligand and memal ligand, generate a supramolecular tetramer, which mimics to produce a 3-D supramolecular framework. Besides this fascinating and yet uncommon crystallographic phenomenon in 3, the structural differences found in these complexes arise from the substituted groups in the malonato dianion and in the bipyridine ligands. These compounds exhibit weak ferromagnetic-exchange interactions.     

Separation Studies of Metal Ions in Sodium Thioglycolate Medium by Thin Layer Partition Chromatography

Abstract

A thin layer partition chromatographic method has been developed for separation of Fe(III), Ni(II), Zn(II), Cu(II), Pb(II) and Mn(II) on thin layers of silica gel-G as an adsorbent. The R_f values were determined using 0.01–0.2 aqueous solution of sodium thioglycolate as a mobile phase. The dependence of R_f values on the migration time, pH and concentration of mobile phase has been studied. The optimum conditions for possible 3-component separation have been determined. Metal ions have been separated, detected, eluted and quantitatively determined by atomic absorption spectroscopy. The present method was applied to the separation and determination of zinc in forensic samples.     

Janus Pyrrolopyrrole Aza-dipyrrin: Hydrogen-Bonded Assemblies and Slow Magnetic Relaxation of the Cobalt(II) Complex in the Solid State

A novel pyrrolopyrrole azadipyrrin ( Janus-PPAD ) with Janus duality was synthesized by a Schiff base–forming reaction of diketopyrrolopyrrole. The orthogonal interactions of the hydrogen-bonding ketopyrrole and metal-coordinating azadipyrrin moieties in Janus-PPAD enabled the metal ions to be arranged at regular intervals: zinc(II) and cobalt(II) coordination provided metal-coordinated Janus-PPAD dimers, which can subsequently form hydrogen-bonded one-dimensional arrays both in solution and in the solid state. The supramolecular assembly of the zinc(II) complex in solution was investigated by ¹H NMR spectroscopy based on the isodesmic model, in which a binding constant for the elongation of assemblies is constant. Owing to the tetrahedral coordination, in the solid state, the cobalt(II) complex exhibited a slow magnetic relaxation due to the negative D value of −27.1 cm⁻¹ with an effective relaxation energy barrier U_eff of 38.0 cm⁻¹. The effect of magnetic dilution on the relaxation behavior is discussed. The relaxation mechanism at low temperature was analyzed by considering spin lattice interactions and quantum tunneling effects. The easy-axis magnetic anisotropy was confirmed, and the relevant wave functions were obtained by ab initio CASSCF calculations.     

Synthesis and characterization of manganese(II), nickel(II), copper(II) and zinc(II) Schiff-base complexes derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-mercaptoethylamine is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-mercaptoethylamine leads to 2,9-bis(2-ethanthiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with manganese, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptoethyl)-2-azaethene]-1,10-phenanthroline (L). The [M(L)Cl₂] complexes [where M = Mn(II), Ni(II), Cu(II) and Zn(II) ions] were characterized by physical and spectroscopic measurements which indicated that the ligand is a tetradentate N₄ chelating agent.