One-dimensional copper(II) coordination polymers based on carboxylate anions and rigid pyridyl-donor ligands

Two copper(II) compounds named [Cu₂(μ-O₂CCH₂C₄H₃S)₄(bipy)]_n (1) and [Cu₂(O₂CCH₂C₄H₃S)₄(bpe)₂]_n (2) [(O₂CCH₂C₄H₃S) = 3-thiopheneacetate anion; bipy = 4,4′-bipyridine and bpe = 1,2-bis(4-pyridyl)ethylene] have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 consists of binuclear paddle wheel SBUs connected by bridging bipy ligands resulting on a 1D polymeric chain. On the other hand, compound 2 contains two crystallographically independent copper(II) centers coordinated by 3-thiopheneacetate ions in a monodentate fashion and by bpe ligands acting in a bridging mode to form 1D polymeric chains. In both cases, the 1D polymeric chains are linked through non-classical hydrogen bondings C-H···O, that apparently control the crystal packing.     

Copper(II) complexes derived from (2-carboxymethoxy-phenylamino)acetic acid and analogue

The synthesis and characterization of mononuclear copper complex of (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-acetic acid (1) and a tetranuclear copper complex of (2-carboxymethoxy-phenylamino)acetic acid (2) is reported. The sodium salt 1 on reaction with copper(II) chloride hexahydrate followed by treatment with pyridine gave a mononuclear copper complex; whereas, a tetra-nuclear complex in the case of reaction of 2 with copper(II) chloride hexahydrate and 2,2′-bipyridine was obtained. In tetra-nuclear copper(II) complex the NH group co-ordinates to copper and cluster has five co-ordination around copper(II).     

Synthesis, structure and properties of copper(II) and manganese(II) coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate

Two new metal-organic coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate (NNDC), [Cu₂(NNDC)₂(DMF)_1.8(DMSO)_2.2(H₂O)₂]·H₂O (1) and [Mn₃(NNDC)₃(DMSO)₄]·2DMSO (2) have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction and Thermogravimetric Analysis (TGA). The structure of compound 1 consists of one-dimensional chains with copper ions being linked by the dicarboxylate ligands. The coordination chains are associated into ladder-like double chains through O-H?O hydrogen bonds and π-π interactions, and the ladders are packed in a cross fashion through further π-π interactions to give the three-dimensional structure. The Mn(II) compound exhibits a 3D framework with the pcu topology, in which [Mn₃(COO)₆] clusters as octahedral secondary building blocks are linked by the naphthalene spacers. Magnetic analyses were carried out based on both temperature- and field-dependent data, consistently suggesting relatively weak antiferromagnetic interactions within the carboxylate bridged [Mn₃(COO)₆] cluster.     

Zinc(II) and copper(II) 1D coordination polymeric complexes of a reduced Schiff base ligand

The reaction of Zn(ClO₄)₂ · 6H₂O and Cu(ClO₄)₂ · 6H₂O with H₃Sas (H₃Sas = N-(2-hydroxybenzyl)-L-aspartic acid in water afforded the complexes [Zn₆(Sas)₄(H₂O)₈]·5H₂O (1) and [Cu(HSas)(H₂O)] (2), respectively, which were characterized by infrared spectroscopy, elemental analysis, thermogravimetry and single-crystal X-ray crystallography. In 1, the pentanuclear clusters formed by four H₃Sas ligands and five Zn(II) metal ions are bridged by the “[Zn(H₂O)₄]²⁺” cations to form 1D polymeric chains. While in 2, the mononuclear [Cu(HSas)(H₂O)] repeating units form a 1D zigzag chain and further extended by strong intermolecular hydrogen bonds to form a 2D sheet. The different coordination geometries of Cu(II) and Zn(II) show significant influence on the polymeric structures.     

Syntheses and characterizations of two lanthanide(III)-copper(II) coordination polymers constructed by pyridine-2,6-dicarboxylic acid

The hydrothermal reaction of La₂O₃ and Pr₂O₃ with pyridine-2,6-dicarboxylic acid (H₂pydc), CuO, and H₂O with a mole ratio of 1:2:4:300 resulted in the formation of two polymeric Cu(II)-Ln(III) complexes, [{Ln₄Cu₂(pydc)₈(H₂O)₈} · 18H₂O]_n (Ln = La (1); Pr (2)). 1 and 2 are isomorphous and crystallize in monoclinic space group C2/c. Complexes 1 and 2 have one-dimensional infinite chains with “∞” shape. The 1D chains are linked by the hydrogen bonds and π?π stacking interactions to form layer structures which are further linked by the hydrogen bonds and π?π stacking interactions to form the three-dimensional (3D) structures with nanoscale porosities. Temperature-dependent magnetic susceptibilities and the thermal stabilities of complexes 1 and 2 were studied.     

A mixed-valence Cu(I)-Cu(II) and metal-metal bond containing coordination polymer obtained from an in situ oxidation reaction route

A new mixed-valence copper coordination polymer with copper-copper metal bonds in a two-dimensional network was generated from an in situ oxidation reaction route under hydrothermal conditions. The synthesis of this coordination polymer demonstrated that the novel compounds that may not be accessible using the known methods could be synthesized via an oxidation reaction route. The reaction conditions are mild enough to keep the building blocks intact during the oxidation and self-assembly process under hydrothermal conditions.     

Molecular double chains and 3-D supramolecular frameworks with open channels assembled from 1D copper(II) maleate coordination polymers with chelating aromatic amine ligands by noncovalent interactions

Two 1D coordination polymers, [Cu(mal)(Hdpa)]_n (1) and {[Cu(mal)(tpy)] · 4H₂O}_n (2) (mal = maleate, Hdpa = 2, 2′-dipyridylamine and tpy = 2,2′:6′,2″-terpyridine), have been synthesized and their crystal structures, IR spectra, thermal analyses, magnetic properties were determined. In 1 and 2, the maleate ligands link adjacent metal centers to form 1D coordination polymeric chains. Furthermore, the carboxylate oxygen atoms and the aromatic chelate ligands provide potential supramolecular recognition sites for noncovalent interactions to form higher dimensionality. In 1, each pair of 1D chains recognize each other through strong hydrogen bond formed by active amine (-NH-) hydrogen and aromatic π-π stacking interactions to generate a zipperlike double-stranded chain. In contrast, when the substitutions of tpy for dpa further enhance the π-π aromatic stacking interactions, complex 2 is directly constructed into 2D zipperlike layers by the unprecedented aromatic π-π stacking interactions that same orientated aromatic chelate ligands are simultaneously attached to both sides of the chain and the significant C-H?O hydrogen bonds. These layers are constructed through hydrogen bonds and result in a 3D supramolecular network with 1D open channels, in which exists an unprecedented one-dimensional water chain. Both were magnetically characterized, showing weak ferromagnetic behavior.     

Copper(II) complexes of 3-amino-1,2,4-triazine and 2-aminopyrazine: Strategies for designing crystalline materials using coordination polymers

Reaction of 3-amino-1,2,4-triazine (3-atz) or 2-aminopyrazine (2-apz) with Cu(hfac)₂·xH₂O led to the formation of the monometallic and trimetallic complexes Cu(hfac)₂(3-atz)₂ (1), Cu₃(hfac)₆(3-atz)₂ (2), Cu(hfac)₂(2-apz)₂ (3) and Cu₃(hfac)₆(2-apz)₂ (4). The azine molecules behave as both monodentate and bridging bidentate ligands. The Cu(II) ions exhibit a range of coordination geometries. In 1 and 3, the complex is distorted octahedral with the Jahn-Teller axis lying along one of the O-Cu-O axes. In 2 and 4, the central Cu(II) ion is also distorted octahedral with the Jahn-Teller axis lying along the N-Cu-N axis, while the terminal Cu(II) ions are five-coordinate. Structure analysis reveals that addition of the amino-substituent makes the ligands more coordinating, leading to shorter CuN bonds. In the case of 4, this results in a stronger magnetic superexchange pathway and the complex exhibits antiferromagnetic behavior at low temperatures.     

1,4-Di(1,2,3,4-tetrazol-2-yl)butane as a precursor of new 2D and 3D coordination polymers of Cu(II)

A series of new coordination polymers of Cu(II) have been prepared in a reaction between copper(II) perchlorate or tetrafluoroborate salt and a novel ligand 1,4-di(1,2,3,4-tetrazol-2-yl)butane (bbtz). The compounds were characterised by an elemental analysis, TG measurements, IR, EPR and UV-Vis spectroscopy. Crystal structures of bbtz and five complexes of Cu(II) were determined by a single crystal X-ray diffraction measurement performed at 100 K. The composition and architecture of the obtained complexes strongly depend on the reaction conditions especially on the kind of solvent. Investigated complexes are composed of polymeric macrocations and non-coordinated anions. In all cases the bbtz molecules act as the bidentate ligand coordinated to metal(II) ions via N4, N4^′ nitrogen atoms from tetrazole rings. The complexes {[Cu(bbtz)₂(MeOH)₂]X₂}_∞ (X=ClO₄⁻, BF₄⁻) crystallise from methanol as 2D coordination polymers. In these compounds central metal ions are coplanar linked by molecules of bbtz and a coordination sphere is completed by axially coordinated solvent molecules. The complexes {[Cu(bbtz)₃]X₂}_∞ (X=ClO₄⁻, BF₄⁻) were synthesised in EtOH/H₂O solvent system and posses a common network topology. In this group of complexes each central atom is linked by ligand molecules to six other in plane arranged central atoms resulting in 2D networks. Reactions between Cu(II) salts and bbtz performed in absolute ethanol resulted in the formation of the next type of product. In {[Cu(bbtz)₃](ClO₄)₂·2EtOH}_∞ neighboured copper(II) ions are linked by ligand molecules in the three directions what leads to the formation of 3D net. A crystal of this complex is composed of two mutually interpenetrated 3D networks.     

One-dimensional zig-zag type coordination polymers of Ni(II) and Cu(II) containing 1,3-benzenedicarboxylate and 1,3-diaminopropane: Structural, spectral and thermal studies

Two coordination polymers [Ni(ipt)(dap)₂]_n (1) and [Cu(ipt)(dap)H₂O]_n · nH₂O (2) with an overall one-dimensional arrangement and having isophthalate (ipt) as bridging moieties and chelating 1,3-diaminopropane (dap) as structure modulating units have been prepared and characterized by crystallographic, spectroscopic and thermo-analytical studies. Both have an overall one-dimensional zig-zag nature but with a distorted octahedral NiN₄O₂ chromophore for 1 and a distorted square pyramidal CuN₂O₃ chromophore for 2. Even though the ipt units are acting as bridging units through mono-dentatively coordinating carboxylate functions in both polymers, compound 1 has the carboxylate oxygen linkages at the trans positions, while in 2 the oxygen linkages occur at the cis positions leading to a different type of zig-zag arrangement. Relevant spectral and bonding parameters also could be evaluated for the compounds using UV-Vis and EPR spectra. Thermal stability and possible structural modifications on thermal treatment of the compounds were also investigated and the relevant thermodynamic and kinetic parameters evaluated from the thermal data.     

Two-dimensional coordination polymers of Zn(II) and Cd(II) derived from 3,3′,5,5′-azobenzenetetracarboxylic acid exhibiting solvent facilitated structure reversibility

Two Cd(II) and Zn(II) coordination polymers based on 3,3′,5,5′-azobenzenetetracarboxylic acid (H₄abtc): [Cd₂(abtc)(H₂O)₆]·DMF·0.5H₂O (1) and [Zn₂(abtc)(bpy)(H₂O)₂]·DMF·H₂O (2) are synthesized and structurally characterized. Both 1 and 2 are 2D polymers but interconnected by solvent molecules to generate 3D suprastructures. Solvent expulsion leads to rupture of both structures, but upon re-exposure to the solvent mixture they exhibit remarkable ability to regain the original structure reversibly from the almost amorphous solvent-expelled form. Compounds with such structural flexibility and reversibility are expected to have some useful functionality.     

Hydrothermal synthesis, crystal structures and photoluminescent properties of four cadmium(II) coordination polymers derived from diphenic acid and auxiliary ligands

Four novel metal coordination polymers, [Cd(dpa)(H₂O)]_n (1), [Cd(dpa)(2,2′-bipy)]_n (2), {[Cd₂(dpa)₂(4,4′-bipy)₃](4,4′-bipy)(H₂O)₂}_n (3) and [Cd(dpa)(bim)₂(H₂O)]}_n (4) (H₂dpa = 2,4′-biphenyl-dicarboxylic acid, 2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine, bim = benzimidazole), have been synthesized and structurally characterized by elemental analysis, IR and X-ray diffraction. Single-crystal X-ray analyses reveal that the 2,4′-diphenic acids acts as bridging ligands, exhibiting rich coordination modes to link metal ions: bis-monodentate, bidentate chelating, chelating/bridging, monoatomic bridging and monodentate modes. In addition, the luminescent properties for compound 1-4 are also investigated in this work.     

Preparation of dehydro-L-ascorbic acid dimer by air oxidation of L-ascorbic acid in the presence of catalytic amounts of copper(II) acetate and pyridine

The catalytic system Cu(AcO)2-pyridine 1:4 mol% in methanol, slowly catalyses the air oxidation of ascorbic acid to the 2-methyl hemi-ketal of dehydroascorbic acid 5, and hydrogen peroxide. However, with Cu(AcO)2-pyridine 3:4 mol% the air oxidation is quite fast and no hydrogen peroxide is present at the end of the reaction. Removal of the catalyst and refluxing the foamy 5 in MeCN gives the oxidized, dimeric, dehydroascorbic acid in very good yields (approximately 70%) contaminated by approximately 1-2% MeCN.     

Copper (II) complex-catalyzed oxidation of NADH by hydrogen peroxide

Among various metal ions of physiological interest, Cu²⁺ is uniquely capable of catalyzing the oxidation of NADH by H₂O₂. This oxidation is stimulated about fivefold in the presence of imidazole. A similar activating effect is found for some imidazole derivatives (1-methyl imidazole, 2-methyl imidazole, andN-acetyl-L-histidine). Some other imidazole-containing compounds (L-histidine,L-histidine methyl ester, andL-carnosine), however, inhibit the Cu²⁺-catalyzed peroxidation of NADH. Other chelating agents such as EDTA andL-alanine are also inhibitory. Stoichiometry for NADH oxidation per mole of H₂O₂ utilized is 1, which excludes the possibility of a two-step oxidation mechanism with a nucleotide free-radical intermediate. About 92% of the NADH oxidation product can be identified as enzymatically active NAD⁺. D₂O, 2,5-dimethylfuran, and 1,4-diazabicyclo [2.2.2]-octane have no significant effect on the oxidation, thus excluding¹O₂ as a mediator. Similarly, OH· is also not a likely intermediate, since the system is not affected by various scavengers of this radical. The results suggest that a copper-hydrogen peroxide intermediate, when complexed with suitable ligands, can generate still another oxygen species much more reactive than its parent compound, H₂O₂.     

Syntheses, structures and luminescence of a series of Cd(II)-containing coordination polymers constructed from a long flexible bis-triazole ligand

Six novel Cd(II) coordination polymers based on 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl (btmb), namely, [Cd(btmb)₂I₂]_n (1), [Cd(btmb)I₂]_n (2), {[Cd(btmb)₂(NO₃)₂]·H₂O}_n (3), {[Cd(btmb)₂(SCN)₂]·3H₂O}_n (4), {[Cd(btmb)(CH₃COO)₂(H₂O)]·CH₃CN}_n (5) and [Cd(btmb)Cl₂(H₂O)]_n (6) have been synthesized by the reactions of btmb with Cd(II) salts in the presence of different anions (I⁻, , NCS⁻, CH₃COO⁻ or Cl⁻) under appropriate reaction conditions. The assemblies of btmb with CdI₂ afford two different structures: two-dimensional (2D) rhombohedral grid layer network structure 1 and 2D layer structure 2 involved with one-dimensional (1D) linear cadmium chains. Treatment of btmb with Cd(NO₃)₂·4H₂O gives rise to a 2D grid network structure 3 which is similar to 1. When the I⁻ or NO₃⁻ anions were replaced by NCS⁻, CH₃COO⁻ or Cl⁻, different 1D coordination polymers 4-6 were obtained, respectively. Polymer 4 displays a 1D double-chain structure, while both polymers 5 and 6 show 1D zigzag chain structures. In addition, the luminescence measurements reveal that polymers 1-6 exhibit different fluorescent emissions in the solid-state at room temperature, which can be attributed to the various coordination environments of Cd(II), solvent molecules and different packing interactions in these polymers.     

Heterometallic coordination compounds of dipicolinic acid with Ce(III, IV) and Cu(II): Synthesis, crystal structure and spectral studies

Reaction of pyridine-2,6-dicarboxylic acid (dipicH₂) with ammonium ceric nitrate and Cu(II) salts yielded three heterometallic compounds all of which contain [Ce(dipic)₃]²⁻ linked to aquo-Cu(II) complex units. Part of the Ce(IV) gets reduced by solvent during the reaction leading to [(Ce(dipic)₃Ce(H₂O)₈)₂Cu(H₂O)₄][Ce(dipic)₃]₂·12H₂O (1). Other lanthanide(III) ions could take the place of Ce(III) as demonstrated by the preparation of [(Ce(dipic)₃La(H₂O)₈)₂Cu(H₂O)₄][Ce(dipic)₃]₂·12H₂O (4), which is isomorphous with compound 1. [Ce(dipic)₃Cu(H₂O)₄]·8H₂O (2) is a one-dimensional coordination polymer in which two types of aquo-Cu(II) complex units which differ in the orientation of the tetragonal axis alternate along the chain. The central Cu(H₂O)₂²⁺ unit in the trinuclear anion of [Cu(H₂O)₆][Ce(dipic)₃Cu(H₂O)₂Ce(dipic)₃]·8H₂O (3) is chelated by two carboxylate groups in trans positions in off-axis mode. In all the four complexes, the Cu(II) centres are magnetically isolated leading well-resolved EPR spectra in polycrystalline samples.     

The effect of organic acid on self-assembly process: Syntheses and characterizations of six novel cadmium(II)/zinc(II) complexes derived from mixed ligands

Using the principle of crystal engineering, six metal-organic coordination polymers, [Cd(bdc)(3-pytpy)]_n · 2nH₂O (1), [Cd(bdc)_0.5(3-pytpy)]_n · n(ClO₄) (2), Cd(ndc)_0.5(3-pytpy)]_n · n(ClO₄) (3), [Zn(ndc)(3-pytpy)]_n (4), [Cd(bqdc)(3-pytpy)]_n (5), and [Zn(pam)(3-pytpy)]_n · 2nH₂O (6) (H₂bdc = benzene-1,4-dicarboxylic acid, H₂ndc = naphthalene-2,6-dicarboxylic acid, H₂bqdc = 2,2′-biquinoline-4,4′-dicarboxylic acid, H₂pam = pamoic acid), were synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Compounds 1-6 crystallize in the presence of organic-acid linkers as well as multi-functional N-donor ligand 4′-(3-pyridyl)-2,2′:6′,2′′-terpyridine (3-pytpy). In complexes 1, 4, 5, and 6, the dicarboxylate as bridging ligand connects metal atoms to form the main body of 1D zigzag chains for 1 and 4, nearly linear chain for 5 and helical chain for 6, while 3-pytpy as tridentate chelating ligand is just like lateral arm grafting on both sides of these chains. In complexes 2 and 3, both the dicarboxylate and 3-pytpy as bridging ligands connect metal atoms into 2D polymeric structure for 2 and 1D chain of alternating loops and rods for 3. The weak interactions such as hydrogen bonding and π···π stacking were investigated on the formation of superamolecular structures and the influence of organic acid on the formation of the final structures was discussed. In addition, the photoluminescent properties of 1-6 were also determined.     

Porous coordination polymer of copper(II) assembled from mixed organic ligands pyridine-2,4-dicarboxylic acid and trans-1,2-bis(4-pyridyl)ethylene: Synthesis, crystal structure and magnetic study

A 3-D porous coordination polymer of Cu(II) has been synthesized using two different organic bridging ligands, pyridine-2,4-dicarboxylate (pydc) and trans-1,2-bis(4-pyridyl)ethylene (bpe). Here, pydc and bpe connect two adjacent Cu(II) centers, resulting in a rectangular grid-like 2-D sheet with grid dimensions 10.058 × 15.258 Å. The channels are formed when 2-D networks running along the b-axis which are filled by solvent water molecules. The stability of porous networks, after removal of guest water molecules is confirmed by thermogravimetric analysis and X-ray powder diffraction technique. The low temperature magnetic study has been carried out, which indicates the presence of weak antiferromagnetic coupling with J = −0.59 cm⁻¹.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.