Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

Two helical one-dimensional copper(II) coordination polymers based on N-(2-hydroxylbenzyl)glycine and N-(2-hydroxylbenzyl)-l-alanine: Syntheses,crystal structures and magnetic studies

Two new helical Cu(II) coordination polymers, [Cu(2,2′-bpy)(Hsgly)]Cl · 2H₂O(H₂sgly = N-(2-hydroxylbenzyl)glycine) (1) and [Cu(2,2′-bpy)(Hsala)](NO₃) · 2H₂O(H₂sala = N-(2-hydroxylbenzyl)-l-alanine) (2) were synthesized. Single crystal X-ray diffraction analysis indicated that both complexes showed helical chains arrangement of Cu(II) centers bridged by carboxyl groups. The magnetic measurements showed complex 1 exhibited ferromagnetic interaction while there was no interaction between the Cu(II) centers in complex 2.     

Removal of Cu(II) by biosorption onto coconut shell in fixed-bed column systems

Biosorption of Cu(II) onto coconut shell, an agricultural biomaterial, was studied in a fixed-bed column. The Cu(II) biosorption column had the best performance at 10 mg L^?1 inlet Cu(II) concentration, 10 mL min^?1 flow rate and 20 cm bed depth. The equilibrium uptake of Cu(II) amounted to 7.25 mg g^?1. The simulation of the breakthrough curve was successful with the BDST and Yoon–Nelson models, but the entire breakthrough curve was best predicted by the Clark model. The design of a fixed bed column for Cu(II) removal from wastewater by biosorption onto coconut shell can be done based on these models.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

An unique trinuclear triply bridged Cu(II) compound containing double acetato and single azido bridges: Synthesis,X-ray structure and magnetism of [Cu3(dpyam)2(μ1,1-N3)2(μ-CH3COO- κ-O1)2(μ-CH3COO-κ-O1,O2)2] · 2(H2O) (dpyam = di-2-pyridylamine)

The synthesis, characterization, crystal structure and magnetic properties of the unique azido-acetato bridged trinuclear triply bridged Cu(II) compound, [Cu₃(dpyam)₂(μ_1,1-N₃)₂(μ-CH₃COO-κ-O¹)₂(μ-CH₃COO-κ-O¹,O²)₂] · 2(H₂O), is reported. In the centrosymmetric compound, the central Cu atom is linked to two terminal Cu atoms by a double acetato bridge and an azido bridge, thereby providing a linear trinuclear unit. The coordination geometry around each of the terminal Cu(II) ions is distorted square pyramidal, while the geometry of the central Cu(II) ion is elongated octahedral. The magnetic susceptibility measurements, measured from 5 to 300 K revealed a weak antiferromagnetic interaction between the Cu(II) ions with a J value of −10.2 cm⁻¹. In the EPR no signals for the low-lying doublet are resolved at 77 K.     

Structure and magnetic properties of A Cu(II) coordination polymer supported by a tetrapodal Schiff base ligand

A Cu(II) Schiff base coordination polymer, {[Cu₃L(μ₂-NO₃)₂·(H₂O)₂].3H₂O}_n, is readily prepared by complexation of the tetrapodal Schiff base, H₄L (H₄L = 1,1,1,1-tetrakis[(salicylaldimino)methyl]methane), with cupric nitrate trihydrate. It has been demonstrated that the coordination polymer consists of linear trinuclear Cu(II) entities, and displays a cooperative coordination mode for nitrate anions, coordinated water molecules, and Schiff base ligands to Cu(II) ions. In addition, variable-temperature magnetic susceptibility measurements reveal a strong antiferromagnetic coupling interaction between adjacent copper(II) ions with large J value of − 289.66 cm^− 1.     

Phosphate diester hydrolysis promoted by new Cu(II) alkoxide complexes

Three Cu(II) complexes of N3 donor pyridyl-amine ligands, bis-(2-pyridin-2-yl-ethyl)-amine (L¹), which does not have an alcohol pendant, and 2-[bis-(2-pyridin-2-yl-ethyl)-amino]-ethanol (L²) and 3-[bis-(2-pyridin-2-yl-ethyl)-amino]-propan-1-ol (L³), both containing alcohol pendants, have been synthesized and structurally characterized. The reactivities of CuL¹ (1), CuL² (2), and CuL³ (3) for promoting the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) have been investigated, showing that 3 is much more active (observed second order rate constant k = 6.1 × 10⁻¹ M⁻¹ s⁻¹ at pH 8.4, 50 °C) than 1 (k = 9.4 × 10⁻³ M⁻¹ s⁻¹ at pH 8.4, 50 °C) or 3 (observed second order rate constant k = 5.2 × 10⁻³ M⁻¹ s⁻¹ at pH 8.4, 50 °C) at promoting the hydrolysis of BNPP. The much higher reactivity of 3 compared to 2 and 1 may be explained by the higher flexibility of the alkoxide tether in 3, which may allow the nucleophilic alkoxide O-atom in 3 better access to attack a metal-bound BNPP substrate, whereas 2, which has a shorter alkoxide tether, may resort to hydrolyzing the BNPP substrate with a metal-bound hydroxide instead of utilizing its alkoxide moiety because of constraints in the ligand tether. The similar reactivities of 1 and 2 suggest that this is a possible scenario. Another possible explanation for the difference in reactivity between 3 and 2 may be attributed to the alcohol pendant in 3 being better oriented to serve as a proton acceptor from a Cu(II)-bound aqua ligand, which would facilitate its deprotonation and the subsequent nucleophilic attack of the Cu(II)-hydroxide moiety towards the substrate. The reactivities of 2 and 3 towards hydrolyzing BNPP are also compared with that of their Zn(II) analogues, showing that the Cu(II) complexes of the same ligand sets are more hydrolytically active than the corresponding Zn(II) complexes. Single crystal X-ray structures of 1, 2, and 3 are also reported, which show that complexes 2 and 3 form dimers with bridging alkoxide ligands in the solid state, while 1 forms a dimer with bridging chloride ligands in the solid state.     

Spectroscopic studies on bis(1-amidino-O-alkylurea) copper(II) sulfate complexes where alkyl = methyl,ethyl, n-propyl or n-butyl: EPR evidence for binuclear complexes

Four new Cu(II) Complexes viz. [Cu(II)(1-amidino-O-methylurea)₂]SO₄·2H₂O (1), [Cu(II)(1-amidino-O-ethylurea)₂](SO₄)₂·2H₂O (2), [Cu(II)(1-amidino-O-n-propylurea)₂] SO₄·2H₂O (3), [Cu(II)(1-amidino-O-n-butylurea)₂]₂(SO₄)₂·2H₂O (4) have been synthesized and characterized. EPR spectrum of complex 4 at RT consisted of fine-structure transitions (ΔMs = ±1) with zero-field splitting (ZFS) of 0.0485 cm^?1 and a half-field signal (ΔMs = ±2) at ca. 1600 G, revealed formation of binuclear complex (S = 1). Whereas EPR spectrum of complex 2 in DMSO showed a mixture of mononuclear and binuclear complex in the ratio 0.75:1.0 with ZFS of 0.0385 cm^?1. From the temperature dependence of the EPR signal intensity, the isotropic exchange-interaction constant J was evaluated.     

A new copper(II) di-μ2-carboxylato bridged dinuclear complex: [Cu(oda)phen]2 · 6H2O (oda = oxydiacetate,phen = phenanthroline)

The oxydiacetate-bridged copper(II) complex [Cu(oda)(1,10-phen)] · 3H₂O (oda = oxydiacetate dianion, 1,10-phen = 1,10-phenanthroline) has been characterized. The complex is dinuclear and centrosymmetric with each copper atom residing in a CuN₂O₄ octahedral environment. The Cu(II) ions are bridged by two carboxylate-oxygen atoms in a strictly planar Cu₂O₂ core with a Cu–Cu distance of 3.417(2) Å. The magnetic susceptibility measurements (2–300 K) show weak ferromagnetic coupling between the copper ions with J = 3.3 cm⁻¹. The results are compared with those of the homologous [Cu(tda)(1,10-phen)]₂tda (tda = thiodiacetate dianion). A model proposed for the electronic structures of the complexes based on the density functional theory (DFT) satisfactorily accounts for the magnetic results.     

Dicyanamido-metal(II) complexes. Part 5: First example for a unit cell containing dinuclear and 1-D polymeric Cu(II) complexes bridging by dicyanamide

The reaction of Cu(ClO₄)₂, N,N,N′,N″,N″-pentamethylethylenetriamine (pmedien) and sodium dicyanamide (Nadca) in aqueous medium led to the isolation of {[Cu(pmedien)(μ_1,5-dca)]₂(ClO₄)₂,[Cu(pmedien)(μ_1,5-dca)]_n(ClO₄)_n} (1). The complex was structurally and magnetically characterized. Single X-ray crystallography for 1 reveals the existence of two independent molecules in the unit cell: dinuclear doubly bridging complex and a 1-D polymeric chain with dca in both cases acting as a μ_1,5-bridging ligand via the terminal nitrile nitrogen atoms. Magnetic susceptibility measurements of the complex showed that the Cu(II) ions are weakly coupled with ferromagnetic interaction in the dinuclear unit (J_d = 0.9 cm^–1) and antiferromagnetic interaction in the polymeric chain (J_c = ? 0.6 cm^? 1).     

Copper(II) azide complexes of [Cu(acac)(N3)(dpyam)] and [Cu(μ-N3-κN1)(C2N3-κN1)(dpyam)]2: Synthesis,crystal structure and magnetism

Two new compounds, [Cu(acac)(N₃)(dpyam)] (1), (acac = acetylacetonate; dpyam = di-2-pyridylamine) and [Cu(μ-N₃-κ^N1)(C₂N₃- κ^N1) (dpyam)]₂ (2), have been synthesized and characterized by single-crystal X-ray diffraction and magnetic analyses. Compound 1 is a mononuclear compound in which each of two independent Cu(II) ions is penta-coordinated with a distorted square pyramidal geometry with distortion parameters τ = 0.21 and 0.16. In contrast, compound 2 is an azido-bridged dinuclear compound with monodentate dicyanamide anions and the Cu(II) ions display a distorted trigonal bipyramidal geometry with τ = 0.73 and end-on azido bridges providing an equatorial–axial position between the metal ions. The EPR spectra of powdered samples for 1 and 2 have also been investigated. Magnetic susceptibility measurements of compound 2 reveal a very weak ferromagnetic interaction between the Cu(II) ions with a J value of +5.8 cm⁻¹.     

Stereo-regulated methyl methacrylate (MMA) polymerization catalyzed by asymmetric Salen-type Schiff-base Cu(II) complexes

A series of mononuclear asymmetric Salen-type Schiff-base complexes [Cu(Lⁿ)] (n = 1–5, 1–5) were obtained by the Cu(II)-templated approach in the presence of one of five salicylaldehyde derivatives, respectively. These complexes could effectively catalyze the metal-coordinative polymerization of MMA for the formation of the syndio-enriched PMMAs (poly(methyl methacrylates)) in the presence of AIBN, where the Cu(II)-to-chelate-plane distances are positively relative to the catalytic activity. Moreover, the introduction of the encumbering substituent ortho to the phenoxide ring of the ligands plays a much more important and influential role on the tacticity and chain-growth of the obtained PMMAs than the variation of reaction conditions under the controllable polymerization.     

Influence of anion induced proton abstraction on Cu(II) adsorption by alginic acid

Alginic acid (AA) synthesized by acidification of commercial sodium alginate was investigated for its Cu(II) adsorption efficiency in the presence of different counter ions. The results of batch adsorption studies indicated an adsorption of 169.86 mg/g of Cu(II) by AA in the presence of acetate ions, however, it significantly decreased in the presence of chloride (126.36 mg/g), sulphate (115.24 mg/g) and nitrate (113.28 mg/g) as counter ions. This can be accounted to the tendency of conjugate base (anion) to abstract proton from AA, which determines the extent of deprotonation of carboxylic acid. The FTIR and TGA/DTA studies support the difference in the coordination of carboxylate to Cu(II) in the presence of various counter anions. Acetate showed strong chelate coordination between Cu(II) and AA, whereas in the presence of Cl⁻, NO₃⁻ and SO₄^2 −, Cu(II) was complexed by weak bridging coordination with AA.     

New μ-oxo-bridged tetranuclear Cu(II) complex with Schiff-base ligand: Synthesis,crystal structure and magnetic properties

A new μ-oxo-bridged Cu(II) complex with cubane-like tetranuclear copper(II) complex, [Cu₄(L¹)₄] · 4H₂O (1) (H₂L¹ = 2-(3-methoxy-salicylidene-amino)-benzyl-alcohol), has been prepared, and structurally characterized by X-ray crystallography. Complex 1 crystallized in the monoclinic space group P₂₁/n and has a tetranuclear core of Cu₄O₄. The temperature dependence of magnetic susceptibility measurements shown that complex 1 exhibits a strong antiferromagnetic interaction with J = −103.4 cm⁻¹.     

Synthesis,structure and characterization of 1D threefold-bridging copper(II) chain with strong ferromagnetic coupling

A 1D chain Cu(II) complex: [Cu(2-Clnic)(μ_1,1-N₃)(CH₃OH)]_n(1) (2-Clnic=2-chloronicotinate) has been synthesized and characterized by IR, elemental analysis, X-ray crystal diffraction and magnetic properties. Single-crystal structural analysis shows that complex 1 consists of 1D Cu(II) chains containing threefold bridging ligands, one μ_1,1-azido, one (syn–syn) 2-chloronicotinate and one methanol molecule. The magnetic susceptibilities of 1 has been investigated, indicating strong ferromagnetic interactions with J = 81.22 cm^?1.     

Decomposition of allantoin in the presence of Cu(II) ions resulting in the formation of a coordination polymer containing oxalate species

A novel Cu(II) coordination polymer, [Cu(ox)(DMSO)₂]_n (1) (ox-oxalate dianion, DMSO-dimethyl sulphoxide) has been prepared in the reaction of copper nitrate dihydrate and allantoin (5-ureidohydantoin) in DMSO/water solution. Compound (1) crystallizes in the monoclinic, space group P121/c1 with a = 5.1785(7), b = 13.6311(18), c = 8.5386(12) Å, β = 107.524(12)°, V = 574,76(14) Å³, Z = 4, D_cal = 1779 mg/m³, R₁ = 0.0449. The metal ion coordinates through four oxygen atoms belonging to two bidentate bridging oxalate ligands, and two oxygen atoms from two DMSO ligands forming an elongated octahedron. The crystal structure was confirmed by FT-IR and Uv–vis spectroscopic data.     

Synthesis,crystal structure,and magnetic property of a stepped tetranuclear copper(II) complex of 3,5-diisopropylpyrazole-1-methoxide

Reaction of copper(II) chloride dihydrate in methanol with deprotonated 3,5-diisopropylpyrazole-1-methanol (dippmOH) led to the tetranuclear copper(II) complex [(dippmO)CuCl]₄ (1). The crystal structure of 1 indicates that two copper(II) ions connect via the oxygen atoms of dippmO⁻ ligands each other in which two dimeric units are formed. Furthermore, one of the coordinated oxygen atoms in a dimer is bonded to an adjacent copper(II) ion positioned other dimer, which gives rise to a stepped tetranuclear structure. 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J₁ = − 239 cm^− 1) and weak antiferromagnetic couplings between the dimers (J₂ = − 15 cm^− 1).     

Imidazolate-bridged dinuclear copper(II) complex with new macrocyclic ligand bearing two 1H-imidazol-4-yl-pendants

A new imidazolate-bridged dicopper complex [Cu₂(L)(Im)](ClO₄)₃·H₂O has been synthesized by reaction of new macrocyclic ligand 6, 20-bis(1H-imidazol-4-ylmethyl)-3, 6, 9, 17, 20, 23-hexaazatricyclo[24.3.1.1^11,15]hentriaconta-1(29), 11, 13, 15(31), 26(30), 27-hexaene (L) with Cu(ClO₄)_2?6H₂O and imidazole, and structurally characterized as a model compound of Cu₂Zn₂-SOD. There is antiferromagnetic interaction with g = 2.08, ? 2 J = 66.5 cm^? 1 between the two imidazolate-bridged Cu(II) atoms. The complex displays moderate SOD activity with IC₅₀ of 1.42 μM.     

Structure and magnetism of novel dinuclear cobalt(II) complexes

Two dinuclear cobalt(II) complexes of the formula [Co₂X₄(isonia)₄] have been synthesized and structurally characterized; isonia is unidentate neutral iso-nicotinamide and X are furan-3- or furan-2-carboxylate ligands. The chromophore {CoO₄N₂} is formed of two iso-nicotinamide ligands and three furancarboxylate ligands where two of them bear a bridging function and one is a terminal-bidentate ligand. The magnetic data confirm a weak exchange interaction (J / hc = − 2 cm^− 1) and a high single-ion zero-field splitting (D / hc = 63 and 33 cm^− 1, respectively).     

Intraligand fluorescence of Zn(II) and Pt(II) complexes of pyridoxal thiosemicarbazone

Pyridoxal (vitamin B₆ aldehyde) thiosemicarbazone (B₆TSC) is deprotonated to its anion (B₆TSC – H⁺) in basic solution at pH = 9. It shows an intense green fluorescence with λ_max = 500 nm and a quantum yield of unity. Zn(II)(B₆TSC – H⁺)(acetate) displays an blue-green intraligand (B₆TSC) fluorescence of moderate intensity. The complex cation [Pt(II)(B₆TSC)Cl]⁺ is isolated as tetraphenylborate. In basic solution (pH = 9) this cation is deprotonated to the neutral complex [Pt(II)(B₆TSC – H⁺)Cl] which exhibits the same green intraligand fluorescence as the free anion (B₆TSC – H⁺)⁻. However, in the platinum complex this emission is much less intense. It is reduced to φ = 10^− 2.