Competitive sorption of Cu(II) and Eu(III) ions on olive-cake carbon in aqueous solutions—a potentiometric study

The competitive sorption of Cu(II) and Eu(III) ions from aqueous solutions by olive-cake carbon, has been investigated by potentiometry at pH 6, I=0.1 M NaClO₄, 25°C and under normal atmospheric conditions. Evaluation of the experimental data supports the formation of inner-sphere surface complexes and results in the calculation of the formation constant of the surface complexes ((=S–O)₂Cu), which is found to amount log β _Cu=5.3±0.3. Addition of competing Eu(III) ions in the aqueous system leads to replacement of the Cu(II) by the competitor metal ion. Evaluation of the potentiometric data obtained from competition experiments indicates an ion-exchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake carbon is found to be log β _Eu=5.1±0.5. Comparison of the complex formation constants of the olive-cake carbon with the corresponding complex formation constants for of olive cake and humic acid with the two metal ions, indicates that the same type of active sites is responsible for the metal ion complexation on the surface of the different types natural organic matter (e.g. olive-cake carbon, olive-cake and humic acid).     

Sorption of Cu(II) and Eu(III) ions from aqueous solution by olive cake

The sorption of Cu(II) on olive cake, a biomass by-product of olive oil production, has been investigated by potentiometry at pH 6, I=0.1 M NaClO₄, 25 °C and under atmospheric conditions. Numerical analysis of the experimental data supports the formation of surface complexes and allows the evaluation of the corresponding formation constant, which is found to amount log β=5.1±0.4. This value is close to corresponding values given in literature for Cu(II)-humate complexes, indicating that the same type of active sites (e.g. carboxylic and phenolic groups) is responsible for the Cu(II) binding by olive cake. Addition of a competing metal ion (e.g. Eu(III) ion) in the system leads to replacement of the Cu(II) by Eu(III). Evaluation of the potentiometric data obtained from competition experiments indicates on a ionexchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake is found to be log β=5.4±0.9. The results of this study are of particular interest with respect to waste water treatment technologies using biomass products as adsorbent material and environmental impact assessments regarding disposal of biomass by products in the geosphere.     

Cation exchange column chromatography in aqueous ammonium acetate: Separation of U(VI), Al(III), Sr(II), Ba(II) and Hg(II) from other metal ions

Summary A rigorous analysis of the effect of various concentrations (0.02–1.60M) of ammonium acetate on the distribution coefficients (K) of a number of metal ions using cation exchanger Dowex 50W-X8 (100–200 mesh NH₄ ⁺-form) has been made. On account of the low affinity of U(VI) for resin in 0.20M NH₄OAc it can be separated from all other metal ions. HighK values of Sr(II), Ba(II) and Hg(II) at higher 0.50M NH₄OAc are responsible for their separation from others. The abnormal column Chromatographic behaviour of Al(III) permits its separation from other metal ions including U(VI), Sr(II), Ba(II), Hg(II). A number of binary and ternary separations have been achieved.     

Spectral,magnetic, thermal,antimicrobial, and eukaryotic DNA studies on acetone [<Emphasis Type="Italic">N</Emphasis>-(3-hydroxy-2-naphthoyl)]hydrazone complexes

Abstract  Acetone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂AHNH) has been prepared and its structure confirmed by elemental analysis and ¹H NMR spectroscopy. It has been used to produce diverse complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and U(VI)O₂ ions. The complexes obtained have been investigated by thermal analysis, spectral studies (¹H NMR, IR, UV–visible, ESR), and magnetic measurements. IR spectra suggest that H₂AHNH acts as a bidentate ligand. The electronic spectra of the complexes and their magnetic moments provide information about geometries. The ESR spectra give evidence for the proposed structure and the bonding for some Cu(II) complexes. Thermal decomposition of the Ni(II) and Cu(II) complexes afforded metal oxides as final products. Kinetic data were obtained for each stage of thermal degradation of some of the complexes using the Coats–Redfern method. The formation of complexes in solution was studied pH-metrically and the order of their stability constants (log K) was found to be U(VI)O₂ > Cu(II) > Zn(II) > Ni(II) > Cd(II) > Co(II). Antimicrobial and eukaryotic DNA studies were carried out. Graphical abstract        

Europium (III) and Uranium (VI) complexation by natural organic matter (NOM): Effect of source

For the safe long‐term storage of high‐level radioactive waste (HLW), detailed information about geo‐chemical behavior of radioactive and toxic metal ions under environmental conditions is important. Natural organic matter (NOM) can play a crucial role in the immobilization or mobilization of these metal ions due to its complexation and colloid formation tendency. In this study, the complexation of europium (as chemical homologue of trivalent actinides such as americium) and uranium (as main component of HLW) by ten humic acids (HA) from different sources and Suwannee NOM river extract has been analyzed. Capillary electrophoresis in combination with inductively coupled plasma mass spectrometry has been used for the evaluation of complex stability constants log β. In order to determine the complex stability constants a conservative single site model was used in this study. In dependence of their source and thus of NOM structure the log β values for the analyzed humic acids are in the range of 6.1–7.0 for Eu(III) and 5.2–6.4 for U(VI) (UO₂²⁺), respectively. In contrast to the results for HA the used Suwannee river NOM reveals log β values in the range of nearly two orders of magnitude lower (4.6 for Eu³⁺ and 4.5 for UO₂²⁺) under the geochemical conditions applied in this study.     

A new spot test for cerium(IV)

Summary A new colour reaction for the detection of cerram(IV) which can be carried out both in a test tube and on a spot plate has been described. The test solution is treated with methylene blue in nitric acid solution (11) to form a rose-red colour. This simple procedure has an advantage over the existing tests in that it is applicable in the presence of oxidising agents like chromium(VI), vanadium(V), nitrate, perchlorate and of coloured ions like copper(II), cobalt(II), nickel(II), chromium(III), iron(III), vanadium(IV), uranium(VI).

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Zusammenfassung Eine neue, sowohl in der Eprouvette wie auf der Tüpfelplatte ausführbare Farbreaktion zum Nachweis von Cer(IV) wurde angegeben. Die Probelösung wird mit salpetersaurer Methylenblaulösung behandelt und gibt eine rosarote Färbung. Die Reaktion hat gegenüber bekannten Tests den Vorteil, in Gegenwart von Oxydationsmitteln wie Cr(VI), V(V), NO₃ ^–, ClO₄ ^– bzw. in Anwesenheit gefärbter Ionen wie Cu(II), Co(II), Ni(II), Cr(III), Fe(III), V(IV) oder U(VI) anwendbar zu sein.

     

Novel M(II)–Hg(II) coordination polymers generated from metal-containing building blocks M(2-pyrazinecarboxylate)2 · (H2O)2 (M=Cu, Ni, Co) and HgCl2

A new class of M(II)–Hg(II) (M=Cu(II), Co(II), Ni(II)) mixed-metal coordination polymers, Cu(2-pyrazinecarboxylate)₂HgCl₂ (4), [Co(2-pyrazinecarboxylate)₂(HgCl₂)₂] · 0.61H₂O (5) and [Ni(2-pyrazinecarboxylate)₂(HgCl₂)₂] · 0.77H₂O (6), have been prepared by self assembly of metal-containing building blocks, M(2-pyrazinecarboxylate)₂ · (H₂O)₂(M=Cu(II), Co(II), Ni(II)), with HgCl₂. Compounds 4–6 were characterized fully by IR, elemental analysis and single crystal X-ray diffraction. Compound 4 crystallized in the monoclinic space group C2/c, with a=17.916(5) Å, b=7.223(2) Å, c=13.335(4) Å, β=128.726(3)°, V=1346.2(6) ų, Z=4. It contains alternating Hg(II) and Cu(II) metal centers that are cross-linked by 2-pyrazinecarboxylate spacers and chlorine co-ligands to generate a unique three-dimensional Hg(II)–Cu(II) mixed metal framework. Compound 5 crystallized in the triclinic space group P , with a=6.3879(7) Å, b=6.6626(8) Å, c=13.2286(15) Å, α=96.339(2)°, β=91.590(2)°, γ=113.462(2)°, V=511.71(10) ų, Z=1. Compound 6 also crystallized in the triclinic space group P , with a=6.3543(8) Å, b=6.6194(8) Å, c=13.2801(16) Å, α=96.449(2)°, β=92.263(2)°, γ=113.541(2)°, V=506.67(11) ų, Z=1. Compounds 5 and 6 are isostructural and in the solid state the Hg(II)M(II)Hg(II) units are connected by Hg₂Cl₂ linkages to produce a novel M(II)–Hg(II) (M=Co(II), Ni(II)) zigzag mixed-metal chain, in which a new type of M–M′–M′–M array was observed. The metal containing building blocks, M(2-pyrazinecarboxylate)₂ · (H₂O)₂ (M=Cu(II), Co(II), Ni(II)), exhibit different connectivities to HgCl₂ depending on the metal cation contained within them.     

Synthesis, structure and DNA binding studies of mononuclear copper(II) complexes with mixed donor macroacyclic ligands, 2,6-bis({N-[2&3-(phenylselenato)alkyl]}benzimidoyl)-4-methylphenol

Two new phenol based macroacyclic Schiff base ligands, 2,6-bis({N-[2-(phenylselenato)ethyl]}benzimidoyl)-4-methylphenol (bpebmpH, 1) and 2,6-bis({N-[3-(phenylselenato)propyl]}benzimidoyl)-4-methylphenol (bppbmpH, 2) of the Se₂N₂O type have been prepared by the condensation of 4-methyl-2,6-dibenzoylphenol (mdbpH) with the appropriate (for specific reactions) phenylselenato(alkyl)amine. These ligands with Cu(II) acetate monohydrate in a 2:1 molar ratio in methanol form complexes of the composition [(C₆H₂(O)(CH₃){(C₆H₅)CN(CH₂)_nSe(C₆H₅)}{(C₆H₅)CO}₂Cu] (3 (n = 2), 4 (n = 3)) with the loss of phenylselenato(alkyl)amine and acetic acid. In both these complexes, one arm of the ligand molecule undergoes hydrolysis, and links with Cu(II) in a bidentate (NO) fashion, as confirmed by single crystal X-ray crystallography of complex 3. The selenium atoms do not form part of the copper(II) distorted square planar coordination sphere which has a trans-CuN₂O₂ core. The average Cu–N and Cu–O distances are, respectively, 1.973(3) and 1.898(2) Å. The N–Cu–N and O–Cu–O angles are, respectively, 167.4(11)° and 164.5(12)°. The compounds 1–4 have been characterized by elemental analysis, conductivity measurements, mass spectrometry, IR, electronic, ¹H and ⁷⁷Se{¹H} NMR spectroscopy and cyclic voltammetry. The interaction of complex 3 with calf thymus DNA has been investigated by a spectrophotometric method and cyclic voltammetry.     

Spectrophotometric determination of molybdenum by extraction of its thiosulphate complex

A simple and rapid spectrophotometric determination of molybdenum is described. The molybdenum thiosulphate complex is extracted into isoamyl alcohol from 1·0–1·5M hydrochloric acid containing 36–40 mg of Na₂S₂O₃·5H₂O per ml. The absorbance at λ_max = 475 nm obeys Beer's law over the range 0–32 μg of Mo per ml of solvent phase. Up to 5 mg/ml of Ti(IV), V(V), Cr(VI), Fe(III), Co(II), Ni(II), U(VI), W(VI), Sb(III), 1 mg/ml of Cu(II), Sn(II), Bi(V) and 10 μg/ml of Pt(IV) and Pd(II) do not interfere. Large amounts of complexing agents interfere. The method has been applied to analysis of synthetic and industrial samples.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

Search for optimal conditions for the extraction of thiosulfate complexes of Cu(II) by 4-(5-nonyl)pyridine from aqueous mineral acid solutions

Solvent extraction of Cu(II) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiosulfate ions has been studied at room temperature (23±2°C). Mineral acid solutions alone constitute an aqueous phase from which Cu(II) is not extracted. Addition of small amounts of thiosulfate ions augments the extraction to an extent that quantitative recovery is possible. Stoichiometric studies reveal the involvement of ion-pair type complexes (NPy·H)₂·Cu(S₂O₃)₂ which are responsible for extraction. Stability constants lg K_ex for this complex are 7.2±0.2; 9.1±0.2 and 9.5±0.2 for HCl, HNO₃ and H₂SO₄, respectively. The presence of 0.01 mol/l of some complexing ions like ascorbate, acetate, citrate, oxalate, tartrate or iodide does not affect the extraction, thus allowing the recovery of the metal from diverse matrices. Under optimal conditions (0.1M NPy in benzene-0.1M HNO₃ or H₂SO₄+0.01M S₂O ₃ ^?2 or 0.5M HCl+0.05 M S₂O ₃ ^?2 ) a clean separation from some elements, e.g. Cs(I). Co(II), Fe(III), Eu(III), Ce(III), Se(IV) and Cr(VI) can be achieved.     

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10⁻⁶ M and the progress of reaction was followed spectrophotometrically at 525 nm (λ_max of purple-red complex [Ru(CN)₅NRS]³⁻,  = 3.1 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 8.75 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 3.50 × 10⁻⁴ M [nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10⁻⁷ M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.     

DNA binding and oxidative cleavage activity of ternary (l-proline)copper(II) complexes of heterocyclic bases

Ternary copper(II) complexes [Cu(l-pro)(B)(H₂O)](NO₃) (1, 2) where l-pro = l-proline, B is a N,N-donor heterocyclic base, viz. 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), are synthesized, characterized, and their DNA binding and cleavage activity studied. The bpy complex (1) is structurally characterized by single-crystal X-ray crystallography. The complexes show the presence of a distorted square-pyramidal (4 + 1) CuN₃O₂ coordination geometry. Complex [Cu(l-pro)(bpy)(H₂O)](NO₃) (1) crystallizes in the triclinic space group P1 with unit cell parameters: a = 7.082(3) Å, b = 10.483(5) Å, c = 11.581(5) Å, α = 89.700(7)°, β = 83.488(8)°, γ = 84.109(8)° and V = 849.7(7) Å³. The one-electron paramagnetic complexes display a d–d band near 600 nm in water and show a cyclic voltammetric response due to Cu(II)/Cu(I) couple near 0.1 V (versus SCE) in Tris–HCl buffer–0.1 M KCl. Binding interactions of the complexes with calf thymus (CT) DNA have been investigated by emission, absorption, viscosity and DNA thermal denaturation studies. The phen complex displays significant binding propensity to the CT DNA giving an order: 2 (phen)  1 (bpy). The bpy complex does not show any apparent binding to the DNA and hence poor cleavage efficiency. Complex 2 shows efficient oxidative cleavage of SC-DNA in the presence of 3-mercaptopropionic acid (MPA) involving hydroxyl radical species as evidenced from the control data showing inhibition of DNA cleavage in the presence of DMSO and catalase.     

Study of the kinetics of the transport of Cu(II), Cd(II) and Ni(II) ions through a liquid membrane

The coupled transport of Cu(II), Cd(II) and Ni(II) ions through a bulk liquid membrane (BLM) containing pyridine-2-acetaldehyde benzoylhydrazone (2-APBH) as carrier dissolved in toluene has been studied. Once the optimal conditions of extraction of each metal were established, a comparative study of the transport kinetics for these metals was performed by means of a kinetic model involving two consecutive irreversible first-order reactions. The kinetic parameters (apparent rate constants of the metal extraction and re-extraction reactions (k ₁, k ₂), the maximum reduced concentration of the metal in the liquid membrane (), the time of the maximum value of R _o ( t _max) and the maximum entry and exit fluxes of the metal through the liquid membrane ( and ) of the extraction and stripping reactions were evaluated and results showed good agreement between experimental data and theoretical predictions. Complete transport through the membrane took place according to the following order: Cd(II)>Cu(II)>Ni(II), with similar kinetic parameters obtained for Cu(II) and Cd(III). The transport behaviour of Ni(II) was different to that of Cu(II) and Cd(III), probably due to the different stoichiometry of the nickel complex compared to those of the other metal ions and the different chemical conditions required for its formation. The influence of the sample salinity on the transport kinetics was studied. k ₁ values decreased slightly when the feed solution salinity was increased for Cu(II) and Ni(II), but not for Cd(II). Values of k ₂ were practically unaffected. The proposed BLM was applied to the preconcentration and separation of metal ions (prior to their determination) in water samples with different saline matrices (CRM, river water and seawater), and good agreement with the certified values was obtained.     

Spectral, magnetic, thermal, antimicrobial, and eukaryotic DNA studies on acetone [N-(3-hydroxy-2-naphthoyl)]hydrazone complexes

Abstract  

Acetone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂AHNH) has been prepared and its structure confirmed by elemental analysis and ¹H NMR spectroscopy. It has been used to produce diverse complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and U(VI)O₂ ions. The complexes obtained have been investigated by thermal analysis, spectral studies (¹H NMR, IR, UV–visible, ESR), and magnetic measurements. IR spectra suggest that H₂AHNH acts as a bidentate ligand. The electronic spectra of the complexes and their magnetic moments provide information about geometries. The ESR spectra give evidence for the proposed structure and the bonding for some Cu(II) complexes. Thermal decomposition of the Ni(II) and Cu(II) complexes afforded metal oxides as final products. Kinetic data were obtained for each stage of thermal degradation of some of the complexes using the Coats–Redfern method. The formation of complexes in solution was studied pH-metrically and the order of their stability constants (log K) was found to be U(VI)O₂ > Cu(II) > Zn(II) > Ni(II) > Cd(II) > Co(II). Antimicrobial and eukaryotic DNA studies were carried out.     

Spectrophotometric and potentiometric study of the complexes originated by the trisodium salt of 2-(p-sulfophenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid (SPADNS) and several metal ions

A study of the complexes originated by U(VI), Cu(II), Pb(II), Ni(II), Co(II), Zn(II), Cd(II), Mn(II), Ca(II), Mg(II), Ba(II), and Sr(II), and SPADNS (trisodium salt of 2-(p-sulfophenylazo)-1, 8-dihydroxynaphthalene-3,6-disulfonic acid) has been made by means of spectrophotometric and potentiometric methods. The dissociation constants of the ligand and the formation constants of the metal ion-SPADNS complexes have been determined at 25 ± 0.1 °C and ionic strength 0.1 (NaClO₄).     

Ion exchange separation of Eu(III), Th(IV), U(VI) and Pu(IV) ions on Amberlyst A-15 in non-aqueous solutions

Distribution ratios of europium(III), thorium(IV), uranium(VI) and plutonium(IV) ions on Amberlyst A-15, a macroreticular polystyrene sulfonate resin, after extraction in HTTA-TBP-Shell Sol-T and HTTA-TOPO-benzene solutions have been determined as a function of the aqueous acidity. The affinity orders were EuPu>Th>U and Eu>Th>Pu>U in the former and the latter solutions, respectively. Separation factors were computed from the observed K_d values. A procedure for the separation of a mixture of Eu(III), Th(IV), and U(VI) ions in HTTA-TOPO-benzene solution in an ion-exchange column is described.     

Synthesis, characterization and biological evaluation of a novel Cu(II) complex with the mixed ligands 2,6-pyridinedicarboxylic acid and 2-aminopyridine

A novel bridged binuclear Cu(II) complex with mixed ligands, di-μ-(2-aminopyridine(N,N′))-bis[(2,6-pyridinedicarboxylate)aquacopper(II)] tetrahydrate, formulated as [Cu(μ-ap)(dipic)(H₂O)]₂·4H₂O (1) (dipic = 2,6-pyridinedicarboxylate, ap = 2-aminopyridine), has been synthesized and characterized by elemental, spectral (IR and UV–Vis.), thermal analysis, magnetic measurements and single crystal X-ray diffraction analysis. The central Cu(II) ion resides on a centre of symmetry in a distorted square-pyramid coordination environment comprising of two N atoms, one from dipic and one from the ap ring, two carboxylate O atoms from dipic, and one O atom from water. Intermolecular N–HO and O–HO hydrogen bonds and π–π stacking interactions seem to be effective in the stabilization of the crystal structure. The free ligands and the complex were also evaluated for their antimicrobial and radical scavenging activities (DPPH = 1,1-diphenyl-2-picrylhydrazyl hydrate) using in vitro microdilution methods. Antimicrobial screening of the free ligands and their complex showed that the free ligands and the complex possess antifungal activity against Candida sp.     

Preparation, characterization and application of an cellulose ion-exchanger with acetoacetamide functional groups

Summary A method is described for functionalizing acetoacetamide chelating groups onto microcrystalline cellulose (Cell-AcAc). This material shows a significant affinity for Fe(III), Cu(II) and U(VI) and no or very less affinity for the M(I) ions (M=Na, K), M(II) ions (M= Mg, Ca; Fe, Co, Ni, Zn), La(III) and Y(III) including Th(IV). The obtained K _d values offer a column separation method for U(VI) ions from the rest of above-mentioned metal ions except Fe(III). Cell-AcAc and its Cu(II) complexes are characterized by means of FT-IR spectra.

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Darstellung, Charakterisierung und Anwendung von Ionenaustauschmaterial aus Cellulose mit chemisch gebundener Acetoacetamid-Gruppe

Zusammenfassung Die Darstellung von immobilisiertem Acetoacetamid auf mikrokristallinem Cellulosepulver (Cell-AcAc) wird beschrieben. Der Ionenaustauscher Cell-AcAc hat eine ausgeprägte Affinität für Fe(III), Cu(II) and U(VI), aber nahezu keine für die M(I)-Ionen (M=Na, K) M(II)-Ionen (M=Mg, Ca; Fe, Co, Ni, Zn), La(III), Y(III) sowie Th(IV). Die erhaltenen K _d-Werte ermöglichen für U(VI)-Ionen eine quantitative säulen-chromatographische Trennung von den anderen genannten Kationen mit Ausnahme von Fe(III). Das Ionenaustauschmaterial Cell-AcAc und sein Cu(II)-Komplex wurden durch FT-IR-Spektren charakterisiert.

     

O-phenylenebis(oxamato) bridged trinuclear copper(II) complexes: synthesis and magnetic properties

Summary Four new trinuclear copper(II) complexes bridged by o-phenylenebis(oxamato) (opba) and end-capped with 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO₂-phen), 2,2-bipyridyl (bipy) or 4,4-dimethyl-2,2-bipyridyl (Me₂bipy), {[Cu(opba)][Cu(L)]₂}(ClO₄)₂ (L = phen, NO₂-phen, bipy or Me₂bipy), have been synthesized and characterized. Based on i.r., elemental analyses, conductivity measurements and electronic spectra, oxamato-bridged structures consisting of three copper(II) ions in which each copper(II) ion has a square-planar environment are proposed. The temperature-dependent magnetic susceptibility of {[Cu(opba)][Cu(phen)]₂} (ClO₄)₂ has been studied in the 4.2–300 K range, giving the exchange integral J = -134.4cm^–1. The result revealed the operation of an antiferromagnetic spin-exchange interaction between the adjacent copper ions.