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The success of platinum-based chemotherapeutic drugs for clinical cancer treatments has inspired tremendous research efforts on developing new metallic anticancer agents with improved cytotoxic activity and reduced side effects. 2,2′;6′,2″-Terpyridine and its 4′-substituted derivatives have showed great potential as ligand compartments for designing new anticancer drug candidates involving base metals. In this work, we synthesized a series of cobalt and iron coordination compounds based on 4′-pyridyl-2,2′;6′,2″-terpyridine, including homoleptic complexes, a dinuclear bridged complex and 1- and 2-dimensional coordination polymers/networks. The polymorphism of two homoleptic CoII and FeII complexes has been described along with the structural characterization of a CoII coordination polymer and dinuclear FeIII complex by X-ray crystallography. These compounds were tested preliminarily as precatalysts for the regioselective hydrosilylation of styrene. Their cytotoxic activities against two human breast cancer cell lines (MCF-7 and MDA-MB 468) and a normal breast epithelial cell line (MCF-10A) were investigated in order to observe the best-performing drug candidates. [ABSTRACT FROM AUTHOR]

This paper presents study on the facilitated transport of cadmium(II), cobalt(II) and nickel(II) ions from aqueous chloride solutions through polymer inclusion membranes (PIMs) with phosphonium ionic liquid. Cyphos IL 101 (trihexyl(tetradecyl) phosphonium chloride) was used as a selective carrier for synthesis of cellulose triacetate membranes containing o-nitrophenyl pentyl ether (ONPPE) as a plasticizer. Effect of different parameters such as hydrochloric acid concentration in the source phase as well as ion carrier concentration in the polymer membrane on metal ions transport has been investigated. Cd(II) was transported preferably from hydrochloric acid solutions containing Co(II) and Ni(II) through PIM containing 18.8 wt.% CTA and 26.0 wt.% Cyphos 101 and 55.1 wt.% ONPPE into 0.5 M HNO3 as the receiving phase. The obtained results suggest that there is a possibility of application of this membrane with Cyphos IL 101 as ion carrier for separation of Cd(II) over Co(II) and Ni(II) from hydrochloric acid solutions. [ABSTRACT FROM AUTHOR]

To search for more high-performance crystalline proton conducting materials and to accelerate the related research progress, in this paper, a one-dimensional coordination polymer (CP), [Co(BBOT) 2 (H 2 O) 3 ·2H 2 O] n (1) (H 2 BBOT = N-benzoyl-N′-(4-benzoxy)thiourea) was firstly prepared by solvent volatilization approach. Subsequently, the thermal, H 2 O and chemical stabilities of the CP were tested and its high structural stability was confirmed. Furthermore, in 1 , a stable solid three-dimensional framework can be constructed by intermolecular H-bonds and stacking interactions between phenyl units. Then, utilizing the AC impedance determination, the dependence of the proton conductivity of this CP on temperature and humidity in the water vapor environment was explored and the positive correlation was verified. Excitingly, the optimized proton conductivity of this compound under specific test conditions (100 °C/98 % relative humidity) can be as high as 10−4 S/cm, being in the forefront of similar crystalline solid materials. Finally, according to the value of activation energy and the characteristics of crystal structure, we speculate on the proton conduction mechanism. Proton conductivity of a CP under variable humidity and temperatures was explored. Its highest proton conductivity can attain up to 10−4 S/cm, and its proton-conduction mechanism was speculated. [Display omitted] • One carboxylate-based Co(II) coordination polymer was prepared. • Its structure was characterized by single-crystal X-ray diffraction. • Its water-assisted proton conduction was explored. • The proton-conducting mechanism was speculated. [ABSTRACT FROM AUTHOR]

This paper presents sustainable hydrometallurgical recovery of Co(II) from wastewater, achieved by application of two ionic liquids (Cyphos IL 101 or 104) and an acidic extractant (Cyanex 272). The separation of Co(II) is carried out from model aqueous chloride and sulfate solutions, as well as from a real waste sulfate solution containing also Ni(II). The extractants were investigated both as single carriers and as synergic mixtures, the latter giving no positive synergistic effect. Cyanex 272 does not allow Co(II) to be transferred from chloride solutions effectively, while extraction from sulfate mixtures reaches totally up to 100% after two stages. Cyphos IL 101 does not give satisfactory results of Co(II) recovery from sulfate solutions, while both Co(II) and Ni(II) are transferred efficiently from chloride ones. Stripping of Co(II) from the loaded organic phases with 1 M H 2 SO 4 is very efficient (95–100%), regardless of the type of extractant (Cyanex 272 or Cyphos IL 104) and its concentration. Application of 1 M H 2 SO 4 allows Co(II) to be recovered from the loaded organic phase (up to 100%) in one stage of stripping and to be enriched even three-to fivefold relative to that in the feed. It also allows the organic phase to be reused for further extractions. Theoretical considerations of economic feasibility of the process proposed indicated that the value of cobalt in solutions after proposed steps increases from 0.32 USD/dm3 (after two stages of extraction) to 1.42 USD/dm3 after stripping. The major novelty of this work is the design of hydrometallurgical recovery of Co(II) from real sulfate wastewater in the presence of Ni(II), which permits sustainable processing of waste, recycling and recovery of critical element and also regeneration and reuse of organic chemicals applied for extraction. Image 1 • Sustainable hydrometallurgical recovery of Co(II) from wastewater is proposed. • Cyphos IL 101 or 104 and an acidic Cyanex 272 are applied as Co(II) extractants. • Flow sheet for Co(II) separation from real waste sulfate solution is proposed. • Process includes: 2 steps of extraction, stripping, 3 steps of organic phase scrubbing. • After stripping Co(II) is separated from Ni(II), concentrated and ready for electrowinning. [ABSTRACT FROM AUTHOR]

The hexacoordinate Co(II) complex [Co(neo)2(cin)][BPh4]·½Me2CO (1·½Me2CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me2CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm−1. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me2CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations. [ABSTRACT FROM AUTHOR]

Four new metal–organic frameworks based on cobalt(II) salts and 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide (odabco) were obtained. Their crystallographic formulae are [Co3(odabco)2(OAc)6] (1, OAc− = acetate), [Co(H2O)2(HCOO)2]·odabco (2), [Co2(H2O)(NO3)(odabco)5](NO3)3·3.65H2O (3), and [Co2(DMF)2(odabco)4](NO3)4·3H2O (4; DMF = N,N-dimethylformamide). Crystal structures of 1–4 were determined by single-crystal X-ray crystallography. Coordination polymer 1 comprises binuclear and mononuclear metal–acetate blocks alternating within uncharged one-dimensional chains, in which odabco acts as a bridging ligand. A layered Co(II) formate 2 contains odabco only as guest molecules located in the interlayer space. Layered compound 3 and three-dimensional 4 have cationic coordination frameworks with 26% and 34% specific void volumes, respectively, unveiling high structural diversity of Co(II)-odabco MOFs based on quite a rare aliphatic moiety. Magnetization measurements were performed for 1, 3, and 4 and the obtained data were interpreted on the basis of their crystal structures. A strong (J/kB~100 K) antiferromagnetic coupling was found within binuclear metal blocks in 1. Ion exchange experiments revealed a considerable iodide uptake by 3 resulting in an up to 75% guest nitrate substitution within the voids of a coordination framework, found by capillary zone electrophoresis data and confirmed by single-crystal XRD. A preservation of 3 crystallinity during the exchange allowed for the guest I− positions within a new adduct with the formula [Co2(H2O)(NO3)(odabco)5]I2(NO3)·1.85H2O (3-I) to be successfully determined and the odabco aliphatic core to be revealed as a main adsorption center for quite large and easily polarizable iodide anions. In summary, this work presents a comprehensive study for a series of 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide-based MOFs of cobalt(II) within the framework of magnetic properties and reports the first example of anion exchange in odabco-based coordination networks, supported by direct X-ray structural data. The reported results unveil promising applications of such frameworks bearing ligands with an aliphatic core in the diverse structural design of selective adsorbents and other types of functional materials. [ABSTRACT FROM AUTHOR]

The selective extraction of metals from aqueous solutions is a very important stage in the hydrometallurgical processing of metallic waste. Leach solutions are usually a multicomponent mixture. The main impurity of aqueous solutions obtained after leaching using inorganic acids is iron. In this work, the membrane separation of iron(III) from nickel(II), cobalt(II), and lithium(I) was studied. The facilitated transport of metal ions using polymer inclusion membranes (PIMs) with tetrabutylammonium bromide (TBAB) as an ion carrier under various conditions was analyzed in detail. Several factors, such as the ion carrier concentration in the membrane as well as the effect of the inorganic acid concentration in the source/receiving phases on the kinetic parameters, were investigated. The results show that ionic liquid TBAB is a very selective ion carrier of Fe(III) towards Ni(II), Co(II), and Li(I). [ABSTRACT FROM AUTHOR]

Seven new coordination networks, [Fe(tbbt)3](BF4)2 (1), [Co(tbbt)3](BF4)2 (2), [Fe(tbbt)3](ClO4)2 (3), [Co(tbbt)3](ClO4)2 (4), [Fe(NCS)2(tbbt)2] (5), [Co(NCS)2(tbbt)2] (6), and [Fe(H2O)2(tbbt)2]Br2·2H2O (7), were synthesized with the linker 1,1'-(trans-2-butene-1,4-diyl)bis-1,2,4-triazole (tbbt) and structurally investigated. The structure of complexes 1–4 is composed of three interpenetrating, symmetry-related 3D networks. Each individual 3D network forms a primitive, nearly cubic lattice (pcu) with BF4– or ClO4– anions present in the interstitial spaces. The structure of compounds 5 and 6 is composed of two-dimensional sql layers, which are parallel to each other in the AB stacking type. These layers are interpenetrated by one-dimensional chains, both having the same formula unit, [M(NCS)2(tbbt)2] (M = Fe, Co). The structure of compound 7 consists of parallel, two-dimensional sql layers in the ABCD stacking type. The interpenetration in 1–6 is not controlled by π–π-interactions between the triazole rings or C=C bonds, as could have been expected, but by (triazole)C-H⋯F4B, C-H⋯O4Cl, and C-H⋯SCN anion hydrogen bonds, which suggests a template effect of the respective non-coordinated or coordinated anion for the interpenetration. In 7, the (triazole)C-H⋯Br anion interactions are supplemented by O-H⋯O and O-H⋯Br hydrogen bonds involving the aqua ligand and crystal water molecules. It is evident that the coordinated and non-coordinated anions play an essential role in the formation of the networks and guide the interpenetration. All iron(II) coordination networks are colorless, off-white to yellow-orange, and have the metal ions in the high-spin state down to 77 K. Compound 5 stays in the high spin state even at temperatures down to 10 K. [ABSTRACT FROM AUTHOR]

Pertraction of Co(II) through novel supported liquid membranes prepared by ultrasound, using bis-2-ethylhexyl phosphoric acid as carrier, sulfuric acid as stripping agent and a counter-transport mechanism, is studied in this paper. Supported liquid membrane characterization through scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy shows the impregnation of the microporous polymer support by the membrane phase by the action of ultrasound. The effect on the initial flux of Co(II) of different experimental conditions is analyzed to optimize the transport process. At these optimal experimental conditions (feed phase pH 6, 0.5 M sulfuric acid in product phase, carrier concentration 0.65 M in membrane phase and stirring speed of 300 rpm in both phases) supported liquid membrane shows great stability. From the relation between the inverse of Co(II) initial permeability and the inverse of the square of carrier concentration in the membrane phase, in the optimized experimental conditions, the transport resistance due to diffusion through both the aqueous feed boundary layer (3.7576 × 104 s·m−1) and the membrane phase (1.1434 × 1010 s·m−1), the thickness of the aqueous feed boundary layer (4.0206 × 10−6 m) and the diffusion coefficient of the Co(II)-carrier in the bulk membrane (4.0490 × 10−14 m2·s−1), have been determined. [ABSTRACT FROM AUTHOR]

The electrochemical sensing potential of two isostructural one-dimensional nickel(II) and cobalt(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy) and 6-oxonicotinate (6-Onic), namely, {[Ni(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n and {[Co(4,4′-bpy)(H2O)4](6-Onic)2×2H2O}n, was investigated along with the polymers' potential applications in the catalytic oxidation of methanol. The highly oxidative species from redox pairs Ni(II)/Ni(III) and Co(II)/Co(III) in these compounds represent catalytically active centres for oxidation of small molecules. A glassy carbon electrode (GCE) modified with a Ni polymer showed stability and reproducibility in 0.1 M NaOH, while the oxidation current inc 2reased with the increasing methanol concentration, suggesting that the Ni-polymer-modified electrode possess good sensing ability with respect to methanol. The GC electrode modified with the Co polymer is not reproducible and cannot be used for electroanalytical purposes under these experimental conditions. The GC electrode modified with the Ni polymer was successfully applied in the determination of methanol. This method showed favourable linear concentration dependence with a good sensitivity of 2.65 and 11.0 mA mM−1, a wide concentration range (0.001–4 mM), and a detection limit of 0.8 μM, which indicates its excellent application potential for methanol oxidation and thus its determination. [ABSTRACT FROM AUTHOR]

A ditopic nitrogen ligand (E)-N′-(pyridin-4-ylmethylene)isonicotinohydrazide (L) containing both divergent pyridyl coordination sites and a hydrogen-bonding hydrazide–hydrazone moiety was synthesized. The Co(NCS)2-mediated self-assembly of L has resulted in the synthesis of a novel 3-dimensional (3D) supramolecular framework (1) that features both coordination and hydrogen bonding interactions. X-ray structural analysis reveals the formation and coordination mode of 1 in the solid state. The rational utilization of coordination bonds and hydrogen bonding interactions is confirmed and responsible for constructing the 3D materials. Catalytic studies using 1 in the presence of an activator are performed for the hydroboration and hydrosilylation reactions of ketones and aldehydes, and the results are compared with previously reported cobalt-based polymeric catalysts. [ABSTRACT FROM AUTHOR]

Four transition metal complexes, [Co(H2L)2Cl2] (1) [Co(H2L)2NO3]NO3 (2) [Ni(H2L)2Cl2] (3) and [Ni(H2L)2NO3]NO3 (4) were synthesized from the Schiff base, 5-[{(2-hydroxyphenyl)imino}methyl]-6-methoxy phenol(H2L). The characterization study of all the complexes was done using elemental studies, molar conductance measurements, magnetic moment studies, FT-IR, 1H NMR, Electronic spectroscopy, thermal analysis, and PXRD. The antimicrobial screening of H2L and the metal complexes was conducted in-vitro against gram-negative bacteria like Escherichia coli, Aeromonas hydrophila, and Vibrio parahaemolyticus; gram-positive Bacillus subtilis and the fungi Aspergillus niger and Trichophyton tonsurans. Complexation was found to increase the biocidal activity of the ligand towards all microorganisms. [ABSTRACT FROM AUTHOR]

The synthesis of ionic complexes of cadmium(II) chloride and cobalt(II) chloride with N,N'-diethylthiourea (detu) ligands has not been previously reported. Therefore, in this research, the synthesis was carried out to study the structure and characterization of the two ionic complex compounds. The cadmium(II)-detu ionic complex was synthesized using the direct reaction method with a ratio between Cd(II) salt and detu ligand of 1:2. Meanwhile, the cobalt(II)-detu ionic complex was synthesized with a ratio between Co(II) salt and detu ligand of 2:4. The cadmium(II)-detu and cobalt(II)-detu ionic complexes have melting points of 105-108 °C and 122-125 °C, respectively. The electrical conductivity of the cadmium(II)-detu and cobalt(II)-detu complexes showed that the complexes were ionic. The FTIR analysis showed the shifting of the C=S functional group's band to the smaller wavenumber, which indicates the coordinating detu ligand to the cadmium(II) and cobalt(II) through the S atom. The indirect evidence from ¹H-NMR showed that CH3 and CH2 only slightly shifted between the free detu ligand and the Cd-detu and Co-detu complexes. [ABSTRACT FROM AUTHOR]

Two penta-coordinate CoII complexes with formulae [Co(14-TMC)Cl](BF4) (1, 14-TMC = 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [Co(12-TBC)Cl](ClO4)-(MeCN) (2, 12-TBC = 1,4,7,10-Tetrabenzyl-1,4,7,10-tetraazacyclododecane) were synthesized and characterized. Structural analysis revealed that ligand coordinates to the CoII centre in a tetradentate fashion and the fifth position is occupied by chloride ion and the geometries around CoII centres are best described as distorted square pyramidal. Detailed magnetic measurements disclose the presence of significant easy-plane magnetic anisotropy and field induced slow magnetic relaxation behaviours of the studied complexes. More insight into the magnetic anisotropy has been given using ab initio theory calculations, which agree well with the experimental values and further confirmed the easy-plane magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Pertraction of Co(II) through novel supported liquid membranes prepared by ultrasound, using bis-2-ethylhexyl phosphoric acid as carrier, sulfuric acid as stripping agent and a counter-transport mechanism, is studied in this paper. Supported liquid membrane characterization through scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy shows the impregnation of the microporous polymer support by the membrane phase by the action of ultrasound. The effect on the initial flux of Co(II) of different experimental conditions is analyzed to optimize the transport process. At these optimal experimental conditions (feed phase pH 6, 0.5 M sulfuric acid in product phase, carrier concentration 0.65 M in membrane phase and stirring speed of 300 rpm in both phases) supported liquid membrane shows great stability. From the relation between the inverse of Co(II) initial permeability and the inverse of the square of carrier concentration in the membrane phase, in the optimized experimental conditions, the transport resistance due to diffusion through both the aqueous feed boundary layer (3.7576 × 104 s·m−1) and the membrane phase (1.1434 × 1010 s·m−1), the thickness of the aqueous feed boundary layer (4.0206 × 10−6 m) and the diffusion coefficient of the Co(II)-carrier in the bulk membrane (4.0490 × 10−14 m2·s−1), have been determined.

We herein reported the syntheses, crystal structures, and magnetic properties of a two-dimensional coordination polymer {[CoII(TPT)2/3(H2O)4][CH3COO]2·(H2O)4}n (1) and a chain compound {[CoII(TPT)2(CHOO)2(H2O)2]}n (2) based on the 2,4,6-Tris(4-pyridyl)-1,3,5-triazine (TPT) ligand. Structure analyses showed that complex 1 had a cationic hexagonal framework structure, while 2 was a neutral zig-zag chain structure with different distorted octahedral coordination environments. Magnetic measurements revealed that both complexes exhibit large easy-plane magnetic anisotropy with the zero-field splitting parameter D = 47.7 and 62.1 cm-1 for 1 and 2, respectively. This magnetic anisotropy leads to the field-induced slow magnetic relaxation behaviour. However, their magnetic dynamics are quite different; while complex 1 experienced a dominating thermally activated Orbach relaxation at the whole measured temperature region, 2 exhibited multiple relaxation pathways involving direct, Raman, and quantum tunneling (QTM) processes at low temperatures and Orbach relaxation at high temperatures. The present complexes enlarge the family of framework-based single-ion magnets (SIMs) and highlight the significance of the structural dimensionality to the final magnetic properties. [ABSTRACT FROM AUTHOR]

Careful choice of the organic ligands is one of the most important parameters in the rational design and synthesis of coordination polymers. Aromatic polycarboxylates have been widely used in the preparation of metal-organic polymers since they can utilize various coordination modes to form diverse structures and can act as hydrogen-bond acceptors and donors in the assembly of supramolecular structures. Nitrogen-heterocyclic organic compounds have also been used extensively as ligands for the construction of polymers with interesting structures. In the polymers catena-poly[[[diaquabis{2-[(1 H-imidazol-1-yl)methyl]-6-methyl-1 H-benzimidazole-κ N3}cobalt(II)]-μ2-benzene-1,4-dicarboxylato-κ2 O1: O4] dihydrate], {[Co(C8H4O4)(C12H11N4)2(H2O)2]·2H2O} n, (I), and catena-poly[[[diaquabis{2-[(1 H-imidazol-1-yl)methyl]-6-methyl-1 H-benzimidazole-κ N3}nickel(II)]-μ2-benzene-1,4-dicarboxylato-κ2 O1: O4] dihydrate], {[Ni(C8H4O4)(C12H11N4)2(H2O)2]·2H2O} n, (II), the CoII or NiII ion lies on an inversion centre and exhibits a slightly distorted octahedral coordination geometry, coordinated by two N atoms from two imidazole rings and four O atoms from two monodentate carboxylate groups and two water molecules. The dicarboxylate ligands bridge metal ions forming a polymeric chain. The 2-[(1 H-imidazol-1-yl)methyl]-6-methyl-1 H-benzimidazole ligands coordinate to the CoII or NiII centres in monodentate modes through an imidazole N atom and are pendant on opposite sides of the main chain. The two structures are isomorphous. In the crystal, the one-dimensional chains are further connected through O-H...O, O-H...N and N-H...O hydrogen bonds, leading to a three-dimensional supramolecular architecture. In addition, the IR spectroscopic properties, PXRD patterns, thermogravimetric behaviours and fluorescence properties of both polymers have been investigated. [ABSTRACT FROM AUTHOR]

The crystal structures of two new bimetallic uranyl-transition metal compounds with diglycolic acid [or 2-(carboxymethoxy)acetic acid] have been hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction. The compounds, namely catena-poly[[[tetraaquamanganese(II)]-μ-2,2′-oxydiacetato-[dioxidouranium(VI)]-μ-2,2′-oxydiacetato] dihydrate], {[MnU(C4H4O5)2O2(H2O)4]·2H2O} n, and catena-poly[[[tetraaquacobalt(II)]-μ-2,2′-oxydiacetato-[dioxidouranium(VI)]-μ-2,2′-oxydiacetato] dihydrate], {[CoU(C4H4O5)2O2(H2O)4]·2H2O} n, both crystallize in the triclinic space group P. These compounds form one-dimensional chains via alternating uranyl and transition metal building units. The chains then assemble into three-dimensional supramolecular networks through several hydrogen bonds between water molecules and diglycolate ligands. Luminescence measurements were conducted and no uranyl emission was observed in either compound. [ABSTRACT FROM AUTHOR]

Hydrazone complexes of Cu(II), Co(II), Zn(II), Ni(II) and Pt(II) with N-isonicotinoyl-N'-(3-metoxy-2 hydroxybenzaldehyde)-hydrazone (HL) were synthesized and characterized by different physico-chemical techniques including elemental and thermal analysis, magnetic susceptibility measurements, molar electric conductivity, as well as IR (infrared), 1H-NMR and 13C-NMR (hydrogen and carbon nuclear magnetic resonance, UV-Vis (ultraviolet-visible), FAB (fast atom bombardment), EPR (electron paramagnetic resonance), and mass spectroscopies. The crystal structure of ligand was determined by single crystal X-ray diffraction studies. Spectral data showed that hydrazone behaves as an ONO tridentate ligand through the azomethine nitrogen, phenolate and keto oxygen atoms. For the copper(II) complexes, metal-ligand bonding parameters were evaluated from the EPR spectra. These parameters indicate the presence of in-plane π bonding. In addition, the f values of complexes 1-4 indicate small distortion from planarity. The effect of these complexes on proliferation of human breast cancer (MCF-7 and SKBR-3), human melanoma (A375), lung adenocarcinoma cells (NCI-H1573) and their antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus and Candida albicans strains were studied and compared with those of free ligand. The ligand and complexes 1-3 showed significant antimicrobial activity against the Gram-positive bacteria Staphylococcus aureus and Candida albicans in comparison to the control drugs. The complexes 2-4 could be potential antitumor agents, leading to a significant improvement of the cytotoxic activity when compared with HL. [ABSTRACT FROM AUTHOR]

High-spin cobalt(II) complexes are considered useful building blocks for the synthesis of single-molecule magnets (SMM) because of their intrinsic magnetic anisotropy. In this work, three new cobalt(II) chloride adducts with labile ligands have been synthesized from anhydrous CoCl2, to be subsequently employed as starting materials for heterobimetallic compounds. The products were characterized by elemental, spectroscopic (EPR and FT-IR) and single-crystal X-ray diffraction analyses. trans-Tetrakis(acetonitrile-κ N)bis(tetrahydrofuran-κ O)cobalt(II) bis[(acetonitrile-κ N)trichloridocobaltate(II)], [Co(C2H3N)4(C4H8O)2][CoCl3(C2H3N)]2, (1), comprises mononuclear ions and contains both acetonitrile and tetrahydrofuran (thf) ligands, The coordination polymer catena-poly[[tetrakis(propan-2-ol-κ O)cobalt(II)]-μ-chlorido-[dichloridocobalt(II)]-μ-chlorido], [Co2Cl4(C3H8O)4], (2′), was prepared by direct reaction between anhydrous CoCl2 and propan-2-ol in an attempt to rationalize the formation of the CoCl2-alcohol adduct (2), probably CoCl2(HOiPr) m. The binuclear complex di-μ-chlorido-1:2κ4 Cl: Cl-dichlorido-2κ2 Cl-tetrakis(tetrahydrofuran-1κ O)dicobalt(II), [Co2Cl4(C4H8O)4], (3), was obtained from (2) after recrystallization from tetrahydrofuran. All three products present cobalt(II) centres in both octahedral and tetrahedral environments, the former usually less distorted than the latter, regardless of the nature of the neutral ligand. Product (2′) is stabilized by an intramolecular hydrogen-bond network that appears to favour a trans arrangement of the chloride ligands in the octahedral moiety; this differs from the cis disposition found in (3). The expected easy displacement of the bound solvent molecules from the metal coordination sphere makes the three compounds good candidates for suitable starting materials in a number of synthetic applications. [ABSTRACT FROM AUTHOR]

The design of nonlinear optical (NLO) materials with large NLO responses has been a challenge for materials scientists and chemists. Recently, organic polymers have received attention regarding their NLO properties and fast nonlinear response, and clusters involving delocalized dπ- pπ systems and conjugated dπ- pπ systems are expected to be a new class of NLO materials. Metal-organic coordination polymers combine the advantages of the organic and inorganic species. Thus far, tuning the third-order NLO properties of these materials has been a significant challenge. A two-dimensional coordination polymer, namely poly[(μ-benzene-1,2-dicarboxylato-κ3 O1, O1′: O3){μ-1,2-bis[(1 H-imidazol-1-yl)methyl]benzene-κ2 N3: N3′}cobalt(II)], [Co(C8H4O4)(C14H14N4)] n, was synthesized by hydrothermal methods. In the structure, the CoII ion is pentacoordinated by two N atoms from two different 1,2-bis[(1 H-imidazol-1-yl)methyl]benzene (1,2-BIB) ligands and three O atoms from two symmetry-related benzene-1,2-dicarboxylate (isophthalate, PA) anions. The pentacoordinated CoII ions are linked by PA ligands to form a chain structure parallel to the c axis. Adjacent chains are further connected by 1,2-BIB ligands to produce a two-dimensional layered structure. The compound exhibits strong third-order nonlinear absorption and nonlinear refraction effects as a thin film. The third-order susceptibility χ(3) is calculated to be 1.07 × 10−8 esu, which is much larger than the values found for pure inorganic semiconductors and some polymers. [ABSTRACT FROM AUTHOR]

A series of alkyl- and aryl-substituted iminopyridine Fe(II) complexes 1a-7a and Co(II) complexes 2b, 3b, 5b, and 6b were synthesized. The activator effect, influence of temperature, and, particularly, the alkyl and aryl substituents' effect on catalytic activity, polymer molecular weight, and regio-/stereoselectivity were investigated when these complexes were applied in isoprene polymerization. All of the Fe(II) complexes afforded polyisoprene with high molecular weight and moderate cis-1,4 selectivity. In contrast, the Co(II) complexes produced polymers with low molecular weight and relatively high cis-1,4 selectivity. In the iminopyridine Fe(II) system, the alkyl and aryl substituents' effect exhibits significant variation on the isoprene polymerization. In the iminopyridine Co(II) system, there is little influence observed on isoprene polymerization by alkyl and aryl substituents. [ABSTRACT FROM AUTHOR]

The removal of Co(II) and Zn(II) from model and real crude nickel sulphate (CNS) solutions by extraction with sodium bis(2,4,4-trimethylpentyl)phosphinate (Na-Cyanex 272) is studied and compared with the effect of using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272). The proposed novel approach to manage both hazardous metal ions from CNS with sodium salt of Cyanex 272 focuses on the following issues: (i) effect of the initial pH of feeds on the extraction efficiency, (ii) leaching of metal ions from CNS, (iii) efficiency and selectivity of metal ion extraction from real CNS, and (iv) FT-IR analysis of structure of complexes formed by the metal ions with the extractant studied. It is concluded that converting Cyanex 272 into its sodium salt greatly improves the efficiency of the extraction in comparison to the conversion into the acidic form of the extractant, regardless of the type of metal ion considered, whether Zn(II) or Co(II). These phenomena occurring in the extraction system are confirmed by the obtained FT-IR spectra of the organic phases after extraction and stripping. [ABSTRACT FROM AUTHOR]

Analytical performance of conventional spectrophotometer was developed by coupling of effective dispersive liquid-liquid micro-extraction method with spectrophotometric determination for ultra-trace determination of cobalt. The method was based on the formation of Co(II)–alpha-benzoin oxime complex and its extraction using a dispersive liquid-liquid micro-extraction technique. During the present work, several important variables such as pH, ligand concentration, amount and type of dispersive, and extracting solvent were optimized. It was found that the crucial factor for the Co(II)–alpha benzoin oxime complex formation is the pH of the alkaline alcoholic medium. Under the optimized condition, the calibration graph was linear in the ranges of 1.0–110 μg L−1 with the detection limit (S/N=3) of 0.5 μg L−1. The preconcentration operation of 25 mL of sample gave enhancement factor of 75. The proposed method was applied for determination of Co(II) in soil samples. [ABSTRACT FROM AUTHOR]

The coordination chemistry of mixed-ligand complexes continues to be an active area of research since these compounds have a wide range of applications. Many coordination polymers and metal-organic framworks are emerging as novel functional materials. Aminopyrimidine and its derivatives are flexible ligands with versatile binding and coordination modes which have been proven to be useful in the construction of organic-inorganic hybrid materials and coordination polymers. Thiophenecarboxylic acid, its derivatives and their complexes exhibit pharmacological properties. Cobalt(II) and copper(II) complexes of thiophenecarboxylate have many biological applications, for example, as antifungal and antitumor agents. Two new cobalt(II) and copper(II) complexes incorporating thiophene-2-carboxylate (2-TPC) and 2-amino-4,6-dimethoxypyrimidine (OMP) ligands have been synthesized and characterized by X-ray diffraction studies, namely (2-amino-4,6-dimethoxypyrimidine-κ N)aquachlorido(thiophene-2-carboxylato-κ O)cobalt(II) monohydrate, [Co(C5H3O2S)Cl(C6H9N3O2)(H2O)]·H2O, (I), and catena-poly[copper(II)-tetrakis(μ-thiophene-2-carboxylato-κ2 O: O′)-copper(II)-(μ-2-amino-4,6-dimethoxypyrimidine-κ2 N1: N3)], [Cu2(C5H3O2S)4(C6H9N3O2)] n, (II). In (I), the CoII ion has a distorted tetrahedral coordination environment involving one O atom from a monodentate 2-TPC ligand, one N atom from an OMP ligand, one chloride ligand and one O atom of a water molecule. An additional water molecule is present in the asymmetric unit. The amino group of the coordinated OMP molecule and the coordinated carboxylate O atom of the 2-TPC ligand form an interligand N-H...O hydrogen bond, generating an S(6) ring motif. The pyrimidine molecules also form a base pair [ R22(8) motif] via a pair of N-H...N hydrogen bonds. These interactions, together with O-H...O and O-H...Cl hydrogen bonds and π-π stacking interactions, generate a three-dimensional supramolecular architecture. The one-dimensional coordination polymer (II) contains the classical paddle-wheel [Cu2(CH3COO)4(H2O)2] unit, where each carboxylate group of four 2-TPC ligands bridges two square-pyramidally coordinated CuII ions and the apically coordinated OMP ligands bridge the dinuclear copper units. Each dinuclear copper unit has a crystallographic inversion centre, whereas the bridging OMP ligand has crystallographic twofold symmetry. The one-dimensional polymeric chains self-assemble via N-H...O, π-π and C-H...π interactions, generating a three-dimensional supramolecular architecture. [ABSTRACT FROM AUTHOR]

The title compound, [Co(C5H7O2)2 (C6H12N2)]n, was obtained as a one-dimensional coordination polymer from bis(acetylacetonato)di-aquacobalt(II), [Co(acac)2 (OH2)2], and 1,4-diaza-bicyclo[2.2.2]octane (DABCO), a diamine with good bridging ability and rod-like spacer function. In the chain complex that extends along the c axis, the CoII atom is six-coordinated, the O-donor atoms of the chelating acac ligands occupying the equatorial positions and the bridging DABCO ligands being in trans-axial positions. In the crystal structure, the DABCO ligand is conformationally disordered in a 50:50 manner as a result of its location across a crystallographic mirror plane. The metal-metal distance is very close to that in a related compound exhibiting weak antiferromagnetic exchange between the CoII ions, and the title compound can thus be useful for obtaining more information about the contribution of different bridges to the magnetic coupling between paramagnetic ions. [ABSTRACT FROM AUTHOR]

Coordination polymers constructed from metal ions and organic ligands have attracted considerable attention owing to their diverse structural topologies and potential applications. Ligands containing carboxylate groups are among the most extensively studied because of their versatile coordination modes. Reactions of benzene-1,4-dicarboxylic acid (H2BDC) and pyridine (py) with ZnII or CoII yielded two new coordination polymers, namely, poly[(μ4-benzene-1,4-dicarboxylato-κ4 O: O′: O′′: O′′′)(pyridine-κ N)zinc(II)], [Zn(C8H4O2)(C5H5N)] n, (I), and catena-poly[aqua(μ3-benzene-1,4-dicarboxylato-κ3 O: O′: O′′)bis(pyridine-κ N)cobalt(II)], [Co(C8H4O2)(C5H5N)2(H2O)] n, (II). In compound (I), the ZnII cation is five-coordinated by four carboxylate O atoms from four BDC2− ligands and one pyridine N atom in a distorted square-pyramidal coordination geometry. Four carboxylate groups bridge two ZnII ions to form centrosymmetric paddle-wheel-like Zn2(μ2-COO)4 units, which are linked by the benzene rings of the BDC2− ligands to generate a two-dimensional layered structure. The two-dimensional layer is extended into a three-dimensional supramolecular structure with the help of π-π stacking interactions between the aromatic rings. Compound (II) has a one-dimensional double-chain structure based on Co2(μ2-COO)2 units. The CoII cations are bridged by BDC2− ligands and are octahedrally coordinated by three carboxylate O atoms from three BDC2− ligands, one water O atom and two pyridine N atoms. Interchain O-H...O hydrogen-bonding interactions link these chains to form a three-dimensional supramolecular architecture. [ABSTRACT FROM AUTHOR]

Crystal engineering can be described as the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding to design new solids with desired physical and chemical properties. Free-energy differences between supramolecular isomers are generally small and minor changes in the crystallization conditions may result in the occurrence of new isomers. The study of supramolecular isomerism will help us to understand the mechanism of crystallization, a very central concept of crystal engineering. Two supramolecular isomers of dichloridobis(1,10-phenanthroline-κ2 N, N′)cobalt(II), [CoCl2(C12H8N2)2], i.e. (I A) (orthorhombic) and (I B) (monoclinic), and two supramolecular isomers of dichloridobis(1,10-phenanthroline-κ2 N, N′)cobalt(II) N, N-dimethylformamide monosolvate, [CoCl2(C12H8N2)2]·C3H7NO, i.e. (II A) (orthorhombic) and (II B) (monoclinic), were synthesized in dimethylformamide (DMF) and structurally characterized. Of these, (I A) and (II A) have been prepared and structurally characterized previously [Li et al. (2007). Acta Cryst. E 63, m1880-m1880; Cai et al. (2008). Acta Cryst. E 64, m1328-m1329]. We found that the heating rate is a key factor for the crystallization of (I A) or (I B), while the temperature difference is responsible for the crystallization of (II A) or (II B). Based on the crystallization conditions, isomerization behaviour, the KPI (Kitajgorodskij packing index) values and the density data, (I B) and (II A) are assigned as the thermodynamic and stable kinetic isomers, respectively, while (I A) and (II B) are assigned as the metastable kinetic products. The 1,10-phenanthroline (phen) ligands interact with each other through offset face-to-face (OFF) π-π stacking in (I B) and (II B), but by edge-to-face (EF) C-H...π interactions in (I A) and (II A). Meanwhile, the DMF molecules in (II B) connect to neighbouring [CoCl2(phen)2] units through two C-H...Cl hydrogen bonds, whereas there are no obvious interactions between DMF molecules and [CoCl2(phen)2] units in (II A). Since OFF π-π stacking is generally stronger than EF C-H...π interactions for transition-metal complexes with nitrogen-containing aromatic ligands, (II A) is among the uncommon examples that are stable and densely packed but that do not following Etter's intermolecular interaction hierarchy. [ABSTRACT FROM AUTHOR]

Batch-wise biosorption of Co(II) from aqueous cobalt nitrate solution of different concentrations has been carried out on raw and NaOH-treated lemon peels. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and Brunauer-Emmett-Teller surface area analysis. The influence of biosorbent dose, pH, contact time and temperature on the adsorption process has been studied. Maximum adsorption was observed at pH 6. The equilibrium adsorption on raw and NaOH-treated lemon peels was achieved in 150 and 210 min, the maximum adsorption capacity being 20.83 and 35.71 mg/g, respectively. Energy-dispersive X-ray spectroscopy and desorption study confirmed that the mechanism of adsorption is ion exchange. The Langmuir isotherm and pseudosecond-order kinetic model gave the best fit for the adsorption of Co(II). The desorption was found to be more than 96 % using 0.1 N HCl, and the adsorbent could be reused three times with intermediate alkaline regeneration stage. Experiments to establish the effect of competing metal ions on biosorption capacity were also performed. Thus, NaOH-treated lemon peels have shown the potential as a good biosorbent for treating industrial wastewater at low cobalt concentration. [ABSTRACT FROM AUTHOR]

The interaction of binuclear Co(II) pivalate [Co2(H2O)Piv4(HPiv)4] with nitronyl nitroxide HL¹ (2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl) in organic solvents led to the formation of a pentanuclear heterospin complex [Co5(Piv)4L¹4L²2]. A nontrivial peculiarity of the complex is the presence of both the starting nitronyl nitroxide L¹ and its deoxygenated derivative imino nitroxide L² (HL²: 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl) in its coordination sphere. Based on this, a new synthetic approach was developed, which suggests the use of both the starting radical and the product of its reduction in the reaction with the metal. The suggested approach is a new method for the synthesis of heterospin compounds, including those that cannot be obtained by other methods. It was shown that the reaction of Co(II) pivalate with a mixture of HL¹ and HL² can give a trinuclear heterospin complex [Co3(Piv)2L¹2L²2]. The replacement of Co(II) by Ni(II) completely suppresses the reduction of HL¹ into HL2, and Ni(II) pivalate does not react with HL¹. The use of a known mixture of HL¹ and HL² in the reaction with [Ni2(H2O)Piv4(HPiv)4], however, led to the formation of a heterospin complex [Ni3L¹L²2(Piv)3(HPiv)3] also containing both nitronyl nitroxide and imino nitroxide. [ABSTRACT FROM AUTHOR]

In this study, palladium-modifi ed nickel foam substrate was applied to examine ethanol oxidation reaction (EOR) in 0.1 The transport of cobalt(II), nickel(II), copper(II), and zinc(II) ions from chloride solutions across polymer inclusion membranes (PIMs), which 1-heptylimidazole (1) or 1-heptyl-2-methylimidazole (2) or 1-heptyl-4-methylimidazole (3) as the ion carrier was reported. The steric effect for carriers 2 and 3 decreases the transport of all ions except Cu(II). The initial fluxes of metal ions transport across PIMs with the 1 - 2 decrease in the sequence: Cu(II) > Zn(II) > Co(II) > Ni(II), whereas for 3 they were Cu(II) > Zn(II) > Ni(II) > Co(II). The highest recovery values were obtained for Cu(II), this being 99 and 85% for carrier 1 and 2, respectively. In both membranes the degree of deposition of the Zn(II) ions was comparable. Zn(II), Co(II) and Cd(II) ions, which form complexes with coordination numbers 4 and 6, are more easily recovered with the use of carriers 2 and 3. Ni(II) ions, which form complexes with coordination number 6 only, practically remain in the feeding phase. PIMs with alkylimidazoles were characterized by non-contact atomic force microscopy. [ABSTRACT FROM AUTHOR]

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In this work the selective transport of cobalt(II) and lithium(I) ions from aqueous chloride solutions through polymer inclusion membranes (PIMs) is presented. Triisooctylamine (TIOA) has been applied as the ion carrier in membrane. The effects of various parameters on the transport of Co(II) and Li(I) were studied. The obtained results show that Co(II) ions were effectively removed from source phase through PIM containing 32 wt.% TIOA, 22 wt.% CTA (cellulose triacetate) and 46 wt.% ONPOE (o-nitrophenyl octyl ether) or ONPPE (o-nitrophenyl pentyl ether) into deionized water as the receiving phase. The results indicate that there is a possibility of polymer inclusion membranes application to recover Co(II) and Li(I) from aqueous chloride solutions [ABSTRACT FROM AUTHOR]

Treatment of a hyperthermophilic enzyme, alkaline phosphatase from Pyrococcus furiosus ( PfuAP), with EDTA completely deactivated PfuAP, indicating that the presence of one or more divalent metal ions is essential for its catalytic activity. Subsequent addition of various divalent metal ions to the apoprotein recovered the enzymatic activity and, in particular, the addition of Co(II) resulted in an over 50-fold increase in activity compared with PfuAP before EDTA treatment. Intriguingly, PfuAP with Co(II) exhibited weaker stability toward heat treatment, suggesting that Co destabilizes the tertiary structure of PfuAP at high temperature. [ABSTRACT FROM AUTHOR]

Formation equilibria of cobalt(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Co(AMBI)L (L = aliphatic or aromatic dicarboxylic acids) were investigated in aqueous solutions at 25 °C and 0.1 mol⋅dm ionic strength. Stoichiometry and stability constants are reported for the complexes formed. The speciation of the complexes was resolved. Values of $\log_{10}\ (K_{\mathrm{Co(AMBI)L}}^{\mathrm{Co(AMBI)}})$ and Δlog K are calculated and discussed. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. The effect of temperature on the dissociation constant of AMBI, CBDCA, and the formation constant of Co(AMBI) and Co(AMBI)-CBDCA complexes was studied and the thermodynamic parameters were calculated. Formation of the metal complexes has been found to be spontaneous, exothermic and entropically favorable. The solid complexes of [Co(AMBI)L] (L = oxalic acid, 1,1-cyclobutanedicarboxylic acid (CBDCAH) and malonic acid) have been synthesized and characterized by elemental analysis, infrared, spectra, magnetic and conductance measurements. Electronic spectra and μ values suggest a tetrahedral geometry for Co(II)-complexes. The isolated metal chelates have been screened for their antibacterial activities and the complexes show a significant antibacterial activity against Pseudomonas fluorescence (Gram −ve) and Bacillus subtilis (Gram +ve). The activity increases at higher concentration of the compounds. [ABSTRACT FROM AUTHOR]

Polynuclear complexes are an important class of inorganic functional materials and are of interest particularly for their applications in molecular magnets. Multidentate chelating ligands play an important role in the design and syntheses of polynuclear metal clusters. A novel linear tetranuclear CoII cluster, namely bis{μ3-( E)-2-[(2-oxidobenzylidene)amino]phenolato}bis{μ2-( E)-2-[(2-oxidobenzylidene)amino]phenolato}bis(1,10-phenanthroline)tetracobalt(II), [Co4(C14H11NO2)4(C12H8N2)2], was prepared under solvothermal conditions through a mixed-ligand synthetic strategy. The structure was determined by X-ray single-crystal diffraction and bulk purity was confirmed by powder X-ray diffraction. The complex molecule has a centrosymmetric tetranuclear chain-like structure and the four CoII ions are located in two different coordination environments. The CoII ions at the ends of the chain are in a slightly distorted octahedral geometry, while the two inner CoII ions are in five-coordinate distorted trigonal bipyramidal environments. A magnetic study reveals ferromagnetic CoII...CoII exchange interactions for the complex. [ABSTRACT FROM AUTHOR]

Supramolecular isomerism for coordination networks refers to the existence of different architectures having the same building blocks and identical stoichiometries. For a given building block, different arrangements can lead to the formation of a series of supramolecular isomers. Two one-dimensional CoII coordination polymers based on N, N′-bis(pyridin-3-yl)oxalamide (BPO), both catena-poly[[[dichloridocobalt(II)]-bis[μ- N, N′-bis(pyridin-3-yl)oxalamide-κ2 N: N′]] dimethylformamide disolvate], {[CoCl2(C12H10N4O2)2]·2C3H7NO} n, have been assembled by the solvothermal method. Single-crystal X-ray diffraction analyses reveal that the two compounds are supramolecular isomers, the isomerism being induced by the orientation of the dimethylformamide (DMF) molecules in the crystal lattice. [ABSTRACT FROM AUTHOR]

By simple reactions involving various cobalt(II) carboxylates (acetate and in situ prepared pivalate and 4-hydroxybenzoate salts) and neocuproine (neo), we were able to prepare three different carboxylate complexes with the general formula [Co(neo)(RCOO)2] (R = –CH3 for 1, (CH3)3C– for 2, and 4OH-C4H6– for 3). The [Co(neo)(RCOO)2] molecules in the crystal structures of 1–3 adopt a rather distorted coordination environment, with the largest trigonal distortion observed for 1, whereas 2 and 3 are similarly distorted from ideal octahedral geometry. The combined theoretical and experimental investigations of magnetic properties revealed that the spin Hamiltonian formalism was not a valid approach and the L-S Hamiltonian had to be used to reveal very large magnetic anisotropies for 1–3. The measurements of AC susceptibility showed that all three compounds exhibited slow-relaxation of magnetization in a weak external static magnetic field, and thus can be classified as field-induced single-ion magnets. It is noteworthy that 1 also exhibits a weak AC signal in a zero-external magnetic field. [ABSTRACT FROM AUTHOR]

The 6-oxonicotinate (6-Onic) salts of a one-dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4,4′-bipyridine (4,4′-bpy), namely {[Co(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (1) and {[Ni(4,4′-bpy)(H2O)4](6-Onic)2·2H2O}n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,4′-bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {[M(4,4′-bpy)(H2O)4]2+}n (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N–H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R23(10) motif, the centrosymmetric tetrameric R24(8) and R24(12) motifs and the pentameric R45(12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II)). [ABSTRACT FROM AUTHOR]

The kinetics of formation and dissociation of the binuclear complex of cobalt(II) with pyridine-2-carboxylato(pentaammine) cobalt(III) have been studied in the temperature range 10-25°C and at I=0·3 mol dm (ClO. The formation of (NH)CoOCCHNCo in the pH range 2·35-3·20 involves the reaction of Co(OH) with the protonated (pyridine-N) and the deprotonated forms of the complex. The rate and activation parameters for the formation reaction are consistent with an I mechanism. The binuclear species undergoes dissociation to yield the parent cobalt(III) substrate and cobalt(II) via spontaneous and acid-catalysed paths. The rate data at 20°C for the spontaneous dissociation of the binuclear complex and of mono(pyridine-2-carboxylato) cobalt(II) are comparable indicating the chelating nature of the binuclear species. [ABSTRACT FROM AUTHOR]