Cobalt Coordination Chemistry Research Articles

Effects of structural cobalt on the stability and reactivity of hausmannite and manganite: Cobalt coordination chemistry and arsenite oxidation

Hausmannite and manganite, the most abundant Mn(II/III) oxides in the environment, commonly contain cobalt (Co) as a structural impurity, yet the effects of Co substitution on the structure, stability, and reactivity of Mn(II/III) oxides have not been experimentally assessed. Using pristine and Co-substituted minerals with varying Co loadings (1 and 2 wt%), the present study observed changes in the structural properties, as well as stability and reactivity of these minerals toward acidic and reductive dissolution with arsenite (As(III)). Cobalt substitution in hausmannite produced significant changes in the lattice parameters and surface areas of the mineral, while manganite presented little to no Co substitution effects. In both minerals, Mn and Co release was accelerated in reductive dissolution, although more than 85% of the Co remained in the mineral structure. Only hausmannite showed increased oxidation of As(III) to As(V) with increased Co substitution, where the stoichiometric [Mn(II)]aq to [As(V)]aq ratio was at/close to 2. X-ray absorption spectroscopy analysis indicated the co-presence of Co(II) and Co(III) at tetrahedral and octahedral sites, respectively, with structural Co(II) dominating in hausmannite. The sole occupancy of Co(II) at octahedral sites in manganite appeared to induce changes in the average Mn oxidation state. Multiple surface complexes of arsenate were observed on the mineral surfaces, with the bidentate binuclear mode being the major species. Thus, Co substitution altered the stability and reactivity of the Mn(II/III) oxides under dissolution conditions, although the extent varied by the Co coordination chemistry, valence, and quantity in the mineral structures.

The Supramolecular and Coordination Chemistry of Cobalt(II) Extraction by Phosphinic Acids

A combination of mass spectrometry, DFT calculations and 31P{1H} NMR spectroscopy has been used to define the mode of action of the commercial cobalt extractant, bis(2,4,4‐trimethylpentyl)phosphinic acid (CYANEX®272, L1H) in Co recovery. The nature of the CoII complexes formed in the water‐immiscible phase is determined largely by the propensity of phosphinates to form strong interligand H‐bonds in the outer coordination sphere and also to form stable µ2‐Co–O–P–O–Co bridges. At low Co loading levels, the predominant species is the 4:1 complex, [Co(L1·L1H)2], in which coordinated neutral phosphinic acid ligands form strong H‐bonds to adjacent anionic phosphinates. At higher Co loading, oligomers such as [(L1·L1H)Co(L12Co)n(L1·L1H)] are formed with µ2‐phosphinate bridging, resulting in a substantial increase in the viscosity of the water‐immiscible phase. The presence of tris(2,4,4‐trimethylpentyl)phosphine oxide (L2) in the commercial formulation reduces the viscosity because its incorporation into oligomeric complexes such as [(L2)Co{L13CoL1CoL13Co}mL1] can terminate chains, resulting in a lower average molecular weight. The uptake of Zn by L1H shows a very similar dependence of viscosity on loading, and DOSY spectra and mass spectrometry demonstrate that higher molecular weight species are present at high Zn loading.

Microsphere Assemblies via Phosphonate Monoester Coordination Chemistry.

By complexing a bent phosphonate monoester ligand with cobalt(II), coupled with in situ ester hydrolysis, coordination microspheres (CALS=CALgary Sphere) are formed whereas the use of the phosphonic acid directly resulted in a sheet-like structure. Manipulation of the synthetic conditions gave spheres with different sizes, mechanical stabilities, and porosities. Time-dependent studies determined that the sphere formation likely occurred through the formation of a Co2+ and ligand chain that propagates in three dimensions through different sets of interactions. The relative rates of these assembly processes versus annealing by ester hydrolysis and metal dehydration determine the growth of the microspheres. Hardness testing by nanoindentation is carried out on the spheres and sheets. Notably, no templates or capping agents are employed, the growth of the spheres is intrinsic to the ligand geometry and the coordination chemistry of cobalt(II) and the phosphonate monoester.

Syntheses, structures, and magnetic properties of a cubane-like {Co4O4} cluster and a dinuclear CuII compound constructed from a tridentate Schiff base ligand

The employment of a tridentate Schiff base ligand, 1-(((2-hydroxy-2,3-dihydro-1H-inden-1-yl)imino)methyl)naphthalen-2-ol (H2L) in the coordination chemistry of cobalt(II) acetate and copper(II) acetate is reported. One cubane-like cluster of formula [Co4L4]·CH3OH (1·CH3OH) and one alkoxo-bridged dinuclear copper compound of composition [Cu2L2] (2) were achieved by the reactions of metal acetates with H2L under solvothermal conditions. The structures of 1·CH3OH and 2 have been established by single-crystal X-ray diffraction studies. Complex 1·CH3OH has a cubane-like {Co4O4} core with divalent metal atoms and alkoxo atoms (originated from the L2− ligands) occupying alternating vertices. The magnetic properties of 1·CH3OH and 2 have been investigated. The variable-temperature dc magnetic susceptibility studies indicate ferromagnetic CoII⋯CoII exchange interactions for 1·CH3OH and antiferromagnetic CuII⋯CuII couplings for 2. The ac magnetic susceptibility investigation reveals that complex 1·CH3OH shows the slow magnetic relaxation (SMM) behavior.

Abstract 4399: Utilizing cobalt coordination chemistry as a traceless prodrug strategy in targeted drug delivery

Abstract We recently reported the synthesis of albumin nanoparticles using cobalt as a traceless, reductively labile crosslinker. Here, we report in vitro characterization of particle uptake for fluorescently labeled cobalt crosslinked albumin nanoparticles (Co-Alb-FITC NPs) via image-based flow cytometry as well as preliminary toxicity data. Uptake of Co-Alb-FITC NPs by gastric carcinoma cells (SNU-5) was rapid, but could be dramatically reduced through the addition of an inhibitor of macropinocytosis. High levels of non-specific uptake of other particle types were also observed suggesting SNU-5 cells possess high macropinocytic activity. Cancers harboring mutated Ras (>20% of all cancers) are known to take up protein via macropinocytosis to satisfy metabolic demands. Because SNU-5 cells are not known harbor mutated Ras, our findings may indicate that other cancers rely on this mechanism as well, which would have important implications for observing selectivity in active nanoparticle targeting strategies. The Co-Alb NPs themselves were found to exhibit no inherent toxicity. Based on these initial findings, Co-Alb NPs were loaded with the active metabolite of camptothecin, SN-38, to explore their potential as a delivery vector for hydrophobic drugs. An albumin-topotecan prodrug conjugate was also synthesized by crosslinking the amine group in topotecan with lysine residues in the protein, which should be applicable to other amine-containing therapeutics. Characterization of drug loading and release will be discussed along with preliminary in vitro characterization. Citation Format: Robby A. Petros, Duong T. Nguyen, Ronaldo J. Cavazos, Clifford S. Morrison, Jana B. Lampe, Alesha N. Harris, Brian K. McFarlin. Utilizing cobalt coordination chemistry as a traceless prodrug strategy in targeted drug delivery. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4399. doi:10.1158/1538-7445.AM2015-4399

An Alkaline Flow Battery Based on the Coordination Chemistry of Iron and Cobalt

We present the first alkaline redox flow battery (a-RFB) based on the coordination chemistry of cobalt with 1-[Bis(2-hydroxyethyl)amino]-2-propanol (mTEA) and iron with triethanolamine (TEA) in 5 M NaOH. The overall redox system has a cell voltage of 0.93 V in the charged state. Importantly, the coordination compounds are negatively charged and have limited transport through the cation exchange membrane (e.g., Nafion), minimizing the extent of redox species crossover during charge-discharge cycling. Fe-TEA is electrochemically reversible and soluble up to 0.8 M, whereas Co-mTEA presents quasireversible electron transfer kinetics and can be solubilized up to 0.7 M. Cyclability was tested with a flow cell at a concentration 0.5 M up to 30 cycles using a 50 μm thick Nafion membrane, at 30 mA/cm2, with minimal crossover (less than 4% of net concentration) or evolution of gases detected.

Conductance of a Cobalt(II) Terpyridine Complex Based Molecular Transistor: A Computational Analysis

A recent experiment, in which a molecular transistor based on the coordination chemistry of cobalt(II) and organic self-assembled monolayers is formed by means of self-aligned lithography,2 is analyzed with a computational approach. The calculations reveal that a complex involving two cobalt(II) ions bridged by acetate ions can effectively span the nanogap. This bridged complex is shown to be both more flexible and more conductive than the alternative structure involving a single cobalt(II) ion. The single cobalt(II) ion complex is the more stable structure in a nonconfined environment (i.e., in solution) but is found to be less effective at connecting the leads of the fabricated gap and is less likely to result in a conductive device.

Monomeric and polymeric structures of silver salts of cobalt(III) bis(dicarbollide) ions

The coordination chemistry of cobalt(III) bis(dicarbollide) ions is explored by studying the crystal structures of their silver(I) salts. Each structure has a different coordination motif, which could not be predicted from knowledge of the constituent parts, showing the subtlety and diversity of silver–carborane coordination chemistry.

Spectroscopy and coordination chemistry of cobalt in molecular sieves

Abstract The catalytic potential of Co-containing molecular sieves has stimulated zeolite scientists to study the spectroscopy and siting of Co2+ ions. In this review, a critical overview is given of the spectroscopic tools used: (1) to decide about the cation sites of Co2+ and their occupancy; (2) to determine the spectroscopic signatures of framework and extra-framework cobalt; (3) to determine the amount of Co incorporated into the framework of molecular sieves; and (4) to discuss local distortions of framework cobalt.

Comparative study on the coordination chemistry of cobalt(II), nickel(II), and copper(II) with derivatives of salen and tetrahydrosalen: metal-catalyzed oxidative dehydrogenation of the carbon-nitrogen bond in coordinated tetrahydrosalen

The salen complexes ML (M II =Cu, Ni, Co) and the corresponding tetrahydrosalen complexes M[H 4 ]L (M II =Cu, Ni) were prepared and characterized by their vis absorption and EPR spectra, by their magnetic moments, and by cyclic voltammetry in acetonitrile