![]() Today, some cobalt is produced specifically from one of a number of metallic-lustered ores, such as cobaltite (CoAsS). In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold. Miners had long used the name kobold ore ( German for goblin ore) for some of the blue pigment-producing minerals they were so named because they were poor in known metals and gave off poisonous arsenic-containing fumes when smelted. The free element, produced by reductive smelting, is a hard, lustrous, silver metal.Ĭobalt-based blue pigments ( cobalt blue) have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was for a long time thought to be due to the known metal bismuth. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ISBN 2-4.Cobalt is a chemical element with the symbol Co and atomic number 27. Introduction to Macromolecular Crystallography. "Solution structure of Cobalt(III)hexammine complexed to the GAAA tetraloop, and metal-ion binding to G.A mismatches". ![]() "Near-atomic resolution crystal structure of an A-DNA decamer d(CCCGATCGGG): cobalt hexammine interaction with A-DNA". "Complexes of Cobalt Containing Ammonia or Ethylene Diamine: Hexaamminecobalt(III) Salts". Tris(ethylenediamine)cobalt(III) chloride.The compound induced the transition of DNA structure from the classical B-form to the Z-form. 3+ is an unusual example of a water-soluble trivalent metal complex and is of utility for charge-shielding applications such as the stabilization of highly negatively charged complexes, such as interactions with and between nucleic acids. In the biological system, the counterions would more probably be Mg 2+, but the heavy atoms of cobalt (or sometimes iridium, as in PDB: 2GIS) provide anomalous scattering to solve the phase problem and produce an electron-density map of the structure. 3+ is a component of some structural biology methods (especially for DNA or RNA, where positive ions stabilize tertiary structure of the phosphate backbone), to help solve their structures by X-ray crystallography or by nuclear magnetic resonance. ![]() The acetate salt is highly water-soluble to the level of 1.9 M (20 ☌), versus 0.26 M for the trichloride. The acetate salt can be prepared by aerobic oxidation of cobalt(II) acetate, ammonium acetate, and ammonia in methanol. This salt appears to have been first reported by Fremy. Oxidants include hydrogen peroxide or oxygen in the presence of charcoal catalyst. The chloride ion can be also exchanged with more complex anions such as the hexathiocyanatochromate(III), yielding a pink compound with formula, or the ferricyanide ion.Ĭl 3 is prepared by treating cobalt(II) chloride with ammonia and ammonium chloride followed by oxidation. Such salts are orange or bright yellow and display varying degrees of water solubility. ![]() The chloride ions in Cl 3 can be exchanged with a variety of other anions such as nitrate, bromide, iodide, sulfamate to afford the corresponding X 3 derivative. Upon heating, hexamminecobalt(III) begins to lose some of its ammine ligands, eventually producing a stronger oxidant. In contrast, labile metal ammine complexes, such as Cl 2, react rapidly with acids, reflecting the lability of the Ni(II)–NH 3 bonds. As a manifestation of its inertness, Cl 3 can be recrystallized unchanged from concentrated hydrochloric acid: the NH 3 is so tightly bound to the Co(III) centers that it does not dissociate to allow its protonation. The cation obeys the 18-electron rule and is considered to be a classic example of an exchange inert metal complex. 3+ is diamagnetic, with a low-spin 3d 6 octahedral Co(III) center. Other similar complexes also had color names, such as purpureo (Latin: purple) for a cobalt pentammine complex, and praseo (Greek: green) and violeo (Latin: violet) for two isomeric tetrammine complexes. This name has been discarded as modern chemistry considers color less important than molecular structure. Originally salts of 3+ were described as the luteo (Latin: yellow) complex of cobalt. The cation itself is a metal ammine complex with six ammonia ligands attached to the cobalt(III) ion. It is the chloride salt of the coordination complex 3+, which is considered an archetypal "Werner complex", named after the pioneer of coordination chemistry, Alfred Werner. Hexaamminecobalt(III) chloride is the chemical compound with the formula Cl 3.
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