This coordination complex, a typical Werner-type complex, consists of a central cobalt atom coordinated by six ammine orthogonal ligands and three chloride counteranions. One of the isomers determined was cobalt(III) hexammine chloride. Īlfred Werner, a Nobel-prize winning pioneer in coordination chemistry, worked with compounds of empirical formula [Co(NH caesium hexafluorocobaltate(IV) (Cs 2CoF 6) and potassium percobaltate (K 3CoO 4). The more electronegative (and harder) oxide and fluoride can stabilize Co 4+ and Co 5+ derivatives, e.g. Because phosphorus is softer than nitrogen, phosphine ligands tend to feature the softer Co 2+ and Co +, an example being tris(triphenylphosphine)cobalt(I) chloride ( P(CģCoCl). For example, Co 3+ complexes tend to have ammine ligands. These attached groups affect the stability of oxidation states of the cobalt atoms, according to general principles of electronegativity and of the hardness–softness. , as in the green triscarbonatocobaltate(III) [Co(CO (the anion of Erdmann's salt), and in [Co(NH This pink-colored complex is the predominant cation in solid cobalt sulfate CoSOĢO) x, with x = 6 or 7, as well as in water solutions thereof.ģ, as in cis-diaquotetraamminecobalt(III) [Co(NH These can be combinations of a potentially infinite variety of molecules and ions, such as:ĢO, as in the cation hexaaquocobalt(II) [Co(H It can be obtained by precipitation from solution.Īs for all metals, molecular compounds and polyatomic ions of cobalt are classified as coordination complexes, that is, molecules or ions that contain cobalt linked to one or more ligands. Cobalt nitrate hexahydrate (Co(NO 3) 2♶H 2O) is a red deliquescence crystal that is easily soluble in water, and its molecule contains cobalt(II) hydrated ions ( 2+) and free nitrate ions. Cobalt(II) nitrate exists in the anhydrous form and the hydrate form, of which the hexahydrate is the most common. Ĭobalt can easily react with nitric acid to form cobalt(II) nitrate Co(NO 3) 2. Hydrogen bonding of water stabilizes this molecule. This compound can be obtained by reacting (N 5) 6(H 3O) 3(NH 4) 4Cl or Na(H 2O)(N 5)]♲H 2O and (NO 3) 2 at room temperature. It decomposes at 50~145 ☌ to form cobalt(II) azide, becoming anhydrous and releasing nitrogen, and exploding when heated further. Cobalt pentazolide Co(N 5) 2 was discovered in 2017, and it exists in the form of the hydrate ♴H 2O. Cobalt(II) and azide can form Co(NĤ complexes. Ĭobalt(II) azide (Co(N 3) 2) is another binary compound of cobalt and nitrogen that can explode when heated. The former three compounds are of interest as catalysts for water electrolysis. Cobalt reacts with phosphorus or arsenic to form Co 2P, CoP, CoP 2, CoAs 2 and other substances. Pnictogenides Cobalt(II) nitrate hexahydrateĬobalt powder reacts with ammonia to form two kinds of nitrides, Co 2N and Co 3N. Soluble cobalt salts react with sodium hydroxide to obtain cobalt(II) hydroxide (Co(OH) 2): Co(NO 3) 2 + 2 NaOH → Co(OH) 2↓ + 2 NaNO 3Ĭobalt(II) hydroxide can be oxidized to the Co(III) compound CoO(OH) under alkaline conditions. Oxides and hydroxides Cobalt(II,III) oxideĬobalt can form various oxides, such as CoO, Co 2O 3 and Co 3O 4. It is a fluorinated reagent and reacts violently with water. The potential from F 2 to F − is as high as +2.87 V, and cobalt(III) fluoride (CoF 3) can exist stably. Therefore, the interaction of Co 3+ with Cl− produces Co 2+ and releases chlorine gas. , the potential is +1.92 V, which is higher than that of Cl 2 to Cl − (+1.36 V). The complex of cobalt halides and triethylphosphine ((C 2H 5) 3P) can absorb nitric monoxide in benzene to form the diamagnetic material Co(NO)X 2(P(C 2H 5) 3) Because the color change of cobalt(II) chloride in different hydrates, it can be used to manufacture color-changing silica gel.Īnhydrous cobalt halides react with nitric oxide at 70~120 ☌ to generate 2 (X = Cl, Br or I). Anhydrous cobalt(II) chloride is blue, while the hexahydrate is red-purple. In addition to the anhydrous forms, these cobalt halides also have hydrates. Many halides of cobalt(II) are known.e cobalt(II) fluoride (CoF 2) which is a pink solid, cobalt(II) chloride (CoCl 2) which is a blue solid, cobalt(II) bromide (CoBr 2) which is a green solid, and cobalt(II) iodide (CoI 2) which is a blue-black solid. Inorganic compounds Halides Red-orange CoCl 2♶H 2O Chemical compound containing the element cobaltĬobalt compounds are chemical compounds formed by cobalt with other elements.
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