Cobalt(II) nitrate

Composition and structures

As well as the anhydrous compound Co(NO3)2, several hydrates of cobalt(II) nitrate exist. These hydrates have the chemical formula Co(NO3)2·nH2O, where n = 0, 2, 4, 6.

Anhydrous cobalt(II) nitrate adopts a three-dimensional polymeric network structure, with each cobalt(II) atom approximately octahedrally coordinated by six oxygen atoms, each from a different nitrate ion. Each nitrate ion coordinates to three cobalts. The dihydrate is a two-dimensional polymer, with nitrate bridges between Co(II) centres and hydrogen bonding holding the layers together. The tetrahydrate consists of discrete, octahedral [(H2O)4Co(NO3)2] molecules. The hexahydrate is better described as hexaaquacobalt(II) nitrate, [Co(OH2)6][NO3]2, as it consists of discrete [Co(OH2)6]2+ and [NO3]− ions. Above 55 °C, the hexahydrate converts to the trihydrate and at higher temperatures to the monohydrate.

Cobalt(II)-nitrate-xtal-2002-CM-3D-SF.png|Co(NO3)2 Cobalt(II)-nitrate-dihydrate-xtal-1976-CM-3D-balls.png|Co(NO3)2·2H2O Cobalt(II)-nitrate-tetrahydrate-xtal-1975-CM-3D-balls.png|Co(NO3)2·4H2O Hexaaquacobalt(II)-nitrate-xtal-1973-unit-cell-CM-3D-balls.png|Co(NO3)2·6H2O

Uses and reactions

It is commonly reduced to metallic high purity cobalt. It is used in the preparation of dyes and inks.

Cobalt sulfides form by treating an aqueous solution of cobalt(II) nitrate with hydrogen sulfide according to the following idealized equation: :

Cobalt(II) nitrate is a common starting material for the preparation of coordination complexes such as cobaloximes, carbonatotetraamminecobalt(III), and others.

Production

The hexahydrate is prepared treating metallic cobalt or one of its oxides, hydroxides, or carbonate with nitric acid: :Co + 4 HNO3 + 4 H2O → Co(H2O)6(NO3)2 + 2 NO2 :CoO + 2 HNO3 + 5 H2O → Co(H2O)6(NO3)2 :CoCO3 + 2 HNO3 + 5 H2O → Co(H2O)6(NO3)2 + CO2

References

References

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2. John Dallas Donaldson, Detmar Beyersmann, "Cobalt and Cobalt Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. {{doi. 10.1002/14356007.a07_281.pub2
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