Cobalt compounds

[1] Because the color change of cobalt(II) chloride in different hydrates, it can be used to manufacture color-changing silica gel.

Anhydrous cobalt halides react with nitric oxide at 70~120 °C to generate [Co(NO)2X]2 (X = Cl, Br or I).

The complex of cobalt halides and triethylphosphine ((C2H5)3P) can absorb nitric monoxide in benzene to form the diamagnetic material Co(NO)X2(P(C2H5)3)[2] In the reaction Co3+ + e− → Co2+, the potential is +1.92 V, which is higher than that of Cl2 to Cl− (+1.36 V).

It decomposes at 50~145 °C to form cobalt(II) azide, becoming anhydrous and releasing nitrogen, and exploding when heated further.

These can be combinations of a potentially infinite variety of molecules and ions, such as: These attached groups affect the stability of oxidation states of the cobalt atoms, according to general principles of electronegativity and of the hardness–softness.

The more electronegative (and harder) oxide and fluoride can stabilize Co4+ and Co5+ derivatives, e.g. caesium hexafluorocobaltate(IV) (Cs2CoF6) and potassium percobaltate (K3CoO4).

[17] Alfred Werner, a Nobel-prize winning pioneer in coordination chemistry, worked with compounds of empirical formula [Co(NH3)6]3+.

[18][19] Vitamin B12 is a cobalt-centered organic biomolecule, soluble in water, and involved in the methylation and synthesis of nucleic acid and neurotransmitter.

[21] Dicobalt octacarbonyl (Co2(CO)8) is an orange-red crystal with two isomers in solution:[22] It reacts with hydrogen or sodium to form HCo(CO)4 or NaCo(CO)4.