Reaction of the anhydrous compound with sodium cyclopentadienide gives cobaltocene Co(CĢ. The structure of a cobalt(IV) coordination complex with the norbornyl anion The tetrachlorocobaltate ion 2− is the blue ion that forms upon addition of hydrochloric acid to aqueous solutions of hydrated cobalt chloride, which are pink. Salts of the anionic complex CoCl 4 2− can be prepared using tetraethylammonium chloride: CoClĢ + 2 Cl → 2 It forms an octahedral complex with pyridine ( C The adducts are usually either octahedral or tetrahedral. The hexahydrate and the anhydrous salt are weak Lewis acids. For example, such solutions give a precipitate of cobalt sulfide CoS upon treatment with hydrogen sulfide H Generally, diluted aqueous solutions of the salt behave like other cobalt(II) salts since these solutions consist of the [Co(H In the laboratory, cobalt(II) chloride serves as a common precursor to other cobalt compounds. The anhydrous compound can be purified by sublimation in vacuum. ĭehydration can also be effected with trimethylsilyl chloride: CoCl If the partial pressure of the water vapor is in equilibrium with the solid, as in a confined but not pressurized contained, the decomposition occurs at about 115☌, 145☌, and 195☌, respectively. On slow heating in an open container, so that the water vapor pressure over the solid is practically zero, water evaporates out of each of the solid 6-, 2-, and 1- hydrates, leaving the next lower hydrate, at about 40☌, 89☌, and 125☌, respectively. On rapid heating or in a closed container, each of the 6-, 2-, and 1- hydrates partially melts into a mixture of the next lower hydrate and a saturated solution-at 51.25 ☌, 206 ☌, and 335 ☌, respectively.
The anhydrous compound can be prepared by heating the hydrates. The monohydrate and the anhydrous forms can be obtained by cooling solutions only under high pressure, above 206 ☌ and 335 ☌, respectively. Water ice, rather than cobalt chloride, will crystallize from solutions with concentration below 29%. Cooling saturated aqueous solutions yields the dihydrate between 120.2 ☌ and 51.25 ☌, and the hexahydrate below 51.25 ☌. The solid dihydrate and hexahydrate can be obtained by evaporation. Preparation Ĭobalt chloride can be prepared in aqueous solution from cobalt(II) hydroxide or cobalt(II) carbonate and hydrochloric acid:
The octahedron is completed by a pair of mutually trans aquo ligands. Each Co center is coordinated to four doubly bridging chloride ligands. The dihydrate, CoCl 2(H 2O) 2, is a coordination polymer. The anhydrous salt is hygroscopic and the hexahydrate is deliquescent. This species dissolves readily in water and alcohol. The crystal unit of the solid hexahydrate CoClĢO contains the neutral molecule trans- CoClĤ and two molecules of water of crystallization. Concentrated solutions are red at room temperature but become blue at higher temperatures. Under atmospheric pressure, the mass concentration of a saturated solution of CoClĢ in water is about 54% at the boiling point, 120.2 ☌ 48% at 51.25 ☌ 35% at 25 ☌ 33% at 0 ☌ and 29% at −27.8 ☌. Solutions Ĭobalt chloride is fairly soluble in water. The vapor pressure has been reported as 7.6 mmHg at the melting point. At about 706 ☌ (20 degrees below the melting point), the coordination is believed to change to tetrahedral. Properties Anhydrous Īt room temperature, anhydrous cobalt chloride has the cadmium chloride structure ( CdClĢ) (R 3m) in which the cobalt(II) ions are octahedrally coordinated. Commercial samples are usually the hexahydrate, which is one of the most commonly used cobalt compounds in the lab. The anhydrous form is a blue crystalline solid the dihydrate is purple and the hexahydrate is pink. Claims of the formation of tri- and tetrahydrates have not been confirmed. The compound forms several hydrates CoClĢO, for n = 1, 2, 6, and 9. Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula CoClĢ.
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