Cobalt blue halides

Cobalt II) halides can be obtained by direct combination of the elements, or by dehydration of their hydrates. Anhydrous cobalt(II) chloride is blue, and the solid contains octahedrally-coordinated cobalt the hydrated salt C0CI2. bHjO is pink, with each cobalt surrounded by four water molecules and two chloride ions in a distorted octahedron. 

Hydrazine forms68 a 2 1 complex with eobalt(ii) bromide Co(N2H4)Br2,2H20 and phenylhydrazine forms69 2 1 complexes with all cobalt(n) halides. The latter seem to be octahedral in the solid state but dissolve in acetone to give blue solutions with characteristic pseudotetrahedral electronic spectra. 

Sulphuric acid (concentrated). Widely used in desiccators. Suitable for drying bromine, saturated hydrocarbons, alkyl and aryl halides. Also suitable for drying the following gases hydrogen, nitrogen, carbon dioxide, carbon monoxide, chlorine, methane and paraffins. Unsuitable for alcohols, bases, ketones or phenols. Also available with an indicator (a cobalt salt, blue when dry and pink when wet) under the name Sicacide (from Merck) for desiccators. 

The treatment of diorganozincs or organozinc halides with cobalt bromide in THF NMP mixtures provides blue solutions of organocobalt reagents, which have a half-life of several hours at -20 °C.25,26 Carbonylation reactions with these new cobalt reagents proceed well simply by bubbling carbon monoxide... 

The anhydrous halides CoX2 may be made from the hydrated halides by heating or treatment with SOCl2 Cobalt difluoride is obtained by reacting CoCl2 with HF it has the rutile structure. Like the dichlorides of Mg, Mn, and Fe, blue CoCl2 adopts the CdCl2 structure. 

The Methylene (and Ethylene) Blue method has been applied in determinations of sulphur in plants [86], biological materials [87], waters [12,88], air [5,12,16,20], hydrocarbons [89], iron alloys [90,91], cobalt and zirconium [91], titanium [92], thallium and its halides [93], arsenic [94], selenium [95], and various reagents (including barium chloride) [14]. Flow-injection analysis has been applied in the determination of sulphur by the Methylene Blue method [96]. 

Of particular interest are the solubilities of cobalt-, nickel- and copper-halide complexes in dense supercritical aqueous phases. Aquo- and halide complexes have higher coordination numbers at higher density. Several of gaseous solutions are highly coloured (for example dark blue cobalt-II solutions). Visible and UV-spectra, which permit to determine the stability ranges of various complexes have been reported by us up to 500 °C and 6000 bar [43-45]. The results may have interest for hiture catalyst developments. We have used near-UV spectroscopy to determine the solubility of organic solids in various dense gases. Examples are anthracene [46] and caffeine [47] to 200 °C and 2000 bar. Supercritical extraction has become a widely applied procedure in the food, pharmaceuticals and other industries. 

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